2 Problems: Rough idle at cold start. Radiator fan not working when hot.

Rick_Leuce

Registered User
Hello everyone.

My car has 2 main problems I'm trying to solve. It idles rough when cold and the radiator fan doesn't kick on when it's supposed to.

I'm putting together a video of my 1991 SC 5-Speed starting up and running. I'm hoping someone out there with more Super Coupe experience can help me track down the sources of these problems. I used 3 cameras, so I'm going to need some time to edit it. I'll reply to my own post with the finished video soon.

For starters, the car has a really hard time idling for the first minute or two. If I don't rev it, the car stalls. After revving the car at 2,000 RPM for 1-2 minutes, it can idle normally around 900-1,000 RPM. It's annoying, but I can live with it. I wasn't sure if someone out there might know what I could adjust or tweak to fix it. I keep starting it up and letting it rev/idle every few weeks or months, so I know the fuel is fresh because I keep filling it to about 1/4 tank of gas. I put in a bottle of Techron injector cleaner a while ago, but I don't know how much it's helping. My battery terminals are a little corroded, so I had to run a second ground just to enable the car to start.

Secondly, and more importantly, this car has had a cooling problem for years and it has been garaged ever since Spring 2015. The radiator fan does not always come on when it should. It's always been like this since I owned it. Even when it had the original IRCM relay and radiator fan, the fan WOULD NOT come on if I turned the AC to max. I first tried replacing the IRCM relay with one from a junkyard, but it didn't work. Since 2013, I have replaced the radiator fan motor (which is 1 speed) the IRCM relay (with a Chinese-made one), and I bought some aftermarket thermometer/relay kit from Autozone that was supposed to trigger the fan when the included thermometer (which I stabbed into the radiator) gets hot and trips the relay. However, the radiator fan does not always come on even when the radiator is up to temperature. I'm giving up on this crappy relay and was wondering if there was a good kit out there I could buy that would just make my fan come on when it is supposed to. I've almost overheated my car 6 times (including today) so I desperately want to know what to do to get my fan to come on when it should.

Also, my radiator go so hot today that coolant started steaming out (which you will see in the video). It actually happened a second AFTER I turned the car off. I was wondering if there are things now that I need to be on the lookout for that could have been damaged. I will mention that I turned the engine off, but left the key in the ON position so that the car's vents could cool off the engine while I stuck a battery-powered fan in front of the radiator to cool it off. The car was in the shade with it's hood and front-bumper assembly removed, so I'm hoping things didn't get too hot and were able to cool down relatively quickly.

I'm thinking my crappy little Autozone relay is the problem, but could my Chinese IRCM relay (image below) be a problem too?

Thanks in advance!

View attachment 69540View attachment 69541
 

KMT

Registered User
If you do a KOEO code read self-test with an OBD1 code reader, does the fan run right after beginning the test?

Any codes?

Any bubbles in the expansion tank? How often do you add water? How fresh is the radiator cap? How old is the thermostat? What temp is it?

Is the IRCM always hanging free like that?

When you replaced the fan motor, what did you do with the lo and hi wires from the original setup?

If you start the car and remove the connector at the ECT, does the fan run then?
 

Rick_Leuce

Registered User
If you do a KOEO code read self-test with an OBD1 code reader, does the fan run right after beginning the test?

Any codes?

Any bubbles in the expansion tank? How often do you add water? How fresh is the radiator cap? How old is the thermostat? What temp is it?

Is the IRCM always hanging free like that?

When you replaced the fan motor, what did you do with the lo and hi wires from the original setup?

If you start the car and remove the connector at the ECT, does the fan run then?

Thanks for the fast reply. I’ll answer what I can.

My car is a 1991, is it possible to read codes with an OBD1 code reader? I thought that was for 1994 or newer cars.

I dont think there were any bubbles in the expansion tank, but it was was very full.
I just flushed out this car’s coolant a couple weeks ago, so it has fresh 50/50 Prestone and Distilled water. It was full before starting the car.
Radiator cap is old and the seal looks like the rubber is cracking. I will replace.
The Autozone aftermarket thermostat that dictates when the fan comes on is from 2014. I think the problem is the wires are too small so the massive current keeps popping the re-usable fuse (that funny green thing in the photo).

I dont know what temp it is for off the top of my head, but it usually comes on when the temp sensor in my car is on the M on NORM. I put it right next to the upper radiator hose where its hottest so it would turn on the soonest.

My IRCM is not usually like that. I just removed my hoodpin and airbox to look at it. My aftermarket thingy is plugged into it.

I’ll need to ask my dad about what we did with the lo and hi wires (he set it up for me). I think the original plug is hanging there because we bypassed it, but I’ll check on it.

I may remove my crappy Autozone thing and hook up the IRCM like normal to see if your trick with the ECT will work. I think my Autozone relay bypasses some of the car’s systems.

Thank you again :)
 

KMT

Registered User
My car is a 1991, is it possible to read codes with an OBD1 code reader? I thought that was for 1994 or newer cars.
Later models are OBD-II. Yours should be OBD-I

A code reader is a handy tool to have on hand...it beats throwing parts at a repair and pays for itself in that way alone. Also an EVTM...wiring manual - often found on ebay for a decent price.

For sure get a new cap, straight 16#. Do your best to bleed air out of the system (speak up if you need help w/that process, or feel free to search here)...it can cause several issues, from poor heater performance to the ECT sensor not reading properly, which can raise heck with fan operation.

And while I have experience w/aftermarket fans & their controllers, I've been lucky enough to solve the cooling issues on my '90 SC over the years sticking w/the stock systems. Went thru everything on the cooling system over time, but these days it's reliable and works like new - fingers crossed ;)

I'll keep an eye out for your video(s).
 

Rick_Leuce

Registered User
Later models are OBD-II. Yours should be OBD-I

A code reader is a handy tool to have on hand...it beats throwing parts at a repair and pays for itself in that way alone. Also an EVTM...wiring manual - often found on ebay for a decent price.

For sure get a new cap, straight 16#. Do your best to bleed air out of the system (speak up if you need help w/that process, or feel free to search here)...it can cause several issues, from poor heater performance to the ECT sensor not reading properly, which can raise heck with fan operation.

And while I have experience w/aftermarket fans & their controllers, I've been lucky enough to solve the cooling issues on my '90 SC over the years sticking w/the stock systems. Went thru everything on the cooling system over time, but these days it's reliable and works like new - fingers crossed ;)

I'll keep an eye out for your video(s).

I just did a Google search. It never occurred to me that my car could be OBD-I (I just looked for the convenient plug-in that's on all new cars, didn't see it, and gave up). I found one for sale at Autozone, it appears it would cover my model year vehicle.

https://www.autozone.com/test-scan-...eader/innova-ford-obd1-code-reader/273350_0_0

When I was bleeding air out of my cooling system, I watched a series of videos in which someone did a coolant change in a 1997 Thunderbird. I know about the bolt that sits high up on the engine with a sort-of plastic cap thing that says something like: "Remove when filling with coolant. Replace before starting engine." I also jacked up the front of the car a little bit and would leave the radiator cap off until the car got up to temperature, adding coolant in as the levels went down. I also squeezed the upper radiator hose just because I sometimes noticed air bubbles escape when I do that. I also filled my overflow tank way higher than it needed to be. Please let me know if there is something else I should or should not do. I also did a coolant change in my 1990 (about a week ago) doing the same things and haven't noticed a problem yet. I keep checking my radiator cap before I start the car every time, just in case.

I'm starting to wonder if the IRCM relay actually could handle what we want it to. If I remember correctly, back when I was first troubleshooting, I got a used IRCM relay from a 1990 SC in a junkyard. I put it in, but the fan didn't come on, so I got three new Chinese-made IRCM relays. That didn't work either, even though we popped one of them open and tried to force it to work. So I got the crappy little aftermarket kit from Autozone, but it just popped fuses all the time (so we got one of those little re-usable fuses that "resets" itself after a while, but it doesn't help if the fan doesn't kick on when it should). At that point, we realized my fan motor was bad and had a lot of friction, so we replaced it. My crappy little Autozone temperature relay thing worked about 80% of the time (because it draws so much current). I'm starting to wonder if we never gave the IRCM relays a fair shot with the new motor (and just kept expecting them to work with the old one without ever trying them on the new one). Maybe we tried one of the Chinese-made ones, but never the original Ford one again. I'm beginning to wonder if my new fan motor and a good old IRCM relay would be enough.

I think I'll disconnect that Autozone relay thermometer thing and just let the Chinese IRCM relay do it's thing. If that doesn't work, I can use my other Chinese IRCM relay that we didn't gut open (it had actually been missing for years and we might have tried to use it but couldn't find it all those years ago). If that doesn't work either, would it be safe to "borrow" the IRCM relay from the 1990 SC? I don't want to ruin it because then I would be down to zero running SCs (which is why I'll start with the Chinese ones).

Regarding the video, I think I'm just going to show the rough idle when the car first starts up (from inside the car and looking at the engine) and also some footage of me walking around the car getting close to the exhaust and whatnot. My temperature gauge in the car actually went out on me twice, so I'm glad I caught it on camera in case someone knows what would cause it. I'll also include the part where coolant starts gurgling out of my radiator cap after I turned it off (hopefully no damage occurred, but I don't know yet).

Thanks again for your help.
 

DrFishbone

SCCoA Member
With a stock fan that operates properly, the IRCM should do just fine. The radiator is so small, you can't really keep from overheating badly and quickly without a nice, strong two-speed fan, like the stock one. Aftermarket fans are not the way to go on an SC.
 

Rick_Leuce

Registered User
With a stock fan that operates properly, the IRCM should do just fine. The radiator is so small, you can't really keep from overheating badly and quickly without a nice, strong two-speed fan, like the stock one. Aftermarket fans are not the way to go on an SC.

The aftermarket fan I have is pretty powerful. Its basically permanently set to hi speed. However, I don’t mind buying a stock fan and stock IRCM relay if that will fix the problem.
 

KMT

Registered User
My temperature gauge in the car actually went out on me twice, so I'm glad I caught it on camera in case someone knows what would cause it. I'll also include the part where coolant starts gurgling out of my radiator cap after I turned it off (hopefully no damage occurred, but I don't know yet)..

About the gauge...it's single wire sender is on the thermostat housing. Be sure the wire is pushed on firmly and the post and connector are shiny clean to provide a good electrical connection. If it doesn't want to fit snug on the post, gently squeeze it smaller with pliers until it does. We can get into where it should read later, but let's just say if it goes past M you risk damage.

About the cap - never remove it when there is any heat in the system and resist removing it once the system has run and stabilized and air has had a chance to bleed out via the tube on the neck to the expansion tank. Check the level in the expansion tank, not the radiator. Confirm the upper hose doesn't collapse when the engine cools down. The factory repair manual says to set the level when hot at the HOT marker on the expansion tank. Cold should be at or above the COLD mark, as a reference only, not a set point. Coolant should be nice and clean, not oily/dark/smell like exhaust. Remove the small tube at the neck and confirm you can blow thru it into the expansion tank next time you have an excuse to remove the cap.

Removing the cap when the system is hot removes pressure and allows the coolant to boil which is why it gurgles into the expansion tank....again, don't do that.

If there is gurgleing past the new cap when shut off, you may have a problem with air getting into the cooling system...usually head gaskets. AutoZone has a rental test kit to check for exhaust/combustion gases in the cooling system if it comes to that.

Sorry if I missed it...when was the last time you added coolant? Do you smell coolant when the car is running?

I tried seeing if that Advance (?) IRCM fits our cars, but couldn't find anything that said it would. If I had it here, I could test it easy enough, but I get the feeling it won't work properly on an SC.

Need more info to make a good guess if all you need is an IRCM & stock fan to make the system work as it should. Might be even an aftermarket fan wouldn't help, but I'm not sure I'd even recommend that route in this example. The stock fan pulls approx. 35 amps through the wiring from the IRCM when running, and remember that if hi is hot, lo is too. If you could rely on a stock IRCM to work properly, I'd see no reason to not use a stock fan.
 
Last edited:

Rick_Leuce

Registered User
Here's the video I was talking about.

https://youtu.be/WyAU7uPAhOg

It's nothing fancy, but I figured I should get it out there so that it's easier to show what I'm dealing with.

I show the rough startup (in the car and looking at the engine). It's brief, I should have let it run longer without touching the throttle to help it.

Most of the video is me letting the car warm up to see what kind of issues it would have. The temp gauge gets weird, the engine acts like it is "bogging down" a couple times and my radiator spews hot steam after I turn the car off.

I'm planning on removing the Autozone relay in my car and letting the IRCM relay do it's job.

Thanks for your help and patience.

https://youtu.be/WyAU7uPAhOg
 

sam jones

Registered User
Good evening


Fuel injector cleaner is not what I would recommend for addressing the fuel system issue. Fuel system cleaner is what you need. The injector cleaner is a "water down" product. Get fuel system cleaner with a good PEA concentrate.

Check fuel pressure. It might be low. I suspect the filter has pick up some contamination even with the fuel injector cleaner.

The corrosion in the battery cables has probably advanced past the terminals. If the battery voltage is good (12.6 volts or higher) this could be the problem of the slow crank just before start. Remove all the corrosion or replace the cables

Do a chemical engine block test for possible head gaskets leaks as suggested by KMT.


Get a laser thermometer (suggestion: Harbor Freight) and obd 1-2 capable scanner with live data function. Check temperature entering/exiting the radiator. Use the obd 1 scanner to check live data of the ECT sensor which is what the EEC uses for temperature. If the temperatures wildly fluctuates at the ECT or the laser thermometer indicates no significant temperature drop at the exit vs the inlet of the radiator suspect (in your case) air in the coolant system, condenser fins blockage and or a weak fan motor.

Does you lower radiator hose have the wire internal structure installed?
 

TbirdSCFan

Registered User
Don't know if this was discussed, but how old is your fuel? My white SC sat up for 2+ years and would start, cough, sputter, and then run fine until the next day. Had to mix in a gallon of good fuel here and there to get it going reliably. :)
 

KMT

Registered User
Here's the video I was talking about.

Nice job...thanks.

I'll assume that since the video you've installed a new radiator cap, checked the connector at the temp sender as noted above, and cleaned up the connections at the battery.

Not an offer to sort out your aftermarket fan, specifically, but I notice from the photos that the extra relay seems to be using the HIGH speed fan feed wire (BR/O) off the IRCM to trigger the relay, which means your aftermarket fan won't come on until the higher temp. Looks like BK/O is the power feed to the fan...any idea how many amps the aftermarket fan draws? Do you have it's specs or part number? Is it just another (single speed?) motor in the stock shroud, or an entire assembly?

The stock fan speed strategy is as follows:
  • Lo speed on: 222°
  • Lo speed off: 214°
    -=-
  • Hi speed on: 228°
  • Hi speed off: 220°
Lo is always on whenever hi is on - when the hi speed turn off is reached (220°) the lo speed circuit is still on and works to continue to drive the temp down until 214°. In your example, the aftermarket fan wouldn't be turned on until 228°, and never attempt to push the temp below 220°. I wouldn't be comfortable using that as a normal operating range, even if the ECT is in range. The ECU decides when to activate both circuits based on info that includes the ECT signal, but we don't know if the IRCM has both fan circuits, so...

Note that when A/C is on, it activates the lo speed circuit. Using the hi speed circuit as a feed means that A/C can be used without the fan, further stressing the cooling system.

Such are the pitfalls of aftermarket fan hybridizing on these cars when sticking with the stock circuits, etc. As I said before, if the stock IRCM can be relied upon, I see no reason to not use a stock fan.

I don't advocate swapping parts without data to support it, but a new ECT sensor isn't that expensive and easy enough to install, if you're not up to testing it in operation first. Check it's connector for corrosion and good fit.

Next time you run it, shut it down when it moves past the middle of the 'M' on the temp gauge if the fan isn't running. Never run it past M if you can avoid it at. This assumes your temp gauge is anywhere near accurate. But I have to say, overheating it like that 6~7 times is pure Russian roulette.

Once the cooling system is sorted out, you can move to seeing what's up with the idle.
 
Last edited:

Rick_Leuce

Registered User
Thanks for the fast responses everyone!

Don't know if this was discussed, but how old is your fuel? My white SC sat up for 2+ years and would start, cough, sputter, and then run fine until the next day. Had to mix in a gallon of good fuel here and there to get it going reliably. :)

The car has not driven since Spring 2015, but I've run out the fuel and replaced it a couple times since then. I last put in 5 gallons about a month ago, and the car is currently at a quarter tank, so the fuel is mostly fresh.

Thank you sam jones. I have quite a bit of HEET injector cleaner on hand (didn't use it yet), so I'm glad you said something. The last fuel additive I put in was a bottle of Techron, which showed up as a "fuel system cleaner" when I was Googling my options. Is there something else you would recommend?

You are correct, the corrosion goes beyond the terminals. I will do my best to remove as much corrosion as possible.

I've never had a head gasket blow on me yet, so I'm paranoid it could happen any day now (especially when the car has almost overheated a few times already) I will definitely get a kit to check for possible failure.

I'm planning on picking up an OBD-1 scanner tool like the one below. It looks like the same one Autozone carries but like $10 cheaper.

https://www.walmart.com/ip/INNOVA-3145-Ford-Digital-OBD1-Code-Reader/16606975


Nice job...thanks.

I'll assume that since the video you've installed a new radiator cap, checked the connector at the temp sender as noted above, and cleaned up the connections at the battery.

Note that when A/C is on, it activates the lo speed circuit. Using the hi speed circuit as a feed means that A/C can be used without the fan, further stressing the cooling system.

Next time you run it, shut it down when it moves past the middle of the 'M' on the temp gauge if the fan isn't running. Never run it past M if you can avoid it at. This assumes your temp gauge is anywhere near accurate. But I have to say, overheating it like that 6~7 times is pure Russian roulette.

Once the cooling system is sorted out, you can move to seeing what's up with the idle.

Sadly, I've not really done anything to the car since the video except top off the coolant to see how much spewed out :eek:

The air conditioning in my car does not work (I was told the Freon leaks) so I never run the air conditioning, but I do run the defroster and the vent. it's probably a good thing my AC didn't work while I had the aftermarket fan hooked up.

I will never ever let the car creep that high again. I'm also going to buy a real thermometer that tells me precisely how hot the car is.

Other than head gasket failure, what else should I be on the lookout for when the car gets this hot? Should I drain the coolant and replace it (because it's chemical properties could have been compromised?). Should I test my radiator for damage or buy a new one? I'm definitely getting a chemical engine block test kit of some kind to check for headgasket failure, but I wasn't sure if there was anything else I should do. I'm really mad at myself that I didn't turn the car off sooner.

Thanks again for the help.

-Rick Leuce
 

sam jones

Registered User
Thanks for the fast responses everyone!



The car has not driven since Spring 2015, but I've run out the fuel and replaced it a couple times since then. I last put in 5 gallons about a month ago, and the car is currently at a quarter tank, so the fuel is mostly fresh.

Thank you sam jones. I have quite a bit of HEET injector cleaner on hand (didn't use it yet), so I'm glad you said something. The last fuel additive I put in was a bottle of Techron, which showed up as a "fuel system cleaner" when I was Googling my options. Is there something else you would recommend?

You are correct, the corrosion goes beyond the terminals. I will do my best to remove as much corrosion as possible.

I've never had a head gasket blow on me yet, so I'm paranoid it could happen any day now (especially when the car has almost overheated a few times already) I will definitely get a kit to check for possible failure.

I'm planning on picking up an OBD-1 scanner tool like the one below. It looks like the same one Autozone carries but like $10 cheaper.

https://www.walmart.com/ip/INNOVA-3145-Ford-Digital-OBD1-Code-Reader/16606975




Sadly, I've not really done anything to the car since the video except top off the coolant to see how much spewed out :eek:

The air conditioning in my car does not work (I was told the Freon leaks) so I never run the air conditioning, but I do run the defroster and the vent. it's probably a good thing my AC didn't work while I had the aftermarket fan hooked up.

I will never ever let the car creep that high again. I'm also going to buy a real thermometer that tells me precisely how hot the car is.

Other than head gasket failure, what else should I be on the lookout for when the car gets this hot? Should I drain the coolant and replace it (because it's chemical properties could have been compromised?). Should I test my radiator for damage or buy a new one? I'm definitely getting a chemical engine block test kit of some kind to check for headgasket failure, but I wasn't sure if there was anything else I should do. I'm really mad at myself that I didn't turn the car off sooner.

Thanks again for the help.

-Rick Leuce




Good evening


Everyone has a favorite fuel system cleaner. When the car is prolong storage but will be started at least once a month I use Gumout with Regain and Gumout Multi-System Tune-Up to address cleaning and fuel stability. HEET is best used if the car is up and running. I use this site regarding oil, fuel and or additives in cars.

https://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=262951
 

Rick_Leuce

Registered User
Hello everyone,

I finally started the 1991 SC for the first time since nearly overheating it. No white smoke out the exhaust and no steam coming out of the oil dipstick tube, so hopefully I'm ok for now.

I bought a new radiator cap and a new Coolant Temperature Sender. I forgot to test the coolant temp sender before installing it so my gauge is probably not accurate. My temp gauge is on the M in NORM when my radiator hose is just getting warm (Supposedly when the car is at normal running temperature). So my gauge works, but reads way higher than I'm used to. I used a laser thermometer and the radiator was at 178 degrees Fahrenheit and the engine was at 182 degrees Fahrenheit when my needle was pointing at the M in NORM.

After warming up the engine, I got a paperclip and connected it to the EEC TEST plug.

I watched these YouTube videos and I connected my paperclip into the same connectors, but my Check Engine and/or Check Gauge light did not flash (I waited about 2-3 minutes each time before giving up). I removed and reinserted the paperclip about 3-4 times and left it in once while I started up the car for a Key On Engine Running Test, but it still didn't flash then either (to be fair, I didn't pump my brakes or turn my steering wheel like I was supposed to in the video). I know the car recognizes something is different because when there is no paperclip put into the EEC TEST, the car beeps when the key is on and the Shift light is on. However, when the paperclip is connected, the car DOES NOT beep and the shift light is off. In both cases the Check Gauge light is on and nothing is flashing.

Here's the YouTube videos I watched. Let me know if there is something else I should try. Should I just buy the $29.99 OBD-1 Ford scanner tool from Autozone?

KOER
https://www.youtube.com/watch?v=nl2lqqS7vvE

KOEO
https://www.youtube.com/watch?v=-YYQKssOEOs

View attachment 69572View attachment 69573View attachment 69574
 

KMT

Registered User
About the temps. When the engine is 'just getting' warm Feel warmth in the upper hose, but can lay your hand on the radiator still), and the thermostat is open(ing), the temp wouldn't quite be near normal operating, and on the gauge would not be anywhere near M, I believe. The fan should come on before/at that point. If it's actually that hot and the fans are quiet, the fan circuit is suspect. What temp does the IR gun report at the coolant air bleed bolt? M would be right around 200°~203° I think. If the gauge is mis-reporting (not sure yours is), that's another issue. I'd want to finish self-testing the IRCM/fan/ECT first.

And just to note, there have been TSB's on mis-reading SC gauges - search here, just be wary of getting a mismatched sender from the aftermarket today. See comment #6 in this thread:
http://www.sccoa.com/forums/showthre...795#post914795

> Should I just buy the $29.99 OBD-1 Ford scanner tool from Autozone?

Code reader for the win.

Don't get me wrong, back in the day I was all over jumpering the self-test connector, but not since code readers became common and affordable to the public. I created this image back in 1982, which, funny enough, is still being circulated on the 'net today:
1263d1209859818-how-read-check-engine-code-1995-without-obd2-self-test.jpg


I used that process to demonstrate to a Ford dealer that their $10k STAR tester was wrong when it said the ECU in my nearly new '85 Turbo Coupe was not stuck in limp mode. They brought in another STAR, re-tested, agreed w/me and fixed my 'bird.

Are you sure you're using the VIP Self-Test connector and not the ARC test connector?

...but the code reader makes the process easier, more reliable and more comprehensive. They usually come with a guide, but the 'net has tons of info on the different tests that can be performed and what the codes mean. I like this list, which calls out SC-centric codes: http://www.njtacc.com/tech/eec_codes.html
 
Last edited:

Rick_Leuce

Registered User
Thanks for your fast response.

It occurred to me less than an hour after posting that I should try doing the same paperclip thing to my 1990 SC (to see if I knew what I was doing). My 1990 SC check engine light does come on and flash. I also heard the radiator fan kick on for 1 second (so I see now what you meant earlier). Im guessing my Check Engine light in my 1991 SC doesnt work and/or has a whole other electrical problem I knew nothing about. Im hoping its the former, because I suspect I could get away with just using a scanner/reader instead of replacing the Check Engine bulb.

I know a guy who said he had something for OBD-1 (for Fords) that he’d give me in a couple days. I’ll try using his and see if my 1991 can flash some codes.

I wished I knew about this OBD-1 stuff sooner. I get a little trigger-happy with the parts canon :rolleyes:
 

KMT

Registered User
My 1990 SC check engine light does come on and flash. I also heard the radiator fan kick on for 1 second (so I see now what you meant earlier).

Nice deduction, it always helps to confirm your tools and process.

>Im guessing my Check Engine light in my 1991 SC doesnt work [clip] ...instead of replacing the Check Engine bulb.

Yes, sounds like something's up. The IRCM has a power relay for the ECU, but if that's borked, I'd not expect the car to run, so...

See this link, long post by jrichker, about 1/2 way down 'Computer will not go into diagnostic mode': https://www.stangnet.com/mustang-fo...-light-wont-work-when-doing-koeo-test.709184/

- explains how to test that circuit.

I'd at least do this much...
How to test the wiring:
With the power off, measure the resistance between the computer test ground (black/white wire) on the self test connector and battery ground. You should see less than 1.5 ohms.


The whole purpose of this exercise is to validate the IRCM and the fan circuits. There are ways to power the relays directly at the IRCM, so while the inability to self test may point to related issues, etc., don't let a self-test be a show stopper for that process.
 
Last edited:

Rick_Leuce

Registered User
And just to note, there have been TSB's on mis-reading SC gauges - search here, just be wary of getting a mismatched sender from the aftermarket today. See comment #6 in this thread:
http://www.sccoa.com/forums/showthre...795#post914795

Don't get me wrong, back in the day I was all over jumpering the self-test connector, but not since code readers became common and affordable to the public. I created this image back in 1982, which, funny enough, is still being circulated on the 'net today:
1263d1209859818-how-read-check-engine-code-1995-without-obd2-self-test.jpg


Are you sure you're using the VIP Self-Test connector and not the ARC test connector?

Thank you so much for this info. My 1990 SC was flashing 67,67, 11111 (I did it 3 times and it was consistent each time).
67 can mean Clutch Switch Circuit Failed (SC only). Its a 5-speed, so this is possible.
67 can ALSO mean Neutral Drive Switch Circuit Open. Im assuming that because my car flashes it twice, I could have both of these issues.

I’m guessing 11111 is a combo of 11 and 111. Both 11 and 111 mean System Pass according to the sheet you provided.

I guess its good Im learning this stuff because it helps me with both cars.

The first link you sent me for the SCCOA thread isn’t working, could you send it again?

I don’t know for sure if I used the VIP Self-Test connector or the ARC test connector. I just used the two plugs that were included in the EEC TEST cover.

I really believe that the Check Engine light does not work in the 1991. In fact, other lights might not be working based on the photo I took in the 1990 today. (Im using iPhone right now, so hopefully it comes out right). Either way, I’m definately using something other than a paperclip going forward.

Thanks again for your help. This OBD-1 stuff is all new to me (even though Ive owned my 1991 SC for over 6 years).
 
Top