Very Random miss every now and then....need some ideas

Tim Groth

SCCoA Member
Pretty well stumped on to where to start on this one.

Car in question is bone stock '89 5spd. It's my daily driver with 207K. Recently replaced Headgaskets at 204K - no driveability issues since or before they went out. Car has been a solid daily driver/beater for my commutes to and from work.

Recently the car has developed an intermitten problem, that doesn't happen regularly at all and it has me stumped. Its kind of like a surge. The car will rev up and then drop idle, rev up then drop idle...it typically will do this for a 15-45 second period of time and then its fine. Prior to doing this the car runs fine, drives fine...it has it's little spasm...then its back to normal. This has happened while the car is parked and also while driving...when it happens while driving I typically down shift and push through and again it clears up. The car will chug if at a low RPM - down shifting to a higher RPM you can feel the miss but nowhere as near intense as at lower RPMs. And when I say chug where talking first time 5 speed driver chug...its pretty intense.

I have checked the balancer - no wobble, bolt is present
Fuel pressure is good (haven't tested it during symptoms however) again so intermitten its hard to do so, for it happens randomly.
All connections to DIS,Cam,Crank sensors are tight and clean.


My thoughts on what it could be

DIS Module
Crank Sensor / Balancer
Key Switch


Also as a sidebar - the car since I have owned it has an electrical surge that can be seen in the headlights and interior lights...its a hint flicker and kind of lines up with this issue. when I did the HGs I replaced the main ground wire to the battery from the block for it was in horrible shape...didn't change the problem.

Any thoughts on where to look next would be great.

-Tim
 
Have you checked for codes and/or disconnected the battery to force the computer to relearn?
 
DIS Mount hasn't been touched since I purchase the car with 199K - I can take it off (have it tested at AAP) and then reinstall with some Artic Silver Grease.

I can add an additional ground - thats simple enough.

Battery was just disconnect a few weeks ago when I used the battery to fire up one of my other cars...I'll scan the codes tonight and see what it comes up with.

Just noticed also that the Air Temp Sensor (one behind the boost gauge hose) isn't hooked up...not sure what driveability issues would become present with that unplugged. Assuming its been unplugged since the HGs were replaced, I wouldn't think it would be the issue.

-Tim
 
I would start with replacing the DIS module with a known good one. Several times I have had one go bad and cause intermittent bucking and misfiring. I've never had one fail and cause an idle surge, but that could just be the IAC trying to compensate for the misfire.
 
Tim, did you have a chance to take the DIS in and run a test? That is the exact issue my 89 5spd had when it went bad. Is the car warmed up or hot? Mine would do it at first when it came up to temp, but I couldn't find it and after sometime it finally started showing up at idle. When the engine and or engine bay was up to temp is when it would start acting up the most.
 
it's going to be the dis or coil pack or both. I had that problem and most of mine was the coil pack. still had some so I changed the dis. it went away almost completely. but I needed fresh plugs and wires too. will see this weekend if it goes away for good. btw I have a new motor with new crank,cam and iac sensors.
 
Tim, did you have a chance to take the DIS in and run a test? That is the exact issue my 89 5spd had when it went bad. Is the car warmed up or hot? Mine would do it at first when it came up to temp, but I couldn't find it and after sometime it finally started showing up at idle. When the engine and or engine bay was up to temp is when it would start acting up the most.

I would say that it typically happens after 10mins of driving, so it seems in line with what you're saying yours did.

Last night on the way home from my girlfriends place it did it after that amount of time. I took a video to capture this (will post tonight). The entire episode lasted 2 mins and then it was once again back to normal.

It hasn't done it today...again it usually will do it on my way to work and or on my way home from. The first time it happened I had driven the car for an hour or more. Car was parked and running and when i came back out to it it was chugging...

As of today it hasn't done anything. I will be near AAP tonight, I will swing by and test the sensor. Guess I always made the assumption that the sensor was either GOOD or BAD...but I suppose with an electrical short it can work when it feels fit.

I'll update this evening.

-Tim
 
it's going to be the dis or coil pack or both. I had that problem and most of mine was the coil pack. still had some so I changed the dis. it went away almost completely. but I needed fresh plugs and wires too. will see this weekend if it goes away for good. btw I have a new motor with new crank,cam and iac sensors.


Interesting on the Coil Pack - I've never had an OEM coil pack fail on one of these cars. I have a stock pile of em I can swap in.


Also If I need a DIS module - are the Ranger Truck Modules the same as the SCs - I might hit up the pick in save first before I drop $100 on a new one.


-Tim
 
Not sure about Rangers, but there is a year or two of the Taurus what use the same DIS. Lift the hoods and you can't miss 'em.
 
Drive home from work car did the same routine but did it twice this time. Stop at advance and tested the module 3 times and all 3 returned a good module. Went ahead and ordered a new one and also snagged some heat sink from another DIS package.

Now at the local watering hole for happy hour...guess I'll pick screw with it some more this weekend.

-Tim
 
Drove the car some today. No issues at all within the usual time frame of 15mins however this time the car just quit. Would crank, had no fire. Wiggled the wiring harness with the DIS and associated sensors and back up we were running.

At this point I'm not sure if it's a dirty connection, a short or a bad sensor. I cleaned the DIS connections and didn't change anything.

Also fixed the Intake Temp Sensor connection. At first the CE light turned off but is now back on...probably EGR related since it's deleted. Cleaned the air filter and also located my AC leak ...guess today wasn't totally lost but still flustered. I'm going to install the new DIS sensor for kicks but really don't think that's it.


Tim
 
A crank sensor might be my issue, I'll certainly have to give that a look too.

I replaced the DIS sensor yesterday with the Aftermarket BWD module. Car runs the same if not worse than before.

I'm wondering at this point if it's not a wiring issue.

For the time being, I've resolved the issue by just driving my other SC till I find patients to try some other fixes.

Tim
 
Just to update this since it's been a few days.

Installed the new BWD sensor from Advance. Over the weekend. Also was talked into using dielectric grease on it since no thermal paste was to be had. Car ran just as bad as it did with the OEM sensor. Again remembering the OE sensor tested good. Car has since, after the sensor swap, cut off and had tach issues. Sometimes I'll be driving the tach will just quit, yet everything else is happy...

Today my Thermal paste for the sensor arrived - I purchase a 30g tube off eBay for $5 shipped. After the car decided once again to die on me. I pulled off to the side of the road, removed the BWD sensor cleaned all the surfaces. Put a generous (way too much) coating of Artic Silver on the OE sensor and bolted it down... when I say too much, I mean the amount a pissed off SC owner who's broken down would put...A LOT.

Needless car fired right up (wouldn't hit prior after it died). After a 20 min drive the only drivability issue I have found is with the AC on and at a stop light the idle seems rather low at 7-800 rpms. I'm sure some sensors got carbed up compensating the firing issues. Thus it tries to die. I let it idle in my driveway with the AC on once home and it did fine. I'm sure the ECU is adjusting for the sensor working properly.

I will update this as things progress. Right now I think the sensor getting too hot was the cause and well the aftermarket unit had zero chance when the dielectric was added for instead of dispersing heat, it made it absorb heat. Only time will tell so I may be writing in a few days to say it's back to its old ways.

Till another day...

-Tim
 
"Drove the car some today. No issues at all within the usual time frame of 15mins however this time the car just quit. Would crank, had no fire. Wiggled the wiring harness with the DIS and associated sensors and back up we were running."

So my $.02 is to check your wiring and/or just replace the harness(es). You could try to troubleshoot the connectors and all (Ive done this) but I'd find one from somebody here and just replace it.
 
"Drove the car some today. No issues at all within the usual time frame of 15mins however this time the car just quit. Would crank, had no fire. Wiggled the wiring harness with the DIS and associated sensors and back up we were running."

So my $.02 is to check your wiring and/or just replace the harness(es). You could try to troubleshoot the connectors and all (Ive done this) but I'd find one from somebody here and just replace it.

I'm going to work on sourcing a wiring harness, certainly think it could be part of the problem. Since the addition of the fresh heat sink paste the issues have been far less frequent than when this first started. Also at this point I am back to using the OE DIS modual for the aftermarket sensor caused more issues than before.

Last night while driving the car once again did its moment of misfiring and then went back to normal.

Given the car has 207K miles I am pretty certain a large majority of the factory sensors are stock...would a Cam sensor or Crank sesor potentially cause such problems? Also I think I will swap coil packs for its simple enough and have several spares.

-Tim
 
I had an intermittent miss while rolling down the hwy. It would suddenly "buck/surge" almost as if running on a rev limiter, totally miss fire on a cycle of maybe 2-3 times a second. When it did this I could watch the tach "twitch" 1-200 rpm. It started with a second or two of this and continued to get worse (longer episodes). The last time it happened it continued for 5-8 MINUTES. I was afraid to shut the car off one the hwy in the middle of the nite and have it not restart. When I finally turned the key off, then back on (not to start, just back to run rolling at hwy speed) I lost all tach signal, no check engine light, and the car ran great the rest of the way home. When I tried restarting in the drive, I had to try several times, and it HARD cranked several times ( dimmed the headlights to almost out) before it started. I replaced the cam sensor with a used spare, and in the month since have not had another episode. During this entire span of time, 6-9 months I never had the typical cam sensor failure symptom of having to try to start the car several times before it "guessed" the right timing.

Long story short, I'm pretty sure a funky cam sensor could cause your intermittent miss, as it did mine, and it's easy to swap out. I'd try it.

Adam
 
I had an intermittent miss while rolling down the hwy. It would suddenly "buck/surge" almost as if running on a rev limiter, totally miss fire on a cycle of maybe 2-3 times a second. When it did this I could watch the tach "twitch" 1-200 rpm. It started with a second or two of this and continued to get worse (longer episodes). The last time it happened it continued for 5-8 MINUTES. I was afraid to shut the car off one the hwy in the middle of the nite and have it not restart. When I finally turned the key off, then back on (not to start, just back to run rolling at hwy speed) I lost all tach signal, no check engine light, and the car ran great the rest of the way home. When I tried restarting in the drive, I had to try several times, and it HARD cranked several times ( dimmed the headlights to almost out) before it started. I replaced the cam sensor with a used spare, and in the month since have not had another episode. During this entire span of time, 6-9 months I never had the typical cam sensor failure symptom of having to try to start the car several times before it "guessed" the right timing.

Long story short, I'm pretty sure a funky cam sensor could cause your intermittent miss, as it did mine, and it's easy to swap out. I'd try it.

Adam

This describes my problem to the T actually. I will swap the cam sensor out I have several spares to see if that helps.

Thanks for your input!

-Tim
 
I really hope it works for you. It's an unpleasant feeling, not knowing whats wrong, how to fix it, or when it's gonna go totally south and leave you stranded. Was kinda hard to describe exactly what was happening too. Glad you understood my description,

Good luck

Adam
 
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