Super coupe bucks at boost what to do next?

Did you test your coil hot or cold? Any visible cracks/damage?

If the store has one, maybe they'll let you check it to compare.
 
cold test

Did you test your coil hot or cold? Any visible cracks/damage?

If the store has one, maybe they'll let you check it to compare.

Tested cold car has been apart but my theory is there would be more resistance when it's hot ?? I'm putting new stuff on now any It may have been the sc belt this one came off soo easy and the new one was not the same to say the least
 
update!!!

New cam sensor, gapped plugs, new belt, new coil, new plug wires
Still the same hard to start when it does it chugs for second the levels out I also cleaned the maf this morning. After starting today I can hear the rpm lower when I unplug iac, when I unplugged the MAF there are no changes in the way it runs still idles and then bogs when in boost still haven't gotten around to fuel and filter trying to run this tank low then do a fill up b4 the filter. Could it be maf
 
What maf will interchange from junkyard?

New cam sensor, gapped plugs, new belt, new coil, new plug wires
Still the same hard to start when it does it chugs for second the levels out I also cleaned the maf this morning. After starting today I can hear the rpm lower when I unplug iac, when I unplugged the MAF there are no changes in the way it runs still idles and then bogs when in boost still haven't gotten around to fuel and filter trying to run this tank low then do a fill up b4 the filter. Could it be maf

I've got a maf off a cougar non sc of the same year I can also get my hands on several 5.0 fox maf on the cougar one I have I can remove the senor portion and put in the larger thunderbird maf housing. Make no different when maf is unplugged what should the voltages be on a scanner for this through the rpm range? I'm pretty shure it should die or at least chug at idle if it's unplugged. I also plugged the cougar 1 in while car was running and I was just holding in my hand and it still ran the same?
 
I've done this

99% of the time bucking is caused by ignition problems which are usually plugs or wires. Sounds to me like you have a bad plug wire which is not uncommon.

David

What else should I do I see several members said dis. I even talked to a local guy who had a couple sc coupes and said he would say dis. Local auto zone said they'll test it. Has new coil, new Motorcraft oem plugs gapped 52, new cam sensor, cleaned maf, when maf un plugged no change in the way it runs can I use the electonic portion from a na 3.8 cougar around the same year. I have new fuel filter just haven't installed it. Little hard to start but runs great other than bucking and loss of power when revving into boost. I noticed if I floor it at idle in park it'll accept boost until about 2500-3000rpm then falls on its face almost like locks up u can here it shutter and rattle the let out its smooth as every other car I own
 
Good afternoon

Have you checked fuel pressure? I would eliminate fuel system components first (fuel pressure regulator, filter, pump, harness). If it passes inspected the DIS harness. Take a close look at the DIS, Crank and Cam connectors for broken, chaffed and or exposed wiring. Inspect the harmonic balancer for broken or missing bolts. Does the harmonic balancer/pulley "wobble" when running? 1989 - 1993 check the Crank sensor for evidence of balancer vane striking.

Good luck.
 
Last edited:
Also another thing to keep in mind, any Auto Zone or Advance Auto should be able to test the DIS module before you buy or replace your current sensor.

-Tim
 
What else should I do I see several members said dis. I even talked to a local guy who had a couple sc coupes and said he would say dis. Local auto zone said they'll test it. Has new coil, new Motorcraft oem plugs gapped 52, new cam sensor, cleaned maf, when maf un plugged no change in the way it runs can I use the electonic portion from a na 3.8 cougar around the same year. I have new fuel filter just haven't installed it. Little hard to start but runs great other than bucking and loss of power when revving into boost. I noticed if I floor it at idle in park it'll accept boost until about 2500-3000rpm then falls on its face almost like locks up u can here it shutter and rattle the let out its smooth as every other car I own

Check engine light on ? Did you take apart the intercooler pipes when installing the plugs and wires ? If so what did you use to reseal them ?

David
 
Little hard to start but runs great other than bucking and loss of power when revving into boost.


Hard to start is usually cam sensor...or also crank sender, DIS and harness/grounds, EEC.

One way to check if it's tied strictly to boost is to remove the supercharger belt and go for a test drive. It should run ok, but accelerate like a 4,000 lb. Pinto with the e-brake on.

I'm still expecting it to be a plug wire issue, tho ;)
 
Last edited:
this is today

This morning started hard about the 3rd try. Tach read 0 for about 1min then came on first time I noticed that. I put a diffrent oem ford dis off the only thunderbird sc at the local U pick junk yard (gave to me free) installed that 5gal premo, and fuel filter still the same. I have to order the Ford connector to connect to ford fuel rail because can't find my adapter. Has new plugs and wires double checked everything except fuel psi.
 
I did the dis test to best of understanding

DIS/Coil see:

http://mnharms.com/tutorials/disnostart/

...and for an overview:

http://www.dainst.com/info/edis/edis.html

IAC:

FORD IDLE AIR BYPASS

Ford doesn't use idle air bypass to regulate idle speed on its older throttle body (CFI) applications, but uses a solenoid or vacuum diaphragm instead to open the throttle linkage. Idle air bypass is used only on multipoint injection applications. On older pre-OBD II cars, codes 12, 13, 16, 17 & 19 all indicate idle speed is out of spec (too high or too low). Codes 47 and 48 indicate a fuel mixture problem which could be caused by an air leak. On OBD II vehicles (1996 & newer), codes P505 to P509 indicate a fault with the idle speed control system.

The diagnostic procedure when any of these codes are found is to turn the engine off, unplug the ISC bypass air solenoid connector, then restart the engine to see if the idle rpm drops (it should if the ISC solenoid is working). No change would indicate a problem in the motor or wiring.

The ISC solenoid can be checked by measuring its resistance. With the positive lead of a digital volt/ohm meter on the VPWR pin and the negative lead on the ISC pin, measure the resistance of the solenoid. On many applications, the spec calls for 7.0 to 13.0 ohms. If it is out of specs, the ISC solenoid is bad. Also check for shorts between both ISC solenoid terminals and the case.

If the ISC checks out okay, check for battery voltage between the ISC connector terminals while the key is on. Voltage should also vary when the engine is running. No voltage indicates a wiring or computer problem.

Suggest you pick up an EVTM off eBay if you like checking wiring, etc.


I followed the trouble shoot page the best I could. Up until the point it tells you to skip to like n22 n23 where u have to take a test light from pin 4 or 7 to the pin 4 on the crank sensor harness (I'm not to shure on the actual numbers since I'm not reading them) detecting which post on dis is easy bc there numbered but how do I know which one to test on the crank sesor plug if there were a pic or 2 of the plugs would help. But I did the test as follows connected the test light to the two points it told me to (I guessed at the crank sensor plug because it said + bat in instructions so I checked for the hot wire with a test light first) then I used test light and had a buddy turn the car on and the light was supposed to come on and it did not!! The next step was to repair / replace harness I just want to make shure I conducted the test properly. And I'm shure the two dis modules are bad and male the car run the same.

The car does not cut off and not start back up it always runs good until the boost pressure rises I can make it turn 5000rpm plus without missing a lick without boost as soon as I boost it blahhhhhh no more than 3k rpm.

As for boost tunes we did remove top when I did plugs the first time the joints were sealed with grey silicone to match pipes. I did not re seal them but they are goodentight lol. I'm Pissed bc friends borrow my stuff an can't return now I'm the one searching for fuel pressure testing products arrghh
 
What are the readings on multimeter. Do know where I can get a pic diagram of the plug to properly test it.

Connectors/pin-outs are all detailed in an EVTM for your year SC. As I said earlier, if you're the type to start probing, you'll need one sooner than later. They usually don't cost that much used off eBay, and they're packed with SC goodness.

Crank sensor is just hall effect, so on/off...send/or not. Black is alwayd ground, and in case you're not aware, (1) SCs are electronics heavy (including minimum volts and reliable/multiple grounds) and (2) Ford loved to use ground to make/break circuits back then.

Be careful making run conclusions as the EEC substitutes default look up values when certain sensors go missing. As well, it can rely on them when a new sensor is added, making it important to remove power to the EEC long enough to force it to relearn, while you drive around so it can re-sample.
 
Last edited:
I don't remember for sure, but aren't there only 2 or 3 terminals in the crank sensor plug? I think that, as long as you use the right test light, it won't matter which direction you have it hooked up. But for the crank sensor test, I think you need a LED, 12V, test light. And since LEDs are one-way (diodes, after all), the kind you need really has 2 LEDS, one each way. If you use a 5V LED, it can mislead you, because it will flash at a voltage level that is too low for proper EEC operation. And if you use an incandescent test lamp, it may not show any flashes, or may just glow dimly.

You know the cam sensor helps with starting and ignition, but isn't really needed for the car to run. To rule it out, you can simply unplug it. The car will take a few tries to start, but should run fine once started.

Crank sensor is critical for the car to run. Bad crank sensor, you get no ignition. Failing crank sensor, well, it can act weird.
 
runs good without sc

Hard to start is usually cam sensor...or also crank sender, DIS and harness/grounds, EEC.

One way to check if it's tied strictly to boost is to remove the supercharger belt and go for a test drive. It should run ok, but accelerate like a 4,000 lb. Pinto with the e-brake on.

I'm still expecting it to be a plug wire issue, tho ;)

I've rechecked wiring etc installed another crank sensor, waiting on my fuel pressure tester to come in that I ordered since I couldn't find my ford adapter.

I removed supercharger belt and it turns up without missing a lick just like I say like pullin 4,000lb trailer but revvs.out 5000+ rpm without bucking what your idea on that case?
 
The dense air in the cylinder under boost acts like an insulator, so it does make the job of the ignition system more difficult. So an ignition problem (at least in the secondary or high-voltage side) will probably show up first under boost. RPM also stresses the ignition system, but in a little different way.

Boost also requires a higher fuel pressure, so a fueling problem would also show up first under boost.

Probably best to wait for the fuel pressure results and then go from there. It sounds very fixable.
 
Back
Top