long story short I put my 2.5L back in my 88 and sold my 3.4L swap to buy a fastback daily driver. ================================== here's the details:
Starts fine, idles good for a couple minutes
after a couple minutes the idle rpm's sort of wander very oddly. not reving up and down, but gradual
when driving it sometimes wants to stall (and does) while shifting into another gear (manual) or when coming to a stop.
when I'm stopped in traffic the rps kick down then up A LOT, to the point I need to keep my foot on the gas so kids don't think I want to race them...lol
when the engine is running it sounds like it's very slightly putt putting. ========== ========== here are the things that are new or have be tested and have ZERO ISSUES:
brake booster (and all connections between the booster and the engine) fuel pump - new Pump Strainer - new fuel filter - new fuel pressure regulator - new Every engine seal and gasket was replace (full deconstruction and rebuid - this problem was happening before I did this) MSD Coil Packs ignition module - new Crank Sensor - new Spark Plugs - new Spark Plug Wires - new Power and Ground cables - new PCV - new EVAP System has been checked and bypassed - issue doesn't go away EGR - new Computer (PCM) has been swapped (1988 5-speed and 1987 5 speed, no change) no catalytic convertor (though I'm going to be putting a high flow unit on to quiet it down again
With the engine warm and idling at the correct speed, unplug the IAC. That will freeze the IAC's pintle at that particular spot. Then see if you still have the idle speed error. If so - then why is the ECM commanding a changing idle speed. If not - then what is actually causing the idle speed changes?
Try clean the IAC passage and the throttle body and backside of the throllle body blade. Over time they get carbon build up and reduce the amount of air that flows through them at idle. When the engine tries to idle too low, then it kicks into stall saver mode and will shoot the RPM's up.
You might also try blocking off the EGR at the manifold... the last new one I had for an 88 2.5 wouldn't seal shut properly and was flowing all the time. Idled like a champ once I blocked it off (welded the port in the EGR housing closed).
[This message has been edited by fieroguru (edited 11-09-2012).]
1. check battery and alt volts etc. Iffy power will be a problem. Check when engine is cold and hot.
2. get ECM scan tool Monitor ECM volts. ECM should see battery volts +- 1v max at all times. If not check all grounds etc... G201 and G202 too. See my Cave, Scan Tool Help, Wire Service
2a. Maybe ECM w/ heat issues. ECM won't set a code etc for heat problems... maybe bogus codes. If cooling help, get a new ECM and read ECM Heat
3. Get stock coils. Car starts and runs but has problem when hot is a likely sign Coils have heat issues. What brand/type of plugs? DIS hates "Performance" coils and many types of plugs. If shield is missing, find a used one or make one. See my Cave, DIS Ignition
Coil AIRTEX / WELLS Part # 5C1058 STANDARD MOTOR PRODUCTS Part # DR39 (But not cheap DR39T)
4. You switch ECM PROM... What number on the PROM? May need PROM update. See my Cave, 87-88 DIS Duke ECM
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
Might check the coil pack connector harness end. I was having random loss of power and sometimes a really low idle that would come and go. Eventually it stayed in the low power mode and was able to limp it home. Never set a code... but this was the culprit:
Might check the coil pack connector harness end. I was having random loss of power and sometimes a really low idle that would come and go. Eventually it stayed in the low power mode and was able to limp it home. Never set a code... but this was the culprit:
both connectors that attach to the ICM are good, though the rubber weather seals have become enlarged from absorbing Dielectric grease...very weird.
I had to wire my tachometer into the large conector as it was faulty (about 2 years ago), removing it and not having it connected to the tach doesn't change anything.
this really has had me puzzled. I've been living with it for years, and this last year it got worse to where it will actually stall out.
but I've just completely rebuilt the engine and replaced EVERYTHING.
it has to be harness related as it's the only thing I haven't restored to perfection on the drivetrain...and the original fuel injector.
Fuel pressure regulator has already been replaced. Everything ignition and fuel related has been replaced except the fuel injector. I swapped out the fuel injector for another 1 and it didn't change anything so I put the original 1 back in.
What I'm thinking all do is put some stock style coil packs back on and replace the icm harness end ( which I already ordered from the Fiero store) I also have a few spare O2 sensors so Ill replace that too as Its a year old.
replaced the ICM connector and there is no difference... now literally the only thing that hasn't been replaced is the injector... I continue to get a random code 42 every once in awhile. which I believe is evap system... but when I plug of the Evap at vac lines from the throttle body it doesn't change anything and I still get the code every once in awhile.
so it is!! everything ignition related is brand new... I'll try playing around with the wires on the harness thats will spark plug wires. I had the same issue with my V 6 swap so maybe I'm having it now too. that would make a lot of sense! I'll try and figure it out tomorrow as my fastback is pretty much done.
Check Grounds bolted to Trans bell housing. DIS ground goes to bell housing. (This is G504)
Random DTC 42 could be need a PROM update but need to eliminate grounds etc first.
Could be a Dieing ECM. Pull console and Carefully Try warming up ECM w/ hair drier. See my Cave, ECM Heat
thanks for the info!!!
my ECM in Remanufactured. I have tried several ECM's and the problem doesn't go away . I'll recheck my grounds. I added a bunch of extra grounds just for the heck of it. I should know more later tonight after the big bird stops dancing in my gut. lol
so here's a list of parts that are new in the last 1-2 years. (the problem has existed for 3ish years)
replaced: ICM Harness section (with fiero store part) computer wires plugs IAC PCV Rubber Vacuum Lines Fuel Pump Fuel Filter ICM Crank Sensor Coils O2 Sensor added 2 more grounding straps to the engine and transmission (6 or 8 gauge I believe) Battery Alternator Starter Positive Power Cable
Brake Booster and line have no leaks did a vacuum test at the brake booster, holds pressure perfectly with no loss after a few minutes, and immediately had pressure on first pump of the tester.
there are no bad wires on the harness that are pinched, cut, or bare.
getting low 20's for MPG's (about 20-23) swapping the fuel injector didn't solve anything either...
I know it is Timing/ignition related.
when the ALDL is jumped it takes about 15-20 seconds of cranking to start the engine when cold. when not jumped it takes about 1-3 at cold
with ALDL jumped the engine sounds more throaty and has a lower tone to the exhaust, obviously this is due to not having the computer advance the timing.
swapping to a remanufactured ECM didn't help, nor did any of the ECM's I have in my parts collection...
so the computer is not in the cards...
from all the help folks have given me I believe it to be in the Ignition area with the Crank Sensor/ICM/Coils/Harness/grounding of ICM
after all the work and trouble shooting I still can't find the source to this invisible but noticeable gremlin.... anyone care to come in person to help me? gas cost is on me of course.
In the mean time I'm still driving it (or trying to...lol), and finishing my 1987 GT Project which is literally 1 part away from running.
I replaced the entire Igniton set up on my 88 coupe with a known good one. and it actually ran worse...lol
I'm figuring out exactly what I originally thought is the answer...the harness is bad.
because it's the only part I haven't swapped off yet...
I'd love for someone to come her and help me figure it out before I replace the harness... though because it's a 2.5L the harness is so simple to swap out, it's still money I'd like not to spend
The stalling when pushing in the clutch might be VSS related. Sure your speedo is working so the VSS is fine, but the speedo sends a buffered signal to the ecm. When the ECM sees the fiero in motion from the buffered signal, it raises the idle RPM set point to avoid the common issue of off throttle stalling when the clutch is pressed. I suspect the ecm might not be seeing this buffered signal for some reason (bad buffer board or wire). Might be worth swapping instrument clusters (or just the speedo) to check.
Have you tried unplugging the A/C relay and driving the car with the defrost on? With defrost or AC on, the ecm will bump the idle RPM to overcome the pumping loss of the a/c compressor. By unplugging the AC relay, the compressor clutch will not engage and the pump will remain off, but the ecm will raise the idle RPM... which might be enough to stop the stalling condition temporarily and allow you to drive it more.
The stalling when pushing in the clutch might be VSS related. Sure your speedo is working so the VSS is fine, but the speedo sends a buffered signal to the ecm. When the ECM sees the fiero in motion from the buffered signal, it raises the idle RPM set point to avoid the common issue of off throttle stalling when the clutch is pressed. I suspect the ecm might not be seeing this buffered signal for some reason (bad buffer board or wire). Might be worth swapping instrument clusters (or just the speedo) to check.
Have you tried unplugging the A/C relay and driving the car with the defrost on? With defrost or AC on, the ecm will bump the idle RPM to overcome the pumping loss of the a/c compressor. By unplugging the AC relay, the compressor clutch will not engage and the pump will remain off, but the ecm will raise the idle RPM... which might be enough to stop the stalling condition temporarily and allow you to drive it more.
my 88 coupe has Zero options. as for switching the gauge cluster out I've already tried it... but just for the heck of it I'll try it again hey make sure the connections are all good
all gauges function properly. ignition module was replaced a little over year ago. the spark plugs and wires are brand new. I have already tried swapping computers, coil packs, ignition modules, the heat sink backing plate on the ignition module, gauge cluster, idle air control valve, through trying different ones of all those parts nothing changed.
I tried rerouting the spark plug wires nothing changed.
I have checked all electrical connections as well as the harness...no damage found anywhere.
You are going to have to stop throwing parts/spares at this issue and start doing some true diagnostic checks if you want to solve this issue. The good thing about it setting codes is it gives you a few places to start.
If you don't have an 88 service manual, get one. It has troubleshooting flow charts for every diagnostic code and will walk you through the troubleshooting process.
This may or may not be the method in the service manual, but this is how I check for MAP sensor issues: Turn the key on and check for 5V at Pin C (grey wire). This 5V wire is shared with the TPS as well, so if you don't get the full 5V, unplug the TPS sensor and check it again. If the reading changes, there might actually be something wrong with the TPS sensor that is pulling down 5V ref signal that both sensors use. Then check the ground wire Pin A (black wire) and measure the ohms between it and the engine block and between it and the negative on the battery... if either of these measurements isn't very close to zero, then you have some poor ground connections. Last check the map signal wire pin B (light green). It helps to have a mighty vac or some external means to apply a varying amount of vacuum to the sensor, as you do this you want to see a gradual change in the sensor reading and no dead spots.
You can do the same multimeter checks on the ground and power wires on the coil pack to rule out a basic power/ground issue...
You are going to have to stop throwing parts/spares at this issue and start doing some true diagnostic checks if you want to solve this issue. The good thing about it setting codes is it gives you a few places to start.
If you don't have an 88 service manual, get one. It has troubleshooting flow charts for every diagnostic code and will walk you through the troubleshooting process.
This may or may not be the method in the service manual, but this is how I check for MAP sensor issues: Turn the key on and check for 5V at Pin C (grey wire). This 5V wire is shared with the TPS as well, so if you don't get the full 5V, unplug the TPS sensor and check it again. If the reading changes, there might actually be something wrong with the TPS sensor that is pulling down 5V ref signal that both sensors use. Then check the ground wire Pin A (black wire) and measure the ohms between it and the engine block and between it and the negative on the battery... if either of these measurements isn't very close to zero, then you have some poor ground connections. Last check the map signal wire pin B (light green). It helps to have a mighty vac or some external means to apply a varying amount of vacuum to the sensor, as you do this you want to see a gradual change in the sensor reading and no dead spots.
You can do the same multimeter checks on the ground and power wires on the coil pack to rule out a basic power/ground issue...
nope. all sensors are new. did new wires and plugs, coils, crank sensor, module, coolant temp sensor, air temp sensor, egr, etc etc. even the computer is new.
WD-40 will clean contacts and let them make better contact. If you don't believe me, try this experiment. Take an ordinary toy battery operated motor. Connect a battery and listen to how fast it runs. Now put a couple of drops of WD-40 on the motor's brushes and commutator and connect the battery again. The motor will run noticeably faster. It's not because of lubrication -- there's very little drag on a toy battery motor's brushes. It's because of better contact. Edit: PS. Sometimes a V6 Fiero will show symptoms of a bad ignition module when the problem is actually a contact problem. It happened to me. I removed the low voltage connections from the spark coil, and the connections on the ignition module, sprayed with WD-40, replaced them, and the car ran perfectly again. When folks replace their ignition modules, often the old module is actually not bad, but in doing the replacement, they have wiped the contacts by virtue of removing and replacing them. The dry wiping helps, but WD-40 makes it better.
[This message has been edited by TopNotch (edited 07-30-2013).]
WD-40 will clean contacts and let them make better contact. If you don't believe me, try this experiment. Take an ordinary toy battery operated motor. Connect a battery and listen to how fast it runs. Now put a couple of drops of WD-40 on the motor's brushes and commutator and connect the battery again. The motor will run noticeably faster. It's not because of lubrication -- there's very little drag on a toy battery motor's brushes. It's because of better contact. Edit: PS. Sometimes a V6 Fiero will show symptoms of a bad ignition module when the problem is actually a contact problem. It happened to me. I removed the low voltage connections from the spark coil, and the connections on the ignition module, sprayed with WD-40, replaced them, and the car ran perfectly again. When folks replace their ignition modules, often the old module is actually not bad, but in doing the replacement, they have wiped the contacts by virtue of removing and replacing them. The dry wiping helps, but WD-40 makes it better.
you misunderstand. I completely agree and know you are right. but when a replacement ICM costs $60-100 I dont want to risk signals crossing because or the wd40. but Ill take a q-tip and wd40 and touch each individual contact instead of spray.
the issue only happens when the engine is warmed up.
no change with wd40. have codes 15 - coolant temp 24 - speed sensor 33 - map sensor (only happens when it stalls) 42 - ignition
I wish I could get the replacement harness (with AC) I asked for. the issue has to be in the wires. Id love to make a new harness but at the cost I could do a v6 swap.
