In the 15 years of working on Fiero's I have never came across this. I jump in, turn the key on, for a split second the check engine comes on normal then starts to flicker. I start the car up and it continues to flicker. I can tell the car is either completely in diagnostic mode or partially in diagnostic mode. Fuel mileage is decreased, and engine does not want to rev up past 5000 very well, its like its hitting a soft touch rev limiter. (which I don't have)

Now here is the interesting part, after the car has completely warmed up, at some random point the light stops flickering and we resume normal operation.

So far I have checked all the plugs, harness connections and such around the ECM, changed the ECM, changed to 2 different prom chips. Checked the ground at the battery, checked the power at the battery. Checked that at no point is the wire from the ECM to the ALDL is cut or rubbing on any metal surface. Checked the ECM ground in the center console near the ECM.

Anyone else got any suggestions.

This is a completely stock 88GT. Only changes are Dawgs Big Bore intake system for the 2.8/3.4 motors. The intake did not alter any of the wiring or sensors.

My gas mileage has went from 30mpg down to about 15 and you can smell the raw fuel coming out the tail pipe. My biggest problem is I almost never take the car for a long enough drive to totally warm it up. It takes about 20 Min's of driving to get rid of the light, and most of my drives are about 10-15mins zipping across town.

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85GT Soon to be 87GT,93 Eldorado 4.9, 5spd Dual O2 Custom Chip, Custom Exhaust. MSD Everything Capt Fiero --- My Over View Cadero Pics Yellow 88GT 5spd Full Poly Suspension, Lowered 1/2" in front, Corner Carver.

The flashing light while running normally happens when A&B terminals are jumpered. I would suggest taking out the console and try moving the ALDL and ECM around (disconnect them from their respective mounts and move them around) while the engine is running to see if doing so makes the flashing stop. My guess is you have a short between the ALDL and the ECM. Also, check the ALDL connector to make sure the terminals are not touching within the connector (could be cracked).

Turn the key on, engine off. At this point the SES light should be on solid. Now take off the 5 torx screws from the back of the dash panel and see why the check engine light is flickering. Fix it. Then figure out why you are getting the SES light to come on when you start driving.

The flickering is a problem in the dash most likely

The SES light appears to be coming on but you are seeing the flickering and thinking it's something other than a normal check engine flash because of the flickering.

I don't see it as a problem with the ALDL since the ALDL can't make the light flicker.

That's my thoughts at least. See what you find with the dash light.

[This message has been edited by phonedawgz (edited 01-23-2011).]

Hey Guru, I'll give that a 2nd look. However the flashing you are talking about is the On/Off cycle that tells you if the O2 is reading lean or rich, and this is a much much faster flicker. Damn it I can't remember what they are called, but the long tube white lights you see in many businesses, and just as they are dying or the ballast is going, they get dim and flicker, really really fast. That is pretty much the way my check engine light is. And it does not change flicker speed if I have my foot to the floor or if I am lifting off the gas and engine braking down a hill.

I'll go out and check the connector again just in case. Hell I might get frustrated enough and cut the damn thing off, LOL. Just kidding, I'll grab my ohm meter and check to see if I have any continuity where I am not suppose to.

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85GT Soon to be 87GT,93 Eldorado 4.9, 5spd Dual O2 Custom Chip, Custom Exhaust. MSD Everything Capt Fiero --- My Over View Cadero Pics Yellow 88GT 5spd Full Poly Suspension, Lowered 1/2" in front, Corner Carver.

That's usually a sign that the Microprocessor in the ECM has stopped functioning correctly. Since changing the EPROM didn't help, I would have thought changing the ECM would have helped. But... You are still having issues somehow.

Also, be sure to check that the calpack is correctly seated. It's been a while since I've messed with them, but I think the Fiero's computer has a calpack next to the EPROM.

[This message has been edited by Fierobsessed (edited 01-23-2011).]

If the ECM and wiring is not the problem start checking relay resistance. They can go bad over the years and develop a coil short which can overheat the driver. Check your grounds also. Are you able to get a code with the ALDL grounded or proper light function under that circumstance? An improvement with driving time suggests a bad connection or a function affected by temperature change.

[This message has been edited by Joseph Upson (edited 01-23-2011).]

quote Originally posted by Fierobsessed: That's usually a sign that the Microprocessor in the ECM has stopped functioning correctly. Since changing the EPROM didn't help, I would have thought changing the ECM would have helped. But... You are still having issues somehow.

Second this.
I believe it's in limp-home mode. The running rich and not having any power are classic symptoms. If you have A/C, the compressor will be disabled, too.
My 3.4 used to do that when it got really hot (like sitting in traffic or in line at the drive through, in summer.) One of the down sides of removing the firewall insulation. The ECM gets hotter than hell, especially with headers. (FWIW, you can remove the EPROM from the ECM, and it will still probably run. Just poorly.)

Obviously, that's not your problem, though.

Check all the switched and unswitched voltage sources to the ECM.
If you have a scan tool, try to see if there are any sensors operating "on the edge". I've never heard of a single sensor taking down the ECM, but I suppose it could happen.
Maybe try changing your ignition module, just for grins. Suggesting that because it's about the only active electronic device that I can think of that's connected to the ECM.

[This message has been edited by Raydar (edited 01-23-2011).]

Ok one really really out there thing. I did not mention it as I am not sure if it is in my head or not, but on several occasions, when I turned the heat to the "vents" I noticed that the problem went away much sooner.

I'll check the bulb as well when I am out there checking the wiring.

Quick off the wall question, aside from the main ECM harness ground in the centre tunnel below the ECM is there any other major harness grounds. I have had a moisture issue in the cabin of the car for a while now and I really seem to think the issue is going to swing in the direction of something corroding and causing just enough resistance to trip the problem.

i will also grab the scan tool and run through all the sensor data. However IIRC I did that when the problem started and everything checked out fine. Not even a single stored code.

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85GT Soon to be 87GT,93 Eldorado 4.9, 5spd Dual O2 Custom Chip, Custom Exhaust. MSD Everything Capt Fiero --- My Over View Cadero Pics Yellow 88GT 5spd Full Poly Suspension, Lowered 1/2" in front, Corner Carver.

I had the same issue last june. Idk if you've checked but take your icm and have it tested. The whole flickering and rev limiting could be the control module. For me the "break voltage" was bad.....idk what that meant it was just a light on the tester that went red.....funny cuz I kept testing it over and over to wamr it up and eventually it passed....but smelt really bad. Then it wouldn't pass.

Anyways not sure if it was covered but its where id start.

P.s. I did jump my a&b and it would give me any codes when it happened.

My wife's Fiero had an intermittent CEL flicker, and the engine would cut for a split-second each time it flashed. It turned out to be a bad splice in the battery positive cable. Cut it, soldered and heat shrunk, and good to go. I know you said you checked yours but do a resistance test on both of your battery cables.

Just curious if you found anything.

Ok Update.

Removed the battery cleaned the terminals and installed a NEW optima yellow top.

Still flickering

Removed the cheap KEM ignition control module and installed a NEW GM AC Delco module

Still flickering

unplugged and plugged in the ECM connectors and the main connector that feeds the interior wiring.

Still flickering

This is driving me nuts. I am tempted to try a 3rd or 4th ECM just to see if the symptoms change.

Of special note, and I really should have put this in the first post.

I jump in the car, turn the key to the run position before I start it. The check engine lights up briefly like normal and then starts is flickering, even before I have started the car.

So this flickering does not seem to matter if the engine is running or not. I have even given it a shot, driving down the highway, with the car in gear, turned the ignition off, and gave it a 2 or 3 count and turned it back on. No change.

However still, if I drive it long enough to get totally warmed up, about 15mins or so, the check engine light stops flickering and engine power comes back to normal and away I go.

I drove the pants off the car today, just having a ball driving around, running 1st gear out to 6500rpms, grabbing 2nd running WOT all the way through 4th gear redline, downshifting hard into the corners and then powering through the corners with the tires howling.

Once the check engine light goes out, the car drives amazingly well.

I am going to keep trying things as I get time to play with it and when I find the solution I'll post it up here.

Thanks for all the tips guys.

I have not had time to get in there with a volt meter but that will be my next test.

p.s. no trouble codes show up on the scan tool and all the sensors are reporting as fine.

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85GT Soon to be 87GT,93 Eldorado 4.9, 5spd Dual O2 Custom Chip, Custom Exhaust. MSD Everything Capt Fiero --- My Over View Cadero Pics Yellow 88GT 5spd Full Poly Suspension, Lowered 1/2" in front, Corner Carver.

You've gotta do a datalog, something has to show up out of order during the malfunction. You may have a sensor that reads intermittently. The sensor that gave me the worst time was the MAP sensor and it wasn't until I noticed the Kpa value did not change with throttle input that I realized it was bad. The ECM never set a code.

You should also hit your dash when the light flickers to see if it's a bad connection at one of the two terminals, otherwise chase your engine light circuit to and from the ECM. I'm not sure if it's the same for the Fiero ECM but I found out while trying to do a bench setup with a 749 ECM during the process of making an ALDL cable that the engine light would not respond to grounding the ALDL terminal with either certain or nearly all of the sensors connected to it so that maybe a hint that there is a short somewhere and you might have to tear your harness down to find it as I discovered one while rewiring for the 730 ECM.

quote Originally posted by Capt Fiero: Ok Update. Removed the battery cleaned the terminals and installed a NEW optima yellow top. Still flickering Removed the cheap KEM ignition control module and installed a NEW GM AC Delco module Still flickering unplugged and plugged in the ECM connectors and the main connector that feeds the interior wiring. Still flickering This is driving me nuts. I am tempted to try a 3rd or 4th ECM just to see if the symptoms change. Of special note, and I really should have put this in the first post. I jump in the car, turn the key to the run position before I start it. The check engine lights up briefly like normal and then starts is flickering, even before I have started the car. So this flickering does not seem to matter if the engine is running or not. I have even given it a shot, driving down the highway, with the car in gear, turned the ignition off, and gave it a 2 or 3 count and turned it back on. No change. However still, if I drive it long enough to get totally warmed up, about 15mins or so, the check engine light stops flickering and engine power comes back to normal and away I go. I drove the pants off the car today, just having a ball driving around, running 1st gear out to 6500rpms, grabbing 2nd running WOT all the way through 4th gear redline, downshifting hard into the corners and then powering through the corners with the tires howling. Once the check engine light goes out, the car drives amazingly well. I am going to keep trying things as I get time to play with it and when I find the solution I'll post it up here. Thanks for all the tips guys. I have not had time to get in there with a volt meter but that will be my next test. p.s. no trouble codes show up on the scan tool and all the sensors are reporting as fine.

Dave, change your O2 sensor. Don't just assume its still good, change it. BTW, check if the O2 sensor wire isn't touching the exhaust crossover pipe. Check too (or once you replace the O2 sensor) the pigtail connector for corrsion or water.

BTW, is the car exhaust smelling rich all the time??

Try this...take the rear cover off from the speedo / tach gauges and replace the SES light bulb. Start the engine an hold the bulb with your hand and the grey plastic insert (what the bulb is put into) and check for flickering.

This humidty / damp issue you have doesn't help. Putting the car in a garage and let it sit for 2-3 night in a dry area may be a good idea.

Let us know you findings.

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fierogt28

88 GT, Loaded, 5-speed.
88 GT, 5-speed. All original.

Ok so today I needed to zip out for a quick trip to the corner store. I went outside and turned the key on, the light began its flickering. So I popped the deck lid and one by one unplugged each sensor checked the check engine light. No change whatsoever.

I got in the car pulled the centre console and chased all the wires from the ALDL plug to the ECM harness, everything looked good. Un bolted the ALDL and checked really close for any sign of debris, it was fine. As a last ditch, with the ignition on, I pulled one ECM plug and then the other, the check engine light went out completely.

I went into the garage grabbed a 3rd ECM from an unknown year Fiero and an unknown custom prom in it. (all my stacks of ECM's have custom proms designed for the car that they came out of)

I slapped that ECM in and POOF like magic. The Check engine light came on solid, I started the car and the light went right out. Idle was perfect and all the power was there. Actually more power than expected, enough so that seat of the pants dyno could feel it. I am guessing this ECM has a higher advance in the timing table and richer fuel mixture. I am fairly sure it has EGR delete as well, as most of my chips get that straight off. I need EGR delete as my intake has no provision for an EGR tube at all. (custom larger intake and larger Throttle Body by forum member Dawg)

There is considerably more bottom end but it felt like it was fighting a bit around 5800rpms. Usually 1st gear will scream to 6500 without a hint of any issue.

So thats it guys, I am guessing that the original ECM went bad and took out the chip. When I was originally testing with the 2nd ECM, first I tried swapping chips, then I tried swapping entire ECM's, however leaving my bad chip in the good ECM, and the Good chip was in the bad ECM so they both tested bad. I am going to have to sit down and start testing my ECM's and take all my chips down to the local chip guy have him erase all of them and then burn the same program onto all the chips for me. So I won't ever worry about accidentally putting a chip coded for 19# injectors into a car with 15# and burn a piston or have a timing table that is meant for a huge cam and put it on a stock cam engine.

So thats it, she is back to running great.

Thanks again for all the tips and suggestions.

David aka Capt Fiero

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85GT Soon to be 87GT,93 Eldorado 4.9, 5spd Dual O2 Custom Chip, Custom Exhaust. MSD Everything Capt Fiero --- My Over View Cadero Pics Yellow 88GT 5spd Full Poly Suspension, Lowered 1/2" in front, Corner Carver.

I think it's great when someone finds a solution for a problem and then take the time to post it so other people know what the final fix is. Thanks Capt

That makes some more sense. My gut feeling was that the ECM's Microprocessor was malfunctioning. I guess it was just dumb luck that you happen to have had 2 ECM's go bad. It's not unheard of, Perhaps the chip wasn't seated correctly? a pin broken? Bad burn on the chip? All these issues would result in the microprocessor messing up, and a rapidly blinking or flashing Check Engine light is a common symptom.

On a related note, the Microprocessor has a back up system, called a cop or watchdog, that monitors the microprocessor. If for any reason it sees that the micro isn't processing anything, it sends out a one wire high signal to all the IC's on the ECM, telling them to ignore the processor and run to the defaulted values as defined by the resistor networks on the calpack. In this mode, the engine will barely work, gas mileage will be horrible, and the check engine light will be on. Either of these circumstances are defined as limp home mode. However in some circumstances, the processor is down only for an instant, causing the light to flicker.