i have an 84 2.5l fiero that has been nothing but problems the whole time i’ve had it. i just had it all sorted for about 2 weeks. yesterday i was driving across town on the highway and the car started to die for maybe a quarter to half second and come back. the check engine light would come on when this happened. i eventually figured out if i just lower the revs by disengaging the clutch or putting it in neutral it would stop doing that for a little bit. it’s not a fuel system issue (i think) as i replaced every part in it at this point (fuel pump, filter, regulator, injector) it only does it after a little while of cruising at higher rpms. it doesn’t do anything weird if i accelerate hard. only when i’m cruising at around 2-3k rpm. ignition maybe?
When was the last time that you changed the fuel filter?
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Possibly the TPS has developed a dead spot. Check the TPS for continuous readings from idle to wide open.
I got 6.7 ohms with the butterfly valve closed to 3.92 ohms at WOT. I have a second throttle body with the sensor on it (same year, different sensor for some reason. that one reads around 3.9 ohms with the valve closed, 6.7 ohms at WOT. reversed for some reason? it's from another 84. measured across the b and c terminals.
i have an 84 2.5l fiero that has been nothing but problems the whole time i’ve had it. i just had it all sorted for about 2 weeks. yesterday i was driving across town on the highway and the car started to die for maybe a quarter to half second and come back. the check engine light would come on when this happened. i eventually figured out if i just lower the revs by disengaging the clutch or putting it in neutral it would stop doing that for a little bit. it’s not a fuel system issue (i think) as i replaced every part in it at this point (fuel pump, filter, regulator, injector) it only does it after a little while of cruising at higher rpms. it doesn’t do anything weird if i accelerate hard. only when I’m cruising at around 2-3k rpm. ignition maybe?
Cruising may not have anything to do with it. How is your tach needle responding when the engine begins to die? Does it quiver a little or does it take a deep dive and then recover quickly? Either one may point to ignition. Try holding the rpm at 2500 rpm in neutral for a minute and see if engine starts to die and monitor the tach. If it does dies or stumbles watch the tach needle to see how its reacting. A quick drop of the needle could mean an intermittent break in the ignition circuit.
If so, then find a willing subject and have him/her hold a 2500 rpm and you can start wiggling the engine wire harness & connectors to see if that causes the problem. In addition pull the center console to gain access to the ECM and wiggle those wires (each one of them) as well with engine running. I had same problem with my 2.8 and it was a loose wire in one of the ECM connectors that fed the ignition module. I could make the engine rpm take a dive by merely pushing the wire side to side at the ECM connector.
I deliberately didn't mention to check all the ground wires. I'm sure ORGE will be along shortly to mention those important details.
Spoon
------------------ "Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut
If you're going to be checking for resistance, then as stated earlier, just make sure there are no "dead" spots. I have no idea why the resistance readings are reversed on your two different Throttle Position Sensors, except for one possibly being incorrect for a Fiero.
When I check a TPS, it's by using WinALDL and reading the voltage values.
If you're going to be checking for resistance, then as stated earlier, just make sure there are no "dead" spots. I have no idea why the resistance readings are reversed on your two different Throttle Position Sensors, except for one possibly being incorrect for a Fiero.
When I check a TPS, it's by using WinALDL and reading the voltage values.
sorry, I meant to include in that. the sweep seems fine. I used an analog multimeter and the needle doesn't do anything funny from closed to wot. didn't see any dead spots.
Cruising may not have anything to do with it. How is your tach needle responding when the engine begins to die? Does it quiver a little or does it take a deep dive and then recover quickly? Either one may point to ignition. Try holding the rpm at 2500 rpm in neutral for a minute and see if engine starts to die and monitor the tach. If it does dies or stumbles watch the tach needle to see how its reacting. A quick drop of the needle could mean an intermittent break in the ignition circuit.
If so, then find a willing subject and have him/her hold a 2500 rpm and you can start wiggling the engine wire harness & connectors to see if that causes the problem. In addition pull the center console to gain access to the ECM and wiggle those wires (each one of them) as well with engine running. I had same problem with my 2.8 and it was a loose wire in one of the ECM connectors that fed the ignition module. I could make the engine rpm take a dive by merely pushing the wire side to side at the ECM connector.
I deliberately didn't mention to check all the ground wires. I'm sure ORGE will be along shortly to mention those important details.
Spoon
it's been a couple days since I drove it but I do believe the tach was jumping around, at the same time as the engine freaking out and the engine light. i have a feeling it is ignition related and not a bad ground since the problem IMMEDIATELY stops when I let the rpms drop. I will try doing that in neutral to see if I can replicate the issue. I think I'd have to drive it for a bit before that so the engine is nice and toasty since I had been driving at temp for around 10 mins before the issue began.
I've also been having another issue. it seems to be a more recent one. when I start the engine and it's hot and it dies immediately unless I rev it. once I start driving it's fine again. it doesn't do that when it's cold. not a huge deal but if anyone would know off the top of their head.
I've also been having another issue. it seems to be a more recent one. when I start the engine and it's hot and it dies immediately unless I rev it. once I start driving it's fine again. it doesn't do that when it's cold. not a huge deal but if anyone would know off the top of their head.
You should check the ignition timing of the engine.
did that a couple weeks ago. it's right on the money. (did it in service mode or whatever as described on the sticker.)
What did you replace 2 weeks ago that fixed the problem? Perhaps you bought cheap components and they broke already, that has happened to me a lot. It never has happened with my ac delco parts however
What did you replace 2 weeks ago that fixed the problem? Perhaps you bought cheap components and they broke already, that has happened to me a lot. It never has happened with my ac delco parts however
I meant I set the timing with a timing light. never done it before but it was pretty easy. I replaced the fuel pump, injector, filter, regulator, breather filter and pcv valve, and cleaned the gas tank. the issue only started earlier this week. it was totally fine until earlier this week. like I said earlier I drove the same highway I was on (to the same destination even) and it was fine. I drove home and didn't do anything and drove that highway again when it did the thing. I have a feeling it's the ignition coil. its sorta beat up looking and is certainly the original. I read somewhere that those are prone to failing on fieros. It really only died for what felt like a few revolutions of the engine, just kept doing it every few seconds til I let it idle down.
Yea id replace all the ignition components either way, like the coil, icm, pickup coil, maybe even the sparkplugs and wires. Also i may be blind, but I dont think you said you checked the fuel pressure yet. check it while its primed but off, and also when its running. perhaps because it only happens while cruising it has something to do with the egr or even the ecu. this probably isnt your problem but i remember once my engine would shut off for 1/2 a second whenever i pressed on the breaks or turned up the radio. i fixed it by cleaning the battery terminals and putting some dielectric grease on it. perhaps do the same with your battery and ground. You could also try adding an new ground strap, alongside the stock one somewhere on the engine
Yea id replace all the ignition components either way, like the coil, icm, pickup coil, maybe even the sparkplugs and wires. Also i may be blind, but I dont think you said you checked the fuel pressure yet. check it while its primed but off, and also when its running. perhaps because it only happens while cruising it has something to do with the egr or even the ecu. this probably isnt your problem but i remember once my engine would shut off for 1/2 a second whenever i pressed on the breaks or turned up the radio. i fixed it by cleaning the battery terminals and putting some dielectric grease on it. perhaps do the same with your battery and ground. You could also try adding an new ground strap, alongside the stock one somewhere on the engine
sorry for suggesting a shotgun approach lol
I've replaced the plug wires and plugs, they have less than 2.5k miles on them. I didn't check the fuel pressure with the new pump, as it is a brand new pump. I don't think it's fuel pressure in the slightest as I was just experiencing a fuel pressure issue and it was TOTALLY different. if I accelerated hard it would stumble a whole lot til it got it together and if I was cruising it would start to stumble and wouldn't stop til I lowered the revs (same fix, different issue). it would also throw a check engine light after the 50 seconds for lean fuel condition, not so with my current issue. the battery terminals are also very clean, the positive is kinda janky because it must've been broken at one point (previous owner was an idiot) but the ground is clean and the strap is fresh (I replaced it when the engine was out). it was one of the things I didn't skip (skipped the AC compressor and the oil pan gasket, both bit me in the ass. ac because I am actually a tiny little baby and it gets up to 95 here in summer. it's fine though because my other ac evaporator popped and needs to be replaced so now neither of my cars have ac.) I'm really sick of fixing my fiero, I'm just gonna replace the ignition coil and see if it helps. it's cheap enough and mine looks pretty old and ratty.
Yea id replace all the ignition components either way, like the coil, icm, pickup coil, maybe even the sparkplugs and wires. Also i may be blind, but I dont think you said you checked the fuel pressure yet. check it while its primed but off, and also when its running. perhaps because it only happens while cruising it has something to do with the egr or even the ecu. this probably isnt your problem but i remember once my engine would shut off for 1/2 a second whenever i pressed on the breaks or turned up the radio. i fixed it by cleaning the battery terminals and putting some dielectric grease on it. perhaps do the same with your battery and ground. You could also try adding an new ground strap, alongside the stock one somewhere on the engine
sorry for suggesting a shotgun approach lol
I replaced the ignition coil and it did not fix the problem. how would I actually diagnose it.
Yea id replace all the ignition components either way, like the coil, icm, pickup coil, maybe even the sparkplugs and wires. Also i may be blind, but I dont think you said you checked the fuel pressure yet. check it while its primed but off, and also when its running. perhaps because it only happens while cruising it has something to do with the egr or even the ecu. this probably isnt your problem but i remember once my engine would shut off for 1/2 a second whenever i pressed on the breaks or turned up the radio. i fixed it by cleaning the battery terminals and putting some dielectric grease on it. perhaps do the same with your battery and ground. You could also try adding an new ground strap, alongside the stock one somewhere on the engine
sorry for suggesting a shotgun approach lol
I'll start replacing ignition components if this video doesn't help with anything.
I replaced the ignition coil and it did not fix the problem. how would I actually diagnose it.
For the pickup coil, test the resistance between the two contacts, it should be between 500-1500 ohms. if not, replace. also make the the magnet is in good condition.
I couldnt find out how to test the icm for the 84 i4, seems to be specific for that year. if its the pickup coil unfortunately youll have to pull the distributor out to replace it.
oh and also check the sparkplugs to see if they have any clues to whats going on, and also check the gap.
I just took this, it lurches when I let off the throttle while I'm cruising. it started doing it at low speeds too.
atleast for the v6's, the icm is what controls the tachometer. if the tachometer glitches like that i would think it would be the icm having problems. make sure it has a good ground, clean the mounting screws, clean the mating surface to the distributer housing, put computer thermal paste there.
I'll start replacing ignition components if this video doesn't help with anything.
I just took this, it lurches when I let off the throttle while I'm cruising. it started doing it at low speeds too.
Are you able to retrieve any Trouble Codes after the CEL flashes like that?
Similar to what Xenoblast has stated...
Occasionally when an ICM "fails", it's actually just a poor connection. Take off the distributor cap, unplug the pickup coil from the ICM, clean the connections, apply dielectric grease, and re-connect. Do the same with the external connections to the ICM and to the ignition coil.
If none of that resolves the issue, and no other faults can be found, replace the ICM and pickup coil. Make sure to use proper heat sink compound between the ICM and the base of the distributor.
[This message has been edited by Patrick (edited 09-03-2021).]
Are you able to retrieve any Trouble Codes after the CEL flashes like that?
Similar to what Xenoblast has stated...
Occasionally when an ICM "fails", it's actually just a poor connection. Take off the distributor cap, unplug the pickup coil from the ICM, clean the connections, apply dielectric grease, and re-connect. Do the same with the external connections to the ICM and to the ignition coil.
If none of that resolves the issue, and no other faults can be found, replace the ICM and pickup coil. Make sure to use proper heat sink compound between the ICM and the base of the distributor.
I don't get any codes. I checked the pickup coil resistance, it was around 950 ohms. I cleaned the connections on the ICM and the issue still persists. I have a feeling it isn't an electronic component, since the issue stops as soon as the transmission is either not in gear or in neutral. Honesty I might take it to a shop at this point. this might be beyond me. I think I'll check fuel pressure again (I swear to god if I have to replace the fuel pump or something I'll drive this car off a cliff.)
edit: I still haven't tried revving it and messing with wires yet so I will try that when I get the chance.
[This message has been edited by katie80 (edited 09-03-2021).]
I have a feeling it isn't an electronic component, since the issue stops as soon as the transmission is either not in gear or in neutral.
When the transmission is taken out of gear, the engine shifts position somewhat. I suspect (similar to Spoon's suspicion) that your issue is a poor electrical connection of some sort which is possibly cutting power to the ignition... or maybe even to the fuel pump.
When the transmission is taken out of gear, the engine shifts position somewhat. I suspect (similar to Spoon's suspicion) that your issue is a poor electrical connection of some sort which is possibly cutting power to the ignition... or maybe even to the fuel pump.
it's possible, I meant I don't think it's a bad sensor. could certainly be wiring. I'll try and diagnose it tomorrow or Sunday.
Are you able to retrieve any Trouble Codes after the CEL flashes like that?
Similar to what Xenoblast has stated...
Occasionally when an ICM "fails", it's actually just a poor connection. Take off the distributor cap, unplug the pickup coil from the ICM, clean the connections, apply dielectric grease, and re-connect. Do the same with the external connections to the ICM and to the ignition coil.
If none of that resolves the issue, and no other faults can be found, replace the ICM and pickup coil. Make sure to use proper heat sink compound between the ICM and the base of the distributor.
https://youtu.be/XHke4Ee0dlU I had my partner hold the revs up to pull on wires but it immediately started doing it again, no wires were being moved at all. I drove on the route I've been driving to test it and it didn't do it at all till I got back onto my street (up to temp + 15 mins of driving). it didn't do it til I was trying to accelerate in 2nd gear again, like the other video. the shift light was also blinking? is my ECM bad maybe? I wasn't in gear or moving.
the shift light was also blinking? I wasn't in gear or moving.
Hmmm... I find it very strange that the Shift light is also blinking while this issue is occurring, especially when the engine is not in gear. That might mean something to someone who understands the Shift light/ECM programming better than me.
Does the Shift light work normally when the engine is running properly?
[This message has been edited by Patrick (edited 09-04-2021).]
Hmmm... I find it very strange that the Shift light is also blinking while this issue is occurring, especially when the engine is not in gear. That might mean something to someone who understands the Shift light/ECM programming better than me.
Does the Shift light work normally when the engine is running properly?
yes the shift light works just fine normally. it didn't seem to work the other day when it was freaking out in 2nd gear. I got to like 3k at half throttle and the shift light didn't come on.
Interesting. The ICM certainly has a history of failing (for various reasons) with the 2.8, but not so much with a duke. That's not to say that an ICM never fails with the 2.5, but some of your issues/symptoms seem rather irregular for an ICM failure.
Anyway, glad you finally got your car running properly.
Interesting. The ICM certainly has a history of failing (for various reasons) with the 2.8, but not so much with a duke. That's not to say that an ICM never fails with the 2.5, but some of your issues/symptoms seem rather irregular for an ICM failure.
Anyway, glad you finally got your car running properly.
I think it failed because it was the original with 120k miles but it sat outside in the car for 15 years and then started being used a whole lot by me. and maybe it was just getting weak.
Since it was sitting for 15 years, possibly the two attachment screws (which ground the ICM?) were corroded and making intermittent connection ? We know Fiero's can get pretty goofy when they sit idle for a long time.
Since it was sitting for 15 years, possibly the two attachment screws (which ground the ICM?) were corroded and making intermittent connection ? We know Fiero's can get pretty goofy when they sit idle for a long time.
I didn't even consider that, but the screws are still the originals and the issue is gone now.
Since it was sitting for 15 years, possibly the two attachment screws (which ground the ICM?) were corroded and making intermittent connection?
I should've also specifically mentioned the attachment/grounding ICM screws... but yes, I still feel this might've been an electrical "connection" problem.
Occasionally when an ICM "fails", it's actually just a poor connection. Take off the distributor cap, unplug the pickup coil from the ICM, clean the connections, apply dielectric grease, and re-connect. Do the same with the external connections to the ICM and to the ignition coil.
I should've also specifically mentioned the attachment/grounding ICM screws... but yes, I still feel this might've been an electrical "connection" problem.
Occasionally when an ICM "fails", it's actually just a poor connection. Take off the distributor cap, unplug the pickup coil from the ICM, clean the connections, apply dielectric grease, and re-connect. Do the same with the external connections to the ICM and to the ignition coil.
[/QUOTE]
I did try the things you suggested in that post, they didn't fix the issue.
I did try the things you suggested in that post, they didn't fix the issue.
But did you loosen and re-tighten the original ICM attachment/grounding screws (to create a fresh ground path) as Rexgirl specifically (and I should have) mentioned?
[This message has been edited by Patrick (edited 09-16-2021).]
That might mean something to someone who understands the Shift light/ECM programming better than me. 
