So i bought my Fiero a couple of months ago and have been fighting some problems recently. Sometimes it starts and runs perfectly with no issues, other times it starts fine and runs fine for a bit and then suddenly feels like it loses 80HP and will barely hold 40mph (but doesn't die at idle), sometimes this problem is present as soon as you turn on the car. i have a code 42 and 33, I already replaced my coil, cap and rotor and my ICM. I've tried unplugging the map sensor and when I do it runs even worse. Any help would be much appreciated.
Code 42: Electronic Spark Timing *Measure the Voltage: The ignition module will ground terminal B4 (EST) on the ECM when the system is (supposed to be) running on the ignition module. If this does not happen (ECM is seeing a voltage on terminal B4), the ECM will set code 42. When the RPM for Electronic Spark Timing is reached (400 RPM) a by-pass voltage will be applied to the ignition module, and the ignition module should no longer ground EST. If it still does, the ECM will set code 42.
*Check all wires coming from the ignition module and sparkplug wires. Replace sparkplug wires or try rerouting them.
Code 33: Manifold Absolute Pressure (MAP) Sensor *Measure the Vacuum Check the vacuum hoses from the MAP sensor. Check all connections and replace the MAP sensor if necessary.
...other times it starts fine and runs fine for a bit and then suddenly feels like it loses 80HP and will barely hold 40mph (but doesn't die at idle)
One possibility... If the cat has broken up inside, sometimes (but not all the time) chunks will partially block the exit end of the cat. This will result in an engine that idles fine and appears to run okay at lower revs... but the engine cannot breathe properly and higher revs are impossible.
When this happened to my '86 GT years ago, it eventually cooked my ICM... probably due to the very high engine bay temps due to the engine struggling to rev.
[This message has been edited by Patrick (edited 08-16-2023).]
One possibility... If the cat has broken up inside, sometimes (but not all the time) chunks will partially block the exit end of the cat. This will result in an engine that idles fine and appears to run okay at lower revs... but the engine cannot breathe properly and higher revs are impossible.
When this happened to my '86 GT years ago, it eventually cooked my ICM... probably due to the very high engine bay temps due to the engine struggling to rev.
Could this problem really be intermittent? because sometimes the car runs perfectly and pulls right up to 5400 rpms. i guess I could just throw a test pipe on it for free horsepower anyways since my state has no e-checks.(but I'm not super motivated to do that, i'd like to get it running good first)
You haven't given us much to work with. No mention made of year, of engine, of spark plug wire condition, of spark plug condition, of fuel pressure etc.
Basic maintenance needs to be done, and a scanner or laptap with WinALDL (and cable) will tell you what information your ECU is getting from the sensors.
I know you have already replaced the ICM, but I was wondering if that made any change at all?
I'm asking because a few years ago my ICM was responsible for similar problems and when I replaced the ICM (with a cheap one I got from the internet), the problem did not go away. Turned out the ICM I got was crap too - even though it was new. So I replaced it with one from a reputable brand and the problems went away.
Also, as Vintage-Nut mentioned, check the spark plug wires. Last year my car would start to sputter under acceleration, especially when cold. When I checked the spark plug wires while the engine was still running, I got zapped big time just by touching them. So I replaced them and the problem went away.
I know you have already replaced the ICM, but I was wondering if that made any change at all?
I'm asking because a few years ago my ICM was responsible for similar problems and when I replaced the ICM (with a cheap one I got from the internet), the problem did not go away. Turned out the ICM I got was crap too - even though it was new. So I replaced it with one from a reputable brand and the problems went away.
Also, as Vintage-Nut mentioned, check the spark plug wires. Last year my car would start to sputter under acceleration, especially when cold. When I checked the spark plug wires while the engine was still running, I got zapped big time just by touching them. So I replaced them and the problem went away.
I think my next step is probably to buy a Delco ICM just to take that variable out of it, the spark plug wires are brand new Delcos so I really don't think they're causing the problem.
I think my next step is probably to buy a Delco ICM just to take that variable out of it, the spark plug wires are brand new Delcos so I really don't think they're causing the problem.
New, out of box parts can be bad. It happens. At least the wires are easy enough to test with a multimeter.
Why get rid of a functional component that does nothing to impair engine performance while at the same time reduces engine emissions? If the cat has been compromised in some manner, that's a completely different situation.
[This message has been edited by Patrick (edited 09-18-2023).]
You haven't given us much to work with. No mention made of year, of engine, of spark plug wire condition, of spark plug condition, of fuel pressure etc.
Basic maintenance needs to be done, and a scanner or laptap with WinALDL (and cable) will tell you what information your ECU is getting from the sensors.
87 gt 2.8 128,000 miles, brand new plug wires, spark plugs are fairly new and good, fuel pressure is good. Basic stuff has been done, grounds have been checked and I even added some additional ground cables, the harness has been checked and all the connections are good. new coil, distributor cap and rotor. I have a GM ICM in the mail now aswell as a ACDelco upgraded map sensor (even if it isn't the problem I've seen some people say it helps the "hunting idle" issue which mine does) I'm usually able to troubleshoot problems reasonably easily by myself so I'm not as good at communicating all the info sorry. I have an OBD2 scanner so I figure that won't work, I'll try to find an adapter
I have thought about doing this, because I have a little shudder while cruising and have heard that could be a cat issue, but I don't suspect it to be the issue in this case.
I figured i'd continue this, still having problems even with the car. I have good fuel pressure (43 psi prime and about 36 at idle), I checked my MAP sensor readings and they are spot on. The way the car feels when it starts running poorly is similar to if I remove one of my fuel injector bank fuses, but I've checked all the injectors and actually had them out and cleaned them not too long ago. Tested the wires running to the injectors and they have about 11v source with the car off so it should be acceptable. I am close to trying to find an ECM to swap in just to confirm that's not it. The worst part is its completely random when it decides to run bad, one drive it will run perfect and go right up to speed and idle smooth, but then randomly when I start it after letting it set overnight it feels like I'm running on 3 cylinders.
Why get rid of a functional component that does nothing to impair engine performance while at the same time reduces engine emissions? If the cat has been compromised in some manner, that's a completely different situation.
We don't know what kind of cat he has... but I definitely recommend replacing the catalytic converter if he has one of these (which was factory):
These cats are the older charcoal "pellet style" of catalytic converters which were factory on I ... THINK? all Fieros? I know every 84 that I've had has had one of these. But I can't remember if any of my V6s have had them...
But it's the much much older style of cat. They are far less likely to clog, but they are more restrictive... and actually aren't as efficient in converting the emissions to less harmful gasses as the newer ones are anyway.
I think there's a happy medium for catalytic converters that can benefit both emissions and performance. On my 2006 Pontiac Solstice (years ago), I replaced the factory catalytic converter (which was the newer style), with a free-er flowing 300cfm catalytic converter. It made an ENORMOUS difference in performance from the mid to upper RPMs. I think to some degree, the 1-7/8ths inch exhaust piping is just a little bit too small for the V6 Fiero also... and when upgrading to a ~2" or a little larger, it makes sense to go with a larger flowing cat too.
EGR though... man, that's just old technology. When I replace the ECM / engine control system in my 87 Fiero... I'm going to disable the EGR, and the cold start injector as well. I know the EGR can be used to "cool" the engine as well, but that can also be done with a better air/fuel mixture.
Originally posted by 82-T/A [At Work]: We don't know what kind of cat he has... but I definitely recommend replacing the catalytic converter if he has one of these (which was factory):
These cats are the older charcoal "pellet style" of catalytic converters which were factory on I ... THINK? all Fieros? I know every 84 that I've had has had one of these. But I can't remember if any of my V6s have had them...
But it's the much much older style of cat. They are far less likely to clog, but they are more restrictive... and actually aren't as efficient in converting the emissions to less harmful gasses as the newer ones are anyway.
I think there's a happy medium for catalytic converters that can benefit both emissions and performance. On my 2006 Pontiac Solstice (years ago), I replaced the factory catalytic converter (which was the newer style), with a free-er flowing 300cfm catalytic converter. It made an ENORMOUS difference in performance from the mid to upper RPMs. I think to some degree, the 1-7/8ths inch exhaust piping is just a little bit too small for the V6 Fiero also... and when upgrading to a ~2" or a little larger, it makes sense to go with a larger flowing cat too.
EGR though... man, that's just old technology. When I replace the ECM / engine control system in my 87 Fiero... I'm going to disable the EGR, and the cold start injector as well. I know the EGR can be used to "cool" the engine as well, but that can also be done with a better air/fuel mixture.
Im reasonably confident its the factory catalytic converter, its an 87 GT as I said previously, don't know if that helps. I can agree that a cat change/delete could be beneficial, but I don't think its contributing to this particular problem, which Is currently making the car undrivable. So i'd like to get it running good before i worry about upgrades.
My '88 Formula daily driver (and autocrossed for four years) still has the original factory pellet style cat installed. Unknown mileage, as the entire instrument pod was missing when I acquired the car.
I bought an aftermarket cat for it ten years ago, as insurance for when the cat fails (as I have had a cat fail and clog in my '86 GT). However, the Formula's engine continues to run strong... and judging from the relatively "clean" smell of the exhaust, the cat is continuing to do its job just fine after all these years.
Originally posted by Patrick:My '88 Formula daily driver (and autocrossed for four years) still has the original factory pellet style cat installed. Unknown mileage, as the entire instrument pod was missing when I acquired the car.
I bought an aftermarket cat for it ten years ago, as insurance for when the cat fails (as I have had a cat fail and clog in my '86 GT). However, the Formula's engine continues to run strong... and judging from the relatively "clean" smell of the exhaust, the cat is continuing to do its job just fine after all these years.
Yeah, those original cats basically last forever... as long as they don't rust out. If they're rust free, they'll work forever.
But... I take a lot of issue with those older cats, but I'll save that for another forum section. Basically, the newer kinds that cars use today were already available then, but someone paid off someone, and the pellet-style was mandated. The newer ones existed, but never got implemented. They didn't start converting to those until sometime in like 88 or 89... apparently when the government stopped regulating specific equipment, and instead was concerned more with numbers. Air pumps / AIR injection, pellet cats, and even EGRs started dropping off.
Yeah, those original cats basically last forever... as long as they don't rust out. If they're rust free, they'll work forever.
Excessive oil consumption, anti-freeze (from internal coolant leak), overly rich condition (misfiring plugs etc) will all contribute to the demise of a cat.
