Fiero random power loss and engine codes (Page 1/3)
Nytfury AUG 16, 12:44 PM
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.
Vintage-Nut AUG 16, 02:41 PM
ECM Diagnostics Codes
https://www.fiero.nl/cgi-bin/main.cgi?ECMCodes

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.
Patrick AUG 16, 05:28 PM

quote
Originally posted by Nytfury:

...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).]

Nytfury AUG 16, 11:54 PM

quote
Originally posted by Patrick:

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)
Patrick AUG 17, 12:17 AM

quote
Originally posted by Nytfury:

Could this problem really be intermittent?



Possibly. It depends on whether or nor a chunk or two of broken up matrix shifts position and plugs the exit (and then falls out of position later).

Get (safely) under the back of the car and pound the cat with your fist. If the matrix is broken, you'll hear chunks of it rattling around.

I'm not saying this is your issue. I'm saying it's a possibility.
Nytfury AUG 17, 01:11 AM

quote
Originally posted by Patrick:

Possibly. It depends on whether or nor a chunk or two of broken up matrix shifts position and plugs the exit (and then falls out of position later).

Get (safely) under the back of the car and pound the cat with your fist. If the matrix is broken, you'll hear chunks of it rattling around.

I'm not saying this is your issue. I'm saying it's a possibility.



I've got it up on jacks right now so I will do this in the morning, thanks.
Nytfury AUG 18, 12:43 AM
I checked it today and it doesn't feel like there's anything lose inside the cat, you have any other ideas?
Patrick AUG 18, 01:04 AM

quote
Originally posted by Nytfury:

...you have any other ideas?



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.
Cliff Pennock AUG 18, 04:46 AM
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.
Nytfury AUG 18, 10:31 AM

quote
Originally posted by Cliff Pennock:

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.