Hey guys need your help on this one, I have been daily driving my car for a few months now and it ran perfect! And was very powerful, responsive etc... But just yesterday it started being weird. First off it seems to have lost power in general at low speeds just not as jumpy. It also sounds different too, less basey and v8 sounding and more 4 cylinder importy sounding. Now the big problem, whenever I go above 1/4 throttle, and around 3,000 rpm it starts to stop accelerating, start popping and shakes the whole car. The worst is if I hold it where it starts acting up the engine light will start to flash! If I let off the throttle the light will turnoff, it will stop stuttering, and it will actually speed up. Also if I hold the throttle down to where it starts doing it, it will cut in and out. This just started yesterday, and is continuing today. Any ideas? Let me know if you need more info. It's a 98 3800sc.

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86 Fiero GTX project now tearing up the street, My build thread! 3800sc, interior, wheels, suspension and more! https://www.fiero.nl/forum/Forum1/HTML/089483.html

Side note- no codes, no engine light either (it works because it gave me codes before)

Start by checking your fuel pressure. It could also be a plugged exhaust. Does it have a catalytic converter?

quote Originally posted by FieroMaster88: Start by checking your fuel pressure. It could also be a plugged exhaust. Does it have a catalytic converter?

I can do that, just it's a new pump, and new filter. Tank was very clean too, however I'm thinking it cutting the timing, so maybe due to lack of fuel. Also no cat, straightpipe, with inline mufflers.

If the check engine light flashes, then the PCM is probably detecting a misfire.

There are a host of things that can cause a misfire from bad plug wires to a crank sensor issue and beyond.

What brand spark plug wires are you using?
What brand and part number spark plugs are you using? What gap?
Where is your coil pack mounted?
Pics?

What is your fuel pressure doing when the misfire occurs (need to have someone watch the gauge while you drive)?

-ryan

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OVERKILL IS UNDERRATED

Custom GM OBD1 & OBD2 Tuning | Engine Conversions & more | www.gmtuners.com

Fixed it for ya!

QUOTE]Originally posted by IanT720:



Tried to record the thumping sound, oh well. Would someone mind fixing this? Thanks, just busy with the car.

[/QUOTE]

Is this Pre ODBII? Do you have anyway to have a scanner connected to it and bring up data stream while driving?
The sound is close to a sound of restricted intake or exhaust. (plugged air filter, crap stuck on the screen in front of the throttle body, crushed exhaust).
Have also had valve problems show sounds like that(exhaust valve not opening enough[cam, rocker problem] causing exhaust to try to return through the intake when intake valve opens).
Also need to check for any mechanical rattle/noise (engine noise, loose brackets, loose trans to engine bolts, cracked flexplate etc.). This can cause a false knock sensor signal, causing PCM to badly disadvance timing.
Fuel pressure should not leak down quickly unless you have a leaking regulator or injector. Have had leaking regulators saturate the intake with fuel through the vacuum port.

Sounds like Spark blowout?

Used coil packs?

Used ICM?

[This message has been edited by nosrac (edited 03-01-2013).]

I got them off Sinister Performance, 1 heat range cooler then stock I believe. Don't quote me but I think they are Autolite 606. Gap was big like 80, I did double check the gap before installation. I used Crane Cams V8 wire kit, mounted the coil packs vertical on the strut tower near the battery. Yes it is OBD2, also when it starts to miss the fuel pressure stays right around 55-60 psi. As for intake, I cheaped out and just stuck a filter on the TB for now. Exhaust is cat less, with inline mufflers.

If it is ignition and you are using ODBII it should have recorded misfire data. Especially on repeated failures.
Even on a Global (generic)ODBII scanner should show a p030? code. p0301 cylinder 1 p0302 cylinder 2 ect.
On that ignition, you will loose 2 cylinders at a time, if it is a coilpack or module.

quote Originally posted by cmechmann: If it is ignition and you are using ODBII it should have recorded misfire data. Especially on repeated failures. Even on a Global (generic)ODBII scanner should show a p030? code. p0301 cylinder 1 p0302 cylinder 2 ect. On that ignition, you will loose 2 cylinders at a time, if it is a coilpack or module.

I have not scanned it yet, because the engine light stays off. I took that as it didnt store any P Codes, I could still try it I suppose but I just have acces to the scanner from Autozone, not a diagnostic tool. I imagine if I could pull up the live data it would show me something, but I can't and like I said the light stays off so I didn't know if it stored a code or not.

Ok some of the earlier ODBIIs (95-98)weren't good at keeping the light on after misfires but they should store a history code for misfire, but a generic scanner may not have the ability to bring up history/pending codes. If it flashed, that means the PCM saw something and it stopped when it stopped flashing. Ignition coils, plugs, and wires will first break down under load. Ignition modules tend to stay failed.
In the meantime, check some of the other things you can physically look at.
Not used to Autolite numbers. Are they Iridium? Copper and Platinum will wear quickly in SC engines. May want to pull the plugs anyway. Just to see how they are burning. If you have an injector/regulator issue, they should look carbon fouled(black deposites). If it is an injector issue, that cylinder's plug would look different than the others.

My guess would be throttle position sensor, I had one go out on my zr2 didn't trip a CEL and did about the same thing.

quote Originally posted by ckrummy: My guess would be throttle position sensor, I had one go out on my zr2 didn't trip a CEL and did about the same thing.

Even the misfires?

quote Originally posted by IanT720: I got them off Sinister Performance, 1 heat range cooler then stock I believe. Don't quote me but I think they are Autolite 606. Gap was big like 80, I did double check the gap before installation. I used Crane Cams V8 wire kit, mounted the coil packs vertical on the strut tower near the battery..

Below is some random Guide off the net. I believe stock Gap is .060". I have 103's Gaped @ .050 on my car.

Autolite® 605 spark plugs (one heat range colder than stock) if you have a 3800 Series II or III engine engine with up to 6 pounds of boost. reduce the spark plug gap to .055"
Autolite® 104 spark plugs (two heat ranges colder than stock) if you have a 3800 Series II or III engine with 6 to 12 pounds of boost. reduce the spark plug gap to .050".
Autolite® 103 spark plugs (three heat ranges colder than stock) if you have a 3800 Series II or III engine with 12 to 18 pounds of boost. reduce the spark plug gap to .045".

quote Originally posted by IanT720: .... Gap was big like 80, I did double check the gap before installation.

Sounds like a pretty big gap.

The o2 could have convinced your car to run richer and wih that big gap it will cause misfires.

Sorry guys, I just can't remeber the gap. I just used the gap size that sinister recommended. My coils are pretty much mounted under the declid vent, and it snows here. Hmm what is the correct way to test the coils? Here's one for you... When it starts to miss, it's very regular. It feels like I'm hitting the rev limiter. Would this be the computer pulling the timing? Or just a very regular multiple misfire?

Would not be the first time I have seen new or fairly new spark plugs fail, running a proper scan would really help diagnose this problem and save changing any unneeded parts. Dan

quote Originally posted by FIEROFLYER: Would not be the first time I have seen new or fairly new spark plugs fail, running a proper scan would really help diagnose this problem and save changing any unneeded parts. Dan

Where do you reccomend to acces a scan tool, is this something a mechanics shop would have and diagnose for me for a nominal fee? I don't know anyone with the tool, and it's not like I want to drop 5000 on one either. Guess I will call around.

Is there some one in your area with a power tuner or HP tuners would be worth a short drive even if needed to get it done. Heck I would do it for you for free but I am a little ways away from you on the wrong side of lake Huron in a nice little town called Southampton Ont.
Check with any local Grand Prix or Bonneville clubs for example to see if some one can help you out. Dan

quote Originally posted by IanT720: Where do you reccomend to acces a scan tool, is this something a mechanics shop would have and diagnose for me for a nominal fee? I don't know anyone with the tool, and it's not like I want to drop 5000 on one either. Guess I will call around.

if you have an android phone you can run a $15 bluetooth scanner on it.

quote Originally posted by darkhorizon: if you have an android phone you can run a $15 bluetooth scanner on it.

Thanks for the tip, I just asked around on Facebook, but sadly I have iOS

I've mounted coil packs under the decklid vent - but in every instance I've also put a cover over them to keep water from getting into them. If your coil pack got water into it, that COULD possibly cause a problem if it wasn't sealed up well.

Truth be told I actually had water get into the crank sensor connector once due to a bad seal on that connector and it caused all sorts of funky running problems.

My suggestion for you is to unplug the module and see if there is any water or moisture in the connector at all. If there is, dry it out, pack it with some dielectric grease, and reinstall. Do the same for the crank sensor and any other electrical connectors that might be exposed to water. If you don't have some kind of a cover to keep water off your coil pack, you might want to think about installing one (a rubber flap will do).

Bad spark plug wires will also cause this same problem - just FYI.

quote Originally posted by Darth Fiero: I've mounted coil packs under the decklid vent - but in every instance I've also put a cover over them to keep water from getting into them. If your coil pack got water into it, that COULD possibly cause a problem if it wasn't sealed up well. Truth be told I actually had water get into the crank sensor connector once due to a bad seal on that connector and it caused all sorts of funky running problems. My suggestion for you is to unplug the module and see if there is any water or moisture in the connector at all. If there is, dry it out, pack it with some dielectric grease, and reinstall. Do the same for the crank sensor and any other electrical connectors that might be exposed to water. If you don't have some kind of a cover to keep water off your coil pack, you might want to think about installing one (a rubber flap will do). Bad spark plug wires will also cause this same problem - just FYI.

Well I took your moisture suggestion, there was no water in the ICM Connecter but, there was a few water droplets under 1 coil pack. I loaded them all up with dielectric grease, so hopefully this will fix it. My Manager at Autozone was a mechanic for 10 years, was pretty convinced it could be the MAF too, how can I test the MAF? Again I get no codes for the problem.

Well I dried the water droplets from the coils, and replaced them with dielectric grease. I also found that the ground for my ICM came off, so I fixed that. It feels like it has a bit more power but, the half throttle backfire/stutter/misfire is still present. No codes still, hmm.

Does it do the same if it's cold or hot?

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Turbo 3800 E85 F23 5spd spec5
11.17@132.6

quote Originally posted by Justinbart: Does it do the same if it's cold or hot?

Yep same, also doesn't really matter which gear. Just worst in 4th because of more load, will not do it in nuetral. Thanks, I'm going to test out a new MAF tomorrow, see how it pans out.

Try running it maf unplugged fist. Does it do the same if you floor it?

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Turbo 3800 E85 F23 5spd spec5
11.17@132.6

quote Originally posted by Justinbart: Try running it maf unplugged fist. Does it do the same if you floor it?

Alright good tip, I haven't because I don't want to chip a piston or something... But, I have given it a good 3/4 throttle... It will start to accelerate hard, cut out and stutter, resume accelerating, cut out and stutter. Just every couple hundred RPM it will cut in and out then if you hold it steady, it will misfire enough to start flashing the cel.

quote Originally posted by IanT720: Just think of it as the rev limiter cutting in and out throughout 3k to 4k, haven't pushed any higher.

quote Originally posted by nosrac: Sounds like Spark blowout?

Wouldn't hurt to get the proper cleaner and clean the MAF but I still think this is spark plugs or wires. Of course I had one two years ago similar that was a bad PCM but that is a pretty rare thing. Dan

quote Originally posted by FIEROFLYER: Wouldn't hurt to get the proper cleaner and clean the MAF but I still think this is spark plugs or wires. Of course I had one two years ago similar that was a bad PCM but that is a pretty rare thing. Dan

Spark blowout, never happend before, could it just happen one day? Wires should be perfect, and plugs too. But I will double check tomorrow for sure!