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ECM? Bad grounds? I dont know anymore. by PontiacLT1
Started on: 04-05-2021 09:02 PM
Replies: 8 (132 views)
Last post by: WKDFIRO on 04-09-2021 08:08 PM
PontiacLT1
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Report this Post04-05-2021 09:02 PM Click Here to See the Profile for PontiacLT1Send a Private Message to PontiacLT1Edit/Delete MessageReply w/QuoteDirect Link to This Post
1985 Fiero GT V6 4 Spd

So i've hit a rock and don't really know where to go from here and you guys are usually relatively helpful so any ideas are helpful, just trying to narrow it down.

Basically I got the fiero back on the road from sitting for years and it had this really bad throttle lag, bad idle, and a sporadic idle, which my first thought was the TPS, replaced that and still had the issues. The check engine light wasn't working but found out it was the "board" (someone really has to make reproductions of those) but got it working and got code 22. Found out I had to set the TPS to the right voltage, moved the TPS from .1 volts to .5 volts, and no check engine light. It even idled smooth, so i drove it to my school. It seemed way better, and when I was leaving it started first try, so I thought I fixed it.

That night I met my parents at a restaurant and the only thing I noticed on the drive was that when taking of from a stop, when i would apply pressure after I was moving, it would buckle until I let of and reapplied. Then when I was trying to leave the restaurant, I started it, it was idling, but then randomly died. When I would try and start it, it would start then die immediately. Then after a couple of those, it went to just spinning the starter. Maybe after 2 minutes of attempting to start it, it came back to life and I drove it back home. It seemed relatively normal besides the starting from a stop as previously mentioned, and when I went for fourth at one point i had no throttle and instead it just backfired, but it worked later after I had went back to third. I have no check engine lights and I have replaced most of the main sensors, and even the fuel injectors, along with the basic maintenance items.

Don't really know where to go from here. Something just isn't 100% and idk if its just the ECM failing or if it's not getting the proper ground.

Anyone else have these issues, any ideas help.
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Patrick
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Report this Post04-05-2021 09:52 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by PontiacLT1:

I have no check engine lights and I have replaced most of the main sensors, and even the fuel injectors, along with the basic maintenance items.


Did that include an ICM? A failing one can appear to work... until it gets hot. When the car won't start, does the tach move while cranking?

[This message has been edited by Patrick (edited 04-05-2021).]

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skywurz
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Report this Post04-05-2021 10:34 PM Click Here to See the Profile for skywurzClick Here to visit skywurz's HomePageSend a Private Message to skywurzEdit/Delete MessageReply w/QuoteDirect Link to This Post
Have you tested your fuel pressure?
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phonedawgz
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Report this Post04-07-2021 03:47 AM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageClick Here to Email phonedawgzSend a Private Message to phonedawgzEdit/Delete MessageReply w/QuoteDirect Link to This Post
The first thing I would check for is low fuel pressure.
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Firezappy
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Report this Post04-07-2021 04:38 AM Click Here to See the Profile for FirezappySend a Private Message to FirezappyEdit/Delete MessageReply w/QuoteDirect Link to This Post
I had similar issues on my old duke. It would seem to run fine then just die out of nowhere. You could crank and crank and nothing would fire. I ended up changing the fuel pump and added a new filter, no dice. Then I noticed it always ran good when it was cold. So I ended up changing the ecm and the prom, along with a new harness connectors on the ecm. After all of that it started working right for me. But yeah, before you start throwing parts at it make sure you have good fuel pressure. Your check engine light comes on when you have the key in the run position right? (I am not near as experienced as the other guys here this is just what I went through, listen to them first.)
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PontiacLT1
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Report this Post04-09-2021 07:36 PM Click Here to See the Profile for PontiacLT1Send a Private Message to PontiacLT1Edit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by phonedawgz:

The first thing I would check for is low fuel pressure.


So today I went and tested the fuel pressure. It was coming up at 15 with key on engine off, and 25 when it was running. That is really low when they what I am told run at 40 something. Replaced the fuel pump and still had the same things, don't know if the gauge is faulty or not as that seems like really low psi and I would think the engine wouldn't run at all, but fuel injection is crazy I guess. I tested it out after I changed the pump, and it would stall when I put the clutch in to slow down for a turn, then would fire back up after I would pop the clutch.
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PontiacLT1
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Report this Post04-09-2021 07:40 PM Click Here to See the Profile for PontiacLT1Send a Private Message to PontiacLT1Edit/Delete MessageReply w/QuoteDirect Link to This Post

PontiacLT1

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quote
Originally posted by Patrick:

Did that include an ICM?


Interesting you say this, cause about a week ago I had no start with no tach, but I had a box of extra parts that I got from a guy that included a distributer. I took the ICM from that and it now will start and the tach will move with it. I assume it is used though so there is a chance that it could be failing, might just have to buy a new one.
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PontiacLT1
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Report this Post04-09-2021 07:43 PM Click Here to See the Profile for PontiacLT1Send a Private Message to PontiacLT1Edit/Delete MessageReply w/QuoteDirect Link to This Post

PontiacLT1

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quote
Originally posted by Firezappy:

make sure you have good fuel pressure. Your check engine light comes on when you have the key in the run position right?


Yeah so the fuel pressure is not good from what im reading off the gauge, 15psi key on engine off, and 25 when running, and thats with a new fuel pump. And yeah the check engine light turns on when key is on and will read out codes, just don't have any right now.

[This message has been edited by PontiacLT1 (edited 04-09-2021).]

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WKDFIRO
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Report this Post04-09-2021 08:08 PM Click Here to See the Profile for WKDFIROClick Here to Email WKDFIROSend a Private Message to WKDFIROEdit/Delete MessageReply w/QuoteDirect Link to This Post
If you are going to replace the module you might as well take care of the pick up coil and cap/rotor (unless you have already done it) and a new ignition coil. Your symptoms do sound like something is getting hot and giving out which typically is a fuel pump, coil or a distributor component. I would work that angle unless you already have before going after the ECM.

If this Fiero is a long term commitment then you definitely want to get your hands on the factory maintenance manual. I have one for my 87 and for my 88 on pdf.

Good luck!
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