95 Starts fine, runs good until warm..then misses,stumbles - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 09-14-2004, 06:49 PM   #1
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Default 95 Starts fine, runs good until warm..then misses,stumbles

My understanding is that it has a DEFAULT mode when starting and once a particular temp. is reached, the ECM changes to NORMAL mode. This is when the trouble begins. On my last journey with the car, it was struggling so poorly for power I had to stop and it died, The CAT was glowing cherry red! once I let it cool down, it started right back up, only to act the same way once back to temp.

I have replaced many things but have yet to find the culpret
Here is what I have done:
New Plugs
New Wires (OEM)
New Coils (OEM)
New Ignition Module (OEM)
New O2 sensor (BOSCH)
New Coolant Temp. Sensor (Borg)
New Catalytic converter (Muff. Bros.)
Cleaned MAF sensor
Fuel pump/strainer/filter less than 1 year old

The plugs seem to be getting gas fouled every time I check them.

I have had it to a shop to see if there were any codes, It is not setting any codes but, they want to replace the plugs, Wires Coils and Module. I said NO they are all new!

Could this be an Electrical issue?
Could this be a Fuel issue?
I am getting low on ideas here. Does this sound familiar to anyone?

Thanks in advance, Mark
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Old 09-14-2004, 07:08 PM   #2
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Hrmmm,

The glowing red cat seems odd for a Bonneville (I've seen it on high performance cars doing runs, but not on daily drivers). How is the air cleaner? I thought I heard Bosch was bad in Bonnevilles (mainly plugs, poor performance and go out frequently). Did all those parts get changed because of just this issue? And you said the plugs looked gas fouled after a while? All the plugs or just some of them? It looks like you have already dug into this a bit.
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Old 09-14-2004, 07:14 PM   #3
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do yourself a favor, return the bosch o2 [say it doesn't work], and get an ac delco unit. I know its twice as much, but its cheap insurance.


-justin
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Old 09-14-2004, 09:38 PM   #4
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Default Re: 95 Starts fine, runs good until warm..then misses,stumbl

Quote:
Originally Posted by mark2112
My understanding is that it has a DEFAULT mode when starting and once a particular temp. is reached, the ECM changes to NORMAL mode.
This is called open and closed loop respectively


Quote:
Originally Posted by mark2112
The CAT was glowing cherry red!
^^^^ Ever seen a car on the side of the road up in flames? ^^^^^^^

I'd say its your catalytic converter man. My guess is either:

1. The engine is running very rich and when the mass of unburnt fuel hits the catalyst it ignites. - While probably not the cause it can't be ruled out. This is a "Catalytic converter meltdown" and can cause the #2 reason

2. Its clogged

Either way your cat is toast and its time to get a new one. It will also explain the other symptoms such as power loss and stalling. Have a mechanic test it, lemme know if ya do
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Old 09-14-2004, 09:52 PM   #5
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Back pressure testing is what doc is talkin' about. I think its 2kpa or something like that which is too high, but 1kpa is okay. the doc has diagnosed your symptoms! ~ i think i'm going to say that after he finishes explaining others' problems.



-justin
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Old 09-14-2004, 11:13 PM   #6
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Hey thanks you guys for the comments! This list is great!
The CAT was the first thing I replaced! The mechanic told me that the cat probably melted down as a result ot a situation, most likely not the cause of it! (sounds logical)
So after realizing the CAT wasn't the problem, I turned to the ignition system. Now that I've replaced it all, I feel safe to say that I've ruled that out also.

The plugs ALL seemed to be gas-soaked, maybe one was a slight bit worse, but nothing to make me suspect any one cylinder.

It always seems to come back to the Closed-Loop mode. Everything seems fine until it hits normal Temp. Then if you give it any kind of push whatsoever, it just wants to PUKE!
I now have a 2 mile test loop around my neighborhood that I know will get it into Normal Mode and still be able to limp home if it'* not proper.

I'm hearing some REALLY great minds tearing away at this thing!

Thanks, Mark
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Old 09-14-2004, 11:17 PM   #7
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Injectors dirty and stuck open, Causing a rich condtion, Causing the PCM to try to correct and run like crap, And killing the cat. Possible?
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Old 09-14-2004, 11:30 PM   #8
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Quote:
Damemorder
PostPosted: Tue Sep 14, 2004 9:17 pm Post subject:
Injectors dirty and stuck open, Causing a rich condtion, Causing the PCM to try to correct and run like crap, And killing the cat. Possible?
Thanks Damemorder,
That'* kinda the direction I was next heading, towards the fuel side of the house. I'm glad to see someone else is leaning that way. Fortunately, I have a new set of injectors from a 2000 Monte Carlo SS (3800) . I'm hoping they are the same part # (does anyone have a parts lookup) If they are, I will put those in tomorrow and back to my test track again!!

Thanks, Mark
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Old 09-15-2004, 12:15 AM   #9
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I saw another post tonight that had similar problems and it turned out to be a Crank Sensor. Could this be a possibility? based on my symptoms?


Thanks, Mark
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Old 09-15-2004, 12:20 AM   #10
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Quote:
Originally Posted by mark2112
I saw another post tonight that had similar problems and it turned out to be a Crank Sensor. Could this be a possibility? based on my symptoms?
Do what you can to get a scan tool on the car. I was lucky for it to finally trip the SES. Until then there weren't any codes. Just because that'* what the code said today, it'* not certain that it'* been causing the problem. It took a long time for Willwren to get that through my skull. Without the code tripping this morning, I'd still be searching for the right tool to pull data while I'm driving to work.
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