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Old 08-28-2009, 10:05 PM
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1991 Olds

Hi all just found this site and need some help. My91 Olds 98 starts and runs fine, until it transitions from cold start to hot run.When it does the timming goes full advance and it dies.All it will do then is back fire through the intake. There is no one in my area that can fix it> They all say (I can put it on the machine and probably fix it).
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Old 08-28-2009, 10:33 PM
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Check the Coolant Temp Sensor and Intake Air Sensor, when engine cold, they should ohm out with a meter close to the same, just don't get near them, they will warm up easily.

Use this chart for resistance: GM sensor information

If there is a closed loop issue, it will run good cold and bad after around 2-3.5 minutes. Unplug the O2 sensor and see if that keeps it running good, this isolates open loop and closed loop, not necessarily if the O2 is bad. Just keep that in mind.

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Hi all just found this site and need some help. My91 Olds 98 starts and runs fine, until it transitions from cold start to hot run.When it does the timming goes full advance and it dies.All it will do then is back fire through the intake. There is no one in my area that can fix it> They all say (I can put it on the machine and probably fix it).
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Cars built by engineers, rather than spreadsheets, tend to go down in history... Tiff Needell

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And now supporting with EFILive!!
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Old 08-29-2009, 11:17 AM
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n0dih Thank you for the reply. Both of the sensors are in the proper range.
It has been sugested to me that this could be a problem with the module under the coil pack.Any further help would be great thanks.... Dave
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Old 08-29-2009, 12:11 PM
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I don't think so, maybe, but I wouldn't rush to it. How have the sensors been tested? I am a big proponent of testing sensors before replacing.

As for the ign module, without PCM control the timing is fixed, like around 10 degrees or so, when the PCM comes into play, it then can delay or adv as needed. So knowing that, IF it is working now in open loop, I personally would not be rushing to think it is bad just yet.

If the CTS and IAT are good (did you ohm them out or read on datalogger?) and very close in temp at cold start, then look at the O2. The important thing on the O2 is disconnecting it will trigger only open loop mode, and if the ign module is good, will run perfectly fine, lower on power and mpg, but run fine, maybe some issues if you get on it.

You can ohm out the coils too, the Magnavox coils can fail (they are generally pretty reliable) and when the PCM is in open loop it runs rich, and when in closed loop it will lean out to 14.7. So if the coils are weak or at least one is, then you have 2 cyls that will be having a weak spark, and the PCM could be reacting badly to it (reading the O2 and messing up fuel mixture due to lots of raw fuel coming out the pipe).

Is the thermostat good? Up to 140F or higher?


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Originally Posted by hoppercarmaker View Post
n0dih Thank you for the reply. Both of the sensors are in the proper range.
It has been sugested to me that this could be a problem with the module under the coil pack.Any further help would be great thanks.... Dave
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And now supporting with EFILive!!
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Old 08-29-2009, 12:32 PM
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I tested the sensors with an ohm meter. Unpluging the o2 makes no differance.I started it this morning and it ran 2.5 mins and died,2min later restarted 3.5 mins died waited two mins restarted, runs great.Ran 15 mins fans came on, everything good. Bad connection mabey? Waiting on it to cool so I can try it again.
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Old 08-29-2009, 01:59 PM
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Ok, if disc O2 doesn't make it run right, you are likely down to the Ign Module or the PCM.

If it was me, I would connect up a wire on the ign module to some meters in the car and drive it and see if the ign module loses power (as commanded from the PCM).

The symptom of dying and restarting is sounding like corrosion, where the resistance is high enough to make it fail, but is on the edge to make it run ok then fail again, so time to fail is random. If it was a Closed Loop issue, the time would NEVER exceed 3.5 min.

Pull the ign module connector, they are up in the area that gets moisture and salt spray. If the seals on the connectors have deteriorated over time, that likely is the problem area. Check the wiring harnesses from there to PCM.

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I tested the sensors with an ohm meter. Unpluging the o2 makes no differance.I started it this morning and it ran 2.5 mins and died,2min later restarted 3.5 mins died waited two mins restarted, runs great.Ran 15 mins fans came on, everything good. Bad connection mabey? Waiting on it to cool so I can try it again.
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And now supporting with EFILive!!
[U]



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Old 08-30-2009, 11:29 AM
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It has apparently fixed its self. Have started it cold five times with no problem. Thanks for the help.
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