Engine Vibration on a '91 Olds 98 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 07-14-2007, 05:30 PM   #1
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Default Engine Vibration on a '91 Olds 98

This week while sitting at a light my car began to stumble and idle very roughly, the car had been running like a top until that moment at the light. My first thought was a problem with the ignition module/coil pack. I switched those out with another set I had, and the car calmed down and idles/revs beautifully now. When I went for a test drive, I still noticed an acceleration stutter from stop. When on the hwy in cruise mode it runs fine, it'* just a slight noticable stutter on acceleation from a stop. Late last summer I replaced the fuel pump (first time in 220k); filter, and pressure regulator, balancer, timing chain, interrupter magnet and gears. I've also replaced the plugs and wires today with no noticable improvement.

What else should I be looking for.....being OBD I my AutoXray 6000 scanner only shows minimal information. Additionally, My checkengine light is NOT on.

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Old 07-14-2007, 05:39 PM   #2
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So this would be the First year for the Newer C body Design correct? And you have a 3800 Tuned Port Injection L27 correct?

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Old 07-14-2007, 08:04 PM   #3
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Yes, that is correct 1st year 98 and I found the problem....I just need some guidance now where to go. My #2 Injector is not firing. I put a test light on the wiring and it'* not lighting as the others....... Where does this harness go AND is there an easy way to run it down without undoing each individual wire. Could there be another problem that would keep just that one from not firing that is NOT a 'broken' wire type issue.

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Old 07-14-2007, 08:59 PM   #4
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Test both wire coming from the #2 connector, the common line is lightes AND my volt meter gives me voltage on the hot line right to the fire wall. My next thought would be a bad injector chip in the ECM?
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Old 07-14-2007, 09:06 PM   #5
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So you do not see a Pulse on #2, do the other 5 Pulse?

The PCM could be possible... It has an individual driver for each of the 6 injectors...

Do you also have continuity in that wire from the injector pigtail to the firewall connector?

This is very interesting

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Old 07-14-2007, 09:34 PM   #6
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All the other injector connectors fire the NOID light except for the #2. I checked continuity on each line ..... I had juice on both wires from my test light and from my meter to the firewall on the other line (it'* a black/light green wire). From there it goes into the PCM......my wonder is what makes the PCM fire......if it was the crank sensor more than just the #2 would not work......if it were a bent fin on the Balancer then it would damage the crank sensor and it would not start. I tried several coil packs that I had around with no change......if a coil pack was bad it would look like the #6 would not work as well since the 2/6 pack are together?

Thanks....it helps to put the ol' noggin together to solve an issue.
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Old 07-14-2007, 09:40 PM   #7
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Hmm I am very tempted to say try another ECM..

There are instances where part of the crank sensor can fail and the car will still start and run, it will fire all 6 injectors... and the other failure will leave you dead in the water..

The Cam sensor is merely used for the #1 TDC reference so that the PCM will run in True Sequential Fuel Injection...

Being that #2 is the only one not firing it would seem to me that the rules out a crank sensor failure.. The PCM seems like the most likely culprit....

always hard to say 100% for sure tho... Might be worth a shot tho, it seems you have ruled everything else out..

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Old 07-14-2007, 09:55 PM   #8
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That'* as I'm thinking....my fear is to wonder what caused the failure. I was just sitting a light 2 miles from home one day last week when the engine bucked and then started the vibration (right out of the blue.) We have a "Pick and Pull" junk yard here in town. Neatest junk yard I've ever seen. It cost $1.00 to get in and pull anything you want. They rotate cars in/out in 30 days. All cars are in neat rows by manufacturer and the yard is covered with crush and run (no high weeds/puddles). They supply wheel barrows and engine hoists on wheels....the rest is up to you. The prices are great and I can probably get another ECM for under $20. That'* what we'll try next week.
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Old 07-14-2007, 11:25 PM   #9
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Just for Hmmmm? value. If my #2 is the only not working, what would happen if I jumped the line from the #6? They fire at the same time.....would it work or would it burn up the 6? Don't know if I have the guts to try it, but a hmmmmmm.
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Old 07-15-2007, 04:06 PM   #10
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It might work, But I don't have the guts to try it either... lol

Wish I had a test PCM to send your way

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