1996 Oldsmobile 88 96 Oldsmobile 88 Engine Misfires

EPJENSEN

MEMBER
1996 OLDSMOBILE 88
6 CYL
FWD
AUTOMATIC
130,000 MILES

Hi,

I've got a 1996 Oldsmobile 88 with a 3.8L v6. In September it started running pretty rough, and I borrowed a friend's OBDII scanner and it had a P0300 code. I have had the car parked over the winter (about the same time the problem started we bought and started driving a minivan because we had our 4th kid), but recently pulled it out to try and get it running again. A coworker suggested that it could be due to dirty fuel injectors, so I drove it through a tank of gas with injector cleaner, but that did not help. I read the codes on it again, and it now has P0300 (random misfire), P0336 (crankshaft position sensor) and P1200 (injector control circuit) codes. The rough running/misfiring occurs both while it is idling and while it is driving. When driving it will be especially bad at some rpm's, and cause vibration in the vehicle, and reving it up or down a bit smooths this out, but it is obviously rough and underpowered all the time. I would appreciate any assistance/advice you could give on where the source of the problem might be. The onset of the problem was fairly sudden (running smoothly, then over the course of a single drive it started misfiring and running rough and has continued to run rough ever since). Thanks for your help.

Eric

5 Replies

DOCFIXIT

MECHANIC
18,828 POSTS

Hi
The P1200 was set because of P0300 need a scan tool on FREEZE FRAME mode to see which cylinder has most misses. Then repair or replace injector or drive circuit.
P0336 is likely the Ignition Control Module.
Hope this helps
Thanks for donate

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Wednesday, March 24th, 2010 AT 10:13 AM

BUICKDAD

MEMBER
6 POSTS
1998 OLDSMOBILE 88
3.8L
V6
FWD
AUTOMATIC
150,000 MILES

Hello:
From Rochester NY. >>> A few days ago the MIL came on. Initially steady, not flashing. FYI this followed shortly after my wife adding gas. ( Noteworthy perhaps, but really doubt "bad" gas or water / ice in fuel. Already had some isopropyl in the tank. Plus, I transferred about 10 gallons into another vehicle, which is running fine after a few days and extreme cold temps ). >>> Following morning MIL began to flash at first start, and idle was very rough. Some raw gas smell. Did not drive it. Later, pulled off 2 codes: PO300 and P1404. Removed the linear EGR. No signs of carbon build-up, and stem travel seemed fine, but cleaned pintle / seat / stem with carb cleaner and tiny dental brush. Gasket looked a bit suspicious, so replaced. To verify fuel flow ( to rule out plugged filter, ice in line, etc. ) Ran clear tube from fuel rail Scrader valve into gas can and jumpered past the FP relay. Filled can quite rapidly, and no signs of crud, ice. Etc. >>> Cleared codes and started engine. Initially idled rough, then steady MIL, then flashing MIL. Let run for about 5 mins and rough idle smoothed out significantly ( can't say 100% ). But try to drive, and immediately runs rough with slightest acceleration. Seems like might stall also. >>> Ran a scan. EGR code gone, but PO300 still there. Cleared codes again then drove with scanner on record. If I basically "coast", idle seems smooth, and no code kicked out. But begin to accelerate, engine runs rough, MIL comes on, then shortly begins flashing. Immediately PO300 comes up on scanner. >>> I do most all my own work, and have 4 vehicles between 1998 and 2000. Spent many hours researching PO300 causes / cures on internet, so essentially know how I need to try to diagnose. But hoping to come across someone ( professional ) who has encountered PO300's before on GM 3.8's in the age range as mine. If so, what specific causes / cures did you find? For this engine, what would you say is most likely cause, then 2nd, 3rd etc. I realize there are many possible PO 300 causes and even possible linkages between problems. Just trying to streamline my diagnostic efforts via some real world experiences.

Will donate $50 for the right technician. Please note: If you say you suspect the "widget" is bad, need you to clearly explain why you think this.

Thank you in advance,
Mark

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Tuesday, December 20th, 2016 AT 10:32 AM (Merged)

HMAC300

MECHANIC
48,601 POSTS

300 codes are difficult to find you need to freeze frame and see if you can find any sensor acting up. It can also be an injector, basic engine problem like wire/plug or a compression issue so start anywhere you want on this. Might be the maf though.

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Tuesday, December 20th, 2016 AT 10:32 AM (Merged)

KEN L

MASTER CERTIFIED MECHANIC
47,690 POSTS

First of all we need to start at the basic's. Lets pull the plugs to see if they are carbon fouled,

More info here:

https://www.2carpros.com/articles/engine-misfires-or-runs-rough/page/2

While the plugs are out, lets do a compression test:

https://www.2carpros.com/articles/how-to-test-engine-compression

if all tests okay, it sounds like it could be a computer issue which pledged those years of GM's, also older computers do not like the cold, (much like people, haha.)

Check all engine/computer grounds at the intake and engine block. Make sure the battery terminals are clean and tight.

Please get back to me so we can continues once you have performed the checks

Best, Ken

Look forward to hear from you :-)

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Tuesday, December 20th, 2016 AT 10:32 AM (Merged)

HMAC300

MECHANIC
48,601 POSTS

From rereading your description it might be a small vacuum leak like a broken hose etc. As when it warms up the closed loop may be richening the mix up to try to take care of it. Use choke cleaner to check around it. The reason I said to have a pro look at this is because these are very hard to diagnose and he can freeze frame it and that will check a lot of the sensors while it's actually running and he can make kind of a guestimate on what is causing it. This will save you time, money from wasted part replacement as well as the aggravation of trying to figure out exactly what it is.