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I have a 1998 Olds 88 with a 3.8 V-6 and only 25K ...

Sent to Car Experts March 29 2006 at 5:01 AM
   

I have a 1998 Olds 88 with a 3.8 V-6 and only 25K miles that once it gets warmed up, will shudder upon moderate acceleration. This is what I have done as I have another 1998 Olds 88 that I can use to swap parts. First, I found that the intake manifold had warped, so this was replaced and greatly improved performance, however the stumble on accelertaion still exists. Then I replaced the plugs and wires, no luck. I have swapped the main computer, as well as the ignition assembly, neither resulted in any improvement. If I drive the car hard enough to generate a trouble code, the same code P0306, #6 cylinder misfire, is all I get (although upon more diagnostic review, the #3 cylinder also indicates some misfiring as well). While driving both cars with my AutoXray EZ-Link scanner, the operating parameters appear very similar between the cars. I've explored everything I can and still no success. Any suggestions??? Thanks...JCT

 

Optional Information:
1998 Oldsmobile 88 LS 3.8L

Already Tried:
See comments in initial question/p>

Customer (name blocked for privacy)
Status:  Closed   Value: $10
Answer
March 29 2006 at 5:15 AM (13 minutes and 22 seconds later)
         
REPLIEDCheck Mark

Does the shuddering feel like a rumble strip on the road? Does it stop if you keep your foot on the gas when it is doing it and lightly put your foot on the brake just enough to turn on the brake lights? You may be experiencing a torque converter shudder. Sometimes when this happens it will set a misfire code because the computer is looking for a change in rpm at certain times. If it sees a change in rpm it could think the engine is misfiring when the torque converter clutch is slipping causing the "rumble strip effect". Also here is a tsb from GM regarding a shudder.

Bulletin No.: 99-07-30-007

Date: May, 1999

TECHNICAL

Subject:
Vehicle Shudder When Reapplying Throttle (Greater than 50%) Alter Stopping (Reprogram PCM)

Models:
1998 Buick LeSabre, Park Avenue
1998 Oldsmobile Eighty-Eight
1998 Pontiac Bonneville
with 3.8 L V6 Engine (VIN K - RPO L36)
and Hydra-Matic 4T65-E Transaxle (RPOs MN3, M15)

Condition

Some owners may comment about a vehicle shudder after slowing for a stop and reapplying the throttle at greater than 50 percent.

Cause

Condition may be due to insufficient line pressure causing improper clutch apply.

Correction

Reprogram the Powertrain Control Module.



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1 Other Expert Agrees with this!
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autodoc_2000 -- Auto Service Technician -- 98% Positive Feedback on 945 Car Accepts
ASE Master Tech w/ Advance Engine Performance
Reply
March 29 2006 at 5:58 AM (43 minutes and 16 seconds later)
         
Reply to autodoc_2000's Post: The shudder really feels like an ignition misfire to me from my experience from earlier years of tinkering with cars. This car had the fuel pressure regulator replaced a while back as part of a GM recall. The studder or misfire becomes noticible once the engine temp gets to 150 degrees and when the ignition timing advance (upon acceleration) drops below 15 degrees. If you accelerate gently (15 to 20 degress of advance), no apparant problem. But I drive more towards the hard side and accelerate fairly quickly and therefore I notice this situation more readily. Also, if you accelerate from 50 MPH to 70 MPH for example, the sensation feels more like a varying surge in power.
Customer (name blocked for privacy)
Answer
March 29 2006 at 3:18 PM (9 hours and 19 minutes and 42 seconds later)
         
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autodoc_2000 -- Auto Service Technician -- 98% Positive Feedback on 945 Car Accepts
ASE Master Tech w/ Advance Engine Performance
Reply
March 30 2006 at 8:57 AM (17 hours and 39 minutes and 35 seconds later)
         
Relist: I still need help.
I appreciate the two responses, however I am still without the help I had hoped for. I (along with my mechanic friend) have tried swapping about everthing of major importance (computer and ignition module assembly), and or checking functionality (injectors, wires, new plugs)not to mention several cans of 44K and replacing a warped intake manifold. The car drives fine when cold. At about 150 degrees, the misfire or stumbling starts but only when under moderate acceleration, especially when the timing advance drops to and below 15 degrees. I just drove 140 miles in the car this morning and at crusing speeds (70-75) it performed very well. However, while accelerating onto the highway, the stumbling is apparant, but only if the throttle is pressed more than minimal to get up to speed. This car only has about 28K miles and for a 1998, obviously has not been driven much. I don't believe that the trans is the problem as shifting and crusing are flawless. While crusing the interstate on cruise control, the studder condition was not obvious. When I controlled the throttle, to pass a car, I could percieve a stumble or slight, intermittent surginging of power. Back off the throttle a little bit, and the surging / stumbling stops. I also do not believe the problem is due to a bad injector. Finally, the only trouble code I get is a P0306, cylinder #6 misfire, which tells me nothing.

I don't mind paying the $10 and will even if I don't get a solution to my problem. However, I was hoping that someone had some specific experience with GM cars that exhibited the same symptoms as I have listed. Generic suggestions I have already obtained from other sources, thus the swapping, replacing and checking as I previously mentioned. And I really do not want to take to a dealership and have them play what-if's or guess and replace all at my ultimate expense. So, I am still hopefull that someone may have seen this situation before and can offer a solution. Weill see.

Thanks...JCT
Customer (name blocked for privacy)
Reply
April 1 2006 at 12:53 PM (2 days and 3 hours later)
         
Relist: I want a different opinion.
1998 Oldsmobile 88 LS w/3.8 L V-6 and 28K miles

Drives good when cold up to about 150 degrees

Starts to misfire when at normal operating temperature and when there is moderate to heavy acceleration(feels like a shudder upon acceleration although light acceleration usually does not cause symptoms) also only occurs when the timing drops below 15 degrees during acceleration.

Replaced the ECU/PCU unit with no change
Replaced the complete ignition module with no change
Replaced the plugs and wires with no change
Had my mechanic test and verify that the injectors were operation as they should and there are - also used 3 cans of 44k in the beginning

Transmission shifts fine. The misfiring occurs in every gear during moderate to heavy acceleration. Lightly pressing on the brake causes no change with the misfire.

I compared another 1998 Olds 88 LS diagnostic operational output on my AutoXray EZ-Link scanner with the above referenced car and could not ascertain any unusual differences between the two cars.

Although I am not an auto mechanic, I have worked on and maintained numerous cars for the past 40 years and have a lot of troubleshooting experience myself. Neither my mechanic (30 years in the business) nor I have been able to figure this problem out, and yes, we have checked, swapped and tested all of the obvious things.

The previous two responses to my initial question were nice but generic, and I had already ruled out those possible answers long before I contacted ASK. So, in any event, I am relisting my car's bizaar situation for hopefully another round of answers, hopefully from someone that has specifically experienced the same symptoms as I am.

If anyone needs more detail on what I have done or how the car performs, please do not hesitate to ask.

Thanks...JCT

Customer (name blocked for privacy)
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