Hello I have a 1995 960 with about 120,000 miles on it and noticed what I believe is the engine misfiring when accelerating on the freeway. The car stutters as I try to accelerate and it feels like it isn't accelerating as fast as it should be. The car seems to be fine when accelerating to get onto the freeway. I think that I have also pinpointed that this only happens once the car has warmed up (~15-20mins).

This all started after having the spark plugs changed at the shop. The car was originally brought in for repairs to the gas evap system because it failed the CA smog test. They ended up changing the plugs as well since the car was also putting out high levels of HC and NO. The following day I discovered the problem so I took it back in but was unable to replicate the problem. So we have used the car for a few months and recently noticed it again. Since we don't drive the car on the freeway much I believe that's why it took so long for us to rediscover the problem.

I have done a visual inspection of the ignition coils and wiring harnesses and they seem fine. I haven't pulled out the spark plugs and I do not know what kind the shop installed other than they are Bosch (from what I can see on the spark plugs).

At this point I am not sure what to do next and any suggestions and help would be greatly appreciated.

 

Wait for the pro's on this one. I know the 960's don't like other plugs, other than oem but there may be something else.

Did the car pop a CEL? If so, you should get that code pulled and post it as well.

 

Because this started when the plugs were changed, you should start there.

Did the car pass the emissions test after the new plugs were installed? How did it run before the plugs were changed? Has this car been maintained or just serviced when something goes wrong?

How is the idle? Is there a miss? Could this be a trans problem, the trans not downshifting at the correct moment, or the lock up solenoid is not releasing when it should? Giving the impression that it is a power problem?

I would start by inspecting the wires to the coils, the insulation should be pretty brittle by now on a '95. Look for some wire touching ground. Take note of where the wires join the connector, all of mine have had to be renewed because of wire breaks right at that transition. Inspect that all connectors are clean and are making solid contact. While inspect connectors, look at the two for the power stages.

Does it start ok when hot? A bad or missing coolant sensor signal could cause this problem.

Does your check engine light up when the ignition is turned on but the engine is not running?

Are there any stored codes, some codes do not light up the check engine light.

Keep us posted on what you uncover.

DanR '94 964 348,000 miles (104,000 on the new engine)

 

Chances are, they installed Bosch Platinums. Remove them immediately, and installed a standard copper plug, such as an NGK BKR6E. The platinums should universally be regarded as trash. It's nice, because these cars take the same plug as my BMW


But I'd start with plugs. They'll cost you ~$12 and a half hour of your time. If it still happens, report back;.

 

What exactly did they fix on the evap system? The wiring on these cars ain't the most durable, and they may have knocked it about when working on the evap.

What I would look for is this: The wiring goes through a gap at the intake manifold just forward of the throttle body. This is a really common area that wears through and causes intermittent problems like this. You can pull it up a bit and see if you can see copper...

 

Thanks to everyone for the responses. The CEL does not light up and I am not sure how to check if there are any stored codes. The car's emissions levels were much better after the plugs were changed. The shop found a cracked hose above the gas tank which was causing it to fail the evap test.

I try my best to follow the regular schedule maintenance of the car though it has some other issues such as a small oil leak somewhere under the engine and the transmission lever can't be switched out of park unless I use the switchlock override button. Sometimes the car does have a little trouble starting and I think that it can happen both when it is cold or warm. The car's idle seems to be ok.

I'll inspect the wiring further and probably go ahead and change out the plugs this weekend. Will keep you all posted.

 

Just wanted to give an update on my situation. I switched out the spark plugs with NGK BKR6E. The shop had put in Bosch platinum +2 plugs. So far I have not experienced any engine misfires. However the problem was intermittent to begin with so hopefully it has been solved.

 

BKR6E is the correct plug for the car. It's what I run in mine, and actually, the same plug I run in my BMW's as well. Work great in the track cars.