Hi,

I hope that I can get some advice.

The car starts to misfire with the odd backfire when I push the accelerator hard. The car will then run continuously rough until I shut it off and restart it.

Is this the O2 sensors??

Help would be appreciated.

Thanks

You most likely have a secondary side ignition component breaking down causing the initial miss fire then, the ECM is shutting down that particular cylinder to prevent the cat from overheating. A oxygen sensor does not usually cause high roughness and won't cause a specific cylinder to drop out.

I know for sure that the 97 ME - SFI system does this, not sure if the 96 has HFM - SFI this level of control or not.

Run the scan tool and look at miss fire counts, if you see a cylinder with high counts, move that coil / wire / plug to another cylinder and see if the problem follows.

It seems that the coil on plug side of the coil fails more often than the wire side. ( One coil runs 2 plugs.)

I believe 97SL320 means the "connector" on the plug side of the coil.

That said, there are a few possibilities, but the place to start is not with a guess, but by pulling codes to see what is showing up. AutoZone and some other parts places will read them for free.

Good luck.

Thanks for the replies. Will look at the codes and try the recommendations. Will report back.

'With a 96 MB you need to check the condition of your electrical harness under the hood.

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1992 940T

"If you dont have time to do it safely, you dont have time to do it"

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Thanks again for the replies.

I have done a scan....a pile of errors. However, while changing the spark plugs, I noticed that I had two vac lines that were broken. The y may have broken while removing the cover? They were extremely brittle. I replaced them with rubber hose.

So far....no misfires. Scan said that there was a misfire in cylinders 5 and 6. It is running better. Need more time to know for sure.

While changing spark plugs, the tiny screws for the ignition coil broke (one per coil). It is just one little screw, do you recommend that it be replaced? Will it be OK without them.


Thanks again for your help!

Are these the headless screws ( studs ) that thread into the valve cover?

If so, these are more or less to hold the coil in place while yo install the coil cover. They also provide a ground path for the coil laminations, while this ground path isn't needed to run the engine, not having it might contribute to radio noise. These studs don't get removed when pulling coils.

Also, you still might have a bad coil. New spark plugs have a lower firing voltage requirement and this can mask a coil that is arcing over internally. For example, if a failing coil has a flash over voltage of 30 KV and flash over voltage of the spark plugs is lower, the cylinder won't miss fire. As the plugs wear, gap increases, voltage requirement increases, coil flashes over.

Thanks for the help!

The screws are still there, they don't really do much, as they no longer have a head. The heads (a standard head) broke when I tried to remove them. The coils just sit on the posts?


Still don't have the misfire. If it happens again, I will check the coils.

On the 95 and 97 engines I have, there never were heads on the screws. I wonder if someone replaced them. For the engines I have, the coils have a clip that engages the screws to hold everything together. The coil cover screws are what hold the coils down.