3.4l DOHC misfire - DTC p1640
 

HI everyone, New member here. I drive a 1995 Oldsmobile Cutlass Supreme with the vin "x" 3.4L.

I am having a few issues. I'll list them most problematic first.

1. Misfire on #6 cylinder
2. DTC p1640
3. starter is a new reman unit but clicks but doesn't engage everytime.

Any and all help would be appreciated!

1. Misfire....how long since the last tune up?
2. This could be a bad PCM, its a QDM failure. This could take awhile to diagnose.
3. Inspect/Clean battery cables including the smaller starter wire.

Last tune up was about 1500 miles ago if that, I am running ngk vpower plugs and Ac delco plug wires.

I bought a new canister purge solenoid to see if that was the problem with the qdm failure but to no avail it didnt fix it.

I will check the cables tomorrow weather permitting. lol

Try disconnecting the battery cables for 30 minutes, following by touching the two wire ends to each other for a few seconds. That may reset your computer and clear the code.

How do you know cylinder 6 is misfiring unless you are getting additional trouble codes?

I have an old actron scanner I bought off of ebay which scans pre OBD 2 cars. Anyways it shows what Cylinder is bad - misfiring in the data stream and it always shows #6.

I can also clear codes with the scan tool, which I did this afternoon because I had the p1640 fault stored in the memory. Otherwise there isn't any other codes present. I'll rescan after I get off work tonight to see if it reappears.

Good deal Doug, keep us posted, and NEVER EVER get rid of that scanner.

EDIT: The misfire is intermittent and usually occurs at idle, but whenever the scan tool is hooked up the only cylinder that shows up for being bad is #6.

Disconnecting the battery and touching the cables together is not just to reset the codes, it may reset the computer and correct the problem.

Most misfires are due to a bad plug or plug wire. If you are convinced the plugs and wires are good I would try switching the #6 injector with one of the other positions and see if the misfire follows the injector. Also, try switching coils around and see if the misfire follows the coil from #6. If it is not a bad plug, bad plug wire, bad injector or bad coil, I would do a compression test to see if #6 is low, which would indicate an internal engine mechanical issue.

Even if the plug wires are new, you might want to check the resistance on the #6 wire. It wouldn't be the first time an issue is related to a new part.

The more I think about it, the more I think its a bad injector.

Okay I didnt know that! Thanks.

The other suggestions ill have to try but the injectors and coils are in the most ingorant spots. So it'll be an all day adventure to ge to them.

I also need to get a compression test done. Who knows I might have a few burnt exhaust valves?