: intermittent misfire on #1 cylinder. Help Please.

03-27-04, 09:03 AM
:banghead: I have a 96 Eldorado with a Northstar engine which had developed an intermittent misfire on #1 cylinder. I've changed the plugs and replaced the plug wire which seemed to cure the problem for a while but after a few days the misfire came back. The strange this is that, the car may run fine for several days and then the misfire will come back and may only happen a few time and disappear for several days again or it may decide to stay around and agitate me for a while. Sometimes it will set a "#1 cyl misfire trouble code" and sometimes it won't. I've had it to a good tech twice now but as things go, the darn thing wouldn't misfire when it was in the shop and everything checked out OK. Weather conditions don't seem to matter so I don't think it's a problem with ignition components drawing moisture in wet weather. Anyone out there have a similar problem?


03-27-04, 04:18 PM
I don't know if it is always the same cylinder it should narrow it down to only a few items.

You already replaced the plugs, and plug wire. It may be an injector problem.

It is also possible that you are pulling in condensation from the gas tank and it is "putting out the fire" (although I don't think it would be limited to only one cylinder).

I will run about ten ounces of Marvel Mystery Oil in a full tank of gas, about three time a year, to help keep my fuel system clean and the injectors working free.

I will also substitute a quart during an oil change three times a year to help keep varnish from building in the hydraulic lifters and keep the rings freed up.

I am not a big fan of fuel or oil additives, but Marvel Mystery Oil has always helped out and you cannot hurt anything by trying it.


03-27-04, 05:11 PM
A couple of thoughts...

Double check the new plug wire to ensure the ends are on and did not get pulled loose. Are any of the others bad and causing a misfire on #1? I think each coil fires 2 plugs, check the other cylinder on that coil. I would put in the whole set of wires.

Was there any corrosion on the coil?

03-27-04, 09:51 PM
You can swap the coil for 1 to another location and see if the miss goes with the coil....

Double check the spark plug end of the wire to make sure the rubber "umbrella" that seals to the cam cover surface is not pulling the plug boot upward and off the plug terminal. The umbrella should contact the cam cover at the top at about the same time the terminal inside snaps onto the plug. If you have to preload the umbrella too much to get the terminal to engage then it may be tugging the plug boot upward and disconnecting it occasionally...

03-28-04, 08:39 AM
Thanks guys for all of the good suggestions but, other than trying a new injector and a different coil, I have checked and double checked everything else numerous times. As for fuel contamination, that was my first suspicion because the misfire started about a day after I had bought gas at a station that I don't normally patronize but, that wasn't the problem. BTW, Marvel Mystery Oil has many uses and is some great stuff and I have been a fan of it for many years now!

Since the Misfire is intermittent and only occurs on number 1 cylinder according the the trouble code I am suspecting it's either an injector or the coil but the intermittence of the misfire makes me a little hesitant to start parts changing in hopes of stumbling across the culprit. However I did not know that I could interchange coils in the pack so I will try that and see if the misfire moves to a different cylinder if so, I guess we found the problem and I thank you all very much for your help.

I bought my 96 Eldorado two years ago from and old couple in St. Louis who bought it new. The car only had 29,000 miles on it (now has 59,000) and had always been garaged and well maintained according the the file full of maintenance records that the gentleman gave me when I bought the car. Other than this misfire problem, I really love the car!

Thanks again guys!