Missing with minor backfiring, Cyl. 4 plug black

94svtturbo · Mar 19, 2011

So last night i fired up the car and it was idling really rough and had some minor backfires. I though it was cuz i went another step colder on the plugs. But when i got up this morning and changed went to change the plugs back to what i had in it before all the plugs look like they are super clean except for Cyl. 4. Its totally black!!! but i went ahead im put the new plugs in. started it up and im having the same issue! so i pulled the cyl. 4 plug and its completely black again. the other plugs look brand new. Both times the car only ran for 10 minutes. also tried changing ou the cap, rotor, and wires to rule those out. the problem still persists

When i drove the car over to my buddys garage it drove perfectly normal!!! all I did was change the plugs, put in a Griffin radiator, ceramic coat my exhaust, and tuck the fuse block and wiring harness!!

IDK what to check!!! any ideas would be awesome!

Car is a 1994 Cobra 5.0

auto_x5.0 · Mar 19, 2011

Check the gap again, you may have bumped it a little when putting the plugs in and changed the gap...that's the only thing I can think off

94svtturbo · Mar 19, 2011

Yeah. I will have to check that tmrw but I find it hard to believe hat I would have done that to both plugs I put in that cylinder

Addermk2 · Mar 20, 2011

loosen up your fuel rail, remove the #4 injector and switch it with the #1 injector.

put a clean set of plugs in and see if the problem remains. If the car still runs poorly, check the #1 and #4 plugs. See which one is causing the issue.

If #4 is STILL the problem, you have an engine issue, and will need to take it apart.
If #1 becomes the issue, you have a bad injector.

94svtturbo · Mar 20, 2011

Ok. I will try this tonight after I get off work. After readig up on some studf im. thinking it is a bad injectors cuz that can happen randomly. and if it was an engine problem I would think there world be more of a warning.

So if I swap the injectors around and its still is having trouble on Cyl.4 what kind of engine problem are we talking? Head gasket? Or some more internal?

Thanks for the help Addermk2!!!

modo · Mar 20, 2011

black with soot or oil?

if it is soot you have a ignition problem. if the injector was not firing the plug would be clean... also the backfire is more then likely the raw fuel igniting in the exhaust since you don't have spark on that cylinder

94svtturbo · Mar 20, 2011

I just got home from working and going to swap the injectors. swapped them and put in a new plug and the same thing happened even with the injector moved. Cyl 4 plug is still black.

94svtturbo · Mar 20, 2011

modo said:
black with soot or oil?

if it is soot you have a ignition problem. if the injector was not firing the plug would be clean... also the backfire is more then likely the raw fuel igniting in the exhaust since you don't have spark on that cylinder

It is black with soot. Any ideas of what i could try checking to find the ignition problem? Its just that one cylinder that is fouling. So what would cause just that one cylinder not to fire? I have swapped that plug wire with one of my old ones that i know worked when i pulled the wires

I tucked the front wiring harness with fuse block. everything is plugged in correctly. i have checked and rechecked it all to make sure its plugged in correctly. I will have to look but i believe the ICM is connected to that harness somewhere. but i would imagine it would make me cylinders misfire if that wasnt operating.

94svtturbo · Mar 21, 2011

I forgot to put in my last post that i put an inline spark tester on that plug and the light was flashing indicating it was getting power through the wire

inline spark tester used was just like this one:
http://www.google.com/products/cata...=X&ei=2M2GTaWBO5G4sAPQoYjmAQ&ved=0CFYQ8wIwAA#

modo · Mar 21, 2011

94svtturbo said:
I forgot to put in my last post that i put an inline spark tester on that plug and the light was flashing indicating it was getting power through the wire

inline spark tester used was just like this one:
http://www.google.com/products/cata...=X&ei=2M2GTaWBO5G4sAPQoYjmAQ&ved=0CFYQ8wIwAA#

through the wire is one thing, through a plug is another. with a spark plug in the boot hold it against the header and see if it has spark that way...

if it has spark i would leak that cylinder down

94svtturbo · Mar 22, 2011

Alright. So officially im an idiot. Last night i went to go check some more stuff on the car to see if i could figure it out. I started by tracing the wires to make sure they were on right. Sure enough cyl. 4 and 5 were backwards!! I had already checked that this weekend 2 times!!! must have just been too frustrated or something and missed it.

So Modo looks like you were right. It was an ignition problem. Thanks for all the advice/help

Matt94GT · Mar 22, 2011

Glad to hear you got it solved.

Addermk2 · Mar 22, 2011

lol.. so the next time you do a tune up and the car starts running funny... the firing order is going to be the first thing you check..

Perfect example of learning from our mistakes. Glad you got it fixed!