Hey guys,
I went mudding yesterday, came home and did some light cleaning of the engine bay. I didnt soak anything in there, and I stayed away from the intake, electronics and the alternator. I took it for a ride when I was done, no problems, and brought it here to work today with no problems (about a 10 mile drive). I went to go to lunch today, and about 3 miles down the road I noticed a little blip in the smoothness in the engine a couple times. So off the next light, I gave it a little gas to see whats going on, and the engine light started blinking after it shifted out of first gear. It then ran like crap. It idles rough and doesnt ride smooth going down the road. Im getting a cylinder 8 misfire. For your viewing pleasure:
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I just replaced the plugs with 3923s less than 100 miles ago. I highly doubt the plug has fouled in cylinder 8, and since it is so far back Im hoping I just didnt tighten it all the way and it just wobbled loose. What are the chances its just a loose plug?
Ive looked up on google what can cause a misfire, and they brought up vacuum leaks. I did just replace the TB, so its a possibility. What are the chances that it would just make one cylinder misfire though if there was a vacuum leak?
Like I said, it ran completly fine until today at lunch. So I think its safe to rule out the water, but what are your guy's thoughts?

 

I would say if you had an intake leak you wouldn't have a misfire. And if you did, it would be random and not the same one.

I would check the plug, and the coil pack.

 

Is it safe to drive home the 10 miles if I go easy on it? The engine light only blinks under heavy acceleration, and then it will go off. Under light driving it only runs rough, I just dont have any tools with me to check it out here in the parking lot.

 

based on that its still difficult to diagnose. my guess is still something to do with spark if it is only throwing a code for #8

 

Yeah, I just dont want to end up blowing a head off by driving it home if the plug is loose. It wouldnt suprise me if it was a loose plug. With that one being so far back, and it was the last one I did, its definetly possible that it wasnt completly tightened.

 

Are you running any type of aggressive tuning on Superchips or SCT? Our coils arent the best at dealing with the aggressive pull of the vacuum system. This happens to be from time to time.

Check your #8 coil connection as well as the fuel injector for that cylinder. If the connections are wet, they may not transfer the signal effeciently.

If the fuel injector is not spraying, you can get the same. If you get air into the fuel rail it can cause this also.

 

I do have the 91 SC tune running with 93 octane gas. Im going to get it home and hopefully find a loose plug, otherwise Ill go to switching coils around. Im just hoping its not anything too serious.

 

If its not the plug, try setting the tune back to stock and see if it continues. Every so often that happens to me because our Coils are certainly not performance grade, lol.

 

Blown doesn't the rear most inj portion of the rail sit lower than the forward most? wouldn't that cause the air bubble to go the the front one?

 

It certainly could, but when the fuel system is charged it can move. If its air in the line, simply put a rag under the relief valve on the rail and slowly press in. If its air it will bleed out, if there isn't air in the sytem you will just get fuel.