New bad stumble/misfire? HELP!!

[94v6GT]

let me thank you in advance for your help.
-Yesterday i had complete exhaust installed. BBK equal-length shorties,O/R-X, and Flows out back. So when i pick it up its outside idling horrible. It barly makes it to the gas station a block away as it dies. i popped the hood (should've done while still there) and spy the #6 plug wire dangling in mid air
-so im like ok makes sense, put it on, check the others and start it up. idles fine. drive off=misfire?? entire rev-range ,every gear. at cruise it runs good but ANY tip-in results in misfire until you back off to cruise.
-Thinking the plug fouled while unplugged, i swap in a newbie=misfire. maybe the wire fryed while swinging next to header, so i swap with newbie=misfire?? Maybe others burnt next to a hotter header; swapped em all = misfire.

Im worried something is still unconnected since, after i convinced them the headers WERE designed for my car, they said they had to hoist the motor up in the air jus to get them to fit considering they forgot the plugwire and all.

-Where do i look now?

Car is 94 gt 5-sp with PIH SWAP. All else is stock. It ran beautiful when dropped off.

 

[red95gtconvert]

My guess would be a damaged spark plug wire.

 

[Blackened302]

also might wanna check for exhaust leaks.

when we put my headers and X-pipe in, we forgot to tighten the X-pipe bolts--this lead to a huge exhaust leak at teh collectors and the car wasn't idling and backfiring horribly.

just a thought..

 

[Bosko5.0]

O2 sensors are they hooked up. also equal lentghs tend to burn wires more


Run codes.

 

[94v6GT]

-is there a connector in the engine bay for the O2's? maybe they're bolted in but unplugged? im gonna scan tomorrow.
-i think i wouldve noticed an exhaust leak, but ill poke my head around some more?

 

[1TallMF]

Disconnected O2's should trigger the cel, at least it did on mine.

This is a long shot, but when they put the plug wires back on, is there a chance they might have crossed two of them? As in, put them back on in the wrong order? Can't hurt to double-check the firing order.
Also check to make sure nothing got crunched near the firewall when they hoisted the motor up. My last thought is that maybe they accidentally dropped an O2 sensor and it got damaged.

 

[94v6GT]

there is no CEL btw, but still gonna scan at lunch. I double checked firing order when i swapped wire. im not sure where else to check. hopefully the scan will yield something useful.

-Is there a chance the it being idled and driven a block without that plug wire on caused an issue thats causing all this?

 

[divit250r]

I just had a similar problem with my car after I pulled the engine to replace all the gaskets. I had somehow broken the number one spark plug's porcelain section right above the hex and it was arcing to the head instead of firing the plug. $1.69 for a new plug and the car and I are both happy campers again. You might try checking each plug to make sure they didn't crack any of them. Also, look for vacuum leaks as a general rule once you do any work to it, since most of those hoses are probably original.

Scott

 

[94v6GT]

I just scanned it and it came back clear, no codes. After driving a lil bit more it SEEMS to be running better with less stumble during cruise. Any thing resembling brisk acceleration is met with stumble.

- Could i be wrong in assuming its an ignition misfire when it may be a fuel stumble? i cant see why the stock fuel system couldnt keep up with a new exhaust on a stock motor but im searching for answers.
gonna try a cylinder balance test today and see what turns up.

-btw the exhaust sounds nice with x-pipe smoothness, until it stumbles during acceleration and turns h-pipe gross lol

 

[HISSIN50]

Have you run a cylinder balance test? It can detect a lack of contribution from a given cylinder a lot easier than we can (esp if your idle is naturally lumpy at all).

If this was done at a shop, if not having them fix it (it doesnt sound like it was missing when you took it in), I'd pull your plugs and inspect them. It's entirely possible one was broken. With one bad plug or wire, it will idle seemingly ok but will miss under any sort of load. A CBT should pick up such an issue in the first place.

Good luck.

 

[red95gtconvert]

HISSIN50, I have read you recommend a cylinder balance test many times, can you give a play by play on how to perform this test. Thanks in advance.

 

[JNeidlinger]

Was the ECU ever reset by disconnecting the battery? Pull negative post, flip on headlights (to help drain the system), and leave for 15 minutes.

 

[HISSIN50]

HISSIN50, I have read you recommend a cylinder balance test many times, can you give a play by play on how to perform this test. Thanks in advance.

I actually use the book that came with my code reader but this synopsis covers it pretty well. You do the test after pulling KOER codes - see page 4 of this link.

 

[red95gtconvert]

Thanks HISSIN50.

 

[94v6GT]

I disconnected the battery while i was changing wires and snooping around the engine bay for anything outta place. didnt turn the lights on or anything but prob had it disconnected for about 20min. Im gonna try the cyl. balance test again today. I tried it yesterday with the parts store scanner and nothing happend(no instructions so i prob did something wrong) so im jus gonna try the 'jumper wire' method at lunch.

 

[divit250r]

Have you run a cylinder balance test? It can detect a lack of contribution from a given cylinder a lot easier than we can (esp if your idle is naturally lumpy at all).

For what it's worth, I tried this test too. Ran it three times in succession which is supposed to make it refine it's parameters each time, and it passed each time. I only found my problem because it was getting late and I was getting pissed. I shut off the lights while it was running and watched the blue spark show around the number one plug.

Scott

 

[94v6GT]

Im going to use the 'jumper wire' method to run the cylinder balance test. what prong on the the big connector do i attach the jumper wire to? the other end of the jumper goes to the single connector(gray) connector?

 

[JNeidlinger]

If you flip the big connector so it looks like a "house", that is the angled sides are at the top, you plug your jumper wire from the top right connector, to the single connector that was also housed in your ECU test bracket. BTW I dont know if you knew exactly how to do the cylinder test, but after all your KOER tests are done, quickly stab the throttle to WOT. Then your engine will begin disabling 1 cylinder at a time, and when its done it will report which, if any, cylinders are troublesome, these codes are simple, just blinks as many times as the cylinder it is. 5 quick blinks= number 5 cylinder.

 

[94v6GT]

SUCCESS!! took it to a pitch black parking lot with the lights off, #2 plug was intermittently arcing to head. had to blink a couple times to make sure of what i was seeing. it was also making an audible sound that i had dismissed earlier as insignificant but it was daylight so i wouldnt have seen it anyway. thanks alot guys:SNSign:


btw JNeidlinger you were right i was completly botching that test