Tried Everything! Need Help

[nocturnal396]

Hey! I know it's not a truck, but it is a GM so I figured one of the GM techs on here may be able to help. I already stumped two former GM techs that work at the shop I work at so it's not looking good lol...

 

I bought a 94 Impala SS and decided to get it up to par and get it performing top notch as it had overall loss of power and misfires. After ohming out a bad injector, finding a bad injector wiring harness confirmed with a noid light and doing a bunch of other small things, I am at my wits end figuring out a misfire that remains.

 

Here is what I have done so far

 

New Delphi Optispark

New Delco plugs

New wires

new flow matched injectors

new header gaskets (no leaks at all)

 

EGR and AIR deleted and tuned for by a very well known tuner (bryan H of PCMforless.com)

 

swapped MAF, MAP and 02 sensors from known working ones off my 96 SS.

New ECT

 

Here is the problem. I have a misfire on cyl 7 at idle and anything under around 2500rpm's. Exhaust out the back smells pig rich. BLM's at idle are as follows: Bank 1: 148 Bank 2: 159

 

On cyl 7 I rewired the injector wiring as before I was getting no pulse. Now it seems to be working fine as confirmed with a noid light but I am still getting part throttle/low rpm and idle misfiring. Compression test showed ALL cylinders to be good.

 

So just when I figured it could be a weak valve spring or a lose rocker arm nut, the problem goes away out of nowhere for one trip...misfire free...only to return the next time I started the car.

 

What is causing the misfire? And further more, what is causing both banks to be almost maxed out rich according to the block learn multipliers?

 

 

Any help is appreciated! This is my daily driver and the gas bills are killing me! Not to mention the sloppy low rpm performance. thanks!

[Jsdirt]

Check for air leaks around the intake manifold or vacuum lines, for starters. Then verify you are getting good spark to that cylinder. A compression test wouldn't hurt either to rule out any valve leakage or worn rings. Another possibility is that the plug may have been carbon fouled from extended misfiring. Double check all plug wires, etc.

[nocturnal396]

Check for air leaks around the intake manifold or vacuum lines, for starters. Then verify you are getting good spark to that cylinder. A compression test wouldn't hurt either to rule out any valve leakage or worn rings. Another possibility is that the plug may have been carbon fouled from extended misfiring. Double check all plug wires, etc.

 

 

Thank you for the reply!!

 

I already did a compression test on the missing cyl. 180 PSI in 3 cranks, just as good if not better than any of the other cyls. I have been taking out the plugs occasionally and cleaning them with QD contact cleaner after every repair I have made to assure they aren't fouled. I put a brand new plug on the cylinder that was misfiring just in case. It kept misfiring away with the new plug.

 

The vacuum leak is the ONLY thing I can think of right now that could be causing the wicked high BLM's, I do have a bad oil leak from the back of the intake manifold so I guess there is a chance I am getting a vacuumleak as well. That will be my next thing to check and fix on my to-do list. Still don't know what would be causing the mis though...im going to make sure I am getting a full 12 volts to the injector but after that I am out of ideas...

[nocturnal396]

Check for air leaks around the intake manifold or vacuum lines, for starters. Then verify you are getting good spark to that cylinder. A compression test wouldn't hurt either to rule out any valve leakage or worn rings. Another possibility is that the plug may have been carbon fouled from extended misfiring. Double check all plug wires, etc.

 

 

Thank you for the reply!!

 

I already did a compression test on the missing cyl. 180 PSI in 3 cranks, just as good if not better than any of the other cyls. I have been taking out the plugs occasionally and cleaning them with QD contact cleaner after every repair I have made to assure they aren't fouled. I put a brand new plug on the cylinder that was misfiring just in case. It kept misfiring away with the new plug.

 

The vacuum leak is the ONLY thing I can think of right now that could be causing the wicked high BLM's, I do have a bad oil leak from the back of the intake manifold so I guess there is a chance I am getting a vacuumleak as well. That will be my next thing to check and fix on my to-do list. Still don't know what would be causing the mis though...im going to make sure I am getting a full 12 volts to the injector but after that I am out of ideas...

 

 

 

I had a little spare time yesterday before work so I did some testing. Didn't get a chance to do all of what I wanted to do but I poked around...here is what I found

 

 

Vacuum: a little over 20psi at idle. Sounds good? Doesn't seem like there is a vacuum leak with that kind of vacuum

 

11.88 volts at the missing cyl injector wiring with key on but car not running. Sounded about right

 

Checked for combustion gasses in coolant: nada

 

MAF readings on scanner says 6 gps at idle

 

[coconutwil]

Hey! I know it's not a truck, but it is a GM so I figured one of the GM techs on here may be able to help. I already stumped two former GM techs that work at the shop I work at so it's not looking good lol...

 

I bought a 94 Impala SS and decided to get it up to par and get it performing top notch as it had overall loss of power and misfires. After ohming out a bad injector, finding a bad injector wiring harness confirmed with a noid light and doing a bunch of other small things, I am at my wits end figuring out a misfire that remains.

 

Here is what I have done so far

 

New Delphi Optispark

New Delco plugs

New wires

new flow matched injectors

new header gaskets (no leaks at all)

 

EGR and AIR deleted and tuned for by a very well known tuner (bryan H of PCMforless.com)

 

swapped MAF, MAP and 02 sensors from known working ones off my 96 SS.

New ECT

 

Here is the problem. I have a misfire on cyl 7 at idle and anything under around 2500rpm's. Exhaust out the back smells pig rich. BLM's at idle are as follows: Bank 1: 148 Bank 2: 159

 

On cyl 7 I rewired the injector wiring as before I was getting no pulse. Now it seems to be working fine as confirmed with a noid light but I am still getting part throttle/low rpm and idle misfiring. Compression test showed ALL cylinders to be good.

 

So just when I figured it could be a weak valve spring or a lose rocker arm nut, the problem goes away out of nowhere for one trip...misfire free...only to return the next time I started the car.

 

What is causing the misfire? And further more, what is causing both banks to be almost maxed out rich according to the block learn multipliers?

 

 

Any help is appreciated! This is my daily driver and the gas bills are killing me! Not to mention the sloppy low rpm performance. thanks!

[WaterGuy]

Can you swap plug wires around?

 

I've seen new wires with a poor crimp.

[nocturnal396]

Can you swap plug wires around?

 

I've seen new wires with a poor crimp.

 

 

Already tried that, made no change...

 

Here is what I found. I had an oil leak at the back of the manifold. Supposedly the heat from the EGR pipe over time lifts the silicon and breaks the seal. When spraying T/B cleaner around it, I saw NO change in idle....BUT, BLM's would sharply decrease from 150 to the 130's, then VERY slowly climb back up afterwards...

 

Now I had 22 inches of vacuum at idle, and spraying around the manifold didn't raise the idle at all...but being that there was some correlation between BLM's when spraying and the fact that I had an oil leak anyway I decided to do the manifold gaskets last night. Just need to button up a few things after work and i'll let you guys know if it helped any.

 

thanks

[mtm700]

I'd do a cylinder leak down test if the problem still exsists after new intake gaskets.

[nocturnal396]

I'd do a cylinder leak down test if the problem still exsists after new intake gaskets.

 

I was thinking of doing that, I probably will just to rule out another possibility, but I already did a compression test on most of the cylinders and got a nice 180psi in three cranks in all of them.

Running out of ideas though so it's worth a shot.

 

Just to make an update, after I did the new intake manifold gasket, let it dry over night and then sprayed around it with t/b cleaner to make sure it wasn't leaking, I looked at BLM's. Now they are closer at idle, and the bank that was previously being seen as lean by the 02's is now being seen as RICH, with a BLM of 137 at idle. Bank 1 is 140. Not too shabby, but here is the catch. Tap the gas, even a tiny bit, and both banks jump to 145 or higher. Also, now not only do I have a misfire on bank 1 cyl 7, but I also have a misfire on bank 2 (haven't tried to pinpoint it to a cyl yet).

 

Being that all I touched was injector wiring when removing the manifold, I put a noid light to every injector harness again and found em all to be ok. I also checked voltage and all were around 12.2 vots with key on. So now I have ANOTHER misifire! WTF!!!

[superjim]

If you have a timing light....

Hook it to EACH WIRE...and see if the actual WIRE is good.

 

This may help to narrow down the problem

[nocturnal396]

If you have a timing light....

Hook it to EACH WIRE...and see if the actual WIRE is good.

 

This may help to narrow down the problem

 

I have an ignition wire test light that I can use to check for breaks, or just take them out and check em with the multimeter...but what doesn't add up is that when revved the BLM's sky rocket UP which means the 02's are sensing lean. I am getting a misfire on each bank, but one bank is 140BLM's at idle meaning it's sensing that bank lean as well.... How could an ignition related misfire make it go lean?

 

It's worth a shot though....I am really leaning towards something IAC related...I don't know why, but it just seems like that is the only other thing that can be letting in more air than needed if there are no vacuum leaks.

 

I was thinking MAF too, but at idle the scanner is showing around 7 GPS, and it goes up accordingly with throttle...doesn't max out for no reason or anything, so it seems good although I am not 100% sure on what it is supposed to be reading.