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High knock-runs like crap.

R

rickisrad

New member
Well I have switched my 04 comp G back to gas from e85. Something is very wrong and I can't figure it out. It has constantly high knock. At one point it pinned out at 14.9* and wouldn't change. There is knock at idle, cruise, and high throttle. There is no check engine light. it sputters at light throttle and seems to have power at full throttle. the opposite of what it was doing on e85. Before I switched to e85 the car ran perfect.

Here is what I tried and or replaced recently. the problem existed before and after these changes.
Put on brand new Delco stock injectors.
Put on autolite copper 104 copper plugs
Put on the 3.4 pulley.
I pulled the supercharger belt to see if the supercharger was causing knock and it was not. the knock was still there.

Any ideas of what I should look for?? I am at a loss. The car ran so good before I changed over. so something with the e85 messed something up

here is a scan from HPT.
https://www.dropbox.com/s/nojf71bo5pxj61y/scan 14 gas switch over bad knock runs bad.hpl?dl=0
 


Agree, check pressure, the e85 tends to clean out the tank and lines, something could be clogged, ie, fuel line, filter, etc.

Your sig says Overkill tune, was the tune adjusted for e85?

Before I switched to E85 the car ran perfect!
Click to expand...

Sucks right? Is a Pontiac, you never know what you'll get when you play... Lol
 
The pressure is holding at 58 psi
yes the overkill was adjusted for E85 by me and the help of the guys here. I have a HPT pro tuner.





... yeah it sucks. I messed up a great running car.
 


GTPpower said:
Can you take a scan of the car running and send it to me?
Click to expand...

There is a scan attached from drop box in the first post. If you want me to send it in email just pm me your email address.

Scottydoggs- yes I saved my original overkill tune several times and kept them safe.
 
if your back on your good tune id say its not the tune, or the corn's tune, something went wrong with the engine, maybe the blower is now shot? if its got kr in park when revved thats where id start.

take the sc belt off and jump on it, if no kr, im back at the blower being bad. seen this in person, was fighting this guys tune, then im like lets see wtf happens when revved in park, 2º kr. took the belt off, no kr at all. he was was getting up to 9º kr when he got on it too. no matter what his timing was, high or cut to 9º.
 
I did take the supercharger belt off and nothing changed. It had knock at idle and while revving while off.

I'm going to have to make an appointment for the dealer to diagnose. If it's something major I'll probably part it out.
 


Scottydoggs said:
thats not good at all. try both belts off?
Click to expand...

Curious, what would both belts off eliminate?

I took it to a reputable GM dealer and they did not find the problem. The service advisor said that their best guess was either a Maf sensor but those usually will throw a code or a PCM. So now I'm stuck at square 1.
Any guesses on what I should check next. The issues are surging/bogging, high knock, and random cylinders misfiring. None of this is turning on the Engine light!! Any help is greatly appreciated
 
have you scanned for pending codes? drive it around, dont turn it off, then scan it running still. might have one hiding on you.

could be a beat maf, sometimes they dont set a code. if you got a junk yard local see if you can find one there.
 
Yes, no pending codes which baffles me because it runs like crap and shows the knock and misfires. It sounds like all the dealer did was put it on the tech II. I thought I seen a way to bypass the maf. Something like VE tune??? Can that be done to check the maf?
 
Read the tune on the car. Don't look at what you loaded, actually read the tune off the car. Check that your expected changes took.

That would be my starting point as long as the car ran good on E85.
 
Also.. scan the car.. is it running super rich like you tune for E85? You said you have HP Pro.. which means you have all the tools to see a possible tune related issue. It's tough to believe that it was running perfectly, you put in gasoline vs e85, tuned it back for the fuel and it's all of a sudden running poorly.

To me that screams tune or something that you had to change to get to E85 and forgot to change back.
 


It didn't run good on e85. It ran good in normal driving on e85 but bad at wot or high rpm. But it had nowhere near the knock or misfires it has now. I will read the pcm and see what it says. I saved the overkill gas tune in a separate place so I didn't change it. But definitely worth a try. I don't have a wideband so a little limited. I think it is running lean, around 16%.

Thanks
 
I checked the tune and compared it with the old good one and they are exact. The maf frequency is reading where it normally did. It is running lean with the maf and I unplugged it and it went very rich. With the maf unplugged it seemed like it wanted to stall every so often but didn't. When unplugged it had a pending code of p0102 which was expected. No other codes pending. I guess I will try a compression test this weekend to see what that shows.
 
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