Backfire at WOT

[TrAb]

He has a LS1 maf... nobody has mentioned the possibility of the car going lean and backfiring... that's always the 1st thing I check, as the consequences are by far the most expensive.... are you sure the fuel pressure is correct and rising 1:1 with boost?

I do not have the LS1 maf installed yet.

 

[TrAb]

+1

Op did the car backfire from the intake or exhaust?

Exhaust for sure...

 

[TrAb]

You REALLY need to do your homework on these cars.
Lesson 1 grasshopper...MAF (not MAS) Mass AIr Flow sensor

Does your stock MAF have any screens in it?

How did the cam sensor check work out?

Yeah the MAF is completly stock and has both screens. I am not going to be able to check the cam sensor tonight as i got home late. But i will do it ASAP and report back. I read the directions over and over and when i first dropped the cam sensor in i did not look at the dot on the very bottom. Caspers instructions did not say anything about this so im not sure if it is really that important (althought it seems it would be fairly important).

 

[bmackinnon]

Where did you get the 'new' coil pack/ignition module? Aftermarket (non-GM) units are definitely hit and miss.... Once I verified fuel pressure and cam sensor setting, I'd be looking there next....

 

[bmackinnon]

You think there could be a vaccum leak with the FMIC piping i put on? Ill try to look it over when i get home. Or better yet i may slap the stocker back on and see if the problem continues or not.

Don't worry about putting the stocker back on... but check, double check, and then re-check that all the hose clamps are tight as hell....

 

[TrAb]

Where did you get the 'new' coil pack/ignition module? Aftermarket (non-GM) units are definitely hit and miss.... Once I verified fuel pressure and cam sensor setting, I'd be looking there next....

I got them both from autozone. The coil pack looks great. The ignition module was kinda weird. Let me try to explain. The directions told me that there are two versions of the ignition module and that i would have to try wiring it two different ways, why they couldent just tell me which module i had i do not know. It just said that if the car did not run like it did before that i should try the other wiring style. Do you guys think this could be it? I figured it meant if the car did not idle/daily drive correctly.

 

[TrAb]

Don't worry about putting the stocker back on... but check, double check, and then re-check that all the hose clamps are tight as hell....

Yeah i looked them over and there all great.

 

[bmackinnon]

I got them both from autozone. The coil pack looks great. The ignition module was kinda weird. Let me try to explain. The directions told me that there are two versions of the ignition module and that i would have to try wiring it two different ways, why they couldent just tell me which module i had i do not know. It just said that if the car did not run like it did before that i should try the other wiring style. Do you guys think this could be it? I figured it meant if the car did not idle/daily drive correctly.

Yup.... I've never heard the '2 different versions garbage', which sounds like BS, but the autozone/advance/oreilly/etc. modules seem to work correctly about half the time.... I suspect you've located the problem.... but verify the cam sensor and fuel pressure as well... you are better off to break down ($) and get yourself an OEM GM module... some will disagree, and sometimes the aftermarket modules work fine, but you'll find just as many who have had major headaches with them... sometimes it will take 3-4 trips to the 'zone to get a good one.... a good source for the OEM module is nos4gn (dot com)... about as good a price as you're going to find, and definitely a quality part with a vendor who will back it up...

 

[TrAb]

Yeah im going to try flipping the wires around on that ignition module tommorow and see what that does. If that doesnt help out im going to check out the cam sensor. If theres no problem there ill just order me another ignition module since im going to need a spare anyways...

 

[bmackinnon]

also ohm your plug wires and coil pack and report back

I got them both from autozone. The coil pack looks great.

If theres no problem there ill just order me another ignition module since im going to need a spare anyways...

Didn't see if you ohmed the coil packs as suggested by b231... a weak coil pack WILL cause a backfire as the boost comes up.... and is a very common problem/cause with these cars.... use a meter and ohm the 3-pairs of coil towers, front to rear.... should be 11k-13k... not surefire proof of a good coil, but surefire proof of a bad one.... autozone coilpack.... hmmmm... Don't just throw parts at it... and if you can afford it, avoid all brands of ignition parts except ac delco (for these cars, that is....)

 

[TrAb]

Checked the FP and it is fine, also made sure there was no leaks in the intercooler piping. Im am going to try and flip these wires around on the ignition module like the directions say and see what it does. If that doesnt do it ill get some AC Delco stuff...

 

[daily driver]

You have a scanmaster? did you check for a stored MAL code? Don't got WOT if you don't not have to with this kind of problem, just put some load on it.

 

[TrAb]

I have one but have not installed it yet. Trying to figure out where to put it / how i want to have it hooked up. Im going to be checking that cam sensor a little later. Hopefully that will be it, because it really has to be something i changed when i did the timing belt. Because the car pulled fine before this.

 

[TrAb]

I checked the cam sensor and it is perfect.

 

[TrAb]

I ohmed the plug wires, i wasnt sure how to do it so i set the meter on 20k ohms. Anyways all of them were around .55 give or take a few. But on the drivers side one was 65 and another was 77 ...Does that mean anything to you guys.

 

[TrAb]

Another thing i noticed while it is sluttering / backfiring the check engine light blinks on and off really quickly.

 

[TrAb]

I ordered me a new coil pack and iginition module from NOSGN. Gonna take these back to autozone, tired of worrying if its that or not.

 

[TrAb]

Hey guys i got home early tonight and wanted to try something on the car. So i got my old coil pack, which i had just replaced and put it on. Car now runs 90% better ... Only problem im having now is that when i press the gas ALL the way down, the car wants to bog down. But if i let off the gas pedal just a hair it pulls just fine. Im thinking it may be my spark plugs or something along those lines. But its diffenatly nothing major like it was before

 

[bmackinnon]

OK.... a few comments..

nobody has mentioned the possibility of the car going lean and backfiring... that's always the 1st thing I check, as the consequences are by far the most expensive.... are you sure the fuel pressure is correct and rising 1:1 with boost?

Checked the FP and it is fine,

What is 'fine'? The only way to check the fuel pressure is to be driving the car while you can see a fp gage... the fp MUST rise 1 psi per 1 psi boost... as the pump gets weak, fp will start to rise as boost comes up, then start DROPPING as boost (and thus fuel demand) increases. This, of course, causes a lean condition/power loss/backfire/blown headgasket. VERY common problem. Just noting the base/line off pressure verifies nothing. So, say 43 psi base fp and 18 psi boost, wot fuel pressure should read 43+18= 61 psi. Adjust numbers to your conditions...

Another thing i noticed while it is sluttering / backfiring the check engine light blinks on and off really quickly.

When the CEL blinks very quickly, it generally indicates a problem with the ecm or bad connection with the chip..

when i press the gas ALL the way down, the car wants to bog down. But if i let off the gas pedal just a hair it pulls just fine. Im thinking it may be my spark plugs or something along those lines. But its diffenatly nothing major like it was before

The car bogging at wot, and picking back up if you let off the gas a hair is very often indicative of insufficient fuel pressure/fuel pump going weak. If you haven't verified with your own eyes that the fp is increasing in a 1:1 ratio with boost, you are risking near certain catastrophic disaster. I wouldn't floor the gas again until I had a fp gage hooked up.... just get an extension hose and tape the gage to the windshield for testing purposes. VERY NEXT thing you should do if you haven't already... :wink:

 

[yullose]

Only problem im having now is that when i press the gas ALL the way down, the car wants to bog down. But if i let off the gas pedal just a hair it pulls just fine.

Also... after confirming adequate fuel delivery, make sure the TPS is adjusted correctly... and test it to make sure it doesn't have a dead spot at WOT.

You DID put a good fuel pump, hotwire kit and fuel filter on it, right ? Adjustable FP regulator too ?