Well as always at the end of a project I have run into issues. Have recently done some mods to my car, and it is now backfiring very badly out of the exhuast.

Mods done were:

• Victor Reinz .026 Head Gaskets
• SA GMPP 1.6 RRs
• Comp 987 Springs
• Comp Ti Retainers
• Comp 10* Race Locks
• Comp Hi-Tech push Rods (7.050)
• OEM Valves
• Valve Stem Seals
• LS7 Lifters
• Battery Relocation
• MSD coil (used)

and several other things not related to the problem like coolant catch can, and wieght mods.

The car sat for 6-7 months with a full tank of gas and no stabul, it smells bad, but I've run some out, and put 10+ gallons of 93 Chevron in it. I looked at the plugs, and they were totally toasted with maybe 40 miles on them. So we've swapped in some new plugs, started it, and the backfire is still there. I have track day next Saturday, and really need to get this taken care of.

The wires are in good shape, plugs are new. The coil is new to me (perhaps the culprit?) and I followed Shoebox's instructions on rocker adjustments and they sound good no ticking other then the normal sewing machine sound. I measured my pushrods (rookie at it) and the 7.050s were closest to my measurement.

I had no head work done, but have good compression as far as I can tell by turning the crank.

Ideas? Suggestions?

 

The only things i can think of is fuel filter or pump doesnt seem like on ignition problem or else it would miss or hesitate badly, just a guess. Does it backfire when you let off the gas were in the rpms does it happen and when, just out of curiousity.

 

I backfires at idle, ans on acceleration. Its pretty stready and very loud. It is killing the plugs so it is hard to say if it hesitates cause the problem of the bad plugs the problem is causing.

 

As stated on LS1 Tech, check the routing of your plug wires VERY carefully. That is exactly what it reads like what is wrong.

 

Here is the plan of attack today. I will check the spark wires, and makes sure they are hooked up right, If they are then I will borrow a coil from a friend and swap it with mine. Another board is going on and on about the MSD coils being faulty. If that doesn't fix it then I will readjust my rockers, and if that doesnt do it, Ill throw a fit, and probably replace the Optispark.

 

I have an acell coil and it works great. I actually had and MSD coil gernade on my car but it was a cheap one. I'm not going to be like the other board. but i dont think it would be ur coil.

 

I swapped coils and had the same results. I checked the wires and they were right. It will idle great 3-4 minutes then start backfiring. i am guessing the increased heat has something to do with the backfire.

If it was the new valves I installed then it would be bad all the time correct?

 

I think it would depend on the heat on the heads. it takes them a while to heat up. sounds like it may be a bad valve job.

 

Why would a bad valve job be ok when the heads are cool, and get worse as they heat up?

Any chance this could be a optispark issue?

 

Its possible its an opti issue. i was saying valve job because when the heads are cool they may seat properly and when they heat up they may not.

 

Running fine on cold start, then running poorly after 3-4 minutes may coincide with the PCM going into closed loop. Might point to a problem with the O2 sensors.

What do you mean by the plugs were "toasted"..... could you possibly mean "fouled"? That may correlate with running rich, which can be traced to closed loop problems due to the O2 sensors.... or something that screws up the O2 sensors, like exhaust leaks, misfires or incorrectly adjusted valves.

 

By toasted I mean completely coated/caked in carbon. I do not hear any exhuast leaks with the car running, but the exhuast was left open for 6 months, I am not sure f that is going to damage the O2s or not.

The closed loop posibility is a good one. I am not getting a SES light though. I do not think my scanner will tell me if its closed loop or not. What are some good methods of testing for this?

Im wondering if its not electrical since it seems to start backfiring as the car warms up. I noticed last night that the headlights are on when the key is on, and the switch is off. I also have the right blicker light on (not flashing) the dash on when the key is on and blinker off. In addition the blinker light is on (not flashing) when I turn the lights on without the key on. Bad ground perhaps? I did have the battery relocated during the mods so that could be it.

Im gonna connect a jumper cable to the battery and the other end to the block just to double check.

 

I assume the exhaust is fully hooked up now. If your scanner shows the O2's then see what is going on after the car warms up a bit.

 

Use the scanner to look at the short-term fuel corrections. On startup, they will be locked at 128 (or "0%" on OBD-II scanners), indicating that it is in open loop. As the coolant heats up, the O2 sensors heat up, and the time since startup hits 206 seconds, the short-terms should start to swing rapidly back and forth above and below 128. That will confirm its in closed loop. If you are using DataMaster, there is a set of flags that show the status of open and closed loop.