marlar98

I'm dealing with a situation that has me stumped after getting my heads and intake ported. I got my top end back together and installed a BBK 58mm Throttle Body and now my engine backfires at idle. Prior to the top end upgrade, I installed the Tick Hatermaker Stage 1 cam and had the care tuned by Strong Speed Works. Car ran great. Just wanted the heads and intake done to maximize the potential of the cam.

I have a Scanmaster LTI installed and don't have any DTC codes or check engine light. I've checked plug wires, Opti connector, ignition coil and connector. All checked out fine. I have adequate fuel pressure. I did install an electric water pump as well with a new coolent temp sensor if that helps anything.

What else could I be missing? I really appreciate your help.

Injuneer

Is this "backfiring" into the intake manifold, or into the exhaust?

Issue with a sticky valve, incorrect valve adjustment, incorrect A/F mixture, incorrect ignition timing.

Who ported the heads?

marlar98

Thank you Fred for your response.

It's backfiring through the exhaust mostly. I say mostly because there were a couple of occasions where it backfired through the intake after I installed the BBK throttle body. I checked the voltage of the IAC at idle and it's at .60 volts so it's within range.

The heads and intake were ported by Lloyd Elliott.

marlar98

I should have also mentioned, the car won't start on first crank unless I push the accelerator but once it starts it stays running.

Injuneer

Putting the accel pedal on the floor and holding it there (if that's what you did) puts it in "clear flood" mode, which will offset a problem with leaking injectors. Excess fuel will pop in the exhaust. Are the intake end O-rings on the injectors all OK??

If all you did was heads/intake the ignition timing should be OK, as long as you didn't take the Opti off for any reason. All wires on the correct plugs?? All the wires tight on the plugs?? Possibly cross firing between plug wires??

Are you certain the valve adjustment is spot on?? For a backfire into the intake it would seem like a valve has to be open a bit to allow the combustion to extend into the intake.

Just shooting out random thoughts at this point.

marlar98

I don't put the accelerator to the floor but I do have to peddle the accelerator to get the car to start. Once it's started it stays running and sounds great until it randomly backfires.

The O-rings on the fuel injectors are new so they should be in good shape.

I didn't remove the opti so timing should be fine I would think.

I've checked the spark plug wires to make sure they're routed correctly and are.

I thought I was thorough with valve adjustment, but this is my next step sometime this week in my trouble shooting process. Here is the method I used to set lifter preload:

Injuneer

I usually recommend this:

4th Gen LT1 F-body Tech Articles

Not sure how it compares to what you used, but it's been the standard “go to” on this site for 20+ years.

marlar98

It's comparable to Method 2. I went 3/4 turn past 0 lash. May back off to 1/2 and see if there's any change.

Injuneer

I never had to adjust the valves in my 94 (purchased new). And in 2000 when I had the build below put together we opted for a solid roller cam so it would be functional with the nitrous up to at least 7,400 RPM. So it was feeler gauge time.

marlar98

Thanks for all that helped me with this. I got it figured out and quite embarrassed what the issue was.

It was the dog on #5 & #3 spark plug wires swapped. I swore I checked the wires beforehand and guess I didn’t.

Nevertheless it’s running and sounds great! Now I need a retune, lol.

Thanks again guys. I really appreciate it.

Injuneer

Thanks for the follow up.

Glad I asked about the plug wires in post #5…….