2002 Lm7, CAI, shorties, Truck Norris,

Been going down the diagnosis chain for a while now and haven’t come up with anything for why it backfires so much throughout the entire rpm range

When key gets out into in position, IAC makes a noise. Along the lines of “wawawawawa, brrrrrrrr” as if the valve was closing. When engines running it doesn’t move. When keys off makes the noises again.

With it out of the throttle body and key off. It was extended, so I would push the plunger back in. Once key hits on, noise happens and it would extend back out. After key turns back off, noise happens and it stays extended out.

With the truck on and just tape over the orifice, it actually sounded normal for about 30 seconds then would start backfiring again.
And the plunger would not move with the engine on too


ive got 12v at 2 of the pins and the other 2 are grounds I believe.

Would an IAC valve that is stuck closed cause a misfire w/o code?

Ive done all the first steps (compression; swapped plugs, coils, plug wires; swapped injectors, etc) just boiling down to all the stupid small ****

 

If it is backfiring throughout the entire RPM range I doubt it is the IAC. Especially if it does it when you taped over the port and the IAC wasn't installed. Sounds like a large vacuum leak. Have you checked for vacuum leaks ?
Also, more info. Is this a stock engine and harness or modified?

 

It’s a 99’ s10 2.2 4l60e —>

02’ Lm7 Th350, Cammed, stainless dual exhaust, “cold air intake”, PSI standalone but modified to fit into the truck harness. Is tuned for the swap and cam

If I’m being honest, when it was taped over, I don’t recall any backfiring and a smooth idle. However I had to turn it off as what I believe was my power steering pump low in fluid making an ear splitting whine.

A question I have, is that are IACs supposed to make any clearly audible noises? I mentioned it before that it makes a noise when the key turns on and off

 

It's a stepper motor, it will make noise.

 

IAC valves are just stepper motors, so they can and do make some noises.

 

Check DTC's. Did you check pushrod length/lifter preload when you did the camshaft install?

 

I don’t get any DTCs any more, if I did it was P0300 and only P0300. No lean codes, etc. I stopped getting codes some where down the line of diagnosis where something must’ve changed it just enough to not cause a code but enough to run like dogshit?

it’s got a truck Norris, .560 lift springs, and 7.400 pushrods. All new parts.

I’ve already pulled valve covers and checked For broken springs, pushrod straightness, torque specs, etc.

ive got 170-180 compression on all cylinders

No audible hissing of a gnarly vacuum leak

 

Monitor O2 STFT's and post results

 

I will report back with fuel trims shortly, the weird thing is that when the orifice is taped over and iac isnt mounted but still plugged in the backfiring completely goes away and it idles smoothly

Could there be something messed up with the tune involving IAC considering when the tape is acting like the IAC is all the way open resulting in a clean idle?

 

That could be a possibility.

 

i had one get (stuck) and do same thing, replaced it and was fine after that. just put a new one in and go from there. i dont like breaking out the parts cannon but if you replace it and it still has a problem then two things, you have a spare and can now check that off as not the problem. i think people forget that some parts on these are now 20+ years old and can/will fail like o2 sensors/tps sensors/iac/intake gaskets/temp sensor/knock sensor/etc etc........... they dont last forever.

 

Lmao I actually already bought one before I made this thread. I’ll admit I actually broke the IAC I had in there…. I was messing around with it as it was extended out and I pulled it out further by hand and turned the key on. It then shot the plunger off to narnia and I couldn’t find it… The new one should be here Friday along with my fuel pressure gauge

Another thing, I’m not sure what has to happen to trigger a LTFT but could something like that, that it gets at idle, be causing the backfiring to extend throughout the rpm range?

 

id just put it in and go from there. if slight back fire/miss is cleaned up you found it, if not you got more to figure out. also do a iac relearn when you install it.

 

Is there a thread that covers how to do that?

 

really easy. put key in on position then unplug iac, then turn key off and wait 30sec. then turn key to on and leave for 30sec. turn key off. plug iac back in, then turn key to on, done start it up.

 

the IAC goes into a parking position when the key is turned off, then goes into a "cranking" position at key on. Those are the times when the noise will be most noticeable. It makes minor adjustments while the engine is running, and you may not hear it.

If it's really noisy it can be a sign it's failing.

it shouldn't cause a backfire, only idle issues. backfires are usually from ignition or valve timing being incorrect, burnt valves, unburnt fuel in the exhaust, etc.

 

Backfiring is a term for popping "back" through the intake system. Afterfiring is a term used for out the exhaust

 

I thought I had a IAC issue a while back. I tried a Ebay IAC and a Duralast IAC and neither worked as well as my old factory IAC.

 

I got a new Delphi IAC and did a relearn.
It seemed to help it quite a bit from what it was before. However now, for maybe a minute or so it has a nice idle. Then it goes back to heavily backfiring

I was able to log it,I’m just unaware of how to read it as it was logged through Torque on an android tablet and is saved as a .csv file.

Edit: I dont't believe I had my logging set up correctly to be able to show you guys. I opened the .csv file into sheets and only shows GPS and location based stuff