thunderstruck507

iTrader: (18)

Trying to help a friend diagnose his Suburban with the LQ4/4l80e combo.

It makes crap for power, revs slow, and intermittently you can go WOT and it acts more like 25% throttle but then will randomly (but rarely) come alive in bursts.

He just replaced the intake gaskets and said it ran great for a couple miles then once it was turned off and back on again went back to misbehaving.

We have confirmed good fuel pressure and MAF readings. Tried alternate MAP sensor. The throttle blade visually opens all the way in park.

It's getting a little KR but nothing bad enough to justify the behavior.



I originally wanted to point fingers at the electronic throttle but it seems to be functioning.

Any other ideas to check? Possibly an issue with the throttle pedal sensor?

gagliano7

Make sure the injectors aren't leaking. I had a similar problem where one injector was dumping to much fuel and that cylinder wouldn't fire. Ran like ****. I would also take a infrared temp gun and check the temp of each exhaust primary to make sure all cylinders are firing. If all your injectors and coils are good I would turn off the 02's in the tune so you are in open loop and see if it runs good without the 02's.

thunderstruck507

iTrader: (18)

Thanks, I'll pass that along.

I do think there is something fishy going on with the pedal module. I can see the blade opening like it's at WOT but the HP Tuners scanner he has really only shows about 75% unless you bury the pedal hard into the floor and then you can get up to 101%.

It runs like **** about 99% of the time, but you can have the throttle pinned and once in a blue moon it will just come alive all of a sudden.

It's all stock so far and he hasn't even messed with the tune, it had this issue when he bought it and wanted to diagnose and try to repair before tuning, but the B1S1 O2 is acting lazy a lot of the time. I was going to toss on a spare but his truck has a different style plug than the square ones I have.

Old Geezer

iTrader: (3)

Data log it??
He has HPT, so why not?

thunderstruck507

iTrader: (18)

Seems the problem ended up being an EVAP solenoid o ring that was leaking under load.

G Atsma

So it's fixed?

thunderstruck507

iTrader: (18)

I haven't been able to talk to him more to confirm. He has been working nights and long hours.

He said he found the bad o-ring and replaced it but the one he had was not the correct size so it was better but still had minor issues. He was ordering the correct o-ring last I heard

G Atsma

Well, let's hope that's it then for his sake. What a pain!