My predator log is showing that LTFT at both banks is pegged at +25% and never fluctuates. Given that they do not fluctuate at all I'm thinking I have bad 02 sensors... Anything else I should check before I replace them? Running a completely stock fuel system and I replaced the fuel filter about 7K miles ago.

 

What MODs do you have??

Can you view the O2 Sensor Live data signals with the predator????

If you can, the O2 sensors (once properly warmed up) should be varying in output. The output should be swinging from approx 200 millivolts to approx 850 millivolts if there working properly and responding. IF,, there STUCK on one voltage (like 450mv) it not working correctly. MAKE SURE that the heater circuit is functioning correctly. Go to the O2 sensor fuse and MAKE SURE that there full battery voltage on it. Its switch thru the ignition switch and can have insufficient voltage. The sensor grounds must also be examined and verified clean and proper!

There located on a Splice Pack (SP-122) near the battery on a wiring harness:

This is what it will look like if its corroded!!



This is NOT SP-122 but it will look just like this:


Heres the H2SO Circuit:



Hope this helps!

BC

 

Thanks Bill. Very helpful as always! I don't know if I can see live data signals with the predator or not; I'll check later. If not I'll pull them off and test them with a meter. I cleaned all the grounds (including sp122) a few months ago, but I'll check it again just to be sure... I've got 95K miles on the car now and original 02 sensors.

Performance Mods are: Borla Stingers, Diablo Predator Performance Tune, Halltech Venom Intake

 

Its CRITICAL that the O2 SEN Fuse have FULL battery voltage to ground on it. Read that fuse (at the test points on top of the fuse) to chassis ground and see what it reads (IGNITION ON!)

Autozone normally has a ACTRON Scanner that will read that value. See if they will let you borrow it or read it for you.

BC

 

Also, the reason I checked this in the first place was due to an intermittent CEL set by P0171 and P0174... Strange that the LTFT's are still pegged and I haven't seen the CEL for about two weeks.

 

I have a scanner that will read that value. I'll check it when I get home tonight. Thanks!

 

I ran out to the car real quick and plugged the predator in; turns out it can read live data for 02 sensor voltages. All 4 sensors were reading changing values at idle, they weren't stuck. Grounds and fuses when I get home later...

 

Sounds like a grantanelli maf with "cold air intake tune" built in.
Mine where that way. So I changed it for a new stock one.
Problem solved


Maybe it get the same way with your CAI if you spray i with some airfilter spray, like KN has, that has gotten on to the maf strings?



Just some thoughts

 

12 Volts to the fuse, grounds are clean (touched them up just to be sure) and 02 sensors are reading within acceptable range (one of the rears is a little lazy though so I'll probably replace it). I'm thinking I have a vacuum leak. I'll look into that this weekend.

Any other thoughts?

Hmmm... To tell you the truth I have no idea if I have a stock MAF or not. Are there GM markings on the stock one?

 

Well, HELL,,, a VACUUM leak will most certinaly cause that issue. Look at the PVC hoses and all the vacuum lines and MAKE sure there not rotted/damaged.

Check the intake ducting between the MAF and the TB. It has to be 100% air tight!

Dont worry about those O2 sensor lazy readings until you get this issue resolved

 

Thanks Bill... You know, someone were to give you even half of the money you've saved me and others on this forum you'd have a fleet of corvettes and an airplane hangar to put them in.

I'll check the lines this weekend. I just replaced the supply line from the back of the manifold to the fitting under the canister inside the rf fender... maybe it slipped out (don't think so since the ac actuators are working properly). I didn't actually see any evidence of a vacuum leak but I think that's what it most likely is given the other things I've ruled out. I wish the auto parts stores rented smoke machines...

 

When you 1st start up your engine either dead cold or after warmed--The LTFT readings are meaningless----There may be some #'s shown in there BUT when started the ECM is in "OPEN LOOP" and the 02's/LTFT's are NOT being used--The 02's are just warming up--dead cold the ECM will swith to "CLOSED LOOP" when the ECT reaches 140*-- When warm it uses a timer usually about 20 seconds before it switches to closed loop----Make sure your ECM is swithing to closed loop -THEN check the LTFT's
If they are still pegged---follow Bill's reccomd.--
If your 02's seem to be oscilating correctly---Try cleaning the internal MAF wires and the MAF pigtail--with brake-clean--
Check for vacuum leaks--
Check manifold pressure or vacuum---At idle it should be around 30 KPA /or 20" of vacuum

 

It just occurred to me earlier while I was changing my oil and doing a little data logging that I never posted the resolution to this issue. For anyone else who might have a similar issue later and finds this thread by searching I wanted to close it out...

My PCV line was broken right where it attaches to the intake by the throttle body. It was broken in half but the break was VERY small and the two broken ends were still pointed at each other so from all but very close examination it looked like it was connected an okay... I'm annoyed it took me a day to figure that out after cleaning my MAF, recharging my CAI checking voltages and grounds I found a broken vacuum line I have absolutely no idea what could have caused it to break like that...

Anyway, I've had it resolved for a while now and my LTFT's are happy and no more annoying surging at idle. I replaced the PCV valve since it's only a $4 part, replaced that 4 inch section of line and sea-foamed the top end of the block via the newly repaired PCV line.

Just an observation, I can't believe how much oil blow-by there is in these motors... After this experience with the PCV system I decided I'm going with a catch-can setup. It's on my list of things to do over the winter.