Please help me troubleshoot insane LTFTs and non-functional emissions stuff

[derekf]

Hi all,

I'm new to all this computer-controlled engine stuff so my apologies if the answer is simple.

I bought a 98 Z earlier this month. From what I can tell, it's got shorty headers, a different air lid, and a ported MAF. There may be other modifications done, but the guy I bought it from had bought it at auction and didn't have a way to get a list from the previous owner.

When I got it, the SES light was on - the codes indicated that both banks were running too lean, which made sense as both sides needed new header gaskets. When I looked at the LTFTs in EFILive before replacing the gaskets, it showed them all at +25%.

Now that I've replaced the gaskets and reset the trims, I took one drive and already some of the trims are back at +22 on Bank 1, +24% on bank 2. Driveability is great - but if I'm wasting fuel, that's bad... and will be a problem when I renew the state inspection, which is due in just a couple of days.

When I go into the System Readiness Tests status screen, the Catalyst, Evaporative Purge System, Oxygen Sensor, Oxygen Sensor Heater, and EGR system all show as "Not Ready", and I'm pretty sure that the inspection checks the status of those. The EGR and AIR stuff appears to be intact under the hood, but I don't know how to confirm that it actually works other than asking the computer.

If I look at the O2 sensors in the program, I only see B1S1 and B2S1 - shouldn't there be a second sensor listed on each bank? (and would that explain the cats being "not ready"?) When I looked under the car, I could definitely see one after the cat on the driver's side at least and it appeared to be plugged in. No oxygen sensor codes have been thrown other than the "too lean" that I'm assuming happens with LTFTs are maxed out.

I pulled the current settings off the computer and compared it with the factory 98 tune I found on a site linked from here, and EFILive says my tune is the same as the factory tune, so I would think that that would indicate that the sensor isn't turned off?

Any suggestions as to where to start? I'm guessing that the MAF porting would have thrown some stuff of - I can probably borrow/steal a stock MAF from a coworker to troubleshoot, if that's helpful.

[Tydriver]

FWIW, I "upgraded" to a Granatelli MAF on my '02 Silverado... It didnt come with any documention (I found out later that it should have).. This mod and only this mod made my FT's jump to about 22% (and ultimately a check engine light)...

I eventually was able to pacify this with some minor tweaks but ultimately its only purpose at the moment is for IAT.. I am running a Speed Density tune now thats been tuned with AutoVE.

I realize that this isnt really answering your questions directly, but what I can say is I can see how just the ported MAF would cause issues with the LTFTs you describe without a correction made or the tune updated, let alone headers or other mods. I'm sure that someone will chime in with other suggestions or comments on what to try. I just wanted to let you know that I've seen these changes on just a MAF alone..

With that said, anyone wanna buy a Granatelli MAF sensor ?? lol

[derekf]

Thanks. I got the MAF (descreened stocker), put it in, and cleared the LTFTs. My bank 1 trims are now less than 10% (4% or so for most cells) and bank 2 is 6% or less, and 0% in some cells.

My cats are still showing as "not ready" and I'm still only showing B1S1 and B2S1 o2 sensors though.

[Tydriver]

coolio.. Not sure if you can get away with it on your emissions or not. But you should be able to disable those flags in the PCM to extinguish the check engine light..

best wishes.

[derekf]

Today I guess I've driven enough cycles. LTFTs remain in the 4-8% positive range, which is good enough for now. All of the System Readiness Tests now come up as Ready with the exception of "Evaporative Purge System".

I still only show B1S1 and B2S1 in the O2 report though - should I not have the other two?

(edit) Oh - and Check Engine was off even when I was getting +22% LTFTs, I guess because it wasn't quite at +25%.