Negative LTFT, out of ideas

[Moozery]

For about a month I've started observing my LTFT and other parameters to see if there are any patterns in my KR (seeing up to 5 degrees), and I've found that my LTFT is way in the negative. It averages maybe -15, but the worst I've seen it is at least -20 and the best I've had is about -5.

- Injectors are very new with only a few thousand miles on them
- Happened before & after installing my Intense PCM
- Just replaced & cleaned MAF
- Just inspected & cleaned EGR
- Just replaced both O2 sensors with Denso's
- Just cleaned TB
- Checked for vac leaks twice now, found nothing
- Can experience hard starts when hasn't been driven for at least ~16-20hrs, although fires up perfectly if primed twice (maybe related?)
- 60 psi key-on fuel pressure, 55 psi running
- Small exhaust leak where downpipe bolts to manifold (past the upstream O2)

Only codes I get are P0300 and occasionally P0703

Any ideas, suggestions?

[SgtMarshal]

Sounds like it needs a Maf sensor adjustment

[industrialfish]

What injectors do you have? That sounds exactly what mine was doing when I put my 42s in but didn't have them programmed in yet.

[industrialfish]

As for the P0703, finding the cause of that one is a head scratcher to everyone including the dealership. All it seems to do is intermittently shut off the cruise control. It can be anything in the brake circuit. Loose or corroded bulbs, or connector, brake pedal position switch. Etc. It won't set the CEL itself, just stores the code to taunt you.

The P0300 is probably due to having too cold of plugs for those mods.

[Moozery]

Never heard of a MAF adjustment, do you mean the rotation of it?

I have stock level Bosch injectors that i threw in while trying to fix the P0300 issue, which ive had since i got the car when it had stock plugs as well.It got better as I kept working on it, and I had the issue totally fixed for a little bit after i did some heavy flushing (had a bad LIM gasket) and then when I installed the Intense PCM it completely came back. The AL104 plugs was John at Intense Racing's idea, he found it odd that I was experiencing this much KR and suggested using those plugs gapped at 50, but it made no difference.

[Scottydoggs]

put the stock pcm back in if you still have it. see if the trims are better, might even have less or no kr. canned tunes often set the timing to 18º. being you got a comp g, they are 18 stock, so maybe they added more timing? hard to tell with out seeing a scan.

maf adjustment is part of the tune. we are all human, mistakes happen when doing canned tunes sometimes. or your car just dont like the tune you got.

[blueguy91]

703 is a torque converter code...could lock up be happening/not happening causing the KR? Not sure.

P0300 is a random misfire. Get a live scan on it and see what cylinder.

As for the exhaust leak; it might not be helping the cause, so fix that as well.

[industrialfish]

703 is a torque converter code...could lock up be happening/not happening causing the KR? Not sure.

It's not really a torque converter code though. It's a brake switch circuit fault. The TCC engage/disengage issue would be a symptom of the code, but not the cause.

[MonzaRacer]

I had my 98 Regal giving me fits with jumping tach, cruise shutting off and if I tapped brake it would quit.
Never guess what my issue was. mis adjusted brake light swtich. Reset it and never had jumpy tach nor any other issue again. I believe that is what made the orginal trans die at 133k, I bought car with 131k, had brand new Napa/Belden wires on it, had been stolen and sat for year and a half. Repalced rear brakes, turned front rotors, installed 2 new tire and my battery out of my wrecked cavalier. And changed oil. It had minor elbow leak, and needed 2 tires and tie rodend and battery before I bought it.
Gave $350 for it, got it legal and drove till trans finally failed. had insurance settlement by then and bought trans and tie rod end and swapped them, did the alignment and drove it 2 and a half years before wrecking it.
Now have 04 GP that needs engine.
But check the brake light switch. Make sure its out toward pedal far enough. Found mine while playing with my new Snap On scanner in graph mode. Brake light switch signal looked more like o2 sensor.
Bet its bad/out of adjustment/?

[99GPGTP]

try doing a cam and crank relearn to fix the p0300
my car did this and i did the relearn and it stopped the p0300

[Flashman]

Negative LTFT should produce running rich codes with stock calibrations. Fuel pressure seem high, 55psi at idle, measure vacuum at pressure regulator. Compare with another intake manifold source. Reading should be identical. ECT reading?

[Moozery]

So after a little more time observing the LTFT, I've found that it seems to get worse the more filled the gas tank is. This week I was on about a quarter tank or less and the LTFT were doing surprisingly well, although still well into the negative. I did a fill up and then went into a drivethrough, and after idling for a few minutes I noticed my LTFT was between -22 and -25 (seems that -25 is LTFT's max), and this isn't the first time I've noticed this happening. I've ordered a new EVAP purge solenoid and we'll see if that makes a difference.

I tried putting my original PCM back in, but even though I tried reconnecting the connections multiple times it wouldn't work, might've been damaged from when I had it in my trunk for a little while. The LTFT issue was still present on the stock one anyways.

As for the P0300, it's mostly (pretty much only) on cyl 4, and only when started 15-50 minutes after a fully warmed up drive. I switched from AL104's to 605's and it made it a bit better again. I've tried doing the CASE learn on my Aeroforce Interceptor many times but cant seem to get it to work. Been considering popping off the rear valve cover and checking the stiffness of the lifters on cyl 4 through the rockers.

P0703 has been gone for weeks now.

[Swiggles]

Try swapping a coil pack with another one and see if the misfire follows, if so bad coil pack.

[coolone]

For about a month I've started observing my LTFT and other parameters to see if there are any patterns in my KR (seeing up to 5 degrees), and I've found that my LTFT is way in the negative. It averages maybe -15, but the worst I've seen it is at least -20 and the best I've had is about -5.

- Injectors are very new with only a few thousand miles on them
- Happened before & after installing my Intense PCM
- Just replaced & cleaned MAF
- Just inspected & cleaned EGR
- Just replaced both O2 sensors with Denso's
- Just cleaned TB
- Checked for vac leaks twice now, found nothing
- Can experience hard starts when hasn't been driven for at least ~16-20hrs, although fires up perfectly if primed twice (maybe related?)
- 60 psi key-on fuel pressure, 55 psi running
- Small exhaust leak where downpipe bolts to manifold (past the upstream O2)

Only codes I get are P0300 and occasionally P0703

Any ideas, suggestions?

Injectors, did you replace the o-rings? Are they all seated well?
Replaced MAF? Why?
Took off EGR, might have kinked and made small leak in tube. Smoke test?
TB - seated good?
How did you check for leaks?

Air/Fuel/Spark
You swap coils as Scotty mentioned? Swap wires too, check plugs, gap, etc.
injectors - NEW? If Used did you check them, stethoscope or old screw driver trick, see if they're clicking?
MAF - New? Replaced stock or is it used? Correct MAF?
makes no sense to check lifters if you haven't done a compressio test first to see if there's an issue there, why do you think "lifter"?