Strange P08 issue

[rjdrew1986]

I thought I would reach out in hopes that someone could shed some light on what could be causing this issue. I recently purchased a 1999 Chevy Cavalier with low miles that has an issue. When starting the car it runs for about 2 seconds and dies. The previous owner came up with some very fancy & aggressive throttle movement while starting and refined a technique where he could start the car every time. Once the car starts, the cars runs fine and there are no abnormal lights on the dash. My throttle movement skills are not near as good as his, I'm hoping to resolve it. After ruling out a fuel pressure issue, I then directed my attention to a possible VATs related issue.

HP Tuners
I Read the original program
In HPT software (3) VATs options are shown.
A.) VAT's Control (this was turned off)
B.) VATs Control B (this was turned on)
C.) VATs fuel cut off (this was turned off).

I switched off 'VATs Control B' in the HPT software and wrote the calibration with the HPT SW.
This is where things get a bit strange...
- The car then starts fine as expected and runs smooth. However there is a battery & Theft light on the dash. Also, when I test drive it the car has very little power.
- I rewrote the original program with HPT and it's back to the original problem (the engine dies after about 2 seconds and requires some fancy throttle movement to get it to start, once it starts, the car runs fine with plenty of power and no abnormal dash lights).

I was hoping by switching off the 'VATs Control B' that all the VATs would be fully disabled (which is my preference anyway) but it seems that I possibly resolved one VATs related issue and swapped it for another.

Can anyone shed any light as to what might be happening?

I attached the Original HPT file, the HPT file with 'Vats Control B' switched off and the original Bin read with PCMH.

[zack4200]

This sounds strangely similar to an intermittent no-start I get with my 98 s10, which also uses a P08. I can usually get it to start by just holding the throttle wide open while cranking and it'll end up starting up.

Because of WOT getting mine to start, I've been sort of assuming it's somehow over-fueling during cranking, and holding WOT enables clear flood mode and gets it to start up? I have yet to actually dig in any further to figure out what exactly is going on let alone to fix it, so I'm definitely interested if you can find anything out.

[rjdrew1986]

Thanks, this is good to know. I'm not certain but I 'think' mine more behaves like the injectors (and possibly the ignition) stop firing. It just doesn't seem to have a too-rich like behavior.

Just curious, is your PCM a Service Number 16228016? And have you ever tried swapping the PCM just to see if it might resolve the issue? Initially, I thought one possible explanation (if I understand this accurately) is the CPS and ICM directly manage the injectors and coils during cranking and after just a couple of successful CPS pulses, the ICM hands control to the PCM. Even though I've ordered a spare PCM, I'm not so sure this is a plausible explanation because after switching off the 'VATs Control B' in HPT, it starts fine. I've since switch the VATs control B signal back on because it seemed to bring on other undesirable behaviors (for reasons that I don't yet understand). The thought being is if the hand-off successfully occurs with the VATs Control B off, I would think this hand-off would always work. But I will try to swap it just to check it off the list. Perhaps someone in the forum can shed some new light on the issue.

[rjdrew1986]

I should have included in my previous posts, this PCM just doesn't seem to show or log any errors codes which makes me suspect it 'could' be an obscure issue with this PCM. I won't know until Saturday.

[antus]

In some of the other early PCMs there are codes for VATs fail that need to be turned off as well. I'd expect 1 or 2 codes to be set, and then set them to "dont process" and see where you are at. The error light on the dash is a give away. If there are definatly no codes then we can point AI at it and see what it can figure our and see if we can add some kind of code patch. It's also possible the cluster light is in the cluster or BCM, not the PCM, but I wouldn't spend too long thinking about that yet.

[AngelMarc]

No VATS and disconnect VPW line on PCM so it doesn't talk to anything else. I'm just making a shot in the dark guess here.

[rjdrew1986]

After confirming all relevant areas (fuel pressure, compression, CKP and testing injectors in my test machine), I found that by reducing the cranking fuel pulses made a significant improvement. I had a very similar issue years ago with one of our 3.8L LeSabre's, it was easy to correct in the P04 calibration with so many crank related adjustment options. The P08 is just the opposite. It appears that cranking fuel pulses can only be adjusted in (2) areas of the calibration; 1.) applying a pulse width multiplier in the 90-100 Kpa range or 2.) by adjusting the idle VE table (0% throttle @ <1,000 RPM in the 90-100 Kpa range). I prefer the latter because it only impacts cranking (but either seems to be equally effective for adjusting the cranking fuel pulses). Where it is now is good (quick) starts when the engine is cold or at normal operating temp. But when the ECT is warm (say 110-140-f range), it takes longer to start (generally 2 attempts). As far as I can see, there is nothing in the P08 calibration that effects the cranking pulses relative to ECT temperature. Does anyone in the forum (who is familiar with the P08) able to think of anywhere that I could adjust the cranking pulse relative to ECT? With all of Antus's success with A.I. this year, I've turned to A.I. (which seems to be quite familiar with P08 calibration details & limitations) says the one thing that 'may' help is to try swapping the IAC (which I have one on order) because there have some reports of IACs that don't always fully retract the number of commanded pulses during starting in some temperature ranges. I don't think this will help as the idle control RPMs seems to work fine, but I'll give it a try. I just wanted to reach out in case anyone can think of anything else in the P08 calibration that might impact cranking pulse when the ECT is in the 110-140-f range).

[kur4o]

Best route is to find the primary and secondary fuel pulse width vs crank pulse tables. And alternatively the crank spark advance table vs coolant.
Chances gm didn`t use these in p08 is next to zero.

Both affect starting and needs very precise tuning. Playing with ve table is very bad idea. Cranking usually happens in 300-500rpm area, and ve and maf are not taken into account. dwell is also maxed out. What Ve might help is to enlean after very rich start condition so it doesn`t flood.

[rjdrew1986]

Hi Kur40, thank you for replying. At least with HPT, there is no 'secondary fuel pulse width vs crank pulse tables' nor 'crank spark advance table vs coolant'. I don't know if these were available and HPT did not include them? There is an 'ECT Spark vs. ECT vs. Map' defined, but I assumed this only impacts spark. Please permit me to ask...my only changes to the VE area is 'VE Idle in the 90-100 KPa VAC range and less than 900 RPMs', I 'think' this specific area should only be active during cranking. I just want to be sure that I understand, If your thinking that it's not a good idea to alter this specific area, the only other available table that I have found that impacts pulse width during cranking is the 'Injector Pulse Width Multiplier vs. VAC' (only changing the 90-100 KPa range). I've monitored KPa while driving, and at least for my style of driving, I'll never see the 90-100 KPa range. It would be so helpful if a 'secondary fuel pulse width vs crank pulse table' was defined in HPT but I don't see it.