Weird 3S problem (not mine)

[mjannusch]

My thought is that you started with multiple issues, and the process of troubleshooting and fixing things got the car to a spot where it wouldn't start because of remaining issues.

When it was still running, the ECU probably had the IAC wide open to keep it idling because the BISS wasn't letting any air through the bypass passage. "Something" broke (let's say the crank sensor for the sake of argument).

In troubleshooting that, the battery was probably disconnected and the ECU reset to its default IAC position, which is probably something like 20% open. The IAC itself maybe works, maybe it doesn't - I don't recall what all has been tested. Maybe one of the IAC windings is bad in such a way that it can only close the IAC but not open. Now the car won't start because there's so little airflow, which could also explain the lower than usual compression readings when tested with the throttle closed. It sputtered a bit, but wouldn't reliably ignite the mixture to bring RPMs up high enough to get out of the default cranking program so it just keeps injecting fuel waiting for the engine to start.

Saturate spark plugs in fuel for long enough and they foul to the point of not being able to ignite the mixture anymore. At that point, you basically have to replace the plugs or it is never going to start.

Seems plausible, and you don't need a bunch of sudden failures to start the chain of events, just a few things that aren't working right (FIAV/BISS/IAC) and one hard failure (crank sensor) and you could end up in this sort of difficult troubleshooting scenario chasing your tail.

[Monochrome]

To build on that:

The OBD1 coding maybe different than the 98/99 but assuming they are similar, the code considers 450 RPMs to be the switch point between "cranking mode" and "running mode".

During cranking mode, the MAF isn't used. Simply put, the ECU just fires the injectors at a certain pulse width. This number starts with an initial pulse then it switches to a fixed IPW that varies depending on COOLANT temp. This then tapers a percentage away from that IPW with every "cranking resolution". The ISC maintains a fixed position (believe it's full open and there is no correction factor for this) and the fuel pump is switched to "high speed" mode.

After the RPMs jump above 450rpms (engine fires), then the ECU will use the MAF to control the injectors with a certain enrichment multiplier added in which also varies with coolant temp. Closed loop is disabled during this time for 40 seconds to 15 seconds depending again on coolant temp. Fuel pump remains in high speed mode for a set time and the ISC position is determined from the base table plus or minus the ISC error (which stays stored as long as battery power is supplied to the ECU like the long fuel trims).

It amazes me that guys can even get their cars to start with large injectors and a piggy back when there no tunability for cranking mode and an uncorrectable enrichment applied after the engine fired... That's OT though.

The starter only spins the motor over between 200 and 250 RPMs so the ECU just keeps spraying fuel in cranking mode which has no compensation for the lack of air being restricted into the cylinders by the messed up throttle body. During the random blips where the motor does seem to show life, the motor doesn't stay running because (once again) all the restriction from the throttle body plus the extra enrichment plus the soaked lower intake from cranking mode all adds up to a very rich AFR that fouls the plugs.

Now why won't the motor fire with the foot on the gas pedal? Probably because that surge of air isn't enough or comes as too much too late, maybe the code is registering that change in TPS as another enrichment factor (which it does but I can't remember if that is factored in just after start up), or maybe it's to do with the idle switch not being tripped putting the code into crusing mode which is again too much fuel.

[BATMAN]

If this were your car what would be your next step?

This is a list of things that have been done. Hopefully i listed everything.
Cam angle
Crank angle
Actuator wheel-crank only
Timing marks
Compression
Fuel tank
Fuel filter
Coil pack
Plugs
Plug wires
PTU
Fuel resistor pack
MAF unplug
Fuel pressure
Looked for shorts between ECU and parts like the coil pack, PTU, MAF and the fuel relay that's in cab
Tried starting fluid

Suggestions that I have not done (some listed were NOT suggested by members on BAWC)
pull start
Known working TB
Light the car on fire
Sell it and move on
Tear the engine harness out and go over it inch by inch
Part it out

And my favorite from my loving parents and sisters
Take it to a shop and have them discover the problem. Ha ha ha.

[DCIV]

have you done something as simple as pressure testing? I know with maf unplugged it should start but mine wouldn't when i blew a pipe.


Coop

[BATMAN]

[quote=""DCIV""]have you done something as simple as pressure testing? I know with maf unplugged it should start but mine wouldn't when i blew a pipe.


Coop[/quote]

Funny you bring this up.

I've always thought about doing it but haven't yet. Since I pull the Biss screw I can't do it until I get a known good TB to test.

It started briefly like milliseconds briefly the last time Jeff was over. I got excited and WOT the pedal and it immediately died. I had blown off the y pipe from the FMIC.

[DCIV]

yeah, try it man, could be a HUGE leak at the lower intake mani or something.


Coop

[BATMAN]

I need a Biss screw at least first....

[DCIV]

I would block it off to at least get the car to start. It will start with a blocked biss screw. I drove like that for 5kish once lol. i also think you should unplug your IAC though.


Coop

[Hans_GZP]

If it ain't starting with starting fluid, then an intake leak is less likely a culprit.

[DCIV]

lol, you are very right but here is what I am thinking.

He is working alone, so he sprays some, hooks back up where ever he spray it, goes and tries to start it. well of course thats not gonna let it run. but he did get smoke once...wonder if that was starting fluid...just a little bit of starting fluid.


Coop

[BATMAN]

Flames were seen when directing sparying into brake booster line in the intake while cranking. We stopped that experiment...

[DCIV]

So you have high enough EGT's to cause that? have you checked if your turbos spin freely?


Coop

[BATMAN]

Not since the install, no

[DCIV]

check them.


Coop

[Jeff V.]

Bypass the entire turbo and IC setup. Stick an NA intake tube on the throttle body. I think I have one from a Diamante...

Put a piece of electrical tape over the idle screw if you're worried about that.

[Monochrome]

[quote=""Jeff V.""]Bypass the entire turbo and IC setup. Stick an NA intake tube on the throttle body. I think I have one from a Diamante...

Put a piece of electrical tape over the idle screw if you're worried about that.[/quote]

This is exactly what I used to do.

[BATMAN]

What part do you not own, Jeff?

[Jeff V.]

Umm....


I think I have all of them.

[Hans_GZP]

That's how we move turbo cars around the lot that have major issues. NA intake tube

[DCIV]

Get that to him Jeff.


Coop