Truck won't start, and I can't figure out why....

Metalcrack · Mar 16, 2015

('99 3.0 FFV) It seems like everything is in place for my truck to start, but doesn't. It cranks, and starts maybe every 3rd or 4th day during my diagnostics. The problems started after one night of bad weather (ran to store for wife's ice cream..... the essentials). Came home and no go a week later during another storm.

What I know:

-~55psi to the rail when trying to start (pump, relay, inertia good)

-12V signal to injector when trying to start. I don't know if I am getting the signal from the Pcm to pulse yet (plugs were wet when I pulled them). I can Verify I do get pulsing on cylinder 1. I have to get the right kind of probes to measure the others.

-Spark on all 6 plugs confirmed during the no-start periods (noid plug) Crank sensor should be good. Coil pack passes resistance checks on primary and secondary.

-Other folks lead me to check my CamPS, which was out of time. I reset, and replaced the sensor to be sure.

-No CELs/codes, light is there and reader connects/checks.....fuses ok for PCM power, PCM should be okay?

-I've tried to start with my remote start (Viper) and my key, so I doubt the ig switch is bad.......

-The theft light goes out 3 seconds after cranking so PATs shouldn't be an issue. Tried 2nd key to be sure.

-Compression test shows 143-151 for all 6 cylinders.

-Pulled the PCM connection and was pristine, and opened up the PCM and it too was spotless

What I cannot confirm:

-Pulses on cylinders 2-6 (even though they were wet during compression check)
-PCM is good as I don't have a spare

Any clues? I have spark, compression, (most likely) fuel and air.

RonD · Mar 16, 2015

Wow, looks like you have done a through check of all the possible "no start" culprits.

Did the 55psi pressure at the rail hold after key was off, it should?
And fuel pressure for '99 should be 65psi to 70psi

All EFI computers have a "clear flooded engine" routine
Key off
Press gas pedal to the floor and hold it down all the way
Turn key on, TPS(throttle position sensor) voltage is now above 4.6volts(wide open throttle) since Engine RPMs are 0 this tells computer to shut off all the fuel injectors.
Crank engine(try to start), keep gas pedal to the floor.
If engine tries to fire at all then fuel is getting into engine from somewhere.
Check Pulse Damper vacuum line for fuel(end of fuel rail)
Could be stuck open injector.

As soon as you release the gas pedal injectors will start working again, even while cranking engine.

I would get a can of Quick Start(ether)
I would unplug the MAF sensor(sanity check for Computer), and spray some ether into the intake then try to start engine.
If engine fires up then dies maybe you have some "bad gas" or Failed flex fuel sensor, it is adding to much gasoline thinking its E85, never heard of that but........

Your CEL(check engine light) should now be on, because MAF sensor is unplugged, if not then computer could be the culprit.
It will go off after you plug MAF sensor back in, if not disconnect battery's ground cable for 5 minutes, that will cause computer to reboot, which might not be a bad idea to do in any case, when any computer locks up or goofs, what do you do?
Cut power for reboot

Metalcrack · Mar 23, 2015

Your idea about the clear flood may have been onto something. Whenever I would try to start (and it wouldn't) it would crank away without any sputter. Once in a great while, it would make an attempt with a slight hiccup (perhaps a little fuel did enter). I pulled off the TPS and saw the connection on the cable was corroded (the wiper arm feeding back to the PCM). I cleaned it up and it has fired every time since.

I did order an OBDII USB cable and Forscan and didn't find any outstanding DTCs, but I did find out which ABS sensor is causing the light.

RonD · Mar 23, 2015

That's a new symptom/test for the TPS and Clear flooded engine mode, lol.
But I would think the corroded connector would make voltage less.

Metalcrack · Apr 7, 2015

It acted up again after 1 week of starting and driving. Finally captured the data I needed. The throttle was reading 99% WOT.......anti-flood mode!

I rang the wires back to the PCM and tested good with no resistance. Replaced the TPS and showed up at 14%/0.75 volts.

Thanks for the tip RonD!

RonD · Apr 7, 2015

Good work

That is a new one for me, but it does make sense, if Computer sees TPS at WOT before starting it will shut off the injectors.

pjtoledo · Apr 12, 2015

RonD said:
Wow, looks like you have done a through check of all the possible "no start" culprits.

Did the 55psi pressure at the rail hold after key was off, it should?
And fuel pressure for '99 should be 65psi to 70psi

All EFI computers have a "clear flooded engine" routine
Key off
Press gas pedal to the floor and hold it down all the way
Turn key on, TPS(throttle position sensor) voltage is now above 4.6volts(wide open throttle) since Engine RPMs are 0 this tells computer to shut off all the fuel injectors.
Crank engine(try to start), keep gas pedal to the floor.
If engine tries to fire at all then fuel is getting into engine from somewhere.
Check Pulse Damper vacuum line for fuel(end of fuel rail)
Could be stuck open injector.

As soon as you release the gas pedal injectors will start working again, even while cranking engine.

I would get a can of Quick Start(ether)
I would unplug the MAF sensor(sanity check for Computer), and spray some ether into the intake then try to start engine.
If engine fires up then dies maybe you have some "bad gas" or Failed flex fuel sensor, it is adding to much gasoline thinking its E85, never heard of that but........Your CEL(check engine light) should now be on, because MAF sensor is unplugged, if not then computer could be the culprit.
It will go off after you plug MAF sensor back in, if not disconnect battery's ground cable for 5 minutes, that will cause computer to reboot, which might not be a bad idea to do in any case, when any computer locks up or goofs, what do you do?
Cut power for reboot

thats how the FF sensor died on my 2000 a few years ago, it was flooding the engine. been running a FF simulator ever since.

Perry

Truck won't start, and I can't figure out why....

Metalcrack

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RonD

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Metalcrack

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pjtoledo

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