Engine stalling, a penny for your thoughts

[chewy012]

Ok, so, my engine is stalling out.

Here's what I'm currently observing. On a cooled down engine, it starts up, idles for about 30 sec. to a minute, then bogs out and dies. Plugged in my scanner, no codes, but watching to data stream, at the time of bogging fuel injector pulse width jumps from 1.6ms to 10 ms. Opening up the throttle doesn't bring the RPMs up, only prolongs the final shut down buy 10 or 15 miserable seconds.

Can't figure it out, when I was warm, I could run it down the highway basically until I had to lift my foot off the throttle then it would die, cool, it dies shortly after start up.

MAF, TPS, IAT, and ECT check out, truck didn't over heat at all. Also, fuel pressure is solid, and regulator is not leaking. I also considered vapor lock, but fuel shoots outta the schrader valve nice and steadily.

My next thought is IAC but, I would think opening the throttle plate when it starts bogging would bring the RPMs up.

Anyway, any thoughts are appreciated. I reset the codes, and unhooked the battery, no solution.

Also, turning the key to on no longer illuminates the CEL, but when I had the scanner hooked up, when it would click the relays and what have yous, the CEL flashed with the clicks.

I'm almost stumped. I've got a few experiments I'm gonna try tomorrow.

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[chewy012]

Ok, update for anyone keeping score,

Next morning; IAC is good. The truck chugged twice while warming up from idle, but recovered on its own. Now that's it's warm, it's not showing any problems whiles it's idled the last 20 minutes...... and counting.

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[chewy012]

Theory,

Yesterday was about 95 degrees, spent a few hours driving around town house hunting (constant up and down 15 - 30 mph). It's high elevation (~4700 ft. and dry).

I think it was vapor locking, because it would go, but as soon as I let off the gas (which should how lowered fuel pressure) it died. The manifold was pretty damn hot if I remember correcly

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[chewy012]

Dude, does any know if the intake manifold was designed to act as a heat sink?

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[RonD]

Intake is heated by coolant as engine warms up, so operating temp of 195-215degF would be normal, so I wouldn't think outside temp of 100+ degF would effect fuel system at the intake.
Near the exhaust pipes was the usual place for vapor lock but doesn't normally effect Fuel injection systems, it was more of an issue with carb setups.
Higher pressure = higher boiling point for a liquid, so 30-40psi fuel pressure would have to be VERY hot to get vapor lock
Carb systems basically had gravity/siphon feed from tank to mechanical fuel pump on the engine, 0psi pressure, so while not common, the metal fuel line near the exhaust could get hot enough to cause a vapor lock.

The longer opening of the injectors would mean O2s were reporting high oxygen in the exhaust, Lean.

But O2s are not used at cold start, only after about 4 minutes or so, they need to be above 600degF to work right, which is why they are heated.

So in Open Loop, no O2s, computer should only be using MAF data, TPS(throttle position), and RPMs to calculate open time for fuel injectors.

Open Loop is also determined by Coolant Temp, ECT sensor, after startup computer looks to see if this is a cold start or warm start, "can it use the O2 sensors"
So ECT sensor could be telling computer engine is already warmed up, it looks at O2s and engine dies.
ECT sensor gets 5volts on 1 wire and sends back above 2volts cold, and under 1 volt warmed up.
Because there is lower voltage when warmed up a corroded ECT wire could cause computer to "think" engine is warmed up any time you start it up.


The No CEL, could mean computer issue but if you can still "talk" with it then would be a long shot

 

[chewy012]

I'm pretty sure it was vapor locking. I bled the rail on the side of the high way and a second or two's worth of vapor came out, then fuel. If the o2s were reading
lean, something was preventing fuel from entering the engine, hence, injector pulse jumping to 10ms.

Trucks running cool and strong today.

CEL not coming on I think was due to my scanner being plugged into the computer.

I'm tellin' ya, the intake manifold was HOT. And relieving fuel pressure but letting off the throttle (re-establishing vacuum to the regulator) lowers the boil point.

I wish I had my scanner with my so I could've read the IAT, it had to have been 140+. I couldn't touch it for more than a half second and usually I can rest my hand on it at op. temp.

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[YungICY]

Make sure you don't have any exhaust leaks. My expo kept getting vapor locked last summer because of my bad exhaust leak. I finally got around to replacing my y pipe and so far no issues.

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[chewy012]

Will definitely check that, thanks for the tip!

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