Good Fuel Pressure, But No Spark When Hot

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cmdsm

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Hi everyone, I have a 2001 2500 5.9L 5spd. I just replaced the steering gear (can't see how this would be related) and started getting a stalling/no start issue. After it's warmed up to operating temp for 5 min or so, it will stall 50% of the time. It won't start until it cools down (5-10 min).

I have 47psi at the fuel rail under all conditions. But I'm not getting spark when it stalls. I tracked it back as far as the power wire to the coil pack. When it has stalled and won't start, there is no power to the pack. I checked the ASD relay when cold and it activates fine, also power at terminals 30 and 86 (85 actually, I think this is a typo in Haynes) when ignition is on. Warming up the truck now to see if I can get it to shut off and test under hot condition.

Any advice? Do these relays tend to fail under hot conditions before they finally go?
 

joepizuro

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Well when it warms up it switches to open loop. Takes a reading from o2 sensor then adjusts fuel. Unplug the o2 sensor and see what happens. Although I don't believe it starts in open loop so kinda doesn't make sense.. must be something else.
 

dapepper9

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^^Joe might be on to something. Easy enough testy. Closed loop is when it will adjust firm ratio in attempt to keep it stoichiometric (14.7:1).

It actually starts in open loop and stays until reaching operating temp.

The terms are kinda confusing. Think of it like an electrical circuit: an open loop has a signal that starts at one end but never reaches the other. Closed loop is a complete circuit where a signal starts at one end and goes all the way to the end with no interruptions.

Other than that i would ohm check the coil for 11-15k ohms between the tower and either plug pin. If it ohms good pcm isn't sending switching signal which is often caused by crank sensor
 

joepizuro

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Oops had it backwards my bad lol
 

joepizuro

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Long story short this rules out ecu and o2
 
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cmdsm

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Thanks for the ideas. I had checked the coil and it specked out fine. I wasn't able to get the truck to stall out yesterday after warming it up for a good 20 minutes and then driving it around my yard (I'm betting it switched to closed loop by then). I had tested the ASD and Fuel pump relays at that point. If the ASD was a bit corroded inside and I loosened it up, that could account for the 'fix'. I ended up switching the horn and ASD relays. Only time and a few trips to town will tell if that was the problem.

My plan was to test the relay and crank sensor if I got the no start condition again. That will be my next step if it does happen.
 
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cmdsm

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Long story short this rules out ecu and o2

Thanks Joe, but help me understand this a bit more. I was worried I'd have to start looking for a new ecu. How are you thinking it's ruled out?
 

dapepper9

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02 won't rule out pcm as crank sensor, cam pickup, ignition, asd relay will all keep it from sending switching signal to the coil
 

joepizuro

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Dapepper is the expert, I'm just the redneck so thank him and follow his lead
 

joepizuro

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Wife's in labor and no one in the lounge except me lol. She's getting her epidural ain't allowed in..
 

gofishn

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Wife's in labor and no one in the lounge except me lol. She's getting her epidural ain't allowed in..

Congratulations !!

Keep your eyes, wide open and do NOT blink.
Else it will be 34 yrs later, the youngest will be getting her drivers license and you wonder who that old man in the mirror is.....

Seriously, treasure every moment.
 

Joe w.

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That's true my son will soon be 12 seems like only a few years ago time only gets faster or so it seems
 
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