Fuel Pump Relay issue...maybe?

[doncaruana]

The coil and icm are ac Delco - as close to "gm" as I could get. Fuel pressure was good. I went through the p1351 guide and I think the only thing I left unchecked was the VCM or wiring to same. Also haven't looked at fuse relay panel. The weirdest thing to me about this whole thing is the inconsistency. It just went a week without an issue.

 

[jc98ss]

Copy and paste from another forum, this guy seems to have figured it out.... I found this while trying to track down this same exact start-die-start-run perfect issue and P1351 code on my 99 2dr Tahoe

"The situation you described fit a faulty check valve in the fuel pump.

This would allow pressure to bleed back into the tank, and ultimately ,on a warmed up engine , cause the fuel line to go dry. Leaving only the fuel at the spider.

Then when restart is tried, the pump pressures up the system, but has a huge air pocket, however makes pressure nonetheless . That pressures the fuel laying in the spider and the truck starts, but then immediately dies because the vapor in the line ,under pressure has reached the spider, and has to bleed out the injectors and the return system. Enough vapor passes through the injector to stall the engine, and bleed the vapor off , then eventually pushing fuel back into the spider and to the tnk Via the return system.

This would set a p1351 because the Electronic spark timing would be active and the engine would be lower than 250 rpm because of the stall."

Check fuel pressure bleed off

 

[doncaruana]

Thanks! This is definitely interesting!

The fact that this all started when I had the distributor assembly replaced though does have me thinking maybe I should just go ahead and replace the cap and rotor with actual ac delco whatever the shop that did it put on.

 

[jc98ss]

Probably wouldn't be a bad idea to swap those parts even if you weren't dealing with the code...i stuck with all AC Delco on my tune up, coming from the LS1 world I learned a long time ago to not cut any corners.....these old L31's are cool motors, i like how simple they are, but the operating systems are completely different than what I'm used to.


In the research I've done so far, it seems like a bunch of the drop in fuel pump assemblies use plastic squeeze clamps on the hose circled in red...this hose has to hold fairly high psi for its size and over time the plastic clamps lose their ability to seal....might be worth a shot to pull the pump and add metal worm gear clamps. If the pump already has metal clamps, its probably safe to assume the check valve is toast, and replacement would be the fix.

 

[doncaruana]

Probably wouldn't be a bad idea to swap those parts even if you weren't dealing with the code...i stuck with all AC Delco on my tune up, coming from the LS1 world I learned a long time ago to not cut any corners.....these old L31's are cool motors, i like how simple they are, but the operating systems are completely different than what I'm used to.
View attachment 391625

In the research I've done so far, it seems like a bunch of the drop in fuel pump assemblies use plastic squeeze clamps on the hose circled in red...this hose has to hold fairly high psi for its size and over time the plastic clamps lose their ability to seal....might be worth a shot to pull the pump and add metal worm gear clamps. If the pump already has metal clamps, its probably safe to assume the check valve is toast, and replacement would be the fix.

The more I think about it the more I want to fix the fuel pump. Although I think you may have to drop the gas tank to do it - not something I can do myself and $$$. It's literally less than 5 years since I had it replaced but who knows what kind of garbage they put in there.

In the other forum you found that, was that start/die thing frequent? On mine sometimes it just won't start at all on the crank but then does the next crank. And it will go days with normal starts as well.

 

[jc98ss]

Mine is pretty consistent which makes me believe its losing pressure and not a loose wire or connection (I've already checked them all anyways and added several extra ground straps).... this issue never happens when the truck is cold....first thing in the morning it always fires up, after sitting all day in thr parking lot at work it fires right up on the first try.....but if it has been up to operating temp with the last couple of hours, it'll start-die, throw the code, then start and run fine...performance isnt affected and idle is perfect.

Only when it starts and dies does it throw the code...i bought an obd2 scanner so i can clear it anytime...before i had the scanner, the service engine light was intermittent, it would stay on for several days, sometimes go out, sometimes it would stay on for weeks.....once i had the scanner it was much easier to pinpoint what was kicking the code....if i clear it out, all cold starts fire on the first crank

 

[doncaruana]

That's interesting. I have to monitor that now to see if it does it ever completely cold vs having been warm. Today it did it after sitting for just under 2 hours after it was warmed up.

 

[doncaruana]

@jc98ss (or anyone paying attention to this thread...)
Does this scenario fit the above?
This morning, after sitting all night, no issue starting.
After sitting for almost 8 hours, again starts right up with no issue.
20 minute drive and then sits for a half hour until attempting to start - hard start.
15 minute drive and then sits for another 15 minutes - hard start

When I say hard start, there are two versions of that. In one, it just won't start at all after cranking it for a few seconds. Stop and try again and it starts. In the other, it's a long crank but then it starts and runs for one second and dies. It was one of each tonight, but my daughter was driving and can't remember which one was first.

 

[east302]

Hard hot restarts sometimes result from a flaky coolant temperature sensor. A scanner can be used to see what it is reporting. It should be somewhere between ambient and the thermostat setpoint, depending.

If it’s an oddball number it can cause the computer to call for too much fuel and flood it out. The workaround is to hold the gas to the floor while cranking. This temporarily stops injector pulses.

 

[doncaruana]

Hard hot restarts sometimes result from a flaky coolant temperature sensor. A scanner can be used to see what it is reporting. It should be somewhere between ambient and the thermostat setpoint, depending.

If it’s an oddball number it can cause the computer to call for too much fuel and flood it out. The workaround is to hold the gas to the floor while cranking. This temporarily stops injector pulses.

I don't think that would explain the one second stall, which I also get, that jc98ss explained and detailed a few posts above does it? Also I don't need to floor it - the second attempt works perfectly.