'86 Jimmy 4in Lift, 40’s, tons, 8.1 Swap- 700r4 said PNNNNN

[Blue85]

Pressure shouldn’t drop that fast. You either have a pressure regulator that is bleeding it off or an injector hanging up and bleeding it into a cylinder.

Also, there is a check-valve of sort in the fuel pump. I had a rapid pressure-drop for years which wasn't affected by regulator mods. I used to prime with the key 3x before starting and later changed the prime time to 6 seconds to make up for this. When I changed the fuel pump later, the bleed-off was gone and starting was normal.

 

[imiceman44]

Also, there is a check-valve of sort in the fuel pump. I had a rapid pressure-drop for years which wasn't affected by regulator mods. I used to prime with the key 3x before starting and later changed the prime time to 6 seconds to make up for this. When I changed the fuel pump later, the bleed-off was gone and starting was normal.

I have been waiting for someone having the same problem and getting it solved.
I have had the fuel pump in my cart on rockauto for a month, and the regulator sitting at napa. I guess I am getting the pump

 

[GWeakland620]

I had a similar issue with my pedal not responding initially. After some tracing I figured out my throttle control module didn't have a good ground. I'd start with verifying that you have power and ground going to your module first.

When you first key on the throttle will do it's little test to reset where it needs to be for idle cranking, that's normal. When you have a working pedal, with key on, engine off, the throttle will move a full range of motion matching your pedal input. If it's quiet you can hear the throttle blade open and close. You can also watch it in real time with a scanner.

What setup do you have for your pedal?


I also had a fuel delivery issue as well when I was testing it on the stand a while back. I had fuel pressure but no injection. It would run on starting fluid. I ended up tracing it down to the injectors. A noid light confirmed I had injector pulse. I figured what are the chances all 8 injectors are plugged up or seized? Surely some must be firing enough for the thing to cough or sputter, but it would crank and crank and nothing. Sure enough I replaced the injectors and it fired on the first half crank.
How long have your injectors been sitting? Have they been dry or sitting with old fuel in the rail?

This is my current setup for the pedal and module.

 

[GWeakland620]

Ok so letting pressure build before starting has allowed me to start on its own, but it dies within 2-3 seconds.

The APPS did nothing, so I’m wondering if I have a faulty module.

 

[ZooMad75]

That’s promising. Curious if there are any codes set to indicate why it’s stalling.

 

[GWeakland620]

That’s promising. Curious if there are any codes set to indicate why it’s stalling.

My code reader only shows accelerator related codes.

 

[GWeakland620]

I think I found my fuel problem.

The pump I was running with my last system was a high psi pump, but I’d be lying if I said I remembered what it was rated for. Well, it turns out it’s only rated for 45psi which is why it’s bleeding off so fast. So when primed it builds up enough to crack it off, but then drops and cuts the fuel supply.

That still doesn’t answer my question about the throttle, but I’m not moving forward until I get a better pump.

 

[GWeakland620]

Snagged this for $50. Going to toss it on and see if that takes care of it dying after start up.



I’m not 100% that this is the final plan for fuel supply/delivery. Still thinking heavily about going to a factory style efi tank and a super beefy skid plate. But this should move me forward for now.

 

[GWeakland620]

So, new pump is on. Primes to 62psi then holds great. Crank over and it fires right off…….and immediately dies.

Without a scanner, I am at a complete loss.

Honestly sounds like vats is still on, but I don’t have any way of knowing.

 

[6872xtc]

So, new pump is on. Primes to 62psi then holds great. Crank over and it fires right off…….and immediately dies.

Without a scanner, I am at a complete loss.

Honestly sounds like vats is still on, but I don’t have any way of knowing.

Well, that's still progress!
Still frustrating too.

 

[Blue85]

Is the oil pressure sensor wired up to the ECM?

I can't remember. Did this ECM come with the engine or could there be some basic parameters mismatched? For example, the crank and start don't need the MAP and MAF, but shortly after, those readings are used. When you had a scanner, did you scan MAF? You could try unplugging one or the other and see if it runs longer. Not conclusive, but you could take your attention off VATS.

 

[Truckman4life]

Pretty sure they don't care about oil pressure. Ran my wife's '08 6.2L for a long time with a dead oil pressure sensor. Sure sounds like VATS to me with the start and die thing.

 

[ZooMad75]

Sounds like vats to me. Mine doesn’t have a oil pressure signal going to the pcm at all.

 

[Wes Harden]

How would one fix the vats issue send pcm out for programing or can hp tuners do it ?

 

[ZooMad75]

How would one fix the vats issue send pcm out for programing or can hp tuners do it ?

I was lazy. I had Howell do my tune using Larry’s file. Deleted all security and a couple of other torque management bs.

But here’s the thing, he needs to check the codes and data again just to make sure it isn’t a vats issue. There should be security related codes if it’s not getting the signal from the passlock sensor to the BCM. Since his truck has no BCM or passlock it obviously won’t have it. I’d hate to have him send off the pcm to make sure the security is turned off and find out it was and something else is causing the stall.

Flying blind without any way to see any data just makes the process all the more frustrating and prone to firing off the parts cannon full of stuff you might not need.

Spend $20 on a Bluetooth device to plug into the ALDL connector and download the right app to run it on your phone. At minimum you’ll be able to read codes. If you pay the few bucks for the pro-version of the Torque app (droid) you can watch live engine data on multiple pids. It does not replace a real scan tool but it sure beats slamming your head against the wall not knowing what the damn pcm is doing or not doing.

 

[ZooMad75]

I forgot to mention if the harness, pcm and tune came from Howell you can always call them back and get in touch with the guy that writes the tunes and he should be able to validate if vats was shut off or not.

Those guys are usually pretty good to make sure that vats is off by all the information they ask for to set up the pcm in the first place.

If you confirmed the security is disabled we really need to know data from the pcm to see what value is dropping off.

 

[Blue85]

Spend $20 on a Bluetooth device to plug into the ALDL connector and download the right app to run it on your phone

Yeah, when the tool costs less than any parts you might replace, I never understand anybody working on a car doesn't have a tool to AT LEAST read codes. Pretty sure you can get in for $13 .

 

[Wes Harden]

yeah elm327 I keep one in my travel bag, lol have used when visiting family i can't say how many times

 

[GWeakland620]

My handheld only shows codes for the APPS.

 

[imiceman44]

So, new pump is on. Primes to 62psi then holds great. Crank over and it fires right off…….and immediately dies.

Without a scanner, I am at a complete loss.

Honestly sounds like vats is still on, but I don’t have any way of knowing.

That does sound like vats