P1351 after replacing ignition coil and icm

[doncaruana]

Good Work! These can be a pain to find. You got thru quicker than most.
Try this or alternate numbers-

More Information for UNITED MOTOR PRODUCTS CON76

As my buddy told me - you already have the equivalent of what's in the junk yard. Buy a new one.

 

[doncaruana]

So...update...I'm an idiot. The reason that one pin was dead is because I had disconnected the other end that goes to the coil when I tested it. That's why I couldn't duplicate it. However...

I decided to test the actual ignition coil while I was at it. You're supposed to check the resistance in 3 places. Well, the resistance between the outer most pins (B and C) is essentially supposed to be about zero (technically the manuals say 0.1). On my just pulled out of the box AC Delco ignition coil, it's a flat 0.5 no matter what. But on the Autozone one that's in the truck, it meters all over the place - 0.9. 10, 1, 25, 1.5, 50... So I'm gonna try and change that coil out...

 

[doncaruana]

And problem still exists. The only thing I never checked was the vcm, but it just doesn't make sense why it would suddenly have an issue. I didn't really check step 3 where you monitor the voltage coming to ICM B while cranking because the next step on that was unplugging the VCM, etc. But, strictly speaking, if I'm following the troubleshooting guide, that's really about all there is left. Although I could consider using a piercing probe to get the resistance of the line without actually taking the connector off - that is if I can even get to it (I think the one I need to get to is one of the bottom ones).

When the weather warms up again, I guess I'll get out there and jiggle the hell out of the wires and see what I can see. I've replaced the autozone icm and coil with ac delco ones already. I'm just so disappointed I can't put words to it.

 

[exp500]

Check your grounds, check computer plugs for corrosion.

 

[doncaruana]

Check your grounds, check computer plugs for corrosion.

Which plugs? You mean into the vcm?

 

[exp500]

All 4 of them. Look closely with a bright light, Corrosion/water/bent pins/loose connector.

 

[doncaruana]

That will be fun getting to them. Lol

 

[Tanner Peterson]

Hey!
I’ve got the exact same issue as you with the start and stall and the P1351. Did you ever come to any resolution?

I’ve tried so many things it’s insane… and this is happening to me on a new GM crate engine.

 

[doncaruana]

Hey!
I’ve got the exact same issue as you with the start and stall and the P1351. Did you ever come to any resolution?

I’ve tried so many things it’s insane… and this is happening to me on a new GM crate engine.

I still haven't resolved it. My next thing is replacing the connector to the brake control module. Just gotta find the time and weather to do it.

 

[exp500]

Don, don't sweat about the relearn if you disconnect computer. It fixes itself in 50 miles.I just wanted you to get everything else done before you got a it runs different.
Testing of the ABS connecter - use a 45 degree pick or similar to bend the femle contact a bit tighter.
Spray with contact cleaner and use dielectric grease. I grease the rubbers too.
Have you Tested ICM White wire? Try both ways- Test light grounded then connect to white wire and crank engine. Should flash strong every hit. Swap test light for voltmeter, crank engine.
Last test- when computer disconnected, Ohm test white wire Icm to Computer. Ohms should be about the same as 5-6 feet of 20 ga. I have replaced a couple white wires.

 

[Tanner Peterson]

I still haven't resolved it. My next thing is replacing the connector to the brake control module. Just gotta find the time and weather to do it.

What ABS connector are you guys referencing? I’ve read the thread twice but must be missing the post referencing that…

 

[doncaruana]

Ok. I'm an idiot. Lol. I said brake control module and it's the ignition control module. And I think that threw off exp500 or it was an autocorrect. I'm relatively certain the issue is the line between my ignition control module and the the ecm. I'm just nervous about disconnecting or even messing with the wires around that thing since the truck is almost 2t years old.

 

[Tanner Peterson]

No big deal. that makes alot more sense!

I just retested my ICM connector today with a test lamp and it all passes. I replaced that connector at the beginning of this problem.

 

[doncaruana]

Resurrecting this thread for an update...it appears as if this was actually due to an issue with the fuel pump relay, surprisingly. It's all in this thread but the reader's digest version is that the 5 pin relay you use for the fuel pump doesn't function properly (something funky with that 5th pin in the panel or whatever it's attached to - and it's just for testing anyway) but a standard 4-pin relay (like the A/C relay) works fine.

 

[exp500]

Don, Likely only a temp fix with relay swap. Look thru the diagrams for fuel pump and find the common areas- grounds especially. Being that your voltage goes Hi to set P1351. Also look for corrosion at the fuse block.
Did you ever unplug and clean the ECM plugs?

 

[doncaruana]

Don, Likely only a temp fix with relay swap. Look thru the diagrams for fuel pump and find the common areas- grounds especially. Being that your voltage goes Hi to set P1351. Also look for corrosion at the fuse block.
Did you ever unplug and clean the ECM plugs?

I never messed with the ECM plugs because I honestly didn't want to poke that turd, so to speak. I'd be willing to bet there's an issue in the fuse block itself based on the behavior. I mean it went like this:
Before, w 5-pin relay - intermittent, but regular occurrence of hard start, which throws P1351
Put in 4-pin relay - perfect start every time, no code
Put new 5-pin relay in - A little trouble starting but started. Drove home from shop, would NOT turn over at all
Put new 4-pin relay in - Back to normal functioning - good starts, no P1351. I will say though that I got P0507 at this point, which is completely new and a bit of a headscratcher.

 

[exp500]

Don- check your service manual for the ground locations relative to your issues. There is a main one on the frame about at drivers feet and, acouple under the dash I think you can reach from the floor or with cluster removed. Another one is the firewall ground strap rt side by trans dipstick.Follow both the Light switch and Fuel pump relay wiring too.
It is getting to be common now to have corrosion at the fuse block and ECM connectors due to age and Dielectric grease drying out.

 

[doncaruana]

Reading through the service manual and after talking to the mechanic who found that the relay switch worked, I think I'm coming to a better understanding...maybe? He said the P1351 was a result of the long cranking that would take place (which jibes with what I saw). Reading the service manual, I see this: "An inoperative fuel pump relay can result in long cranking times. The time necessary for the oil pressure to reach the pressure required in order to close the oil pressure switch and supply the necessary current for the fuel pump causes the extended crank period."

That 5th pin just goes out to a capped wire, as east302 showed me here. I have to believe the issue is in the fuse/relay block but I'm having a hard time resolving exactly how this works and doesn't work. That 5th pin, pin 87a, is the one that connects through to the fuel pump when the relay is *not* being energized, ie the fuel pump prime connector. As I type this, I'm thinking that the issue is really next to the middle pin, pin 87a. Because when you turn it over, the relay flips to pin 87, which is the battery feed, and sends it on to the fuel pump. The thing is, at that point, pin 87a isn't engaged.

But if the blade in the relay being inserted actually causes pin 87 to ground out or even causes pin 85 (the signal to energize the relay) to do the same, that would make the relay not work right. That either stop the relay from opening at all, or it would just ground the power out before it gets to the pump.

Does that make sense? And, more importantly, how in the world would you even address that?? Wouldn't you have to pull that whole block off, wires and all??

 

[east302]

It’s probably worth a look under the fuse block to see if anything stands out (or is even visible). Going by memory here, but I think it sits on three or four legs that just bolt through the fender liner and are accessed from above the tire.

 

[doncaruana]

A friend suggested deoxit. Think I'll order some to have on hand...