Hard Start

[Black_Cloud]

Hey guys, I just got the truck back together after doing HGs and injectors. Truck started fine for the first few test idles, put it through its first WOT tests last night, ran like a dream.

Started the truck this morning no problem, went to work and it started fine again at the end of the day. Drove it home and went to start it back up about 30 minutes later and it didn't want to start. I cranked it for about 8-10 seconds and no fire. I then left the key on to let the lift pump run and it cranked right up. Did the same thing after experimenting all night.

Things to note here. The problem only seems to happen when the engine is hot. Letting the lift pump run allows it to fire right up. The problem surfaced only after I took it out for a few WOT tests, before that it cranked just fine multiple times while checking for leaks right after it was back together. I dont think it's injectors as they are brand new from a trusted company. I'm also getting a p0370 code. Primer on top of fuel filter is rock hard before trying to start.

I know you guys are going to ask for logs, but unfortunately I have no way to check those at the moment. I'm just hoping you guys can point me in the directionof possibilities.

Fuel line collapse when the engine gets hot? Air getting in the system? Bad cp3? (Hope not). Help! Thanks!

 

[2004LB7]

Fuel line collapse when the engine gets hot? Air getting in the system? Bad cp3? (Hope not). Help! Thanks!

All possibilities, start withe the cheap ones first. The cp3 is unlikely. You can always put a clear fuel line on and look for bubbles.

When the engine is up to temp and running how does the primer bulb feel? Does it still feel like it has good spring pressure or does it feel like it is getting sucked down? May need to put a vacuum gauge on it

 

[danzick]

How much fuel in the tank? Mine has acted like this before when it gets down around or below 1/4 tank. Also would lope at idle a little.

 

[Black_Cloud]

All possibilities, start withe the cheap ones first. The cp3 is unlikely. You can always put a clear fuel line on and look for bubbles.

When the engine is up to temp and running how does the primer bulb feel? Does it still feel like it has good spring pressure or does it feel like it is getting sucked down? May need to put a vacuum gauge on it

Primer bulb is rock hard when running, I can't hardly get the thing to even move lol. Where would I put the vacuum gauge on it? Would that help identify if there is an air leak somewhere?

 

[Black_Cloud]

How much fuel in the tank? Mine has acted like this before when it gets down around or below 1/4 tank. Also would lope at idle a little.

About 3/4 of a tank right now. It's funny you mention a lope because it did have a lope when I first got it put back together, ended up being the FPR though. Replaced that and the lope went away completely.

 

[2004LB7]

Primer bulb is rock hard when running, I can't hardly get the thing to even move lol. Where would I put the vacuum gauge on it? Would that help identify if there is an air leak somewhere?

Primer shouldn't be hard while running. Maybe look into that a little more. Filter housings have been a constant source of hard or no starts for the duramax, from cracked WIF sensor, bad seals and O rings, bleed screws or even cracked filter housing. Most lead to loss of prime or air getting in while running. The primer bulb should be, while the engine is off, be forcing fuel into the cp3. It should get hard once full because it is now having to push fuel out of the release valve which is set a about 75 psi. While the engine is running the cp3 is constantly pulling fuel so the bulb should never get hard. Double check that you didn't cross any fuel lines or mix up the supply and return on the cp3

The fuel vacuum test port is next to the alternator just to the left (passenger side)

 

[Black_Cloud]

Primer shouldn't be hard while running. Maybe look into that a little more. Filter housings have been a constant source of hard or no starts for the duramax, from cracked WIF sensor, bad seals and O rings, bleed screws or even cracked filter housing. Most lead to loss of prime or air getting in while running. The primer bulb should be, while the engine is off, be forcing fuel into the cp3. It should get hard once full because it is now having to push fuel out of the release valve which is set a about 75 psi. While the engine is running the cp3 is constantly pulling fuel so the bulb should never get hard. Double check that you didn't cross any fuel lines or mix up the supply and return on the cp3

The fuel vacuum test port is next to the alternator just to the left (passenger side)

Well hell, that's concerning it's not supposed to stay hard. Even with the lift pump it should soften up?

I'll double check the lines and put a vacuum gauge on it, I know exactly where that port is that you speak of.

 

[Awenta]

It will stay hard with a lift pump and any small leaks won't matter because you aren't losing prime. Vacuum won't show anything because with a lift pump you have positive pressure not vacuum.

I assume your filters have been replaced.

What kind of cranking pressure are you seeing? What injectors did you use?

Do a return rate test.


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[2004LB7]

Opps, forgot you had a lift pump.

 

[Black_Cloud]

It will stay hard with a lift pump and any small leaks won't matter because you aren't losing prime. Vacuum won't show anything because with a lift pump you have positive pressure not vacuum.

I assume your filters have been replaced.

What kind of cranking pressure are you seeing? What injectors did you use?

Do a return rate test.


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Good to know it should be hard with a lift pump, that's what I thought but questioned my understanding with what 2004lb7 said, I'm no expert on this stuff by any means lol

All filters replaced while doing injectors and HGs.

I used bosch remans from Lincoln diesel. Possible they are bad I suppose, but I'm skeptical of that because LDS has a good reputation in the community.

I haven't checked cranking pressures, I have no EFI or tech 2 software to do so. I know I need to do that. I'll try and track someone down who can hook it up to find out crank pressure and return rates. I'm sure that'll help you guys help me.

 

[Black_Cloud]

Opps, forgot you had a lift pump.

Lol no worries! I simply appreciate all the help trying to troubleshoot. Every little bit helps point me in the right direction.

 

[Black_Cloud]

Well, I think I may have found a potential culprit, in an unfortunate way. Was on my way back to work from lunch just now and I hear a pop and the truck goes into instant limp mode, and sounds like a kubota tractor. 12 trouble codes pulled. P0201, 0204, 0206, 0207 etc etc....so an electrical issue no doubt I'm sure. I'm honing in on the FICM connections, or connections at the injectors, would you all agree?

 

[danzick]

Could be. I was going to suggest getting a desired vs actual for rail pressure if you can.

 

[Black_Cloud]

Alright guys, I did find a loose fuel line and thought that fixed the issue, but it did not. Now it's intermittently stalling. Would a high return rate on the injectors cause stalling? I'm starting to get frustrated.

 

[2004LB7]

Yes, if the flow exceeds what the cp3 is capable of providing then it will drop the fuel pressure to the point of stalling. If it is that bad normally you would have a very difficult time getting it to start in the first place.

 

[Black_Cloud]

Yes, if the flow exceeds what the cp3 is capable of providing then it will drop the fuel pressure to the point of stalling. If it is that bad normally you would have a very difficult time getting it to start in the first place.

Sometimes it does have trouble starting, but it's random. At times it fires up like a champ, others it just cranks for a while then starts, and now it's starting to crank for awhile, start, then studder and die. Then it's back to starting just fine.

 

[WVRigrat05]

My returns were damn near wide open, a lift pump and a race plug masked it great.

I would do a return test on your cp3, that lift pump could be making the fpr stick open, but I could be way off.

 

[torqued2dmax]

I saw three posts just the other day that sounded like your problem. In one case it was the ficm not plugged in completely another the person touched the battery terminal on the ecm lastly,an ecm not fully plugged in .In each situation there was just enough contact to run ok sometimes and other times not. In all of these cases the problems started just after head gasket replacement.

 

[2004LB7]

I had a similar issue where the large bale connectors had a few pins not seeted all the way and was barely making contact. Couldn't figure it out for days. Then checked the pins and saw a few that looked shorter then the others. Pulled them out so thay where lile the rest and haven't had an issue since

 

[Black_Cloud]

Thanks for all your input guys. I'm going to give it one more detailed once over for loose lines, wires, pins etc, and if everything checks out, run a return rate test and see how that plays out. I'll post back the results. This truck is gonna be the death of me