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Discussion Starter · #1 ·
I'll try to keep this as short as possible without leaving any important details. Got a '13 work truck with about 190k. Use it every day pulling a trailer. Been running the same economy/two tune since I deleted four years ago.
Filled it up on Wednesday, ran it about 200 miles and serviced it on Saturday (a few weeks ago). Service meaning new oil and filter, new fuel filter and tire rotation. Same as I've always done. The only thing I did different was when I completed the service I didn't crank the truck for another 24 hours or so and even then I just let it idle for about 10 minutes. The next morning (Monday) it cranked normally, ran it for a couple hours (about 20 miles or so with some stops and idle in between) and when I slowed to an idle it shut down. Had a hell of a time priming and starting it. I figured just some air in the lines or maybe a bad fuel filter. Ended up leaving me at a stoplight later in the day. A guy pulled me over to a side street where I replaced the filter and still couldn't get it started. Drained the fuel from the old filter into a clear bottle and it looked fine. Had to call a rollback. I replaced the primer housing and it seemed to do a little better but still wouldn't start correctly. Called the rollback again and took it to the shop. My diesel guy got it primed and cranked. Connected the scanner and commanded rail pressure to 19,500. Everything else seemed to be ok. He parked it to the side to do some research. Every time he tried to crank it after that it did fine. Left it several hours, started fine. Left it over night, started fine. I picked it up that afternoon, started fine. We were thinking that maybe I pushed the air into the high pressure side during the one million times or so I pushed the primer and it couldn't get out until he commanded the rail pressure and it was forced out. For the next couple weeks it would start fine 80% of the time but every now and then it would turn over a couple extra times or maybe even turn over several seconds before it would start. I thought maybe as the fuel level in the tank got around half it was worse, meaning there's a problem in the tank, but I'm not fully convinced. Over the last week or so it had gotten worse. More often than not it would turn over several times before starting but I haven't had to prime it. On two different occasions I stomped it pretty good (without pulling a trailer) and it ran strong until it hit 5th then fell on it's face. On Monday I was pulling the trailer and a stoplight caught me on a little incline. I would call it a hill but keep on mind I'm in the coastal plains of NC so we don't have hills. Anyway, when the light turned green I started out and before I could crest the hill she fell on her face again. And that was normal driving, not giving it hell. It had about 5/8 of a tank at that time. Finally yesterday we had to prime it to get her started. Lots of air coming out of the bleed screw along with fuel. Drove it home pulling the trailer, about 10 miles or so, ran fine. When I turned onto my road I stomped it and she ran strong until about 60 then fell on her face again. Backed in the driveway and she shut down, havent been able to prime and start it since.

For those of you that skipped the BS and want the summary...truck ran fine, changed the fuel filter, not fine anymore. Replaced filter, same. Replaced primer assembly, same. Commanded high fuel rail pressure with computer, did much better but still not corrected. Starts without priming for a couple weeks but mostly turns over way more than normal. Fuel rail seems to run dry at high speeds or when high fuel level is needed. Pickup assembly in the tank bad? Fuel lines between the tank and filter leaking air? Lift pump? High pressure pump? Isn't there a check valve in the return line? If so, could it be stuck open? Idk. I'm thinking about ordering an Airdog or Fass and see what results from that. Not to fix the problem but because I'd like to supplement the CP4 anyway and I'd like the improved filtration and water separation. I think my next move is to disconnect the incoming line to the primer housing and replace it with a hose coming from a jug of fuel to see if the problem is before or after the filter. Any suggestions would be greatly appreciated.
 

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Derick, Once you get that lift pump installed we need to help you data log it and see what is going on. To me it sounds like the CP4 is not producing enough pressure to keep the rails loaded. We need to look at what is commanded and what is the actual rail pressure to understand better.
 

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Discussion Starter · #3 ·
Ok will do. The good folks at PPEI, who are very helpful btw, recommended the same thing. With everything that has been going on work wise I didn't take the initiative nor respond to their last message as I should have. I will do the data log and pass the info on asap. Thanks
 

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I'll try to keep this as short as possible without leaving any important details.
Followed by 43 lines of text as I scroll down.....
Cracked me up. :rofl
(like I'm known for short posts :rolleyes:)

While a small lift pump with additional filtration is a good mod, I would find the problem source 1st, lest you put a band-aid over it with a LP. (complicating later troubleshooting)

5/8 reading on the gauge, is actually below 1/2 level left. Supply problems at lower levels point to the tank, fuel module and/or the fuel line quick connect end attached to it.

Try to bypass the supply line feeding the filter, via the container you suggested. See if you can duplicate, which could be hard to do while parked, but even an improvement in priming ease and quicker starts says a lot.

It could be the fuel module is cracked (broke weld), but with age, that O-ring seal in the rear flex line quick connect can also be a common source for sucking air.

Most LP installs, require removing that flex line and replacing with 1/2" bulk fuel line, which eliminates that leaking seal. Afterwards, it's proudly proclaimed a success in a lift pump solving the problem.
When it was the supply line swap that fixed it.

If it is the fuel module, adding a LP will just have it sucking air still. (see-complicating later troubleshooting above)
Then you could be wondering why the pump is so noisy at lower tank levels, leading you to pursue cutting a hole in the tank bottom for a sump draw point.

Bigger bandage over the not found issue, but a solution nonetheless.

Test with the aux container. You could still have a leak at the filter head (not all areas are serviceable with a rebuild kit).
Then test with a full tank.
At the lower (below 1/2) level, add some air pressure.
You can assemble some things from the plumbing aisle, and apply (no more than 5-6psi) pressure to the tank fill nozzle, helps to locate a then positive pressure air leak at the tank top fuel module, or that supply line connection to it.



Have you been running a fuel additive for those 190k miles?
Hopefully it's not the beginning of a CP4 suicide blow. 'uhNo
 

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Discussion Starter · #5 ·
Yeah I was thinking of the contradiction as I wrote my small novel. But you never know what minor detail may raise a flag to someone with more experience.

Nice little test rig you built there, Horns. Looks like something you don't want to get caught with at the airport. I think I'll copy that and do just what you said. Gonna go ahead with a data log as well.

I'm kinda weird about fuel additives but to again contradict myself, I have added a half quart of ATF into a full tank of fuel at service on a few occasions. Makes me feel like a convict knowing I have red fuel in the tank. For those of you in SF, by "convict" I meant "justice involved person". Or would anyone from SF even be on a diesel forum?

Anyway, after a work-filled day I wasn't able to make any progress with the truck but plan to over the weekend and will post accordingly. Got a neat Airdog 165 on the way courtesy of Synthetic Motorsports and a small loan from my mom. Maybe she'll pay for a CP3 conversion as well! Thanks again Willie
 

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Just prepare yourself with any 150/165 liftpump they are well know for 1/3 - 1/4 tank issues and higher than recommended fuel PSI for the Duramax, which is 8-10 psi.
The fix has been having to install a sump, if you don't mine drilling a big a$$ hole in the bottom of a perfectly good fuel tank, you'll be ok.
If your liftpump your getting has a PSI adjustment, you should be ok, but you'll need to check the PSI to know so you can adjust it properly.
Installing a sump to correct the surging issues will NOT reduce the fuel PSI to the engine.

Everyone I know, including me, that installed a 150/165 had no less than 12 psi idling that put the effort out to check the fuel PSI, mine was 12-13 psi with no adjustment and had the 1/3 -1/4 tank surging issues.
I ended up changing my 4G165 motor out for a 4G100 motor 8-10 PSI and no more 1/3-1/4 tank issues.

FYI, a FASS 95 and AirDog 100 both are good enough for up to 600hp, this 500hp claim is for pushing larger LP's so you can buy more stuff, borrow more money if you have these problems mentioned above.

The ATF theory was with the much older diesels after about 2002-2003 that idea was shelved.
You need to use a actual diesel fuel additive which is safe for todays diesels.
I like Diesel Kleen but there are many other good products.
 

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Discussion Starter · #9 ·
Well good news so far...replaced the incoming hose from the tank to the filter housing with a hose from a jug of fuel. Got a stream coming through the bleed screw (not frothy like before) closed it up and got it to prime and start. Tried it several times since then and has started correctly every time. Tomorrow morning I will pressurize the tank and see if I can find a leak. Hopefully it won't be in an impossible place.
 

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Discussion Starter · #11 ·
Then I plugged them both and put 5 psi on the tank. Air is coming from the area shown. Now I know any tank needs a vent, but I assumed the only vent is in the fuel cap. It almost looks like there should be a hose on this piece but I've never taken a look at it before. Keep in mind I have a Knapheide service body and not a regular pickup bed. The vent shown is attached to where the overflow hose comes in from the fill nozzle.
 

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1/2" supply
3/8" return
 

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Discussion Starter · #14 ·
Well it's been a battle but I found a leak and what I hope to be the culprit. GM part number 12645582 shown in the picture below. Not gonna be easy to replace but could be worse and thankfully isn't expensive. Apparently it's a low pressure return line to the fuel rail. This doesn't make sense to me. The hard line coming from the tank turns up in front of the firewall right by the steering shaft, switches over to a hard braided flex line then back to metal and through a clamp (actually both 1/2 supply and 3/8 return do the same thing) but then the supply switches over to the rubber hose that has the split in it and it ties into the fuel rail. That would mean unfiltered fuel from the tank is going straight to the rail. I know that isn't the case but I can follow the line directly and that's what it's doing. Someone please explain so I'll understand what I'm replacing instead of just replacing it.
 

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There's a shared junction, but the two remain separate flows I think.
 

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Discussion Starter · #17 ·
Hmm, ok. I removed the incoming line at the fuel filter and plugged it. Then disconnected the supply line at the red arrow and applied low pressure air at the blue arrow. That's how I found the leak. But I was thrown because I knew unfiltered fuel doesn't feed the fuel rail. The shared junction helps to explain that.

Now I'm wondering if the split hose is actually causing the loss of prime issue. Seems like if it's a return line then the answer would be no but if it shares a junction with a low pressure supply line then maybe yes. Also, just because it leaks with positive air pressure doesn't necessarily mean it will leak with fuel being drawn through it. We'll see I suppose
 

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Discussion Starter · #18 ·
New hose should be in today. Hopefully have some time to work on it this evening. I need to remove the part shown in this picture to get to the hose clamps. What is this? I'm assuming it's part of the EGR cooler. I removed the three bolts and broke it loose but it was connected internally somehow. I decided to do some research to figure out what I'm getting into but haven't had much luck. You can spend hours reading online looking for something and it may get you nowhere. I hate to ask every time I don't know about something but I don't have time to sit around with my nose in my phone all day. Is it time for a EGR cooler delete? I've been thinking about doing that anyway. Coolant tank is smoked on the inside and I'm thinking the EGR cooler may be leaking exhaust into the coolant, thus smutting up the tank. Is smutting a word? Anyway, if someone could answer this for me or help me find a "emissions system 101 for LML" tutorial. Thanks
 

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Discussion Starter · #20 ·
Not having my primary work truck on the road this long is killing me. Thankfully the ol LLY has been pulling me through. Replaced the return line and pressurized the system like before and now she's holding air. Started feeling better about the situation. See pic below for future reference if someone is having the same issue.
It was taken with my phone positioned where the AC compressor would normally be (removed it for FPR replacement).
 

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