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Discussion Starter #1 (Edited)
A couple of things,
if you are not an Experienced Diesel Technician PLEASE DO NOT respond to this thread I need real help, I sorry if this offends you.

If you are using an Acronym please do so like this eg; FICM (Fuel injection control module) I'm not a mechanic and do not know what most of them are reffering to.

Second I apologise for being so long winded.

The first time this happened was 2 years ago. Coming back from a golf trip. I was in a hurry and pushing the truck pretty hard about 95mph to 100mph. All of a sudden it fell on its face, started chugging and I couldn’t get more than 2000 rpm out of it. It went into limp mode, I guess. After pulling over and letting it sit for a few minutes it cleared up.

Last winter it happened again. This time it was a couple of things going on. I was out in Alberta and it got down to -30C. The truck wouldn’t start even after being plugged in overnight. It seemed like it wasn’t getting any fuel, (just cranking over and not firing) so I primed the fuel filter pump, and it fired right up.

Then on a fishing trip up into the mountains around here it happened again. It fell on its face and I couldn’t get any power when I stepped on the accelerator and couldn’t get more than 2000 rpm.

So I pulled over and primed the pump again, this seemed to clear it up. It happened several more times and each time it was around -15C. Thinking that the pump was losing prime because it was sucking in air, we changed the o-rings on the pump, again this seemed to do the trick.

I have learnt that it needs a new glow plug module. (the second part of the problem)

Last week like a fool I ran out of fuel. After putting some fuel in the truck and priming the pump it fired up. I took it down and fuelled it up.

The next morning I drove into my shop and it seemed fine, but after I hooked onto my haul trailer and got down the road a few miles it started doing it again. Thinking I didn’t bleed all the air out I primed the pump again. It didn’t work this time and I took the truck back and unhooked the trailer.

Now this is what has been done since then.

Fuel filter changed – Twice - the second shop changed it after I already did!!!
Codes reset and injectors bled (So they say) The injectors didn’t look like they had been touched so I it took it to another shop.

This shop tried a FICM (Fuel injection control module) That didn’t work
Then he tried a ECM (engine control module) that didn’t work
Also this is one code he pulled off the truck; P1093, Fuel Rail Pressure Low During Power Enrichment. He did also get the P0670 for the glow plug module.

Then after talking to his “source” they figured it had to be the Fuel pressure regulator. He said they were 90% sure it was the problem! So he changed that out, took it for a drive and could not get it to go into limp mode and called it fixed. This was this past Saturday Sept. 24. I picked up the truck and brought it home.

Monday morning I drove into town to my shop, which is about 30km away, then I drove back home and picked up my helper and we were on our way to do a pick-up about 45 km away in another town. We got 12km down the road and the truck went into limp mode again. No power, chugging and won’t go past 2000 rpm. WHAT THE F&@K

Now I had to break down and take the truck into the stealership. I have to get a proper diagnosis and get the dam thing fixed I depend on it to run my business.

They had it for a couple for hours and got the same codes off of it that the other guy did. P0670, and a low fuel pressure code ( I’m not sure if it was the P1093 code or not). They called me and said they “thought” it might be the Fuel Rail Pressure sensor, but they weren’t positive because they couldn’t get the truck to recreate the problem. I told them that they need to take it for a long drive and make it work, and it will happen. So they have it overnight and I’m waiting.

The past few nights I have spent hours searching this forum and some others for answers. No one seems to know the correct solution. Is there ANYBODY out there that can lead me down the right path? I'm into this for over $1000 so far and it is not fixed :mad:

:help PLEASE

here is my sig.
__________________
2004/5 2500HD GMC Seirra 4x4 SB Crew
Stock Truck No Mods, 6.6 LLY Duramax
 

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I will help you out a TON here so you can get some help from one of the many diesel guru's here.

FILL OUT YOUR SIGNATURE WITH ALL RELEVANT INFO ABOUT YOUR TRUCK

YEAR, MODS, If it is a by year like 04/05 , 05/06 , 06/07 List what your 8th Vin number is so the person can identify your engine.


Do this and you will get much much MUCH more help.
 

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Sounds like a leaking FPRV Fuel pressure relief valve if it is a 2004.5 to 2011. The spring gets fatigued and needs a shim kit to correct the pop off pressure. What is your fuel pressure doing when it limps and what year is it?
 

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Discussion Starter #4
I will help you out a TON here so you can get some help from one of the many diesel guru's here.

FILL OUT YOUR SIGNATURE WITH ALL RELEVANT INFO ABOUT YOUR TRUCK

YEAR, MODS, If it is a by year like 04/05 , 05/06 , 06/07 List what your 8th Vin number is so the person can identify your engine.


Do this and you will get much much MUCH more help.
point taken thank you
I enterd everything except the 8th number of my Vin, it is with the truck which is in the shop. When I get it I will add it. The truck is a 2004/5 with the LLY engine
 

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Discussion Starter #5
Sounds like a leaking FPRV Fuel pressure relief valve if it is a 2004.5 to 2011. The spring gets fatigued and needs a shim kit to correct the pop off pressure. What is your fuel pressure doing when it limps and what year is it?
Yes the truck is an 2004/5, from what I've been told the fuel pressure drops when in limp mode, dumping excess fuel back to the tank. When driving, if you put your foot into it then it goes into limp and the pressure drops from say 150 to 60
 

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I don't wanna say that I'm 100% without knowing all of the codes...but it sounds like it could be the darn fuel temperature sensor. If they went the usual route of replacing the Regulator, testing the injectors, checking the FPRV and it still isn't fixed, the rail pressure sensor and the fuel temp sensor are the next things to look at.
 

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Yes the truck is an 2004/5, from what I've been told the fuel pressure drops when in limp mode, dumping excess fuel back to the tank. When driving, if you put your foot into it then it goes into limp and the pressure drops from say 150 to 60
It is your FPRV, fuel pressure relife valve. It is a common issue with LLY's. The truck is commanding 23,000 at wot and limps if actual fuel pressure drops below 18,000. Buy a fprv shim kit for 10 bucks and it will be fixed.
 

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I don't wanna say that I'm 100% without knowing all of the codes...but it sounds like it could be the darn fuel temperature sensor. If they went the usual route of replacing the Regulator, testing the injectors, checking the FPRV and it still isn't fixed, the rail pressure sensor and the fuel temp sensor are the next things to look at.
Look at these two sensors if your truck fails the bottle test. Fuel temp sensor can cause some very similar issues.
 

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This is a common problem for most LLY engines---On the passenger side of the alternator, you will find the FICM wire harness-- it is tied down with a Zip tie--- cut the zip and pull the wires from the wire harness-- inspect carefully for cuts and bare wires. The sharp corner of the bracket it is tied down to, cuts into the wires and causes shorts. This may not always throw a code.

Insulate with a piece of heater hose, to prevent further problems.

Common problem for a 4.5-- 5 LLY engine. Everyone with a LLY engine should do this easy fix NOW!
 

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point taken thank you
I enterd everything except the 8th number of my Vin, it is with the truck which is in the shop. When I get it I will add it. The truck is a 2004/5 with the LLY engine
You don't need the 8th vin number if you know for sure its an LLY

I just say that for the ones who don't really know which motor they have in their trucks on those weird by/half years
 

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Discussion Starter #11
Hey Guys, thanks for the ideas.

Well there goes another $224 bucks and I STILL don’t have a definitive answer to what my problem is!

I spoke with the tech that drove the truck home last night, he couldn’t get it to go into limp mode. He didn’t stick his foot into it either. He did have his scanner hooked up and did say the fuel pressures were out to lunch. The codes that came up were; P1093 and P0670 (I know it needs a glow plug mode)

I had no problem getting it to happen after I picked up the truck. I took it straight back to the technician, all he did was drive it around their lot and he could see what was happening. No he didn’t hook his scanner up. He said “ going from his experience” that he was pretty sure it was the FRPS “fuel rail pressure sensor” that was causing the issue.

The service guy and the tech both say I should replace the FRPS. But they can’t say that for sure 100% it is going to solve my problems.

The tech did check the wiring harness for the FICM and the main engine harness connector (he did find chaffed wire there) All the wiring harnesses are OK, and were not causing the problem. I will add the piece of heater hose myself.

He installed a vacuum gauge and ran through the fuel system diagnosis, everything was OK. He said fuel pressure ramped up OK. But the truck was NOT in limp mode either. He also check all fuel lines for leaks and kinks, there were none.

Both the tech and the service guy think I should replace the FRPS, but what IF it’s NOT the problem? Then I’m out another $500 bucks and still haven’t got it fixed. They aren’t 100% sure it is the problem. WTF is up with that, the GM dealer can’t give me an answer either!!!

I’m not prepared to spend another $500 on a part that MIGHT fix my problems.

What is the bottle test? I read about it in another forum but it was for an LB7 not the LLY, and it was a little sketchy. Is there a clear explanation of how to perform it, are there any pics to follow along.

Also where can I buy “Buy a fprv shim kit” if I need one?

Thanks for the advice fellas, it’s greatly appreciated
 

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You can get an fprv shim kit at any vendor on this forum. Just post in the vendor jungle, I want a fprv shim kit.

I can almost garnantee this is your issue. the shim kit is 10 bucks and is very easy to install. Just go to PPE's website and download the instructions for the shim kit instsall.

When the spring is fatigued it only has issues after you drive it for a bit over 55 then jam on it to pass or catch up to traffic then it limps.

The bottle test is easy, google it. Duramax FPRV bottle test. You hook a piece of hose to the fuel return to see if it is poping open.
 

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Discussion Starter #13
You can get an fprv shim kit at any vendor on this forum. Just post in the vendor jungle, I want a fprv shim kit.

I can almost garnantee this is your issue. the shim kit is 10 bucks and is very easy to install. Just go to PPE's website and download the instructions for the shim kit instsall.

When the spring is fatigued it only has issues after you drive it for a bit over 55 then jam on it to pass or catch up to traffic then it limps.

The bottle test is easy, google it. Duramax FPRV bottle test. You hook a piece of hose to the fuel return to see if it is poping open.
Thanks Smokilmm,
I did as you said and Googled the bottle test, after reading a through a few of the links I found 1 that made sense. I got the installation guide for the shim kit from the PPE site. I will put it to the test tomorrow. I guess if it fills the bottle then I need the shim kit is that correct?

Thanks for your help, this sounds a hell of a lot better than a $500 fuel rail pressure sensor!!
 

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I guess if it fills the bottle then I need the shim kit is that correct?
Yep, if there is any fuel in the bottle you need to shim it. When you go to test it, take it for a drive and then jam on it repeatedly to reproduce what it is doing when it limps out on you.
 

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Let me know what the bottle test shows. I have another thread "2000 max RPM" where I am having the exact same issue. I have not had a chance to do the bottle test yet but hope to tonight or tomorrow night. I will be very interested in your results. I will post mine as well as soon as I get a chance to try it out.
 

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Discussion Starter #17
smokinlmm,
Another question,
If the FPRV is leaking, will the fuel pressures be all over the place even when the truck isn't limping?

I ask because when the Tech drove the truck home he couldn't get it to limp but said the fuel pressures were all over the place.

Quantum673,
I'm doing the bottle test today and I'll post my findings along with the copy of the bottle test procedure that I found, it was a lot easier to understand than most I had read.
 

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smokinlmm,
Another question,
If the FPRV is leaking, will the fuel pressures be all over the place even when the truck isn't limping?

I ask because when the Tech drove the truck home he couldn't get it to limp but said the fuel pressures were all over the place.
Yes, if it is leaking bad enough the pressure will be very erractic. They can get so bad the truck won't even start, that is what happened to Tyler Meyer of Meyer Performance.
 

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Sounds like a leaking FPRV Fuel pressure relief valve if it is a 2004.5 to 2011. The spring gets fatigued and needs a shim kit to correct the pop off pressure. What is your fuel pressure doing when it limps and what year is it?
X2 mine limped all the time, it was tuned but limped, put a race plug in and I cannot get it to limp. Basically the truck is not getting the proper fuel rail pressure, and theres only 3 things that limits that. fuel rail pressure relief valve, which is usually what causes this on the 04.5-05 LLY engines, cheap fix, or your injection pump (cp3) not your case, and fuel press. regulator. but if your getting a glow plug control modual code, the module controls both the injectors and the glow plugs. if it were me I would start with the cheapest part, the fuel rail press. relief valve. you can plug it, which will never wear out, but some claim it can cause injector failure, I havent seen it but they say it can, I m running one. the other is a shim kit , it allows for more pressure to build before the relief valve opens so you dont get the code but they get weak over time and cause the same problems. hope this helps.
 

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Discussion Starter #20
Well my FPRV failed the bottle test miserably!! I didn’t even have to take the truck out on the hi-way. As soon as I got to a small hill I stepped on the accelerator and as soon as I reached 2000 rpm the fuel came rushing into the bottle. I secured my bottle in the lower left side of my windshield so I could watch it. Got some pretty strange looks LOL.

I guess my next step is to get a shim kit.

From looking at the shim kit instructions, is the FPRV located underneath the glow plug module?

I found this version of the test VERY easy to follow, it took me about 10 minutes to set it up once I got my act together. Very easy!!

Bottle Test
This test can be used to aid in troubleshooting a low fuel rail pressure condition when other things such as clogged fuel filter has already been checked.

This will check to see if your Fuel Pressure Regulator Valve is allowing fuel to be sent back to the tank rather than holding the pressure in the rail.

Pop bottle, 5/16" fuel line 3-4 feet, 5/16" bolt less than 1/2" in length, I used a ½” drill bit for the hole in the bottle cap, with a little reaming (Not too much) I got a nice snug fit.

Drill a hole in the bottle cap and stuff the line through.

Go to your driver-side fuel rail using needle nose pliers disconnect, the hose that’s on the end of the fuel rail, and then slide off the clamp.

Put the 1/2" bolt into the end of the line you just removed, to keep fuel that may be in there from running out.

Take the clamp you removed earlier and slide it on the 5/16" bottle test fuel line, then take the line and slide it over the barb that you exposed by removing the return line on the end of the rail, slide the clamp down to secure the line.

Secure the bottle somewhere out of the way, and there you go, I filled a 20 oz soda bottle halfway full in 1 run so I’d recommend a run or 2 and then check your status.

When you go to test it, take it for a drive and then jam on it repeatedly to reproduce what it is doing when it limps out on you.
 
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