Dmax Guru Needed EMERGENCY HELP!!!(Master dmax techs or pros please)

[blk smoke lb7]

http://m.youtube.com/watch?v=3LoPLqhxKBM. Could be a hung Injector this truck has 100 overs in it I believe but if you get a light mist out of any of the glow plug holes You most likely have hung injectors.If you can't build I believe it 1500 psi for fuel pressure the truck won't even fire.You also may have a bad fuel pressure relief valve which is the plug in the drivers side fuel rail in the back.If it relieved and did not reset squarely it will be cooked and relieving and making it hard to build pressure.

 

[Duramax One]

Start with the basics, pull the supply line off at the CP3 and make sure you have steady fuel there. This will sound stupid, but are you sure the CP3 lines got hooked up correctly? They didn't happen to reverse teh feed and return did they? The return is the one on top pointing upwards, and the supply is the one pointing rearward. If it has fuel to it, take the hard line off at the CP3 and see if fuel comes out. If no fuel comes out of the CP3 high pressure side or the return side, a piece of debris got into the supply line and when you hooked it up it plugged the FCA(regulator). If you have fuel there but not at teh engine then you have a kinked line or the popoff is hung wide open. In that case you neeed to do a bottle test on it. Start with the basics FIRST! Quit looking at control issues and unplug the FCA and eliminate any chance of something else affecting it.

+1

 

[DAVe3283]

Has anyone ever had ecm failure create these symptoms.

Not that I am aware of. The problem sounds mechanical.

Is low fuel pressure regulator duty cycle enough to keep it from starting?

The regulator is default open. The higher the current (high duty cycle = high current) the more it shuts off the fuel. So the ~15% duty cycle is good. The reason it isn't 20% is because the ECU sees there is not rail pressure, and is trying to compensate.

Has anyone ever had bad bosch cp3 or regulator?

It could happen. Honestly, the old CP3 probably should not have been replaced. The low rail pressure code could have been caused by something as simple as a clogged filter, or bad tuning (you mentioned it has switchable tunes).

im really at a loss with this truck. Great fuel up to back of new cp3 and no start.

Not to pile on you here, but are you 100% sure the fuel lines are hooked up right?

Another quick question can anyone post Key on engine off fuel data readings from a truck that starts and runs. like frpr duty cycle,desired mpa, fuel rail pressure.baro and maf voltages

I don't have a log offhand, but I can tell you what my truck does from memory (I've spent way too much time staring at logs...).
Desired Rail MPa: 35-50, depending on the tune, coolant temperature, and barometric pressure.
Actual Rail MPa: 1-3 MPa after sitting (this is just error in the pressure sensor, the real pressure is 0). Cranking it will rise to meet the desired very quickly (less than a second).
Baro: should match the actual barometric pressure, and should match MAP when the engine is off (or idling). Sea level is ~100 kPa on an ideal day, higher elevations may see ~80 (or less, depending on how high).
FPR duty cycle: My truck is so modded that my values are no longer relevant. The numbers you said earlier sound reasonable, though. I wouldn't worry.

(I think my readings are off and a 5v ref driver is causing my no start and no fuel) any info again guys is greatly appreciated.Thanks to all that have posted so far every little idea helps

I really doubt that a bad 5V reference is causing no fuel. Like has been said, unplug your FPR and look at the rail pressure. If you get rail pressure, then you can suspect an electrical problem. If you do not (which I suspect you will not), you have a mechanical problem.

 

[THEFERMANATOR]

The single best thing you can do right now is put the scanner down, quit thinking electrically, and start with the mechanical side of things. You have stated you barely had a trickle of fuel coming out of the rail when you disconnected a high pressure line. So you either reversed the fuel hookups, have a plugged supply line, plugged FCA, or somehow got a CP3 that is FUBAR. The ONLY use you have for a scanner right now is to monitor rail pressure while cranking. Unplug the FCA so there is NO electrical input influencing what is happening. And like has been said above, you will not be able to start it until it reaches roughly 1500 PSI as the injectors need a 1200 PSI pressure differential to pop.

I'm not trying to rub salt in the wound here, but step back and look at this with an old school approach. She aint gonna start without fuel and pressure, so you have to DIAGNOSE that problem FIRST. And throwing parts at it will only make the problem worse. Like was said above, you probably had a plugged filter, collapsed fuel supply line, or bad injector(yes LBZ's can have bad inejctors to) causing your P0087. Throwing the CP3 at it just complicated it since now you have to backtrace what work has been done as well as the origanal problem.

 

[07DuallyDmax]

I have re-installed everything and put the truck back to the way it should be and started fresh doing all of the test my self.. no more buddies. Pulled up the harness and got a clear view of the top of engine and i am 100% certain that the fuel pump is correctly hooked up.I was able to personally test for injector return with that kent moore tool and during cranking im not getting any fuel from the injector return into containers, but i am getting fuel out of the injector return hoses leading me to believe i have a bad or dirty fuel pressure regulator.(or im using the tool wrong.I am using the return hose clips to hold the adapter in the injector and the return line sits in the top of the adapter.During engine cranking fuel bubbles up out of the top area of the adapter.There are no clips holding the return lines in the top of the adapter and the ones that hold return line to injector dont fit the top side of the adapters)I was told by the dealership that the pump is almost without a doubt not bad due to the fact it is a bosch pump. I cant think of any other reason why i would have return but no flow to injectors other than bad fuel pressure regulator.When using the return tool, should there be clips to hold the return lines tight in top of the adapters I... dont know... im about sick of stinking like diesel fuel and ready to catch this truck on fire. I should have never taken his keys this all was def not worth it.

 

[meshanic]

A bad pressure relief valve could be returning fuel to the tank as well.

 

[07DuallyDmax]

I thought that also and pulled the hose off of the back of the drivers side rail and plugged the hose i removed.I installed a new hose on the rail and ran it into a container and its dry as a bone.I got this test from a place called kennedy diesel i assume there test is legit enough to trust.

 

[THEFERMANATOR]

You have yet to say if you did the basics. Check for fuel to the CP3 FIRST. Take the rubber line off and make sure you get a steady stream when you pump the primer. Next take the return line off and the high pressure feed line off. You should have just a small amount of fuel bypassing through the return line, but you should get a good spray of fuel from the high pressure feed port. If you don't then pull the FCA out of the CP3 and check it for being plugged. If you do get a steady stream of fuel then you have a kinked line or something blocking the CP3 feed line. Do all of this with the FCA UNPLUGGED. Until you start here anything else is a WASTE OF TIME.

 

[07DuallyDmax]

As stated earlier i have great fuel up to the inlet side of the pump,and with the rail supply off i have just a trickle.I haven't tried the pump return because i was unable to find a spec for what is good and what is bad.I have tried it now after reading the last post and with the fuel pressure regulator unplugged and with 3 seconds of cranking the pump returned 30ml of fuel. I'm guessing that's allot i don't know i don't have a spec.

 

[LBZ]

You have yet to say if you did the basics. Check for fuel to the CP3 FIRST. Take the rubber line off and make sure you get a steady stream when you pump the primer. Next take the return line off and the high pressure feed line off. You should have just a small amount of fuel bypassing through the return line, but you should get a good spray of fuel from the high pressure feed port. If you don't then pull the FCA out of the CP3 and check it for being plugged. If you do get a steady stream of fuel then you have a kinked line or something blocking the CP3 feed line. Do all of this with the FCA UNPLUGGED. Until you start here anything else is a WASTE OF TIME.

Basically what I said to do last night.
I doubt it is electrical due to the fact his RP sensor is reading so low.
He said he did do a fuel return test and had very little return. I'm assuming this was a bottle test.
Last summer my buddy had an Lbz that was doing the same thing. Replaced the cp3 still no start. Pulled the fuel return line off where it T's at the back of the d/s head and had almost no fuel there and very little pressure from the high pressure hard lines. Replaced the CP3 with another new one and good to go. So yes, new pumps can be bad out of the box.

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[LBZ]

As stated earlier i have great fuel up to the inlet side of the pump,and with the rail supply off i have just a trickle.I haven't tried the pump return because i was unable to find a spec for what is good and what is bad.I have tried it now after reading the last post and with the fuel pressure regulator unplugged and with 3 seconds of cranking the pump returned 30ml of fuel. I'm guessing that's allot i don't know i don't have a spec.

Is there any pressure in the outlet side of the CP3 pump when cranking. That is if you put your finger over it does fuel pressure blow your finger off and spray everywhere? If not you have the cp3 lines backwards, kinked, or your pump inlet is restricted or pump is f'd.


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[07DuallyDmax]

THEFERMANATOR stated i should pull the pump return off of the pump and only a small amount should come out.I was hesitant to perform this test because i had no spec of what is good or bad. Does anyone know what an ok amount should be.3 seconds of cranking got me 30ml of fuel is this good or bad? Also I found on this forum an old post about crank no start and "super diesel" said about testing Fuel pressure regulator for sticking "Yes. Turn the truck on and go to the reg plug on the cp3. Unplug it and listen if you hear the humming stop. you may hear a very slight click sound from the slide inside of it slap to the back of the reg. When you plug it back in the humming should continue." When i unplug mine it sounds like a single string of a banjo is plucked than it hums very quietly but no clicking again is this a valid test or is this normal.

 

[07DuallyDmax]

Spoke to fella at diesel performance shop and he has never herd of a fprv making the noise mine is.We spoke for a bit about the fuel pressure regulator and how it is controlled.He said "gm has a test where they want you to inspect koeo fprv duty % and if not at 20% suspect an ecm fault or wiring issue".He gave me some amperage readings and i used a low amp probe to measure current.My ECM was sending 400ma instead of the desired 64ma.After speaking with him again we concluded a shorted driver circuit in the ecm was allowing to much current to flow to the fuel pressure regulator valve which most likely has it shorted or damaged in some way. I'm in the process re looking my original idea of an ecm and going to be replacing the damaged fprv and replacing the ECM.

 

[07DuallyDmax]

I will be putting a used fuel pressure regulator on tonight to test the theory.I will not be plugging this one in to avoid damage.

 

[THEFERMANATOR]

Spoke to fella at diesel performance shop and he has never herd of a fprv making the noise mine is.We spoke for a bit about the fuel pressure regulator and how it is controlled.He said "gm has a test where they want you to inspect koeo fprv duty % and if not at 20% suspect an ecm fault or wiring issue".He gave me some amperage readings and i used a low amp probe to measure current.My ECM was sending 400ma instead of the desired 64ma.After speaking with him again we concluded a shorted driver circuit in the ecm was allowing to much current to flow to the fuel pressure regulator valve which most likely has it shorted or damaged in some way. I'm in the process re looking my original idea of an ecm and going to be replacing the damaged fprv and replacing the ECM.

Unplug the FPRV and take the control out of the equation. Don't look to the elctrical side until you verify the mechanical side. The FPRV WILL hum with the key on engine off, so noise from it is normal. Not everybody notices it, and not all do it, but don't be alarmed by it. The return of the CP3(the 1/4" nipple pointing upwards) should return no more than 2 onces(35 ML) of fuel after 15 seconds of cranking. This is part of the return rate test and outlined in the GM directions(don't know if it is included in other DIY write ups or not). If the FPRV(known as an FCA) is unplugged, then the ECM has NO INPUT ON PRESSURE. And if it is unplugged and you don't have pressure, then the ECM is NOT your problem. If you take the hard line high pressure line off at the CP3 and turn it over, and only get a small trickle of diesel, then I would suspect a plugged FPRV or bad CP3. If you want to rule it out, remove the FPRV and hold your finger over the hole and turn the engine over. Fuel should come flying out of the high pressure line doing this, if it doesn't your CP3 is bad.

The ONLY input the ECM has on the CP3 is the FPRV/FCA, unplug it and the ECM is out of the equation ENTIRELY. Also I don't know wehre you got the 64 MA of current to the FPRV, but the max flow calls for 400 MA which is the lowest current flow the ECM will for except under a low rail pressure correction condition where it can dip down a little lower while setting a code.

 

[07DuallyDmax]

I understand entirely the control the ecm has on the Fuel pressure regulator but if you read up again i have already done every test in the book 3 or more times and i have the same results every time.Fuel return and no pressure.The reason i am looking at the ecm is because i now believe the over powered Fuel pressure regulator circuit has shorted my brand new regulator.We will have a new/used regulator in shortly and i will update immediately after it does or doesn't start.

 

[THEFERMANATOR]

I understand entirely the control the ecm has on the Fuel pressure regulator but if you read up again i have already done every test in the book 3 or more times and i have the same results every time.Fuel return and no pressure.The reason i am looking at the ecm is because i now believe the over powered Fuel pressure regulator circuit has shorted my brand new regulator.We will have a new/used regulator in shortly and i will update immediately after it does or doesn't start.

Unplug the regulator then and the ECM has no input. If the ECM was to somehow over power it and supply it with full battery voltage, it would have burned out the coil and went full pressure, not no pressure. It was stated early on that as you send it more current it sends less fuel. So if you sent it so much current as to burn it out, it would default back to no current and supply all the fuel it could. And 400 MA is not overpowered, and by this very measurement proves the coil is not burned out(if it has current flow, that means there is resisatance which means the magnetic coil inside the FPRV is still good). Stock current can vary from 1550 MA for 0 fuel(full closed FPRV) to 400 MA for max stock flow. Normal current should be roughly 1200-1350MA at idle, and around 700-900MA at WOT depending on tune.

 

[Duramax One]

And 400 MA is not overpowered

My ECM was sending 400ma instead of the desired 64ma.

These are the FPR current values pulled from a stock LBZ tune. 400 mA is the lowest the ECU commands, and it corresponds to maximum flow to the injectors (minimal fuel return). Since your ECU was providing 400 mA it is functioning exactly as it should to build pressure quickly.

 

[07DuallyDmax]

Quick update. We did get the truck running last night but i was unable to leave a post i had to be at school early today. The amperage readings i posted are way off.. i was told to set the fluke to mv he didnt tell me id need to convert anything.The readings we pulled on the fluke were 400mv(i never converted to ma) so according to the tool (1mv/10ma) is 4000ma i guess thats bad.. going off of that chart posted idk. all i know is Once we got the regulator off we could clearly see it was stuck even when plugged in which would have been returning all of my fuel. I dont know what kind of damage over power did or what happened but today when im home ill have a new regulator from dealer to install and we are going to try and see if the ecm does the same to this used regulator if it does we will replace ecm or start looking for short to voltages of some kind.Thank you all to have hung in there as long as you did.This is an awesome community so far and without all of the ideas i don't think this truck would be running.

 

[DAVe3283]

Quick update. We did get the truck running last night but i was unable to leave a post i had to be at school early today. The amperage readings i posted are way off.. i was told to set the fluke to mv he didnt tell me id need to convert anything.The readings we pulled on the fluke were 400mv(i never converted to ma) so according to the tool (1mv/10ma) is 4000ma i guess thats bad.. going off of that chart posted idk. all i know is Once we got the regulator off we could clearly see it was stuck even when plugged in which would have been returning all of my fuel. I dont know what kind of damage over power did or what happened but today when im home ill have a new regulator from dealer to install and we are going to try and see if the ecm does the same to this used regulator if it does we will replace ecm or start looking for short to voltages of some kind.Thank you all to have hung in there as long as you did.This is an awesome community so far and without all of the ideas i don't think this truck would be running.

The regulator does not return excess fuel, it just blocks off the supply side. So excess fuel return is a mechanical problem with the pump, and is not influenced by a bad regulator.

Were you using a current clamp? Was the clamp rated for DC? Most current clamps do NOT read DC current. If those values are from a current clamp, I would not trust them.

A better way to get amperage: splice the meter in-line with the FPR. The 2nd best way (if you don't want to cut the harness, which I also hate doing): measure the resistance of the FPR with it disconnected, then measure voltage across it plugged in and functioning (key on).

The current is the voltage you measure divided by the resistance you measured with the FPR unplugged. I bet is it nowhere near 4 amps.

Glad you got the truck started, sounds like you are starting to make progress.