Engine wont start - no fuel pressure

mick

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Aug 15, 2006
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Forestdale. Brisbane.Australia
Off the wall question. Where is your ECM? Is it covered like it should be? If it is touching something metalic that might be the problem The housing must not be grounded. If it is all kids of weird stuff happen.

ECMs not touching anything John. Took the glowplugs out last night and cranked it - had fuel puff out of no 5. Tok it out changed heads on it and cleaned internals. Cranked again - no fuel coming out - put glowplugs back in cranked it - wouldnt start - hooked up efi - still only 200 psi. Im wondering if its not electrical.
 

JoshH

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Do you have another rail pressure sensor laying around? Maybe a wire shorted somewhere?
 

mick

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Aug 15, 2006
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Forestdale. Brisbane.Australia
The cranking actual fuel pressure you are seeing is in line. The problem is not the cranking pressure. Those pressures are usually in the lower 200's. It has got to be debris in the nozzles or an electrical connection problem.

There seems to be a conflict of opinion between whether there should be high fuel pressure when cranking the engine before it starts or not. You are saying its normal to only have app 200 psi when cranking the engine? Maybe you are right and if so that may not be the problem. Is there any reference available that can sort this out for sure? Thanks for your input by the way.
 

mick

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Aug 15, 2006
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Forestdale. Brisbane.Australia
Do you have another rail pressure sensor laying around? Maybe a wire shorted somewhere?

I have an LB7 but they have a smaller fitting. Otherwise I could pull the one out of my 05 I guess. mmm but I really would like to know the answer one way or the other on whether there is meant to be (4000) psi at cranking or not. Theres a big difference between 200 and 4000
 

JoshH

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Pull the IGN fuse on your 05 and crank it while watching rail pressure with the scan tool. If it build pressure while cranking, that should answer your question.
 

JOHNBOY

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Aug 30, 2006
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There seems to be a conflict of opinion between whether there should be high fuel pressure when cranking the engine before it starts or not. You are saying its normal to only have app 200 psi when cranking the engine? Maybe you are right and if so that may not be the problem. Is there any reference available that can sort this out for sure? Thanks for your input by the way.

Per the the GM service bulletin I have you need more than 10 MPa (1,450 psi) and 100rpm at cranking before it will fire.

The attached Doc is for LB7 but it maybe of some help.




Bluemax. It can cause no start and or rough idle and running. It will also throw communication codes like crazy. There is a good reason the housing is so sheilded.
 

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JoshH

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Ill have to setup efi on that truck. But your right.
No need to do anything truck specific to data log. Just hook it up, select your controller from the scan tool, and connect.
 

mick

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Aug 15, 2006
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Forestdale. Brisbane.Australia
Finally got efi to work in my 05. I disconnected ficu plugs and cranked it over and it shot straight up to 4000+ - so we can lay that one to rest about only having 200psi when cranking. So we definately have a fuel pressure problem but its looking more electrically related now.....
 

Mike

hmmm....
Feb 17, 2007
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San Angelo, TX
Here's basically how your fuel system works:

The CP3 has lift pump in the back, that is a fixed displacement gear-style, like an oil pump. This rotates at crank speed any time the engine turns. A regulator is mounted in the back near the gear pump, which closes when you apply current to it. When it closes, most all the fuel returns to the tank. When you remove current, some of the fuel goes into the 3 high pressure piston bores in the body. The crank in the CP3 pressures this fuel as it rotates at engine speed. The high pressure fuel goes out the metal line and into the rails, first the driver's rail, then a cross-over tube feeds the passenger rail (this contains a .75mm restrictor). HP fuel is now at all the injectors. When the injector gets power, it retracts the needle, and allows fuel to spray in the cylinder. When power is removed, the trapped fuel is allowed to go out the return line so the needle can return to the closed position. If one of the check balls is missing or stuck, the HP fuel can go straight into the return. This can keep the rail for any of the cylinders from reaching high pressure. Volume does not change, just where the fuel goes.

So far a leaky injector is possible. That injector has been replaced.

With the return to the tank disconnected lift pump on, only droplets come through. Turning the engine over nets no additional return through the line.
 

SmokeShow

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Nov 30, 2006
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I can't remember if you've tried cranking with the the fprv unplugged so the cp3 defaults to wide open?

If so, what was the result? If not, try it. :D
 

Mike

hmmm....
Feb 17, 2007
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San Angelo, TX
I can't remember if you've tried cranking with the the fprv unplugged so the cp3 defaults to wide open?

If so, what was the result? If not, try it. :D

Mitch we did try it but not after changing the possible leaky injector. Thanks for the remind.

And, how the hell have you been Mitch?
 

mick

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Aug 15, 2006
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Forestdale. Brisbane.Australia
Im going to put a new set of injectors in so we can eliminate that one and then go from there. Waiting on Guy at the moment as he seems to have a handle on them. I like the part about them being flow tested and balanced too. I'll be back soon. Thanks all in the meantime