LB7: Hard start when cold?

briencolgan

brien colgan
Jan 26, 2017
61
0
0
Ithaca, NY
Good morning all. I’m using starting fluid to get this old thing going most mornings. Even at 30 deg and up. I was wondering if you could take a look at this graph and see what you think. It looks like a bad fuel pressure relief valve or fuel pressure regulator. I know I have a bad injector #4 balance rate is -6.

But I think there are other problems. This started as a cold-weather issue and I thought it was glow plug related so I replaced that relay. But I think the cold weather might just be a coincidence because it’s almost 50° here today and still tough to start. It seems to start a little easier in the mornings if it’s nosed downhill.

I have attached a video. The first part is just the truck starting and running. And then after a bit I commanded cylinder four on for power balance. Does that command turnoff that injector?
Whether it command it off or adjusts its flow it smooths out the idle.

I also commanded off the FPR which seems
To lengthen that janky actual fuel pressure wave.

I just wanted to get some input from some more seasoned mechanics. I was thinking it was time for a new cp3 because I repaired the fuel pressure relief valve. And replace the fuel pressure regulator. But it could also be that that repair I made is not holding.


https://youtu.be/srRsBxGvrvw


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Last edited:

2004LB7

Active member
Dec 15, 2010
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I bet its the injectors but wouldn't rule out the regulator either

The relief valve is mechanical only and rarely go bad on the LB7, at least not anything that will effect starting and idle.

Have you done any basics like return rate tests for the injectors or CP3? Check for leaking injectors with glow plugs removed? Etc?
 

briencolgan

brien colgan
Jan 26, 2017
61
0
0
Ithaca, NY
No haven’t run those tests yet. I am planning to later when I get this truck home.

All the injectors are within spec except #4 which is at a -6 on the balance rates.


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2004LB7

Active member
Dec 15, 2010
2,473
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38
Norcal
Balance rates wont show anything related to return rates. And with the engine loping like that I wouldn't trust the balance rates either

Maybe just replace the regulator and go from there if it continues