lb7 low rail pressure

[Yellow Jacket]

I have a 2002 lb7 that has a 1093 low rail pressure and a regulator performance codes... I hooked up efilive and rail pressure is nearly 10,000 psi. I rev engine and rail went up, still above commanded. FPR is clearly bad. I command 160 MPA at idle, stays at nearly 10,000 psi. So I assumed injectors were returning excessively.

I tore into it to perform the correct bottle test, I have a banjo off each head and from cp3. I ran the truck shortly, 20-30 seconds and had 16 ounces from cp3 and not really measurable from each injector bank. And nothing from the relief valve. I disabled injectors and cranked for 15 seconds, 4 ounces of fuel from cp3, and hardly drips from each injector bank.

I searched and searched, I cannot find an allowable leak rate from cp3?

 

[IOWA LLY]

Sounds like the regulator is stuck in one position.

Sorry, I don't know the return spec.

 

[Yellow Jacket]

Sounds like the regulator is stuck in one position.

Sorry, I don't know the return spec.

Thanks, I was assuming that also, but I hate to put a $225 for on it Just to find it needs a pump after that.

 

[Brent@LDS]

Let us know if you need any parts. We stock the LB7 fpr for $188.

 

[jacobdewey]

I had a bad FPR that was stuck at 9k. Switched it out and away I went!

 

[onebaddmaxxx]

Take the fuel filter off and fill it with transmission fluid and reinstall. Seen it get rid of surgey regulators and help balance rates. ATF is very lubricative.

 

[Yellow Jacket]

Switched out FPR, idles at desired now, still only makes 14,000 to 16,000 psi at idle, rev it to 1250 rpm and it will make 22,000 psi...

Must need a cp3.

 

[IOWA LLY]

How many miles on the truck?

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[Yellow Jacket]

How many miles on the truck?

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25x,xxx miles, I've honestly only ever seen 2 failed cp3's before, one was a less than 20,000 mile 85% industrial injection POS, other was an over 200,000 mile lb7 and it would do really flakey things. I'm pretty hesitant to put a cp3 in anything, lol. My little brother's '06 DMAX has 335,000 miles and will hold 21,000 rail pressure on a 535 hp race tune with no lift pump, lol. I think the only reason it doesn't maintain is the injectors are, I'm sure returning a little excess fuel from wear...

I just don't see them fail enough to assume it could be the problem...

 

[THEFERMANATOR]

If you do some searches you will see 01-02 trucks seem to lose CP3's around 200K miles. I know I was warned to do mine, and didn't. Well at 200K miles mine started getting hard to start because the CP3 had failed. And the return spec for the CP3 is 1.8 onces(25ML) IIRC(I'm not 100% on what it is, but it shouldn't return much).

 

[Yellow Jacket]

If you do some searches you will see 01-02 trucks seem to lose CP3's around 200K miles. I know I was warned to do mine, and didn't. Well at 200K miles mine started getting hard to start because the CP3 had failed. And the return spec for the CP3 is 1.8 onces(25ML) IIRC(I'm not 100% on what it is, but it shouldn't return much).

I'm getting 4-5 ounces in 15 seconds of cranking, and 16 ounces with 15-20 seconds of running...

 

[Yellow Jacket]

If you do some searches you will see 01-02 trucks seem to lose CP3's around 200K miles. I know I was warned to do mine, and didn't. Well at 200K miles mine started getting hard to start because the CP3 had failed. And the return spec for the CP3 is 1.8 onces(25ML) IIRC(I'm not 100% on what it is, but it shouldn't return much).

This one is starting right up when cranked, I've done injectors on multiple trucks that started hard and had insane fuel return from injectors, and one lb7 with a leaking relief valve, I was expecting injectors on this one when it wouldn't make 23,000 rail pressure at idle.

 

[catman3126]

Just did one on a 02 and it was return alot of fuel but had not hard start issue. it would only run 5-6k going down the hiway. changed it out yesterday and its all good now.

 

[IOWA LLY]

Pumps are kind of a crapshoot. Ive seen stock one's fail at 90,000 miles. Some strong at 200,000+.

Bad fuel, filter maintenance, poor quality filters, and running them dry by running them out of fuel all play a big role in pump life.

Regardless, I wouldn't waste the money on a regulator on a high mile pump. For the money difference between just a regulator and a whole new pump, and the amount of labor involved to swap either one I would always recommend a new pump on a high mile pickup.

Glad you found the problem at least.

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[THEFERMANATOR]

I went and rechecked my notes, and the CP3 return spec is 1.2 onces or 20 ML for 15 seconds of cranking with the injectors disabled. Anything more and it means the rings in the CP3 are shot and it is just pumping the fuel out the return instead of to the injectors.

 

[Yellow Jacket]

I went and rechecked my notes, and the CP3 return spec is 1.2 onces or 20 ML for 15 seconds of cranking with the injectors disabled. Anything more and it means the rings in the CP3 are shot and it is just pumping the fuel out the return instead of to the injectors.

SWEET!!! That's what I was looking for and now it's a permanent note in one of my own threads to look back on! I couldn't find an amount of allowable return on ShopKey or Google searching. Thank you very much!

 

[Yellow Jacket]

Pump fixed it, I could freewheel old pump with little or no resistance unlike other used pumps and the new pump, it spikes to 24,000 psi and runs at 160 Mpa at idle now.

 

[minerigger]

Glad your up and running

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