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Crank no start LB7

W

wastefarmer

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I'm the owner of an 03 2500 HD lb7 California emissions truck. Only 107,000 MI. Had a crank with very hard start when I bought it figured it was the hand pump housing. Deleted the hand pump housing put on a FASS. Seemed to help just a bit.
Sent to my mechanic who did the fuel bypass test for the lb7 which showed injectors in spec but CP3 was out of spec so we replace the CP3 with the fuel pressure regulator. Also replaced the fuel pressure sensor fuel pressure relief valve. Replaced all the rubber lines. Getting plenty of fuel to the Schrader valve with no air visually.
Fuel rail pressure cranking is only 500 or 600 lb at about 25,000 lb running with the new CP3 which is a bit low but not much. Power good idle is good no smoke. Runs smooth as a kitten once it started. The only way it will start is with the puff of either. Cracking speed is good and in spec.
My mechanic says since the scanner says desired fuel rail pressure at cranking is 5,000, that this says that all the sensors are telling the CP3 to deliver that so the crankshaft sensor or the camshaft sensor should be good and that the wiring should be good (and connections). Remember the actual fuel rail pressure is 500 or 600 lb.
MY QUESTION IS: IS HE CORRECT on the scanner?
 
Hello WF, I know knottt one thing about the LB7 and just wanted to throw in a post to welcome You to the forum.
There are some that is a lot smarter than I on such that matters with these trucks and I am sure that they will het in and reply after they start awakening in a hour or six.
 
I know the risk with the glow plugs and ether. That's why I'm not driving it.

Any thoughts on what my problem might be? Did you see what all I've done to it?
 
Yes definitely. Do you have any experience with scanners? my mechanic tell me if desired is 5,000 on rail pressure at cranking that everything else is okay it should be a fuel problem however we've done everything related to fuel other than putting injectors in when the return rates show that they're fine. Do you have any experience with scanners and diagnosis to know if he's right or not I've seen cam sensor and crankshaft sensor as possible problems however he says the scanner says that it's fuel not electrical he says all messages are being sent correctly to the CP3.
 
Cranking rail pressure should be 5000psi or higher. Any lower and you will have starting issues. You already replaced everything so im leaning towards over returning injectors. What are your return specs? Cranking specs are 3ml per injector at 15 seconds of cranking.

Also balance rates at low rail pressure will lie to you. I ramp up rail pressure to 20k and check balance rates. You also have to look at the fuel rate to determine the correct balance rates. There is a great write up on here about it.
https://www.thetruckstop.us/forum/threads/proper-way-to-check-balance-rates.41579/
 
Thanks for your quick reply. We did check the injector balance rates by pulling off of valve covers my mechanic did it so I'm not sure exactly the procedure but each injector was checked. All the injectors showed in spec. CP3 did not so we replace the CP3 all the sensors all the regulator the fuel pressure relief valve getting plenty of fuel at the Schrader valve on the front of the engine no Air have not done a vacuum test from the tank although the fast pump was pumping fuel well. Did you see my question on the scanner as to desire being 5000 actual being 5 or 600. My mechanic says since it says desired is 5,000 that all the sensors and electrical connections are correct and undamaged and the CP3 is being given instructions to furnish 5,000 lb. Is he correct or do you have experience with a scanner and electrical problems or sensor problems?
 
Injector return rates not balance rates is what we checked although the balance rate look perfect on the scanner.
 
I read the article seems like a good article but it's kind of over my head.
Question since we did the return rate test on the injectors and the CP3 the return rate test trumps the balance rate reading correct? I don't know the return rates but they were well within specs on the injectors but the CP3 was out so we replace the CP3 and the regulator all the sensors and the relief valve.
 
Common rail injectors need at least 1200 psi to function, PERIOD! Anything less than 1200 psi and they cannot open. 5000 psi is the desired, but actual is the important number. You say your only getting 500-600 cranking, so that is why it will not start on it's own. Low rail pressure during cranking is either a grenaded cp3 or bad injectors returning to much fuel.

You say he did a return rate test, how much fuel were the injectors returning? Factory spec is confusing as they say 3ml for each injector, but no more than 10 ml per bank, or 20 ml for both banks(and 20ml return WILL cause an extended crank time). Either you're sucking air or bleeding off fuel pressure to cause low rail pressure during cranking. You're going to have to find out where the fuel is going during cranking to not allow it to build rail pressure.
 
Actual and desired fuel pressure must match. If it dosen't you have a issue somewhere.

Lb7 injectors have an extremely high failure rate. Thats where I would focus my attention and double check your injector return volume.
 
THEFERMANATOR said:
Common rail injectors need at least 1200 psi to function, PERIOD! Anything less than 1200 psi and they cannot open. 5000 psi is the desired, but actual is the important number. You say your only getting 500-600 cranking, so that is why it will not start on it's own. Low rail pressure during cranking is either a grenaded cp3 or bad injectors returning to much fuel.

You say he did a return rate test, how much fuel were the injectors returning? Factory spec is confusing as they say 3ml for each injector, but no more than 10 ml per bank, or 20 ml for both banks(and 20ml return WILL cause an extended crank time). Either you're sucking air or bleeding off fuel pressure to cause low rail pressure during cranking. You're going to have to find out where the fuel is going during cranking to not allow it to build rail pressure.
Click to expand...
So are you saying it couldnt be a crankshaft or cam sensor or wiring/electrical? As a reason why actual is not desired? If so,
 
wastefarmer said:
So are you saying it couldnt be a crankshaft or cam sensor or wiring/electrical? As a reason why actual is not desired? If so,
Click to expand...
You stated your actual rail pressure while cranking was only 500-600 psi, that is not enough to open the injectors. Common rail injectors cannot open without 1200 psi of pressure and even at that it is hit or miss(1500-1800 is much better). The 1st thing you need to do is fix the low rail pressure while cranking. You need to isolate each banks injector return lines, the cp3 return, and the popoff valves return and find where your fuel is going during cranking.

And how did he determine the cp3 was bad? This sounds like injectors to me and a good cp3 got replaced in the process.
 
sounds like you know what you're talking about, yes we know about the fuel pressure needs to be about 1500 to fire and desired is about 5000.

he pulled the valve covers, checked all the injectors individually and took into consideration each Bank total they were in spec. the CP3 was checked while he did this and it showed bypassing too much, and it was replaced with one from Thoroughbred Diesel along with the fuel pressure regulator. I'm not sure how you measure that but he supposedly knew how.

If so, can injectors be bad and still have in spec return rates?

Also remember we've replaced the fuel pressure sensor, fuel pressure relief valve. Fuel rail pressure while cranking is still around 600 lb.
 
wastefarmer said:
sounds like you know what you're talking about, yes we know about the fuel pressure needs to be about 1500 to fire and desired is about 5000.

he pulled the valve covers, checked all the injectors individually and took into consideration each Bank total they were in spec. the CP3 was checked while he did this and it showed bypassing too much, and it was replaced with one from Thoroughbred Diesel along with the fuel pressure regulator. I'm not sure how you measure that but he supposedly knew how.

If so, can injectors be bad and still have in spec return rates?

Also remember we've replaced the fuel pressure sensor, fuel pressure relief valve. Fuel rail pressure while cranking is still around 600 lb.
Click to expand...
Pull all the return lines off and isolate them, then measure how much fuel each bank is returning while cranking, how much the cp3 is returning, and then see if the popoff valve is bypassing anything. This is the only way you will find the problem. If it's the popoff you'll see it coming out of it, if it's the cp3 it will be pumping out of it's return, or if it's injectors you'll see it from them.
 
THEFERMANATOR said:
Pull all the return lines off and isolate them, then measure how much fuel each bank is returning while cranking, how much the cp3 is returning, and then see if the popoff valve is bypassing anything. This is the only way you will find the problem. If it's the popoff you'll see it coming out of it, if it's the cp3 it will be pumping out of it's return, or if it's injectors you'll see it from them.
Click to expand...
My mechanic pulled valve covers, checked injectors, in spec really good. CP3 returned too much. Replaced with Thoroughbred Reman. Replaced fuel pressure relief valve with new Bosch. Still desired 5000, actual at crank6 500 or 600. Still crank no start. Now what should I do?

Can injectors be bad and still have in spec return rates?
 
Here's another idea. Have your mechanic block off each bank one at a time with a block off plug and see if rail pressure comes up to spec while cranking.

I have a block off tool for each of the big 3 common rails. They work great to isolate problems. You can block off injectors one by one or the whole bank if needed. Just remove the injection line and screw on the plug.
20220113_093138.jpg
 
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