LB7 injector return test

[millerman04]

So i did a return rate test today. Bottom line on bottle is 40 ml. Top line is the amount returned after 15 seconds of cranking. Can one injector with a high return rate cause my no start problem ive described? It goes to garage next week to see which one or ones is bad. Ok so pic wont load from phone. Basically i pumped out double the 40 ml that it shoulda been with 20 ml a side.

 

[millerman04]

 

[LBZMIKE]

Bad orings can also do this...i have a lb7 that im just finishing up doing all 8 injectors in get it to a shop and have the run diagnostic on it is really the best way to do it and if you have all 8 injectors done witch i would suggest as its not quick to change injectors on a lb7 plan on spending 3500-4500$

 

[02greysixer]

To answer your question, yes one or two injectors can be stuck and dump all of your high pressure fuel to return. Causing a no start or hard start. It's likely you have wear/high returns in all 8 though. If you wanted to and have a couple spare high pressure injector lines laying around you can cut them and weld the end that attaches to the rail shut. This will make a plug and you can eliminate one or two injectors at a time. If the truck starts with one injector fuel supply blocked you know to start there.

Which O-Rings do you mean? To my knowledge there are no o-rings on the high pressure side of the fuel system. Besides the one on injector body that seals oil out from the cup and the one on the fuel inlet on the injector. It is not there to seal high pressure fuel though.

 

[millerman04]

Yea the guy at the shop has tools to shut the injector returns off to see which one or ones are causing the issues. Since you guys agree that thats my problem heres my next guess. Instead of havin him take the time to find the bad injector(s), should i just have him take them all out and have them all checked and tested and rebuilt if needed? Or just fix the problem one(s). Its $50 to check each one.

 

[millerman04]

Hard to believe how much problem I was having with this sophisticated system. It's amazing to learn all this.

 

[02greysixer]

How many miles on the current injectors? Originals, Bosch remans or otherwise? If you don't know the history of them at the very least I would replace one side at a time. If one side can be isolated that is. If both sides have high returns or problem injectors it's reasonable to assume all 8 will need replaced sooner than later. If you have the funds your best bet is likely replace all 8. Better to pay more in parts now than to pay the same labor again in a month.

Bosch remans sell for around $250 a piece. Lincoln diesel is a vendor here for Bosch remans and they're great to deal with

 

[millerman04]

The injectors were replaced before 100K. The guy I got the truck from had them fixed. There is now 192,000 on the truck. The guy at the shop said the place he sends his injectors to charges $50 and injector to check them. Which to me isn't that bad. The balance rates seem to be in check every time I've checked them. The only reason I'm wondering this is because he wants to pinpoint which one(s) is causing the problem. So instead of wasting his time and my money with that, since we know the issue, just have him pull all 8 out to have them checked. Then I'll know for sure putting them back in, they shouldn't give me any more fits. Key word there "shouldn't". :thumb:

 

[WolfLMM]

The injectors were replaced before 100K. The guy I got the truck from had them fixed. There is now 192,000 on the truck. The guy at the shop said the place he sends his injectors to charges $50 and injector to check them. Which to me isn't that bad. The balance rates seem to be in check every time I've checked them. The only reason I'm wondering this is because he wants to pinpoint which one(s) is causing the problem. So instead of wasting his time and my money with that, since we know the issue, just have him pull all 8 out to have them checked. Then I'll know for sure putting them back in, they shouldn't give me any more fits. Key word there "shouldn't". :thumb:

92,000 miles. More than likely you need new injectors. I would replace all 8 man. Generally speaking 100k is the service life for lb7 injectors.

 

[millerman04]

Makes sense to me while there out to be checked anyways. Wasnt aware 100k was the life of them.

 

[onebaddmaxxx]

Nor will shutting off an injector with a scan tool tell you which injector is returning.

 

[POWER Freak]

Nor will shutting off an injector with a scan tool tell you which injector is returning.

What he said.

HP fuel goes from the inlet of the injector and splits to supply HP fuel to the nozzle and the valve set(holds nozzle shut). If your valve set is leaking (80% of bad CR injectors) it won't mater if you aren't energizing the solenoid as fuel will push right through and out the return.

Also, millerman, the trick to longer injector life is good filtration. Get a good 2-3micron filter and change it regularly and your injectors will last much longer. When your running up to 23k PSI the particles basically act like a sand blaster and eats hard parts up faster.

 

[millerman04]

Somehow hes got a way of trying to figure how many are bad. Said he can try the same as he did on a cummins. I gotta talk more with him and see. As far as filtration i have an airdog on the frame and a cat filter up top. I just need to buy more additives when i get fuel.

 

[onebaddmaxxx]

Only thing you can really do if you don't want to do a return rate test, is look with the scanner at command mm3 rate. you'll probably see one that has a higher value then the rest. then from there you can pull the injector line off and cap the rail. Thats it.

 

[millerman04]

Actually i think thats what he wants to do. I think he wants to take each injector line off one at a time and try to start the engine. Just to see or get an idea which injector it is. If this will work. How many injectors can the dmax run on?

 

[02greysixer]

A common rail 5.9 will run on one scared the sheet out of me when that thing cranked up with 5 injectors capped off.

 

[bmc1025]

The caps are a godsend, you would be susuprised how well a duramax runs with one injector capped off.
It's one thing if you are DIY and have some spare time. If you are paying someone you might as well bite the bullet on an LB7 and just have Bosch remans installed while it's apart.

 

[millerman04]

See that's my thoughts too. But he wants to check and be sure that the injectors are the problem before I order a new set. After doing the return test though, I'm pretty sure that's the problem. I've eliminated everything else but the cp3. But I cant see that being the problem due to how well the truck runs after I get it started.

 

[Brent@LDS]

If you end up needing injectors let us know and we will get you taken care of. We carry OEM Bosch units at a very competitive price.

 

[millerman04]

Yea I've been on your site a lot lately. I'm liken the prices. I have found them a touch cheaper, but your a vendor. I'd rather give you the business before the other place. Plus your the first to offer Can you give me some details on your injectors? Are they all tested and ready to go with no issue? And can you set me up with everything for the install if need be?