i jus recently bought a 2001 duramax from a guy who sold it to me fairly cheap because it wont start unless u squirt a lil starting fluid in the air filter. it runs great once it starts. he was thinkin the injectors need replaced. Im wondering if this is a common problem when the injectors go bad?? er could it be like the line getting air locked or bad fuel filter?? i havent looked into it much. any input is greatly appreciated

 

seems to be common enough with the LB7s.

shooting from the hip, i would say the return rate on one or more injectors are a wee too high.

it may also be a week CP3, a leak on the suction side of the fuel line, or a plugged fuel filter, or even weak batteries that don't crank it over fast enough to build the required pressure.

how many miles on the truck, do you know if the injectors have ever been replaced? is it making oil?

try priming it till hard first, see if that helps. also, rule out the batteries too. and replace the fuel filter.

with the engine idling, command max psi. EFI Live or Tech 2 can do this. otherwise unplug the FPR and monitor the fuel pressure with a capable scan tool. it should reach about 160 MPa. a little less is normal. this will check the CP3 to see how healthy it is. (really bad return rates will still make the CP3 look bad)

last check is to pull the return lines and measure the amount of fuel coming out for the CP3 and injectors. don't remember what the max is though.

 

the odometer of the truck reads 260000 miles but he said motor and tranny only have 180000 and were professionally installed. he did tell me it started acting up this winter and he put new glow plugs in it and that help for a lil bit but then it started doin it again. it does have an edge programmer plugged into it but it dont work right because he bought it used from his buddy and i think its still locked on that guys truck so you cant actually turn up the settings of the truck. one battery was just replaced. fuel filter does look really old. ill prolly replace it and see if it would happen to help.

 

ya, start with the easy stuff first. filters, etc

the batteries are best replaced in pairs. if one is weak and has a higher self discharge rate then the good battery will drain into the old one. unless the older one was tested and you know it is a good battery then try replacing it with the same one as the newer one.

use the edge to monitor fuel pressure while cranking. should reach about 1450~psi or 10 Mpa before it can fire the injectors.

180K miles is pretty good for a set of injectors. mine lasted to about 120K before needing replacement.

 

ill try put a battery charger on it and see if that happens to help. i doubt it will, it seems to turn over great. Also im not sure how to use the edge to check the fuel pressure deal. i seen a feature where it showed it would show injector #1-8s settings and if there were problems while its running. i couldnt get it to do anything. im thinkin it may not work since its probably still locked on that other guys truck maybe?? i tried to pump the hand pump on top of the fuel filter till it got hard. it was loose for bout 6 pumps then it got hard. It still didnt start tho. ima change the filter when i get time an see what happens an what it looks like

 

having to pump the primer 6 times till hard make me think it may be an air leak issue. after priming. try starting for a few seconds and repriming. do this several times and see if it starts. if it does then thats good news.

what you probably saw on the edge was the balance rates of the injectors. with the engine idleing and in park get the numbers and do it in drive with foot on the brake, post up those numbers too.

 

Ill try priming it tomorrow and pumping it up. Is there a screw that i should loosen that would maybe help? i thought maybe there was, But if the truck is running and you shut it off and try restart it 3 seconds later it still wont start but i suppose it could still possibly be a leak?

 

there is a plastic screw on top of the filter housing. it is used when replacing the filter. you loosen up the screw then pump the primer. the air will come out, when fuel starts to come out you tighten the screw and pump the primer till hard.

if it looses prime after only 3 seconds then it would be a large enough one to cause it to idle rough.

sounds to me like you need to have the fuel PSI monitored while cranking. also an injector balance rate & a fuel return rate test done to determine if the injectors are gone.

the edge should be able to do the balance rate and fuel PSI. see if you could get those numbers for us

 

i was able to get the edge to show the balance rates of injectors. the numbers seem to move around pretty good. heres the numbers of the injectors whiles the truck was in park.
#1 1.3
#2-0.3
#3 -1.3
#4-3.2
#5 -0.8
#6 1.8
#7 0.6
#8 1.7

the edge said the numbers should be +/- 4 while in park. all these numbers are it looks like. do these numbers look good? also, im not sure how to get it to show fuel pressure on the edge

 

they seem fine, #4 is the only one a little off but still within spec. where you able to get numbers while in drive? they might go up. good balance rates is probably the reason it seems to run ok once you get it going.

unfortunately balance rates wont tell you anything about the return rates which is what i believe may be the problem.

to rule out in air leak issue, get a piece of clear tubing and replace the short section on the output side of the filter housing. then you can see if there are air bubbles in the fuel while running. if no air then it is ether a weak CP3 or injectors. it can be tricky on the LB7s to be able to tell which one it is. on the newer models you can check the returns on each injector, but on the LB7 you can only check the banks.