ok so I changed the fuel filter about a week ago made sure it was all bleed out nice and good. It has been running great till yesterday. When at idle it is very rough but when at speed its smooth. to me this sounds like a bad injector or two this thing has a grip of miles on it what do you think?

any help is appreciated.

if it is a bad injector is there a way to "sniff" it out with out pulling them all and testing the whole bunch.

Well, if you do think it's an injector, you can crack the injector lines loose one by one with the engine idling to see which one is bad... Sounds like it might be an air leak to me, however.

Can you verify the idle speed?

What's a 'grip' of miles?

What's your ambient temps?

Did you just re-fuel, recently?

If you had a misfire, you could check the injectors - since it's running rough, you probably wouldn't notice any difference.

well now its quite running. I had it idling outside my office went out put it in gear and it quite then it wouldnt hardly turn over. so I loaded it up on my slideback and brought it home.

I estimate the rig has 140-150k but the odom says 940k but it went crazy a few monthes ago and just started going crazy and racking up the mileage then it just quite.

I suspect that there is a/few bad injectors as I suspected there was one/few going bad. I will try to restart it and do the crack the line trick but not sure what that will do. it is "loading" up like a gasser would do. it smoked a whole lot this morning while warming up and this eve. when gettin ready to go home.

the ambient temp is averaging 0-17*F I fueled about a week ago and still have a tad over a half tank. It also gets plugged in when ever its gonna sit for more then a few hours. and has two block heaters(one each side). I have a set of injectors from a spare motor that I just had tested so guess I'll get a copper kit and throw them in and see what happens. And its a fresh rebuilt IP as of about 3 monthes ago. and has run fine untell a month ago when I started to suspect the injectors.

How's the air filter - Diesels can't run with as dirty air an filter as a gasser can.

Could be the HPCA isn't working, so IP can't get any advance.

If return line is plugged, no advance.

I'll check those things I just replaced the air cleaner not to long ago.

well checked it out a bit, offloaded it at my house tried to start it to no avail. poped the hood and found the brand new battery terminal on the main battery melted off the cable. so I fixed that and it still would start jumped it with the slide back and it fired right up ran ok for about 5sec. then started to "miss" again. unhooked the cables. moved the rig blocking the garage. went back to my truck and it had died. tried to start it and like before Click Brrrrrrrrrr. so re jumped it. moved it about 100 ft to the garage put it in park and it died. thats where it sits as of now trying to decide if I wanna work on it tonight or start a fresh in the AM. I will start by checking the lift pump cause I did not hear it runing during this little episode. then I'm gonna so a pressure test on the return line to make sure its clear. Then if its still messed up I'm gonna swap in my spare set of injectors. hopefully that clears it up if not then its time for it to come out and get rebuild as have been planning on and starting all over with this motor in a different truck.

Have you tried to re-bleed the fuel filter to see if you have any air in it?? I would start there and maybe presureise the fuel tank with a few lbs of air psi if you have an air compressor and check the lines over real good for a leak between the tank and lift pump, they can leak air in without visably leaking fuel until you add pressure to the system.

well I re bleed everything didn't get any air out am not seeing any bubbles in the return line. I did the crack the injector test and most of then with just a small crack it would kill the motor. two-three of them it would crack and stumble and take a few turns off the line to get it to die, I'm assuming those injectors may be bad? should I swap those out for my good tested spares? and see what happens. I did notice that if I pulled the fuse for the lift pump it would run a little rougher. WTH?

I bought this truck just for the motor so I could put it in my 78 so if it takes much more work to get this thing going I'm gonna pull the motor rebuild it and put it in the 78 like originally planned.

I thought it was in my sig but this is a 1988 GMC k3500

ok so I think I found the problem. when I could keep it running I noticed that there was some fuel in the valley of the engine. I took off the intake and started it back up and noticed the very bottom pipe nut is leaking. now how the heck do you get a wrench on that one? hope this solves the problem. it must to keeping the psi from getting to where it'll pop the injector. I also noticed that on cyl 3 it seems as tho air is blowing out the intake. I'll have to wave a piece of paper over it to know for sure.

well I did a comp test on the cyl I thought was bad and It came in at 295 where the cyl on either side of it were well over 350(gauge stops at 350). so I popped the injector lines off and pulled the valve cover. man there is ALLOT of slop in the closed rockers I mean ALLOT of slop. how much slop is normal for these things?

That reduces friction - you'll notice they're positioned by nylon buttons.

As rocker action is pivoted on the shaft, the bottom of the rocker is the only contact - the upper diameter is unimportant to the fulcrum.

Pull the rocker shafts, see if they're deeply worn - if not, go back with them with new buttons, and you're good to go

just seems like they lose allot of valve lift because of the slop.

At TDC, both rockers should have less than 0.030" clearance - yours are more than that?

at random rest some of the rockers have enough slop that I can almost pop the push rods out of the sockets.

on a side note I think I'm gonna just pull it out and start the rebuild and I poped the heads of the engine I purchased from the DRMO and it still has the hone marks in the cyl. and the pistons are barely dirty. so I'm gonna throw it on the stand and take a look at the bottom end to see if I can figure out why they pulled it and sold it. there is no sign of a blown head gasket or a cracked head on the port side(only head I've pulled so far). I had the injectors tested and there was one leaky one I don't think they would have pulled the whole motor for one bad injector would they? I just took the hard parted db2 to the shop to have them look it over hopefully it will be in good shape as well. so far its looking to have been a good $145 purchase. heres a off topic question The intake on the 88 is a J code but it much taller then the one on the military engine. why? and which is better?

Limited real estate in the hummer - use the 6.2J for air filter housing clearance

kk thanks for the info.

well I thought I had it all fixed. pressurised the tank at 2.7psi and left it for two hours. went back and it was 2.3psi crawled up and down and over and under the entire truck tracing fuel lines to find NO leaks. I did find one bad injector and at first start up it runs fine. but after about 45sec to a minute it will sound like its "loading up" and then just like I turned off the key it dies. and when I go to restart it it barely cranks over like its almost hydro locked. if I let it sit for about 30min it will start up after a few sec of cranking. but then after about a min it will load up and die. I'm at my whits end with this thing. I have been working on industrial diesels for almost 20yrs and never ran into this type of problem. I put a clear hose on the return line and there is no bubbles or anything.