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6.2 Diesel rough idle and misfire

Flyboy207

Flyboy207

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Hello all,
My '82 GMC 6.2 just blew a lift pump and I replaced it. I reconnected everything, bled it out and got it running, but somethings strange. It runs fine on startup, but the first time you move it, is starts to surge at stoplights. Then if you get on it, it revs up into second and at high RPM almost into third, I lose all power and I get a misfire and some grey smoke. Then it clears out, shifts and it's fine. This goes away after driving for maybe 10 minutes, no matter hot or cold. Then if you shut it off for a minute, start it back up and it will do it again. On top of all this it has less power than normal. Sometimes when it's just been started I get a little surge that gives a lot of power, then it's gone again. I have replaced the filters twice now, and no change. I also ran some injector cleaner through today, also nothing. I'm trying to nurse it back to health, but if it needs any major work (valves, I.P.) I'm probably just going to put a 6BT in. Any help is appreciated, I'm going nuts about this! :mad2:
 
I'd check for air, put a piece of clear tubing on thereturn line coming out of the IP and watch for bubbles
 
I'm with AK on this,lack of fuel or air coming in the system.it wouldn't hurt to read the fuel pressure either.
I believe you have a mech LP on this truck..right?,it can be a bitch to get fuel flowing with just cranking.Pressuring up the tank helps to push the fuel to the LP.

Running for any length of time without a working LP can do serious damage to these 6.2 iP's though.
 
All right, I'll try that. And bison the fuel pump just started leaking from the little weep hole. It didn't seem like the old LP was having any trouble getting fuel to the IP, it just sprayed half the fuel onto the road.
 
What goes on the road won't be avalable to the IP.

Maybe the new LP is bad,...it happens, i had a bad one twice in a row..made in china
 
Any leaks from the lift pump mean it is defective. I can't think of any debris you would be getting to puncture the diaphragm, but pour the pump out into a cup and check for any.

I've also cracked the fuel line at the pump causing leaks.

The fuel filter boxes, the base, are known to leak air. Restriction sensor as I recall. Not sure what style filter you have on this year.

Air or lack of pressure from the lift pump will cause the timing to go retarded - white smoke. Lack of lift pump pressure will also not allow the pumping plunger to fill causing a lack of power from little fuel delivery. Air does the same thing to fuel delivery and timing by compressing.
 
I'll recheck my LP, it isn't leaking visibly though. I'll check all the lines and hoses I can, but right now it pulled air from somewhere in the system on top of a 4x4 trail and is still there. I thought it was fixed, but I was wrong!
 
I might double check the install on the new lift pump. The rod that runs on the cam sometimes slips down before you get the pump bolted up leaving you with a defunct lift pump.
 
are the fuel lines still the factory steel ones? don't forget to check to short rubber section that goes from the tank to the steel section. You may be chasing a pinhole, that's all it takes.

have you tried the jerry can method. a short section of hose just to feed the pump. it'll tell you if the pump is bad or if your chasing the suction side of the line
 
All right everyone, I got it back off the mountain using a jerry can and a little electric pump. Now I'm trying to get everything sorted out. Does anyone know where I can get a diagram of how all the filters and lines go? I've looked through the Haynes manual I have and nothing about diesels. By the way it's an 82, first year of production so it has spin on filters.
 
The spin on filter setup is better than the box style filter of 84+.

Here's how the fuel flows through the filters and lift pump.

From the frame mounted fuel lines it runs up to the filter on the firewall. Then it goes to the suction side of the lift pump on the block. From there it is pumped to the filter on the back of the intake. Then it leaves the second filter and goes to the IP inlet fitting. Somewhere in there is the inline fuel heater. The heater is part of a steel piece of line and has a single wire to it. It grounds through the line/bracket that keeps the line from moving.

The first filter is the water separator/primary filter(coarse filter) which is drained by the valve on the bottom of the filter. The second filter is a 10 micron filter.

I'd prefer the spin on filters over the box filter as the box filter pukes fuel all over the exhaust when changed. At least it used to, until i found a handy way of draining it before removing it.
 
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