86 6.9 starting problems
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New User
Joined: Mar 2010
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86 6.9 starting problems
i recently bought this truck and since ive had it i have to use ether to start it... i changed glow plugs and the relay.... and the mech fuel pump.... there are no leaks!! when i do get it running it runs perfect!!!! but when i shut it off the longer it sits the harder to start..... any help is greatly apppreciated!!!!!!!!!
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 16
From: Nutter Fort, WV
Welcome to FTE and the IDI diesel forum.
Have you changed the return lines?
Ther are two O rings under each injector cap and the fuel lines between the return tees let air leak into the fuel system.
That air breaks the vacuum that keeps fuel up in the engine, so it returns to the fuel tank.
Have you changed the return lines?
Ther are two O rings under each injector cap and the fuel lines between the return tees let air leak into the fuel system.
That air breaks the vacuum that keeps fuel up in the engine, so it returns to the fuel tank.
Freshman User
Joined: Sep 2009
Posts: 26
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From: San Diego, CA
Man I JUST came out the other side of a month worth of overcoming this problem. I have the exact same 1986 6.9 Diesel and wow was it ever a pain to fix. The bottom line is, you've got air in the fuel system. In my case the tiniest little leak caused huge starting problems. What I found when I started working on it was that once I fixed one leak, the increase in vacuum seems to have caused other leaks to occur. One day I thought I had everything fixed and then after a day of driving, suddenly there are more leaks. Soapy water really helped find the leaks (bubbles). Of course each time you replace something you fill the lines with air and have to purge it all over again. And those rings that Sponaugle mentioned? All brand new rings and I still managed to smash one and develop a leak in it.
Man...I'm still having nightmares from chasing air leaks. But once you get it fixed the difference is huge. Firing on a single crank after sitting all night is bliss.
Man...I'm still having nightmares from chasing air leaks. But once you get it fixed the difference is huge. Firing on a single crank after sitting all night is bliss.
Fleet Mechanic
Joined: Nov 2007
Posts: 1,770
Likes: 29
From: Northeast Nebraska
isn't it great digging up old threads?
how about this one...an 86 w/ a 6.9 and an auto tranny that (as far as i've been told) starts fine every time, but once you throttle up and let her come back down, she dies. do you guys think this could be caused by an air leak into the fuel system as well? a local *gas engine* mechanic hypothesized a vacuum leak, but as far as i ever knew, there wasn't anything on those 86's fuel systems that was vacuum actuated...or as far as i could see at first glance anyway. my initial instinct was a timing problem, but a little doubtful on that as it doesn't smoke, doesn't start hard, and idles fine.
any thoughts?
how about this one...an 86 w/ a 6.9 and an auto tranny that (as far as i've been told) starts fine every time, but once you throttle up and let her come back down, she dies. do you guys think this could be caused by an air leak into the fuel system as well? a local *gas engine* mechanic hypothesized a vacuum leak, but as far as i ever knew, there wasn't anything on those 86's fuel systems that was vacuum actuated...or as far as i could see at first glance anyway. my initial instinct was a timing problem, but a little doubtful on that as it doesn't smoke, doesn't start hard, and idles fine.
any thoughts?
Lead Driver
Joined: Mar 2006
Posts: 5,111
Likes: 1,546
From: western SD
Snowman, what you described is the govenor/metering rod in the injector pump sticking, not allowing the pump to catch it self when letting off the peddle. The fix is to install a new fuel filter filled with your favorite fuel additive ie diesel klean, howes ect. Add 3 or 4 times the amount called for to the fuel tank, start the engine letting it run for 30-45 seconds then shutting it off. Let the additive soak for a while, overnight if possible, then take the truck out for a hard drive. The 85 in my signture was doing this when I got her, and this cured her within 5 minutes of doing this.
Fleet Mechanic
Joined: Nov 2007
Posts: 1,770
Likes: 29
From: Northeast Nebraska
ok, that sounds pretty logical. i'll have to give it a try, i figured it would be something to do with the IP but i don't know too much about the inner workings of those rotary pumps. thanks for the input, farmert!
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