Idle surge problem, tech advice requested

[maxspeed250]

I'm soliciting advice from RKI's (reasonably knowledgeable individuals) about the surging idle on my deuce. Here is a little history on it first so we can eliminate some possibilities. After towing truck home (it was a non runner), drained and replaced fuel with fresh diesel. Changed ALL filters, starting with primary and purging lines as I went along. Found bad (seized) hydraulic head, replaced with new Ambac head and installed new injector lines as well. Now it starts right up, and runs well with plenty of power, no problems except for surging idle. It is the worst when cold, hunts up and down about 3-4 hundred RPM - but will still do it slightly when warm. Also when you let off the throttle suddenly, it may or may not die, drops very low in revs even when warm (< 350 rpm) before recovering to about 750 rpm idle. Lines are not leaking or pinched, runs good at speed, looks like a new in tank pump that is definately running, turbo is turning ok, I can hear it coast to a stop when shut down. I did the search thing and didn't really find anything of use for help, so pleeease don't bring that up! Thanks in advance for any insight offered. -Bill-

 

[Warthog]

When you reinstalled the hydraulic head, did you make sure the Fuel Control rod was seated properly?

Also did you clean the Fuel Control Rod passages and make sur eth plunger moved freelY?

Don't know if that is causing the issues but I have seen many trucks with very sticky Fuel Control Rods.

Of course YMMV.....

 

[doghead]

Have you simply adjusted your idle up, to around 750-800 rpm? that may be all you need.

If that does not help I would try adjusting the droop screw in the IP. It controls fuel rate from idle to midrange.

 

[russojap]

So whatever happened with this, how did you fix it?

 

[Floridianson]

So whatever happened with this, how did you fix it?

Don't believe he has posted anything since 2012.

 

[russojap]

Don't believe he has posted anything since 2012.

Yeah, I just realized that, maybe he never even got it fixed, I'm going to try bleeding it first.

 

[yolner]

I had a similar issue when I first got my truck and it quit doing it after I swapped to spin on fuel filters (primary and secondary both). So I'd start there.

 

[russojap]

I bled the fuel filters and some air sputtered out. Then after starting it idled smoothly, until I touched the gas pedal revving the engine slightly. What happened?
https://m.youtube.com/watch?v=Jcz8lMHxYno

https://m.youtube.com/watch?v=zypQ1nnRARI

 

[cattlerepairman]

I wonder if it is drawing air into the lines. The fuel system is essentially self-bleeding when the engine is running. It would need to be a big leak to upset idle the way it does in your clip. I would probably run it, drive the cr*p out of it for an hour and see if it learned any better manners after that. Sometimes that really helps.