Hi All,
I could not find any threads posted about this - if I missed some please let me know. My 91 1st gen non inter-cooled baby has NEVER liked when the weather gets hot...of course I Ilve in AZ where it gets extremely hot. When the temperature outside heats up the engine has terrible idle. Many times it dies while stopping at intersections. Have always thought about adding electric fans, a new radiator, or adding an inter-cooler but have never done any those since I don't know if any would solve this problem. Any clue what can be done to have it idle better when it is running in hotter weather. Any and all ideas greatly appreciated. P.S. I don't pull a trailer with it, it never red-lines/overheats and it idles fine if it's under 90 degrees out.

 

Is the KSB still plugged in?

 

Not an unusual problem with the VE. It is the first indication that your injection pump is suffering from normal wear out. At low RPM, your pump produces low internal pressure (normal). With use, clearances within the pump open allowing fuel to bypass back into the low pressure side instead of into the higher pressure injection side, Hence the decreasing idle. Heat causes metal to expand make those clearance worse lowering the idle even further. It's more noticeable with an automatic. Put it in neutral or park and idle returns to or close to normal. I lived with mine that way for a few years then replaced the injection pump.

 

I also suspect this might the cause. I listed the KSB wire as a possible, but less likely, CHEAP solution to check before jumping right at the most expensive part on a Cummins motor.
I listed the KSB as IIRC the non intercooled motors will advance the timing all the time if they don't have the wire hooked up.

I have heard several people discuss pouring cool water on the VE pump when it is acting up like described as a way to diagnose the problem.
If it runs better after you cool it down, you know the pump is the issue.

I have also heard people say that this is bad for the pump...which is understandable, but if you are faced with getting a new pump anyway, might be a mute point.

 

Thanks guys. I have had to replace the injector pump twice over the last 20 years I have owned it. The crappy idle when hot has alway been an issue before, during, and after the 2 replacements of the pump. I don"t know if I have ever replaced or messed with the KSB or any other sensors around that area.

 

Two VE pump swaps, for a total of 3 different VE pumps on it and it has always acted like that?
Wow, I am currently stumped.

If it is a manual truck, I guess you could bump up the idle a bit....Might help keep you from stalling in the intersections.

 

Yep, and I use a place that specializes in rebuilding and installing those diesel pumps. That's why I am thinking it's a sensor or find way(s) to keep it running cool. In the winter/cooler months it runs like a kitten and even now it runs well...it just cannot keep a good idle when hot. Maybe some function of the vacuum system?? Is there a way to bump the idle up on an automatic??

 

You can bump the idle up the same way on the pump, just with an auto, I would assume at some point the RPM it would try to push you in D at idle.

I am sure some 1st gen auto guys will chime in.
All my 1st gens I drive are stick shift when I bought them, or they are now.

 

As Oliver said, is the wire to the KSB hot with the key on?

 

Does your 91 have the high (er) idle pull cable? Mine did this before I replaced the IP and the idle would come up a bit, but enough...Mark

 

There is a place around here that specializes in rebuilding and installing those diesel pumps as well. I wouldn't trust him any further than I can throw a grand piano. There are overhauls and there are OVERHAULS. The difference being do the hard parts meet new part specifications (dimensions) or does the hard part meet used part serviceable limits (looser dimensions). A used serviceable part is already worn past new part specs meaning is already has loose clearances. New seals only mask this wear and in a short time you will see the symptoms of a worn out pump again. Unless these parts are replaced with new or parts that meet new part specs, it is in my opinion a reseal and not a true overhaul. Also consider wear has a cumulative effect on the amount of fuel that gets bypassed. The original design only allows for a limited amount of leakage to remain in spec. Leakage beyond this limit diminishes the pumps performance, particularly at low RPMs.
My 92 is an automatic. I had to resort to shifting into neutral at stops to keep it running through the summer. It was fine in the winter. Got tired of it and replaced the pump. Upping the idle is not the best solution because it raises the transmission fluid temperature and wears on your brakes.

 

My son is putting in heavy hours at work so I will check the KSB wire and idle pull cable when it comes available. I just hope the cure is truly not a new or even rebuild VE. Though a/the solution is what I'm after.

 

If the local shop has just been re-sealing your pump without checking or replacing out of spec. internal parts and giving the same pump back to you...That may very well be your problem.

 

Sorry this has taken so long. Finally got my truck to run in hot temps! Had a friend of mine, who is a full time diesel mechanic, adjust the idle setting(s). Took awhile to get it just right but I took it out yesterday in 110 degree heat for over an hour and ran it great even when stopped, the AC on etc. You can tell it still doesn't love being driven while its extremely hot...when I started it after getting fuel it kicked over a bit "off" like bad compression but it still started. The KSB is functioning correctly. Thanks for everyone's input.