cold idle, hard shift
 

Hello Gentlemen,

(I have scoured the Forum for related topics, this is different)

When my 85 300sd is cold it seems as though the engine doesn't want to take fuel under load. I have had the vacuum assemblies adjusted and bypassed by a professional (a very competant man). The cold shifts are jarring and the vehicle is, well, unsafe to drive due to its unresponsiveness. That condition lasts for a minute or two, and then the car responds and shifts smoothly. There is no black smoke.

A prolonged idle does not change the condition, only 1/8 of a mile of driving does.

The mechanic has fully adjusted the set screw on the IP and says there is accumulated wear that prevents a proper idle. He said, "Run it and see what happens." The car runs and shifts beautifully when warmed up.

The ALDA was bypassed and the sensor is set to let the turbo engage at lower RPMs.

It just doesn't seem possible that the diesel that can run so quietly and powerfully could have a damaged Injection Pump. I am worried that the cold winter starts will be very difficult.

Somebody please tell me I don't have to tear apart an IP to fix a cold idle.

Suggestions?

(1) Hard shifts are almost always due to lack of sufficient vacuum to the transmission modulator. Since the problem goes away once the car has been driven awhilem it's probably not the modulator. You need to monitor the vacuum to the modulator (tee the line and use your Mityvac or some other vacuum gauge). Should be 12-15 inches Hg at idle and 0 at full throttle.

(2) Your sentence "The ALDA was bypassed and the sensor is set to let the turbo engage at lower RPMs" does not make sense to me at all. Perhaps I'm just tired, it's late. You can "adjust" or "remove" an ALDA but "bypass?" What is that? Additionally, there is no sensor that would "let the turbo engage at lower RPMs." I'm totally lost trying to understand what you are trying to say here. Sorry to be slow on the uptake tonight.

(3) I agree that your IP is probably not the cause.

cold idle, hard shift
 

Thanks for reply Jeremy,

The confusion regarding my description has to do with a 2nd person conversation and 3rd person recapitulation. So, I take full responsibility for the ambiguity and, if you are tired, respond later.

point 1) Hard shifts are due to lack of vacuum. I can check that, but I suspect the number of hose placement changes may be the villian here. Maybe the solution to the entire problem.

point 2) I am mechanically fearless, but I may have mixed a mechanical metaphor here because of my lack of diesel experience. The "alda" I referred to is a black tube-like thing on the firewall. It has vacuum hoses (now "bypassed") and a electrical clip attached to it. The turbo engaging at lower RPMs is a direct quote from the mechanic. Perhaps, bypassing or removal is the same exercise. The "adjusting" mentioned in the post was done to a set screw with nut around it on a rectangular device set upon the IP. That adjustment is now fully CCW.

point 3) I hope we are right about the IP. The mechanic was not optimistic regarding the fully adjusted set screw. But, the engine did run strong (but shifted hard) before he started moving hoses.

I suspect, we would agree on this course of action: find and old vacuum diagram and put the diesel back to "factory."

Now, don't give up on me. I am resolute and I see every project to an end. I apologize if my imprecise lexicon confused you.

Joe Marroso

Take a step backward to move forward
 

I experienced similar hard shifts and some sluggishness...I ended up doing just what Jeremy indicated...checked and adjusted the vacuum as well as some miner adjustment to the Bowden cable (search that one) Be a bit patient -- I've learned this is an art and becomes a balancing act. Suggest you go back to original vacuum setup. There's plenty of threads on this site, including diagrams of the system.

My sluggishness was caused by a dirty fuel filter -- simple fix Have you checked that. Unlike gassers, I've found I can't ignore the fuel filter.

My hard shifts went away by adjusting the vacuum down to 9-10 Hg. (0 at full throttle) and chaging the shift points slightly w/the Bowden cable. Discovered by some trial & error. (use small adjustments & then drive it)

Good luck...this forum is incredible, so you'll find nearly any scenario here.