Help please: 90 300D (2.5 turbo) won't rev - sometimes
 

Father-in-law type person Ed drives a 90 300D (2.5 turbo). Complained night before last that it "hasn't been able to rev over 3800 rpm for a while." Says he just "stands on it getting on the freeway, goes up to 3800 and won't rev any higher, won't shift until I let off the gas a bit."

Of course, it's dark and raining at this point..... goes well with my complete lack of experience with diesels. I poke around looking for open vacuum lines (he's got a couple that are prone to pulling off any time he goes under the hood), can't see anything obviously amiss. Start the car, idles fine, pull the throttle cable under the hood, revs up fine. Sit down, confirm rev's up well past 4k in neutral. Out for a test drive, shifts normally, revs to ~ 4500 or so before doing so if I'm pushing it. Out on the highway, all seems normal. Return the car to Ed, call it a night.

He didn't drive it yesterday. Today he did, calls me to say "won't rev past 3800 rpm again."

Any hints as to where I should start looking to trouble shoot? Guessing fuel related, if for no other reason than he's been walking the bottom of the tank for the past several weeks (well and truly cash strapped).

Thanks in advance!

Hitting max stop? Fuel filters?

Check the condition of the filters. Also check the amount of play in the linkage cable that connects to the fuel pedal.

Sounds like a fuel problem if it revs in neutral but not under load. How long since the filters were replaced?

That model has electronic boost control. If the ECU senses something amiss such as a problem with EGR, it withholds boost which reduces power. Is it possible to get a boost gauge in view of the driver? There's no real fixing this problem since it uses archaic and esoteric OBD. Best to retrofit a boost actuated wastegate - http://www.peachparts.com/shopforum/diesel-discussion/212097-wastegate-actuator-swap-om602-962-a.html

Move the throttle to WOT at the IP then have someone do it using the pedal. Is the pedal able to get the IP to WOT?

Sixto
87 300D