RE: a 1987 300TDT. This is my brother-in-law's car, he's in Maryland, I'm in New England. He called the other day and asked me why the car would seem to be sluggish upon acceleration - worse than he's ever seen this car. Once up to speed on the highway, it seems OK. While the car was at my house this August I did some repairs. After I gave him back the car it ran beautifully, he said. One repair involved removing the turbocharger to access something else under it. While it was out, I checked to make sure it spun freely, which it did. Just the usual minor resistance, which is normal. The clear in-line fuel filter is clean he told me. This is what's been done to it in the recent past:
new Bosch fuel injection pump (two-years ago)
Diesel Purge was run through engine (this September)
new air filter (no obstructions in air tube either)
both fuel filters are new
no obvious vacuum leaks

I know I'm missing some other stuff that would be a process of elimination approach. Can some of you throw some hints my way? I'm blanking out right now. I have to walk him through some of the easier points over the phone.

I have the same engine. Seems you have addressed likely issues, but sluggish response indicates a problem!

If in your shoes, with similar, I guess I would start with the secondary fuel filter....replace it...if the same continues upon replacement of that filter, I think I would start thinking!

What else?

I think I would begin looking at, and with, a vacuum guage! See if you are getting ALDA response. If you do not known from here what I'm talking about, I would suggest taking the car into a shop, with somebody who really knows Mercedes Benz OM603 diesels.

There may be others here who will be more interested to carry you more forward..................BB

Make sure the line from the manifold to the overboost switchover valve is clear and in place as is the line from the valve to the ALDA. Can he blow through the valve with the engine running? He can temporarity bypass the valve to test.

Sixto
87 300SDL

Sixto is correct.

The usual culprit is the banjo fitting and/or the line from the manifold to the overboost protection valve on the firewall. The valve, itself, may also be clogged. Remove these lines and make sure they are clear. You can't clean the valve effectively without damaging it, so, just bypass it and see if the problem is eliminated.

If the line or the valve is clogged, you don't get any boost and the vehicle feels "sluggish".

Of course, it could also be similar to my problem that I'm fairly sure is a clogged screen in the tank. Every time I run the tank down to 3 gallons or so, I lose the boost for the next 100-200 miles or so. The situation is getting worse and I'm going to have to find some fungus treatment, or drop the screen.

Mine was VERY slow until I finally installed a working Overboost valve. Took me just a few min to bypass and was shocked at the difference.

Also on the '87s they had that cat converter or what-have-you downstream of the turbo. I hollowed the one out on the new pipe I installed on my L before bolting it up to the vehicle. Reason I bring that up is they do seem to clog up.

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

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