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Old 08-18-2006, 03:30 PM
Registered User
Join Date: Dec 2005
Posts: 8
85 300TD top end power question

Hi All,

I've got a new-to-me 85 300TD with 203K on the clock, and it has a minor(?) power/acceleration issue. It takes at least 5/8-3/4 throttle to get the engine much over idle. This is consistent whether I use the pedal or move the injection pump arm under the hood by hand. I've adjusted the throttle linkage so that pedal bottom is equal with the IP maximum throttle and run it on the road a bit with the following results:

The car runs like a scared cat off the line and through the low gears (if the pedal is floored or nearly so). But on the flat or especially on any incline I basically cannot go over about 45-50 MPH even when floored. Downhill I can make some speed, but It's hard to plan all my trips to go downhill and still get everywhere.

I've replaced both underhood filters, checked compression and valve timing, with at least reasonable results (310+/-5 psi in all cylinders). I suppose I need to check the in-tank screen for junk, but the lack of IP response at low throttle input just seems wrong to me. Is there another adjustment somewhere that I'm missing? Perhaps something else that's limiting the IP's ability to respond at low inputs? Any suggestions are greatly appreciated.


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Old 08-18-2006, 04:07 PM
Join Date: May 2005
Location: CALIF
Posts: 508
Low Power

1984 300d Turbo 140k
Use 2 Cans Diesel Purge From Dieselgiant. Com, They Have Kits, Clean The Alda Line On The Ip
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Old 08-19-2006, 01:43 AM
Join Date: Dec 2005
Location: CA... No. of S.F.
Posts: 890
If after you purge her and check for the obvious...

fuel starvation things others have suggested you check... then also check the EGR system.

Our '80 300D had similar symptoms and it turned out to be the EGR system and as soon as it was shut off, the problem was completely solved.

To check this out, just put a golf "T" in the vacuum line... and look to see if the EGR is in fact closed and NOT partially stuck open. Then once you are certain it is shut, drive her and see if the problem is still there.

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Old 08-19-2006, 01:58 AM
dkveuro's Avatar
Sword of Damocles
Join Date: Jun 2003
Location: Here an' there.
Posts: 2,548
There's a square aluminum canister on top of the injection pump.
It has a sealed adjustment cap on top...pry out the black plastic seal and loosen the nut....turn the screw out about one turn...lock the nut and test drive. Continue adjustment until best performance.

This adjustment controls the tip-in fueling of the pump. They are set lean from the factory...they get leaner over the years.

Also check to see if WOT is moving the i/p arm to the stop located between the engine and the pump.....try this with engine off !

You could see if the turbo boost control is not opening too soon.
On the drivers side inner fender is a electric vacuum valve that opens/closes boost pressure to the the vac' lines to by-pass this switch for a test.

[ ]

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Last edited by dkveuro; 08-19-2006 at 02:04 AM.
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Old 08-19-2006, 02:23 AM
Registered User
Join Date: Jul 2006
Location: Near Atlanta, GA
Posts: 83
I had a similar problem. My throttle linkage bushing that attached to the firewall was completely shot and was causing enormous amounts of slack in my linkage. I did not notice it at first, because I was checking everything by moving my "stop lever". Hope this helps.


1984 Astral Grey 300TDT - The French Fry
1979 Yellow 300SD - The Pomme - SOLD
1985 Light Ivory 300DT - Fritz
1987 Anthracite Grey 300SDL - ?
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