Hi,
I am a decent machanic but a diesel dummy as in my log-in name.
I have a 1991 300d 2.5 turbo that is having intermintant boost issues that seem to be and electronic based problem. I installed a boost gauge so I can track whats going on and half, some, most, or none of the time my car will boost and when it's not, I can get it to attain full boost just my activating the Accl. lever of the cruise control. Once it starts to boost it runs great and may go 1 min./day/week working correctly before the boost drops out again.
Whatever electrical device the Cruise Control circut is controling must be getting or not getting a signel from whatever is supposed to control it. What controls the boost system, is it the CPU or something else? What can I look at ?
thanks in advance!
kevin

You might read wbda####'s post on 2.5T boost problems on this thread:

617 in 124 lOOK

__________________
'91 300D 2.5 Turbo 330K
'00 VW TDI Golf, 190K
'67 BMW R50/2
'73 Norton Commando Interstate

1.check the mechanical "Doggie Bones" and cable connections between the :
accelerator pedal and the injection pump.[Lengths and ease of operation(lubrication)]
2.check the mechanical connectios between the cruise control actuator (motor)
and the I.P., the transmission, the accelerator linkage.[Lengths and ease of operation (lubrication)]

There is no direct electrical connection between the cruise system and the EDS
(Electronic Diesel System)[engine computer].

What you describe is that the cruise system is somehow affecting the boost...
Only possible through the "Fuel Rack Position Sensor" getting stronger information from the mechanical connection between the cruise and the I.P ; than the information from the accelerator pedal mechanicals.

The boost is controlled by the EDS through two Vacuum/Electric Transducers.

Look at the Vacuum/Electric mess just in front of the coolant surge/overflow tank(in front of the battery) on the passenger wheelwell.

If compress ignite's suggestion doesn't work....

Try looking for a code with a home made pulse counter.

93 300D 2.5L Turbodiesel Power Loss

Do a couple of searches for "2.5 powerloss" also search using GSXR as poster for "turbo"

Also check for posts by TimFreeh

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47,000mi

04 VW TDI Passat 80,000mi
(Techno)

How to eliminate oil dependency through market-driven approaches.
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Thanks for the replys!
Here's more info I sent to one of you!

Hi and thanks for the thoughts.

I have worked through many things on the car as best as I can fumble through them. This car has 3 vacuum transducers, one boost control, one EGR, and one flapper valve gizzmo. This entire set-up was only on 90-91 300d's and was completely changed on the 92 model. The boost control(waste gate) transducer is in the best shape of the 3 loosing the least amount of pressure of the 3, loosing only 20 (whatever the units are?) the other 2 loose about about 40 units each of a system total of close to 600.
The change is instant when you hit the CC Accl. lever, doing let say 45 mph with sluggish pull and showing maybe 1/3 of full boost with pedel on the floor. Hit the Accl. lever and in less than 1 sec. full boost and the car takes off great. That's why I think it's some elec. thing because it happens much faster than the Cruise can even react mechaniclly.
Thanks for any more thoughts and help.

kevin

DD,

When you push the cruise control lever for Accelerate (Electrical)I.E.
INSTANTANEOUSLY the cruise control MOTOR (Electric) moves the
MECHANICAL linkage[which connects with the "Rack Position Sensor"(
senses the frequency of fuel distribution of the Injector Pump)which
inputs Electrically to the EDS...which CONTROLS the wastegate functions.

Look under the hood ,when you move the accelerator the connection to
the I.P. should move the exact amount AS IF THE CRUISE LINKAGE WERE
PROVIDING THE MOVEMENT.Any difference needs to be adjusted.

The linkage performs other tasks simultaneously,most notably increasing
fuel distribution.

YOU most likely have a LINKAGE problem...Cable,"Doggie Bones",adjustment.

The wastegate on these models begins bleed off of the precious BOOST
long before the set maximum P.S.I.
Even if the system is functioning perfectly.

I found that both Y31/1 and Y31/5 are leaking badly (I can here a leaking noise). I can't pump more than 100mbar of vacuum (while blocking the other port), it drops to zero within a second or two.

Then, tried the Intake valve actuator and tried to put vacuum with hand pump: same problem, the actuator is internally leaking and will only allow for a very small displacement of the butterfly in the intake pipe (although the buterrfly moves freely when disconnected). So it was impossible to reach 385mbar vacuum at which point the control arm of the actuator should be completely retracted inside. (I believe that 0 vacuum = butterfly wide open, 385mbar vacuum applied = butterfly completely closed and thus allowing exhaust gases to be recirculated).

Here is an update on part numbers, for my 1992, 300D 2,5 Turbo :


Y31/1 and Y31/5 = MB # 000 545 0327 @ 168,60$ Can each.

Intake flap actuator = MB # 603 090 1066 @ 298,00$ Can.

Prices are from Chatel Automobiles, in Qc City as of 26 March 2007.

Dast ist teuer!

Bye

__________________
BigBen

'98 E300 Turbodiesel 244 000km
RIP '92 300D 2,5 Turbo 632 859,4km due to engine failure

Here is a picture on my Y31/5.



Can I reverse the wires in the connector without problems? I cannot be sure it's even hooked on correctly right now!

Am I right that when applying vacuum with hand pump on port "VAC" of the Y31/5, and blocking tightly port "OUT", I should be able to hold vacuum constantly?

Because when I do that, I can only reach something like 100mbar and then it drops to nil in just a few seconds...

Thanks,

Bye

__________________
BigBen

'98 E300 Turbodiesel 244 000km
RIP '92 300D 2,5 Turbo 632 859,4km due to engine failure