Wayne

I don't mean to sound rude but if you re-read this thread I think you will find the answer to your question of "where do I start"

It's difficult to troubleshoot problems like this over the internet. We can say things like 'check your boost control vaccum control solenoid" but if you don't know what that is, when it should be working and how to check it your not going to be too successful.

At a minimum you are going to need an impulse counter, a 602/603 engine book, a VOM, a mity-vac and be able and willing to read schematic diagrams on the particulars of the EDS controls that is responsible for boost control on this car. If you don't have these things about the only thing you can do is to just start replacing parts.....

Tim

I used an analog meter. X11 cover removed. Negative meter to ground, positive meter to pin X11/4, a jumper wire from X11/4 to ground. Followed instructions for 602.962 engine from 124 CD manual and also pulse list.

Computer codes extracted are 2, 3, 4, 5, 8, and 14

I resolved them in this manner and erased the fault codes

Fix for 2 was to clean the fitting for L7
Fix for 3 was to completely wash out the Air Box and clean the fitting for B2/1, not ready to replace B2/1 yet
No fix for 4, yet, not ready to replace N39
Fix for 5 was to replace Y31/1
Fix for 8 was to replace the B11/4
Fix for 14 was to replace B5/1

******** in Pompano Beach FL supplied the parts

Will road test the car this evening, going out to dinner. I hope I don't have to replace N39 and B2/1 due to the costs involved.

I will report back with results.

Thank you TimFreeh and to all the posters for their support.

Hey Wayne, reconnect your EGR, the EDS computer knows it is disconnected and is killing your "VACUUM CONTROLLED" wastegate signal. Been there, 11 years ago, done that.

Road test was successful. Boost is back but only 9 lbs. I replaced the other vacuum valve transducer Y31/5, the one under the air box. Replaced the vacuum lines as well. "BIG" difference.
Boost is now 11 psi and hits 16 psi when it upshifts, but only briefly then returns to 11 psi

I made 3 timed runs with a Full tank of diesel, A/C on, Driver weight 200 lbs.

0-60 MPH
10.7 seconds
10.6 seconds
10.1 seconds, power braked

Test done with a G-Tech

I found that the G-Tech numbers were way optimistic, by about a second for my G-Tech. Use a stopwatch and the speedometer for an alternate method. Still, 10-11 seconds is fantastic...!

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Check out my website photos, documents, and movies!

Those are very good numbers for a 2.5 turbo. I just finished some work on my 2.5 turbo - I'll have to borrow my friends G-tech and see what it will do. I'm pretty sure I won't be able to beat your numbers though.

Tim

That reminds me - I have a G-Tech Pro I want to sell, if anyone is interested. I got a RaceTech AP-22 which kicks G-Tech butt. Damn I like that thing!

BTW - factory spec for 0-60 time on a 124.128 is mid/high 11 seconds, so anything near 11 or better is truly excellent. Drat. Now y'all have me wanting to go diddle with my injection pump and try to get my OM603 into the 9's...

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Check out my website photos, documents, and movies!

Two Words: PROPANE INJECTION

i appreciate you linking this thread to my egr thread, im trying to figure out the EDS test now, thats the next thing i want to do. a few questions though.

ive got the service manual and i printed out the part for the 602.962. but in the service manual, they use a pulse counter, which has 3 wires (+ gnd -), but a meter only has 2. im guessing thats why you used a jumper from X11/4 to gnd. but was this jumper something you made? and by ground, do you mean the battery or X11/1?

also, which test did you follow? the "a) short-test" or the "b) testing with pulse counter" both seem to check the same codes and use the same tools in the service manual, but "b" seems to have much more complicated steps. whats the difference?

and what kind of meter did you use? multimeter, voltmeter or ammeter?

since none of these count the pulses, im guessing you have to count the number of times the volts spike. is this right?

i also havent bought a meter yet, so what kind is best?

thanks alot tony. before i read this thread, i thought checking the computer required special tools, but apparently not.

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1991 300 D 2.5 Turbo, 220k
also in the family:
1981 240 D 185k
1991 350 SD 185k
2006 S 500
2005 SLK 350

Analog Voltage Meter
Set Meter to 12 volts or higher, positive lead to X11/4, negative lead to battery ground.
12" piece of 16 gauge wire with 1/4" stripped on one end and 1/2" stripped from other end.
Start engine, make sure it is at operating temperature.
Insert 1/2" stripped end into X11/4.
Watch the meter. It should read 12 volts.
Touch 1/4" piece to bare metal, I used Strut Tower bracket because it was close by, voltage should drop to Zero. Hold for 2-3 seconds then release. Count pulses. Repeat the process. It should give you the same errors twice. Do it again, test and retest until you begin with the first error or gives you just 1 pulse.
To clear the computer codes start the test again. When the first error code reads clear it by holding the wire for 8 seconds instead of 2-3 seconds.
A clean computer just gives 1 pulse

I bet a nickel you get a code 5.

no doubt bro. thanks alot. ill post the results when i do it.

__________________
1991 300 D 2.5 Turbo, 220k
also in the family:
1981 240 D 185k
1991 350 SD 185k
2006 S 500
2005 SLK 350

Fixed 1992 300D...

throttle cable adjustment
overload protection relay


thanks for all of the help

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Wayne Jockers
1992 300D

ok, so i cheched the codes using the method above, but it took me a few times to figure out how to read it. i checked it 4-5 times and im pretty sure i got a 5 every time, no other codes i dont think (i would recommend an analog meter for this test, i imagine it would be easier to read the pulses, i used a digital).

after i did it a few times, it stopped giving me code 5. did i clear the code by accident? will the code come back?

__________________
1991 300 D 2.5 Turbo, 220k
also in the family:
1981 240 D 185k
1991 350 SD 185k
2006 S 500
2005 SLK 350

It is possible that you may have cleared the code. It will come back if you did not fix the cause of the code. Give it a few days/miles and then check it again.

In my case, anytime the engine acts weird, loss of power, hesitation, anything unusual, I first check for codes. It has saved me time and money. Good habit to develop.

What do you think is the cause of your code 5?

i cant remember, but isnt y31/1 the EGR transducer? if it is the cause is because i had it unplugged from the vacuum! i was going to check it with it plugged in, but i accidently cleared the code the first time i checked it.

__________________
1991 300 D 2.5 Turbo, 220k
also in the family:
1981 240 D 185k
1991 350 SD 185k
2006 S 500
2005 SLK 350

Yes sir Y31/1 is the EGR Vacuum Valve Transducer. Replacing that valve eliminated the code, but if the egr port from the EGR valve through to the intake flap pipe is plugged it will spit the same code.

I replaced the valve and cleaned the port. The code has not returned, yet.

When I replaced Y31/5, the Vacuum Valve Transducer under the airbox, the boost returned to 11 psi and the power, drivability and fuel economy returned as well.

The Auto Transmission shifts smoother and always seems to be in the right gear.