92 300D OM 602 Low Power Fix in Progress - PeachParts Mercedes-Benz Forum

bobodaclown · #1 02-07-2008, 05:30 PM

Hello,
First Thanks for the Great Site. Learning lots.

Background: 92 300D 2.5L OM 602 engine.
MPG 30-31. Doesn't Burn Oil. ODO Milage 265K, Engine Replaced 120K due to shop not putting in oil plug. Orig engine shot. Have paperwork showing.

Low power: 18+ 0-60 No Boost.

What I've done.. Read Read Read then attempt to understand what was read.

Got the codes from the EDS, Used analog meter, Pins 1/4 and then short pin 4 (to ground) for 2-3 sec to get code, short pin 4, 6-8 sec to clear code.

Had codes 3, 11, 14, 15. Cleared codes. Get 1 flash only. Great. All OK. Took for a drive 5 minutes. No increase in power.

Recheck codes. No error codes only "1".

QUESTION: How long does it take for computer to do its diagnostic check? Or for codes to form?

Check all vacuum lines. Hmmm... This isn't right...
Line that goes to EGR Valve and the Boost Pressure Control Valve are switched. WOW.. Let me double check and correct.

Keep following lines. Wow.. Do you ever need a road map, and a highlighter.

OK... Hmmm... The VAC from the Boost Pressure Control/Pressure control flap Vacuum Transducer is going to ATM line..HMMMM... Must be another swapped.. Keep looking... ATM line from the Boost PSI Switchover Valve and Boost Pressure control are going to VAC not ATM....

OK.. Found the 2 switched.lines. Swap them. Double check..

Hooked up VAC Guage got good VAC 10PSI.

Road Test... Better Acceleration above 2200 RPM.
0-60 times approx 15 Sec. I know it could be better.

Need to get a Boost gage. Check Boost at the ALDA Banjo fitting.
ALDA Banjo fitting and fitting at manifold are clean.

At idle 0 should be the boost, at open throttle (underload, accelerating) above 2200 RPM Boost should be??????

I know this is a long first post. I wanted to give as much info to help you help me.

compress ignite · #2 02-07-2008, 07:15 PM

12 to 14 PSI (with 80MPH headwind,20 degree upslope gradient,pedal down)

'You gotta Mity Vac Yet? 'For testing integrity of vacuum system.

bobodaclown · #3 02-07-2008, 09:36 PM

Yeap. Got a MityVac. Tested the EGR Valve. Pumped it up then removed hose heard it slap shut. Also checked the Pressure Control flap, it moved with vac applied. and checked 2 of the switchover valves. They worked.

And hooked the gauge up with the engine at idle. Was getting I believe descent vacuum on the Vac side of the transducers. I don't remember what the reading was.

If you know what it should be that would be great. I'll double check it. hmmmm...

2.5Turbo · #4 02-07-2008, 11:40 PM

I seem to remember the transducers having four ports, a VAC port that is connected to the vacuum supply, two ATM ports that are hooked to the atmosphere lines that run through that fuel filter looking thing and into the passenger compartment, and an OUT port that is connected to the device being controlled. Make sure everything is hooked up in this way. Do a search on here as well on the subject as I seem to remember finding some diagrams and other useful information that may help.

The 92 is different than my 90 in that it has switchover valves that control the EGR stuff instead of a third transducer. I was having no boost problems too, and after a lot of hunting around, I found that the transducer had gone bad and was not closing the wastegate. To check, I swapped the transducer with the one on the EGR. It worked great until the computer found out the EGR wasn't working

Also, try driving around with straight vacuum to the wastegate actuator and see if performance improves any. Be careful and don't overboost too much while it's connected like this because I think they eliminated the overboost protection switchover valve in 92.

bobodaclown · #5 02-08-2008, 12:36 AM

I found your post and thanks for all the info you've provided.

The 92 OM 602 transducers have 4 ports. VAC/OUT/2 ATM. I really didn't find any good testing procedures for those transducers.

I did find 2 things wrong with connections the Transducer outputs were switched.
1. EGR/PSI Control Flap Swapped.
2. Boost PSI Control Transducer OUT going to VAC Line

I'm getting boost now not sure how much. But pulling out into traffic is a bit quicker.

Off to the store to get a boost gauge. I'm concerned about hooking a straigh vacuum to the wastegate actuator and getting overboost. I'm going to hook up the boost gauge at the manifold connection leading to the ALDA before the Orifice .03" (.7mm). I think the orifice acts as a damper.

I hope some one can let me know.

capeburke · #6 02-08-2008, 01:21 AM

I have been told by a very good diesel teck that the 90-93 2.5t some times get carbon buld up in the exaust manifold (a dirty Job).

bobodaclown · #7 02-09-2008, 03:33 PM

I picked up a vac/boost gauge at Advanced AP here if FLA. It was about $26. The vac side reads to 30 lbs and the boost side reads to 10. I wanted a 15 or so but it works for what I needed.

I hooked it to the banjo fitting that comes from the Intake Manifold. When I step hard on the pedal from a stop it pegs out at 10 PSI (GAUGE max) then comes down. So turbo is now working. Gauge confirms seat of the pants feeling.

I'm glad to see it. So all is running well.
Next project....
Replacing the Combination Switch. (and I've got the Air bag to remove). Hi beam position doesn't work. But works intermittently if I pull it towards me.

I'll take some pictures. And post a DIY.