92 300D 2.5 LOW POWER, SOMETIMES - PeachParts Mercedes-Benz Forum

300TD/WI · #1 01-31-2013, 12:13 AM

Hi all new to the forum, but ive been reading it for quite a while.

I have a 1993 300 D 2.5 turbo. This is not my first Mercedes diesel. but I have run into a difficult problem with this 1. I have an intermittent low power issue. When you started up cold hot turbo seems to work great has excellent power. But after it warms up or after a little bit of driving the power seems to go away.it feels really slow and sluggish like I can put my foot down and it's almost going nowhere. It seems like the power comes back after you shut it off and started back up. But that maybe a mistake but I do know that power is best when cold.

I have deleted the Egr but haven't completely removed it. I put a block off plate between the Egr and manifold and disconnected the vacuum hose to the EgR and plug it off I also disconnected the electronic actuator for the EgR.fuel filters have both been done in the last 3 months. I know my turbo works because when power is there it feels really good. But it just intermittently goes away. last time I check mileage average was about 28.5 with about 50/50 highway city.

at this point I will take any ideas anyone has. what could be causing interment low power brain storms and ideas are welcome from anyone and very much appreciated. I have provided all information I can think of. If any other info is needed please ask Thanks in advance

vstech · #2 01-31-2013, 06:09 AM

Welcome to the forum.
there is an air box under the air filter, it can shut off airflow. removing it, and installing a section of tubing to connect the filter to the fender can help.

300TD/WI · #3 01-31-2013, 08:22 AM

ok.. that may help but... would that cause it to be intermitent. i have read up on the egr... it says the EDS system cuts boost if it doesnt see egr. how accurate is that.
if i connect the egr actuator electrical connector but leave the vac line plugged off will that help.
has anyone else come up with a correct way to bypass Egr on this system. Please help

DieselDummy · #4 01-31-2013, 11:16 PM

I had similar power issues on My 91 2.5t. It had a faulty Overboost valve, which is located on the drivers side strut tower. I left the electrical plug in, but disconnected the boost hose. Fix my power issue.

DD

ROLLGUY · #5 02-01-2013, 09:04 PM

Quote:

Originally Posted by DieselDummy

I had similar power issues on My 91 2.5t. It had a faulty Overboost valve, which is located on the drivers side strut tower. I left the electrical plug in, but disconnected the boost hose. Fix my power issue.

DD

My brother had the exact problem with his 1991 300D 2.5. I bypassed the OPV and it runs "like a greased cheetah chasing a bullet train" now.

biopete · #6 01-31-2013, 11:27 PM

Just to be sure , its not that your trans is shifting too early right? my 1992 feels slow when it shifts into fourth and it should be in second thus eliminating any boost i might get if it was in second or third. Whenever i feel i have power issues i mannually shift through gears and make sure its not that.

vstech · #7 02-01-2013, 06:22 AM

by the way, I looked at my 93, and there is no shut off box under the intake filter on it. I wonder now how the computer is regulating air for the egr...
anybody know? gotta find that and repair it.

pmckechnie · #8 02-01-2013, 08:07 AM

The 90 to 93 2.5 engine control system will disable boost if it sees a problem in the EGR system. Restarting will make the problem go away until it test the EGR system again. Most common fix is to replace the vacuum operated wastegate actuator on the turbo with a boost pressure type, or reconnect the EGR and repair what ever problems there are with the rest of the system. This is going to sound crazy but this is what I did. On the cross over part of the manifold between the turbo and the intake side of the engine there is a valve that can restrict the boost going to the intake. It is part of the EGR test system. If it doesn't work, you will get the same no boost condition as the EGR not working. I modified that valve and made it a pressure operated valve so if the boost goes over 15 lbs, it will restrict the airflow which will regulate the boost. I then hooked full time vacuum to the wastegate so it stays closed at all times. It has been like that for about 6 years now. You can find a lot of post about replacing the wastegate with one that can be made to work. If you choose to do this, just leave the engine control installed as it also does the idle control.

Paul

Chris_ · #9 02-05-2013, 12:24 PM

Quote:

Originally Posted by pmckechnie

The 90 to 93 2.5 engine control system will disable boost if it sees a problem in the EGR system. Restarting will make the problem go away until it test the EGR system again. Most common fix is to replace the vacuum operated wastegate actuator on the turbo with a boost pressure type, or reconnect the EGR and repair what ever problems there are with the rest of the system. This is going to sound crazy but this is what I did. On the cross over part of the manifold between the turbo and the intake side of the engine there is a valve that can restrict the boost going to the intake. It is part of the EGR test system. If it doesn't work, you will get the same no boost condition as the EGR not working. I modified that valve and made it a pressure operated valve so if the boost goes over 15 lbs, it will restrict the airflow which will regulate the boost. I then hooked full time vacuum to the wastegate so it stays closed at all times. It has been like that for about 6 years now. You can find a lot of post about replacing the wastegate with one that can be made to work. If you choose to do this, just leave the engine control installed as it also does the idle control.

Paul

With full time vacuum applied to the wastegate - what prevents it from regularly ecceeding 15 psi ?
and
I may be entirely incorrect but isnt it the case generally speaking that to restrict airflow regularly can promote other issues such as the tendency for the engine to attempt to obtain the air elsewhere causing other failures... could be totally wrong just my perception.
also
I have given serious thought to how to modify the stock setup to fool the computer into thinking that the EGR system is working ..making it "see" the pressures that it is calling for ... but all in all I came to the same conclusion as many that for simplicity sake ..I just ordered the pressure style actuator.

thanks

pmckechnie · #10 02-05-2013, 01:40 PM

I'll try to explain how my boost control works. With vacuum to the wastgate all the time can let boost go to 20+ psi (That is as high as my gauge will go.) So to control the boost, I use the flapper valve in the intake crossover to restrict the airflow some. It is adjusted so that when the boost gets to 15 psi in the intake manifold it will close off a little. This only restricts enough to drop the boost to the intake manifold. It never restricts enough to cause a vacuum in the intake, just reduce the boost. It has been this way for several years now with no ill effect. In normal driving the boost seldom goes over 10psi. At WOT it will go to 15 psi until you let off some. So the wastegate is just a safety device that keeps the boost at a safe level. The pressure type wastegate lets some of the exhaust bypass the exhaust turbine in the turbo to reduce boost. The other overboost system blocks boost from getting to the ALDA. This cuts down on the amount of fuel the engine gets. Less fuel = less exhaust = less boost from the turbo. There is always more than one way to skin a cat.

Paul

vstech · #11 02-05-2013, 01:54 PM

Quote:

Originally Posted by pmckechnie

I'll try to explain how my boost control works. With vacuum to the wastgate all the time can let boost go to 20+ psi (That is as high as my gauge will go.) So to control the boost, I use the flapper valve in the intake crossover to restrict the airflow some. It is adjusted so that when the boost gets to 15 psi in the intake manifold it will close off a little. This only restricts enough to drop the boost to the intake manifold. It never restricts enough to cause a vacuum in the intake, just reduce the boost. It has been this way for several years now with no ill effect. In normal driving the boost seldom goes over 10psi. At WOT it will go to 15 psi until you let off some. So the wastegate is just a safety device that keeps the boost at a safe level. The pressure type wastegate lets some of the exhaust bypass the exhaust turbine in the turbo to reduce boost. The other overboost system blocks boost from getting to the ALDA. This cuts down on the amount of fuel the engine gets. Less fuel = less exhaust = less boost from the turbo. There is always more than one way to skin a cat.

Paul

sounds interesting, you ought to come over and work on mine...

300TD/WI · #12 02-01-2013, 09:30 AM

i dont mean to sound dumb but i dont see this valve on the crossover. also that seems to be exactly the problem im having, when car is started or restarted it has excellent boost
and power and after a few mins it goes away. if there is any more info this crossover valve and also converting to a manual boost controller. all help is greatly appreciated.
Ed

300TD/WI · #13 02-01-2013, 09:32 AM

also about the over boost valve. could it cause boost to go away after a couple mins of driving,
Ed

rkpatt · #14 02-01-2013, 06:01 PM

Move on to a pressure activated wastegate actuator -
Wastegate actuator swap for OM602.962 - revisited

BigBen · #15 02-01-2013, 10:29 PM

Quote:

Originally Posted by rkpatt

Move on to a pressure activated wastegate actuator -
Wastegate actuator swap for OM602.962 - revisited

This is also my advice. I've quit trying to understand this EDS system.

It never again stopped working perfectly, constant 15-16psi boost, lovely!!!

Bye, Ben

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