I mentionned this in another thread but I've done a few things since and am out of ideas.


1992 300D 2.5

Idling low but smooth like 400rpms.

No tach

No boost (it is my understanding that if the idle computer cuts out the ELR takes the digital wastegate with it)

Here is what I have replaced:

New Bosch reman alternator (car was idling at 13.1 volts)

Tried 3 known good OVPs

New crank position sensor (not currently on the car since it didn't change anything I may return it)



The battery is a month old, some handheld tester my dads friend has says the battery is bad but the store that sold it to us tested it and it tested good. Could a dead cell in a battery cause issues?


I recently put glowplugs in the car and took the intake off, could I have unplugged something that created these issues? The tach worked for a week after I replaced the plugs though.


I'm out of ideas and am already sort of shot gunning parts at the car, any insight would be greatly appreciated.

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68 280SL - 70 280SL - 70 300SEL 3.5 - 72 350SL - 72 280SEL 4.5 - 72 220 - 72 220D - 73 450SL - 84 230GE - 87 200TD - 90 190E 2.0 - 03 G500

Nissan GTR - Nissan Skyline GTS25T - Toyota GTFour - Rover Mini - Toyota Land Cruiser HJ60 - Cadillac Eldorado - BMW E30 - BMW 135i

The ECU on that car has rudimentary diagnostics. You're a few years before OBDII but there is enough intelligence in the controller to report which part is failing.

Job 07.1-1120 in the FSM explains it all. You'll need an impulse counter. The FSM shows a special MB tool but you can make one out of an LED, resistor, pushbutton, and 3 test leads all tucked in a pill bottle.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Swapped batteries with my 87 just out of curiousity, no change.

Is there a link as to how to build the tester?

__________________
68 280SL - 70 280SL - 70 300SEL 3.5 - 72 350SL - 72 280SEL 4.5 - 72 220 - 72 220D - 73 450SL - 84 230GE - 87 200TD - 90 190E 2.0 - 03 G500

Nissan GTR - Nissan Skyline GTS25T - Toyota GTFour - Rover Mini - Toyota Land Cruiser HJ60 - Cadillac Eldorado - BMW E30 - BMW 135i

Check out this thread Reading Codes

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

I'm out of town, a friend has a spare ELR computer from a 92, he is going to take it to my dad and they are going to try it. I read a few cases online where the ELR went bad.

__________________
68 280SL - 70 280SL - 70 300SEL 3.5 - 72 350SL - 72 280SEL 4.5 - 72 220 - 72 220D - 73 450SL - 84 230GE - 87 200TD - 90 190E 2.0 - 03 G500

Nissan GTR - Nissan Skyline GTS25T - Toyota GTFour - Rover Mini - Toyota Land Cruiser HJ60 - Cadillac Eldorado - BMW E30 - BMW 135i

This happened to my OM602 in my 190DT. The resistors and stuff by the battery... a wire was connected poorly and when properly connected the motor would jump up and then settle and the tach would work. Hope you figure it out!

Can you elaborate on what you repaired to fix it?

Thanks!

__________________
68 280SL - 70 280SL - 70 300SEL 3.5 - 72 350SL - 72 280SEL 4.5 - 72 220 - 72 220D - 73 450SL - 84 230GE - 87 200TD - 90 190E 2.0 - 03 G500

Nissan GTR - Nissan Skyline GTS25T - Toyota GTFour - Rover Mini - Toyota Land Cruiser HJ60 - Cadillac Eldorado - BMW E30 - BMW 135i

Well in my case, I think the PO cut some wires or they got stuck under the battery and sliced and they he reconnected them very poorly. Getting a better connection fixed my issue.

Swapped ecus with another car and the car is running perfectly. Car won't idle above 12.7 volts with a new alternator, home battery tester says the battery is bad so my dad is off to the autoparts store to get it replaced under warranty.

__________________
68 280SL - 70 280SL - 70 300SEL 3.5 - 72 350SL - 72 280SEL 4.5 - 72 220 - 72 220D - 73 450SL - 84 230GE - 87 200TD - 90 190E 2.0 - 03 G500

Nissan GTR - Nissan Skyline GTS25T - Toyota GTFour - Rover Mini - Toyota Land Cruiser HJ60 - Cadillac Eldorado - BMW E30 - BMW 135i

I have this exact same problem on my 1992 300D 2.5 Turbo. Started about a month ago.

I'll try checking my wiring near the battery area.

-m

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Now:
2018 Tesla Model X
1999 S500 Grand Edition 164k
1992 300D 2.5 Turbo 287k
2005 E320 4MATIC wagon
1991 Alfa Romeo 164L 99k (sleeping for a while)

Then: 96 Lincoln TC, 93 Lincoln TC, 87 560 SEL, 87 300 SDL, 80 300D, 89 560 SEC

The usual problem is a bad overvoltage protection relay. This is a surge protector that protects the engine control units, anti lock brake system, and a couple of other sensitive components. It's located behind the battery.

Ok, I found the part, not very expensive. Is there easy way to test it before I replace it? Or more specifically, is the typical problem that the relay itself has failed or some other device is sending an electrical overload?

Thanks.

-m

__________________
Now:
2018 Tesla Model X
1999 S500 Grand Edition 164k
1992 300D 2.5 Turbo 287k
2005 E320 4MATIC wagon
1991 Alfa Romeo 164L 99k (sleeping for a while)

Then: 96 Lincoln TC, 93 Lincoln TC, 87 560 SEL, 87 300 SDL, 80 300D, 89 560 SEC

I ordered the part, we'll see if that's it. Thanks.

-m

__________________
Now:
2018 Tesla Model X
1999 S500 Grand Edition 164k
1992 300D 2.5 Turbo 287k
2005 E320 4MATIC wagon
1991 Alfa Romeo 164L 99k (sleeping for a while)

Then: 96 Lincoln TC, 93 Lincoln TC, 87 560 SEL, 87 300 SDL, 80 300D, 89 560 SEC

Yep that did the trick.
To remove it: pull up on the rear of the module and then side it out of the front slot. Then with your other hand pull the connector off the bottom.

FYI My car had a 7-pin module that I replaced with a brand new 9-pin module.

Tach works, idle is back to normal, and boost works again!

Thanks all.

-m


OVP RELAY CHANGE - 1988 300CE PICTORIAL - Mercedes-Benz Forum

__________________
Now:
2018 Tesla Model X
1999 S500 Grand Edition 164k
1992 300D 2.5 Turbo 287k
2005 E320 4MATIC wagon
1991 Alfa Romeo 164L 99k (sleeping for a while)

Then: 96 Lincoln TC, 93 Lincoln TC, 87 560 SEL, 87 300 SDL, 80 300D, 89 560 SEC

i have a 1991 300d and my tach stopped working and now have a very low idle. my ac also stopped working and i believe the problems are related as it all happened at the same time. the fuse on the OVP is good, could the relay still be bad? any help will be appreciated. after a long battle with vacuum leaks which i was declared winner it is soul crushing to have this problem.