'91 W124 Glow Plug Issue

[m2b1]

This past February the glow plug light didn't come on when it was supposed to and came on after the car started. Time to change the plugs. Ordered the plugs from ******** AZ based on what their website was compatible with my car. I get them pull the old plugs out and find the ones that they set were a little bigger than the ones I pulled out. Thought that they might have resigned them since their website said they were compatible. After reaming out the chambers I put them in and everything was fine. The next day as I was driving down the road and the GP light came on for a full cycle and then went off. I went for a week where the GP light wouldn't come on and then would come on. It has been pretty random ever since. I have changed out the OVP relay but that didn't change anything. I am hesitant to get a new GP relay since the plugs were slightly longer than expected. I have changed the GPs myself several times over the past 10 years and this is the first time I have had an issue like this. Anyone have experience getting plugs that were slightly longer than the ones they took out?

[dieselbenz1]

The longer GPs are for the straight prechambers, you engine 602 should have the inclined prechambers which require the shorter GPs.

[Diseasel300]

Originally Posted by dieselbenz1

The longer GPs are for the straight prechambers, you engine 602 should have the inclined prechambers which require the shorter GPs.

^^^ X2

[Diesel911]

Is your Engine starting OK?

What I have in my notes is that the shorter glow plugs are for the glow plug really that has the afterglow set up. That means after the Engine starts a coolant temp sensor allows the glow plug relay to remain on for x amount of time after starting depending on the coolant temp.

That means there is coolant temp sensor. If the coolant temp sensor has issues or the connections have issue it is not going to act correctly.

Of course there can be the other faults not related to the afterglow.

If someone has the site they could post the free online manual and you could see how the system is supposed to function and there might be something on trouble shooting like some values for the temp sensor.

This was on a gasoline engine. My Engine was staying too long on the enriched fuel for starting. I pulled out the Coolant Temp Sensor and found that the Sensor had a rather thick coat of white material (coolant ran through the aluminum intake manifold and the sensor was there).

When I cleaned off the white crude everything returned to normal.

[Dr. Sternschnuppe]

http://w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/Engine/602_603/15-4111.pdf

[m2b1]

Yeah I was afraid of having to do this job twice. Pretty annoyed that their site confirmed that they were compatible with my car. It's a pretty straight forward job I just hate being hunched over for so long plus the money loss. Thanks for your input everyone!!

[Bengoshi2000]

Originally Posted by m2b1

...I just hate being hunched over for so long plus the money loss. Thanks for your input everyone!!

Same here. I've started putting all cars on ramps even if I'm working from the top. My back tends to be happier at the end of the day.