350sd glow plug relay bypass HELP!

[Sausage King]

Has anyone done a glow plug relay bypass on a newer om603 engine. The relay is quite different from the older relays with the fuse. I feel that this may help. I haven't done anything yet, such as new glow plugs or reaming. I wanted some information first. Also, what happens to the small socket with the wiring going to a thermostat and glow plug light, etc. There are many posts regarding this, but I only seem to find this procedure for older om603 engines.

Any help would be appropriate.

Kris

[Diseasel300]

The later style relay just has 1 extra pin for the input from the temperature sensor in the head. If you're bypassing the relay (Why are you doing this?) the same rules apply as for the earlier cars. In fact you can use an earlier relay in your car, it just won't have the temperature based glow timer anymore.

[Maxbumpo]

Kris,

What exactly are you trying to fix?

I think it would be easier to simply fix whatever problem you have by diagnosing the cause and then replacing the failed parts, rather than try to re-engineer that system.

If the cost of new parts is an issue, then ask for used parts or search out used parts at a pick-n-pull salvage yard or an online source.

[Sausage King]

Well, my issue is a violent idle after start. The car starts, no problem. Then when at operating temp. it smoothes out. I haven't done any diagnostics, yet. My first thoughts were fuel related or glow plug related. I was only putting some feelers out there regarding this particular fix.

Thanks,
Kris

[compu_85]

Are you sure the current relay is broken? Have you tested it? Have you tested the glow plugs?

Before you start hacking up the car's wiring, figure out what's wrong.

-J

[Sausage King]

Thanks for the feedback.
Kris

[Diseasel300]

So you're bypassing the glow plug relay because you have a really rough idle? Come on now...

Start by checking the impedance of all of your glow plugs. They should be less than 1 ohm if good. Disconnect the heavy 6 pin plug from the glow plug relay before testing. You can test each pin in that plug to ground, or you can test each glow plug to ground, your choice.

Assuming that isn't the issue have you confirmed that you don't have air in the fuel system or low compression in one or more cylinders? Injectors firing correctly? Fuel leaks anywhere? Last time the fuel filters were changed?

There's a lot you can check before hacking and mowing through the car's electric system and blindly throwing money and time at something that may or may not be the issue.

The earlier 3.0L engine didn't have the afterglow system that yours does and they were known to have some less than smooth starts in colder weather. If you have a dead glow plug expect to have some pretty rough running for the first 15-30 seconds after starting.

[Maxbumpo]

Originally Posted by Diseasel300

....Start by checking the impedance of all of your glow plugs. They should be less than 1 ohm if good. Disconnect the heavy 6 pin plug from the glow plug relay before testing. You can test each pin in that plug to ground, or you can test each glow plug to ground, your choice.



If you have a dead glow plug expect to have some pretty rough running for the first 15-30 seconds after starting.

x1, this is where to start.

You will need a good digital multi-meter to test the very-low resistance of normal glow plugs, which typically are around 0.7 ohms at room temperature. I paid decent money to get a nice Fluke meter years ago, and it is the most useful tool for diagnostic work.

The "official" test from MB is to measure the current flow to each glow plug, which starts out around 15 amps but falls below 8 amps after 10 - 20 seconds. Clamp-on DC current meters are pricey, so I made my own tester with a $20 ammeter from FLAPS and some heavy solid strand copper household wire. The cheapo meter reads up to 30 amps, connect one wire into the same glow-plug connector mentioned above, touch the other wire to the hot battery connection in the pre-glow relay, and watch the meter peak and then drop off.