Glow Plugs: What's Left to Test??? - PeachParts Mercedes-Benz Forum

Bill()C · #1 11-09-2007, 10:54 AM

87 300SDL

Hard start in cold, no glow plug indicator light before startup at all... basically acts like glow plugs aren't working at all...

Put in 6 new Bosch GP's. 4 of the old ones Ohm'd out bad (infinity). 1 seemed fine, .3 and one seemed all over the place I couldn't get my meter to rest. (I don't really understand Ohmmeters)

Tested the Relay. Clicks after 20-30 seconds. Followed all directions at dieselgiant.com. 12+volts at relay points... 12+v going to each wire. 12+volts going to each plug. Each wire Ohm'd out between .3 and 0.0. Fuse strip has 12 volts on each side, etc.

My situation hasn't changed. The car still acts as if the GPs aren't working (will start, but not easily and runs rough) and I have no indicator at all on the dash.

I remember something about coolant sensor, which I thought I had, but now I do not believe I do, there just doesn't seem to be anything else wired up to the Relay and besides it does click off after 20-30 seconds.

I'm at a loss for the next step. I emplore your help!

Thanks,
Bill

junqueyardjim · #2 11-09-2007, 11:10 AM

But we have to remember that glow plugs are only a very necessary starting component on our engines. I think you might have a 603 engine, which is much different then my 617. But some things are the same, and that is that there are a number of factors that contribute to easy starting and good running. It seems to me, from what you list that glow plugs are not the problem. Your glow plug like isn't operational, but it doesn't need it to work. Could be a burned out bub. I would think also that if you have a 603 your valves have hydraulic tappets, so a bad adjustment is not the problem. Valves serve on the air side. The diesel needs air and fuel. If valves are OK, you are going to have to suspect fuel delivery. Either the injectors, or the fuel pump, filters or fuel pump timing. Start with the easy stuff. Is the engine getting enough fuel to start? That is at cranking speeds. It probably is, but check it out. As for the injector system, most of us are ahead of the game there by bringing it to an expert. And I would really try for testing purposes to eliminate that nickol plated grease car system and go with a can of straight diesel on a short hose right into the IP.

sixto · #3 11-09-2007, 12:45 PM

No glow plug relay coolant sensor in a 300SDL. The relay has a built-in temp sensor.

Two things I would do:

- compression test

- check current through each glow plug wire while glowing. I believe it should be around 8 amps.

Sixto
87 300D

gskurka · #4 11-09-2007, 01:13 PM

I'd like to do a compression check on my 1991 350 SD. Is there a procedure available somwhere on this forum?

Greg

sixto · #5 11-09-2007, 01:23 PM

Depends on the compression tester you have. Some have adapters that fit in place of the injectors, some have adapters that fit in place of the glow plugs. Tie the fuel shut off lever in the down position. This is crucial if you do the compression check through the glow plug holes because Diesel fuel does not evaporate like gasoline. If you don't have bent rods to begin with, you might after

It's more telling to do the compression test on a hot engine but it's difficult to prep a hot engine and it won't be that all hot after the prep work. It might be considerably cooler on the last cylinder you test than the first. What's the choice, check one cylinder a day?

In rough numbers, you're looking for at least 350 psi in each cylinder, 400 ideally, with as little variation as possible. 20 psi variation is no cause for concern.

A compression test won't confirm or discount bent rods.

Sixto
87 300D

Hit Man X · #6 11-09-2007, 01:29 PM

Maybe the fuse relay strip? They're under $1, could be worth a shot...

Bill()C · #7 11-09-2007, 01:41 PM

I am fully confident in the compression of the engine. Granted I haven't done a compression test, but I've seen from my '79 what an engine is like that loses compression.

Yes this is the 603 engine. I should state that I can get the engine to start. It will start when it's in the 30's outside. I CHOSE not to at this point because I do not believe it to be good for the engine to try and start it without properly working GP System.

I am not starting on WVO... and since the system will start, car will run fine when warmed up I don't see any problem with fuel delivery at all. I also have some segments of clear fuel line and air in fuel is easy for me to see so I'm ruling that one out.

Basically I think there's something wrong somewhere in the GP system and I'm not testing it correctly. Yes it could be the dashbulb isn't working anymore, but it stopped working at the same time that my GP's stopped (or seemed to have stopped working).

How can I check current through each GP Wire? I don't have a DC Ammeter, just voltmeter. I assume there's such a thing. I only tested 2 or 3 of the new plugs for resistance as a reference to the old plugs but did not hook them up to actual to a battery to glow. I suppose I should pull them (what a royal pain) and test them? I just can't imagine they all are bad.

Perhaps my new plugs aren't grounding???? is that even possible? Maybe if the threads in the block have some corrosion? How would I test this? Disconnect the wire to the relay and OHM from wire to head? What should my Ohm reading be?

Thanks for ideas,
Bill

junqueyardjim · #8 11-09-2007, 01:44 PM

I have checked the compression on a number of Benz diesels without tying the fuel stop back. No excess of fuel on these tests. Now I do or have done it both ways, with the ignition switch and with jumping the terminal box on the passenger fender. Jumping the terminal box would keep the fuel shut off in off position. On the other hand, if all the glow plugs are out, if fuel is getting into the cylinders, it would be ejected through the glow plug hole.

sixto · #9 11-09-2007, 09:57 PM

Yes I do.

Sixto
87 300D

bulletproofair · #10 11-09-2007, 10:27 PM

***I see that you have already put the new ones in. I wouldn't bother taking them out and testing them. Its very likely they work, and you would just be wasting time in my opinion.***(I edited here after I reread)

I hate to say it, but I recommend pulling the glowplugs and testing them with a jumpbox or battery. I went through this a week ago, and was glad I did afterwards. My engine that gave me problems starting starts in under a second of cranking now!

This is only if you haven't put new ones in though. And if you have, just put the old ones through this process and see what happens. They shouldn't work if you were doing the resistance test correctly.

Doing this, you will know definitely. And its really not that bad taking them out...

Using a ratcheting wrench helps quite a bit also. 8mm & 12mm.

You mentioned your car "runs rough." Glowplugs really have no effect whatsoever on how your car runs, so it sounds as if the glowplugs are not the culprit, especially if you replaced all of them with new. Also, test for voltage at the glowplug at the block to make sure you're getting sufficient voltage directly at the glowplugs to ensure there is no bad wires.

In the colder weather, my car always kind of "clanks" for just a few seconds when first starting it up for the day. I think its just the nature of the beast!

Bill()C · #11 11-10-2007, 02:17 AM

Quote:

Originally Posted by bulletproofair

You mentioned your car "runs rough." Glowplugs really have no effect whatsoever on how your car runs,

I disagree... if the cylinder is not up to temperature the car will run rough until the engine has warmed up sufficiently. This is precisely the problem I'm having. I apologize because it appears that I am doing a poor job describing my problem. I also may be a little stubborn because I really do think I've missed something in the whole GP diagnostics or install... This is all classic GP problem stuff I'm having.

Again, I know I'm getting fuel... I can plug the car in to warm the block and it's an easy start that way (no rough run on startup either) plus I have an indicator light saying the GP's aren't working... just can't figure out what I'm missing. Fuse strip tests good as well... ohm and volt wise... at least as far as I understand it.

Thanks again,
Bill

sixto · #12 11-10-2007, 02:34 AM

Did you ream the glow plug holes when you replaced glow plugs? There might be a layer of crud insulating the fuel spray from the glow plug.

Sixto
87 300D

Bill()C · #13 11-10-2007, 11:42 AM

Quote:

Originally Posted by sixto

Did you ream the glow plug holes when you replaced glow plugs? There might be a layer of crud insulating the fuel spray from the glow plug.

That's what I was beginning to think... there WAS
some white crud / corrosion around the old ones I pulled out. In lieu of pulling the plugs and reaming out with (what would I use?!) I did an ohm test on the tip of each plug to the head with the harness disconnected from the GPC. I got about 1 ohm for each plug. So there seems to be connectivity there, enough to operate the glow plug I would think.

Attached is a picture of my meter. Earlier someone said to test DC amperage. I didn't think I had that capability but from my meter it appears I do... although only up to 10 amps. I put one lead on the tip of the GP and another on the head and turned the key... I didn't like the results. I got instant spark and was afraid I was going to burn out my meter. Is what I am trying safe???

The meter moved, but it happened so fast I don't know what I got. Should I do this again and just not be scared? However I tend to think that I might blow my meter because it's probably much more than 10amps...

Anyway my current wonder is if the GPC is giving enough amperage to the GP's. I also figured I could pull the GP's leave them wired to the harness, run a wire from the shell of the GP to the engine block... and see if she glows. Now if that works I'll have to eat crow because obviously they're working and I'm not as smart as I think I am.

Any and all help is appreciated... I think I'll go work on my solar collector and feel like I'm actually accomplishing something today.

Thanks,
Bill

Hit Man X · #14 11-10-2007, 11:54 AM

Did you not see this - http://www.peachparts.com/shopforum/showpost.php?p=1669877&postcount=6

Also, yeah didn't cross my mind to mention the reamer as I figured it was SOP. It's a good investment for the amount of cash. If I could recall where I put mine you could just bum mine.

Bill()C · #15 11-10-2007, 12:14 PM

Yes..., thanks Hit Man. Strip visually looks fine and I have twelve volts and continuity across it...

So there IS a special tool to ream it out with huh? Might be worth while if I pull them out again to test it.

Bill