Hi Tom,

When you say, "sounds as if the spring on the tensioner may be gone" do you mean that it is GONE GONE as in absent/missing or do you mean that it may be gone as in broken/worn out/etc.?

The spring is there, but is loose and there is no tension on the serpentine belt. Any ideas?

The spring (the thing that hooks onto the tensioner and the upper plastic piece) may be broken in the middle, but you can't see it because of the rubber sleeve. Its job is to pull the tensioner upward to keep the belt taut. If it's broken, the belt will flop around!

Interesting, so MB improved the glow plug system on the later cars and got rid of that stupid strip fuse. I'm not sure how to test the system on that car then, again I'd refer to the FSM for testing procedures.


As to the tensioner, the aluminum rocker has a bearing in there. Make sure that ir moves freely without the shock and spring on it. Also make sure the pully spins freely. There is a diagram in the manual in your glove box that shows you how to route the belt, double check that. If all else fails replace the spring they are cheap, see where that gets you.

In reading more on DieselGiant.com, it looks like the GP test procedure would be the same with the exception of testing the strip fuse since it is obviously absent. If one were to test each plug, it seems that it would be possible to find the bad one - OR if all plugs seem to be fine, then the problem would be with the relay itself. My mechanic has already determined that the power TO the relay is fine - it's the power from the relay to the plugs that is down. Apparently, these relays have an internal circuit breaker that will reset when it no longer detects a problem. So, the task at hand is to determine if I have a defective GP (or multiples) that is setting off that circuit breaker, or if the relay itself is the problem. Unfortunately, my mechanic has already ordered the new relay with the plan to install it - it may be installed already, I just don't know. I don't know if he knows about checking each of the glow plugs. Arrghh... if he cannot get to the bottom of it today, then I will have it towed somewhere else Monday morning. This mechanic is a good friend and he really wants to help, so I truly hope he can find the problem - he takes pride in his work, so I hope this one doesn't stump him!

Extended glow period - did that cause this?
 

Also wanted to mention - when starting the car for the last couple weeks, I have been extending my glow period beyond the glow dash light. I have been waiting until the seat belt buzzer stops before I started the motor - could that be related to this GP/GP relay failure???

If your not getting power out of the relay it doesn't matter what your glow plugs are doing. They die one at a time, yet its possible you had several weak ones.

If you are not getting power out of the relay, is there a way to reset it? If not I think you found the problem.

Tell me if you find a flaw in my logic here...

Okay, since I have no power from the relay to the plugs that could mean a couple things. First, it could mean that the relay is defective. Second, it could also mean that there is some other problem downline that is constantly tripping the circuit breaker in the relay. Replacing the relay will certainly determine if the relay is at fault, but I could see the possibility that a new relay COULD do the same thing if the problem is between the relay and the plugs and simply causing the relay to do its job. Unfortunately, replacing the relay is an expensive way to figure this out, but I guess I have a 50/50 chance. What do you think?

Well no one has ever accused me of taking the cheap way out. :D I'd roll the dice, but again I rolled the dice on my Kilma relay to the tune of $150 for so and come up short.:D


PM me your email address I have some PDF files that you may find very usefull.

Ok, I'm coming in late in this discussion, but I assume you already tested you glow plugs for resistance?

2. is your red wire to the relay live (e.g. 12V off it)?

when you turn the key, do you hear a distinct click? The relay should click a 2nd time once you've had the key on too long before you try and start the motor. That's the relay shutting down (so it's a failsafe to keep you from frying plugs and other bits).

If you have 2 or more plugs out on this 603, the light will NOT come on. Second, if all plugs are out it will NOT start. I've already tested this on a 95 degree day. And yes, some smoke will come out the tailpipe, but it won't go.

you can pull the relay out of its housing to see if it's moving or not when you turn the key. As long as you don't touch the 80A wire you can hold it in your hand to watch.

good luck.

Problematic 350SD update......
 

Update: problem not solved........ yet.......

New relay installed - this one is a Beru brand WITH a strip fuse; my mechanic said this is what they make now because it is easier and cheaper to replace the little fuse than it is to replace an entire relay when it fries. Does this sound right or is this taking a step backwards with this setup?

Here's where it gets interesting. When the new relay was installed, he turned the switch and it immediately blew the fuse. So, that means it wasn't the relay to begin with. (Don't worry - my mechanic already said he will pay for the new relay since that wasn't the problem.) Now the task is to find out where the short is - either between the ignition and relay, or between the relay and the plugs. If I were a betting man (which I am not, ironically living in Las Vegas) my bet would be that it has a shorted plug, but I'm not sure. Would just one shorted plug cause this scenario or would it need to be multiples?

The other question relates to the electrical setup in my GreaseCar system. I don't have the original manual/map/photos that came with it (for some reason the mechanic who installed it didn't give it back to me and I haven't called to ask for it back yet) but the switch/fuel gauge is wired with power ALL the time. My current mechanic wants to find out where they hooked up the power to this system and if they piggy-backed it onto the GP line somewhere, and then if that would be enough to cause this problem. I'm still hoping it is something simple that we can easily fix. Obviously, I think the easiest fix would be something downstream from the relay to do with a bad plug(s) and hopefully it is not something upstream between the relay and ignition.

Any other input is welcomed! Thank you all for your help and encouragement!

Ckt breaker
 

If you have a shorted gp, it will trip the breaker immediately and you really wont hear the relays click much. You need to check each gp individually for a reading of around .8 ohms I believe if not someone chime in. I live in S. Miss. and at 94* my 603 won't fire until the plugs are heated. Been there, done that. Look on your drive belt and see if it the right length. OM603 is 2145mm and a 606 is 2140mm. It goes over the ps pump around and under the ac comp around and under the crank pulley, then loops back around the tensioner pulley(smooth side) then under and around the alternator pulley thenup and over the fan and back to the ps pump. Note: it will contact the fan pulley on both going to and coming from the alternator. Make you a crude drawing representing all six pulleys in their respective place and see if that makes sense. Either you have a wrong size belt or it is in the wrong path.:D
Bud

I'm still wondering if using the extended glow period may have had some impact on this. I mentioned it earlier in the thread, but haven't seen anyone comment on it yet. (I ask because my wife keeps telling me, "It's because of the way you've been starting it! You probably broke it!")

Naturally, that type of 'input' doesn't really help much - just seems like salt in a wound at this point! :dizzy2:

I'm thinking the serpentine thing is the spring - when I looked at it again, it is definitely VERY loose, moves up and down easily, and I can turn it very easily - so there is virtually ZERO tension on it whatsoever.

Change all the glow plugs,
 

Since glow plugs can and do fail, why not replace them all and then try the ignition, If the glow plugs weren't bad then you have spares.

Good luck with your problem. If it was me Id change all the glow plugs, go to a junkyard and get a new belt tensioner, and get your mechanic to put them on/in

Belt?
 

Blev, looking at your photos, I can't see the routing but it is probably right. You can check the spring easy. Just remove the nut on the bolt that goes through the top spring loop. Then using a 1/2" bar about 12-16" long put it in the hole in the plastic fulcrum and apply pressure toward the pass. side a bit and push the bolt through the plastic piece until it clears enough for the plastic peice(fulcrum) to rotate freely. If the spring is broken it will not have any pressure against the bar at all. If it has some and retracts some, I would say it is not broken. If it is not the spring and routing or size of the belt then make sure the new tensioner pulley is the right one , right diameter.:D
Bud

I don't think your method of starting the car is causing any problem, I start mine the same way waiting for the seat belt buzzer to stop. It only extends the glow period 5 seconds beyond when the light goes out. Besides, our cars are equiped with a factory after glow feature that allows the plugs to continue to glow after the engine is running for a period of time based on temperature. So no worries there!

I did look at my system tonight and confirmed the relay is the same as yours, no fuse strip which makes it a circuit breaker type relay. So just like in your house, when something causes the breaker to trip, it can be reset/recycled but you need to find the cause in the circuit. As others have suggested, it is likely one or two bad glow plugs or the wiring to them, but doubtful on the wiring unless your grease system is tapped in some how to the circuit (hope not!). Remember, the glow plug light on the dash could still light with one bad plug but will probably not light if a second plug additionally goes bad.

I also just changed the serpentine belt on my car last weekend and the job is pretty easy. You need to have your guy confirm the routing of the belt and ensure all pulleys are spinning with the belt. It would be difficult to route the belt wrong because there just isn't alot of choices. You should have very little lateral movement with the spring when installed. If you can move the spring back and forth its probably broken inside the sheathing. Have him loosen and back off the top bolt to remove the spring and confirm for sure, 5 minute job.