Reluctant starter - troubleshooting process - PeachParts Mercedes-Benz Forum

D_Ryan · #1 10-25-2004, 05:05 PM

All;

My '85 300TD is now reluctant to start since the nighttime temps are dropping into the 40's. This seems too warm to be experiencing problems of this nature based on other posts to this forum.

Aside from the hesitant starting (cranks readily, but no combustion unless I let the starter turn for ~ 7 - 10 seconds), the glow-plug light on the dash does not come on UNLESS I cycle the ignition switch on and off rapidly through several cycles, then it will come on to indicate a pre-heat cycle.

I'm suspecting either glow-plugs and/or glow-plug relay, and am getting ready to get under the hood with a DVM to troubleshoot. Best to start with impedance through the glow plugs, or go straight to the relay fuse?

Thanks,
Dave

Palangi · #2 10-25-2004, 05:12 PM

Very easy to look at both at the same time. Pop the cover off the glow plug relay. Disconnect the 5 wire cable going to the glow plugs and ohm out each glow plug wire. Each wire should be less than one ohm to ground. While you have the cover off the relay, inspect the strip fuse for cracks. Be careful, the strip fuse is always live unless you disconnect the battery.

Gilly · #3 10-25-2004, 06:08 PM

The only valid test for the glowplugs is current consumption.

Gilly

Palangi · #4 10-25-2004, 06:32 PM

Yep, but he said he has a DVM, he didn't mention a clamp-on ammeter. When he finds the one or two plugs reading infinity, he will have found the problem.

kamil · #5 10-25-2004, 06:53 PM

Had the same problem and so did my friend. Just buy new glow plugs since they are only like 12 bucks for bosch ones..... Once I changed the plugs car started like new...

Fisherman · #6 10-25-2004, 07:09 PM

If you go the route that many do and replace the GPs make sure and ream the holes as the buildup of carbon will also diminish the functioning of the GPs.
I use a drill bit in my fingers and just rotate it until it will spin freely. In my fingers so that I don't over ream a hole. On the number 5 hole I had to use a tap just slightly larger than the GP diameter (3/16ths?) as it was the only thing short enough to get into the space by the oil filter housing.

Ream them out, then crank the motor a few times with all the GPs out so that you eject the carbon you cut loose and then put in the new plugs. I find it easier to remove all the fuel lines so that you don't have to deal with the cramped space and bruised knuckles.

I'm still hoping that someone gives some feedback on the "replacement" GP Relay offered by Fastlane/Bosch. This seems like a great idea as it stays on longer (probably shortens the life of your GPs though) and for the price it is really not much more to get the newer style relay and the 4 GPs they offer with it.

Testing them with an ohm meter is okay but I have had them test good yet not start the car. When I replaced them the car would once again start but I keep the ones that tested as good and put them in the 81 SD when a GP tests bad. The 84 is mommie's car and had better start everytime or I will hear about it...

Of course the other way I look at this is that it is cheap winterization protection to just replace them every winter but then I don't mind spending money on this type of insurance. That is ONLY my opinion however and any decisions made due to input from me is without warranty, express or implied...

jayb79 · #7 10-25-2004, 10:57 PM

How old is your battery? Is it the correct size for the car? If it doesn't crank fast enough it will start harder.

phantoms · #8 10-26-2004, 07:34 PM

Quote:

Originally Posted by Fisherman

I'm still hoping that someone gives some feedback on the "replacement" GP Relay offered by Fastlane/Bosch. This seems like a great idea as it stays on longer (probably shortens the life of your GPs though) and for the price it is really not much more to get the newer style relay and the 4 GPs they offer with it.

I just receive the Glow plug upgrade kit and plan on installing it on my daughter's 240D this weekend, changing over from the loop style plugs. Claims on the box that it shortens glow time needed to start to 3-7 seconds. Also that it has an afterstart glow function to help reduce smoke and run smoother. If you're getting it for a 5cyl., then you'll need an additional glowplug and relay according to the instructions. This kit is designed to replace loop style glow plugs with pencil style ones and as such, the thread base is bigger than the later pencil style.

Fisherman · #9 10-27-2004, 09:54 AM

for my old 115 but couldn't justify the moeny for it. besides I liked the 115 with the GP stick because you could control how long you glowed for by just holdin git on longer.

Yeah, this is for the 84 as it starts a little rough if you use the light to control the glow times. I always wait a little longer when it's cold to try an dhelp the engine out a little but I figure that eventually the longer you glow the faster the plugs will deteriorate.

I'd be very interested in your results with the new relay though. Let us know how it goes.