Glow plug relay overide? - PeachParts Mercedes-Benz Forum

peachykeen · #1 10-12-2011, 10:26 PM

I have a very, very high mileage 79 300TD wagon that has become really hard to start 30s even mid-low 40s F...glow plugs are good, fuel has powerservice in it regularly and valves have been adjusted in last couple yrs...plus a recent full diesel purge...

Has anyone overrided their glow plug relay to manually control the time that the plugs are actually glowing? If I am correct, if I could allow my plugs to glow longer, won't my old wagon start a bit easier this winter? There is a place online (**************) that sells a little kit to do this and wondering.....

Thanks for any insight.

Brian Carlton · #2 10-12-2011, 10:35 PM

Quote:

Originally Posted by peachykeen

If I am correct, if I could allow my plugs to glow longer..............

The plugs glow until you release the key from the start position or the relay times out (usually about 35 seconds).

So, if you are waiting 10 seconds or so............until the light goes out.............try waiting for 30 seconds and see if the condition improves.

Additionally, have you checked for any open plugs..............two bad ones will cause starting issues on an older engine?

kerry · #3 10-12-2011, 10:53 PM

I think one bad one will cause a problem on a 79. I think the OE on that year are loop plugs. How have you confirmed that the glowplugs are working correctly? You could just glow it until you heard the relay time out, turn off the key and then turn on and glow again for a double length glow without changing anything.

bigblockchev · #4 10-12-2011, 10:56 PM

If you interrupt the power wire going to the glow plug relay, not the huge one from the connect point by the battery but the small one which goes to the ign switch it will restart the timing cycle for another 35 secs or so if you need it. The plugs are energised when this wire is given 12V to do this you can run a small pair of wires to beside the GP relay, cut the energising wire splice in the pair and lead these back to a momentary contact pushbutton in the normally on position so that when you push the button the power is momentarily removed from this wire thus restarting the cycle. This avoids using a high current 80 - 100 amp relay and a lot of extra wiring it uses the existing GP relay in pretty much the same manner as it was designed to function. I can't remember the exact color code for the wires so if you are not comfortable with wiring in general and circuit tracing DON"T ATTEMPT THIS MOD Cheers Dan

aaa · #5 10-12-2011, 11:08 PM

Why rewire when you can just flip the key back and forth every 35 secs.

Zacharias · #6 10-12-2011, 11:27 PM

Quote:

Originally Posted by peachykeen

Has anyone overrided their glow plug relay to manually control the time that the plugs are actually glowing? If I am correct, if I could allow my plugs to glow longer, won't my old wagon start a bit easier this winter? There is a place online (**************) that sells a little kit to do this and wondering.....

I installed that kit on my CD right after I got it, but I did so because I had the old system like yours, my engine appeared to have significant wear, my glowplugs were worn out and the relay died on me. So for me the package made sense at the time as it was a lot less than buying the components piece by piece to put it back to OEM.

Observation: It isn't quite as easy to install as they make it out to be. Or maybe that was just me.

In any case, as another person mentioned, you can always just give the car two long glow cycles. I routinely did that with my old '79 SD, in winter.

You don't say where you are located, but as your profile pic shows the car in deep snow, I'll assume you aren't in New Mexico... In terms of other starting aids:

- are your battery and starter in top shape (is the engine turning over nice and fast)?
- are you using synthetic oil, at least in the cold months?
- do you have some form of auxiliary heat for the cold temps, such as a block heater or inline coolant hose heater, and/or a battery warmer?

If the starter isn't turning the motor fast enough on cold mornings, your glow cycles may seem less effective.

Good luck with it.

Diesel911 · #7 10-12-2011, 11:30 PM

If it is assumed the Glow Plug System is working correctly most people simply go through the Glow Plug Cycle and repeat the cycles as many times as is needed. To aid starting the Engine.

But, that taxes an old Battery and is worse if the Battery Connectors and Ground Strap (Battery and Engine) have poor connections.

Some people have found thier Engine started easeir after the Reamed or otherwise cleaned out the Carbon From the Glow Plug Holes.

If your Injectors are not atomizing the Fuel well at cranking speeds (low cranking speed is yet another issue) you Engine will be harder to start.

tangofox007 · #8 10-12-2011, 11:38 PM

Retarded injection timing doesn't help starting speed, either.

vstech · #9 10-13-2011, 09:08 AM

depending on how old your 79 is, it either came with loop or pencil plugs, of course, someone may have converted loops to pencil too... which style do you have?

a plug in block heater helps a lot also when it's cold out. as will a timing chain in good condition, you mention MANY miles, so verifying the timing chain and fuel timing will help with starting. how many miles before your last valve adjust, and since? 15K should require valve adjust. if the previous was WAAAAY more than 15K, your "within the last few years" valve adjustment could SERIOUSLY need addressing.

Stevo · #10 10-13-2011, 10:18 AM

About the best upgrade one could make on an early diesel 123 is the newer style GPs. The kit includes the pencil style GPs, relay, 80 amp strip fuse, and jumper wires.

Maxbumpo · #11 10-13-2011, 10:24 AM

The problem is probably poor compression due to failure to adjust the valves this fall. Valves should be adjusted every fall before the onset of cold weather, or every 12.5k or 15k miles (depending on your car - read the owner's manual), which ever comes first.

The best way to verify proper glow plug operation, if you have the parallel "pencil" style, is to measure the current flow to each plug. One way to do so is to get an automotive ammeter gauge meant for dash mounting, preferably with a 30 amp scale and some markings so you can see rough amps (i.e. mark for 10 and 20 amps, or every five amps), and energize each plug through the meter. Amps should initially spike at about 20 or so, then fall off to about 8 as the plug warms up.

Another way to test is pull each plug, and apply power using a set of jumper cables, be VERY careful as the plug tip will glow white hot at ~1500 deg F.

peachykeen · #12 10-13-2011, 09:48 PM

Quote:

Originally Posted by vstech

depending on how old your 79 is, it either came with loop or pencil plugs, of course, someone may have converted loops to pencil too... which style do you have?

a plug in block heater helps a lot also when it's cold out. as will a timing chain in good condition, you mention MANY miles, so verifying the timing chain and fuel timing will help with starting. how many miles before your last valve adjust, and since? 15K should require valve adjust. if the previous was WAAAAY more than 15K, your "within the last few years" valve adjustment could SERIOUSLY need addressing.

Thanks EVERYONE!!! priceless info and feedback...

I definitely use a block heater AND an oil pan heater since I run 15w40 rotella throughout the year because I already have bad oil leaks and 5w40 seems to make it worse...the heaters work great, but even today at low 50s (southern Minnesota) I have to cycle the plugs twice and still had some trouble starting!! ah!!

The engine has over ...hold on...700k...BUT, PO was a retired marine diesel mechanic and took good care of it...he put a new chain and rail in and injectors...and it smokes just a bit...and blow by is moderate (rattles the oil cap, but doesn't blow it off...thankfully)...otherwise, the darn engine 'purrrrs' very, very nicely.

The PO converted to pencil plugs -- I'm guessing like some of you stated that there is a bad plug somewhere..or I need to do some good reaming and replace them..and spend some time to check them w/ the ohm meter.

I'll try and do the valves ASAP -- It has probably been about 10k since they were done...

The battery is new and starter too -- so...I might go back to 5w40 for the winter (dang that was cold last year...-20s a lot here at night) and put up with the leaks...(i know one more thing to fix)...

I think I'll bypass the idea of getting the glow plug override kit and just tackle what has been mentioned here.

thanks a lot and let me know please if you think of anything else..

Zacharias · #13 10-13-2011, 11:19 PM

Well with an engine that old, with 15w40 dino oil in the crankcase, your glass is half full, not half empty.... You are doing well to be starting at all in the winter months.

I think it would be realistic to switch to synthetic and put up with the additional leakage.

By the way, Mobil 1 claims that it actually reduces oil leaks. I put it into a very, very tired old Volvo 740 (gas) Turbo with more than 350k that was leaking oil everywhere, and it did just that. Very significantly. Just throwing that out as food for thought.