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300GD Engine Troubleshooting

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bryant.cw
Posts: 227

Re: 300GD Engine Troubleshooting

Post#11 » Sun Sep 09, 2012 9:35 am

Do a compression check FIRST to make sure any effort spent is worth your time!

The manual glow plug over ride is not necessarily a bad repair. The relays aren't known for being the most reliable system on these motors and so a manual control should work fine, if it was installed correctly that is. Many people repair the system in this way. Verify the glow plugs are actually working.

I would do things in this order:

Compression check (Read the manual that comes with the compression tester and use any washers etc that you are supposed to or you will get the wrong result!)

Glow plug check

Fuel system check (lines, filters, primer pump, pump timing etc)

Cam timing and valve adjustment check

Don't buy parts and throw it at the problem, you are sure to get frustrated! Speaking from experience here!

Suppatime
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Re: 300GD Engine Troubleshooting

Post#12 » Mon Sep 17, 2012 9:08 pm

bryant.cw wrote:Do a compression check FIRST to make sure any effort spent is worth your time!
The manual glow plug over ride is not necessarily a bad repair. The relays aren't known for being the most reliable system on these motors and so a manual control should work fine, if it was installed correctly that is. Many people repair the system in this way. Verify the glow plugs are actually working.
I would do things in this order:
Compression check (Read the manual that comes with the compression tester and use any washers etc that you are supposed to or you will get the wrong result!)
Glow plug check
Fuel system check (lines, filters, primer pump, pump timing etc)
Cam timing and valve adjustment check
Don't buy parts and throw it at the problem, you are sure to get frustrated! Speaking from experience here!


Great advice. I'll do research on how to do a compression check myself. I'll be back in town next week, so I'll do that.

In the mean time, I'll share this photo... this is what came out the exhaust from starting up this morning (80 degrees F, engine cold for 12 hours):

Image

Looks to be a mixture of carbon deposits, water and a little diesel. I think I'm running rich, and the engine is filthy.

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bryant.cw
Posts: 227

Re: 300GD Engine Troubleshooting

Post#13 » Mon Sep 17, 2012 10:32 pm

Not to be a downer but don't beat your head against a wall for too long. My old engine showed the same puke out of the exhaust on startup as yours and nailed badly even when warm. I ended up replacing everything in the fuel system apart from the pump itself, valve adjustment, pump timing, check cam timing (it was right on the money) monark injector nozzles, new exhaust, new primer pump, new lift pump, all the filters, fuel lines, glow plugs etc. Problem was never solved, my mechanic and I agreed all that was left as a culprit was the fuel pump itself. Given the cost of a rebuild I just got a whole new motor with much lower miles and better compression and never looked back.


Run a can of diesel purge through it just for good measure, "Seafoam" is a widely available alternative that can be used in exactly the same way (With the fuel pump supply and return running right into the can with a couple short hoses, like a temporary gas tank) and works great if you can't find the lubromoly diesel purge locally. I found it at NAPA, but nobody else sold it. For some people it works great, others that have a mechanical problem will find no benefit.

Suppatime
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Re: 300GD Engine Troubleshooting

Post#14 » Mon Sep 17, 2012 10:42 pm

I have a bottle of each, and will run them through on the few next tanks. Diesel Purge first.

Suppatime
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Re: 300GD Engine Troubleshooting

Post#15 » Fri Dec 07, 2012 2:51 pm

A long-awaited update:

- Compression is within specs across the board

- Glow Plugs get no power from manual switch/relay (which is why I can start fine in warm weather, but not in cold) but the Bosch Glow Plugs glow when battery-tested

- Fuel system is fine with no leaks, though my secondary fuel filter is showing some contamination and will soon need replacement

- Cam timing and valve adjustment have been done with a new Mercedes timing chain



My fan clutch is seized which explains the rattling noise from the engine bay (bearings) and may explain my lowered mpgs to a degree. I returned 17.8 mpg average on my last tank (about 360 miles per tank).



So the big question now is... what Glow Plug Relay do I buy? Pencil-type Bosch plugs were fitted by jruz (the previous owner) and I'd like to buy a relay and wiring harness that will work with it reliably. I am buying new wires as well, as I don't trust much of anything on this 32 year old truck, electronic-wise.

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vadimivanovich
Posts: 8643

Re: 300GD Engine Troubleshooting

Post#16 » Fri Dec 07, 2012 4:09 pm

Overall great news.

Glow plug relay is relatively cheap new. This is the newer version designed for the parallel type glow plug wiring (better): http://www.ebay.com/itm/Mercedes-w123-7 ... c0&vxp=mtr

Change your fuel filters after you do the Lubro-Moly & Sea Foam treatments. Do not just pour those treatments into your tank. Feed a hose from the can into your secondary fuel filter, and the return line that goes back to the gas tank should go back into the can until it's just about used up. Mercedes Source, Peach Parts, and others have videos for this. Plugged filters can lead you on a wild goose chase and they're cheap-n-easy to replace.

Good call on the timing chain... I should do that too. Did you replace the chain tensioner too? You should. Chain guides are a good idea too but only if necessary.

I have a used spare fan clutch... or you could easily find one at Pick-n-pull for cheap. They'd be the best bet for any wiring you might need too.

Your MPGs are good/normal. If you're expecting to do better, don't. For a 2-1/4 ton truck with 125Hp, that's about what you get. I think I hit 18.8 once, and that was with 35" tires :shock: . I'm usually mid-17s.

Don't be too paranoid about wire. Wire doesn't wear out. It just sits there. If something cuts it or corrodes under it, that's fixable without changing wire. My truck looked like a nightmare under the dash until I spent an hour with a box of zip-ties organizing everything. It turned out that all of my wire was fine, just some turkey was in there poking around, probably for the radio or air blower wires. No big deal.

Did you find your slow electrical drain?

Suppatime
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Re: 300GD Engine Troubleshooting

Post#17 » Fri Dec 07, 2012 4:37 pm

vadimivanovich wrote:This is the newer version designed for the parallel type glow plug wiring (better): http://www.ebay.com/itm/Mercedes-w123-7 ... c0&vxp=mtr


I have seen this one, but I don't have the parallel type plugs... I have Bosch pencil plugs. Hence my confusion here... the previous owner installed the pencil plugs but didn't change the wiring... I assume someone had done a conversion to the whole system before these plugs were installed, but now I don't know what's in there and just want a complete setup. Perhaps a junk yard is a good way to go.

vadimivanovich wrote:Change your fuel filters after you do the Lubro-Moly & Sea Foam treatments. Do not just pour those treatments into your tank. Feed a hose from the can into your secondary fuel filter, and the return line that goes back to the gas tank should go back into the can until it's just about used up. Mercedes Source, Peach Parts, and others have videos for this. Plugged filters can lead you on a wild goose chase and they're cheap-n-easy to replace.


I haven't done the Diesel Purge yet, though I have both a bottle of that and two cans of Sea Foam. The only one I've done at this point is Redline's Diesel Fuel Catalyst, which is recommended for tank use. I've noticed a significant drop in smoke at idle from it.

vadimivanovich wrote:Good call on the timing chain... I should do that too. Did you replace the chain tensioner too? You should. Chain guides are a good idea too but only if necessary.


Chain and chain tensioner were replaced. I was told the chain guides should be replaced every time the chain itself is replaced, but that's from an old Mercedes diesel tech who stopped me in a parking lot to check out the truck earlier this week.

vadimivanovich wrote:I have a used spare fan clutch... or you could easily find one at Pick-n-pull for cheap. They'd be the best bet for any wiring you might need too.


I've been to the local junkyards, and while there are quite a few 300D donor sedans around, most of them have been butchered.

I'm interested in buying a new Glow Plug Relay with the wiring harness because the wiring (and relay) in my truck is aftermarket and unlabeled. I've looked at the stock Mercedes Glow Plug Relay and wiring harness from other vehicles, and my connectors will not work if I just get a new relay... both need to be replaced. And to add to the confusion, it's not the old style or the new style parallel type (which makes sense, as I have pencil plugs), but I want to make sure whatever I get will work with the newer Bosch pencil plugs.

vadimivanovich wrote:Your MPGs are good/normal. If you're expecting to do better, don't. For a 2-1/4 ton truck with 125Hp, that's about what you get. I think I hit 18.8 once, and that was with 35" tires :shock: . I'm usually mid-17s.


Ah, but I have the non-turbo OM617... only 88hp. I've been told 17-23 is about average, and I just want to increase economy as best I can. Either way, it's currently better than my 15.5mpg Nissan Pathfinder I've been driving for 5 years.

vadimivanovich wrote:Don't be too paranoid about wire. Wire doesn't wear out. It just sits there. If something cuts it or corrodes under it, that's fixable without changing wire. My truck looked like a nightmare under the dash until I spent an hour with a box of zip-ties organizing everything. It turned out that all of my wire was fine, just some turkey was in there poking around, probably for the radio or air blower wires. No big deal.

Did you find your slow electrical drain?


I haven't found the electrical drain, which is why I believe wires (shorts, whatever) may be suspect. If I drive it every day (with the exception of today) it's fine. If I let it sit for a couple of days, it dies.

I've run tests with a multimeter on every lose wire I've found in the engine bay, and nothing is hot. Part of the issue, I'm sure, is that I'm running a single 800CCA Optima Red Top and not a dual-battery setup or a larger military-style battery (or even the factory Mercedes one, for that matter). But regardless, a battery shouldn't go from fine to dead in two days.

Any ideas for a pencil-plug relay and wiring harness?

VolvoC303
Posts: 1512

Re: 300GD Engine Troubleshooting

Post#18 » Fri Dec 07, 2012 8:23 pm

It's possible you have a bad battery, slim, but possible. One good battery is all you need unless you are winching heavily or doing lots of powered camping. Did you do an amp test on the battery cable while it's sitting?

Did you see this (partial) harness?
http://fourbyfourclub.com/W460EnginePar ... arness.htm

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vadimivanovich
Posts: 8643

Re: 300GD Engine Troubleshooting

Post#19 » Fri Dec 07, 2012 11:31 pm

If you have the pencil type plugs, they are the newer style PARALLEL plugs. The old style is "series" and everyone converts because if one plug in the series burns out, they all go out. In a parallel system you'd still have at least 4 working to get started again. Series plugs have a loop at the tip that sticks into the head. Can't miss 'em.

What you need is the relay I linked to, and the harness. The harness is simpler than you think - one heavy wire from each glow plug all go to the relay plug. One thinner wire from the head temp sensor between 3&4 plugs (should be black/violet), blue wire from instrument cluster pin 1 (glow light - you probably will have to add this pin if your car was a gassser, but all clusters have the glow light in them), red wire from ignition switch, brown wire (ground) all go to the small relay plug. Finally there's one heavy (10 gauge?) wire that goes from the fat metal tab on the relay (50A fuse) directly to the battery (or terminal block near it, or starter supply cable). It would not be difficult to run those wires yourself, but if you want an original harness, I understand. I yanked mine out of a 300D. If you want to get fancy you can add wiring & other (expensive) stuff for the tachometer, but that's just for kicks.

If you had a live wire partially shorting out against something or another wire your car'd be in flames by now. A partial short will generate heat... 800CCA worth! Even if slight, I just can't believe a partial short is causing your problem. More likely something got hooked up to a battery lead instead of one from the ignition. That means you might have a relay or something that's always on. I'm guessing you don't have any lights left on... but check your dome light wiring anyway - those lenses brake all the time at this age and stuff shorts out easily. Mine was partially melted when I got it. Just unplug everything. Oh, and those are hot full time at the dome light switches, so a likely source of trouble... better check the door switches too.

Your battery is better than what most people use I suspect. Definitely not the problem.

Ooh, you have a 617. Yeah, you could be getting better mileage... but that depends. What were your compression numbers?

I'm heading to a junkyard tomorrow - will look around for a harness for you.

Hey, at least it drives now!

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inkblotz
Posts: 8202

Re: 300GD Engine Troubleshooting

Post#20 » Sat Dec 08, 2012 4:15 am

If you haven't already peruse Diesel Giants service pages. There are some great tutorials there.
http://www.dieselgiant.com/mercedes_die ... e_tips.htm

Mark

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