OM617 - fires then dies! help needed please. - PeachParts Mercedes-Benz Forum

dusty_G · #1 08-01-2017, 09:47 PM

This engine has generally been rebuilt with new or refurbished parts. I have done all but the specialist stuff myself. It is a NA motor with an aftermarket turbo fitted to a G-wagen.

Currently it will fire up for a second then falter and stop. I was able to get it to keep running - by pumping the hand primer pump while cranking - but running was extremely rough, accompanied by clouds of dense white smoke!

I am suspecting 3 things:
1. lift pump not providing enough pressure
2. timing gone out due to problem in the Inj Timing device
3. air getting to the injectors

1. I feel the lift pump pressure by squeezing the banjo fitting between thumb and forefinger while cranking the engine - first having removed it from the fuel filter housing of course. I can feel pulses, but no fuel squirts past my finger like it does when I use the hand pump.

2. When the engine WAS running OK a few months ago, it faltered and died on me. And has been displaying these symptoms since then. I have replaced spring and valves in the lift pump - and fitted a reconditioned injection pump / rebuilt injectors. The other day I decided to check that I had installed the inj pump correctly - I found that the timing was out! If no other course of action comes up, I will again remove the inj pump and check its timing - if it has moved then I really must have a more sinister problem on my hands!

3. I crank until fuel free from bubbles appears at the cracked injector fittings. The motor 'ran' for about 5 min yesterday so I am assuming any trapped air has been voided? There are no fuel leaks in the piping around the pump (new rubber pipes too). Using a local pot of fuel for supply and for return makes no difference.

I am cranking while running another car with cables connected. Getting almost 12V at the glowplugs - which are new!

Any thoughts please? I have run out of parts to replace!

Cheers

snapped_bolt · #2 08-01-2017, 10:05 PM

And what problem is that? Stored in a swamp?
These assemblies are built rather well, but the spring can wear, and possibly break or get jammed. Effect= no timing advance (that's why it's there) when it's not working properly, the effect is like on an old gasser. The curb weights on the distributor jam and there is no spark advance. A contributing problem?

snapped_bolt

Diseasel300 · #3 08-01-2017, 10:26 PM

If it runs when you're pumping the primer, the issue lies in the lift pump somewhere.

dusty_G · #4 08-01-2017, 10:47 PM

Unfortunately, the shaft that connects the timing device to the inj pump has been known to fail.

snapped_bolt · #5 08-02-2017, 12:27 AM

Sad story. They usually fail when the thrust piece has been so worn away that the gears don't properly mesh. At first the gear face is riding on a brass bearing, but that wears away, and all that is left is aluminum.
You can check the thrust piece by removing it- there is a retaining bolt on the side of the block that comes out that just holds onto a groove in the thrust piece. However, on my car, the head prevented it from coming out- I had to grind away a bit before the thrust piece would pull up. Never expected the interference! Clean the top area, pull it out and have a look.
But the drive shaft running form the injection pump to timing device- I would find it hard to believe that could have an effect on the timing, because the gear drives the oil pump. If the gear was damaged, your oil pump wouldn't be driving properly. The shaft running to the timing device should remain intact even if the gear was damaged.
The "plain bearing" at the front can wear, but this shouldn't effect timing either as it is an issue with fore and aft play in the shaft/timing device. About the time you are eating vacuum pumps on a regular basis you can be suspect of this because they do wear out.
I suppose if someone tried to start the engine with a huge pipe wrench on the timing device, the splines on the IP would get destroyed, but I cannot see otherwise how this could get damaged.
When I had mine out, the shaft did want to rotate out of position. It is possible the IP isn't timed correctly. This can be corrected by re-inserting the IP, with all respective parts in the proper place; just handle that IP like it's full of nitroglycerine (very carefully!!!) stick it in and hopefully it hasn't sprung out of position. While you are in there, check the thrust piece and plain shaft for wear, and replace them if they are out of spec! Tear down the timing device and inspect- there are two springs inside that can wear. Take pics as you go. Mercedes still lists those springs at around $6.00 US apeice, so it's not TOO costly. I found two new, old stock thrust pieces on Ebay for less than 1/2 the price of a new one.

I did these things on my 240D along with a new timing chain. The results are nothing short of amazing. I had four of us in the car today at 72MPH on the freeway and there was barely any engine sound. They do like to go! The car was much quieter than on the highway at 55-60.
I have said this before- for a long time I thought it would have taken crazy people with the money to buy a smoky, stinky, noisy diesel for around $30,000 in 1979. Now that nearly all the suspension has been renewed, and some important engine parts have been replaced, I need no further encouragement to continue. I know do know why those folks bought these cars!

Cheers,

snapped_bolt

dusty_G · #6 08-02-2017, 01:20 AM

Thanks Snapped

You have some experience then with this area of the engine! I would also like to know if my symptoms are consistant with the timing being out of whack.

If the timing device needs fixing, I will certainly take your advice and replace any little springs I find.

Diseasel300 · #7 08-02-2017, 10:25 AM

Before tearing into the timing device and IP - remember - you said it runs when you pump the primer, but not when it's running on the lift pump.

Start simple. You have a problem with the lift pump - that much is confirmed by the behavior you describe. Fix that problem first, then if you still have issues move on to frying bigger fish.

jake12tech · #8 08-02-2017, 10:59 AM

It's the lift pump. These cars will run with crazy retarded or advanced timing. There's something internally wrong with the lift pump.

snapped_bolt · #9 08-02-2017, 11:37 AM

Stretch did an exhaustive posting on the vacuum pump and timing device, with loads of good pics here:

More than you are likely to ever want to know about OM61X piston vacuum pumps

Some good pics of the timing device in bits, the IP drive shaft, etc.

"The other day I decided to check that I had installed the inj pump correctly - I found that the timing was out!"

The first thing to do is to re-set the IP.

Which kit did you use to rebuild the lift pump? There is a complete rebuild kit.
If there is very little coming from the IP, it is probably out of sync. Reset the IP and try again. If you didn't use an IP lock when you stuck it in, it could have moved out of the place you set it at as you slid it in. Remember these inline IP's are like small engines- there are cams and everything- and getting it set on mine, it had to sit at a position where is could easily have been disturbed, causing it to rotate off one of the cams.

"It is a NA motor with an aftermarket turbo"

This is very interesting. You upgraded the pistons to turbo type as well?

You have mentioned a lot of changes made to his engine. This tends to multiply exponentially the problems while trying to get it back together. Did this engine ever run properly without the addition of the aftermarket turbo?

I am thinking this may be a short-lived venture. Replacement turbo pistons are hard to find, and cost at least 6 times the price of the NA types. Piston cooling nozzles installed? The pistons can get hot in a turbo without them! Plenty hot enough to fail. I cast aluminum parts- I pour usually around 1350°F- quite close to some turbo exhaust gas temperatures. The internal temperature when the cylinder fires is even higher! And before aluminum is at pouring temperature, it has already failed structurally.

Let's at least track down this "fueling" problem and get it running properly. Then we can look into the "aftermarket turbo". You may want to call it an "after-burner."

snapped_bolt

funola · #10 08-02-2017, 12:04 PM

What is the history of the engine? How many miles? Did it have regular oil changes? Did it ever run out of oil? If it had a good maintenance history, I would not tear into timing device to look for worn parts as it is bathed in oil and does not wear much unless abused.

To eliminate air in fuel as an issue, replace the cigar hose with a temporary clear pvc tubing. Use 1/4 " id, soak ends in boiling water and stretch over the barbs, no hose clamps needed since it is a tight fit. You should see a solid stream of fuel in the clear line. If the fuel is foamy or you see bubbles, you have to find and fix the source of air intrusion.

Maxbumpo · #11 08-02-2017, 01:58 PM

Lift Pump or IP timing, those would be my guess. Testing the lift pump is easy - when you had the two fuel lines going to a temporary fuel tank, what was the discharge like from the return line? If that was weak or non-existent, then that is a problem.

IP timing: It is possible to get the IP installed 180 degrees out of time, and the engine will run but very poorly and like you describe. You would need to remove the IP and set the engine to TDC on #1 on the compression stroke, set the IP correctly, and install. I'm pretty sure that your IP splined drive shaft has a missing spline that should be lined up with a mark on the pump body, and that sets the rough timing when you install the pump.

dusty_G · #12 08-02-2017, 11:30 PM

You have a problem with the lift pump
It's the lift pump.
OK, so the lift pump piston should be producing more pressure.

Which kit did you use to rebuild the lift pump?
I bought individual parts from the Dealer, so the hand pump, valves, o-rings, spring are new. The piston is the original.

If you didn't use an IP lock when you stuck it in, it could have moved out of the place you set it at as you slid it in.
This never occurred to me. When turning the inj pump on the bench it has 'indent positions' where it would not rotate easily off this posn - and the two-marks-line-up occurs in one of these stable positions. So this is possible but not likely I think.

What is the history of the engine?
It was almost certainly neglected, judging by the rest of the car. It had 180k miles, professionally turbo charged from new which was pretty common in this market. I did have it all apart and new liners/pistons/timing chain etc, rebuilt head. I did nothing with the timing device/ vac pump.

As I said, the car was running OK until recently, when it stumbled and died.

replace the cigar hose with a temporary clear pvc tubing
Testing the lift pump
Thanks, I will do that.

IP timing
Turning engine clockwise looking from the front to 24BTDC with the number 1 cyl cam lobes pointing upwards-ish, inj pump installed with its marks in alignment.
set the engine to TDC on #1 on the compression stroke, set the IP correctly, and install. AKAIK this should be at 24BTDC??

Thanks

snapped_bolt · #13 08-03-2017, 01:12 AM

Your fuel filters are new?
I don't think the dealer rebuild kit includes all the parts needed to do a full rebuild. Did the kit come with the 30mm~ copper seal for the huge nut? A new tiny O-ring?
Since the IP and lift pump are Bosch, there are other kits out there that the dealer no longer has- if they ever did. It sounds like fuel is passing, but not enough. Either there is blockage (maybe not?) or you might need to look at that lift pump rebuild.
So you noticed the "camming" effect of the IP...I have hope now that you got it in right. I bought an IP lock but it was for earlier models- I had to gingerly move the IP in and make the connection. But it can work! Shoulda bought a lottery ticket THAT day!

Keep moving forward- you might find something you overlooked- just update us!

Cheers!

snapped_bolt

dusty_G · #14 08-03-2017, 02:09 AM

Hi Snapped

Primer pump - yes the copper sealing ring and tiny o-ring are replaced.

Just thinking out loud: if the lift pump is under-performing, would there still be white smoke (=unburnt fuel) generated as the engine tries to run?

I will have to follow all leads.

Cheers

barry12345 · #15 08-03-2017, 10:07 AM

White smoke makes the timing of the injection pump at least suspect. You also might have two problems. From your description I would verify the fuel is being pumped properly first.

Got overflow from the relief valve on the injection pump when cranking? If not find out why not. When you pump the primer pump with the engine off is there a reasonable stiff resistance or not developed? Say there is no resistance as an example. The check valves for the primer pump are in the lift pump. Or the relief valve can be open. Or you could be piggybacking on the lift pump with the primer pump as the lift pump alone cannot pull fuel through say a bad tank filter otherwise. In other words diagnose what is wrong in the fuel supply system if anything first.

It sounds like you are basically just shot gunning or changing things with no primary diagnosis. This can get very expensive and mentally pain full. At least these cars are service friendly compared to what I ran into yesterday.

I looked at what was a simple brake line failure on my beater.. The young fellow helping me had a jack slip. Took out two lines to and near the equalizer. I told him if we could not access the nuts and get them out. Cut all the six lines and we will mount the equalizer in a higher workable position. I called the car brands dealer. .Six to eight hours labor quoted if things went well. So we should be happy that in general there are only one or two areas in these old 123 types. Plus the earlier 603 engined cars that may cause some real unreasonable difficulties when working on them.