Non-Mercedes 6.5 GM diesel problem - Page 2 - PeachParts Mercedes-Benz Forum

jusme · #16 10-08-2013, 09:19 AM

Have you tried adding 2 cycle oil to the fuel to supply extra lubrication for the IP?

kerry · #17 10-08-2013, 09:24 AM

I put a pint in both tanks when I filled up. Previous owner made no mention of using additives so it's easy to imagine that the ULSD took a toll on the pump.

vstech · #18 10-08-2013, 09:41 AM

Quote:

Originally Posted by kerry

I think it will start within a few seconds but much longer and it just cranks. Lift pump seems fine under all circumstances, at least it always shows pressure on the gauge. If it was an air leak problem, it seems it wouldn't start once it cools down either.
I should add that according to what I've read on numerous sites, problems with a hot start are typical of a worn IP. Here for instance:
Kennedy Diesel
The previous owner, by all appearances, was a stand up guy. I doubt he had tried any additives. He told me things that were wrong with the truck that would not have been evident otherwise.
One thing I don't like about this GMC is that there's no simple way to test the system with an alternate fuel supply. Metal lines in and out of the lift pump and the rubber line to the fuel filer very hard to access between the bell housing and the firewall.

Not sure what you mean by 'test light to B+'.

I agree, the alternate fuel route is a pain. it is nice that the lift pump is right under the driver's door though.

Quote:

Originally Posted by kerry

John, you were getting hard hot starts with bad injectors? What about the big difference in starting between the two tanks of fuel? I can't think of any way to explain that besides a worn pump.

I do agree, the injection pump is the primary suspect, but you knew that from the first post on here. I thought you were looking for alternatives to try before getting a pump.

I have a NA pump sitting on my shelf if you would like it to try...
I've also got a Ds4... if you feel like going electronic...

Diesel911 · #19 10-08-2013, 09:57 AM

Where did you check the Lift Pump Pressure?
If I remember right there is a Diaphragm Type Lift Pump on the Engine (I think they had a Push Rod that would sometimes break) and I know for sure there is another Lift Pump inside of the IP.
The Lift Pump in the IP is the one responsible for creating the Pressure that charges the Head and Pistons.

When it is Hot can you Here the Shutoff Solenoid clicking? If a Shutoff Solenoid is bad it starts showing up when it is hot.

When I ran the DB2s on the Test Stand ran the Pump and checked that it had the Max Fuel and got the Pump nice and hot and then dropped down to cranking Speed to simulate hot starting.
If it did not pass that it was normally wear between the Head and the Rotor.

The other things than can effect it are there is an Air Bleed Fitting inside of the Pump that is supposed to allow X amount of Fuel through the Valve and X rpms. Near all of the Pumps I worked had too much return Fuel.
Another issue depending on if the advance Piston is Steel or not is the Aluminum Housing around the advance Piston wears and while the Advance is not anything at starting Fuel is going around the Piston.
Also wear on the Metering Valve cause excess return fuel.

Diesel911 · #20 10-08-2013, 10:13 AM

I am adding this as a correction.

The Fuel Supply/Lift Pump in the sort of Nose Cone of the Fuel Injection Pump helps to control how much Fuel charges the Head and the Pistons.
If you look at the Nose Cone you see at 12:00 O'clock at the top of the Cone is a small Allen Head Bolt that has a serrated wedge of Metal on it that keeps the Nose Cone from rotating.
When you remove that Allen Bolt is where you tap in to check the Fuel Supply/Lift Pump. You need an adapter that screws into that tiny threaded Hole and you can connect your Fuel Pressure Gauge to that.

To change the pressure of the Fuel Supply/Lift Pump you remove the Fuel Inlet Fitting from the Nose Cone (depending on the ID of it) and you insert an extremely clean Allen Wrench into the center and inside there is an Allen Screw with a small Hole in it and turning it Clockwise increases the Pressure and opposite decreases the press.
Not that the small Hole in the Allen screw is easy to plug up.

Changing the Fuel Pressure there also can change the advance piston timing.

Note: The last time I rebuilt DB2 Fuel Injection Pumps was 1989.

In the pic the Red Arrow points to where the Port is to access the Lift Pump Pressure.
The Green arrow points to where you would be sticking the Allen Wrench in to adjust the Pressure.

kerry · #21 10-08-2013, 10:53 AM

Quote:

Originally Posted by Diesel911

When it is Hot can you Here the Shutoff Solenoid clicking? If a Shutoff Solenoid is bad it starts showing up when it is hot.
l.

I was wondering about that. I'm not sure how that system works and where the shut off solenoid is. I'm not hearing the clicking but I've never heard it so don't know exactly what to listen for.

kerry · #22 10-08-2013, 11:15 AM

Quote:

Originally Posted by vstech

I thought you were looking for alternatives to try before getting a pump.

.

That's true. I'm trying to exclude other possible causes. Do bad injectors cause hard hot starts? I found a supplier of rebuilt pumps with a new head at a pretty reasonable price. 6.5TD DB2-4911 Manual Injection Pump :: SSDiesel Supply :: GM 6.5 TD Specialists

Local shop where ForcedInduction uses to work wanted $2200 for a rebuilt pump + $540 to install.

1project2many · #23 10-08-2013, 12:58 PM

Kerry: The solenoid is attached to the IP. It's under a "cover" on the top of the pump. You could use a screwdriver or stethoscope touching the cover to listen for clicking.

Test light to B+ means one end of your test light is connected to the battery positive lead. When you touch the glow plug electrical connection point you're looking for a path to ground.

While these suggestions are all designed to help troubleshoot, I also believe you'll be needing a pump. Diesel911's information helps you test the pump instead of diagnosing by elimination. Here's a page with more information than the typical service manual: » Stanadyne DB2 Fuel Injection Pump &raquo Motor Mayhem

I have a 5/8" 5 point crow's foot here which is a great help when disconnecting fuel lines from the IP.

kerry · #24 10-08-2013, 02:38 PM

That picture of the solenoid is helpful. From what I read, the standard test for a worn pump is the cold water test--when failing to start when hot, pour cold water on the IP. If it starts, it's a bad pump. but I wondered if the cold water might also stimulate a stuck shut off solenoid to release.

4x4_Welder · #25 10-08-2013, 09:42 PM

If the truck sat for a while, it could be a deposit from old fuel. I had a bad sticking rack issue on a Detroit from old fuel, it ran fine until I took it up to operating temp then the rack stuck the next time I ran it. The excess fuel from that machine did make my 7.3 with a DB2 pump run a bit funny for a while but mixing a quart of Dexron with each tank for a few tanks cleared that up.
The ATF might work in your truck as well, if not try some Diesel Kleen or even run a couple cans of purge through it.

Diesel911 · #26 10-09-2013, 02:48 PM

Quote:

Originally Posted by kerry

That picture of the solenoid is helpful. From what I read, the standard test for a worn pump is the cold water test--when failing to start when hot, pour cold water on the IP. If it starts, it's a bad pump. but I wondered if the cold water might also stimulate a stuck shut off solenoid to release.

It is the other way around.
When Solenoid does not work the Spring keeps the Lever in the shutoff Position. When you turn the Key on to start or run the Solenoid gets voltage and that Lever is pulled back and held there until the Voltage is cut off.

Scribe a line on both Sides of the Cover so it goes back in Exactly the same place.

The only Field Test I know that can be done is to remove the Cover. However, I have no idea what also might be on that Year and Model of Cover.
If you remove the Cover and the Engine Starts Hot like that it very likely the shutoff Solenoid.

(I can not remember if the Cover has tamper proof Screws or not?)

While putting the cover back on is not hard it is possible to mess that up. If you look at that pic 1project2many posted you can see how the Solenoid Lever goes to the left of the Metering Valve Lever (Black).
What that means is that when the Pump is on the Engine the with you standing in front of the Vehicle facing the Fire Wall; you would install the cover with it partly overhanging to the rear of the Pump (towards the Radiator) and slide if forward so it catches on the Metering Valve.
You will feel a slight amount of spring tension when you do that.
All of the Cover Screw parts need to go back to where they were.

You won't want to run it long as the Governor is going to throw a lot of Fuel out of the Pump.

Putting the IP top Cover on wrong may cause the Engine to Run away.

The below pic is a generic one. Your top cover is likely different. Some setups have a Flat Metal ground Strap, so ground directly to the Cover with washers.

kerry · #27 10-09-2013, 03:17 PM

I have some additional thoughts. My starter seems to be drawing a lot of power. Too much power since it's drawing down the dual batteries very quickly when it fails to start. The batteries were new last week and I'm not getting 30 seconds of cranking out of them before the engine is slowing waaay down. I've load checked the batteries and they test fine. I'm wondering if it's drawing enough power to reduce the voltage at the fuel shut off solenoid enough so that it's not activating.

Diesel911 · #28 10-09-2013, 03:27 PM

This is supposed to be how the IP works.

Stanadyne DB2 Injection Pump - Diesel Engine - Diesel Power Magazine

eatont9999 · #29 10-09-2013, 03:33 PM

Time for a new IP. Hard starting when hot is common when the IP seals are no good. DB2 pumps don't last near as long as the Bosch style pumps.

kerry · #30 10-09-2013, 03:45 PM

Yes, I agree that is their reputation but I'm still puzzled by the rapid onset. No problems one day to constant hot no-starts a few days later with no other symptoms. Other people have suggested that a worn pump also smokes and it was squeaky clean at the emissions test 3 weeks ago.