OM603 Idles, But Won't Pick Up Speed

[skelleybenzes]

Greetings all--

I'm about to tear my hair out with my wife's '87 300TD. The vehicle was running like a top, but then started having intermittent power loss--stepping on the throttle would have little effect, then, as if a switch were flipped, it would "cough" then take off like a shot. It now has become immobile. Runs, won't move.

It starts just fine, but idles roughly, and the engine will generally not pick up speed even when parked. At times I can (randomly) get it up to 3000 RPM, but then it dies back down, and usually stalls. Oddly, I have noticed that the manual STOP lever occasionally pulls itself down as the RPM's increase, though even if you hold the lever up, I still can't consistently get the engine to pick up speed.

Replaced all fuel filters (even the tank screen)--no change. Did the LubroMoly diesel purge--no change. Plugged the EGR vacuum line--no change (though I suppose it could be stuck open). Checked vacuum lines and "ALDA" circuit for blockage--no issues. Lift pump is relatively new, and pulls well. Checked turbo--just a little side-to-side play, no "in-and-out" play.

I will now state that I have an Elsbett single-tank WVO system on this car, with 30K miles since the conversion. I also have a '79 300GD (OM617) with the same conversion, running on the same oil, with the same mileage on the conversion--no issues whatsoever. I would like to think that my injection pump has NOT gone south, but I am running out of other culprits to blame, and am seeking y'all's collective wisdom.

Many thanks,
Patrick Skelley
Bedford, Virginia
1970 Unimog 406
1972 350SL 4.5
1972 300SEL 6.3
1978 240GD
1979 300GD
1987 300TD
Other stuff . . .

[vstech]

before blaming wvo... (must... fight... desire... to, blame...) the stop lever moving, are you sure there is not a vacuum line pulling on it? is it possible the shutoff hose has crossed, and is getting vacuum under power?

[babymog]

Perhaps the vacuum valve on the ignition switch is failing?

Start by disconnecting the vacuum line to the shutoff valve. Sounds very much like fuel starvation / filters, have you checked them, the air filter, and the fuel-tank vent & strainer? Does this happen on diesel fuel also?

Try running the car from a tank/jar/can/whatever of fuel under the hood directly into the lift pump to eliminate fuel tank and associated plumbing.

Unlikely that your exhaust cat has become plugged, but it does happen. Pull the plug from the exhaust mainfold to see if that helps.

[skelleybenzes]

Originally Posted by vstech

before blaming wvo... (must... fight... desire... to, blame...) the stop lever moving, are you sure there is not a vacuum line pulling on it? is it possible the shutoff hose has crossed, and is getting vacuum under power?

Hey, I realize the WVO debate--thanks for not sparking that, I just want to diagnose my problem (for now), whether it be a trashed IP or something less dire. I tried disconnecting the vacuum line to the shut-off valve--problem still there.

[BoiseBenz]

Weeeeell, if you must WVO, I suppose Elsbett is the way to go.

To check the EGR, just connect your mity-vac to the diaphragm and pump it up. When you quickly release the vacuum (yank the hose off), you should be able to hear the valve slam shut.

I just went out and disconnected the "stop" vacuum line. The car started and ran as normal. When switched off, it didn't stall but slowed to the mechanical baseline of about 550, as the electronic idle control was disabled. Reconnecting the "stop" line saw the lever immediately pulled all the way down and nearly instant stoppage of the mill.

[skelleybenzes]

Originally Posted by babymog

Perhaps the vacuum valve on the ignition switch is failing?

Start by disconnecting the vacuum line to the shutoff valve. Sounds very much like fuel starvation / filters, have you checked them, the air filter, and the fuel-tank vent & strainer? Does this happen on diesel fuel also?

Try running the car from a tank/jar/can/whatever of fuel under the hood directly into the lift pump to eliminate fuel tank and associated plumbing.

Unlikely that your exhaust cat has become plugged, but it does happen. Pull the plug from the exhaust mainfold to see if that helps.

Fuel filters were the first target--those are all new, including tank strainer. Actually drained tank and put in 5 gallons of good diesel. No change.

When I did the diesel purge, the engine was running off a plastic jar filled with the purge. No change.

Thought about the cat. I'll give that a try, though I don't recall seeing a plug. Then again, I've never looked for a plug. I'll report back when I get a chance to look at it.

Thanks!

[4x4_Welder]

The cat would make a distinct whistling noise out the exhaust, and it would rev up then die. That car does have electronic controls doesn't it? Perhaps there's an issue there, like a bad intake hose?

[babymog]

It's an '87, only electronic idle control.

The plug is in the exhaust mainfold, good luck as it sounds more like fuel.

Have you removed the intake crossover pipe to see if it's an intake restriction (turbo seized? Should still idle).

[Diesel911]

Try runing the Engine without the Fuel Fill Caps on; to eliminate the Tank Vent as a cause.

I was looking in the manual and there is a Fuel Heater and somewhere there what appears to be a Thermostat for the Fuel Heater. I do not know if it could block off the flow or not if it was not working right.

I think I would bypass everthing to the rear by runing a Fuel hose with a pre-filter from the Fuel Supply/Lift Pump to a container of clean Diesel Fuel and see if the Engine will run OK on that. If so you need to trouble shoot the Fuel lines from their back.

There could also be something sticking inside of the Fuel Supply/Lift Pump.

Also one of the other members recently said that if your crakcase pressure cannot vent itself it puts pressure on the Shutoff Valve and will shut you down if it the pressure is high enough.

A different Engine but I put my Thumb over the crankcase breather hose and in about 7 seconds my Engine started to bog down. I tried this several times but did not let it shutoff all the way.

[barry123400]

Badly obstructed crankcase breather hose would produce identical symptoms I think as well. Or more blowby than engine can process causing crankcase pressure. See if symptoms are present with oil filler cap off.

To establish if fuel is adaquate and at enough pressure. Pinch off return line. If no change take the return line end and submerge in a jar of fluid. There should be no air coming out the hose at idle and the fuel level in the container should be gaining. Those two tests should clear the fuel supply as a contributor.

[vstech]

if your egr is still connected, you should pull the 3 bolts and look at the intake crossover tube to see how gunky it is in there, like was mentioned above.

[skelleybenzes]

Thanks all for your collective input. I'll try to condense my responses in one message:

Turbo is not seized.

Issue is not fuel delivery/supply. I had already bypassed everything to do the diesel purge with no change in the vehicle's behavior.

I had the crossover pipe and intake hot tanked less than 6 months ago (yes, they were gunky) when I replaced glow plugs.

I had someone suggest removing the side plate for the IP and observe the motion of the rack when the throttle is operated. This is what I found this morning:

Pulled the side cover from the IP. The rack was 1/2 to 3/4 in its forward (left) travel (toward front of vehicle). Using the stop lever pulled the rack back fully to the right. BUT when operating the throttle, the rack moved only very slooowly to the left. It did not fully travel to the left even at full throttle. When the throttle is released, the rack did not return to the right. The rack is definitely "non linear" with throttle operation, though I've never seen a cutaway/schematic of the IP, and not sure what mechanism(s) lie(s) between the rack and the throttle actuating gizmos. In any event, the IP rack operation intutively doesn't seem to be correct. Thoughts?

[noah brinkman]

I did not read all the posts here but ....
have you read my (noah brinkman) 603 idles but no RPMS (or throttle) thread????

I got it resolved !!
find that post and read ALL THE STUFF I did to it to narrow it down to the problem

In short My 86 SDL 603.961 was fine started it the next mourning ran (idled) fine

step on the pedal RPM's would not come up more than ohh about 100 more than idle so 650-750

I will save you a week of ****** around

take off intake cross-over
start the car
spray WD-40 or diesel in a spray bottle hell you could use an un-lit propane torch if you want

raise linkage by hand while spraying fuel in
your RPM's will rise

after you read my thread you will say damn this guy tried everything
here is what it was!!! drum roll please!

Alda went bad..... yeah I know an un-molested alda on a rebuilt engine was fine one day and the next **** out on me to the tune of OHH maybe $800 after replacing other parts to find the problem
and shipping my IP off to detroit to get worked on

If you live near by (0-300 miles) I'll come help
I gotta pay it forward for all the help I got from Roy

[winmutt]

It could certainly be a bad ALDA.

[skelleybenzes]

Noah, thanks for the tip, and I'll try the WD-40 diagnostic procedure. Sounds like we have had similar symptoms, and I've already burned up enough of my life trying to sort this out. Did you post anything about actually replacing the ALDA? I couldn't find anything after your post re: how to remove the IP.

I'm in Virginia, and though your offer to come help is amazingly kind, I think it would be a little far.

Hope your back is better too--been there myself to a lesser degree (so far), and it ain't no fun.