350sdl runaway engine/injector pump problems

[Robert D.]

Hi all. Here is what happened this morning. I was in a hurry and didn't wait for the glow plugs (not really needed in south Florida). I pushed the accelerator pedal all the way to the floor until it fired. But it stuck wide open and revved up very high. I didn't look at the tach but it was over 4000 rpm. I shut it off and had my wife start it again while I had my hand on the stop lever on the injector pump. It went wide open again. So I shut it off and left it for the day.

A little history. I installed this engine used last year. So I don't know how long it sat for before I bought it or what quality fuel was in it when parked. On initial start up it over revved and I shut it off. I slammed the throttle linkage back and forth a few times and started it back up. It idled fine. I then did two injector cleanings back to back with the feed and return going into a plastic bottle as recommended on this forum. The return fuel turned grey in color on the first try that is why I did it a second time and it cleared up.

I have been driving the car for 10 months now without any fuel system related problems, until this morning.

It seems like something is stuck in the injector pump. I need help to find out what it is and how to unstick it.

So far I have taken the side plate off that covers the rack and it seems to have full movement. I can start the engine and modulate the rpms with the fuel cut off lever on the pump, but if I let it go it will rev uncontrollably. Also I have disconnected the linkage even though it moved freely and have the same results.

Thank you in advance for you help.
Robert

[wstetson3]

Oil being fed to the engine through the turbo? Some of the others know far more about how it can happen but it's a possibility.

[Robert D.]

wstetson3: This is not a issue with the engine running away from consuming its own oil. It is an issue with the injector pump hanging wide open after I had fully depressed the throttle.

Thank you,
Robert

[rocky raccoon]

Check the throttle rod link where it comes through the firewall in the engine compartment. The rubber parts are wear items on the older cars and can hang the throttle movement.

[Robert D.]

rocky: I have eliminated the linkage from contention. It is definitely in the pump.

Thank you,
Robert

[compu_85]

If the pump stuck once it will stick again. You could try taking the back cover of the pump off and spraying penetrating oil inside perhaps? How many miles on this pump? It might be best to send it off for calibration.

EDIT... I'm trying to remember my M Pump theory. If it's one of the pistons which is sticking, holding the rack open, perhaps letting the pump sit with some diesel purge in it would free it up?

-J

[babymog]

One clue might be that the engine is still controlled by the max. RPM setting in the IP, not revving beyond the high-idle setting.

[compu_85]

Good point... the max RPM setting on my pump was around 4200 rpm unloaded.

-J

[Maxbumpo]

Originally Posted by Robert D.

It is definitely in the pump.

I agree. You could try removing the rear, side and bottom plates from the injection pump (bottom plate is very hard but not impossible with the pump still mounted in the car) and see if you can detect anything amiss. If the vacuum shut-off valve is installed incorrectly, it can cause what you describe, but I think that is NOT going to be an intermittent issue. May be worth checking that out, nevertheless.

I helped a fellow years ago who had tried to "fix" a leak from the bottom plate gasket by replacing it with a sheet of rubber, over the entire plate. The rubber inside the injection pump interfered with the internal mechanisms and caused all kinds of strange behavior, all resolved by getting the proper gasket.

Best course of action may be sourcing either a used or rebuilt injection pump.

[97 SL320]

Why are you holding the throttle down when cranking?

With the engine at cranking speed, the fuel rack is already at full fuel. Holding the throttle only serves to rev a engine that has not yet built oil pressure. This leads engine ( bearing ) damage in the long term.

[dieselbenz1]

I had this same problem on a friends 92 w140 maybe 2 months ago. I had checked everything couldn't find anything readjusted the throttle cable added more slack shot the cable with silicon lubricant the problem never returned.

[Robert D.]

97 SL320: I didn't realize that the rack was at would be at full fuel at cranking speed. Good to know.

Thanks

[Robert D.]

I had to remove the cruise control actuator to get the screws for the rear cover plate and with that off I couldn't see much of anything in the pump.

I removed the intake manifold to get a better view. Nothing looks out of place.

But what exactly would I be looking for in there?