W201 190d Vacuum Problem - PeachParts Mercedes-Benz Forum

SonyUser · #1 01-07-2008, 04:28 AM

CAR:

1984 190d 2.2 (w201)

PROBLEM:

Run-away diesel
--Won't shut off when key turned to off position (usually)

SYMPTOMS:

Car usually shuts off with engine warm. Runs-on when engine cold.
On 2 occurrences, roughly idled, continued to run-on at lower than usual idle rpm. Same thing happens if you don't press the fuel injector pump stop valve all the way shut, which is probably what happened.

seems to me climate control response is sluggish, could be wrong tho.

DIAGNOSTIC INFO:

Read directly from Vacuum pump, engine at idle:

Brake booster line port (coming directly off of Vacuum Pump) shows 19 inHg.
Builds vacuum quickly.

The small vacuum port next to it shows about 6-7 inHg, builds to 5 inHg in about 1 second, increases to 6-7 inHg after about 2-3 seconds.

Haynes manual says 500 mmHg is minimum normal vacuum of a working pump.
500 mmHg = 19.6805 inHg

Problem found, eh?

note: Not that I think it matters, but I did not plug the opposite port when I tested and got the above values. If they two ports shared the same vacuum source, they might affect each other if they were connected to leaky circuits.

Following is more info if needed:

Power brakes work, feel like they always have.

Using a hand vacuum pump, they shut-off valve will cut off fuel at about 7 inHg.
I assume this is a normal value, and that vacuum supply should be stronger.
Any less vacuum and the stop lever will lower, but not far enough to cut fuel supply.

Shut-off valve on injector pump has a noticeable, but not obviously extreme vacuum leak when actuated with a hand vacuum-pump

Tested vacuum on lines connected to smaller port on vacuum pump, -- connected by a 4-way connector.
gray line has a small leak-down, this line goes to drivers side firewall, splits into two, I believe a green/org (Climate control?) and a solid orange (vac supply for ign sw.?)
other 2 lines coming from the 4-way connected to small Vacuum Pump port hold vacuum quite well

HYPOTHESIS 1:

I think the problem is the Vacuum Pump.
It appears to me that the vacuum supply is of insufficient pressure, and insufficient availability on the smaller port.
Is smaller port supposed to supply a lower level of vacuum than the brake booster port?
Brake booster port is at low end of normal range as specified by the Haynes manual.
Anyone think this is correct?

HYPOTHESIS 2:

Vacuum pump is OK, but Shut-off valve on injection pump is faulty, it should not noticeably leak vacuum and/or should operate and cut fuel supply at a vacuum less than 7 inHg.

whunter · #2 01-07-2008, 10:21 AM

You do NOT have a runaway, it is a failure to shutdown.
Please read the following thread to understand in depth what a runaway is.

Run away diesel, why does it happen?
Run away diesel, why does it happen?

If the vacuum reads 13 inch mercury or higher = the pump is still functioning.
NOTE: a NEW vacuum pump on a perfect system generally pulls 28 inch vacuum.

Most common cause for your issue = swapped vacuum lines.
What was the last service before you noted this issue, oil change?

Test Engine running:
Use a hand vacuum pump to apply vacuum directly to the shutdown valve, note the reading when the engine stops.

Test Engine OFF:
Use a hand vacuum pump to apply vacuum directly to the shutdown valve, apply maximum vacuum, leave the tool for one hour, note the reading when you return, the reading should not have changed.

Motor / engine keeps running
http://www.peachparts.com/shopforum/diesel-discussion/16287-motor-engine-keeps-running.html#post80108

How to Replace Your Shutoff Valve
http://dieselgiant.com/repairyourshutoffvalve.htm

Have a great day.