'my car won't shut off' challenge thread..need ideas

[dieseldan44]

Guys,

My '85 300D all of the sudden shuts off very slowly, but eventually does. Vacuum leak or bad shut off valve, easy I thought...

Here's what I checked with the MityVac:

(precursor - EGR vacuum stuff is all gone)
1.) Vac Pump puts out 22 mmHg vacuum to master brake line
2.) Brake booster does not leak, held vacuum for a good long time
3.) All underhood rubber replaced or are verified as leak free
4.) Car shuts off after two pumps of mity vac when connected directly to shut off valve.
5.) Additionally, shut off valve holds vacuum
6.) Car shuts off in two pumps of mity vac when connected to shut off valve through ignition shut off switch

7.) The car WILL NOT shut off if only the shut off valve is connected to the master brake line, and everything else is t'eed of. Said another way, with the shut off valve being the only vacuum accessory connected, the car won't shut off from it's own vacuum supply.

Any ideas? Could anyone follow my explantion?

Im stumped. The only things I can think of are somehow the ignition housing vac switch is bad, OR something is wrong with the master brake line. But i dont understand why the mty vac shuts it off easily.

Sorry for the long post...
dd

[jt20]

test your ignition with your mighty vac

[kerry]

When you say it shuts of with a Mity Vac when the shut off valve is connected to the ignition switch, are you pulling that vacuum thru the ignition switch itself? In other words, are you putting a vacuum on the ignition input line with the Mity Vac, turning the key, and then the shut off works? If so, I think you've excluded your ignition switch.
T in the Mity Vac to the shut off valve and turn off the engine with the key and see what kind of vacuum is going to the shut off valve in those conditions.

[dieseldan44]

kerry and jt20:

Originally Posted by kerry

When you say it shuts of with a Mity Vac when the shut off valve is connected to the ignition switch, are you pulling that vacuum thru the ignition switch itself? In other words, are you putting a vacuum on the ignition input line with the Mity Vac, turning the key, and then the shut off works? If so, I think you've excluded your ignition switch.

What I did was:

1.) Attach mity vac to shut off valve through ignition switch.
2.) Start car.
3.) Turn key to 'off' position like I normally would to shut off car, but of course engine doesn't stop.
4.) Pump mity vac and car stops right away.

Did I somehow exclude the ignition switch doing this?

Originally Posted by kerry

\T in the Mity Vac to the shut off valve and turn off the engine with the key and see what kind of vacuum is going to the shut off valve in those conditions.

Ill do this first thing tomorrow.

dd

[kerry]

Originally Posted by dieseldan44

kerry and jt20:




What I did was:

1.) Attach mity vac to shut off valve through ignition switch.
2.) Start car.
3.) Turn key to 'off' position like I normally would to shut off car, but of course engine doesn't stop.
4.) Pump mity vac and car stops right away.

Did I somehow exclude the ignition switch doing this?



Ill do this first thing tomorrow.

dd

Did you pull a vacuum with the Mity Vac before turning the key to the off position? If so, what happened to that vacuum?
I don't think you've excluded the ignition switch given your description.

[dieseldan44]

I did pull a vacuum once, and it went to 0. I figured that there wasn't enough vacuum in the mityvac to pull the valve shut and this was normal.

I'll try this again tomorrow.

I have to pull the stupid ignition housing for this one (if it is the ignition switch) don't I? I LOVE that one

dd

[Brian Carlton]

Originally Posted by dieseldan44

7.) The car WILL NOT shut off if only the shut off valve is connected to the master brake line, and everything else is t'eed of. Said another way, with the shut off valve being the only vacuum accessory connected, the car won't shut off from it's own vacuum supply.

You must begin here.

Please connect the Mityvac to this same port on the master brake line and read the gauge. Do not pump the Mityvac.

[mespe]

When you pump up the mightyvac to stop the engine, how many inches of vacuum are you pumping it up to? A mightyvac can create more vacuum then the vacuum pump on your car.

[dieseldan44]

Originally Posted by Brian Carlton

You must begin here.

Please connect the Mityvac to this same port on the master brake line and read the gauge. Do not pump the Mityvac.

Brian,

To answer your first question:
-22 mmHG. BUT, it comes up very slowly over a period of about 30 seconds. Then when the engine is shut off (vacuum pump shut down) the vacuum bleeds down a few mmHg every 30 seconds or so. So there is a leak somewhere.

For comparison sake, I did the same test on my '82 (running fine, no vac problems due to your help way back in the day ) and the vacuum shot directly up to 21 mmHg after a couple engine rotations, and when the engine is shut off stays at 21 mmHg indefinitely.

Conclusion: There's a leak comparable to the output of the vacuum pump on the '85, or the vacuum pump output is weak.

Anticipating your next question, back to the '85:
-Next test I did was connect a modified fitting I have directly to the spot the master brake vacuum line connects, just aft of the power steering pump. Turned engine on, vacuum shot to 24 mmHG instantly. With engine turned off, vacuum bleeds down 1/2 mmHg per minute. Small volume leak Im concluding since one pump of the mityvac brings it up several mmHg - not the big leak Im looking for.

Next:
I am going to re-test the brake booster. Essentially Im down to the master vacuum line line itself, the master cylinder to booster seal, or booster itself. Is this sound logic?

Thanks for your help...
dd

[Brian Carlton]

Originally Posted by dieseldan44

Brian,

To answer your first question:
-22 mmHG. BUT, it comes up very slowly over a period of about 30 seconds.
dd

Get a .125" drill bit and carefully drill the port on the fitting in the main brake line.

[kerry]

I'd do the test I suggested to see what kind of vacuum your getting at the shut off line when the key is turned off with the engine running.
Brian, are you saying he needs more vacuum to go in the direction of the shut off valve?

[Brian Carlton]

Originally Posted by kerry

I'd do the test I suggested to see what kind of vacuum your getting at the shut off line when the key is turned off with the engine running.
Brian, are you saying he needs more vacuum to go in the direction of the shut off valve?

Those ports are noted to clog over time..........it could simply be blocked slightly. The fact that the engine has good vacuum and the vacuum at the port takes a long time to climb points to this issue.

[dieseldan44]

Faulty master brake vacuum line, this thing:http://catalog.peachparts.com/item.wws?sku=W0133-1627740&itempk=86596&mfr=Cohline&weight=0.30

Part #: 12343007429

- I tested booster again, it held vacuum indefinitely (phew)
- only thing left was the master vacuum line - so I swapped it into the '82 - and the same slow vacuum build up was observed on the gauge as on the '85.

Ordered a new master line this morning on a hunch, just picked it up, installed and presto...fixed.

Thank you Brian and to all who spurred me into thinking more systematically and not making any assumptions.

The old line looks perfect on visual inspection. No visible faults/cracks/leaks/loose lines/ whatsoever. I must have knocked it just right while doing brake work this week.

-dd

PS It was really, really helpful to have the same car next to me to make instant comparisons

[Brian Carlton]

Originally Posted by dieseldan44

The old line looks perfect on visual inspection. No visible faults/cracks/leaks/loose lines/ whatsoever. I must have knocked it just right while doing brake work this week.

-dd

Maybe you could drill out the old line, as recommended above, and check to see if it fixes the problem.............that would confirm that the port was simply clogged.............

[Cr from Texas]

Originally Posted by Brian Carlton

Get a .125" drill bit and carefully drill the port on the fitting in the main brake line.

Do this and you should have a good spare line.