Vacuum leak.... Completely Stumped. - PeachParts Mercedes-Benz Forum

Harrison W · #1 02-15-2011, 04:37 PM

I've posted about my 1993 300D 2.5 Turbo before, and still have not found where this pesky vacuum leak is. I've checked every line i can see (and as many fittings as i could in the "Rat's Nest") Same symptoms: Hard shifting transmission, turbo spools but doesn't boost, and the AC is stuck on defrost. This all happened after I spray cleaned the engine, and got the oil, power steering, and rear diff. fluid changed. One thing i did notice is the part that the transmission modulator vacuum line hooks into (right next to the IP) loses vacuum. Is this an issue?

Anyone that has had this type of problem would be of great help. I can't imagine that a hard shifting transmission is good to drive on every day..

BrianCostello · #2 02-15-2011, 04:50 PM

Quote:

Originally Posted by Harrison W

. One thing i did notice is the part that the transmission modulator vacuum line hooks into (right next to the IP) loses vacuum. Is this an issue?

yes.

did you check the line that goes to the modulator ON the transmission? you could have knocked that off while power washing.

if its attached and loosing vacuum, then the part it attaches too is leaking and needs to be replaced.

EVERY VACUUM LINE should hold vacuum.

kerry · #3 02-15-2011, 05:05 PM

Not that familiar with your model but if it has a Vacuum Control Valve (VCV), it must have a line which bleeds off vacuum.

josha37 · #4 02-15-2011, 05:54 PM

the easiest way it to just start cutting it in half, get a good pair of cutters (hopefully you would need them but just incase), some vacuum caps, and vacuum line and if you can un-plug components/connectors and then plug the line one at a time until the issue goes away. But i imagine since you did something and then the problem started it is under the hood and it got blown off when you cleaned it. get a flash light, be paitient, and follow every line til you find it.

winmutt · #5 02-15-2011, 06:00 PM

The easiest way is to unhook the black line from the VCV to the trans and plug it and see what happens. Cutting in the middle of lines is a bad idea at best. Completely isolating different areas is a good idea. What about the ARV?

sjh · #6 02-15-2011, 06:01 PM

Here's an idea.

1. Do gsxr's wastegate swap.

2. Remove all vacuum stuff on passenger side.

3. Get your car's vac diagram.

4. Start at the intake manifold of the ALDA. Check every line and coupling with a mity-vac.

5. I don't think that car has a vacuum amplifier so all you deal with are the:

A. Vacuum control valve
B. ALDA
C. Switchover valve
D. Vacuum modulator on transmission

All of these can be easily searched on this board.

Your A/C problem sounds weird.

Get your hands dirty!!

winmutt · #7 02-15-2011, 06:06 PM

Personally I would not do the WG swap. Test the system per the FSM. The free 201 FSM on startek has step by step tests for checking the p2 system.

sjh · #8 02-15-2011, 06:26 PM

Quote:

Originally Posted by winmutt

Personally I would not do the WG swap. Test the system per the FSM. The free 201 FSM on startek has step by step tests for checking the p2 system.

OK

josha37 · #9 02-15-2011, 06:36 PM

Cutting it in half is a expression... If you have a system with a failure it is much easier to isolate half of it and determine where the failure is.... normally by un-plugging connectors and plugging them like i suggested

winmutt · #10 02-15-2011, 08:47 PM

Quote:

Originally Posted by Dr_SJH

What's the p2 system?

There in lies the problem. You did what you did without even understanding what you did. You broke the law, among other reasons. Not that this has ever stopped me but I think just gutting everything for no other reason than not being able to figure it out is ridiculous.

Harrison W · #11 02-16-2011, 05:07 PM

BrianCostello,
I got some time to go re-check a couple those lines on the car. Very first thing I noticed was that the vacuum line that was going to the transmission was completely off like you said. So I put it back in the transmission and here are the results: transmission seems to shift a little more smoothly, but still a bit hard at times, and the turbo is still not boosting, AC still on defrost, etc. I also re-checked the part right next to the IP that the transmission modulator line originates from. It loses vacuum quite rapidly. Maybe this is the problem?

Rscurtis,
I wish I knew someone who had one. That would be the easiest way to figure this out

rscurtis · #12 02-16-2011, 05:11 PM

If you know anyone in the repair business with a smoke generator, have them hook it up to your car and you'll find the leak in a couple of minutes.

BrianCostello · #13 02-17-2011, 08:27 AM

The part attached to the IP is called the VCV (vacuum control valve)

It should hold vacuum. If not it needs to be replaced.

That should solve your shifting issues. And maybe the boost issue. The climate control could be a separate problem that showed up at a bad time

engatwork · #14 02-17-2011, 09:22 AM

Quote:

I also re-checked the part right next to the IP that the transmission modulator line originates from. It loses vacuum quite rapidly.

Do you have a picture of this part? If I remember correctly there was an item in the vicinity of the area you are describing and it does bleed off a certain amount based on throttle position but it should not leak down immediately. Are you testing these various circuits with a vacuum tester?

kerry · #15 02-17-2011, 09:53 AM

Simple test #1--push the off button on the climate control. If low-vacuum symptoms disappear, you'll know you have a vacuum leak in the climate control system somwhere.