E300 Wastegate vacuum.. help needed - PeachParts Mercedes-Benz Forum

Tasma · #1 02-25-2008, 02:07 PM

My 1999 E300 has no vacuum at the wastegate transducer. When I clear the error code P0243 the car will run without errors until I step on the accelerator. I ran a separate vacuum line over from the other sided of the engine and now I get turbo boost with no errors until I give it full power and blast off down the road. The CEL comes on as soon as my foot comes off the pedal.

I did have a EGR error also but I found the problem there. A mouse built a nest by the brake booster and chewed though the vacuum line supplying that circuit. I no longer get that error. It just seems odd to me that these two problems happened in the same two week time period.

Owning one of these cars is like having an Italian mistress...nice to have but you just know it's going to get expensive eventually.

scott19_68 · #2 02-25-2008, 03:13 PM

Have you confirmed that the wastegate vacuum actuator is not stuck? Sounds like it was stuck open before and now it is stuck or sticking near the closed position. I'd definitely check for smooth operation with a MityVac before risking an over-boost...

TMAllison · #3 02-25-2008, 03:18 PM

Swap transducers with the EGR; they're the same part.

If the transducer is bad it should then throw an EGR code.

Tasma · #4 02-25-2008, 03:43 PM

There is no vacuum at the transducer so I know it's not the problem. The car runs fine if the wastegate transducer has vacuum from the other side of car. I could almost leave it hooked up like this but I don't like having the car not be correct. I just need to find out where the vacuum is supposed to come from. The hose disappears into the firewall and I can't tell where it goes from there.

The Mercedes dealer was no help at all. I think they are told to not help in order to increase work in the shop there.

Tasma · #5 02-25-2008, 03:47 PM

One more thing. If I put the mini vac on the line going into the firewall it holds vacuum. If I pull the hose out of the pump under the seat the vacuum goes away. Yet, if the pump runs the vacuum does not appear at the transducer. It's almost like there is a check valve in the system somewhere. My guess there is some sort of safety system here that protects the engine if the wastegate transducer sticks. They have provided an alternate way of killing the vacuum in case of failure. This is where the problem appears to be.

KarTek · #6 02-25-2008, 03:58 PM

Can you put the Mity-Vac on the line coming out of the pump and test for vacuum at the transducer?

On edit: Never mind, you've done essentially the same thing by testing for vacuum at the transducer with the pump running... See other post below...

scott19_68 · #7 02-25-2008, 06:15 PM

Disregard my previous post - I misread your explanation. I am guessing that the fact that your CEL comes on when the wastegate should be at its maximum opening rate points to an out of range error in its EGR mapping. Maybe another hole in your vacuum system somewhere that is keeping the vacuum pump from maintaining proper levels?

KarTek · #8 02-25-2008, 06:33 PM

I just went and took the back seat out of the car and also checked the diagram under the hood and I'm thinking that the pump under the seat has little or nothing to do with the under-hood vacuum system.

According to the diagram, the vacuum pump draws from the large line going to the brake booster. Immediately in front of the booster is a check valve with a single feed coming off the bottom. This single feed Y's into the two feeds - one going to the EGR trans. and the other going to the WG trans. Along the way to the WG trans, it T's into a line that goes back into the firewall presumably to the climate control system.

I think that possibly, the feed line going to the pump under the seat is a backup vacuum source in case the pump craps out.

Tasma · #9 02-25-2008, 06:45 PM

Quote:

Along the way to the WG trans, it T's into a line that goes back into the firewall presumably to the climate control system.

Something very strange is happening then. If I pull a vacuum on the line going to the wastegate transducer and the disconnect the line coming up to the tee...there is no vacuum there. It would sort of indicate that the line is pinched somewhere going from the area of the brake booster over to the other side of the car.

Does anyone know what the P0243 code really means in this car? I am sure these codes are written for all cars and I can't help but think it means something a little different on this diesel car.

KarTek · #10 02-25-2008, 07:10 PM

OK, I took my Mityvac and hooked it to the inlet of the "Y" at the check valve. I can pull a vacuum that lasts a little while and slowly bleeds off through the 2 filters after both transducers. It makes the "muttering" sound you get for about a minute after shutting the engine down.

When I pull the line off the WG trans, I can pull vacuum at the "Y" and feel it on the line.

The line from the "Y" to the "T" is hidden for the most part but it would appear yours blocked somehow...

Here's a picture of the "T":

It's located between the passenger side fender wall and the ECU housing - pretty much inaccessable...

Tasma · #11 02-25-2008, 07:47 PM

Wow, the help here is fantastic. Thanks for checking this out. I will now look for a blockage ( going to be difficult) I mentioned in the first post that a mouse had chewed through the line going to the EGR transducer. Now I am wondering if the same bugger somehow cut though and blocked the other line.
The junk I removed by the booster

This is the cut hose

and of course my car.

Tasma · #12 02-25-2008, 07:52 PM

One more thought. Since I ran a seperate hose over to the wastegate ( bypassing the blocked path) the car works. However I still get the error code P0243 when letting off the fuel after a hard run. Could it be there is more than one problem? I read in a different post somewhere that someone could get this code after doing an Italian tune up but he had to get up to 100mph before his showed up. So the key here is to find out what exactly is code P0243

KarTek · #13 02-25-2008, 08:54 PM

Looks just like my car but you have sexier wheels...

Some other thoughts...

When you say you hook the alternate vacuum source to the wastegate, you mean the transducer right? Not directly to the wastegate - just for clarity's sake.

Where are you getting the alternate vacuum from? Should be from the part of the rubber "Y" that splits and goes behind the engine to the "T" on the passenger side.

In summary, you're disconnecting the presumably blocked line from the "Y" and also from the inlet of the WG transducer and running a bypass line straight there. Correct? Just for review...

Are you reading and resetting these codes with some kind of tool? P0243 strikes me as an overboost code but I can't be sure. I'm hunting for a list now.

If you have the vacuum bypass hooked up as described above and you're still getting a code, I would do as Terry suggested and swap transducers between the WG and EGR. I still don't think we've determined for sure that the WG trans. is 100% OK or not.

Larry12 · #14 02-25-2008, 09:49 PM

Code P0243 is Turbo waste gate solenoid malfunction. And mine also has a P0400 code which is an EGR flow malfunction.
I did put a mity mite vacuum pump on my turbo waste gate and kept pumping it open so that I got 20 pounds of boost for 250 miles. I did not get extra fuel but the constant boost helped me go down the road. Water temp stayed at normal. Maybe I need to trick the EGR flow also.

Larry12

Tasma · #15 02-26-2008, 02:49 PM

I am wondering what the system looks for to determine that the transducer is not working. Do they compare mass airflow with expected based on wastegate and engine speed?
It would be nice to know what they are doing so that I could bypass the EGR.
I did that on my 1991 124 diesel by making my own boost control. The computer tries to shut down the turbo when the EGR is not working but since it no longer has control of the turbo everything keeps working. I used the OEM transducer and made my own pressure sensor and controller.