Hi all,

I was handed down my 300D about two years ago, and it ran (more or less) perfect. Stuff broke, I fixed it (usually by reading posts from here, thanks guys), but now I've run into something I can't wrap my head around. As usual, its a boost issue. I've got ~3 PSI at the test RPM/WOT.

I'm 90% sure my lack of boost is from the vacuum transducer for the wastegate (Y31, if you've got the FSM) not working. When the engine is on, there is no voltage across the plugs, and no vacuum on the line going to the wastegate. However, the transducer itself isn't the problem, because run from an external power source it works fine, boost is good, and all is happy.

(From here on, I'm confused as can be)

From looking at wiring diagrams, it looks like this ground is supplied by the manifold pressure sensor (S66) but also goes through the alda's overboost protection solenoid (Y30). I'm pretty sure the sensor is broken (some guidance on how to test it would be great), but connecting the battery's ground to the sensor doesn't fix anything.

I can supply pictures if needed, and thanks in advance.

tl;dr: wastegate vacuum transducer (Y31) isn't receiving power, what do I do?

An '87 300D wastegate is normally closed and opens with a boost signal directly from the compressor outlet. The transducer is for the air recirculation valve (ARV) on the front face of the compressor.

You're testing for boost with the engine under load, right?

Ensure a clear boost signal path between the intake manifold and ALDA atop the IP. If the ALDA doesn't get a good boost signal, there won't be fuel enrichment to continue building boost.

Sixto
87 300D

+1

He's right, Y31 has absolutely nothing to do with the waste gate. That thingy on the turbo is the ARV which can be disconnected.

Double check the solenoid valve on the left side false firewall right next to the washer jug. There is a hose going from the intake manifold, to the valve, and from the valve to the ALDA. If that's plugged then the boost pressure can't get to the ALDA to tell the IP to give more fuel.

Without the ALDA signal you will just be pushing more air but no fuel to back it up.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Well shoot, there goes everything I thought I knew about the turbo system.

I thought I had read something about ARV being another name for the waste gate. What exactly is its function then?

Yep, T in the line between the manifold and alda, tested in 3rd gear and ~3000 rpm.

Just walked out to the car to triple check lines (cleaned them out a few days ago), and I noticed the rubber Y connector that goes to the alda is split. Its covered by a chunk of wiring that I was screwing with, so I might've broken it then, but it still could've had a hole. Don't know how I missed that.

I'm going to replace that, and hope it fixes everything.

Thanks for setting me on the right track guys, I don't know how I could've screwed up reading a diagram that bad.

The ARV bleeds boost back to the compressor inlet. IIRC it has something to do with getting the trap oxidizer to operating temperature more quickly. You can unplug and cap the line with no ill effect.

The Y-fitting in the line between the overboost protection solenoid and ALDA should branch to the transmission vacuum amplifier - the round blue thing ahead of the left suspension tower.

You probably worked with a vacuum diagram for a 90-93 300D. Try this one -



Sixto
87 300D

Sixto, isn't that diagram missing the third switchover valve? I thought I saw a post by you about it.
Be sure to check this as well, my 1987 300d has a manufactur date of 05/87 and had this feature.

Third switchover valve? Not on a US spec '87 300D, federal or California (no difference). Where does your car have a third switchover valve?

What's missing in the diagram that's in my car (IIRC 3/87 build date which I'll confirm when the wifey gets home) is a split just ahead of the VAC port in the BFS (123). A larger black vacuum line goes by the fuse box, runs along the bulkhead and tucks into the passenger side fender behind the wheel to a vacuum reservoir.

Sixto
87 300D

I suspect that reservoir was added to address problems with the transmission shifting control running out of vacuum during periods of high demand (probably caused during repeated braking).

I will check my 87 300TD tomorrow when I get back to Vstech's to finish rebuilding the rear end. I will see if I have that line and the vacuum tank also.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Hmm yes my car had a third SV identical to y29 and y30, also mounted on the firewall.

The valve had a large clear "filter" looking device connected to it that sat down by the glowplug relay box.

The SV was somehow plumbed into the alda and the overboost SV (y30) I can't remember exactly how.

I removed it when the car "thought" there was an overboost and was cutting fuel. When I plumbed the intake just through y29 it fixed this problem. Possibly this third valve was bad.

Sixto, I had thought I saw a post by you concerning this. Something about eliminating cruise surge?

I hope I don't have you confused with another member and/or have lost my mind.

Here is a link to the post I thought was Sixto, it was actually gsxr. My mistake.

Free Horsepower for 1987 300D (and 300SDL?)