That is the over boost pressure switch. Remove it and clean it out. There is not hole for you to push a wire through. The sensor is inside of the threaded portion. The only other connection is the electrical wire that runs over to the overboost protection solenoid.

Mine was completely clogged with oil/junk, thanks to the EGR.

-Jim

(EDIT! I just looked/read again. Remove the tube from the small one and spray something in it. I used WD-40. You are right on track with what you said.)

__________________
1995 S350D, Green with black leather interior.
Bought January 2008 w/ 233,xxx miles.
I did 22,000 miles during the first year of ownership.

That is correct.

The problem is, pushing a wire into the fitting may just push the sludge out of the way temporarily... boost pressure could push it right back into the hole after a while. It's simple to remove, it just unscrews. My recently-purchased '93 300D had this fitting mostly filled with oily, sooty goop. The only way to fully clean it (from both sides, front AND back) is to remove it. The back side has a much larger opening for goop to collect in.

Wjob,
I've been through exactly what you are looking at on your 1987 300d. I've cleaned all of this and checked this and that. Do yourself a favor and release the three bolts that connect the turbo to the downpipe for your exhaust and go for a quick spin. Its 3 bolts and I'm almost willing to wager that your problem is a plugged cat. I don't get the time to wrench on mine because of all the other priorities but I think that is the issue I'm facing, hopefully this weekend I'll get at it and find out if it really is the issue, then I'm going to post back in this same post to let you know how it went.

__________________
87 300D Turbo (still wondering about #14 head)
98 Buick Regal GS (one quick grocery gettr)
07 Honda CBR1000RR
04 Dodge Ram Laramie 4x4 CTD (heaven)
95 Dodge Ram 3500 CTD. Need snow plowed?

Since it should be much easier to remove bolt at the front of “log” (part that replaced Trap Ox.) which is intended for taking exhaust pressure readings, rather than loosening the three down pipe bolts, isn’t that a better way to test whether there is an obstruction?

thanks
Bill

The small hole may not be large enough to allow the engine to run normally. If you could connect a pressure gauge there, the factory spec is max 30psi backpressure (pre-turbo). To see if the car will run properly, you'd need to disconnect the pipe post-turbo, as Jim described. Removing the "log" pipe won't work, as that is what feeds the turbocharger, and you'd never get boost with it removed. (And, it might be a little loud for a test drive, lol.)

Here’s what I’ve done so far with no good results:
Have run it on gallon jug with both supply and return lines terminating in jug, thus by passing tank. When first run off jug used good amount of Diesel Clean with fuel. Also took thermostat out of system and ran directly to lift pump, thus bypassing it too. Lift pump appears to be operating properly since I’m getting continuous spurt-spurt-spurt from return line.

Removed and cleaned the fittings from the intake…the one that carries the plastic tube over to the switchover valve and the Pressure Switch. Both were partially clogged with black goupe

Removed the exhaust test fitting (bolt) from the log pipe. No real loud noise, just some pressure escaping when I put my finger over the opening.
Ran it on the road after I installed jug and again after I removed the exhaust test fitting and both tests were about the same…no boost on gauge, no power, couldn’t get it past 4000 rpm’s (only 3,500 with the exhaust fitting removed). Can rev it up past 4,000 in park. Didn’t take it out on road for trial after cleaning the intake fittings and with exhaust.
fitting back in place but could tell from action in park that it wasn’t improved. It’s very smooth at idle, with no smoke.

Assume feeling is still same, that it’s waste of time at this point to remove Alda and worry about the fuel leaks at the delivery valves before going to the turbo? This brings up several questions:

Dave, you suggested shooting compressed air into the KKK waste gate to test it. What pressure should I use and assume I can shoot the air into one end of the pipe if I’m only able to remove one end while unit still in the car? How do I remove rubber crossover tube that plugs into top of valve cover and runs to the large intake hose from the air cleaner? Guess it probably just pulls out the top of valve cover but some years back I tried this and the plug kind of exploded in the valve cover and made a mess.

Last question. Do I need to use gasket sealer with the appropriate gaskets if and when I remove/replace intake and exhaust manifolds? Also, is there some sort of seal that needs replacing when I loosen/retighten the flange at the exhaust down pipe.?

Thanks again.
Bill


-

Here’s what I’ve done so far, with no good results:

1.) Have run it on gallon jug with both supply and return lines terminating in jug, thus by passing tank. When first run off jug used good amount of Diesel Clean with fuel. Also took thermostat out of system and ran directly to lift pump, thus bypassing it too. Lift pump appears to be operating properly since I’m getting continuous spurt-spurt-spurt from return line.

2.)Removed and cleaned the fittings from the intake…the one that carries the plastic tube over to the switchover valve and the Pressure Switch. Both were partially clogged with black goupe

3.)Removed the exhaust test fitting (bolt) from the log pipe. No real loud noise, just some pressure escaping when I put my finger over the opening.

4.)Ran it on the road after I installed jug and again after I removed the exhaust test fitting and both tests were about the same…no boost on gauge, no power, couldn’t get it past 4000 rpm’s (only 3,500 with the exhaust fitting removed). Can rev it up past 4,000 in Park. Didn’t take it out on road for trial after cleaning the intake fittings and with exhaust.
fitting back in place but could tell from action in Park that it wasn’t improved. It’s very smooth at idle, with no smoke.

Assume feeling is still same, that it’s waste of time at this point to remove Alda and worry about the fuel leaks at the delivery valves before going to the turbo? This brings up several questions:

Dave, you suggested shooting compressed air into the KKK waste gate to test it.

What air pressure should I use and assume I can shoot the air into one end of the pipe if I’m only able to remove one end while unit still in the car?

How do I remove rubber crossover tube that plugs into top of valve cover and runs to the large intake hose from the air cleaner? Guess it probably just pulls out the top of valve cover but some years back I tried this and the plug kind of exploded in the valve cover and made a mess.

Last question. Do I need to use gasket sealer with the appropriate gaskets if and when I remove/replace intake and exhaust manifolds? Also, is there some sort of seal that needs replacing when I loosen/retighten the flange at the exhaust down pipe.?

Thanks again.
Bill

I'm not sure of the size of the "exhaust test fitting" but it's unlikely to be sufficiently large enough to test for a plugged cat.

Your test is inconclusive due to the size of that fitting.

If you could separate the downpipe from the exhaust manifold to allow free exhaust flow without passing through the cat, we'd have some meaningful results as to whether the cat is the culprit here.

It's not normal for a turbo to fail completely and provide zero boost. The only possibility for this is when the impeller/turbine combo won't rotate. I presume that you've spun the rotor by hand to ensure that it's free?

Thanks Brian for your reply.

I will separate the down pipe to see if that’s the problem.

I have not yet taken the hose of the compressor end to feel inside but I will. However, this brings up again the question I raised: "How do I remove rubber crossover tube that plugs into top of valve cover and runs to the large intake hose from the air cleaner? Guess it probably just pulls out the top of valve cover but some years back I tried this and the plug kind of exploded in the valve cover and made a mess."

Also, can you answer my other question: "Do I need to use gasket sealer with the appropriate gaskets if and when I remove/replace intake and exhaust manifolds? Also, is there some sort of seal that needs replacing when I loosen/retighten the flange at the exhaust down pipe.?"

thanks
Bill

1980 300SD
1982 300D
1986 300SDL
1987 300SDL

The rubber tube simply pulls out of the valve cover.

Neither manifold uses any gasket sealer. The OE gaskets do the job acceptably well without any sealer. There's no sealer that would survive the exhaust heat for very long in any case.

There is no seal at the flange for the downpipe. It simply wedges itself against the cone on the exhaust manifold.

Also, on a different note, you can edit your profile to put your name and vehicles in your signature. Saves typing them every time you post. Press the "user CP" key at the top of the page.

hey guys,a non turbo engine will run if you supply fuel and air to it. i once drove a 603 from boston to ky with a bad turbo that caused it to have no power,20-30 mph up any small grade. i posted the experience on the forum.
remove the line going to the alda,place a air pressure (i uses a bycycle pump) take her for a drive,pump up some pressure and see if it runs good,case closed,turbo aint supplying pressure to aldi=little fuel.
larry perkins

Larry, based upon his tests, there is little or no boost. Either the airflow is restricted badly or the turbo is not rotating or the wastegate is stuck open.

The vehicle can't provide any boost to the ALDA to make more power.

Thanks guys for the comments and help.

Probably won’t be able to get back into it until Monday, As soon as I do, I’ll post back.

Thanks
Bill

1980 300SD
1982 300D
1986 300SDL
1987 300SDL

Sorry for the late response. Brian already covered most of it. There's no sealer needed, and no gaskets to replace, unless you remove the exhaust manifold from the head. Then you install a new exhaust manifold gasket, but that's about it.

The plastic PCV tube that goes from the intake snorkel to the valve cover is often brittle after 20+ years. And, the rubber O-ring at the valve cover is often 100% fossilized. It should not be rock hard, it should be soft rubber. If it breaks, get all the pieces out of the valve cover, a shop vac works nicely. Install a new gasket. If the tube/pipe breaks, buy a new one. A fresh pipe with a new gasket will easily pop in & out as needed. Old stuff tends to break if it you look at it the wrong way. The O-ring is a buck or two, but the tube is spendy, something like $25 IIRC.

I'm starting to think either plugged cat, or frozen turbo. Could be a jammed-open wastegate, too.

__________________
Dave
Boise, ID
Check out my website photos, documents, and movies!

Took front tube off compressor side of turbo for inspection. Wheel felt solid, no wobble, no binding, just a a very little oil slime on some of the blades, Then ran engine and blades certainly spinning as they should. Therefore, now need to determine if waste gate is stuck open or have blockage in exhaust, which raises following questions.

If I break one of the studs at the exhaust pipe to manifold flange, what’s the fix? Assume try to remove remaining part of stud with vice grips? Does a new stud screw into the flange, or get pressed in or would I need to buy a new flange piece with the three studs? Before trying to remove nuts, does it make sense to heat first with Mapp gas?

If my problem turns out to be stuck open waste gate which means removing turbo, can I just loosen rear most accordion fitting (leaving rear turbo bracket and exhaust flange in place), then after unbolting forward turbo bracket plus oil lines, just slide unit slightly forward, up and out?

As I understand situation, if I have to remove turbo, without removing exhaust manifold, only new gasket I’ll need is one that goes between oil return line and pan? Good idea also to replace rear most accordion fitting referred to above? Will I need to use gasket sealer between new oil return line gasket or where log pipe bolts to turbo housing (4 bolts), or anywhere else?

How do I determine if there is oil problem in turbo? When I pulled front hose off compressor side, didn’t seem to be over abundance of oil (just a little) inside but underside of waste gate as shown in attached photo (looking up from underneath) shows some oily buildup on waste gate and airline fitting?

Several other points want to question before I go further. My test runs were done with EGR plastic line plugged but not metal EGR itself (has the hose barb unblocked)?

The other attached photo shows a puddle of diesel fuel collecting in engine mount arm dimple under injection pump. This dimple will fill up with leaking fuel if I run the car on the road for 15/20 minutes. It’s very difficult to be sure it’s all coming from the leaking delivery valves? Thought some might be coming from side brass plate on pump, thus used a torx bit to snug up the 4/5 fasteners (were little loose) but didn’t seem to help. Also noted yesterday when under IP that there is a plate on bottom with what looks to be same torx fasteners, but didn’t try to get to those. No question that the delivery valves are leaking and possibly that’s running down and filling dimple.

After this explanation, is it still the feeling that I should continue to concentrate first on the turbo and exhaust side rather than the fuel and intake manifold?

Will appreciate comments.

thanks
Bill

'87 300 SDL

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