My 85 300D (Calf) was been running very well. (Had Trap Oxidizer rplaced at dealer with oxidizing cataylst at before I purchased car, car now has 137,00 mi) Good acceleration, excellent tubo boost at approx 2300-2500 rpm etc. Was running fine on Wed. Thrs. wife took the car and complained about lack of power. I drove the car, and indeed it was sluggish and got worse. Slow starts, dead on hills and no feel of Tubo boost. Starts just fine and idles perfect. Here's the facts and what I have done to no avail.


I did not tank up during during this problem development.
Transmission still shifting OK.
Last week I cleaned out the banjo fitting on intake manifold that feeds vacuum line to gizmo on firewall. ( I believe this is supposed to enrich injection on need and with tubo boost)
I tried replacing entire vacuum line that is part of the the above item as mine was spliced and I had these exact symtoms awhile back when the line kept popping off the manifold/banjo connection.
The gizmo on the firewall holds vacuum when tested with my mighty vac.
Replaced both fuel filters even though they both only had 10K on them. Fuel was clean in both, no trace of algae etc.
Checked all vacuum lines that I could find, all appears ok.
I adjusted the valves about 9K miles ago.
New air filter 500 miles ago and it is clean.

Any suggestions as to where to poke around next?? I doubt it could be something serious to happen as it did. I'd rather not mess with the ALDA since it was running just fine.
I love this car but it's taxing my patience.
Thanks,
Gene

Assune you have a 300TD not a 300D (suggest you update your profile )- it makes a difference in trouble shooting suggestions. Not an expert but - have you checked out the EGR system? It's possible thet the EGR 'plate' has almost closed, and if so that would be a good culprit for what you are seeing.

If it does turn out to be EGR related then you may want to consider an 'off road mod' that puts the EGR plate into a full open position.

It's the other way around. A stuck open ERG will cause a loss of power. The "mod" is to keep the ERG closed. Try disconnecting and plugging the ERG vacuum line to see if that helps.

BTW, I would recheck the line from the banjo bolt to the IP to make sure it didn't come loose someplace.

Really?

You have all the symptoms of no boost.

The only way to confirm what you have is to obtain a boost gauge and T it into the line to the ALDA. Run the gauge into the cabin and take it for a drive.

Make sure you run it at maximum power, above 3K rpm, and read the gauge.

If you have no boost, then we can go further to determine why.

Any leaks in the line from the back of the manifold to the overboost valve on the firewall to the ALDA will drop the level of fuel enrichment. You may wish to double check all those connections. You may also wish to bypass the overboost valve to eliminate it as a culprit.

Brian,
How do I bypass the overboost valve. Is this the pressure switch on top of the intake manifold back towards where the ALDA bango tube connection is? And, do I just pull the electrical connection off of it to bypass it?

Also, I notice a small threaded allen screw type plug on the manifold towards the rear side of of it. Could I unscrew this, replace it with an appropriate connector to feed a line to a pressure guage? Could any pressure guage be used, say with a range of 0-30 lbs, or does it specifically have to be tubo boost guage?
Thanks,
Gene

On the manifold, at the rear, is the banjo fitting where a line runs to the overboost valve on the firewall. Then, from the overboost valve, another line runs to the ALDA on the injection pump. Simply run a rubber hose directly from the manifold connection to the ALDA. If the hose fits tightly, you don't even need the hose clamps for testing purposes.

If you want to use a guage, any pressure guage will do.......15psi is sufficient. Just T it into the line to the ALDA and run it into the cabin so you can watch it while you drive. You can't test for boost in your driveway.

Brian,
I've tried the following, all still yield poor performance. A real slug off start, dead in water on hills etc.

I first tried bypassing the switchover valve (overboost valve). No change. Then I "T'd" in a 0-30 PSI guage and took it for a run. Still bad. Could only get 5 PSI by leaving it in "S" (3rd) and running it up to at least 3200 RPM. I was just able to budge the needle in "D" (4th) at about 2900 RPM at about 60 MPH which took me a long time to get to. I think I almost put my foot through the floor.

Next I hooked my Mighty Vac to the EGR. I can't see the shaft, buy I could definitely feel and hear the plunger working. Seems to spring back down. I pulled the vacuum line off the EGR and plugged it. Still no change.

Loosened the outbound connection on the large fuel filter housing and bled it once again. No change. I think I mentioned I changed both fuel filters yesterday; both were clean and fuel seemed to flow freely from the tank.

About 2 weeks ago, I did replace my entire exhaust system from the first connection off the manifold down pipe all the way back with a factory pipe and two mufflers off my Federal Donor car. (mine is CALIF) Exhaust appears to be flowing freely out the back with no strange noise etc, and I don't think this could have caused any problem??

I also pull out the air filiter (virtually new) and check to make sure som varmit didn't lodge itself in the fender intake or up the tube to the turbo.

A friend of mine pried off the ALDA cover screw but I have never tinkered with it. I'm reluctant to do so since the car ran so darn well before it turned on me overnight. So, what comes first, the chicken or the egg. Does the ALDA have to enrich the intake to juice the turbo, or does the spooling up of the tubo come first so it can trigger the ALDA to enrich the intake etc. The car used to be much quicker from a dead start and I doub't the turbo had time to wind up much during initial pull outs. It really used to kick in strong at 2300 RPM. I could climb from 50-75 MPH in short order.

Could the turbo wastegate by hanging open?? Any way to test it. Looks like the waste gate operates entirely independed of the overboost pressure switch and overboost valve that merely adjusts the richness???
Any ideas of where to go from here?
Frustrated in Saratoga,
Gene

1) Disconnect the line from the ALDA that goes somewhere else.........probably to the transmission vacuum transducer. Make sure you only have ONE LINE from the overboost solenoid to the ALDA.

2) Drive the vehicle again with the gauge and see what the boost reads.

3) If still unsatisfactory, connect the Mityvac PRESSURE OUTPUT (on the top) to the ALDA. Pump it up to 15 psi and see how long it takes to bleed down. It might not hold pressure, but, it should take at least 8 seconds to bleed off. If you can't pump it up whatsoever, then the ALDA has an internal leak or has failed completely.

I still think the ALDA is not seeing the boost.........or not responding to the boost.........for some reason. Nothing else makes much sense.

With regard to the chicken or the egg............it's a bit of both.........you can't make full boost without fuel enrichment from the ALDA..........and you can't get fuel enrichment from the ALDA without some boost. 5-6 psi is typical of an engine with no fuel enrichment.

B.C.

I disonnected the other line going from the ALDA to the transmission transducer. Capped the opening that fed the transducer line. Took the car out. Noticed some very slight improvement but still a dog. Turb seemed to kick in a little sooner, 2900-3000 RPM, and still only 5 PSI.

Tried pressurizing the ALDA, managed to pump up 13 PSI with the Mighty VAC and it holds the pressure.

I'm running out of ideas???? Still appears to have all the symtoms of a turbo boost/ALDA enrichment issue.

Any other suggestions?
Thanks,
Gene

Could you drive the car with the ALDA "pumped up?"

Just to confirm..........connect the Mityvac to the ALDA..........pump it up to 13 psi........and drive it while maintaining 13 psi. Let's see if the performance returns. Keep a boost gauge connected and LMK what it reads during the test.

Great idea. I'll get it hooked back up and try it out tomorrow this way. It's getting late, it's dark, and still raining up here. If it runs better pumped up, would this confirm the ALDA is OK? I should probably recheck the manifold hole that feeds the banjo connection. Could be the intake manifold is packed full of EGR crud and keeps stopping things up??

Thanks everyone for hanging in with me on this.
Gene

or a plugged fuel return line. only way I know to test the screen is remove and inspect.
the return line can be tested by blowing into the cigar line. should easily blow free. remove the fuel tank cap first.
your turbo may have failed as well. pull off the u tube WITH THE CAR OFF! and check to see ifit spins freely and then lift and rock it side to side and see if it has any play. mine moves about 1 MM and my car works ok. also look and see if you have oil all over the blades. you could have a bad seal in the oil line.
just some other things to check sorry I am not an expert on these cars YET. but I am learning.
John

It would also be worthwhile to check the turbo wastegate hose for integrity. Did you clean the hollow bolt in addition to the banjo fitting at the intake manifold?