Sorry for the confussion in my post. My "leak down" was actually a test for how fast the preasure would leak out of the ALDA. Off the IP I couldn't pump it up. On the IP it leaks at about 1psi/sec from 10psi down to 5psi.

Based on the volume of preasure created by the turbo the consensus is that a leakdown this slow shouldn't affect boost preasure. As for the 12.5psi I was quoting Dave's measurement as what I should expect. I haven't measured that on my car since I first got it in 2000 and fixed the preasure line obstructions. But then it definately pushed 12.5.

So I think the main evidence that I need to address is the fact that with the ALDA disconnected from the mainifold preasure I only generate 3.5-4psi of boost preasure. With preasure lines connected (t'd to the gauge) I get 5.5psi and with the shim under the ALDA I hit 7psi.

Maybe wastegate is partially open, exhaust is blocked, turbo fins are broken (slim chance I hope). Any other ideas?

Thanks,

Hmmm. I'd try putting the "T" at the manifold, to make sure the switchover valve isn't partially obstructed and reducing signal to the ALDA. (?) If you get the same readings, and the manifold fitting is clean... hmmm. Is the ARV disabled? EGR valve fully closed and seated?

:confused:

Dave,

I have disconnected the ARV and ERG vacuum lines as I have seen described in this forum. The biggest affect that I've seen from that change is that my preasure line from the manifold doesn't plug up once a year anymore.

I'm taking it in to my indy next week for the vacuum pump replacement and we're going to check on these possibilities. My indy's opinion is that my symptoms best describe a partially blocked exhaust. I'll let you know what we discover.

Thanks,

The exhaust on my SDL was starting to plug. I would estimate that 20% of the oxidation catalyst was clogged with soot.

What you describe could be a partially plugged catalyst. If so, you may want to weld in a straight pipe, if you don't have smog inspection in your state. A new front exhaust pipe is pretty spendy. I hope the problem is that simple!

:D

Don't forget the possibility that the turbo bearings are shot -- this will cause severe lack of boost no matter how well anything else works.

Turbo is cheaper than a new catalyst.....

Easy enough to check -- pull the air pipe off the front and spin the turbo by hand (engine OFF!!!!). It must spin very easily, with no axial play and very minimal side play. If you can feel it move back and forth, or it has "sticky" spots or won't move with very light finger pressure, the bearings are shot and it will never get up to speed.

Usual cause of turbo death is failure to idle it down after hard running. The turbine will be at least red hot, maybe hotter, and if you don't let the engine idle for a couple minutes after driving at speed, the oil on the shaft and bearing will get roasted, causing the accumulation of coke (carbon). Sooner or later, it stops spinning fast enough. Synthetic oil helps enormously, by the way.... This isn't a problem in suburban or city driving, but rest stops on the interstate are death to turbos.

Peter

Very good analogy of what kill's turbos........... :) BB

Not to discount the wisdom of the "cool down" period, but this does not apply to Mercedes turbodiesels in most cases. MB designed the turbo, bearings, and oil system to provide more than adequate cooling for 99% of driving scenarios. After a long freeway jaunt, a cooldown is not needed. After climbing Pikes Peak at WOT, yeah, let it cool down a bit before killing the motor. ;) Freeway driving produces hardly any load unless there's a healthy grade involved (i.e., Grapevine in SoCal, the Rockies, etc). My oil cooler lines aren't warm after light driving, as there's not enough heat to open the oil t-stat. It's not a bad habit to let it cool off a bit before shutdown though. You're sure not going to hurt anything by letting the engine idle for 30-60 seconds before shutdown. (Note that the owner's manual says to turn off the engine if it will idle for more than 2 minutes.) If you use dino oil this is probably something to keep in mind in summertime. If you use good synthetics (Mobil, Amsoil, Red Line) it's almost entirely unecessary except maybe in the aforementioned Pikes Peak scenario. :D :D

BTW - for gas powered turbocharged engines, this is a much bigger deal - what I wrote above is my opinion specifically pertaining to the OM617 and OM60x diesels.

:o :o

Almost forgot - turbo bearings! A slight amount of shaft play is OK, and possibly normal. The impeller should spin quite easily with your finger. The reason the play is OK is because the bearings are designed to float on a film of oil, not ride almost metal-to-metal like wheel bearings, etc do. That's how it deals with spinning at something like 100k RPM. If the shaft is really sloppy, or doesn't spin freely, there could be an issue with the turbo. It's also possible (but not likely) that the exhaust side fins are damaged, although that's usually a result of the trap oxidizer breaking up and puking parts into the turbo. I assume the trap is long gone, and the dealer was *supposed* to check the turbo when the job was done, and replace it for free if it has damaged fins.

:sun_smile

Boost Preasure with no enrichment
 

Guys,

Just want to double check the conventional wisdom about boost preasure measurements WITHOUT enrichment. Dave M. reported that one of his cars pushed 12.5psi with the ALDA disconnected, i.e. running the boost gauge straight off the manifold instead of with at "T".

The reason I ask is that Marshall Booth understands this differently. He put it this way on the MBCA tech form:

"Without fuel enrichment you will NEVER have more than 5-6 psi (~0.3-0.4 bar - usually a little less) boost. There will not be sufficnet heat to generate the boost without enrichmnet! It is the complete burning of the fuel (that requires boost to provide the excess air necessary to burn the aditional fuel) that provides the power to generate the boost. I expect that SOMETING is leaking - perhaps the EGR, perhaps the air bypass, perhaps the presure line up to the wastegate is venting boost."

So I'm curious to hear if anyone else finds that their 603 engine turbo can generate waste gate opening preasures without fuel enrichment. I must admit that the engine manual is very specific about measuring with a "T".

Thanks,

I think Marshall is speaking in general terms, and possibly also about a car with an "as delivered" mixture setup, which was often lean off idle. Properly adjusted, there will be enough fuel to provide well above 5-6psi. Wish I could test this out on my blue car, but it will have to wait a few months until the engine goes back in...

:o

Any way to get the tamper-proof cap off of the ALDA without making it look like a hatchet job?

I cut it off with a fine tooth hack saw with Alda in a vise!

send it to Gus at Pacific Fuel Injection and for a nominal fee he will remove the old cylinder and cap and install a new one without the cap (he will give you a cap so you can shove it on if you like after you finish tweaking)
The teeth in the platic cap engage and absolutely (well, almost never?) can be removed without cutting the metal cylinder away.
Oh yes, you can place a shim washer or two under the alda and obtain the same results without damaging the cap.

Options are:

1) Use shims instead, and leave the cap intact. This makes fine adjustments very difficult unless you have an assortment of very thin shims.

2) Very carefully pry and tweeze the plastic cap out, leaving the metal canister intact. I did this on my one ALDA and it took a LONG time. You need to do enough to get a socket on the nut, then back it ALL the way off, remove the canister, remove the remnants of plastic, and re-assemble. Looks nearly stock (on a 60x) when you're done.

3) Destroy the metal canister to get access to the nut. Then back the nut ALL the way off, remove the canister, remove the remnants of plastic and canister shards, and re-assemble. This should look pretty clean when it's done.

:sun_smile