OM603 W124 300d problem, running out of possibilities

[hschickel]

Hi all,

I acquired a 1987 300d with 250000 miles and have been repairing it over the last few days.

Done so far:
1. New glow plugs (lot of reaming)
2. Cleaned intake and crossover (amazed the engine ran these were so bad)
3. Correctly routed and cleaned or replaced vacuum lines (including manifold/switchover/alda line - tested and working)
4. New air filter - took the airbox apart down to the turbo to look for obstructions - this is clear and the compressor part of the turbo spins freely with little to no play
5. New oil and filter with oil at the correct level - huge difference
6. Purged injectors
7. New fuel filters
8. added 1/2 ccw on the alda - this seems to have just added smoke - I'll probably change it back
9. Killed the EGR with a long screw to firmly seat it closed
10. Killed the ARV by plugging the vacuum

Car is starting to run well but I can't seem to get more than a couple of pounds of boost. 2 at WOT under load & 3 during the upshifts. I have several theories and I'm getting in way over my experience level with this car... thus the post... perhaps someone can help or offer a better theory...

1. Not enough O2. There is a box under the air filter (the MAF?) with a gate on the inside and electrical wires going into it. The gate swings freely and moves more than halfway with a shopvac attached to it. The turbo is probably inhaling a lot more air when properly spooled. I played with various combinations on the electrical side. Nothing seems to open this up - it looks like it just sends an electrical resistance signal at various degrees of open - possibly to a disabled emissions device??? I'm thinking of just propping the gate open to eliminate this possibility but I think it's a long shot...

2. Exhaust - the exhaust seems to work properly... good pressure at the back, but I've heard that this can get plugged and cause my problem. To test I opened that exhaust hole near the EGR and went for a drive. There was zero change/improvement but perhaps that hole is not big enough??? I figured if I got an extra pound or two I would start cutting the exhaust sections out until I solved the problem. Was this test proper? Is there a good place to loosen the exhaust to test this?

3. Turbo - Garret T3/ARV The turbo spins freely at the compressor. There are no blockages between it and the air intake. It is not gunked with oil or sludge at that end. The wastegate starts moving when I apply pressure. Full range seems to be 14-20psi or so. This should be in spec. I have two theories on this...
--A. Wastegate spring is getting weak and not completely closing the wastegate? Would it damage the diaphragm to apply vacuum and see if I can get more motion? Can the spring be replaced? Would it perhaps be simpler to sever the rod and add an adjusting linkage? Is there a built in adjustment somewhere?
--B. Wastegate itself is sludged somehow preventing full closure? Based on what the EGR did to the intake, crossover and vacuum system I'm thinking that this is not an unreasonable possibility? It looks like the turbo must be removed to clean it? I see a lot of exhaust bolts involved!! Do any of these have a tendency to break? Is there a way to get to the exhaust section easily without removing the whole thing? Any other advice on this process?

Other things that may help in diagnosis...
* Engine freely revs to just under 5000 rpm in neutral
* Car does 0-60mph in about 20s at 5280' (it was over 40 when I got it)
* Throttle linkage is missing WOT by a bit (1/4ish") at the IP. I need a helper to tackle this but it seems like it should not affect anything other than shift points (double vs single down & upshift point) and max rpm based on my understanding of the system
* I did not do a compression test but the car starts instantly and runs smoothly at all rpm levels

Thanks for any help,
Hugh