I recently purchased a 1990 2.5 T 300D. It has 250k miles on it but starts up without issue every time. I immediately installed a boost gauge because it was an absolute turd. It was getting 2 psi at 5,000 rpm. Since my initial inspections I have done the following:

- Intake removal, clean out, and new gasket
- Both fuel filters
- Straight pipe exhaust
- GSXR waste gate mod (eliminated all that mess of vacuum garbage)

The car starts great. It cruises great. It makes 14 psi at 4500 rpm. My problem now is fuel. It's an absolute dog until up in the revs. I have no idea what kind of mileage is on the injectors or if anything on the pump has ever been done. It never had any BIO or WVO run on it so that's not going to be an issue. I guess these are my questions:

What else needs to be cleaned and inspected?
Why does the transmission shift super hard now?
It runs rough at idle when cold and is smokey, things to check for this?

I'll be blocking the EGR and probably removing the flappy thing when I make a pipe to fit in there.

Yes, I know there's a search function, but there's SO many pages to sort through. I'm not new to diesels, but my experience is with VW and tuning/performance upgrades were controlled via computer.

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1990 2.5T 300D: 3 inch exhaust, GSXR mod, custom intake, egr and alda delete

Look at adjusting up the ALDA. Its on top of the pump, it has a security cap on it you'll have to break off.

Backing the screw out raises the fuel, turning it in lowers it. You adjust it out until you get excessive smoke on take off, then wind it back down.

Some people do just entirely remove the alda too, but I generally do not.

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68 280SL - 70 280SL - 70 300SEL 3.5 - 72 350SL - 72 280SEL 4.5 - 72 220 - 72 220D - 73 450SL - 84 230GE - 87 200TD - 90 190E 2.0 - 03 G500

Nissan GTR - Nissan Skyline GTS25T - Toyota GTFour - Rover Mini - Toyota Land Cruiser HJ60 - Cadillac Eldorado - BMW E30 - BMW 135i

Low power: ALDA may be leaking off pressure, so that's worth checking as well. It probably has two o-rings that are dead and leaking now.

Smokey rough starts: Glow plugs, old tired injectors, problems in the delivery valves. Start with simple / cheap and work up to expensive / difficult / high risk. Test the glow plugs, see if you can isolate the rough running to one or two cylinders by loosening up the hard injection line at the top of the injector. Another possibility is a leaking fuel line allowing air into the system.

Hard shifts: vacuum leak. If you worked on that system to "fix" the turbo boost, you've now got another issue to fix.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

Thanks for the tips guys.

I had planned on doing the Alda and I guess I'll be chasing more vacuum lines and testing fuel lines. I have read about some sort of banjo bolt being clogged? If the EGR pipe was any indication, it's probably clogged solid as well.

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1990 2.5T 300D: 3 inch exhaust, GSXR mod, custom intake, egr and alda delete

The ALDA leaking and trans shifting issues can be intertwined. Pull the nipple off the ALDA and see if it holds vacuum (if it's good it should). If it won't hold vacuum don't waste your time adjusting it, it needs new seals.

If your car has the "blue UFO" vacuum amplifier for the transmission, the boost signal going to the ALDA is tied into it and directly affects your shifting. If the ALDA leaks, the boost signal is low and will affect the amount of vacuum to the transmission modulator.

All things being equal, the power should come on smoothly if the ALDA is working properly. You'll be a little gutless until you hit ~1500 RPM, then you should start feeling a surge of power as the ALDA enriches the fuel mixture. If it's just a dog until you get over 2000 RPM and suddenly you have power, I'd bet money on the ALDA leaking like a sieve.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

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1985 524TD 167K (TotalDumpster™)

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1986 300SDL (RIP)
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Whoa. Hold on there. When you took "all that vacuum crap" off your engine, where did you how did you connect the wastegate actuator? Did you drill the turbo and install a pressure port? Or did you take the pressure feed from the left side of the manifold?

1) The alda needs to sense pressure to work. Before you do any more ripping out, make sure that it's seeing boost pressure.

2) Your transmission is vacuum modulated. So if you've screwed with the vacuum system, you may well have left a leak or blocked the wrong line somewhere.

3) Idle is computer controlled. What RPM are you seeing? Should be around 700. If not, you will need to troubleshoot the idle control system. If it's idling at the right speed, you may need engine mounts.

Ripping out stuff out of frustration only increases frustration. Now you have a gross polluter that shifts hard. I bet you're also having trouble with the climate control system.

I removed the air box, air meter, and the the 3 dampers. The one vacuum line that was going to all of it I put into a T to the two lines that were left. IP breather and the other vacuum reservoir. I haven't touched the driver's side. I wanted to get boost pressure up before I started addressing vacuum. The original actuator was toasted.

For boost actuation, I tapped the cross over pipe and am seeing 14 psi at peak.

Idle is 700rpm as it should be.

The car is no more or less pollute-y than it was, it just has a turbo that works now. I also commute across town on a 2 stroke dirt bike that smokes more than the car.

I will inspect the alda after work and order seals if necessary. (good source?)

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1990 2.5T 300D: 3 inch exhaust, GSXR mod, custom intake, egr and alda delete

Pull off the manifold pressure signal which goes to ALDA and make sure the manifold nipple is cleaned. If you had a pressure pump you could also test if ALDA holds pressure.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

That's the nipple next to the sensor on the driver's side of the intake manifold? I thoroughly cleaned it when I clean the manifold, so there is definitely pressure there now.

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1990 2.5T 300D: 3 inch exhaust, GSXR mod, custom intake, egr and alda delete

Yes

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

Nothing to fear from simplifying OM60x vacuum routing....just has to be done correctly. See attached.

Attached Thumbnails

 

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

I was considering the deletion of the blue saucer as well. This car is high mileage and is strictly a commuter, so it doesn't need to fit in with the purists.

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1990 2.5T 300D: 3 inch exhaust, GSXR mod, custom intake, egr and alda delete

Does this vehicle have a switchover valve? If so, maybe it is clogged.

No clue. Where would it be and what would it look like? There's so much to learn!

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1990 2.5T 300D: 3 inch exhaust, GSXR mod, custom intake, egr and alda delete

all I can say is if the alda is suspect, just remove it and cap off ur line. I run no alda.

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2011 e320 cdi (132,000) current
2005 Jeep CRD diesel--2.8L (138,000 miles) wrecked, insurance took
1993 Mercedes benz 300D 2.5 Turbo Frybrid powered. (336,000 miles) wrecked and sold as parts car
1990 Mercedes benz 300D 2.5 Turbo (170,000 miles) wrecked and sold as parts car

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