I have been getting poor fuel economy in my 85. Best was 23 mpg and worst was 20. Timing is spot on at 15 deg ATDC, valves adjusted. Starts and runs well. Just a puff of gray smoke if I floor it and no black smoke. Have not pulled the injectors to pop test them yet but from how quick it cold starts, the injectors are probably ok.

I just tee-ed in a boost gauge at the ALDA. Strips of elastic cut from bicycle inner tube works great as very small diameter hose clamps for low pressure application.



Ran the boost gauge out the hood and went for a test drive



To my surprise I was getting max 1 psi when I floored it! Car was not a total dog so it never raised an alarm. So I pulled the line from the manifold to the boost safety solenoid and connected the boost gauge directly to the line, revved the engine at idle and got the needle to move so the manifold line is not completely clogged. Took out the boost safety solenoid and it didn't click when connected to the battery. Blew into it by mouth and was able to blow through it slightly. It was leaking boost constantly, no wonder I wasn't getting any boost to speak of.

I sprayed all 3 ports of the solenoid with solvent then rapped it a few times with a pair of pliers, shook it out and some carbon came out. Repeat a few times then connected it to the battery and it clicked! Some more solvent and blew it out with compressed air and it seems to be working on the bench and sealing and opening with power.


Took it for a drive and felt instantly more power and was able to get max boost of 8 psi in 1st gear going up a slight hill.

I am going to give it an Italian tuneup and see if the boost increases. I think spec is 11 psi max so there is room for improvement.

If it doesn't improve by itself, what should I do next?

Not having boost for however long (I have put on less than 1000 miles since acquiring the car) and don't know how long it's been like that. Can anything bad happen to the turbo having no boost for extended periods?

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked