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Cephis,
I think I can offer some additional advise regarding your turbo issue. I'm sorry we didn't have longer to troubleshoot the problem while you were over at my house on Thursday, but I'm glad that we got the radiator installed.
The turbo that you have in your '89 740 is the Mitsubishi TD05 and I'm 99% sure that your wastegate actuator is ok. While you were at my house, I put it on a Vacuum pump/gauge and it held 25"HG for 5 minutes with no problem. Thus I would assume that the diaphram is good. When the actuator was forced to move back and forth by hand, it did move and the resistance of the spring was noticable. However, since the actuator rod was disconected from the wastegate valve (in the exhaust stream) for an unknown period of time, there may be possible damage to the valve, it's seat, or the casting. This possibility is mentioned in the Brickboard Turbo FAQ towards the end of the Preventive Maintenance section, under the topic of "Wastegate Arm Lube." Before you tear the turbo apart to inspect it, I would suggest a few other things to check that may be the source of the problem (and they're easier to work on).
First, reattach the actuator arm to the wastegate (if you haven't already done so), install a new c-clip to hold it in place, and take a piece of wire from a plastic bread-loaf bag and put it through the tamper hole at the base of the piviot shaft (to keep the actuator rod in place in case the c-clip pops off during testing). A little bit of anti-seize on the linkage at the c-clip would be a good idea to prevent binding.
Next, make sure that the Bypass Valve bolts are nice and snug (the large vacuum assembly on the top of the turbo facing forward). If these are loose, then the boost pressure is being bled off to atmosphere around the mounting flange of the valve.
Check your intake mainfold for leaks. Specifically the gasket where it mates to the head. With the engine running at idle, spray the area with Carb Cleaner or WD-40. If the engine changes pitch/sound/RPMs, then you've found a leak. (Remember, not all leaks will show up under vacuum. Some will only be present under boost conditions.) If the gasket is bad or if in doubt of its integrity, replace it with a new one and make sure it's a hard enough gasket of suitable quality to withstand the boost pressures. Read the two consecutive sections of the Brickboard Turbo FAQ on Gasket Leaks and Poor Idle Quality. Also check the gasket between the intake manifold and the throttle body. You probably shouldn't need to replace this one unless it fails a spray test of WD-40 while the engine is idling.
Personally, I think there's good hope for the turbo without major work. When I took her for a test drive several days ago, she did get up to about 1 or 2 psi of boost, but no further. The acceleration from 1,500 RPMs was nice and smooth, and the fact that it's gotten worse over the past few days would lead me to suspect a serious, and increasing, vacuum/boost leak in a gasket somewhere. (Either the Intake Manifold or Bypass Valve mounting flange.) Both the Wastegate Actuator and the Bypass Valve held 25"HG on the Vacuum pump/gauge so I would assume that they are functioning properly and the diaphrams are not ruptured.
Suggestions, test methods, and opinions of any Turbo experts out there would be greatly welcomed.
God bless,
Fitz Fitzgerald.
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'87 Blue 245, NA 229K
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