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loss of power, etc. 700 1986

posted by  someone claiming to be Oil Eater on  Wed Jul 31 14:50 CST 2002 [RELATED]

It finally happened... loss of performance.

I was taking my 740 TI from southern CT to upstate NY this last weekend. (Geez, it's almost Thursday already)!

The car was missing like crazy, spool up time was terrible. My sleeper morphed into a dog without any notice.

Here's what I have noticed:
At partial throttle/boost around 4,000 RPM I am a black smoke factory. gas mileage is like I'm driving a tank, so it has to be too rich. I made it to NY like this, where I bought new rotor, cap, and splurged for platnum plugs. (I looked at the fouled plugs before I bought new ones and figured platnum was the way to go to get home if this did not fix the issue.

It didn't. Checked timing and all hoses. even pulled the intercooler to check it for a possible leak. good news: not a lot of oil in the IC. I pulled all induction hoses. found the hose from the AMM to the inlet of the compressor hose, where the little "turbo bypass" (by the book's discription) from the oil seperator, had a fair oil trail that was not there before.

This leads me to think that I now am experiencing excessive blow by of the piston rings, causing crank pressure to carry a lot of oil over to the compressor inlet. This is a guess. I planned on doing a compression test when I got back. I have been too busy to get it done yet.

On the return trip, I adjusted the grainger valve down to about 4 psi, where I could at least use a little more throttle before it was spitting black smoke.

I am wondering, could a blown head gasket also cause excessive smoking? would it cause plugs to oil foul?

I still plan on doing a compression test to see where I am at.

I welcome all thoughts on a big loss of power, loss of avaliable throttle (before smoking) and excessive black smoke.

Thanks for helping me brainstorm!

Oil Eater (for real this time)








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    loss of power, etc. 700 1986

    posted by  matt82dl on  Thu Aug 1 00:12 CST 2002
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    last visit: Mon Oct 13 10:46 CST 2014
    [RELATED]

    Fuel pressure regulator?? I think there are some tests listed in the FAQ. If it is faulty I think it casues it to run rich.

    --
    '82 240 - 144k; '87 760T 133k








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    loss of power, etc. 700 1986

    posted by  someone claiming to be Nigel Harding on  Wed Jul 31 16:37 CST 2002 [RELATED]

    This would have to be the engine coolant temperature sensor and/or its associated connections/wiring. It's on the cylinder head under number 3 inlet runner. It's very awkward to get at, but do-able with the right size tube spanner. Small part, huge effects on performance. See the 700/900 FAQ for a full description. I replaced the sensor on my 1987 745T and the problem was fixed, except that every now and then, without warning, the black clouds of exhaust smoke and sputtering performance would return. Turned out the wiring harness under the inlet manifold had succumbed to the flaking harness syndrome also described in the FAQ. Once the harness had been completely replaced (wire by wire by an auto-electrician--it was much cheaper here in Australia than a factory replacment harness), the problem vanished.








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    loss of power, etc. 700 1986

    posted by  Rtilghman on  Wed Jul 31 16:09 CST 2002
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    at least you have black smoke to give you some hints. I've got intermittent power loss under boost with NO visible problems... argh.

    no clues to give you, but I will say that platinums aren't recommended for turbo model cars (I know bosch recommends against it). I would imagine its because of the heat, but I really have no idea.

    good luck,
    rt







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