My '89 740t begins to spool fine, then still blows black smoke above 3000 RPM with loss of power.

Entire intake/intercooler system after the AMM was gone over. No leaks.

A known good AMM was swapped in. No change.

A new FPR installed . No change.

No wires, hoses, pipes loose or deteriorated.

Temp sensor is relatively new.

Garrett T3 turbo itself has a little play, but not a killer. Not blowing much oil.

I cant't figure it out, and don't want to just keep swapping in expensive parts.

Any ideas?

O2 sensor?

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'Can't understand why people abort Volvos, either' '89 740 Turbo, 122,000 miles

If you take a plug of the correct size- the inside diameter of the turbo hose- and install a schrader valve you can use compressed air to check for leaks in the system.

I use a master cylinder cap with a schrader to bleed my brakes using a bicycle pump. Turns out the cap is the correct size for the turbo outlet hose. I use a hose clamp around the outlet hose and turn my regulator on my air compresser down to 15psi. I use that to pressurize the system and the leaks are then apparent. I find leaks I miss with visual inspection. Good luck.

Randy

BTDT.

Pressurized the intercooler and held my hand over the outlet. No leaks.

With hoses and tubes attatched, no hissing anyplace, but it seems that the air does move somewhere.....

Would it not enter a combustion chamber or two and exit the exhaust, given that the appropriate valves would be open somewhere?

Or, should I expect the system to pressurize, but not flow air?

I should add that this problem came on suddenly, over a period of minutes, it worsened. Began as a split-second electrical engine cut-out on sharp a right hand turn at track speed. Then the same blip at paddock speed.

Soon after that, the car began blowing black smoke at moderate boost/3000 RPM with loss of acceleration.

I used shop air applied through a blow gun at 20 psi which I passed through a 1/4" hole made into the cap of a spray paint can. These caps fit nicely into the turbo side of the large hose leading to the intercooler inlet.

I'll have helper hold the air presure while I search again.



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'Can't understand why people abort Volvos, either' '89 740 Turbo, 122,000 miles

Probably no need to repeat the process as it sounds like you have explored that option of finding a leak and apparently have none in the system. My experience is that the 15lbs I used seemed to build pressure against the throttle body plate enough to cause the hoses to expand noticeably.

Sorry I couldn't be more help.

Randy

Had wife help this time to hole the shop air gun to my free paint can top intercooler hose plug.

This gave me the freedom to really explore the sound of air rushing out under the intake manifold.

What I felt frightened me.....

Such a rush of air coming from....

The head gasket??/ !!!

No, cuold it be, Oh, help me, maybe a break in the intake manifold?

Ah, Ah!

A four-inch split in the outside bend of that idle control valve hose bending up to the large nipple on the intake manifold!

Never would have suspected that thick hose would have blown.

Never assume.
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'Can't understand why people abort Volvos, either' '89 740 Turbo, 122,000 miles

Wow, that is strange. Glad you were able to find it. Hope you gave the wife.gov her due credit for assisting :-)

Randy