Volvo RWD 700 Forum
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SAVE 740 Turbo cut out at WOT 700 1992
posted by asc325is on Wed Jul 1 22:04 CST 2009
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last visit: Sun Aug 9 23:00 CST 2009[RELATED]I guess I should clarify:
The car drives fine under NORMAL condition. This only happens under full throttle around 4.5k.
If i keep the boost low, and keep the car in first, I can hit the red line no problem, but if the engine is under atleast (according to the gauge) 3/4 boost, the gauge goes to full vacuum, the engine loses power, but the RPMs stay high and the car drives on (it doesnt lose speed)
This happens in all gears.
I took off the AMM to turbo hose (Volvo part 3514480) and noticed the under side of the hose right next to the turbo connection is very thin and extremly flexible.
No smoke, smooth idle (just under 1000) perfect under normal driving conditions.
This change anything? I got a good deal on the hose from my local indie, Im putting it on tomorrow in hopes this fixes the problem.
Any additional thoughts are welcomed!
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SAVE 740 Turbo cut out at WOT 700 1992
posted by triode52 on Thu Jul 2 11:51 CST 2009
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last visit: Sat Oct 3 16:35 CST 2009[RELATED]I had a similar problem. These cars as far as I know do not have a turbo overboost switch like the earlier 740's. In my case the AMM to turbo hose was soft and flexible like yours. The suction of the turbo at high RPM's caused this hose to collapse and choke out the engine. Removing the foot from the gas let go of the suction, the pipe reformed, and everything was normal again. So, replacing the hose like you are should hopefully fix the problem.
Mike
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SAVE 740 Turbo cut out at WOT 700 1992
posted by hardknocks! on Wed Jul 1 20:03 CST 2009
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last visit: Sat Nov 21 18:12 CST 2009[RELATED]hello
i am not familiar with the 92 740T but i suspect it may be the overboost switch cutting out from too high of boost.
good luck
mike
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SAVE 740 Turbo cut out at WOT 700 1992
posted by rstarkie on Wed Jul 1 17:07 CST 2009
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last visit: Sat Nov 21 20:35 CST 2009[RELATED]It could be a leak in any of the turbo plumbing.
Does it throw black smoke as well? Another indicator of loss of metered air.
The photo below shows a spare master cylinder cap altered to pressurize the turbo or brake system.
Leaks can be hard to find in the turbo system, but if you clamp this device on the hose coming off of the turbo and set your air compressor to about 15lbs output you sure can hear a leak.
Good luck
Randy
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SAVE 740 Turbo cut out at WOT 700 1992
posted by asc325is on Wed Jul 1 17:21 CST 2009
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last visit: Sun Aug 9 23:00 CST 2009[RELATED]No black smoke, thats why i was thinking the hose from the AMM Volvo part 3514480. I think it's "squishing" and closing up at full throttle and boost.
I do not have an air compressor, or Id try this.
The car is OK if i do not have boost running, or I am not at full boost at higher RPMs, also why Im thinking of the hose.
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SAVE 740 Turbo cut out at WOT 700 1992
posted by rstarkie on Wed Jul 1 17:37 CST 2009
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last visit: Sat Nov 21 20:35 CST 2009[RELATED]Unless that hose is especially soft and pliable or you have your boost turned up I am sticking with my ruptured hose theory.
Black smoke or not falling on its nose during boost always leads me to a ruptured pressure hose.
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