If I'm cruising at 40 mph and floor the gas the car hesitates quite a bit before taking off. It seems like there's something wrong with the boost. It bucks 4 or 5 times and then takes off like nothing was wrong.

Here is the list of things I've replaced lately:
Replaced almost all of the vacuum lines with silicone.
Replaced air filter
Replaced fuel filter
Replaced front and rear O2 sensors (had check engine)
Spark plugs were changed at 193K I have about 216K (23K miles on them)
Replaced fuel pump relay (car was stalling)

I'm wondering if it could be the BCS, but I'm not sure the signs of a bad BCS.

Thanks in advance for any suggestions you all may have.

~Scott
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Scott K - 1994 850 Turbo

Scott try this:
Last year I had the same WOT thing happen on my 855. I found a small hose attached to the turbo had slipped off.
To locate it, find the turbocharger on the driver's side of the engine. On the rear of the turbo are attached 3 small hoses: the boost pressure hose (red), the bypass valve hose (white) and the pressure regulator hose (yellow). The yellow hose is the one that had slipped, in my case. Be sure all are attached and not split, particularly check around the clamps.
Good luck!
Don

Turbo control valve? Several things should happen when you go WOT at 40mph, assuming you have the car in drive; the tranny should kick down to 2nd, the injector flow gets increased to maximum, and the turbo starts spooling at about 3-3500 rpm.

You get enough gasoline flow, but not enough air when the engine is only doing 1500-1800 rpm because the turbo is not spooling at that speed. A new TCV might help start up the turbo sooner.

Your spark plugs at 23K should be check for proper gap - .028

Klaus
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Always willing to listen, just not able to take direction.

When I said BCS, I meant Boost Control Solenoid. Do you happen to know where the turbo control valve is located?

On the spark plugs, I gapped them at .028 when I put them in. I change them as close to every 30K miles as possible.

Thanks again for your help.

~Scott

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Scott K - 1994 850 Turbo

I believe it's the device mounted on the engine side of the air filter box, very near the distributor. There's also an actuator on the turbo itself that controls the waste gate if I remember correctly.

What is your boost gauge doing while the car is hesitating?

Erwin

The boost gauge sits at almost full right when the hesitation is happening. I wish I could see what the waste gate was doing during the hesitation. Maybe it's a gas issue. All of the injectors are original. But I thought there would be other signs if the injectors were a problem.

So it sounds like the Boost control Solenoid and Turbo Control Valve are the same thing. From what I understand the BCS has the three vacuum tubes coming out of it and it is attached to the side of the airbox.

Thanks for the help.
--
Scott K - 1994 850 Turbo

If the gauge shows steady pressure, I'd look into fuel and ignition. Also check the hose Don mentioned above. Mine slipped off too.

You said you replaced all the vacuum lines so double check all your work. The plugs are about to hit your replacement mileage so it won't hurt to do them now and also change the spark plug wires, distributor cap and rotor if you haven't.

If that doesn't do it, it's time to attach a fuel pressure gauge to the fuel rail and run it temporarily into the cabin so you can watch for fuel pressure fluctuation while the car hesitates.

Does the transmission downshift?

Are there any modifications to the engine, ECU, intake or exhaust systems?


Erwin
'95 855T, 165,000 miles.
'94 945T, 155,000 miles,
'88 745T, 213,000 miles, regrettably sold.
Memphis