I have an 850 turbo, a 94, with 150k that starts and idles fine but it bogs under acceleration. It will eventually get up to crusing speed but it takes a while. It only throws one code 440, evaporate emissions but that been on more months with no issues. New fuel pump two weeks ago. I did look for an obvious vacume leak but didnt see any. I did notice that my aftermarket boost gauge shows a little lower than usual vacume at idle around 12 instead the usual 16. Fuel filter about 40k ago. This problem just happened abruptly. Any ideas?

 

Sounds like a vacuum leak, your vacuum should be between 18 and 21 at idle depending on load, and climate.

Have you checked your vacuum lines?
When was the last time you did the pvc system?
When was the last time you did a stage 0?

 

Mine does the same thing even after full stage 0, silicone lines everywhere, pcv done late last year (no smoke)

Changed my tcv, fixed the broken hoses on, at, and near the gas tank, changed the gas cap.

I do have to change my evap canister so hopefully that's the culprit.

 

Redid the pvc about 20k ago.

Vacume has always been a little low usually around 16-17 at idle in Park but a little higher when closing the throttle 21-22lbs.

It just happened kind of capriciously today. Not a gradual thing. At first, I thought it could be a MAS issue but I cleaned it and checked it with a scan tool and observed that it is functioning smoothly.

 

My 94 850 turbo had the same problem VERY badly when I first bought. Thus far, after changing out the plugs, repairing an obvious vacuum leak and several other hosings along with a fuel system cleaning, it now runs alot better with only a slight hesitation periodically. The big difference was noted when I replaced the fuel pump relay that sits directly above the cooling fan. I have yet to replace the one in the fuse box near the windshield. This may help but not motivated to change that one at this point.

 

Found the problem it was primarilly the vacume hose that runs from the blow off valve up to the vacume tee.

It still is a little hard to start. I think the fuel pressure regulator is going out.

 

Isn't that the EVAP Canister Purge Valve?

 

I think he is talking about the main relay...

 

After fixing the vacume leaks it's a lot better but not perfect. It still surges, it's like the fuel delivery cant keep up with the throttle position sensor. The shifts are irregular because they are triggered by the throttle position sensor.

I still dont have any codes or misfires. I believe it is the fuel pressure regulator because: 1, they dont trigger a code when they go, 2, It is hard to start cold but it is easy to start right after being shut off, like at a gas station 3, I disconnected the vacume line for the fuel pressure regulator and applied vacume with a hand pump and it no effect on the operation of the motor. 4, The regulator vacume line did not smell like gas a common symptom of a failed regulator however I have had other regulators fail without leaking gas into the vacume line.

The regulator sends excess fuel back to tank. It is my understanding that when the throttle is closed i.e. high vacume that more fuel is sent back to the tank when there is low vacume (open throttle) less fuel is sent back. My thought is that if the regulator is not regulating it is sending too fuel back to the tank thus causing the hesitation.

 

Apologies for wrong wording. Not sure what the relay is actually called. But yes it sits above the radiator fan and is connected to a vacuum line, possibly a ventilation line to cool the points down.

 

Yuppers Vmax was right once again.. Thats the evap valve, I broke mine 4 years ago putting in a radiator and never replaced it... just straight vac line.

 

At idle (high vacuum) the fuel pressure regulator should bleed off more fuel and thus have a lower pressure than when the throttle is opened (low vacuum). You should be able to hook up a gauge to the end of the fuel rail just above the throttle body to read the pressure.