85' 760 turbo B230ET boost problems

[240 drifter]

Hi, Im new here!

Basicaly I have a 85 760 turbo with a few modifications to enable it to drift



Its great Ive fitted a boost controler to it, but i just cant get the boost out of it that i want!! I hit like a boost cut off, Ive read so many different articles but im turning to you people for the answer

The best sugestion I can find so far is that the air mass meter can not flow anough air and then cuts the fuel,

I don't want to run a ridiculous amount of boost just a bit more

This is really bugging me, I cant understand how it sence's overboost because theres no overboost switch or even a map sensor,

Help help help! Im asking now aswell because the engine and loom are going to be fitted to my recently aquired 240 £150 with 12 months mot!


Thanks for any help in advance

[nejones]

What level of boost are you running at the moment?

[240 drifter]

About 0.5 bar is all I can get, Ive driven standard 740 turbo's that feel like they are boosting more than my 760!

[niloc]

Check the operation of the wastegate. Problems with the boost are usually related to the actuator arm coming off the wastegate.

[alsner]

Originally Posted by 240 drifter

About 0.5 bar is all I can get, Ive driven standard 740 turbo's that feel like they are boosting more than my 760!

The 740 turbo and 760 turbo share the same engine and electronics so it should be the same performance wise. The 760 just had higher specs for interior as far as I aware.

About 0.5 Bar works out at about 7psi which is standard (6/7 being standard) it should easily go to 12/13psi easily with no problems. Check for air leaks in piping.

What air filter are you using?

Ali

[baggy798]

The Motronic system detects higher boost levels via the Air Flow Meter. The AFM constantly sends a voltage signal to the ECU, which corresponds to an internally mapped table regarding flap angle (voltage) and engine speed. If the flap is open too wide within the 'opening range' (upto about 4000 RPM), it will detect greater air flow (higher boost!) and cut the fuel.

Although with an '85, I think the boost/fuel cut is activated with a simple pressure switch located under the dash at the top of the pedals. A hose runs from this to the intake manifold See if you've got this...

[1stRaven]

Originally Posted by alsner

The 740 turbo and 760 turbo share the same engine and electronics so it should be the same performance wise. The 760 just had higher specs for interior as far as I aware.

About 0.5 Bar works out at about 7psi which is standard (6/7 being standard) it should easily go to 12/13psi easily with no problems. Check for air leaks in piping.

Ali

Correct, the engine specs should be about the same. As for running 12/13psi - only do this if you have the fuel to do some. Once a stock fuel system and stock ecu, you WONT have. You will either need to chip it or go for megasquirt or ither custom ecu.

Originally Posted by baggy798

The Motronic system detects higher boost levels via the Air Flow Meter. The AFM constantly sends a voltage signal to the ECU, which corresponds to an internally mapped table regarding flap angle (voltage) and engine speed. If the flap is open too wide within the 'opening range' (upto about 4000 RPM), it will detect greater air flow (higher boost!) and cut the fuel.

Although with an '85, I think the boost/fuel cut is activated with a simple pressure switch located under the dash at the top of the pedals. A hose runs from this to the intake manifold See if you've got this...

My 1989 740 had motronic and I never had a boost cut via the ecu. Baggy is right in there there might be a boost pressure sensor in the drivers foot well. Just follow the vac lines to see where they do. should be a matter of unpluging the air line from the manifold and using a blanking bolt from an na manifold to seal the hole.

[alsner]

Originally Posted by 1stRaven

Correct, the engine specs should be about the same. As for running 12/13psi - only do this if you have the fuel to do some. Once a stock fuel system and stock ecu, you WONT have. You will either need to chip it or go for megasquirt or ither custom ecu.

Hi,

What boost settings can you run with a stock ecu and fuelling system? I take it then that the 12/13psi is achievable with the Jetronic system on later models.

ALi

[240 drifter]

Originally Posted by baggy798

The Motronic system detects higher boost levels via the Air Flow Meter. The AFM constantly sends a voltage signal to the ECU, which corresponds to an internally mapped table regarding flap angle (voltage) and engine speed. If the flap is open too wide within the 'opening range' (upto about 4000 RPM), it will detect greater air flow (higher boost!) and cut the fuel.

Although with an '85, I think the boost/fuel cut is activated with a simple pressure switch located under the dash at the top of the pedals. A hose runs from this to the intake manifold See if you've got this...

No theres not a boost cut under the dash (I have no dash! lol)

That confirms the conclusion I had come to, I did read somewhere that you could fit a resistor in a terminal on the meter so the voltage does not raise to the fuel cut level

BUT do you think If there was a problem with the meter it could cut in earlier(im also using a free flow cone filter)? I have to give it a tap ocasionally to sort it out

[1stRaven]

Originally Posted by alsner

Hi,

What boost settings can you run with a stock ecu and fuelling system? I take it then that the 12/13psi is achievable with the Jetronic system on later models.

ALi

Stock on my 740 was about 9-10psi on vpower. There is not a lot of head room in the stock system. people do run 12 psi on the later lh systems in the 940's.