[Prev][Next][Index][Thread]

<e28> Flat spots , airbox testing, carbon buildup

avid Hoerl wrote:

> 

> To really measure the meter, you need to apply voltage between the top and

> bottom of the potentiometer, then measure the voltage coming off the wiper.

> I don't have the pin numbers handy, but can get them if you want to do this.

> I pulled the unit and used a battery charger to apply voltage, then monitored

> the voltage off the wiper as I moved the vane by hand. There should be

> no flat spots (ie, voltage goes to 0 for a fraction of a second).

> 

> More likely you have low fuel pressure. Get a fuel pressure gauge and monitor

> the pressure at the rail. Your car should be 3.0bar (I think), maybe 2.5 bar

> (bar == 14PSI) - check Bentley.

> 

> Based on what you said, I suspect that you have a fuel problem, not an air

> flow meter problem.

> 

> Please post or direct email what you find - I think I have a similiar problem

> which is very poor power at low RPMs (800-2000) - my engine stumbles and

> barely goes until the RPMs get over 1500 RPM.

> 

> David Hoerl

> 84 633CSi



  From: "Eric Huang" <ehuang@domain.elided>

    To: "Mark Conley " <markconley@domain.elided>



Hi Mark:

   If your car is idling smoothly, then in general your electrical (ECU

&

ignition) must be functioning correctly.  Your fuel system, however, can

be

further checked by measuring the pressure.  You should be running around

40-45psi fuel pressure.  Your case sounds the fuel pressure may be on

the low

side, since 28mpg city fuel economy is in the VW/Honda  terratory!

   Air flow meter seldomly go bad.   Do not adjust spring unless the

fuel

pressure is correct to begin with.  Also, air flow meter must be

adjusted in

the open loop condition, with O2 sensor disconnected, but used as a

measurement tool (0.5-0.7v during idle).

   Either air flow meter, or fuel pressure, can be adjusted to make the

ECU do

things you want to do.  But air flow meter, as it leaves factory, is

calibrated with certain air flow volumn at Bosch factory.



Just my 2 cents.  Good luck and happy motoring!



Eric Huang, 79 528i with MM 3.6L









Thanks for the help,



Just wanted to update everyone, I had the airflow meter put on a scope,

it was fine, the shop adjust my mixture to get it back were it should be

using a computerized emissions tester.  The shop said that the fuel

pressure was good, but I probably had carbon build up.  I bought some

Mr. Goodwrench Top Engine clean and let the engine suck in 2 cans

through the fuel presure regulator vacuum line.  I smoked out the whole

block for the next half hour trying to burn the stuff off.  I've put

LubeMoly Viber Saber?? in my last 3 tanks and am seeing major

improvments.  My flat spots have all but disappeared.  Rennie Bryant at

Redline BMW in FL, and  Mike Bartlet at Bench Mark Motors in Columbia MD

have been very helpful in trying to diagnose this problem.  I have to go

pack up my car to goto Summit Point for the day and check out the

October fest club races.  Hope this helps someone.



Mark Conley     

'87 535is

'90 Civic Si

'72 MG Midget