Wedge AFM issues

Wedge AFM issues

Author
Discussion

Bigfish_74

Original Poster:

12 posts

9 months

Thursday 10th January
quotequote all
Learning fast about wedges with all the info out there but one problem ive not come across on any forum. 350i 4CU air flow meter, the voltage measured across terminals 6 and 7 of the ECU actually increases as the flapper is opened from 0.5 to 2.7, Understand it should decrease from 3.7 down to 1.6. Inside the case all looks as new and all other tests as they should be except fuel pump runs continuous with ignition on but switches off when the flapper is opened. Any ideas?

adam quantrill

10,857 posts

188 months

Thursday 10th January
quotequote all
The AFM is just a potentiometer and the wiper gives you the voltage from one terminal sweeping through to the other.
If the voltage at each end of the sweep is the wrong way around it will produce the effect you're observing. Most likely cause is that the loom or teminals at one connector are swapped over somehow?
What is the history of the wiring loom?

Other than that try to borrow a spare ECU and see if it does the same thing - if not there's a fault inside your ECU but it sounds like an unusual type of fault.

Bigfish_74

Original Poster:

12 posts

9 months

Thursday 10th January
quotequote all
Thanks Adam it's what I was thinking although all wire colours seem to be as diagrams but I'll try swapping a few over anyway see if I get any joy. It's a full resto I've taken over, afm and loom are original and seem in good shape.

KKson

2,821 posts

71 months

Thursday 10th January
quotequote all
Where abouts are you in the country? I'm Herefordshire. If you're close and want to borrow a decent AFM and/or ECU to rule components out then let me know.

Bigfish_74

Original Poster:

12 posts

9 months

Thursday 10th January
quotequote all
Sheffield, thanks for the offer though.

mrzigazaga

18,398 posts

111 months

Thursday 10th January
quotequote all
That is a weird one...The pump should prime the fuel rail when the flap is opened..? as Adam said...its sounds like its doing the reverse of what it should be..

pieeater

49 posts

49 months

Thursday 10th January
quotequote all


• Leave voltmeter -ve connected to pin 9 and move voltmeter to pin 7.

• Reading should be 3.7 ± 0.1 volts.

• If voltmeter reads low, check wiring for high resistance.

• With voltmeter still connected to pins 7 & 9, slowly open the air flap.

• Reading should gradually decrease to 1.6 ± 0.1 volts.

• If results are not within those specified above replace air flow meter.

• If OK, refit . this is the correct test. instructions from sd1 site think your reading from wrong pin

adam quantrill

10,857 posts

188 months

Friday 11th January
quotequote all
If the loom is original then I wouldn't start swapping connectors over right now. All the same it would be worth checking with a multimeter end-end that the connections match up at the AFM multiplug and ECU multiplug (to confirm the colours). Then you can take a view on what to do next.


mrzigazaga

18,398 posts

111 months

Friday 11th January
quotequote all
Might also be worth cleaning all the earths...the 3 main ones at least....

1. N/S front suspension turret
2. Top of rear N/S rocker cover
3. One just below that one...this one is for ECU.


I would also check and clean the connections..including the black and white wire (Bullet connector) from distributor to AFM/ECU.

It also worth removing the ECU plug and cleaning up the male & Female connections...But make sure you give it a good firm push until it clicks back on.

Hope this helps


Ziga smile



Bigfish_74

Original Poster:

12 posts

9 months

Friday 11th January
quotequote all
Pieeater is right I was reading from pins 6 and 7 as it says in the wedge epistles. 6 and 9 give a perfect reading, thanks guys.

pieeater

49 posts

49 months

Friday 11th January
quotequote all
Hi what sort of issues are you having. i had plenty with my wedge maybe i or someone on the forum can help

ed_crouch

1,167 posts

188 months

Wednesday 23rd January
quotequote all
Honestly I would toss the 4CU in the bin and fit a MS2 or MS3. 4CU was *okay*, but you'll find more horses with a better ecu.