Fueling Problem with Rebuilt MAF
05-26-2014, 04:49 PM
#31
Rennlist Member
Did you check you have 12v on pin 9 LH ?
John,
- I jumped 30 and 87 on relay XVI (which I believe controls the ECU) but did not turn the key on but from what I read that's not required? I will go back and do it again turning the key on.
- No the car ran fine with the old MAF and ECU's, and when I changed out to the new ECU's to run your EPROMs the car also ran fine, in fact it ran great (very smooth!). The only reason I had the MAF rebuilt was that I had to se the MAF pot to around 900 ohms to keep the idle AFR below 15.
- I jumped 30 and 87 on relay XVI (which I believe controls the ECU) but did not turn the key on but from what I read that's not required? I will go back and do it again turning the key on.
- No the car ran fine with the old MAF and ECU's, and when I changed out to the new ECU's to run your EPROMs the car also ran fine, in fact it ran great (very smooth!). The only reason I had the MAF rebuilt was that I had to se the MAF pot to around 900 ohms to keep the idle AFR below 15.
05-26-2014, 05:37 PM
#32
Instructor
Join Date: Mar 2014
Location: Charlotte, NC
Posts: 112
Likes: 0
Received 0 Likes
on
0 Posts
Wolf,
Have you set the MAF pot using a CO tester or Innovate type system? If you have and the MAF pot is over something like 700 ohms then you know the MAF is on it's way out. Other than bench testing I think this is all you can do regarding whether it's in spec or not. There are several other resistance and voltage test you can do with a VOM if your inclined. Check out Johns website, the link is in his sig.
Have you set the MAF pot using a CO tester or Innovate type system? If you have and the MAF pot is over something like 700 ohms then you know the MAF is on it's way out. Other than bench testing I think this is all you can do regarding whether it's in spec or not. There are several other resistance and voltage test you can do with a VOM if your inclined. Check out Johns website, the link is in his sig.
I also measured the voltage between pin 2 and 4, I got battery voltage.
I measured the resistance between pins 3 and 5 for the sensor resistor and got 4.2 ohms, which is just outside of the range in service manual (3.6 to 4.1).
It sounds like I have an MAF rebuild in my future, or can it be adjusted?
Thanks,
05-26-2014, 06:54 PM
#35
Rennlist Member
The resistance between 3&5 has arrange of typical values, but when MAFs are calibrated all the tolerances are taken into account. As I say on my website, the list of typical readings I give are only to diagnose gross MAF failure.
If your idle pot needs to go to the maximum 1000 ohms, and assuming your fuel pressure and injector flows are OK, then yes, your MAF is at end of life. Typical life is ca. 75k miles.
Although you may be able to get the correct idle CO with the pot set high, the problem is that the correction diminishes relatively as the engine load increases (bigger throttle openings). That's why I suggest a setting of 600ohms as an upper limit.
If your idle pot needs to go to the maximum 1000 ohms, and assuming your fuel pressure and injector flows are OK, then yes, your MAF is at end of life. Typical life is ca. 75k miles.
Although you may be able to get the correct idle CO with the pot set high, the problem is that the correction diminishes relatively as the engine load increases (bigger throttle openings). That's why I suggest a setting of 600ohms as an upper limit.
I was able to measure the MAF idle mixture pot and got 1053 ohms. The MAF FAQ document on John's website said "typically between 300 and 600 ohms", the Service manual says it should be between zero and 1000 ohms. Either way it is above what it should be. Is it gone, or can it be adjusted down into spec with the pot?
I also measured the voltage between pin 2 and 4, I got battery voltage.
I measured the resistance between pins 3 and 5 for the sensor resistor and got 4.2 ohms, which is just outside of the range in service manual (3.6 to 4.1).
It sounds like I have an MAF rebuild in my future, or can it be adjusted?
Thanks,
I also measured the voltage between pin 2 and 4, I got battery voltage.
I measured the resistance between pins 3 and 5 for the sensor resistor and got 4.2 ohms, which is just outside of the range in service manual (3.6 to 4.1).
It sounds like I have an MAF rebuild in my future, or can it be adjusted?
Thanks,
05-26-2014, 07:07 PM
#36
Rennlist Member
The LH relay is XXV. XV1 is the EZ-F relay.
https://www.928gt.com/t-8586fuse.aspx
So you are bridging the wrong relay. I've listened to your video, but not knowing how you were modulating the throttle it's difficult to read the results...
Be very careful bridging relays as the ECUs get upset if you get it wrong !
https://www.928gt.com/t-8586fuse.aspx
So you are bridging the wrong relay. I've listened to your video, but not knowing how you were modulating the throttle it's difficult to read the results...
Be very careful bridging relays as the ECUs get upset if you get it wrong !
05-27-2014, 05:25 PM
#38
Rennlist Member
You previously thought there were no output volts from the MAF, have you rechecked now that you know the correct relay to bridge ?
You will need to tap into the LH plug/socket to get at pin 7 of the LH to check that is OK now.
You will need to tap into the LH plug/socket to get at pin 7 of the LH to check that is OK now.
05-27-2014, 05:57 PM
#39
Three Wheelin'
Thread Starter
You previously thought there were no output volts from the MAF, have you rechecked now that you know the correct relay to bridge ?
I've been at work all day and will check it tonight. Right now I'm on my way to pick up a known good MAF to try as well.
You will need to tap into the LH plug/socket to get at pin 7 of the LH to check that is OK now.
I've been at work all day and will check it tonight. Right now I'm on my way to pick up a known good MAF to try as well.
You will need to tap into the LH plug/socket to get at pin 7 of the LH to check that is OK now.
05-27-2014, 09:33 PM
#40
Three Wheelin'
Thread Starter
John,
I read 1.86V at pin 7 and battery voltage (12.6V) at pin 9. I also changed out my MAF with known good MAF but no luck. At this point I'm going to do a continuity check of the MAF plug wires and the change out the EZF, and then LH with my old units. Any other ideas of things to check?
I read 1.86V at pin 7 and battery voltage (12.6V) at pin 9. I also changed out my MAF with known good MAF but no luck. At this point I'm going to do a continuity check of the MAF plug wires and the change out the EZF, and then LH with my old units. Any other ideas of things to check?
05-27-2014, 10:37 PM
#42
Nordschleife Master
05-28-2014, 08:03 AM
#45
Three Wheelin'
Thread Starter
Honestly, the only problem i had before I had the MAF rebuilt was that I had to tune the CO pot to 900 or so, this is a new problem. I did also check the TPS and found that it isn't working at full throttle, but I'm not sure that would cause my problem at idle???