afm problem?
01-27-2003, 03:55 PM
#1
Three Wheelin'
Thread Starter
afm problem?
First clear day in a couple of weeks and I finally got to drive the car without having to worry about sliding on the snow and ice and it runs like crap.
The car idles fine and runs great as long as you do not give it more than about 1/2 throttle. If I go more than the the car starts to miss and stumble.
According to my arm1 the computer is controlling the air/fuel ratio at idle and part throttle but at more than 1/2 throttle the arm1 goes to the first red light and stays there until I let off the gas. It then goes straight to the first blue for a couple of seconds and then starts to control again.
I tried unhooking the o2 sensor but that made no difference. I also pulled the plug on the #1 cylinder and it does show a fair amount of carbon buildup. The other thing I noticed is that that the arm for the afm seems to be very far to the left at idle. I tried playing with the spring tension but it just made the problem worse.
Any suggestions or tests that I can do on the afm to see if it is working correctly.
The car idles fine and runs great as long as you do not give it more than about 1/2 throttle. If I go more than the the car starts to miss and stumble.
According to my arm1 the computer is controlling the air/fuel ratio at idle and part throttle but at more than 1/2 throttle the arm1 goes to the first red light and stays there until I let off the gas. It then goes straight to the first blue for a couple of seconds and then starts to control again.
I tried unhooking the o2 sensor but that made no difference. I also pulled the plug on the #1 cylinder and it does show a fair amount of carbon buildup. The other thing I noticed is that that the arm for the afm seems to be very far to the left at idle. I tried playing with the spring tension but it just made the problem worse.
Any suggestions or tests that I can do on the afm to see if it is working correctly.
01-28-2003, 12:39 AM
#3
Race Director
Measure the voltage on pin#7 at idle. It should be around 0.79-0.85v for a 850-900rpm idle speed. Adjust the arm's positioning in the AFM to correspond to this voltage.
Also watch what happens to this voltage when the ARM-1 does its big mood swings....
Also watch what happens to this voltage when the ARM-1 does its big mood swings....
01-28-2003, 02:35 PM
#5
Three Wheelin'
Thread Starter
Ok, I adjusted the spring tension on the AFM so I got .81 volts at 950rpm and the Arm1 is now fluctuating between the first red and the first orange at idle.
I checked the voltage from the AFM and it is linear from .23 volts fully closed to 3.89 volts fully open.
I also checked the output of the O2 sensor and at idle it is fluctuating bewteen .32 to .5 volts. If I give the car gas the reading drops down to .16 volts.
I then unplugged the vacuum line to the fuel pressure regulater and the Arm1 starting fluctuating between the 2nd red and the first green LED. Upon accerlation though it drops to the first red and stays there until I let off the gas. As soon as I let off the gas the Arm1 goes to the first blue for about 2 seconds and then starts to dither again.
The car is definately running lean but I'm not sure why. I am beginning to wonder if I have a faulty fuel pressure regulator. Would like to measure the pressure but have no way.
Any other suggestions?
Thanks,
I checked the voltage from the AFM and it is linear from .23 volts fully closed to 3.89 volts fully open.
I also checked the output of the O2 sensor and at idle it is fluctuating bewteen .32 to .5 volts. If I give the car gas the reading drops down to .16 volts.
I then unplugged the vacuum line to the fuel pressure regulater and the Arm1 starting fluctuating between the 2nd red and the first green LED. Upon accerlation though it drops to the first red and stays there until I let off the gas. As soon as I let off the gas the Arm1 goes to the first blue for about 2 seconds and then starts to dither again.
The car is definately running lean but I'm not sure why. I am beginning to wonder if I have a faulty fuel pressure regulator. Would like to measure the pressure but have no way.
Any other suggestions?
Thanks,
01-28-2003, 07:22 PM
#6
Race Director
yeah, sounds like the FPR. Might be a stiction problem with the seal on the diaphram inside. If it runs better with the vacuum disconnected, leave it off. This might cause some incompatibilities with the chip I'm sending you though....
Your car uses a 2.5-bar FPR (early 944NA used 3.0-bar). I wonder if my stock 951 2.5-bar FPR is the same.... anyone have part# for these things?
Your car uses a 2.5-bar FPR (early 944NA used 3.0-bar). I wonder if my stock 951 2.5-bar FPR is the same.... anyone have part# for these things?
