For about the last 3 months my 82 5 speed has been suffering intermittent acceleration hesitations at exactly 3900 rpms. It doesn't matter what gear I am in or how hard I am accelerating.

It is like the fuel is cut off at 3900 rpms, but acceleration is smooth prior to this range.

Car starts within 3 seconds and idles as normal.

The fuel pump and filter are less than 3 years old and verified working, but I did not verify flow rate.

I changed out the fuel pump relay just in case.

Car has new plugs, wires, cap, rotor, green wire, injector harness, Witch Hunter injector cleaning. Injectors are firing via noid light. Fuel dampers NOT leaking fuel out the vacuum ports. No vacuum leaks that I could find.

I pulled the AFM and did the refresh outlined for the 944 AFM that is on YouTube. Essentially, I had a very worn track in the resistance material and moved the wiper arm back about 1mm so it rides on fresh material.

That seems to fix things for a while but the symptoms are coming back.

I pulled the AFM again and the wiper arm looks to be still riding on the new resistance material.

But when I measured impedance across the AFM terminals as instructed in the WSM, the values were all very high in comparison to the WSM values.

For example, between terminal 8-9 the value was 303 ohm and the WSM states 70-140 ohm.

I then puled the L Jet brain to measure the values across those terminal as per the WSM.

All the L Jet grounds, the temp and throttle switches and all the injectors tested within limits.

The L Jet ground is tight on the cam tower as is the injector ground near the left cam gear cover.

But the 5 impedance tests for the Air Flow Sensor through the L Jet harness were all much higher than normal. In 2 cases twice as high as normal.

I am going to try to swap out a known good condition AFM to verify, but does this just sound like an AFM that needs replaced with a rebuilt unit?

Could the L Jet brain is also a part of the problem? If possible, I am going to swap out the brain to confirm mine is ok.

Does this sound like a proper test protocol?

My Brain with a good AFM - check acceleration.

Then good brain and good AFM - check acceleration

Then good brain with my old AFM - check acceleration

Got to go fly for a week, then back at this issue. Thanks for the input.

 

sounds like a drop out in the AFM, as the arm swings, which is cutting fuel. way to test is try another or install a wideband O2 sensor

 

That is exactly what I was thinking. Going to swap in another AFM next Saturday.

I hate it when work gets in the way of a hobby.