I am trying to eliminate every possible alternative to a bad AFM before I order one from 928 International.

I was going to try an swap out a nearby good AFM but the car is running so poorly now, I don't want to chance driving it that far.

The car starts and idles fine. But with any throttle application, there is a hesitation or complete cutout at certain rpms. I am thinking the wiper arm in the AFM is hitting bare resistance material as is sweeps and causing this port acceleration and general bad running.

I did adjust the wiper arm to run on fresh resistance surface but it helped only for a short time.

So far, checked the green wire. It is less than 2 years old and looks ok

Injectors are all clicking. Fuel dampers are not leaking. No vacuum leaks. O2 sensor is less than 2 years old.

Tested L Jet brain and resistance values for the Air Flow Meter are WAY OFF. More than twice as much is a couple of readings. Tested resistance values directly from the AFM and they are way off also. All other readings for L Jet brain are within specs.

I pulled the plugs on the easy 4 holes after inspecting the distributor cap, rotor and wires. They are all 2 years old.

All 4 plugs have a red tint to the end. Would that be from using MMO?

Probably change out plugs just in case, they are about 2 years old and are probably ok.

Bosch WR7DC+ for the 78-82 right? These are actually WR8DC, any difference?

I am going to check the timing marks to ensure the belt didn't jump a tooth, but I seriously doubt that has happened

Any further suggestions with the AFM and or L Jet brain would be treaty appreciated.

Thanks

 

Marty, the red tinge usually come from various brand of octane boosters. If you are using or have used one in the past it will discolor and stain the ceramic coating. Adding MMO to the mix will also contribute to it. I have never seen MMO by itself do this unless you are using cheap gas which does not burn completely.
On the bad side if you are using red antifreeze and have a leak it could possibly discolor the plug as well.
With that exception, nothing to worry about other than they look a little lean.
Lon

 

No coolant leak, levels are constant since the engine rebuild.

I pulled the plugs a while ago and they were a whitish color. Since turned reddish after using MMO.

Someone in the past has messed with the mixture control on the AFM. The cap covering the mixture screw is missing.

Im going to try to enrich the mixture just a tad, but I still think the AFM has had it.

I have about eliminating everything else. Cam gear timing is spot on, injectors are all ticking, starts immediately, idles great with zero misses. The engine runs the same with the FI relay or if you bridge it, so thats not it.

Just have hesitation issues when you press on the accelerator. It has got to be the wiper arm in the AFM.

More investigation to follow.

 

AFMs are pretty robust so there are lost of good used ones out there. See if anyone can lend you one for testing.

 

Just for a visual reference, I just removed these plugs today. They are NGK platinum, 3 years and 14.5K miles.
Never used MMO.




NGK Platinum<br/>BPR6EGP

 

If there were any pre-detonation issues from timing then there would be dark specks on the ceramic as a result of carbon deposits. Its possible that MMO did this if you really overdosed it into the fuel tank. Have you been using any octane booster additive. AFM is a long shot, while the WRDC7 vs DC8 is an issues of hotter plug vs colder plug. I would run the colder DC 7 or 6 plugs which are designed for hotter engines like Ferrari. The hotter DC8> plugs are used in colder engines like the VW since they dissipate the heat more slowly.
OTR 18's plugs are showing a "rich" running environment and possible plug torque issue due to the amount of oil leaking onto the threads. Normally there should be oil deposits at the base + 2-3 threads only.
Your plugs showing lean characteristics for sure.
I would rich it up a little, change the plugs and see if there is any difference in the throttle response along with running pure 93 octane w/o any additive.
Lon

 

I am going to rich up the mixture and order new DC7+ plugs.

I ordered a new O2 sensor as my symptoms also mimic a bad sensor and it is $25 as opposed to $300 for a rebuilt AFM.

Reason I'm leaning toward an AFM is it has a very worn resistance track under the wiper arm.

I adjusted the arm to run on new resistance material and it did solve the hesitation problem to a while.

Now it the symptoms are back, almost identical to before.

I don't think it is the brain as it starts up immediately, injectors are firing and the engine runs fine until the throttle is depressed.

I really need to swap in a known good running AFM after a change out the O2 sensor.

 

Sounds like a plan rich+new plugs+sensor. Run for a while and pull a couple plugs and check their condition. looking forward to seeing results. Are you using recommended gap?

Lon

 

As per my O2 sensor thread, it seems the problem was the white plastic engine harness connector to the O2 sensor line.

It just crumbled in my hand exposing both sets of wires. Maybe were shorting each other. So i spliced them individually to the O2 sensor line and the car runs better than ever.

I also turned up the mixture 3/4 of a turn clockwise and advanced the timing to 26 degrees. Car was definitely too lean!

All hesitation is gone and idle is rock steady with no missing.

I will replace the plugs and O2 sensor when they arrive, but all seems ok now.

Cheap fix for once…..just a lot of hours to figure it out

Thanks

 

Cool, another good win.

 

Those plugs don't look worn. Leave them, won't gain anything replacing them. Save the new ones for next time.

 

Actually was thinking the same thing. Probably will save the O2 sensor as well. Don't think the sensor was bad, just the connectors.

Well unless it acts up again.

 

Marty,

Glad you got it figured out.

 

Marty plugs do look good but they are too hot WR8. You should go with the WR7's or other cooler plug. With the mods on your car the Porsche recommended heat rage WR7 or even 6 will give even better results.
I know plug change is a pita but it will be the last time you will need to do it.

Glad you got it taken care of for little $$.

Lon