AFM and Idle Issues (With Some Fuel Pump Issues Thrown In)

[majicwrench]

I cringe a bit when I see people taking their afm apart. Tis your car. I worked on a ton of these back in the late 70's and 80's, I don't recall having to lube the doors. Seldom would you see a door that was perfectly smooth. Was normal to see some slight marks in housing from flap rubbing.

The rubber ductwork is fine, will last for decades.

[narfire]

BTW, getting the lid of the AFM shouldn't pose much of a problem. Mine just lifts off.

Ha, you're lucky... for the first time removal one needs a sharp box cutter and a corresponding box of band aids....

When I had stumbling issues at the start of acceleration in my FI, ( no air leaks)I popped the top off the afm and loosened the screw on the assembly on the afm flap shaft, slightly bent the arm that runs on the strip and adjusted the assembly up or down to make the pick ups slide on a cleaner bit of the strip. This is only a half a mm shift.
The pick ups spend most of their time on the first third or half of the strip and it wears there compared to the top half.
Chris

[KevAndAndi]

One problem I have seen with a couple AFM is the flap stop bends over time and the wiper on the PC board will run off the board. When the stop is bent the flap in the AFM has actually passed beyond closed and has opened in the opposite direction. Sort of like a swinging door. Could that act like an air leak?

I just took a look at the flap, and it does in fact rest in a position that appears to be "hyperextended" or "beyond closed". In other words, when it rests against the stop (metal angled piece with rubber on the backside, held onto the AFM with two screws), there is an air gap of maybe 1/8". When I push the flap in slightly, it comes up next to a rubber strip on the right side - this would appear to be the normal closed position. However, the stop does not appear to be bent. Hmm.

This is not the way it's s'posed to be, correct? The flap is not a saloon door.

[bradartigue]

Sounds good enough to me - does that metal stop have a kind of rubber piece on it? Not the end of the world if it is missing, after all, air opens the door and it stays open as the engine is pumping.

I would leave the AFM alone for now. Get your air leaks sorted. Propane is fine, but you have to get new/good clamps first. Put everything together the way it should be and then start the car and check for leaks. Correct the leaks (if the big air hose is cracked you have to replace the thing and they can be had new) one by one and then set the idle.

Then report back.

Do not set the idle speed on a cold engine, it is a waste of time. If you have to set it to keep the car running, fine, just adjust it back once warm. Warm = the fan ran twice on-off-on-off.

[spider2081]

Can you post a photo of the PC board and fuel pump switch like the one Wizard124 posted.

[lanciahf]

Also idle air is controlled through the air bypass screw on the AFM, More air higher idle, less air slower idle.

Is your screw exposed or plugged?

[KevAndAndi]

Can you post a photo of the PC board and fuel pump switch like the one Wizard124 posted.

I will do once I get the top off. (I also have to read the instructions for posting pictures, which I have not done yet!)

[KevAndAndi]

Also idle air is controlled through the air bypass screw on the AFM, More air higher idle, less air slower idle.

Is your screw exposed or plugged?

It is exposed. Will chase down those leaks first though. The air snorkel is going to get a cleaning and inspection.

[bradartigue]

Also idle air is controlled through the air bypass screw on the AFM, More air higher idle, less air slower idle.

Is your screw exposed or plugged?

That is not what the screw on the AFM is for. Idle speed is controlled on the plenum/throttle assembly. The screw on the AFM is a calibration for emissions.

[bradartigue]

Let's use this thread to make a point about how L-Jetronic can end up all screwed up and the fuel pump switch on the AFM bypassed, as seems to be the case here. This evolved from an email thread with Andy Truscott, I have to give credit where due after all.

Here is a typical route to the fuel pump being bypassed by someone who doesn't understand how the system works...I think its a good example of why you need to understand each component and the impact it may have on others:

1) An air leak manifests itself (i.e. the idle o-ring deteriorates)
2) Idle speed is adjusted to compensate (the o-ring isn't replaced in this case)
3) L-Jetronic is pulling less air through the AFM and more through the air leak
4) The AFM door isn't moving because air is drawn from the leak and not the AFM
5) The AFM door doesn't turn on the fuel pump
6) The owner/mechanic creates a fuel pump override

A diagnostic procedure would be like this:

1) The fuel pump is running off the key
2) Correct the wiring problem so that the fuel pump works off the dual relay as designed
3) Rotate the AFM door by hand to verify the fuel pump works (then diagnose if not)
4) Start the motor and try to keep it running to warm
5) Set the idle speed (which includes inspecting and replacing the o-ring)
6) Eliminate air leaks
7) etc.

The "eliminate air leaks" could also occur prior to #1, if you are handy with an unlit propane bottle you can find air leaks around the hoses.

[toplessexpat]

This evolved from an email thread with Andy Truscott, I have to give credit where due after all.

you're very kind, although to be fair - my only real contribution to the logic is:

- When you check the O Ring. If it is nice and hard, and forming a static non-moving seal - then it needs replacing! The O Ring should be nice soft and pliable so that it deforms as the screw is tightened.

[KevAndAndi]

Let's use this thread to make a point about how L-Jetronic can end up all screwed up and the fuel pump switch on the AFM bypassed, as seems to be the case here. This evolved from an email thread with Andy Truscott, I have to give credit where due after all.

Here is a typical route to the fuel pump being bypassed by someone who doesn't understand how the system works...I think its a good example of why you need to understand each component and the impact it may have on others:

1) An air leak manifests itself (i.e. the idle o-ring deteriorates)
2) Idle speed is adjusted to compensate (the o-ring isn't replaced in this case)
3) L-Jetronic is pulling less air through the AFM and more through the air leak
4) The AFM door isn't moving because air is drawn from the leak and not the AFM
5) The AFM door doesn't turn on the fuel pump
6) The owner/mechanic creates a fuel pump override

A diagnostic procedure would be like this:

1) The fuel pump is running off the key
2) Correct the wiring problem so that the fuel pump works off the dual relay as designed
3) Rotate the AFM door by hand to verify the fuel pump works (then diagnose if not)
4) Start the motor and try to keep it running to warm
5) Set the idle speed (which includes inspecting and replacing the o-ring)
6) Eliminate air leaks
7) etc.

The "eliminate air leaks" could also occur prior to #1, if you are handy with an unlit propane bottle you can find air leaks around the hoses.

Awesome. Thanks, Brad. Your "problem" list 1 - 6 is exactly what I was thinking, but it's good to hear it from someone who actually knows this stuff. Your "diagnosis" list 1 - 7 is also what I was thinking. In my case, I'm reasonably sure that the bad hose clamp at the AFM to air snorkel connection is the worst and perhaps only air leak. (The idle speed screw o-ring has been changed, leading to a much lower idle speed [suggesting that that leak has been solved], but I will check that and everything else with unlit propane.)

Is the AFM flap at its resting position (engine off) supposed to be slightly cracked open in the "wrong" (outward direction)? Mine is.

I hope this thread can help others, because there are many archived threads here that have been a great help to me. I'll come back with an update after my weekend's work.

[KevAndAndi]

This evolved from an email thread with Andy Truscott, I have to give credit where due after all.

you're very kind, although to be fair - my only real contribution to the logic is:

- When you check the O Ring. If it is nice and hard, and forming a static non-moving seal - then it needs replacing! The O Ring should be nice soft and pliable so that it deforms as the screw is tightened.

By the way, the o-ring that I used as a replacement looked to be exactly the same type as the old one. That is to say, the new o-ring looked very slightly narrower in diameter and very slightly thicker in cross section. I'm sure the old o-ring looked just like that, before it hardened, shrank in cross section, and stretched in diameter. Of course, the old o-ring could very well have been an incorrect size. An unlit propane test should determine whether I've got a good seal, but the idle improvement is encouraging.

Is there supposed to also be a spring around the idle speed screw? Mine doesn't have one.

It's interesting that you can have a car that seems to run great but is doing so in spite of itself, with some basic defects hidden under the hood causing it to not operate at all as designed. (Albeit sometimes due to minor things with inexpensive fixes. I think I might be able to get this solved with just that o-ring, a new clamp, and a straightened fuel pump contact deactivation rod - fingers crossed.) My initial clue was that fuel pump running with the key at the ACC position. I was no car mechanic (notice the past tense - as they say, if you're not, your first Fiat will make you one), but I said, "Boy, that doesn't seem right. What if you want to play the radio?!" My second clue was the idle at 1200 - 1300, which I realized was high when I looked at Brad's book. There was no way I could get it lower, and now I know why. It's at maybe 1100 with the new o-ring, and I should be able to achieve sub-1000.

[RRoller123]

No spring around the idle screw. Check out the Throttle Position Sensor on the side of the throttle plate. It is a black object held in place by 2 screws in slots so it can slightly rotated. Make sure it is completely loosened and then set it according to Brad's manual. It can hold the throttle plate open slightly, resulting in high idle, and cause you to think there is a air leak. This was the case on mine.

[KevAndAndi]

Thanks, Roller.

Someone had expressed concern that I had used a plumbing o-ring for the idle speed screw. I did a little research and found that virtually all common plumbing o-rings that you find in the hardware store are made of nitrile, or Buna-N, a copolymer of acrylonitrile and butadiene that resists water, oil, fuel, grease, ethylene glycol, and many other fluids (but is NOT resistant to some other fluids, the most important of which, for our purposes, is brake fluid). Nitrile clearly has good wear resistance and mechanical properties, as it is used in plumbing valves that turn every day. Therefore, it would appear to be A-OK for this application.