Want to replace air flow meter in my Fuel Injected Spider.

[Betis]

Is it easy to do? Should I try myself or should I take it to a mechanic. Anyone can tell me how to do it.
Thanks

[KevAndAndi]

Replacing the AFM is a very simple job. A couple of mounting bolts and hose clamps.

Do you already have a replacement unit? If so, is the replacement new or used? Why you are replacing it?

[Betis]

I actually read your post about replacing it. My fuel pump is starting at the wrong key position. It made sense to me so I bought a replacement from Fuel Injection Corporation. So I will be getting mine in a couple of days.

[RRoller123]

The fuel pump was probably wired by a PO to run with the ignition on, in order to bypass the dual relay and the control of the pump start by the AFM. The AFM itself is likely not the culprit of the pump starting in the wrong ignition key position.

[KevAndAndi]

The fuel pump was probably wired by a PO to run with the ignition on, in order to bypass the dual relay and the control of the pump start by the AFM. The AFM itself is likely not the culprit of the pump starting in the wrong ignition key position.

True, it's not necessarily the culprit, but it my case, it was. Once I had the AFM refurbished by FIC, not only did the fuel pump come on at the correct time, but the car idled and ran much, much better. As I've been preaching, I think every FI purchaser with an old AFM should start by having the unit refurbed and recalibrated. If FIC happens to have one on the shelf already done, then obviously they can send you that one and you send them your old one plus the $150 or whatever it is.

[So Cal Mark]

how do you intend to adjust the fuel mixture? or do you just slap it in and call it good?

[GeorgeT]

how do you intend to adjust the fuel mixture? or do you just slap it in and call it good?

The computer adjusts the fuel mixture based on the O2 sensor although there is a small adjustment that can be made on the AFM. There is a screw on the side that originally had an aluminum plug covering it that allows for some adjustment. The plug was there to prevent "shade tree" mechanics from upsetting the emissions and the adjustment were only to be made with an exhaust analyzer connected.

[So Cal Mark]

I know very well how it works, I'm curious how you intend to adjust the fuel mixture on a rebuilt unit

[KevAndAndi]

Mark,

The OP said that he bought an AFM from Fuel Injection Corp. When I had mine refurbished by them, they told me that they calibrate the AFMs according to factory specs.

From their website:

Process
1. AFM's are stripped to the component level.
2. All parts, mechanical and electrical are tested to meet OEM specifications.
3. Unit is assembled using known good parts.
4. Simulator then runs AFM through all phases of operation.
5. Spring tension, wiper position and CO screw are calibrated to OEM specification.
6. Once the AFM meets all OEM specifications the unit is sealed and packaged.

Is there a potential problem with this process? Are there adjustments that can only be made with the unit installed on the car?

[So Cal Mark]

every engine is a bit different. You really can only fine tune the fuel mixture with the unit on the car. The O2 sensor in the L-Jet system doesn't have the same effect that other feedback systems use. I'm sure the rebuilt unit will run, but the mixture may not be optimal

[RRoller123]

So how DO you fine tune it?

[KevAndAndi]

I certainly hear what Mark is saying. Every engine is different.

However, my thinking is this: My AFM that has been completely renewed and refurbished - and calibrated on the bench - by the experts at FIC may not be perfectly adjusted for my engine, BUT is it not better than all the AFMs out there with worn wiper tracks, incorrect spring tension, and PO-molested air bypass screws? The perfect should not be the enemy of the good.

That said, I would also like to hear Mark's suggestions as to where one might go to find the expertise to make the fine-tuning adjustments on the car.

[So Cal Mark]

the most accurate way is to use a gas analyzer. You'll find the L-jet system fuel mixture isn't linear; idle CO will be different than cruise rpm CO. You can get it very close by disconnecting the O2 sensor, attach a voltmeter to the O2 wire, hold the rpm at 2000 and adjust the afm screw to achieve .450 on the voltmeter

[RRoller123]

Excellent! Mine has obviously been fiddled with, and I have likely only made it worse. Do this on a warm engine of course, and would this be after doing the best tuning of the other adjustments (clean plugs, throttle cable, Idle jet, AAV) first? I.e. do this last?

Pete

[KevAndAndi]

the most accurate way is to use a gas analyzer. You'll find the L-jet system fuel mixture isn't linear; idle CO will be different than cruise rpm CO. You can get it very close by disconnecting the O2 sensor, attach a voltmeter to the O2 wire, hold the rpm at 2000 and adjust the afm screw to achieve .450 on the voltmeter

Cool. I will do that test to see how close it comes. I will not, however, mess with the screw unless I find a shop with a gas analyzer. I would consider messing with the screw if the AFM hadn't already been bench calibrated. It will be interesting, though, to see what the reading is.

I will try to get from Fuel Injection Corp. a description of their testing procedure. I realize it is not a substitute for calibrating the AFM on the car, but it might be helpful to know exactly how they go about it.