Calibrating Air flow meter

[Joe Papa Sr]

Searched with no luck. Anyone ever calibrate their meter? I understand this is best left alone, requiring special equipment.

Just wondering, having checked all other sensors, etc, if this could be the problem Im having with cra**y gas mileage, sooty exhaust, basically alfaish typical signature ailments Ive been living with, as many of you fellow members know. Maybe its the last thing I should be looking at?

(besides, rainy day here in FL, need a project or go with the wife to Costco.....LOL!!)

Thanks again, guys.

Joe

[ghnl]

There are two things you can do with the AFM. You can adjust the idle air bypass. It is quite easy to do - you need a digital voltmeter and a functioning O2 sensor. Instructions are in the Spider L-jet page - which seems to go 404 from time to time. I assume however that the idle air adjustment really only affects things at, umm, idle.

The other thing is to vary the spring tension on the AFM 'door flap'. That can open the proverbial 'can-o-worms' (especially if the original position of the spring is not marked/recorded as it'd be difficult to get it back to factory specs if you really mess it up). Theoretically, less spring tension allows the AFM's flap to open wider/faster which should tell the ECU (computer) to squirt more gas. However (damn howevers...) final control of the fuel supply is based on input from the O2 sensor (except at wide open throttle when the ECU ignore the O2 sensor and delivers extra fuel).

[Joe Papa Sr]

oK, so is there an original "factory" setting which we can revert to, not having a "mark" on this flap? What is the factory spec? (I have a shop manual, should it be in there?) Cant seem to find any reference to adjust this AFM in there.

What do you mean, "go to 404"?

[ghnl]

404 = file not found - usually when the hosting server is off line or down for maintenance -or- the page is removed.

The AFM's were not marked at the factory. If you desire to fiddle with it, make a paint mark to indicate where the spring originally was so you can return to that position if your 'adjustments' make things worse. Such info won't be in the shop manual as it is NOT advised to mess with the AFM's internals. Owner assumes all risks...

The photo below is of the AFM from a GTV-6 but it is very similar to the one in our Spiders. The screwdriver is pointing at one end of the spring retainer, nearby is the nut that secures it in place. Hold the toothed plate underneath the retaining strap still, loosen the nut holding the retainer then rotate the plate (which is spring loaded and attached to the AFM's flap door) in whatever direction you want to experiment with.

Some have tried moving it to a postion that 'weakened' the spring's force - the idea being the AFM's flap would then open faster/further to improve performance. I don't think the results were dramatic but the possibility that one could screw it up were high.

Perhaps your's was messed with and thus the ECU is getting lousy input causing the engine to run too rich = poor fuel mileage and stinky exhaust? The cover is just glued on. Slice around the edges to cut the glue and carefully pry it off. You can drive the car with that cover off while you are 'adjusting'. If you find a position that improves things, re-glue the cover on with a small bead of RTV or silicone caulk.

[Joe Papa Sr]

Thanks!! Sounds like , based on your previous post, O2 sensor can override this adjusting. Maybe not worth messing with?

I think, though,I will try tightening spring, to cause ECU to run leaner. Maybe 2-3 notches(kinda arbitrary, huh?).

[Tifosi]

You can sorta kinda get close to stock by getting the engine fully warmed up, then with the cover off the spring, adjust the tension until the arm on the potentiometer just stops occilating wildy back and forth.

A little movement OK, and the goal isn't to get it to be rock solid, but you don't want it fluttering all over.

You'll see/hear/feel the idle smooth out a bit too as things stop moving around.

[Joe Papa Sr]

Thanks, Tif! Is it pretty obvious what this potentiometer arm is, when it will be fluttering around? Im pretty sure I can figure it out......

Yeah, stock setting/verification would really make me happy.

OK, I think thats that copper V shaped arm, pointing at the 4:30 position in above photo....right?

[Joe Papa Sr]

Man, theres something I just dont get(scratching head, just back of right ear).

If you say, tightening the spring a few notches on the AFM makes the door open harder, it signals the ecu to apply LESS gas, running it leaner. But, in the meanwhile, with the door now opening less with stiffer door, isnt the effect cancelled since LESS air is also coming in??

[ghnl]

That is why it is a calibrated set up. The spring tension has to be enough so that the AFM's flap doesn't swing widely but not so tight that it doesn't sense small changes in air flow.

Quote:

scratching head, just back of right ear

[Joe Papa Sr]

No dope/rope-a-dope slaps...can promote alzheimers (member what happened to Muhammed Ali?). Scratching will suffice for fleas/head lice.......LOL

OK, Eric, back to serious.....Thanks for offer. Will keep inmind, but I believe, so far , my meter is ok. So, is that potentiometer that V shaped brass/copper thing at 4:30 position in your photo above?

Joe

[ghnl]

Yep.
added words to meet minimum requirement