just like the title says... no idea how much they cost, availability or if there are crossover parts.
i'm getting radically different readings, temps and MPG almost from tank to tank of fuel. the only thing i can think of is the AFM. timing is holding, but about every 150 miles i am getting a hunt/surge/crappy fuel mileage. then, it goes away for about 150 miles.
Notchback mid-engine speedster Little Giant Killer 3
Thats not a signature of the AFM crapping out. In general...its bad....or not.
Hunting idle is a sin of a vacuum leak. Or...of a fuel pressure surge.....which can also be thesign of a vacuum leak.
In the vacuum leak department....these are things that MUST be checked. And...I don't mean with a can of berrymans or a propane torch. For all of these parts...if you yourself have not replaced or sealed the parts I list...then they are 100% suspect.
Modulator valve and hose (replace hose and pull a vacuum on the valve)
Intake boot between AFM and TB (clamp both ends. It must be crack free)
ALL hoses and vacuum lines. I clamp everything.
Intake runner gaskets to heads
runner boots to plenum
TB o-ring to plenum
shaft seals on the throttle body
Cork gasket at oil filler/breather
Auxiliary air regulator. (check that when warmed up...it is 100% closed...no leaks)
Injector seals
Check for sticking TB and WOT switches if you have them
Valve cover gaskets and pushrod tube o-rings
vacuum leaking internally at vacuum advance unit
Vacuum line to fuel pressure regulator
All of these parts are supsect because the vacuum leaks can be non-existent at idle and when cold but open up under heat and vibration.
You need to see what your fuel pressure is while you are doing highway cruising at very small part throttle.
Poor connection at the CHT can cause this type of milage drop.
Improper advance can cause this problem as well. Go through the dizzy.
Leaking injectors....or more precisely...injectors whose intles do not re-seat at WOT fuel pressure. What is your max fuel pressure when running WOT?
Lastly...and this is one of the biggies....the harness. If you have cracks in wire insulation anywhere in the harness.....the resistance could be risng or falling while driving.
One of the things to check on the AFM is to remove the cover from the black box and check for sludge or improper wear to the wipers and contact strips.
Don't bend anything.
Oh..and have you cleaned out that sock filter in the tank? If your pump normally struggles under a load of silt...and you have adjusted teh car during a struggling period....the fuel pressure may spike during driving. Ray
today i swapped out my AFM for another and immediately the fuel mixture improved greatly! my 9mpg jumped to 22mpg. this is based on a 77 mile drive, swap and then 77 mile return trip. it's about time i can afford to drive this thing again!
Notchback mid-engine speedster Little Giant Killer 3
the unit is actually from an air cooled vanagon and is not a direct swap in as i had to modify the mounting between the AFM and the air cleaner. but it is there, done and working! woot! woot!
Notchback mid-engine speedster Little Giant Killer 3
have one small issue... the AFM is from a vanagon like i said and the flapper area is actually a tiny bit smaller, so that might be the issue for all i know... anyway, back to the issue.
at a steady 70mph, when climbing a 5%or steeper grade, when i push the pedal farther, the engine completely falls on its face. there is no audible detonation, but it just falls flat. so, i'm not sure if the smaller afm is causing the mixture under load to go so rich that i lose power, or if i'm running lean under load. if i lift off the pedal some, it seems to go right back to decent power... just not enough to maintain the climb like before the AFM swap.
after the swap was done, we put it on the sniffer at idle and everything was nice.
Notchback mid-engine speedster Little Giant Killer 3
Again...I go back to the original post. You note that thisseems to happen about every 150 miles or so. I'm still notsold on it being the AFM. You need to vrirify fuel pressure at all speeds and throttle settings. What you are seeing is also a symptom of (a) a vehicle that was tuned when output from teh pump or fuel system was low and it is surging in and out of correct to over corrected. (b) an example of a fuel pressure regulator that is surging and leakingeither due to internal issues or vacuum issues. Ray
if there are vacuum issues at this point, i'm not sure where. we have checked and rechecked every line and fitting. this issue is now only happening on a steep incline at 70+ mph... the fuel pump is from a djet type 3 and is set for 28psi... do i need to up the the pressure?
Notchback mid-engine speedster Little Giant Killer 3
One thing that you might look for on your "new" AFM. Pull the top off the AFM and move the flapper to its limits. The wiper needs to stay on the resistance strip and not move off of the end of it.
You might also check it with an Ohm meter to see if the resistance doesn't either spike or drop suddenly at some point along it the travel.
Wait...wait ...wait...how canyour your fuel pressure be set at 28 psi? This is L-jet. You should (a) not have an adjustment on te hregulator and (b) it should be a rising rate regulator with a vacuum line governing it. Also its should be at around 32 psi at idle if it is L-jet....spiking to about 42 at WOT going up a hill.
If you in fact are using a D-jet regulator....that is 100% of your problem. Ray
not a d jet reg.... a d jet pump... it puts out a steady 28psi. it was the only pump i had to replace the bad pump that was in it when i bought the car. of course, it's odd that it had great power and was way rich before on the freeway, but at this point... odd is the best description of this specific car!
Notchback mid-engine speedster Little Giant Killer 3
It is the regulator and not the pump that determines the fuel pressure. If you kept the d-jet regulator you will not have sufficient fuel at lower manifold vacuums. The d-jet regulator has two fuel line attached to it, while the L-jet has two fuel line and a manifold vacuum line.
Exactly. The pump puts out almost no pressure. It only puts out volume. The more volume it puts out against a given restriction....the more pressure it is capable of. It is the regulator that creates the restrictio with a spring and diaphram,
The D-jet pump actually puts out enough volume to create about 70 psi. crimp a line and watch the gauge. For example CiS pumps put out roughly twice the volume....and are capable of about 120-150 psi.
The D-jet ...in the D-jet system (togther) creates 28 psi. This is because it has a fixed pressure adjustable regulator. You set the pressure and it stays at a fixed rate. D-jet can use a fixed pressure because it has two other methods of enrichment that L-jet does not (full load enrichment diaphram in the MPS and the throttle valve switch).
L-jet on the other hand...has a rising rate regulator controlled by a vacuum line. At high vacuum (throttle closed) the diaphram in the regulator is pulled back from the fuel flow orifice. This reduces fuel pressure to about 30-32 psi at idle.
When you open the throttle you lose vacuum. This allows the spring pressure in the diaphram...which the vacuum was holding back....to push hard against the full flow orifice. It pumps pressure up to about 40+ psi for enrichment....for things like climbing hills.
If you have the wrong regulator...you will have no enrichment for climbing hills. Ray
a final tune up fixed the last of the issues! all that running rich really fouled the plugs. pulled the plugs, cleaned them up and reinstalled. no more issues on the hills. i love it when it is a simple fix. i'm finding the hardest thing about working on my VWs anymore is getting uninterupted time to do so. i finally has some, and i got to fix things! amazing
Notchback mid-engine speedster Little Giant Killer 3
