AFM is raising all sorts of heck - Please HELP me!!!

[UtahGOgear]

Hello everyone!

I've been having some extremely stressful times after experimenting on my '82 Westy running fumes directly into the intake boot from where the decel valve hose runs out of it. I unplugged that connection, ran a hose with gas fumes into it, and it backfired and messed up my AFM.

So yeah, that was an interesting experiment in search of better gas milage, but when all is said and done I wish I would have done it on a lawn mower or motorcycle before touching the westy.

So... after the van backfired it started running really bad and eventually wouldn't reach high speeds, and started bucking like crazy.

I've checked many things (fuel pressure, filter, pump, sensors, new spark plugs and wires, vacuum leaks, grounds cleaned, etc etc.) and it's ran fine a few times, but would backfire.

The thing is, when it backfires the needle that shuts off the fuel pump in the AFM somehow gets pushed to the other side of that switch! Like... it gets on the other side of that long copper strip somehow when it backfires and then it causes it to not open all the way (hardly at all) when I try to start it because it doesn't go past the switch and no air can get in! (also without that pin hitting the switch and disconnecting the connection the fuel pump doesn't switch off when the key is turned)

So I guess I've got a lot of problems with my AFM. Is this causing backfire? Maybe... I'm honestly not sure now. But for sure this seems really wack. Like... how does it get there? Do I need to adjust the tension in the spring so it doesn't move back that far to get to the other side of the switch? Is my AFM bad?

Surly it got messed up when I ran fumes into the intake boot. Boy am I regretting that decision...

If you have any advice on how to fix this or adjust it so that my motor can run again without backfiring through the intake and throwing my AFM out of wack that would help a ton!

Thanks and Merry Christmas!

[DanHoug]

AFMs have a V shaped vane. the backside of the side facing incoming air acts to dampen vane movements by being pushed into a blind pocket chamber. you may have bent or broken the vane during a backfire. you can see them if you take the AFM completely free of the air cleaner housing.

-dan

[djkeev]

I worked for Mercedes Benz back in the 1970's and 1980's when this type of EFI was new exciting technology.

Back firing would cause all sorts of running issues.

The cause ended up being a bent Air Flow Meter vane causing it to stick.

A new AFM almost always fixed it.

Dave
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[MarkWard]

I would check the magnets that align the fuel molecules. They may have shifted and the fuel polarity is in conflict.

Back fires occur when engine timing is off or an intake valve is not closing properly. The air flow sensor measures airflow for the ECU so it knows how much fuel to add. So it is unlikely the sensor is causing the backfire.

That said, it sounds like you have damaged your air flow sensor. It will probably need to be replaced now, but you still need to figure out why the engine is backfiring or you may damage the replacement sensor. I would leave the boot clamps loose while you are testing with the new sensor in case it back fires it will pop the boot off instead of possibly damaging the new air flow sensor.
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[Wildthings]

You might try adding both some FI cleaner and some upper cylinder wall lube to your fuel. The cleaner to get the injectors working their best and the upper cylinder wall lube (MMO, 2cycle oil, synthetic motor oil) to free up the valve stems and rings.

[Ahwahnee]

Gents - he knows why it backfired, it was his Mr Wizard experiment with a 'running on fumes' set-up he saw on YouTube. He won't be doing that again.

No more backfiring now, just crappy running possibly due to the damage the big backfire did to the AFM.

[UtahGOgear]

Thanks a ton for the quick replies!

I do think a new AFM is in order. I dumped some sea foam into the tank and intake and it seemed to do miracles. Not to mention all of the other things we've just replaced/cleaned/re-sealed trying to find the problem. It was revving great and even drove wonderful before the AFM was thrown back again.

It must have gotten damaged during backfire.
It's too bad it seems to be quite an expensive replacement. Is re-building it out of the question?? I'm a substitute teacher/ student and have like the next 2 weeks off before school/ work starts up again. This is great because I can have time to rebuild it... not so great because heck, if I worked these two weeks I could almost afford a new one!

Thanks again guys, I sure appreciate it!

[Ahwahnee]

I bought a used AFM to carry as a spare and it seemed fine (installed it to confirm it was good to go).

About the worst ting that usually happens to them over time is that the track gets worn. Sometimes you can see this in a photo, sometimes not. Even that has some remedies though they are not fool-proof.

Anyway, there may be a low cost alternative to a new unit. Obviously you do not throw away your old unit - it has parts that may yet be useful (such as that board that the track is on).

I have not examined one in light of your problem to see if there is a simple fix - that too may be possible.

[UtahGOgear]

I flipped the AFM needle to the correct side of the fuel pump switch, and then adjusted it so that the wipers are on the black tracks (they weren't even on the tracks before) and I did that by loosening the screw behind them and moving the wipers. (I'm sure I need to compensate for that move by moving the tension or something, but it seemed to work

It started up first try and I drove it for a bit, but can't seem to get above 30-40mph and it seems like very low power. There's some white smoke blowing out the back but maybe that's just because it's freezing, but it smells kind of like brakes when they're burning (no, the emergency brake wasn't it sadly)

Also noted; there's a high pitch squeaking noise when I press on the gas pedal. It's like a chirping noise coming from the motor. It's not heard when I decelerate or idle though.

I feel like we're getting close! Can anyone think of what's happening here? Is the AFM totally bad probably? I must have threw it out of wack when I adjusted the wipers to fit on the track, but how do I compensate for that??

Thanks in advance- the support here is amazing and helps us out a ton

[UtahGOgear]

My buddy is letting me pull the AFM off his to see if that's really the problem. Fingers crossed! If the smoke is oil burning... dang.

[E1]

Smoke colors:
— White: coolant
— Blue: oil
— Black: fuel
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[UtahGOgear]

I do think it's oil, and it seems that I might have a bad intake valve on cyl 2 I'm thinking....

It sounds like a very high picked squeak comes from it, and it's been leaking for quite some time now from underneath.

The AFM I swapped in works on my buddy's vanagon but didn't change anything on mine. Actually, it immediately backfired and never started again even with our original one on there! What's up with that?

I'm losing my mind. I've been working on this motor for the past 2 months with my wife and we still can't fine what the problem is. I'm tempted to just buy a re-built motor but terrified if I put it in and it still didn't run. Also considering a Subaru swap, but wow those parts aren't cheap! Nether is a decent Subaru...

Really running out of ideas and frankly motivation.

[E1]

Hang in there Buddy, we've all been there — and Yes, it does suck.

It seems from what you just posted that your #2 cylinder issue may well be the problem.

Heads are not that expensive — at least not when compared to stress.
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‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman

[Wildthings]

A backfire may well have blown a hose off so check all the hoses one more time. A vacuum leak caused be a hose being off could easily lead to further backfires. Damage to the EGR or exhaust from a backfire out the exhaust could also cause a lean running situation.

[DanHoug]

sounds like you're #2 intake valve is sticking. since the engine runs, go to a GM dealer and get a can of GM Top Engine cleaner and follow the directions on the can. essentially you suck it in the engine thru a vacuum port fast enough until the engine dies, then let it sit a number of hours, then start it and use the rest. it's a strong varnish solvent that you suck into your intake system that can loosen a varnished up intake valve stem.

each manufacturer has their own flavor of the Top Engine Cleaner. if you don't have a GM dealership nearby ask another marque. but you want the stuff that you suck up into the intake. used to be you could pour it down a carb throat but those days are gone.

i'm a little concerned about the design of the vanagon intake manifold... the runners aren't at the low spot so it will pool in the stamped intake and not reach the heads as well. might want to get the engine hot, pull the right side intake runner off, and pour it right on the valve stem.

-dan

[DanHoug]

hey, if you can slide the intake boot seal on #2 down on the runner, just put a piece of aquarium tubing in the gap and push it towards the cylinder. wrap some masking tape around it all and start the engine... it'll suck up the cleaner like duck soup.

-dan

[Abscate]

Distributor cap
Rotor
Check for spark at each cylinder with plug removed and grounded

Spark plug wire order. Check this by removing valve cover, confirming TDC #1, then looking at cap rotor wire position , then confirming 1432 firing order, clockwise.

You can't spend two months troubleshooting systematically, that's telling you you need more understanding of the process. That's not meant to be harsh, but if you aren't systematic you can spend a year bouncing around without progress, all time wasted.

A compression test will confirm valve or ring trouble and let you know if it's worthwhile proceeding without a teardown.
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[MarkWard]

Probably not your problem, but a leaking master cylinder can get brake fluid sucked into the engine and will smoke. If the fluid is left in the servo long enough, the servo can fail and become a vacuum leak.
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[DanHoug]

and ironically, i've used brake fluid sucked in the intake to clean intake valves! had a 2 cyl engine with one intake valve stem gummed with varnish from a leaking carb float valve. threw everything i had at it to try to get the valve unstuck and what ended up working was brake fluid.

made HUGE clouds of white smoke. Huge. but it is a pretty good solvent for certain types of paint finishes and gasoline varnish.

-dan

[a1fa]

Why start another thread?
https://www.thesamba.com/vw/forum/viewtopic.php?p=8642342
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