Type 1 Air Flow Meter/Intake Air Sensor

I have a '75 fuel injected super beetle. Upon acceleration, it hesitates and takes a couple of seconds for the revs to come up. I've eliminated the ignition electrics as a problem, and there are no leaks in the fuel system. The fuel pump purrs happily, and I put a new fuel filter on. I have not bought a fuel pressure test kit yet, so that hasn't been checked.

I checked the resistance on the pins coming out of the air flow meter, and 3-4 (leftmost pair) ranges from about 150-380 ohms as I move the flap. Pins 6-9 (middle pair) are stuck at a constant 281 ohms as I move the flap, which I believe is something that will result in the symptoms I described above, i.e. the brain doesn't know more air's coming in, so it doesn't feed more gas to the engine. The car tops out at about 30 mph.

I ordered a "good used" air flow meter, checked the resistance on the pins, and they're EXACTLY THE SAME as the unit that's on my car now. Pins 6-9 are stuck at a constant 281 ohms no matter where I move the flap inside the box.

Before I return the part, could someone who actually knows type 1 FI please tell me that this constant 281 ohms resistance is indeed a problem? It seems odd that two units have the same reading. I spent my youth wrenching on a carburated bug, and have only just begun to become familiar with the FI system.

Also, if both the units I now have in my possession are bad, is there somewhere I can send one of them off to be rebuilt while the other's still on the car. I need to be able to move it for street sweeping and crabby neighbors, so keeping the car mobile is important.

Thanks, Ian

Pins 6 to 9 are supposed to be constant resistance. Look on my web site for the FI info and simplified schematic.

Rarely is the air flow sensor the culprit in FI problems.

I would, in this order, check:

1) Distributor advance. Check for leaks in the vacuum diaphragms and, using a strobe light, check actul advance.

2) Fuel pressure. You don't need a fancy setup. Buy a $10 pressure gauge and connect to the cold-start valve fuel line. Top speed of 30MPH suggests ful starvation but that probably doesn't explain the hesitation.

3) Compression test. Just for grins.

Speedy Jim

Snip

Have you checked the temperature sensor and wiring? Does the engine idle fine? Are you sure the ignition is fine? New points, condenser, rotor cap, ign. coil? Valves adjusted? Fresh oil? No vacuum leaks? later, dave Reminder........ Before you criticize someone, you should walk a mile in their shoes. That way, when you criticize them, you are a mile away from them, and you have their shoes. Frieda Norris

Airflow meter is not the problem. The most common symptom of the airflow meter failing is a flatspot - that is, a completely dead spot at "normal cruising speed" on flat ground holding a steady throttle. By your description I suspect ignition even though you have "eliminated it!" Just for kicks, pull the vacuum line off the fuel pressure regulator while it's running, or pinch it closed and see if there's a change in engine speed. (High vacuum = approx.

2bar pressure / low vacuum = approx 2.5bar pressure) I don't suspect a vacuum leak because you can start it. Other major common problems result in rich running, blubbering, black smoke. I keep coming back to ignition - especially timing being really retarded. Okay. One more possibility: Suffocation! Plenty of air getting in? (remove the air filter element and try it) Plenty of air getting out? (An exhaust blockage can cause symptoms very similar to what you describe)

acceleration, it

come up. I've

are no leaks

put a new fuel

yet, so that

flow meter,

I move the

ohms as I

result in the

more air's

car tops

resistance on the

my car now.

I move the

type 1 FI

indeed a

reading. I spent

begun to

bad, is there

the other's

sweeping

important.

Thanks for the responses!! I wish I could paypal your local liquor store, and put some beers on reserve for all of you!

The Haynes manual is unclear about whether pins 7-8 (not 3-4 as stated in my orig. post) and pins 6-9 should be variable or static resistance. They're attached to a potentiometer, so one might assume variable. I just got the Bentley manual yesterday, so it's hopefully clearer.

Two problems I did manage to fix, which improved things a lot, were leaks in two injector boots.

In any case, I did indeed put on a fresh condensor and set of points, and timed it statically. I'll be checking the list of suggestions, and failing success, it will be going to a Hungarian gent who worked at VW in the 70's. He's apparently unafraid of and expert at VW FI.

I've got a carb, manifold, fuel pump, muffler, j-tubes, etc. waiting to go in the car, but I'm resisting the temptation.

You didn't say, but if the distrib is stock you can't static time; use a strobe.

Speedy Jim

and why can't he static time the distributor?

later, dave Reminder........ Before you criticize someone, you should walk a mile in their shoes. That way, when you criticize them, you are a mile away from them, and you have their shoes. Frieda Norris

.............I'm going to take a stab at this before Speedy Jim can stop me........

..............I think that any kind of centrifical advance mechanism will screw-up a static setting, even when only idling. I tried to use a static setting once on my L-Jetronic 77 bug and for whatever reason, it would barely run. Strobe lights are the only way to go, in my opinion.

Because the stock distrib has both vacuum advance and retard. The initial timing is set at 5 deg AFTER TDC and requires the vacuum signal(s).

I might add that if he has a ruptured vacuum diaphragm, timing will be way off no matter and the thing will run like crap.

Speedy Jim

thanks Speedy, I thought that was the reason. IIRC He still could static time it at around 7-10 degrees before TDC to be close though. It has been too long since I owned one, and I just don't see the FI T1s much anymore. I saw one this year and it was the first since maybe the early 90s. :-(

I thought that VW continued with the single vacuum advance since 74 on the T1s. I don't even remember what was on my 76 Beetle.

Well, the distributor is indeed stock. I timed it statically, as I learned in the Idiot's guide, all those years ago.

I've been rebuilding my tool collection after a theft a while back, and today, bought a pack with a timing gun, compression gauge and vacuum/fuel pump pressure gauge. I'll be checking all your suggestions tomorrow.

So it has the dual diaphram vacuum advance unit on this distributor? Or the single? Where did you set the crank pulley when you static timed the distributor?

later, dave Reminder........ Before you criticize someone, you should walk a mile in their shoes. That way, when you criticize them, you are a mile away from them, and you have their shoes. Frieda Norris