mass air flow problems

frewmanchu · Posted: Thu Jun 07, 2012 6:06 am Post subject: mass air flow problems

Hey everyone,
so so my 79' fuel injected westie will die if i try to start it with the MAF sensor plugged in. When not plugged in it will run and idle, have to feather the gas up though or else if you put the pedal to the floor the engine will cut out. I checked the resistance on the Maf and it is within specs of what it should be, with the ignition on i can physically move the flap inside and hear the fuel pump kick on.
so far i have replaced:
fuel pump,double relay, spark plugs/wires, distributor, rotor. I have looked for vacuum leaks and have not found any significant!
If anyone has any idea why she wont run or helpful tips that would be much appreciated!!!!
thanks.

tootype2crazy · Posted: Thu Jun 07, 2012 7:01 am Post subject:

Check for vacuum leaks, spray starting fluid all around the connections at idle and see if the idle changes, or just check them by hand. There are lots of possible places it could leak so be thorough.
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air-cooled or nothing for me
1978 Sunroof Deluxe Bus (daily driver)
1978 Transporter (mom's, making into a camper)
1970 Single Cab 2.1 turbo/EFI 6 Rib, 78 front beam, vanagon backing plates on rear (project)
2001 GTI VR6 (wife's)

Westfabulous · Posted: Thu Jun 07, 2012 7:32 am Post subject:

It's most likely your Auxilary Air Regulator. When you pull the plug on the AFM, you cut the power to your AAR, so it stays open. It has likely become lazy and needs adjusting to make the air gate bigger, or it needs to be replaced. When you plug in the AFM, the air gate on the AAR slams shut too quickly; then you need to feather the accelerator to give it the air that it is being deprived of.
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"I will gladly pay you Tuesday for a hamburger today."

SGKent · Posted: Thu Jun 07, 2012 12:00 pm Post subject:

darn those lazy AAR's. I had a tire go flat once and found an AAR trying to siphon air from the other 3 tires too. Shot it 3 times with a 45 before it even let loose of that tire - thought it was going to get me next. We fought for close to an hour and I was lucky to get out alive. They look so harmless lying there in the engine but when their dark side comes out - look out. Don't leave spare ones in a closet either or you may be missing children and your pets too. Those AAR are really nasty when they get lazy or an attitude!!!!!! Smile

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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

Randy in Maine · Posted: Thu Jun 07, 2012 12:08 pm Post subject:

Don't be afraid to do a fuel pressure test. I am not sure just why you changed out all of that stuff, but a fuel pressure test is cheap and easy to do.

frewmanchu · Posted: Thu Jun 07, 2012 5:12 pm Post subject:

thanks for all the info!
i will check the AAR , I have replaced the other parts i mentioned because they were all trashed! i bought this van not too long ago and am finally starting to breathe some life into it!

Westfabulous · Posted: Thu Jun 07, 2012 5:14 pm Post subject:

If you want to narrow it down to the AAR with some degree of certainty, reconnect the AFM, and then gently pull the electrical connector of the AAR. Try a cold start. If it runs without conking out on you, then fix or replace the AAR. They are quite fixable.

By the way, when your AFM is unplugged, you cannot give it any throttle, or it will die.....just as you described.

The AAR starts to cool and open within minutes of shutting off your engine, so after 15 minutes or so, it will come back into play when you start the engine.
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"I will gladly pay you Tuesday for a hamburger today."

Wildthings · Samba Member Joined: March 13, 2005 Posts: 50348

There are lots of post about this problem. A search will probably answer your question.

Personally I can't imagine it being the AAR unless it only does it at cold idle with your foot off the gas. The AAR is a pretty dumb valve, it does nothing more than cracking the throttle open slightly with you foot would do.

frewmanchu · Posted: Sat Jun 09, 2012 3:29 pm Post subject:

alright so i tried starting without the AAR plug attached and the same situation happened, runs for about 2 seconds then dies, i check for vacuum leaks and havent found anything. having the AAR plugged in\out doesnt seem to make any difference wether or not the AFM is plugged in or not.
Will run and idle either way as long as the AFM is unplugged.
any other suggestions anyone??
Thanks!!

Westfabulous · Posted: Sat Jun 09, 2012 3:38 pm Post subject:

I would run some tests on the Double Relay. Bentley has a procedure, but the AFM manual has a more detailed procedure IIRC.

Have you looked at TS2?

What's your fuel pressure doing during these issues?
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"I will gladly pay you Tuesday for a hamburger today."

frewmanchu · Posted: Sat Jun 09, 2012 5:02 pm Post subject:

i will have to pick up a bently manual ( i know i should have before i even started!) the double relay is new so it should be in good working order but i will have to test it. i havent checked the TS2 yet as well.

Westfabulous · Posted: Sat Jun 09, 2012 7:32 pm Post subject:

You know, I would be really interested to know if your fuel pump continues to run after cranking. My hunch is that it may not be. Can you try testing it by pushing the flapper in the air box / AFM with a pencil while the ignition is on? You should hear the pump buzz and gas returning to your fuel tank. I think it may be pumping while cranking, and then not running once the bus starts. Thus it runs for 2 seconds while burning off that first shot of crank fuel, and then mwah, mwah, mwaaaahhh.

A fuel pressure gauge would also tell you if the above is an issue.

This little bad boy right here; accessed through the half of the air box that attaches to the AFM:

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"I will gladly pay you Tuesday for a hamburger today."

frewmanchu · Posted: Sat Jun 09, 2012 7:48 pm Post subject:

yeah i have had it plugged in and while it is running i moved the flapper and it will continue to run

Westfabulous · Posted: Sat Jun 09, 2012 8:35 pm Post subject:

Well, you should probably give us some background then: cold start only? All the time? Before or after you replaced the Double Relay? How long has this been an issue? Etc? It will be a easy fix; just need to narrow it down. I am surprised that it is not the AAR or the fuel pump. Have you got the white FI wire connected to the correct terminal on the coil? Check that for sure.
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"I will gladly pay you Tuesday for a hamburger today."

SGKent · Posted: Sat Jun 09, 2012 8:38 pm Post subject:

frewmanchu · Posted: Thu Jun 14, 2012 4:40 pm Post subject:

i will take an indepth look at the vacumm lines to make sure there is no leak, i bought this van and it was not running at the time so i dont have much history on it, as long as i have had it it will always die as soon as i plug in the AFM . I also replaced the TS2 which didnt make any difference, is it possible or highly unlikely that the AFM has never been properly adjusted? from what i understand it is pretty much a variable resistor under the cover. i Havent taken it apart as i dont want to screw it up even more if that doesnt seem like it could be an issue. Next chance i get to work on her i will check to make sure the wiring is correct.
Again, Thanks everyone!

SGKent · Posted: Thu Jun 14, 2012 4:58 pm Post subject:

start with the injector seals. They take just a few minutes to replace and they 100% do go bad over a number of years.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

frewmanchu · Posted: Sat Jun 16, 2012 4:15 pm Post subject:

Progress! i swapped out the FI seals and it now will start with the AFM plugged in, i have to keep giving it gas to keep it from stalling though, i took it for a short drive and was able to give it full gas without it stalling out. i noticed a melted point on one of the fuel injectors though, should this be replaced? i have a picture but it doesn't want to attach.

Westfabulous · Posted: Sat Jun 16, 2012 4:17 pm Post subject:

frewmanchu · Posted: Tue Jun 26, 2012 3:48 pm Post subject:

i replaced one of the injectors and started it up, while it is cold it idled for about 2 mins before dying, i took it for a quick drive which was pretty rough, it doesnt want to maintain an idle now and will die if i dont give it gas. i thoroughly checked for air leaks and havent found any!
restarting the engine while it is warm it wont idle at all and i have to keep giving it gas or it will die.
Any ideas?
thans guys!


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