1977 Bus - Stalls after starting

[Daniels Big Mistake]

Posted this on the samba and am not getting that much help so I figure I would try here

This is a 77 Riviera with a GD engine with FI, hydro lifters, pertronix ignition, new cap, rotor, sparkplugs...

Backstory:

It all started with a dropped exhaust valve seat on my #3. Dropped the engine put 2 new heads on it. Put it back in, started it... needed new fuel pump. After that it was running great! I drove 300 miles roundtrip to a hippie fair!

It started idling real low and occasionally stalling a couple days ago, it also had no balls whatsoever while driving. I pulled out the timing guage, tach/dwell meter, vacuum gauge, and fuel gauge, and this is what Ive got so far.

It starts strong and idles at 800 rpm, after about 30sec-2min its rpms gradually drop untill it stalls, if you give it gas it sounds great untill you let off then it will drop down, run around 400-600 rpm then stall.
The vacuum guage reads around 40 cm hg of vac, which is about 1/4 in below the green, in the late ing. timing zone. But the timing is fine, sitting at 10 btdc. This made me suspect a vacuum leak, and thats what I found, 1 crack in the S boot off the AFM, and one in the elbow off the AAR. I sealed both up with JB weld as a temp fix and I see no way they could still be leaking. Local vw parts store has nothing, but I found a new S boot about 20 miles from me, the elbow I still have nothing to replace with. When I start the bus it has the same symptoms as before. Messing with the AFM wiper will keep it running at a steady 750-800 rpm. In figuring all this out I messed with the idle screw alot, and in hindsight might be where some my problems are coming from?
I dont think fuel pressure is an issue because Im getting a strong 2.5 bar using the ignition on, move the afm flapper method. I tried this with the pressure regulator vacuum line on and off with no difference. I dont want to try it with the engine on because my fuel gauge leaks a little bit and I dont want to die.

This is where Im at, Vacuum guage still sitting below green, with the engine at a low idle. Is this the sign of a vacuum leak that I havent fixed, or something AFM/FI related, since the idle screw is out of whack? If I give it some gas or advance the timing the vacuum guage goes into the green and its fine, but idling is just too low.

I am susposed to get new tires today and a trip to yellowstone on monday...I guess neither are happening =D>

[spiffy]

Welcome!!

I'll just start throwing stuff out there.....

You mentioned the timing was at 10btdc...shouldn't it be 7.5btdc?

Did you check to see if your vacuum hoses are set up correctly? Germansupply's web site has a great diagram on how they should be routed.

Are you getting good spark to all zee plugs?

As far as the vaccum leak theory (which is entirely possible) check the EEC (the coffee can lid with a nipple) located in front of your air filter. Unplug the vacuum hose from the advance off of the dizzy and give it a suck and then quickly stick your tongue in the hole. Release tongue and you should hear the diaphram in the EEC go back out. If it doesn't hold your mouth induced vacuum then you have a little leak going on.

I think german supply sells the AAR boots, IIRC....

If vacuum gets ruled out you should check the resistance on all your AFM terminals to see if they are in spec.....

[bretski]

Welcome! Ok, a couple of things:

Replacement AAR elbow. This has been the bane of many of our existences (yours truly included). DurocShark posted an Ace Hardware hippie fix. Search for it here.
germansupply.com sells the genuine VW part. Don't get aftermarket, they're crap:
http://germansupply.com/home/customer/p ... at=&page=1

Other notorious vacuum leak spots:
1. There's a diaphragm on the side of your air cleaner housing. They fail. Hose goes to a tee just off the vac. advance canister on your distributor.
2. Brake booster tee that goes to the decel valve and air plenum.
3. Throttle body. This one's easy to miss because it's hidden. Follow the vac line to the back of the throttle body to find the port.

Once you get your vacuum leaks squared away, I'd check all your ground connections. Our L-jet FI system hates bad grounds.

Others will chime in, but start there, and let us know what you find!

[bretski]

LOL!

Looks like Spiffy and I were typing at the same time...

[dingo]

40 cm hg ...what is that in pSI ? what does the needle do ? steady,? fluctuating? wavering ? that will tell you a lot

are your hydraulic lifters all fucntioning acceptably? i am always very suspicious of those guys...

[spiffy]

LOL!

Looks like Spiffy and I were typing at the same time...

Also looks like we have taken the same 'lumps' from our buses



Anywho....back to the program

[Daniels Big Mistake]

Holly crap, the replies!!! this is awesome, but embarressing, I found the problem: I had a shop towel stuffed into the throttle body!!! I put one in there to stop dirt from getting in when I took the engine apart, AND I remember thinking that it was probably a bad idea!!! Anyway, I figure this is most definately the problem, but now theres a new problem. I start the engine and it ROOOOAAARRRSSSS to life and keeps revving up and up and sounds like its going to explode, so I have to shut it off. Whaaaat??? it sounds like its full throttle, and the whole throttle piece moves up and down in the body about 1/4 in .

I think I did a bad thing

[spiffy]

Hee hee! Don't ya love what hijinx you can play on yourself?

Check to see if the throttle plate is operating correctly...ie opening and closing all the way.

You can try bringing the idle down with the screw on top of the throttle body as well.

Is that timing still set to 10* BTDC???

[bretski]

I had a shop towel stuffed into the throttle body!!!

PS - We've all been there...heck, we even have a thread for it!
http://itinerant-air-cooled.com/viewtopic.php?t=2887

[Daniels Big Mistake]

My extreme high idle was just my accelerator cable! I can adjust the idle screw and it responds now, and the idle is just money, I cant believe what a stupid mistake all this hassle was. I even made it to the tire shop on time. New RA-08's and my best old tire as a spare.

What I cant believe is that I made a 300 miles round trip with that towel in there. I swear it was purring the whole time, with 3 people and their gear in it! The throttle cable was adjusted incorrectly holding the throttle open at idle, and this is what the timing was adjusted to. What damage could I have done to my engine doing this?

As for the 10BTDC: I was driving south through portland before my head went out, I stopped at Trafton foriegn auto for a tune up and they said to set it at 10BTDC, they even marked it on the pulley scale. Should it be set to 7.5 per bentley?

[spiffy]

My extreme high idle was just my accelerator cable! I can adjust the idle screw and it responds now, and the idle is just money, I cant believe what a stupid mistake all this hassle was. I even made it to the tire shop on time. New RA-08's and my best old tire as a spare.

What I cant believe is that I made a 300 miles round trip with that towel in there. I swear it was purring the whole time, with 3 people and their gear in it! The throttle cable was adjusted incorrectly holding the throttle open at idle, and this is what the timing was adjusted to. What damage could I have done to my engine doing this?

If you replaced the P&C's you probably just gave them a proper break in

[Westy78]

Welcome Daniel. Don't worry to much about making a stupid mistake. We've all been there.

As far as damage done in 300 miles. Probably not to much. A couple of things that might have happened. The towel in the TB would block intake air causing a rich mixture, leading to washing down the cylinder walls which is a bad thing when trying to break in new rings. Again, in 300 miles most likely not that much of a problem. The second thing that comes to mind is that you had the timing either to far advanced or retarded to compensate for the maladjusted throttle cable which could have lead to high head temps. Do you have any instrumentation to know how hot the heads were running?

[Amskeptic]

The towel in the TB would block intake air causing a rich mixture, leading to washing down the cylinder walls which is a bad thing when trying to break in new rings.

Daniel, I am the technical nanny granny here, your towel caused no harm and just a little extra filtration, a good thing.

Jasan, the towel limited the air no differently than a partially closed throttle plate. The AFM was fully aware of this and did not signal any more fuel than the towel-strangled engine could use.

Daniel,
About that towel. . . the factory supplies a nice air filter cartridge and doesn't really need that towel.

Colin

[Westy78]

I was wondering about that. Since the air was restricted after the AFM I thought that it may have affected AFR. But after thinking about it, true the AFM would have seen it just as the engine needing less fuel so.......no harm, no foul. =D> Would it have made a difference if the obstruction was before being metered? I suppose that would be the same as running a dirty air filter.

[Amskeptic]

Would it have made a difference if the obstruction was before being metered? I suppose that would be the same as running a dirty air filter.

The AFM is a beautiful bit of engineering. It has a counteracting chamber that actually cancels out any vacuum effects upstream or downstream of the flapper. It measures airflow and that is all it measures. Beautiful work those engineers did.
Colin