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TGOT Sun Nov 06, 2011 7:21 pm

Alright I did the unplugged AAR test and the engine did not die. It idled well for about 25 minutes then I plugged in the AAR. About a minute in it slowly began to loose rpm but eventually smoothed out and was fine.

Disturbingly though I took SGKents advice to do a cold leak down test before this happened and the results were grim:

#1 90psi
#2 90psi
#3 Maybe 15 psi but the needle fluttered alot so it was hard to sure.
#4 85 psi

This bugged the crap out of me. Got my buddies tester to confirm readings. They were the same. So I performed the AAR test while it warmed up. Here is the compression test warm:

#1 115 psi
#2 115 psi
#3 115 psi What the heck?
#4 110 psi

So my buddy and I checked the valves on number 3 and they were right where I left them at 2 turns past contact. He noticed something odd though about the #3 intake runner, it was burning hot compared to the other 3! Suspecting something fishy we took off the rocker for #3 and #4 The intake valve for #3 sits about 2mm proud of the other 3 valves.

So my buddies and I theory is that the #3 intake is sinking into the head. When cold it leaks at that seat causing the low compression and the intake to heat up. Leaking back into the intake I am sure does wonders for the other cylinders but also heats up the area around TS2 so the engine thinks its ok to lean out when in reality we are still cold. When the engine warms up the the seat seals, causing everything to be right as rain.

This is something of a detective story conclusion! Good thing Ive been stockpiling heads, I even have one of the 79 only ones. Hopefully no other damage has been done and swapping this out will fix the problem.

Does this sounds plausible? Anything else it could be? I guess Ill be tearing this engine down next weekend.

Thanks to SGKent who came up with the theory to check this stuff. Thanks to everyone who tried to help.

I do have one question though, what does running the engine with the AFM disconnected then running with the AAR disconnected prove?

Westfabulous Sun Nov 06, 2011 8:38 pm

TGOT wrote: I do have one question though, what does running the engine with the AFM disconnected then running with the AAR disconnected prove?

It isn't just a coincidence that it ran well in both cases. The AAR will not close when the AFM is disconnected, and the AAR will not close when it's connector is removed. In both cases the engine gets more air at cold start, when it is needed most, as the AAR orifice remains open. So, at the very least, it would seem that you have an air deprived engine at cold start. The AAR is the keeper of start up air, and if it was me, I would be swapping in another AAR to see what happens. Very often they still open and close, but the cold opening has become compromised over time and is too small to really assist with a cold start. Time to put in a known good AAR and see what happens. Your valve is not causing your cold start problem if it runs well when the AAR and the AFM are disconnected.

There are 7 pins on the AFM and it seems that the AAR might be the suspect here, as 2 separate tests revealed the the engine runs when the AAR does not close. If not, then you need to look at what is connected to the other 6 pins...TS1, Double relay, etc. I would also swap in another AFM if the AAR doesn't pan out. Easy for me to say as I have several laying around. You need to fix your sunken valve, but your hard start is FI related in my opinion.

TGOT Sun Nov 06, 2011 9:12 pm

I understand now. I didnt know the AFM and AAR were connected like that. Well I now I know I have something fishy on number 3 that needs investigating. While I have it the engine out I can figure out whats up with the AAR as well. I didnt have visual confirmation of its opening before, just could blow through when cold but not when warm, I didnt realize it could fail to open up enough and therefore close to fast.

Looks like I have multiple problems going on but nothing I cant handle. Thank god that valve got noticed before it failed! Thanks for everything, Ill post back when I get all back together and see how it runs.

Westfabulous Sun Nov 06, 2011 9:21 pm

TGOT wrote: I understand now. I didnt know the AFM and AAR were connected like that. Well I now I know I have something fishy on number 3 that needs investigating. While I have it the engine out I can figure out whats up with the AAR as well. I didnt have visual confirmation of its opening before, just could blow through when cold but not when warm, I didnt realize it could fail to open up enough and therefore close to fast.

Looks like I have multiple problems going on but nothing I cant handle. Thank god that valve got noticed before it failed! Thanks for everything, Ill post back when I get all back together and see how it runs.

If you haven't actually had the AAR out and looked at it closely, then please make this the focus of your investigation. You saw how the engine ran when the circuit was cut off; that is a VERY strong indicator of AAR issues.

What happens with them over time is kind of strange. As the inner spring fails, the cold AAR opening actually becomes more closed, as opposed to more open. This results in too small of a window for your engine to get enough warm up air before the circuit closes the orifice. You can pin open the AAR orifice with a nail or something and then tighten down the nut again (the remove the nail of course). You will probably have to play with it a bit and tweak it, but the goal is to get a bigger orifice opening than you started with. Either that or replace the AAR. I have seen many of these with issues, and they always come up with the same symptoms that you described, and they always respond better when the AFM and AAR are unplugged. Let me know how it goes. I feel good about the AAR diagnosis. Try and swap in a known good one if you can, and before spending money on a new one. The valve needs fixing too, but that is absolutely not your cold start issue. If it was, unplugging the AFM and the AAR would have no effect at all.

SGKent Mon Nov 07, 2011 8:54 am

Westfabulous wrote: TGOT wrote: I understand now. I didnt know the AFM and AAR were connected like that. Well I now I know I have something fishy on number 3 that needs investigating. While I have it the engine out I can figure out whats up with the AAR as well. I didnt have visual confirmation of its opening before, just could blow through when cold but not when warm, I didnt realize it could fail to open up enough and therefore close to fast.

Looks like I have multiple problems going on but nothing I cant handle. Thank god that valve got noticed before it failed! Thanks for everything, Ill post back when I get all back together and see how it runs.

If you haven't actually had the AAR out and looked at it closely, then please make this the focus of your investigation. You saw how the engine ran when the circuit was cut off; that is a VERY strong indicator of AAR issues.

What happens with them over time is kind of strange. As the inner spring fails, the cold AAR opening actually becomes more closed, as opposed to more open. This results in too small of a window for your engine to get enough warm up air before the circuit closes the orifice. You can pin open the AAR orifice with a nail or something and then tighten down the nut again (the remove the nail of course). You will probably have to play with it a bit and tweak it, but the goal is to get a bigger orifice opening than you started with. Either that or replace the AAR. I have seen many of these with issues, and they always come up with the same symptoms that you described, and they always respond better when the AFM and AAR are unplugged. Let me know how it goes. I feel good about the AAR diagnosis. Try and swap in a known good one if you can, and before spending money on a new one. The valve needs fixing too, but that is absolutely not your cold start issue. If it was, unplugging the AFM and the AAR would have no effect at all.

Dan - his number 3 intake valve is failing and the engine is close to imploding. The AAR is not the main problem. The number 3 has sunken into the head and is open when the engine is barely warm. He can't even think of tuning or tweaking this bus until he deals with the #3 issue. Go back and read his notes :) When that problem is dealt with then maybe he will need to make other tweaks but for now he has to deal with that issue.

Quote: So my buddy and I checked the valves on number 3 and they were right where I left them at 2 turns past contact. He noticed something odd though about the #3 intake runner, it was burning hot compared to the other 3! Suspecting something fishy we took off the rocker for #3 and #4 The intake valve for #3 sits about 2mm proud of the other 3 valves.

TGOT Mon Nov 07, 2011 11:20 am

He is right about the AAR though. Took it out last night to find it is barely opening. Yes I can blow through but it clamps tight after 2 minutes of battery voltage. I did not realize the AAR could fail to open fully and close prematurely, I only figured it would fail to close completely so thats how I tested it. So at the very least it is contributing to my running issues.

I am not going to run this engine until I give the engine a once over and replace that head so running problems just took a back burner for now.

Once I get it all back together I'll be able to see if the AAR was the culprit. Again at the very least I know mine is malfunctioning thanks to Westfabulous. I also thank you SGKent for suggesting I check the compression at cold which lead me to the valve issue. You started me on a path that will prevent me from a catasrtophic failure.

SGKent Mon Nov 07, 2011 11:28 am

once the head is fixed then you will know whether the AAR is within spec or not. The AAR is supposed to close within about 1 1/2 to 2 minutes. That is by design and even new they don't open all the way. Their sole purpose in life is to let is just enough air to raise the idle when first starting cold. The AAR cannot improve things if one cylinder is dead and affecting the others. That warm runner is probably a sign that burnt gases are running backwards in the manifold. If it backfires it may damage the AFM.

rustbus Mon Nov 07, 2011 7:46 pm

Easy one -

which spacer is newer? (later?)

any purpose for the change between the two?



Westfabulous Mon Nov 07, 2011 8:32 pm

SGKent wrote: Dan - his number 3 intake valve is failing and the engine is close to imploding. The AAR is not the main problem. The number 3 has sunken into the head and is open when the engine is barely warm. He can't even think of tuning or tweaking this bus until he deals with the #3 issue. Go back and read his notes :) When that problem is dealt with then maybe he will need to make other tweaks but for now he has to deal with that issue.

Steve, I am not minimizing the seriousness of the #3 valve, and I don't disagree with you, except for the fact that the two tests that I asked him to do resulted in an excellent running engine for a full 30 minutes, plus the fact that by his own observation, the AAR is barely opening. As you and I have discussed before, and seen before, AAR's are at that age where they are packing it in. If the #3 valve was the sole cold running issue here, then the tests that I asked him to do would not likely have overcome the problem that he was having, although it is possible that by keeping the AAR open, it was feeding in enough air to cover for that which may have been escaping from the sinking valve. I see it this way:

1) He absolutely needs to deal with the #3 valve
2) He shouldn't do anything until that is fixed
3) That his engine probably had performance issues as a result of the #3 valve
4) And that his AAR is probably contributing to his cold start issues, as born out by the tests that I asked him to do, and from his own observations

OP, I agree with Steve, get the head fixed, then go straight to the AAR if you still have cold starting issues . I have never advocated not dealing with the sunken valve, but I do believe that you could have two separate issues at work here. Two minutes to closure on an AAR is not out of line, so you need to look into that a bit. You should have much more than a sliver opening on a cold engine. First thing's first though.

Westfabulous Mon Nov 07, 2011 8:56 pm

rustbus wrote: Easy one -

which spacer is newer? (later?)

any purpose for the change between the two?




I'm not sure that either of those is original. The true, true, true originals actually have a tiny VW logo embossed into them. Just pulled a set recently and I kept them for reference as they had the logo on them. Considering that the purpose of the phenolic block is to prevent heat transfer to the intake runners, I would favor the thick ones.

Amskeptic Tue Nov 15, 2011 8:09 pm

Westfabulous wrote: Considering that the purpose of the phenolic block is to prevent heat transfer to the intake runners, I would favor the thick ones.

I think you would actually favor whichever ones gives a proper fit between the intake runner and plenum.

Some engines are wider/skinnier than others after who knows what machining ..... 8)

Westfabulous Tue Nov 15, 2011 8:37 pm

Amskeptic wrote: Westfabulous wrote: Considering that the purpose of the phenolic block is to prevent heat transfer to the intake runners, I would favor the thick ones.

I think you would actually favor whichever ones gives a proper fit between the intake runner and plenum.

Some engines are wider/skinnier than others after who knows what machining ..... 8)

That's why I said favor (not use) Colin. Good to hear from you again. Are you driving the Bob D or the new beast these days?

SGKent Tue Nov 15, 2011 10:32 pm

I think he is in Dallas about to pull the engine on the 1600 wishing he had the Bob D.

phishfriend Wed Nov 16, 2011 10:44 am

mine is idling at 2500 RPM's. New to FI also so was wondering what causes this?

SGKent Wed Nov 16, 2011 10:47 am

phishfriend wrote: mine is idling at 2500 RPM's. New to FI also so was wondering what causes this?

probably running a little rich and it has an air leak. HOWEVER make sure the throttle body is coming all the way back to the stop and the throttle cable not sticking. Also the mechanical advance in the distributor can be sticking.

busdaddy Wed Nov 16, 2011 10:49 am

phishfriend wrote: mine is idling at 2500 RPM's. New to FI also so was wondering what causes this?
A vacuum leak would be the first suspect, an unlit propane torch or trickling garden hose on all the joints will effect the idle speed when you find a leak. If that fails disconnect components like the decel valve (cap the connections) and see what happens, also try the AAR and brake booster line. Maybe before getting too carried away confirm the throttle cable has a little slack at idle too.

Westfabulous Wed Nov 16, 2011 11:56 am

Check your idle timing; make sure it isn't too advanced. Have you adjusted the throttle body air bypass screw to see what happens?

phishfriend Wed Nov 16, 2011 1:46 pm

Westfabulous wrote: Check your idle timing; make sure it isn't too advanced. Have you adjusted the throttle body air bypass screw to see what happens?

this is so greek to me coming from carburation. where do i find the air bypass screw?

thanks

Brady

SGKent Wed Nov 16, 2011 2:17 pm

phishfriend wrote: Westfabulous wrote: Check your idle timing; make sure it isn't too advanced. Have you adjusted the throttle body air bypass screw to see what happens?

this is so greek to me coming from carburation. where do i find the air bypass screw?

thanks

Brady

Brady - here is something you should look at. There is also a section in the green factory manual. Don't worry if it seems like learning a foreign language at first. http://www.thesamba.com/vw/archives/manuals/afc_fi...Manual.pdf

tootype2crazy Fri Nov 18, 2011 2:35 pm

I finally got the FI working well and does it ever go well. The problem I'm having now is during the warm-up phase. While warming up the idle will slowly descend until it runs really slow and then it will die. I have to hold the gas pedal to keep it from dying. When it does finally warm up it idles fine and won't die. Any thoughts as to what could cause this before I go diving in?



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