1981 Vanagon backfire through intake

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energyturtle
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1981 Vanagon backfire through intake

Post by energyturtle » Wed Jun 29, 2016 5:27 pm

Here is the run down. As much as it pains me to ask for help, I am at a my limit with patience. The Vanagon was running great. I had logged about 50 miles. This is the longest this Vanagon has driven since 2013. I started it the next day, went for a drive and it started bucking, and starving for fuel under heavy throttle. I had just replaced the fuel filter a day before, so I stupidly eliminated that as a possibility and started "messing" with everything. I have since verified fuel delivery, point gap, static timing, vacuum leaks?, Valve adjustment, plugs, wires, rotor, cap, coil, and everything else I could think of. Here is where were at now. The engine will start and idle. It will not rev up without hiccups and breaking up, it backfires through the intake on all cylinders. I have checked all connections, swapped out the AFM with a known good one that still has the glue intact, went back through the ignition, valve train, fuel, air, and vacuum systems. I have no idea how to proceed from this point. Please help. The specs are Aircooled 2.0, hydraulic lifter, point and condenser, fuel injection, bone stock.
Scottie

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energyturtle
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Re: 1981 Vanagon backfire through intake

Post by energyturtle » Wed Jun 29, 2016 7:55 pm

Here's some additional info. My last valve adjustment was performed with the engine stone cold and dry lifters. I ran them into 1 1/2 turns past 0 lash. My theory is as follows: The lifters being bone dry, could compressing the plunger cause a valve to not close all the way or not open fully once it is filled with oil, resulting in poor ignition of the cylinders causing back flow through the partially closed intake valve? It does not backfire through the exhaust, only the intake.

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Amskeptic
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Re: 1981 Vanagon backfire through intake

Post by Amskeptic » Thu Jun 30, 2016 6:21 am

energyturtle wrote:Here's some additional info. My last valve adjustment was performed with the engine stone cold and dry lifters. I ran them into 1 1/2 turns past 0 lash. My theory is as follows: The lifters being bone dry, could compressing the plunger cause a valve to not close all the way or not open fully once it is filled with oil, resulting in poor ignition of the cylinders causing back flow through the partially closed intake valve? It does not backfire through the exhaust, only the intake.
Firing Order 4-3-2-1.

(experiment only specifications below)

Adjust valves to "0"

Check plug wires for contact, light powdery look is often cross-fire point, inside cap for carbon tracing

Retard timing to "0".

Cessation of intake backfires?
Colin
BobD - 1978 Bus . . . . . . . . . . . 111,155 miles
Chloe - 1970 bus . . . . . . . . . . . 206,820 miles
Naranja - 1977 Westfalia . . . . . 108,000 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,885 miles

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energyturtle
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Re: 1981 Vanagon backfire through intake

Post by energyturtle » Thu Jun 30, 2016 12:42 pm

4-3-2-1?........1-4-3-2?

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asiab3
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Re: 1981 Vanagon backfire through intake

Post by asiab3 » Thu Jun 30, 2016 12:46 pm

energyturtle wrote:4-3-2-1?........1-4-3-2?
1 - 4 - 3 - 2 - 1 - 4 - 3 - 2 - 1 - 4 - 3 - 2 - etc....

1 - 4 - 3 - 2 - 1 - 4 - 3 - 2 - 1 - 4 - 3 - 2 - etc....

:drunken:
Robbie
1969 bus, "Buddy."
119k miles with me.
296k miles on Earth.

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energyturtle
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Re: 1981 Vanagon backfire through intake

Post by energyturtle » Thu Jun 30, 2016 1:16 pm

Valves are at 0. Static time 0=no start.

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SlowLane
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Re: 1981 Vanagon backfire through intake

Post by SlowLane » Thu Jun 30, 2016 1:31 pm

Suggestions:
  • Double-check that you have the ignition wires not only in the correct order, but in the correct phase (ie. make sure that #1 is actually firing when #1 cylinder is at TDC of the compression stroke)
  • Check your AFM harness connector to make sure that one of the plug connectors hasn't slipped into the housing, thus failing to make contact with the AFM connector pin.
'81 Canadian Westfalia (2.0L, manual), now Californiated

"They say a little knowledge is a dangerous thing, but it is not one half so bad as a lot of ignorance."
- Terry Pratchett

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energyturtle
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Re: 1981 Vanagon backfire through intake

Post by energyturtle » Thu Jun 30, 2016 1:32 pm

I static timed again at 7.5 BTDC. Its flooded badly. Plugs are out now. Cylinders will air dry overnight, I shall commence at 1:30 PM tomorrow after work. Patience are thin at best. Its hitting a lick, but no vroom.
Scottie

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Re: 1981 Vanagon backfire through intake

Post by asiab3 » Thu Jun 30, 2016 2:18 pm

Ok, riddle us this:

When backfiring through the intake, L-Jet has several hoses that should not be clamped. From the factory, I considered these "blow off" hoses that would separate themselves from their connections in the event of a high pressure intake backfire. When I had a valve adjusting nut back off and close off the exhaust valve, nearly every fuel injection hose in the engine compartment moved. Several blew off to the point of creating catastrophic vacuum leaks that lead to a no-start. In this no-start, the exhaust smelled horribly rich and the plugs were wet. BUT!! Do you know why it wasn't starting? Vacuum leak creating a LEAN condition that masked itself as a RICH condition. So don't assume you are too rich to start- just assume that your fuel isn't combusting for now.

At this point, you'll need to figure out if you actually are rich or lean. If you pop the cover off your AFM, you can nudge the vane clockwise (making it leaner) or counter-clockwise, (making it richer,) to see what the engine wants. If it picks up RPM and "likes" the motion you made, you have a path to follow. If it doens't change much, then you can start looking for a spark solution. Do this at idle and under a throttling attempt in neutral.

Also, look for the easy stuff, like an AFM that came unplugged. If it did, it's possible it will idle, albeit extremely rich, and it will not rev up.

Let us know how it goes!
Robbie
1969 bus, "Buddy."
119k miles with me.
296k miles on Earth.

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energyturtle
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Re: 1981 Vanagon backfire through intake

Post by energyturtle » Thu Jun 30, 2016 5:31 pm

I have EVERY vacuum line taped, clamped etc., To close off the vacuum system from leaks. After I let Everything air dry overnight from 20 minutes of failed starting attempts, I will revisit tomorrow afternoon. While the engine was running previously, I pulled the AFM cover and the wiper was dancing critically sporadic. This engine had already been tuned prior to this event. My question to myself is WTF happened? For all practical theories, everything being equal, this engine "should run". The systems are intact and functional to the best of my knowledge. I just don't get it. Where is this gremlin hiding?
Scottie

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Re: 1981 Vanagon backfire through intake

Post by asiab3 » Thu Jun 30, 2016 7:35 pm

Ok, I wish Colin would continue on his diagnostic path here, but I understand he has a few Volkswagens on his plate right now…

In the mean time,ow me to continue to virtually sleuth around your engine…

Backfiring through the intake happens when combustion occurs with the intake valve open. Under this case, we can run a few tests to see what is happening. Basically two scenarios can present: First, the combustion could be happening at the wrong time. This can be caused by ignition timing, or poooosssibblllyyyy something else "creating" a spark in the combustion chamber setting off your fuel mixture. L-Jet injectors fire as a set of four simultaneously. and later Motronic injectors fire as banks of two. So either injection system has fuel in the intake on non-intake strokes. Second, could be the intake valve opening at the wrong time.

I will use my crystal ball to look into your engine and play "magical guesser." I guess that because all four cylinders are backfiring, you do NOT have situation #2 above. If all four of your intake valves started opening at inopportune times, your car would not idle. Since it does, let us assume, for now, that your valves are opening at the correct time.

This leaves us with situation #1. Something could be lighting off an air-fuel mixture at the wrong time. I would like to perform "cold engine idiot checks," but I am not there in person. You have several air-cooled Volkswagens with decent road memories, so I will assume you are not an idiot either. But that's what they are called, because, well, weirder things have happened.

- See if your distributor body can turn by hand.
- Make sure your rotor is snapping back and not wandering around when you twist it a tiny bit clockwise and release. It should be consistent and authoritative.
- Make sure your plug wires are oriented correctly. Got any friends that like pranks?
- Make sure your AFM is plugged in……

I look forward to hearing about your most recent exploits. Thank you for reading my verbosity.
Robbie
1969 bus, "Buddy."
119k miles with me.
296k miles on Earth.

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energyturtle
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Re: 1981 Vanagon backfire through intake

Post by energyturtle » Fri Jul 01, 2016 1:57 am

I have a thought. I've become very consistent with valve adjustment. By consistent, I mean each valve I adjust is "equal". The camshaft spins 2 rotations for every 1 off the crankshaft. When I get home today I will do the old screwdriver in the cylinder test on #1, to ensure I am at TDC on the compression stroke. Quite possibly i may have fouled the valve adjustment when returning the valves the 0 lash. I may have been correct on the prior adjustment and by turning the valve adjuster 1 1/2 turns past 0 lash to preload the lifter while it was dry, I quite possibly could have each intake valve not being able to fully close? Just a thought. I'll run through it again at 1:30 PM.
Scottie

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asiab3
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Re: 1981 Vanagon backfire through intake

Post by asiab3 » Fri Jul 01, 2016 7:17 am

Good thinking! Yes, if you are insensitive with your hydraulic lifter adjustment, you may actually be contacting "0 lash" without realizing it. Then when you "feel resistance" that could actually be the hydraulic lifter piston bottoming out, then your 1.5 turns is actually opening the valves that much. This would explain your issues, but let's not let good ideas get in the way of proper sleuthing! 8)

Robbie
1969 bus, "Buddy."
119k miles with me.
296k miles on Earth.

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SlowLane
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Re: 1981 Vanagon backfire through intake

Post by SlowLane » Fri Jul 01, 2016 8:45 am

energyturtle wrote:The camshaft spins 2 rotations for every 1 of the crankshaft.
Nope. Other way 'round. 360 degrees camshaft = 720 degrees crankshaft.
energyturtle wrote:When I get home today I will do the old screwdriver in the cylinder test on #1, to ensure I am at TDC on the compression stroke.
Good idea. Start from fundamentals. Try a plastic straw, or tail end of a zip tie instead of a screwdriver, just to avoid scratching or denting anything in the combustion chamber.

Also, if you have the tools, it might be a good idea to do compression and/or leak-down tests on your cylinders (once you have the valves and ignition adjusted to your satisfaction).

Personally, I find zero-lash on my adjusters by turning the screw with my fingers. The transition from free-turning to valve contact is quite noticeable. Even with fully empty lifters, it's quite hard to finger-turn the screw against the force exerted by the spring in the lifter.
'81 Canadian Westfalia (2.0L, manual), now Californiated

"They say a little knowledge is a dangerous thing, but it is not one half so bad as a lot of ignorance."
- Terry Pratchett

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Re: 1981 Vanagon backfire through intake

Post by energyturtle » Sat Jul 02, 2016 4:37 am

Last night resulted in another no start. I performed a valve adjustment, static timed, again, and no start. Performed a compression test. Results were 125-130 psi on all 4 dry. I checked the spark at the coil wire, it was 1/2 and inch long to ground and solid whit like lightning. The spark from the distributor to spark plug is barely red, very weak. My goal for today is to get the spark good and strong. I'll poll the results this afternoon.
Scottie

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