Need Help--anyone recognize this engine noise???

[weswsimpson]

Hello,

I'm a new member and have been relying on TheSamba to get my new-to-me 1980 vanagon running after it has sat for an unknown number of years. I have a problem that I am hoping a member might recognize and point me in the right direction.

There's this loud "popping" or "snapping" noise on the top of the engine. It's sounds like a backfire--but in the intake manifold.... When it happens, the needle on the AFM jumps wildly as if air is blowing back thru the air intake.

I've driven around the block a few times, noise seems to go away in the higher RPMs or when "lugging" the engine in the wrong gear, but seems down on power in all gears and throughout the rpm range.

Here's a list of things I've already fixed or tested:
New Tank, filter, fuel pump,
New fuel lines,
Removed, cleaned, and replaced seals on the fuel injectors and tested for correct volume including the starter valve,
changed the oil,
New coil, new spark plugs (gaped), new wires are ordered,
removed oil catch screen and looked for chunks of metal, none,
removed valve covers to look for broken springs, etc. looks new.
Checked for obvious air leaks,
have gone thru many of the tests described in the fuel injection sections of the Bentley and Bosch manuals,
cleaned the Aux Air Regulator, verified it opens and closes,
Checked the timing, adjusted the distributor, noise doesn't go away...

Any thoughts or ideas would be greatly appreciated!

Here's a youtube link to a short video (I hope this works);


Link


Thanks! Wes

[djkeev]

A burned or sticky intake valve would allow comression gases back into the intake.

Wildly ofset timing would do likewise. (Set wrong or firing order is incorrect.)

Dave
_________________
Stop Dead Photo Links how to post photos

Ghia
http://www.thesamba.com/vw/forum/viewtopic.php?t=392473

Vanagon
http://www.thesamba.com/vw/forum/viewtopic.php?p=6315537#6315537

Beetle
https://www.thesamba.com/vw/forum/viewtopic.php?t=482968&highlight=74+super+vert

[Terry Kay]

Get your compression gauge out , and check compression in each hole.
It's metallic, it's got a fix rythem, I'll bet it's a smoked valve or seat.
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T.K.

[weswsimpson]

I did a compression test, here's the results:
#1 145
#2 170
#3 145
#4 135

I'd have thought the numbers would be lower with a burnt valve??

Also, I replaced the dual relay (although with testing I didn't find anything wrong with the old one...)

[djkeev]

They would be, look at firing order and timing.

How does it run? At idle and full throttle?

Dave
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Stop Dead Photo Links how to post photos

Ghia
http://www.thesamba.com/vw/forum/viewtopic.php?t=392473

Vanagon
http://www.thesamba.com/vw/forum/viewtopic.php?p=6315537#6315537

Beetle
https://www.thesamba.com/vw/forum/viewtopic.php?t=482968&highlight=74+super+vert

[weswsimpson]

At first, I thought it was a metallic sound as well... but it seems more erratic after listening to it longer, more like a backfire, but not out of the exhaust. It doesn't speed up or down with the RPMs, it just goes away in the higer RPMs.

[weswsimpson]

I've driven it around the block, it doesn't stall, but it barely makes it... low on power, little power in higher RPMs, barely able to make is up a small hill in Second. The "popping" goes away in higher RPMs or when I lug the engine in a higher gear.

My thought was that because it sat so long, perhaps one or more of the hydraulic lifters is still compressed and the valve timing is off as a result.

Should I keep running the engine in hopes that the problem works it self out (or I break something) or pull the lifters, or do more tests?

Thanks guys for the responses so far!

[djkeev]

Check your firing order and timing settings.

Dave
_________________
Stop Dead Photo Links how to post photos

Ghia
http://www.thesamba.com/vw/forum/viewtopic.php?t=392473

Vanagon
http://www.thesamba.com/vw/forum/viewtopic.php?p=6315537#6315537

Beetle
https://www.thesamba.com/vw/forum/viewtopic.php?t=482968&highlight=74+super+vert

[weswsimpson]

The plug wires starting at approx 5 o'clock on the distributor, looking from the rear, go from the distributor to #1 spark plug, continuing clockwise, 4, 3, 2

The ohm resistance test on the wires, doesn't seem to work, maybe because when the manuals were written they used copper wire???

Timing mark seems to coincide with Ratwell's description of how to find it.

Rotating the distributor forward and back didn't seem to effect the popping.

I've been doing the described tests using the ECU PLUG, but I just noticed that the pins on the ECU don't match-up one-to-one with the plug--are they supposed to??? (Seems like they should!)

[weswsimpson]

pin #20 on the ECU seems to be the only missing pin on the ECU that doesn't correspond with the plug. ECU pin #20 is supposed to go to 86b on the double relay for the Federal model, and checks the Pump circuit.

(but checking the plug doesn't do anything if the corresponding pin on the ECU isn't there.... right?)

[weswsimpson]

Anybody know the correct part number for the ECU from a 1980 Federal (non-California) air-cooled vanagon?

[weswsimpson]

Update:

I've done a leak down test, all cylinders tested perfect. So perfect that I tested the gauge thinking it was broken or not working (it did come from harbor freight after all....) Nope, gauge was fine. So I shot an inspection camera down the spark plug holes, no carbon build up on the cylinder walls--I could still see the honing marks. No carbon on the valves, everything looks brand new.... The valve train and heads looked super clean when I took the valve covers off too... I'm thinking that the heads and cylinders and pistons are all new! (No info provided from P.O. he bought it at an auction.)

I've checked my ECU number (039-906-021b) and that correctly corresponds to an 80 federal manual... the only problem I see is the missing pin on the ECU in the 20 position.... Anyone out there have an '80 that could take a look at their ECU for me?

There was also a sticker on the windshield from an oil change in St. George Utah--anyone out there remember an Ivory ASI Riviera camper? The lack of rust makes sense that it was in a dry climate....

[?Waldo?]

Pop the passenger side valve cover off and have someone else rotate the crank while you watch the rockers. Watch the #1 intake rocker (E-I-I-E). You should see it push the valve and then release it. Just after the valve has been released, pull the dist cap. The rotor should be pointing close to #2 plug wire location. Rotate the crank another 180 degrees-ish and you should be at TDC for the crank and the rotor should be pointing at the #1 plug wire location. Confirming this will tell you if the crank, cam, and distributor are timed correctly together.

[jberger]

Well... something is definitely off. That sounds like valve train to me. Sticking valve, combined with collapsed lifter. Your compression numbers are not perfect, you have one at 170 and another at 130.. yet you say the leak down test was perfect.. perfect..? Did you happen to use the short hose from your compression tester with your leak down tester? The one with the check valve that doesn't allow air into the cylinder? Something is not right. That sounds like a lifter is stuck in its bore (by sticking valve or sticking self) then comes loose and smacks the cam. It is erratic because the release from sticking is not consistent. If that engine sat for years the oil can turn into a waxy sludge that acts just like glue.

[weswsimpson]

Thanks for the ideas. I'll verify the valves with the valve cover off shortly.

In the mean time, here's three photos of the static timing positions of the fan on the crankshaft as it relates to the scale, the position of the distributor drive with the distributor rotor pointed at the number one spark plug (notch in distributor) and the points on the distributor lobe just starting to open.

I used the leak down gauge spark plug adapter and verified that it was working by plugging the end with my thumb, pumping it up with air and releasing. When I said "perfect" I meant that each cylinder held air and didn't leak any in the 30 seconds or so that I had the gauge connected. (Which also makes me think that there's new pistons, rings, cylinders..I visually verified this with the inspection camera... odd.)

[jberger]

I'm not saying you have leak down issue, but even with a perfectly sealed top end, air will leak out.. it's just a matter of how much. Piston rings have end gaps in each of .010-.020" that have to let air through. Even just a few percent of what you are feeding it. Something is suspect, 130-170 range in compression means you can't have perfect leak down.

I have heard similar noises, although very RPM dependent and a bit quieter on high compression Type IV's that were tuned too lean. It could be you have a partially clogged injector, vacuum leaks.. the list goes on and on.

[Howesight]

Like JBerger, I suspect a valve train issue, but from a different source. It may well be a collapsed lifter causing the running problem, but since the van sat for so long, I suspect that old gasoline sprayed on the intake valve stems caused varnish to form on the intake valve stems.

Old gas forms varnish compounds. These compounds are quite literally as sticky as Krazy Glue. The Type 4 engine (like all the flat 4 VW's) has rather low valve spring seat pressure and as a result, varnish can keep the intake valves from completely closing. This allows burning mixture on the power stroke to be forced into the intake manifold. Remember that the AFC EFI system injectors are batch-fired instead of sequentially-fired (ie: all injectors spray at the same time, not on the individual cylinders' intake strokes), so an ignition source in the intake manifold can spread to other intake elbows. The funny sound is likely due to the timing of the ignition source and proximity to an adjacent intake elbow full of gasoline.

At higher engine speeds, the inertia of the valve train can assist a sticky intake valve to close. Similarly, at high loads, (eg full throttle), cylinder pressure can assist in closing the sticky valve or valves. This may explain why the popping lessens under a lugging load.

There are a number of home remedies for clearing varnish off intake valve stems. On the AFC Type 4, gaining access to the valve stems is a nightmare, so it might be best to use a brutal but effective approach: Get a gallon (or two!) of Toluene at Home Depot or a paint store and run it through your fuel system. Drain all your gasoline first and run the toluene directly through your tank. You will need to place a load on the engine to get a strong spray of toluene on the valve stems. Using a quality fuel injector cleaner like Techron is also advisable.

Toluene is an aromatic hydrocarbon that used to be used in high-octane gasolines, especially in WW2 Avgas. It is still a component in many premium gasolines, but it can be sold at higher prices in the chemical market, which is why it is no longer used in pump gas. It is found in large fractions in unleaded racing gasoline. So, it should not harm your fuel system. I have used it frequently on "dyno day" when testing new tunes on turbocharged engines to prevent the knock control system from backing off spark timing, which is how I know it will not damage anything in your engine. A simple $20 per gallon fix, if it works on your engine.

One last thought: You may have a cracked distributor cap. The popping effect can also be caused by this.
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'86 Syncro Westy SVX

[?Waldo?]

Do you know why the van was parked 'an unknown number of years' ago?

While I appreciate the pics of the crank mark and distributor gear, it doesn't tell the whole timing picture. The cam could have been installed meshed to the crank incorrectly. That could have been the reason it was parked and sat. Maybe the distributor drive is installed 180° out... e.g. TDC for #3 rather than #1. Would it run like that? A diesel will, it will just run poorly.

[weswsimpson]

Thanks for all the suggestions.

Regarding the leak down test.... the only thing I can surmise is that the leak down test is operating at 15psi, the compression test is 150psi, therefor the leak down test was slower to respond and kept the pressure up at the lower psi? I only watched it for 15-30 seconds, I was looking for a major leak. I performed the leak down test, following the distributor around 1,4,3,2 and in each instance got good pressure, so i don't think I was off 180 degrees.

I stuck my inspection camera down the #1 spark plug hole and watched the valves open and close, just after the intake valve opened and then closed as I continued to push the car forward in 4th gear, the top of the piston became visible--at this point I would be near TDC and the distributor rotor was pointed near the notch where the #1 spark plug wire would be attached to the cap. So I think we're good there?

(By the way, how are you all rotating the engine? I'm just pushing it forward and back in 4th gear as there doesn't seem to be an easy way to get a handle on it...)

No idea why it was parked, but if it acted like it did in my video I wouldn't have driven it either. It doesn't look like there were that many miles on it since it was rebuilt, so my guess the owner got discouraged at that point and got rid of it....

Regarding the issue of varnish, watching the number one cylinder, the valves opened and closed easily and equally. And based on the leak down test it seems they are closing fully. I will check the others with the camera and verify.

I tested the volume pumped-out by the fuel injectors for 30 seconds, they all were in range according to the manual.

I put test lights inline with the spark plug wires and they all lit up, at least near the distributor....

I wouldn't be surprised if there was a stuck lifter. So I'm thinking of adjusting the valves to zero or .006 and running it a bit to see if I can pump up the lifters. Any thoughts? Thanks again guys!

[?Waldo?]