Vanagon running rich, update again on mis-fire

We have had a problem with our 81 air-cooled Vanagon where the spark plugs get fouled (turn sooty black-not oily) and the engine starts mis-firing. If you clean up the plugs the engine starts and runs fine for about 5 minutes, then you will heat a faint tick which gets louder as the engine gets warmer. If you pull the plugs at this point they will be sooty black again (cylinder 2 & 4 more so than 1 &3 for whatever that is worth.)

So far I have replaced the cylinder head temp sensor, oxygen sensor, fuel filter, rotor cap and wires, as well as the injectors.

I have checked and found to be okay or within spec: intake airflow and ambient air sensors;

-Cold start valve

-Thermo time switch

-Coil

-Rotor

-All of the Hall effect gadgets

The fuel pressure is a little on the high side (31 psi). Is that still within the acceptable range? I checked the return fuel line and it appears okay and swapped out pressure regulators but have maintained the 31 psi reading.

I'm running out of ideas on items to check. Does anybody have any further ideas or insights?

Reply to
Bumbletown
Loading thread data ...

Cold start absolutely/positively not leaking?? Maybe even block off the fuel line to it.

How did you determine that the air flow sensor was within spec? The crude resistance values give in the manual are not of much value.

Since you've already replaced the other things that control mixture, I'd be very tempted to alter the airflow calibration as an experiment. Take cover off and note where the adjustment of the arm is set (scribe). Engine idling, manually move the arm toward the "Off" position. If you can move it quite a bit before the thing dies, it's an indication that the signal is way too rich. Loosen the set screw and move the arm about that much. Try running it.

I realize that adjustments like this may be merely masking the real problem, but it seems justified in light of all you've done.

Speedy Jim

formatting link

Reply to
Speedy Jim

Where are you located? I think your 81 uses the digifant controler. Check your local ACVW club for members using VAG COM. You can get a complete computer diagnostic of your digifant system. George

Reply to
George

head temp sensor

John Aircooled.Net Inc.

Reply to
John Connolly

ROFLMAO ! Succinct as always.

Although Bumble *did* replace the sensor, these sure are the symptoms one would expect from an open sensor.

Aside from replacing again, or measuring the sensor resistance, it might be worthwhile wiring in a 5K pot as a "manual" sensor. Often that trick can shed some lignt.

Speedy Jim

formatting link

Reply to
Speedy Jim

I had a van that drove me nuts. New sender wasn't grounded into the head, due to a PO "repair" of JB weld on the threads (non-conductive). Took a while to figure that one out

if it has an O2 sensor that's also a prime suspect

John Aircooled.Net Inc.

Reply to
John Connolly

PS: I do not see where he checked/changed the head temp sensor.

John Aircooled.Net Inc.

Reply to
John Connolly

Speedy Jim- I followed the procedure outlined in Bentley to determine that the cold-start valve is not leaking....remove the electrical connector, remove valve from intake manifold but leave it connector to fuel ring, take wire to distributor off of coil, crank the engine and check for leaks. Did this for roughly 10-15 seconds and didn't see any drips or leaks. Can check it again for longer tonight as I didn't re-install it.

I guess that if the resistance values for the airflow sensor are not of much value then I cannot say that is is good since this is what I checked. Is there an alternate method to verify it's proper function?

I'll try the airflow calibration experiment tonight.

Thanks for the insight. marc

Reply to
milo

OK. Sounds like you have the cold start covered. Before you dive into the airflow, recheck the head sensor resistance. Check it cold- about 2500 Ohms. Then check again after the engine has warmed up- about 100 Ohms.

If you can finbd a ~5K Pot, wire it in place of the sensor and see what effect it has after the engine warms up. As John C suggests, it does have a huge effect on mixture.

Then see what the airflow cal will do. It could be a red-herring though.

Jim

Reply to
Speedy Jim

..............Hey John, I used JBWeld on the threads of an O2 sensor once and it melted...........lol

Reply to
Tim Rogers

All-

Thanks for all of the advise.....a couple of points to clarify:

I have replaced the cylinder head temp sensor....did not add any anti-seize and made sure that there was no corrosion on the head.

I have also replaced the Oxygen sensor....it came with the anti-seize which was pre-applied to the threads by Bosch.

Last night I took the cold start valve out (to check this one more time), taped the hole shut, and started the old girl again....the valve doesn't leak. She started fine and seemed to be running really well. After 5 minutes gave her some additional throttle as she still seemed to be working okay. Somewhere between 10-15 minutes in, the idle started to oscillate, increasing and then decreasing to an almost stall (this is a new condition by the way)...it did this a few times so I gave some more gas.....the surging stopped but when I let my foot off the gas the ticking started again. Shut her down in disgust, pulled the plugs and found cylinder 2 plug to be completely black (the others were nice and golden.)

I'll mess around with the cylinder head temp sensor some more today and try to get a 5K pot to force resistance changes....everyone still seems to be pointing in that direction.

Thanks. marc

Reply to
milo

Hmmmmmmmmmm. Why only #2 plug??

Suspicious.

Any chance the ticking could be coming from #2 injector as it starts to fail open?

Speedy Jim

formatting link

Reply to
Speedy Jim

Speedy Jim-

Your guess is as good as mine as to why only cylinder #2 was fouled. However, the last time around it happened to be cylinder #4. It has never been #1 or #3....they are always clean.

I don't think the ticking is coming from the injector. Can't really locate it but it doesn't seem to be coming from there. Once it starts ticking, if I open up the throttle it (the ticking) get's really loud. Almost to a clang?!?

marc

Reply to
milo

check the rubber orings that seat the fuel injectors to the intake manifold. if they leak air, they may be throwing off your entire fuel injection brain calulations.. if they have been lekaing ari a long time.. casuing engine to run lean.. well, you may have bigger problems.. like cracked heads.. leaky seats, etc..

just guess> All-

Reply to
hyubso

click may be hydraulic valve lifters leaking oil and not becoming solid when compressed.,..

just guessing..

milo wrote:

Reply to
hyubso

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.