'78 Westy idles great, stalls and backfires under load.

Jivermo · Post by **Jivermo** » Sun Dec 30, 2012 5:03 pm

I'm having a troubling time with my recently acquired bus. When I take off, in 1st, she begins to run up, then she stalls, maybe backfires, and loses power. I'll stop and the idle returns OK, or the engine may quit. However, it starts right up again, and will idle me home at low speed. Engine is tuned to specs, valves adjusted, new fuel filter, all new fuel lines replaced and new vacuum lines routed correctly. No kinks in fuel line. I made up a pressure gauge from a new Home Depot gauge, and the fuel pressure measures only about 18. When I take the vacuum line off the pressure regulator and block it, the reading goes up to 25. According to Bentley's, these readings are way low. I don't want to do the random bit and start ordering a bunch of new parts, unless it's pretty certain that something is defective. I've also cleaned the electrical connections on the fuel pump and made certain they are on tight. Any other suggestions as to what I might check?

SlowLane · Post by **SlowLane** » Sun Dec 30, 2012 6:58 pm

Well, you clearly know your way around a bus's engine compartment.

Those pressures, if accurate, are low. How much do you trust the gauge? Personally, I'd check those pressures again with a gauge that is either calibrated or known to show correct readings on a well-running vehicle.

Reason I'm skeptical is that your FPR appears to be doing it's job by varying the pressure proportionally to the manifold vacuum, which suggests that the FPR diaphragm is fine. If the reading is correct, that means that either the fuel pump isn't providing enough pressure or the FPR spring is weaker than it's supposed to be.

Fuel pump failures tend to be all or nothing. FPR springs generally don't weaken with time. I'd get a second gauge's opinion before spending money on a new fuel pump or FPR.

deschutestrout · Post by **deschutestrout** » Sun Dec 30, 2012 7:38 pm

Likely unrelated to your issue ... but noticed you said "valves adjusted". You're aware that if it's a stock 2l the values have hydraulic lifters and are adjusted to zero lash? Just checkin'! Good luck and keep us in the loop what your issue ends up to be.

Jivermo · Post by **Jivermo** » Sun Dec 30, 2012 7:50 pm

Thank you for the response. I'm going to get another gauge and check it again, as I was thinking along those lines, too. I have mixed feelings about not trusting measurement tools...seems like wishful thinking. Live and learn. Valves were adjusted as per Ratwells's hydraulic guidelines, so I think they are OK. Compression is good.

Jivermo · Post by **Jivermo** » Mon Dec 31, 2012 8:38 am

Got a new gauge, and it measures 30psi. With vacuum hose off regulator, and blocked, it jumps up to 38. So, any ideas of where to look next?

Post by **Amskeptic** » Mon Dec 31, 2012 9:09 am

Jivermo wrote:Got a new gauge, and it measures 30psi. With vacuum hose off regulator, and blocked, it jumps up to 38. So, any ideas of where to look next?

Yes.

You will master this situation if you can replicate symptoms at will.

Engine misbehaves when you ask it to do actual work, yaah?

Therefore, you need to read this gauge when the engine is actually misbehaving.

Get thee a competent and caring test driver. Make a code word for "give it a rest" so your driver does not abuse the car. "Cut!" or something, means push in the clutch and release the accelerator.

Kneel in the back seat with the access lid off so you can see the gauge.

If the pressure drops under load and heralds the arrival of your symptoms, then an obstruction is your likely culprit, somewhere from the tank to the filter. p.s. you have the correct filter with the big diameter hose between the filter and the pump?

If no pressure change is observed, are you comfortable with accessing the little wiper in the AFM black box and giving it no more than a 1/4" nudge in either direction to see if you can make the symptoms diminish?

Will this engine give you any decent pull cold/warm? or is it playing totally balky donkey?
Colin

Post by **Amskeptic** » Mon Dec 31, 2012 9:14 am

deschutestrout wrote:Likely unrelated to your issue ... but noticed you said "valves adjusted". You're aware that if it's a stock 2l the values have hydraulic lifters and are adjusted to zero lash? Just checkin'! Good luck and keep us in the loop what your issue ends up to be.

That would be "0" + 1 1/2 turns "preload" for stock hydraulic lifters.

Raby Engines with chrome moly pushrods are adjusted to "0".

Technical Forum Auditor

Jivermo · Post by **Jivermo** » Mon Dec 31, 2012 9:37 am

Right. Going to do the under load test, Colin, and also recheck all of the valve adjustments. I like the idea of "mastery of the situation". Poetic wrenching...that is where it's at!

Jivermo · Post by **Jivermo** » Mon Dec 31, 2012 3:11 pm

Got my son in law in the back to be the gauge reader, and went for a spin. Of course, the bus ran like a top! He reported readings of between 25-35psi, with the pressure going up with acceleration and falling accordingly. Cruising along it was right at 30. This is disconcerting, as I am hesitant to take it for a road trip until I have achieved mastery. Tomorrow, I'll recheck the valves-they are a bit chattery, but the bus has been sitting for the most part and no doubt the oil has eased out of the lifters. It has been my experience in the past that electrical parts fail-period. Might it be electrical related-coil perhaps? Debris in the fuel line may be the culprit here, though. I did visually inspect the tank when I redid all the fuel lines (I emptied the tank out, and looked in with a flashlight.) the tank looked to be very clean and with little evident rust or crud. Fuel filter is new, and correct. I blew out all the metal lines with compressed air when I did the line work. Frustrating stuff. Well, Happy New Year to all you VW aficionados!

SlowLane · Post by **SlowLane** » Mon Dec 31, 2012 4:04 pm

Hydraulic lifters can take awhile to pump up, especially after a long hiatus. There always seems to be one that stubbornly refuses to pump up until you're almost at the point of pulling it out for a manual bleed. Recheck the valve clearance, making note of any loosening/tightening trends, then be patient.

If this bus has sat for awhile, and you are suspicious of the fuel cleanliness, consider replacing the fuel filter a few times over the course of a short period, just to catch as much of the suspected crap as you can. Because the L-Jet system continually re-circulates fuel through the fuel ring, quite a lot of volume gets passed through that filter, even when you're just idling. A few sacrificial filters is a small price to pay for peace of mind. You could even jury-rig a loop of fuel hose from the pump outlet to the tank return pipe and run the pump from an external 12V source so that you don't have to run the engine just to filter the fuel.

Of course, if you really want to do the job justice, there's Ratwell's very detailed fuel tank refresh procedure.

Oh, yeah. If you have water in your fuel, Mr. Funnel really does work.

Post by **Amskeptic** » Tue Jan 01, 2013 6:50 pm

Jivermo wrote:Got my son in law in the back to be the gauge reader, and went for a spin. Of course, the bus ran like a top!
Fuel filter is new, and correct. I blew out all the metal lines with compressed air when I did the line work. Frustrating stuff. Well, Happy New Year to all you VW aficionados!

In moments like that, you extend your test-drive just so that you and bus can build up some trust between you.

There are so many possible causes of misbehavior, that sometimes you just have to forge on ahead and not disrupt the improving karma.

a) spiderweb on points burned off
b) voltage regulator contacts woke up and gave you additional running voltage
c) bad ground went good
d) worked crap gas out of injector bodies
e) cleaned spark plug electrodes when heated up
f) water in gas from lousy local station delivery

Keep driving. Keep in mind the car owes you nothing yet.
Colin

Jivermo · Post by **Jivermo** » Tue Jan 08, 2013 4:29 pm

Well, the karma improved, as I drove. The 2L is running like the old Swiss watch. I don't know what caused the problem; bad gas, sludge in fuel line...who knows? I guess I just drove the problem away. Thanks for all the help.

Jivermo · Post by **Jivermo** » Tue Jan 15, 2013 5:58 am

The good running lasted about 25 miles or so, and then the problem presented itself again. At about 3800RPM, under load, it starts to backfire and stall. I took it over to an oldtime VW mechanic who is still cranking here in Miami, and he drove it around a bit. He suggested that the exhaust system is obstructed-the catalytic converter. Since we have no emission inspection here, I want to replace the system, which has some leaks anyhow. Any recommendations as to the direction to take here?

Westy78 · Post by **Westy78** » Tue Jan 15, 2013 7:35 am

Depending on the extent of work and money you want to spend I would suggest reverting to the '72-'74 exhaust system with an extractor. It's a much more simple set up. That involves new heat exchangers however.

Jivermo · Post by **Jivermo** » Tue Jan 15, 2013 9:05 am

I don't see any catalytic converter here at all. What is inside the heater boxes? In a system like this, where would there likely be a blockage-if there is indeed one? Exhaust system work is at the far bottom of what I like to do on my bus...

https://picasaweb.google.com/1013662011 ... uary152013

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'78 Westy idles great, stalls and backfires under load.

'78 Westy idles great, stalls and backfires under load.

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Re: '78 Westy idles great, stalls and backfires under load.

Re: '78 Westy idles great, stalls and backfires under load.