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Vanagon starts, warms up great, then (invariably) dies
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Merrymeeting Van
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PostPosted: Tue May 04, 2021 6:13 pm    Post subject: Vanagon starts, warms up great, then (invariably) dies Reply with quote

My 88 Vanagon started perfectly after a winter of storage, idled perfectly till it started to warm up (just about when the temp needle starts to move), then over a minute or so idles slower and slower till it stalls completely. As it starts to stall, it no longer responds to opening the throttle either (before, it's completely normal). If I try to drive it, it behaves the same - runs for about a block, then quickly sputters, goes slower and slower, and dies.

Replaced the fuel filter (just in case), temp 2 sensor (no difference), switched ECUs (I have a spare), also no difference. Sparks aren't affected as it sputters.

If I unplug the temp 2 sensor, it continues to run, semi-normally; but won't re-start unless I plug the sensor back in.

Help, please! I live a long way from the nearest Vanagon mechanic Wink
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4Gears4Tires
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PostPosted: Tue May 04, 2021 8:07 pm    Post subject: Re: Vanagon starts, warms up great, then (invariably) dies Reply with quote

Was the replaced temp2 sensor new? Tested it? Pinch vacuum line for FPR when it starts to die then rev, any difference? What did the spark plugs look like? Black?
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Last edited by 4Gears4Tires on Tue May 04, 2021 8:11 pm; edited 2 times in total
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Wildthings
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PostPosted: Tue May 04, 2021 8:11 pm    Post subject: Re: Vanagon starts, warms up great, then (invariably) dies Reply with quote

Buy some Techron "Ethanol" Fuel Injection cleaner and add the recommended amount to your gas. If you have a tank full of gelled ethanol laced fuel it may help a bit, but you may want to drain and clean the tank.

If it is sour fuel and you want to try to run with it, try adding a pint of synthetic oil to a full tank of gas to help lubricate your valve stems to keep the valves from freezing up and having a nasty meeting with your pistons.
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PostPosted: Tue May 04, 2021 8:25 pm    Post subject: Re: Vanagon starts, warms up great, then (invariably) dies Reply with quote

Unplug the O2 sensor and see if it still runs poorly after it warms up. If so, that would rule out a bad O2 sensor.
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campism
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PostPosted: Wed May 05, 2021 4:55 am    Post subject: Re: Vanagon starts, warms up great, then (invariably) dies Reply with quote

On my van, testing with the oxygen sensor unplugged showed that it ran better when warmed up, but be forewarned that replacing the old sensor might be a challenge.
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PostPosted: Wed May 05, 2021 8:28 am    Post subject: Re: Vanagon starts, warms up great, then (invariably) dies Reply with quote

Testing without the oxygen sensor will tell you what the engine is actually doing. The oxygen sensor by it's nature is trying to "hide" a problem. If the tune is out of range, the sensor looses the tug of war.
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Merrymeeting Van
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PostPosted: Thu May 06, 2021 5:02 am    Post subject: Re: Vanagon starts, warms up great, then (invariably) dies Reply with quote

Bingo - unplugged the O2 sensor and it works fine. I always thought O2 sensor problems would make it run too rich, and it was clearly fuel-starved, but that's what happened. New one ordered, we'll see how much fun it is getting the old one out.
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PostPosted: Thu May 06, 2021 6:00 am    Post subject: Re: Vanagon starts, warms up great, then (invariably) dies Reply with quote

Not so fast. The oxygen sensor may be fine. You could have a mixture problem in one cylinder that the sensor is trying to compensate for. The sensor takes an average of all 4 cylinders. So one lean cylinder could cause it to over fuel. Or 1 rich cylinder could cause the other cylinders to be leaned out.
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PostPosted: Thu May 06, 2021 8:32 am    Post subject: Re: Vanagon starts, warms up great, then (invariably) dies Reply with quote

MarkWard wrote:
Not so fast. The oxygen sensor may be fine. You could have a mixture problem in one cylinder that the sensor is trying to compensate for. The sensor takes an average of all 4 cylinders. So one lean cylinder could cause it to over fuel. Or 1 rich cylinder could cause the other cylinders to be leaned out.


Mark, what do you think a good next step would be? Inspect the plugs?

I like these diagnostics threads. I'm good at the wrenching aspects of van ownership but the diagnostics is an art I'm constantly trying to learn.
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PostPosted: Thu May 06, 2021 9:06 am    Post subject: Re: Vanagon starts, warms up great, then (invariably) dies Reply with quote

Do you know the age of the oxygen sensor? Is it the correct one with the factory connectors or did someone install a universal one? 60,000 miles on a decent running engine would be the expected life time of the oxygen sensor.

In other words, if you aren't sure, a new sensor would be a good place to start. If after replacing the sensor you have the same drivability problem, then you can dig further in.

I guess I just wanted to say, a new sensor may or may not fix the problem.
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PostPosted: Thu May 06, 2021 9:24 am    Post subject: Re: Vanagon starts, warms up great, then (invariably) dies Reply with quote

I might be mis-remembering, but my kids were doing something with their bus and forgot to plug the AFM back in, and it acted that way.. Been 3+ years on that memory though..
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PostPosted: Thu May 06, 2021 9:47 am    Post subject: Re: Vanagon starts, warms up great, then (invariably) dies Reply with quote

Merrymeeting Van wrote:
Bingo - unplugged the O2 sensor and it works fine. I always thought O2 sensor problems would make it run too rich, and it was clearly fuel-starved, but that's what happened. New one ordered, we'll see how much fun it is getting the old one out.


If you get a change when you unplug the sensor then the sensor is working, at least somewhat, but maybe perfectly. If one cylinder if off from the others the O2 sensor can not correct that one sensor by itself, instead it will make the same proportional change to the fuel going to all the cylinders. With the O2 sensor trying to balance the mixture out, a very rich running cylinder could still end up somewhat rich, while the other three would all be too lean, or vice versa.
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Merrymeeting Van
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PostPosted: Tue May 18, 2021 8:59 am    Post subject: Re: Vanagon starts, warms up great, then (invariably) dies Reply with quote

Thanks for all the tips! New O2 sensor (and new catalyst to put it in) fixed everything - almost. Now the van starts, idles and runs perfectly, cold or warm, very smoothly with no hint of missing or bucking or anything else... except it runs out of power at about 2600-3000 rpm. It runs and feels perfectly normal till that point, and it's a little bit load-dependent: you don't notice anything at all in 1st gear, seems to run into the "wall of marshmallows" at about 3000-3200 in 2nd, 2700-2800 in 3rd, and more like 2500-2700 in 4th. Won't go more than 55 mph or so on level ground in 4th, but will run up to any rpm you like in neutral, or downhill. Seems to be getting normal fuel mileage; no black smoke or anything.

New o2 sensor, new coolant temp sensor, new fuel filter, grounds checked and cleaned, swapped ECUs (have a spare) which made no difference, no gasoline running out of the pressure regulator, check valve works, checked for vacuum leaks and can't find any. Air flow sensor moves with no interference, has normal resistance when closed (500 ohms) and varies with motion, as much as I can test with only two hands! TPS switches both work and seem adjusted.

What do I check next??? Wink
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PostPosted: Tue May 18, 2021 9:08 am    Post subject: Re: Vanagon starts, warms up great, then (invariably) dies Reply with quote

Sounds like a clogged fuel filter or a failing fuel pump. Put a 0-60 psi gauge on the test nipple on the fuel rail with enough hose that someone in the back seat can hold it and watch it while you drive up a steep hill. The pump should be able to maintain the specified system pressure.
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Merrymeeting Van
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PostPosted: Tue May 18, 2021 3:24 pm    Post subject: Re: Vanagon starts, warms up great, then (invariably) dies Reply with quote

Thanks - got a gauge and tubing. Fuel pressure seems OK, according to some Samba posts; right around 30 psi consistently. Goes as high as 33-34 under initial acceleration from a low-ish speed, drops to 26-27 on deceleration, stays right around 30 at idle or normal running (as fast as the van will go now). Doesn't drop under full throttle or when climbing a hill. Doesn't leak appreciably when I shut off the engine.
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PostPosted: Tue May 18, 2021 4:28 pm    Post subject: Re: Vanagon starts, warms up great, then (invariably) dies Reply with quote

Did you watch the gauge when you got it to sputter and die? If not, do that.

Those numbers are low, but I think it's at the "not full power" level and not the "stumble and die" level. I think it should be 30psi at idle, 39psi at WOT. You can unplug the vacuum line and it should increase.
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