74 Bus w/ 78 FI stalls at idle when warm

OK, I've got a 74 bus with a 78 FI retrofit. Runs like a top! Great
response, perfect acceleration, timing is spot on. But, when it gets
warm (15-20 minutes), it will stall out at idle -- i.e. stopping at
red lights, etc.

There are no indications of any kind of fuel system problems -- the
bus runs absolutely GREAT before idling. Timing is perfect. Points are
good. Just, it stalls when rolling to a stop once it's warm.

I replaced the head temperature sensor, and inspected the aux air
regulator. Somone suggested checking the double relay, which I will
tonight. But, if the double relay was failing, wouldn't I expect
degredation of performance while driving, not just at idle? As I said,
driving performance is perfect.

Someone else suggested checked the thermo-time sensor. Could this
cause idle failures when warm? Perhaps the cold start valve is not
turning off, and flooding the engine? But, wouldn't this cause
problems within minutes, rather than 15-20?

The only other symptom I've had is that on REALLY long drives (i.e.
60-70 minutes over mountain passes) the engine will start to jerk and
hesitate when the throttle is open -- even on flat ground with no
load. Until it cools off.

Any help? I'm at the end of my rope and pretty much out of money.

wrote:
> OK, I've got a 74 bus with a 78 FI retrofit. Runs like a top! Great
> response, perfect acceleration, timing is spot on. But, when it gets
> warm (15-20 minutes), it will stall out at idle -- i.e. stopping at
> red lights, etc.
>
> There are no indications of any kind of fuel system problems -- the
> bus runs absolutely GREAT before idling. Timing is perfect. Points are
> good. Just, it stalls when rolling to a stop once it's warm.
>
> I replaced the head temperature sensor, and inspected the aux air
> regulator. Somone suggested checking the double relay, which I will
> tonight. But, if the double relay was failing, wouldn't I expect
> degredation of performance while driving, not just at idle? As I said,
> driving performance is perfect.
>
> Someone else suggested checked the thermo-time sensor. Could this
> cause idle failures when warm? Perhaps the cold start valve is not
> turning off, and flooding the engine? But, wouldn't this cause
> problems within minutes, rather than 15-20?
>
> The only other symptom I've had is that on REALLY long drives (i.e.
> 60-70 minutes over mountain passes) the engine will start to jerk and
> hesitate when the throttle is open -- even on flat ground with no
> load. Until it cools off.
>
> Any help? I'm at the end of my rope and pretty much out of money.
>


There may be two separate problems: the idle and the jerking.

Concentrating on the idle, my inclination is that there is
a small vacuum leak. The aux air valve may be compensating
for this until it decides that the engine has warmed up.

You might try this: Adjust idle up (or put brick on pedal)
so that the thing will idle at some speed after warmup.
Then go around to every stinking hose and fitting with a
solvent spray. Any change in RPM will show up a leak.
Don't overlook the Decel valve in this.

Less likely, but worth checking, is fuel pressure.
Put a 60 psi gauge on the fuel ring tap and see if the
regulator is functioning per the book.

I don't see anything that suggests a dbl relay failure.

Go to:
http://www.type2.com/
Click "Library"
Click "F" for Fuel In jection troubleshooting.


Speedy Jim
http://www.nls.net/mp/volks/

http://tech.bentleypublishers.com/ca...ame=volkswagen


Clearly either fuel pressure or a vacuum leak....my 80 Vanagon has
relatively the same motor....and the 02 sensor corrects mixture from
the fuel injection, but on yours, I assume you are carb running

In article

om wrote:
> OK, I've got a 74 bus with a 78 FI retrofit. Runs like a top! Great
> response, perfect acceleration, timing is spot on. But, when it gets
> warm (15-20 minutes), it will stall out at idle -- i.e. stopping
> atred lights, etc.

> There are no indications of any kind of fuel system problems -- the
> bus runs absolutely GREAT before idling. Timing is perfect. Points
> aregood. Just, it stalls when rolling to a stop once it's warm.

> I replaced the head temperature sensor, and inspected the aux air
> regulator. Somone suggested checking the double relay, which I will
> tonight. But, if the double relay was failing, wouldn't I expect
> degredation of performance while driving, not just at idle? As I
> said,driving performance is perfect.

> Someone else suggested checked the thermo-time sensor. Could this
> cause idle failures when warm? Perhaps the cold start valve is not
> turning off, and flooding the engine? But, wouldn't this
> causeproblems within minutes, rather than 15-20?

> The only other symptom I've had is that on REALLY long drives (i.e.
> 60-70 minutes over mountain passes) the engine will start to jerk and
> hesitate when the throttle is open -- even on flat ground with
> noload. Until it cools off.

> Any help? I'm at the end of my rope and pretty much out of money.

Defenetly vacuum leak. same exact simptoms on my bug. probably the
same problem/solution.

--
I'm trying a new usenet client for Mac, Nemo OS X.
You can download it at http://www.malcom-mac.com/nemo

Distributor ignition advance components? Sticking shaft for the mechanical
advance or sticking plate for the vacuum advance or a bad vacuum advance
unit.
Weak spark from the ign. coil? Bad or non-Bosch Ignition Rotor?

How is the idle when the engine is cold? Higher than normal?
If you increase the warm idle how does that affect the cold idle?

Maybe it is running too rich when the throttle closes and the engine is
flooding out?
How did you adjust the CO with the Air Flow Box?
Is the flap inside the AF Box sticking?

A large vacuum leak should be hissing at you, and a little carb cleaner
sprayed here and there should help locate any small ones! ;-)
Don't forget about the FI seals too!

Just throwing out some ideas but I know very little about the FI on the
Busses. <:-)
--
later,
dave
(One out of many daves)


"Macsoft" > wrote in message
...
> In article
>
> om wrote:
>> OK, I've got a 74 bus with a 78 FI retrofit. Runs like a top! Great
>> response, perfect acceleration, timing is spot on. But, when it gets
>> warm (15-20 minutes), it will stall out at idle -- i.e. stopping
>> atred lights, etc.
>
>> There are no indications of any kind of fuel system problems -- the
>> bus runs absolutely GREAT before idling. Timing is perfect. Points
>> aregood. Just, it stalls when rolling to a stop once it's warm.
>
>> I replaced the head temperature sensor, and inspected the aux air
>> regulator. Somone suggested checking the double relay, which I will
>> tonight. But, if the double relay was failing, wouldn't I expect
>> degredation of performance while driving, not just at idle? As I
>> said,driving performance is perfect.
>
>> Someone else suggested checked the thermo-time sensor. Could this
>> cause idle failures when warm? Perhaps the cold start valve is not
>> turning off, and flooding the engine? But, wouldn't this
>> causeproblems within minutes, rather than 15-20?
>
>> The only other symptom I've had is that on REALLY long drives (i.e.
>> 60-70 minutes over mountain passes) the engine will start to jerk and
>> hesitate when the throttle is open -- even on flat ground with
>> noload. Until it cools off.
>
>> Any help? I'm at the end of my rope and pretty much out of money.
>
> Defenetly vacuum leak. same exact simptoms on my bug. probably the
> same problem/solution.
>
> --
> I'm trying a new usenet client for Mac, Nemo OS X.
> You can download it at http://www.malcom-mac.com/nemo
>

On Oct 18, 2:31 pm, wrote:
> OK, I've got a 74 bus with a 78 FI retrofit. Runs like a top! Great
> response, perfect acceleration, timing is spot on. But, when it gets
> warm (15-20 minutes), it will stall out at idle -- i.e. stopping at
> red lights, etc.
>
> There are no indications of any kind of fuel system problems -- the
> bus runs absolutely GREAT before idling. Timing is perfect. Points are
> good. Just, it stalls when rolling to a stop once it's warm.
>
> I replaced the head temperature sensor, and inspected the aux air
> regulator. Somone suggested checking the double relay, which I will
> tonight. But, if the double relay was failing, wouldn't I expect
> degredation of performance while driving, not just at idle? As I said,
> driving performance is perfect.
>
> Someone else suggested checked the thermo-time sensor. Could this
> cause idle failures when warm? Perhaps the cold start valve is not
> turning off, and flooding the engine? But, wouldn't this cause
> problems within minutes, rather than 15-20?
>
> The only other symptom I've had is that on REALLY long drives (i.e.
> 60-70 minutes over mountain passes) the engine will start to jerk and
> hesitate when the throttle is open -- even on flat ground with no
> load. Until it cools off.
>
> Any help? I'm at the end of my rope and pretty much out of money.

Thanks for the replies.

OK, I checked and found a (small) vacuum leak near the decel valve,
which I repaired. Took it out on a test drive, and I still got the
same problem. It ran absolutely beautifully, and then POW -- stall
when coming to a red light. I kept driving a bit more, and then the
crap really hit the fan. Cruising along at 55 MPH, suddenly the engine
started losing RPMs, even with the throttle open. I had to keep
downshifting to keep the engine alive, until it finally stalled out.

Of course, the starter solenoid (which has been going bad) chose this
exact moment to give up. I was able to compression start it sometime
later, and it did start up again.

Does this sound like it could be an ignition/coil problem? The weird
thing is that it stalls when warm, but doesn't ALWAYS stall when warm.
The points and rotor looked OK last time I looked at them. Neither are
worn or pitted and the dwell is spot on.

When it rains, it pours.

> Does this sound like it could be an ignition/coil problem? The weird
> thing is that it stalls when warm, but doesn't ALWAYS stall when warm.

I have had that symptom on a brand x with a bad coil

MD

> wrote in message
ups.com...
> On Oct 18, 2:31 pm, wrote:
>> OK, I've got a 74 bus with a 78 FI retrofit. Runs like a top! Great
>> response, perfect acceleration, timing is spot on. But, when it gets
>> warm (15-20 minutes), it will stall out at idle -- i.e. stopping at
>> red lights, etc.
>>
>> There are no indications of any kind of fuel system problems -- the
>> bus runs absolutely GREAT before idling. Timing is perfect. Points are
>> good. Just, it stalls when rolling to a stop once it's warm.
>>
>> I replaced the head temperature sensor, and inspected the aux air
>> regulator. Somone suggested checking the double relay, which I will
>> tonight. But, if the double relay was failing, wouldn't I expect
>> degredation of performance while driving, not just at idle? As I said,
>> driving performance is perfect.
>>
>> Someone else suggested checked the thermo-time sensor. Could this
>> cause idle failures when warm? Perhaps the cold start valve is not
>> turning off, and flooding the engine? But, wouldn't this cause
>> problems within minutes, rather than 15-20?
>>
>> The only other symptom I've had is that on REALLY long drives (i.e.
>> 60-70 minutes over mountain passes) the engine will start to jerk and
>> hesitate when the throttle is open -- even on flat ground with no
>> load. Until it cools off.
>>
>> Any help? I'm at the end of my rope and pretty much out of money.
>
> Thanks for the replies.
>
> OK, I checked and found a (small) vacuum leak near the decel valve,
> which I repaired. Took it out on a test drive, and I still got the
> same problem. It ran absolutely beautifully, and then POW -- stall
> when coming to a red light. I kept driving a bit more, and then the
> crap really hit the fan. Cruising along at 55 MPH, suddenly the engine
> started losing RPMs, even with the throttle open. I had to keep
> downshifting to keep the engine alive, until it finally stalled out.
>
> Of course, the starter solenoid (which has been going bad) chose this
> exact moment to give up. I was able to compression start it sometime
> later, and it did start up again.
>
> Does this sound like it could be an ignition/coil problem? The weird
> thing is that it stalls when warm, but doesn't ALWAYS stall when warm.
> The points and rotor looked OK last time I looked at them. Neither are
> worn or pitted and the dwell is spot on.
>
> When it rains, it pours.
>
>



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I had similar symptoms with another brand of car as well, turned out I got a
load of gas that had a large amount of particulate matter that was plugging
the pickup screen in the fuel tank. Car would run fine for a while, then
lose power as the screen got plugged and the fuel flow dwindled. Stop the
car for a while, the junk fell off the screen, and it would run fine until
it plugged again.

"Mark Dunning" > wrote in message
...
>> Does this sound like it could be an ignition/coil problem? The weird
>> thing is that it stalls when warm, but doesn't ALWAYS stall when warm.
>
> I have had that symptom on a brand x with a bad coil
>
> MD
>
> > wrote in message
> ups.com...
>> On Oct 18, 2:31 pm, wrote:
>>> OK, I've got a 74 bus with a 78 FI retrofit. Runs like a top! Great
>>> response, perfect acceleration, timing is spot on. But, when it gets
>>> warm (15-20 minutes), it will stall out at idle -- i.e. stopping at
>>> red lights, etc.
>>>
>>> There are no indications of any kind of fuel system problems -- the
>>> bus runs absolutely GREAT before idling. Timing is perfect. Points are
>>> good. Just, it stalls when rolling to a stop once it's warm.
>>>
>>> I replaced the head temperature sensor, and inspected the aux air
>>> regulator. Somone suggested checking the double relay, which I will
>>> tonight. But, if the double relay was failing, wouldn't I expect
>>> degredation of performance while driving, not just at idle? As I said,
>>> driving performance is perfect.
>>>
>>> Someone else suggested checked the thermo-time sensor. Could this
>>> cause idle failures when warm? Perhaps the cold start valve is not
>>> turning off, and flooding the engine? But, wouldn't this cause
>>> problems within minutes, rather than 15-20?
>>>
>>> The only other symptom I've had is that on REALLY long drives (i.e.
>>> 60-70 minutes over mountain passes) the engine will start to jerk and
>>> hesitate when the throttle is open -- even on flat ground with no
>>> load. Until it cools off.
>>>
>>> Any help? I'm at the end of my rope and pretty much out of money.
>>
>> Thanks for the replies.
>>
>> OK, I checked and found a (small) vacuum leak near the decel valve,
>> which I repaired. Took it out on a test drive, and I still got the
>> same problem. It ran absolutely beautifully, and then POW -- stall
>> when coming to a red light. I kept driving a bit more, and then the
>> crap really hit the fan. Cruising along at 55 MPH, suddenly the engine
>> started losing RPMs, even with the throttle open. I had to keep
>> downshifting to keep the engine alive, until it finally stalled out.
>>
>> Of course, the starter solenoid (which has been going bad) chose this
>> exact moment to give up. I was able to compression start it sometime
>> later, and it did start up again.
>>
>> Does this sound like it could be an ignition/coil problem? The weird
>> thing is that it stalls when warm, but doesn't ALWAYS stall when warm.
>> The points and rotor looked OK last time I looked at them. Neither are
>> worn or pitted and the dwell is spot on.
>>
>> When it rains, it pours.
>>
>>
>
>
>
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> News==----
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> Newsgroups
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> =----

On Oct 22, 12:21 pm, wrote:
> I replaced the head temperature sensor, and inspected the aux air
> regulator. Somone suggested checking the double relay, which I will
> tonight. But, if the double relay was failing, wouldn't I expect
> degredation of performance while driving, not just at idle? As I said,
> driving performance is perfect.......

> The only other symptom I've had is that on REALLY long drives (i.e.
> 60-70 minutes over mountain passes) the engine will start to jerk and
> hesitate when the throttle is open -- even on flat ground with no
> load. Until it cools off.
>
........
> OK, I checked and found a (small) vacuum leak near the decel valve,
> which I repaired. Took it out on a test drive, and I still got the
> same problem. It ran absolutely beautifully, and then POW -- stall
> when coming to a red light. I kept driving a bit more, and then the
> crap really hit the fan. Cruising along at 55 MPH, suddenly the engine
> started losing RPMs, even with the throttle open. I had to keep
> downshifting to keep the engine alive, until it finally stalled out.

I know that you said you replaced the #3 temperature sensor, but I
would double-check that to make sure that you have a REALLY good
connection. It may also be possible that you have a defective sensor.

The reason I'm saying this is that on my previous 1979 Bus I had
exactly these same symptoms and that temperature sensor was the
problem. The symptoms would start with a little high-speed hesitation,
followed by bucking, then nearly total loss of power, and finally the
inability to keep the engine alive. When the sensor was replaced, the
problem went away and never returned.

--- Robert Winters