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Volkswagen Vanagon: 1980-1991 (T3) Vanagon Acceleration Running problem


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Last Post: Dec 8, 2009 8:53 PM Last Post By: tcovenant2000
vango

Posts: 158
Registered: 03/26/04
Vanagon Acceleration Running problem
Posted: Sep 20, 2009 11:20 AM
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Summary of the problems (we do not know if they are related but we suspect):

1) Three trips in the past 1 yr driving at 65 mph or so on freeway after 1.5 to 3 hours then stopping for 5-10 minutes, it woní t start. Starter cranks fine but the engine wonít start. After 1-2 hours it starts, with little black smoke and runs fine.
2) Intermittent recently and progressively worse after 1 month when in town, engine cold or hot, while stopped at a light,etc then pressing the gas, engine does not pick up for few seconds and then takes off. This does not happen at every stop but random.
3) Doing engines checks, perhaps new because the cover was off, when pressing the gas, a banging noise is at the intake air sensor unit (sensor plate?). How to do the smoke test?

Checks performed (Bentley Official Factory Repair Manual reference).
All plugs clean, minuscule carbon
Return fuel hose at the tank- fine.
Pressure regulator fine (24.25)
Intake air sensor fine. Temperature sensor resistance WRONG. It shows 1000 Ohm instead of required 1500-2000 for ambient temperature of 300 C (24.28).
Auxiliary air regulator not checked (24.28).
Relays fine but changed with correct since both were same part # (24.32).
Throttle valve/deceleration/idle switch fine (24.33).
Full throttle enrichment switch first check fine, second check NO voltage at connectors (24.34).
Canít tell but seems to running rich as the tank seems to be going down but mostly in-town driving plus the tank sensor shifts around a lot. Pressure check 3 months ago was fine but will check again.
Catalytic converter appears fine but not sure how to check if plugged. Not sure how to check the distributor for the vac advance/retard and centrifugal.

FYI: The mechanic said unless we can tell him what's wrong, he can't fix it.
autobahn

Posts: 516
Registered: 08/17/05
Re: Vanagon Acceleration Running problem
Posted: Sep 20, 2009 11:30 AM   in response to: vango in response to: vango
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You got a great mechanic...

If temp-sensor is defect, air-fuel ratio could be way off and this can cost you the cat.
Check cat for restriction --> remove and start engine.
FKH161

Posts: 7,625
Registered: 12/29/05
Re: Vanagon Acceleration Running problem
Posted: Sep 20, 2009 1:19 PM   in response to: autobahn in response to: autobahn
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The banging sound in the intake is a "Lean Misfire"... instead
of a backfire out the exhaust (usually due to a rich mixture)
the fuel is ignited early while the valves are still open and
the flame/combustion travels up the intake manifold.

- vacuum leaks
  • fuel pressure/flow
  • injectors (spray)
  • ignition timing (check advance/retard pods, mech advance)
  • air flow meter

http://www.youtube.com/watch?v=-V_W_SFxYoI

Message was edited by: FKH161

vango

Posts: 158
Registered: 03/26/04
Re: Vanagon Acceleration Running problem
Posted: Sep 30, 2009 8:41 PM   in response to: vango in response to: vango
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Because the problem seems to happen only when the engine is hot (when it will not start if we wait an hour or so it will start and run fine) I have focused on the AFC system to find the problem.
I did the AFC System check with a very good volt/ohmmeter (24.20 and 24.21) and all the values were on specs beside the injectors slightly off (pins 11-7, 12-7, 23-7 and 24-7). They were consistently at 18..4-18.6 ohms instead of the required 16-16.4. I doní t know if it could be a problem.
The auxiliary air regulator passed the tests by pinching the hose with engine cold and hot (24.28).
Checked again temperature sensor I with good ohmmeter and looks inside the specs values (24.28).
Adjusted valve/deceleration/idle switch (24.33).
Did a test drive and after getting warm the engine was starting to loose power when accelerating.
At cold engine after disconnecting the temperature sensor II the engine started fine and run perfectly. After 15 minutes of idling I did a manual shut down and it will not start. With the temperature sensor connected again it started and seems running fine.
Could it be the vanagon syndrome? The vanagon is from 1984.
We did not check for vacuum leaks nor for ignition timing. The problem occurs only after a long drive so I think is something that goes wrong when the engine is hot and is eother starting or driving in traffic (acceleration from stop or very low speed).
Thanks for any tips.
FKH161

Posts: 7,625
Registered: 12/29/05
Re: Vanagon Acceleration Running problem
Posted: Sep 30, 2009 11:21 PM   in response to: vango in response to: vango
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How hot (to the touch) does the ignition coil get once the
engine is fully warmed-up? They usually get warm from regular
operation and from the exhaust heat radiating up... but a
really hot coil could be the cause of the no start & power loss.

I may have missed, but have you check for spark when the
engine does not start? What about injector spray?
eurocar504

Posts: 163
Registered: 10/17/06
Re: Vanagon Acceleration Running problem
Posted: Oct 2, 2009 9:07 AM   in response to: vango in response to: vango
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"FYI: The mechanic said unless we can tell him what's wrong, he can't fix it. "

That's a mechanic ! LOL

Check everything you have, when the engine actually won't start. Is there ignition and injector trigger when engine doesn't start?
vango

Posts: 158
Registered: 03/26/04
Re: Vanagon Acceleration Running problem
Posted: Oct 2, 2009 10:55 AM   in response to: vango in response to: vango
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We'll do checks this weekend in the middle of the day when it's hot and the blood suckers aren't out. There is spark when it won't start (remember the not-start is only after long drive). When this happened one time a tow truck guy put gas somewhere in the engine and it still didn't go but after it "rested" cranked right up but with little black smoke. Never checked injectors, would they do this randomly? Also the book makes it sound simple but are there any special tools/cautions to remove and check? We'll check the the coil for excess heat and the Temp Sensor II when warm.
eurocar504

Posts: 163
Registered: 10/17/06
Re: Vanagon Acceleration Running problem
Posted: Oct 2, 2009 11:21 AM   in response to: vango in response to: vango
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Ok. Sparks there are.
How about fuel injector triggering? Either remove two injectors and see if gas is sprayed when you crank, or remove one injector connector and check if voltage is coming on and off when you crank.

To remove two injectors, unscrew the injector retainer, pull them out, point them where no spark will be created (toward the floor maybe and place towels around to protect more risky area. Watch out for hot exhaust...) and crank for a second or two while somebody watches the injectors.

To check injector trigger, you can buy a test diode (maybe at autozone) and place it on connector. Or use a digital voltmeter.

The best test would be to see the gas going out of injectors.

If you have ignition and gas, most likely you have too much gas going to the cylinders. Unplug the injectors, crank to get rid of the excess gas in cylinder. The engine might actually then almost start which would confirm what I said. If not, try starting it with starting fluid (injectors unplugged).

If it is because of too much fuel, check again fuel pressure before anything.

Good luck.
TomB

Posts: 1,385
Registered: 08/06/02
Re: Vanagon Acceleration Running problem
Posted: Oct 2, 2009 3:30 PM   in response to: eurocar504 in response to: eurocar504
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To check for a flooded condition, simpler and safer than trying to start with pulled injectors would be to pull the fuel pump relay and try to start.
Otherwise I agree starting fluid is a great way to verify it is a fuel problem, although it also ignites more easily than gas, even with a weak spark.
eurocar504

Posts: 163
Registered: 10/17/06
Re: Vanagon Acceleration Running problem
Posted: Oct 2, 2009 7:03 PM   in response to: TomB in response to: TomB
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Agreed. I didn't mean to say to check a flooded condition with the injectors pulled out... Remove the injectors only to see if they are actually sending fuel.

Check the flooded condition by starting with injectors' CONNECTORS unplugged or as TomB said with fuel pump relay removed.
FKH161

Posts: 7,625
Registered: 12/29/05
Re: Vanagon Acceleration Running problem
Posted: Oct 3, 2009 8:51 PM   in response to: eurocar504 in response to: eurocar504
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A suggestion I just posted in another thread:

Attach a good digital voltmeter to the O2 signal wire and
check the voltage while the loss of power is occurring (have
someone drive the van while you sit on the back bench holding
the meter).

Loss of power due to lean or rich conditions can feel the
same, so you want to know which it is.

Once you know if the O2 is stuck lean or rich, you will be
able to decide which route to take for further investigating.
vango

Posts: 158
Registered: 03/26/04
Re: Vanagon Acceleration Running problem
Posted: Oct 4, 2009 2:49 PM   in response to: vango in response to: vango
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Will do, but now the camper is cranking/running fine!**?! A long trip/drive is planned today to see what happens.
vango

Posts: 158
Registered: 03/26/04
Re: Vanagon Acceleration Running problem
Posted: Oct 13, 2009 10:44 AM   in response to: FKH161 in response to: FKH161
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Checks this weekend:
Fuel pressure: 34 PSI idling, pulling vacuum hose SAME (34 PSI), 30 PSI at moderate high rpm, 30 PSI with vacuum hose off (same). Pressure goes to 40 PSI when turning key on.
Injectors: all four injectors were inspected and have same spray pattern. The spray is intermittent when cranking. Tests by cranking with electrical connectors off did not show any leaking.
Plugs: spark plugs were moderately blackened.
Air intake temp sensors: At an ambient temperature around 75 F the resistance value was 628 Ohm. Moving all the way the flap valve with a constant slow motion the value was changing from 628 to approximately 2000 Ohm but not smoothly. Values often jumped down to 1200-1000 from 1600 and 1800 Ohm (flap was continuously moved in one direction only).

So we did a 75 mile drive, 65-75 mph. Came home, turned the engine off, waited about 15 minutes, it cranked and was fine and in town driving with many stops have not has the same issue as before with not going or delay at acceleration.
The gas seems to be going down faster than normal and we're doing a fill the van-run it-fill again to get an idea if it's running rich. Maybe all this checking fixed a lose wire or the spirits in our house have extended their realm to the van too.
TomB

Posts: 1,385
Registered: 08/06/02
Re: Vanagon Acceleration Running problem
Posted: Oct 13, 2009 11:53 AM   in response to: vango in response to: vango
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The fuel pressure the same with the regulator vacuum hose disconnected is a problem. When you change the reference pressure on a regulator the outlet pressure should change a like amount.
Could be either lack of vacuum from the hose (tee in a vacuum gauge to check), defective pressure regulator, or plugged return line to the tank. Make sure the vacuum line goes to the manifold connection.
This has the effect of making the mixture too rich (if the O2 can't compensate enough), especially starting and idling, less while cruising. I helped a guy with a Digifant aircooled MexiBeetle running rich, and a bad pressure regulator was his problem.
vango

Posts: 158
Registered: 03/26/04
Re: Vanagon Acceleration Running problem
Posted: Oct 14, 2009 6:21 PM   in response to: TomB in response to: TomB
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Is there a pressure regulator check? As for the fuel check, we always got 23-24 mpg (including in town) now it's 19.6 mpg. The mechanic said everyone is running 4-5 mpg lower due to the ethanol but that seems like a lot to us.
TomB

Posts: 1,385
Registered: 08/06/02
Re: Vanagon Acceleration Running problem
Posted: Oct 14, 2009 7:21 PM   in response to: vango in response to: vango
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The regulator check is to test pressure with and without vacuum connected, and should show about 5 psig decrease with vacuum. That assumes vacuum signal is correct - so test that directly.
You mention fuel return at the tank is OK - but test from the regulator back in case the line is crimped/plugged.
If these test OK, replace the regulator.
Ethanol does lower mileage, but typ less than 10%.
Ethanol is also bad on some older rubber materials, perhaps on the diaphragm in the regulator?
FKH161

Posts: 7,625
Registered: 12/29/05
Re: Vanagon Acceleration Running problem
Posted: Oct 15, 2009 9:53 PM   in response to: TomB in response to: TomB
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Had an '80 aircooled van this week that would lose power
when driving... the pressure regulator was dumping too much
fuel out the return port, not letting pressure build in the
fuel rail.

New regulator fixed the loss of power and hard starting... all
symptoms were intermittent, and it was by chance that pressure
was low when I was looking at the gauge.
vango

Posts: 158
Registered: 03/26/04
Re: Vanagon Acceleration Running problem
Posted: Oct 24, 2009 11:58 AM   in response to: FKH161 in response to: FKH161
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My other half has been out of town for a week and will be gone another 3 so I'm going to do what I can BUT, the van is purring like a kitten again! My only complaint is that a few months after we purchased the van and had some issues, we changed the fuel pump, 1/04 to be exact. Turned out the problem was something else but the pump had be used as core so it was gone. Pump went out 6 months later and replaced. That one went bad too, changed it 3/08. The pump sounds to me like morse-code when driving low speed, high speed can't hear maybe because of road noise. No one seems to think it's a issue but I still don't think it correct. Will do some looking and get back next month.
TomB

Posts: 1,385
Registered: 08/06/02
Re: Vanagon Acceleration Running problem
Posted: Oct 24, 2009 3:59 PM   in response to: vango in response to: vango
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Flow restriction on the intake side of the pump will make it noisey because it wll cavitate, and this will cause early failure. Some vans have a pre-filter before the pump that can clog, as can the screen inside the tank. The pumps also have an inlet screen that can clog - and the Pierburg pumps have a smaller screen than the Bosch. Just things to check if the pumps are noisey and don't last long.
wohlfarth

Posts: 1,744
Registered: 10/31/03
Re: Vanagon Acceleration Running problem
Posted: Oct 24, 2009 6:49 PM   in response to: vango in response to: vango
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vango,

sounds like the classic symptoms of a fuel tank with crud and rust in it. Has the fuel tank ever been out to clean it or replaced?

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