Bucking L-Jet only on hard acceleration or heavy load

[loveevan]

Hello,

Yes, there are many posts about bucking... ...in this case though, it ONLY happens on hard acceleration or heavy load.

It's a 1981 Vanagon Westfalia, and the bucking is ALWAYS there under ONLY those conditions. Warm or cold doesn't matter. It doesn't even matter if it's in gear driving.

I can just step hard on the accelerator (or push all the way on the throttle body if I'm back by the engine) and the engine, rather than accelerating, will go into a very predictable and very constant wah wah wah wah, as in a second of acceleration followed by a second of deceleration...

...it is so constant that the throttle can be held wide open and the van will never go above maybe 2500 rpm, then down, then up to 2500, then down, etc etc with the throttle held at full open.

When driving it'll do this in every gear if I floor it, or if I'm going up hill or have strong wind resistance... ...but, it also does it in neutral if I floor it, so the issue is in the engine bay somewhere.

meanwhile, if I baby it, ease into acceleration, I can ease right on up to 4000 rpm or more without any issue...

... so it's just a hard acceleration issue (and too much load on hills or against wind)

any thoughts?

thanks,

evan


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[Phishman068]

First thing I'd do is rip your points out and put in a pertronix ignition.

I am 1000% against the points system in these busses, and they cause all kinds of stupid and annoying problems like this.
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http://www.thesamba.com/vw/forum/viewtopic.php?t=559766&highlight=winter+rust
http://www.thesamba.com/vw/forum/viewtopic.php?t=482402&highlight=sunroof+syncro
http://www.thesamba.com/vw/forum/viewtopic.php?t=569774
http://www.thesamba.com/vw/forum/viewtopic.php?p=6864936#6864936

"Along with the ability to go fast, one looses the desire to hurry."

[jlrftype7]

I would want to know Fuel Pressure with the Fuel Pressure Regulator vacuum hose disconnected, regular Fuel Pressure with it connected, and a Fuel Delivery Volume Test after that.
Also, make sure the Air Flap inside your Air Flow meter isn't bent or warped from a Back Fire or just age. If the flap sticks at the portion of where you'd be pulling in enough air for a heavy load or acceleration, but can't advance further in movement, you can get some very weird running behavior with L-Jet.
The Air Flow Meter check is super easy, no special tools needed. Just pop it out of the Engine Comp and use your fingers or a screwdriver to push it from the normal closed position to see if you get full travel out of it.
You can often easily see rubbing marks inside the housing where the flap will bind or just stop if warped.
_________________
'68 Westy- my first VW and vehicle/Bus- long gone.- sold it to a traveling Swiss couple....
'67 Type 3 Fastback, my 2nd car- gone
'69 Semi-Auto Stick Shift Beetle-gone
2017 MINI Coopers, our current DDs
‘84 Tin Top - Hilga....Auto

[steve244]

Isn't there a full throttle switch that enriches the fuel mixture? This might not be working. I'm not sure the effect of this not working.

The ignition system might be affected by RPM or vacuum. Don't think he's in high RPM but it might be a vacuum issue.
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82 AC vanagon approx 200K miles (3K are mine).
DD is a 2015 Leaf
Road Trip to Hell (FL 2023)
The Vanagon's drivetrain and chassis restomod thread. Best sung to the tune of I Did It My Way...

[jlrftype7]

[Howesight]

Here are my thoughts, based on the symptoms described:

1. The hose between the Air Flow Meter and the throttle body may be cracked or not fastened well. When you rapidly open the throttle or place a sudden load on the engine, the engine moves slightly (it's rubber-mounted) and this enables a crack in the hose just mentioned to open up to the point a large vacuum leak is caused. To properly inspect this hose, you need to remove it and flex it, looking for cracks.

2. Your deceleration valve may be partly disconnected or otherwise not functioning correctly. The Bentley manual describes the checks and tests.

3. Your full throttle switch may be incorrectly adjusted or malfunctioning.

4. Your distributor rotor and/or cap may need replacing. Some folks incorrectly install the "rev-limiter" VW rotor which fouls things up and does not belong on a late-model Type 4 engine. It looks like the one in this link:

https://www.cip1.ca/acc-c10-5830/

5. Since your Vanagon has to be a California-equipped vehicle, it also has the primitive early EGR system. If the EGR system is not functioning correctly, it can cause problems, but not usually at the same rpm each time, so this is simply a check to eliminate a possible cause.

6. Here is a link to the AFC trouble shooting manual:

https://www.thesamba.com/vw/archives/manuals/afc_f...Manual.pdf

7. Here is a link to a thread on Itinerant Air Cooled which deals with the AFC bucking phenomenon more fully than I have above:
http://www.itinerant-air-cooled.com/viewtopic.php?...p;start=15
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'86 Syncro Westy SVX

[loveevan]

Thank you all for responding,

I will check all those things again.

The WOT switch itself works, but I was unable to follow the Bentley suggestion of testing it at terminal 18 because the California model doesn't have anything at terminal 18... ...and the switch itself goes through some of the stuff at the left of the engine bay before doing whatever it should do at the ECU.

Does anyone know how to test the WOT circuit on a California air cooled vanagon?

The switch itself is good (it's just and on off switch, easy to test by itself)... ...but I do wonder sometimes if the circuit is not giving extra gas as it should.

The air meter is "rebuilt", though apparently that doesn't mean it has a new wiper board, so there's that.

It was good enough to pass emissions and to drive highway speed with a light foot.

I have sprayed all over for vacuum leaks, though not exactly at the moment of the problem.

I did remove and test the bypass thing, and it did what it was supposed to do.

I had a gage on the gas pressure and it was just as it should be... ...though i didn't watch right at the moment of the issue. It gives plenty of gas to go 4000 rpms on the highway though, and the wah wah wah wah thing doesn't even go 2500 rpms at most while going up and down forever until i let go of the accelerator.

I bought the van with this issue (and other issues I've been able to fix) so I don't know anything about how slowly or quickly the issue came on.

It is serious though, while driving it bucks hard in every gear if I floor it and it does not go away by staying in it, only by backing off, then I can drive normally as long as I don't ever ask it for any real acceleration.

The engine itself is totally rebuilt just 2000 miles ago and very strong other than not being supported by the air, fuel, or spark it needs in those situations.

Please let me know if you know how to test the WOT circuit on a California vanagon, or anything else you can think of.

Thanks,

Evan
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[jlrftype7]

I knew your post sounded familiar once you mentioned you have the complications of the Califonia system enrichment setup.!!!
Read this thread, sounds exactly like your issue .There was a parallel thread on the same issue where one poster had to resolve Altn wiring issues as well since the signal wire to the Speed Relay of their Califonia system wasn’t seeing the voltage drop correctly , and they also found their cat was clogging with too much back pressure.
The exhaust back pressure check should also be done for this OP’s system since it could be adding to their poor hard acceleration attempts, or be the actual main cause.

https://www.thesamba.com/vw/forum/viewtopic.php?t=659727&highlight=california+wot+switch
_________________
'68 Westy- my first VW and vehicle/Bus- long gone.- sold it to a traveling Swiss couple....
'67 Type 3 Fastback, my 2nd car- gone
'69 Semi-Auto Stick Shift Beetle-gone
2017 MINI Coopers, our current DDs
‘84 Tin Top - Hilga....Auto

[RawUmber]

As I understand it, the 'OXS relay' prevents the WOT signal from affecting the ECU while the engine is running <3000 RPM. When running >3000 RPM, the WOT signal is allowed to affect the ECU. And when it does, ECU exits its closed loop, O2 sensor regulated fuel injection function, typically increasing enrichment.

For troubleshooting, you should be able to disconnect the OXS relay and see if the problem persists. WOT signal cannot affect ECU while the OXS relay is disconnected, but the AFC system should perform normally otherwise.

To test the OXS relay in situ, connect one volt meter probe to ground, the other to OXS relay terminal 8. Meter reading should toggle when crossing the ~3000 RPM threshold.

[loveevan]

I tested the OXS the way you said with the terminal 8 and ground...

... I went over 3,600 rpm, and still nothing, no signal from terminal 8 of the OXS

... which would mean no power to the WOT switch, and thus no signal to ECU to add time to the fuel injection and get more gas


So, i guess that could be it...

... could I just jump this thing and power up the WOT switch and see?
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[steve244]

After mulling it over, I don't think the symptoms you have resulted from the WOT switch not working.

The extra fuel would be to cool the incoming mix to lessen knocking.

Switch might be bad but there is another or multiple causes.

Sunday morning armchair mechanic.
_________________
82 AC vanagon approx 200K miles (3K are mine).
DD is a 2015 Leaf
Road Trip to Hell (FL 2023)
The Vanagon's drivetrain and chassis restomod thread. Best sung to the tune of I Did It My Way...

[oceanair]

Definately refresh the ignition system -- all tune up items, so why not?
New Coil, wires, cap, rotor and if you have points, new -- but go electronic and be done with it... Under loads is when you'll feel any weakness in the system. Be sure to buy QUALITY parts! not cheap or non-name brand stuff. Eliminate this system and have it refreshed...
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84 Vanagon Pop Top Conversion from Tin Top, 1970 Ghia - all sweet rides! Love em!
Previous: Green 72 Tin Top, White 72 Westy, Blue 64 Beetle, Yellow 71 Squareback, 2014 Jetta TDI Wagon - wish I could have them all back!

[loveevan]

[Mateo83]

I had this issue because my points were wide open.
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83 Air-cooled 2.0 Tin Top

[1988M5]

If you replace your points, don't forget to wipe the contact surfaces clean. I used to just open them against the spring tension, insert my button down work shirt between the contacts, let the points close and rub up and down a few times.

Cheers,

BK
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1991 tin top GL
2002 Winnebago Vista. VW VR6 24V Eurovan front clip powered class C 21' RV.
Some BMWs.

[loveevan]

The California version is electronic ignition, so no points, but it there are some shavings in there from the center piece being touched by the plastic pieces at both sides.

Still, the wah wah wah comes immediately and at any rpm, so the distributor isn't even doing high rpms when the issue happens.

It's basically dependent only on throttle position, which is to say sudden massive air flow...

... so if i gun it at 1000 rpm, it does it, if i gun it at higher rpm it does it...

... it basically goes into A-fib if it's asked for acceleration or if, while driving, it comes to a hill or something that would require more power to stay at the same drive speed



Does anyone know exactly what should happen in all areas when the throttle is suddenly wide open?

My friend's vanagon just accelerates at the speed it is able to when suddenly opened up, no bogging or anything, not impressive acceleration really, but it does it without fighting back.

So it is not a high rpm thing because it actually bogs so bad it never goes to high rpm...

...plus, if i just ease into it I can go high rpms no problem...

... so it is just the engine not doing the right thing when suddenly given a wide open throttle...

... I would think it would need more gas, right? to even out the ratio... ... and if that is correct (seems logical) then why would it not be getting more gas when it gets more air?

Is this a California version problem, or is it just this particular California vanagon?

Only other thing I can think of is maybe a clogged cat, but wouldn't that show up at high rpm too? Any reason that type of issue would only be at low rpm with a suddenly wide open throttle?

I am open to any and all suggestions and ideas,

thanks.


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[ohhorob]

[loveevan]

[Wellington]

Have you changed your fuel filter, checked flow and pressure?

[steve244]