1979 2.0 L FI stumble

[dlieffering]

Hey guys, this is my first post but I have been lurking around The Samba for the last 5-6 years. I've finally decided to create a post because I've pulled all my hair out trying to figure out whats wrong with my van.

When driving along, my van has a fairly severe stumble, this symptom has been described in a few different ways on this site (bucking, lurching)
After completing a long list of checks and and changing LOTS of parts, I can't for the life of me figure out what is wrong with it.

A list of checks I've preformed:

Compression test: all cylinders within specs 125- 150 psi

Valve check: adjusted to .006

Timing checked: set to 7.5 BTDC

Fuel pressure check while driving: 30 psi when idling, goes to 35 when accelerating. (drained and checked fuel tank for debris)

Vacuum leak check: 15" hg does not appear to have any vaccum leaks.

Went through and cleaned all electrical connections including FI ground wires

Gone through the AFC training and trouble shooting guide: fuel injection components seem to be within specs.

Now for a list of parts Ive changed:

New Heads (within the last 2 years)
temp sensor II
petronix electronic ignition
changed ignition coil with a known working one from my beetle (bosch)
plugs and wires
cap and rotor
new intake S boot (mine was cracked)
rebuilt fuel injectors (tested for flow and spray pattern)
replaced all fuel lines and filter (filter was clean of debris)
changed complete FI wiring harness (with a known working one)
swapped out AFM and ECU (with known working ones)

As I said above, I am at a loss as to what the problem is with my van. Any suggestions or recommendations would be greatly appreciated.

[jdedini]

Is your bus a California or federal model?
_________________
Justin

79' CA FI Tin Top Camper

[cmonSTART]

[scubaseas]

Does the pertronix replace the Ignition Control Unit (ECU) or just the pick up coil in the distributor?

Do you have a catalytic converter? Does it rattle when you hit it with you fist?

Have you tried removing or disconnecting the cold start injector?

When do you have the symptom? At cruise , on level surface, under load, going up hills, etc? Does it resolve after a time or there always? With engine cold or after it's been driven for a while?

Do you have a decell valve? Picture of the rubber boot from AFC to manifold would tell.

Have you tried disconnecting the EGR valve if it has one?
_________________
Al

08/1970 T2a Westphalia owned since 1980

ASE Master certification. 50 years pushing a wrench
Retired

[dlieffering]

Hey guys, thanks for responding!
I believe my bus is a federal model, because when i first got it it had points installed. It also has mechanical lifters instead of hydraulic. Also i don't recall seeing a catalytic converter on my bus.
The stumble usually occurs at a steady cruse and/or when accelerating, and it does seem to worsen when I give it more gas.

The Petronix replaces the ignition points in the distributor.
Thanks scubaseas I will try to bypass the cold start injector, if it is leaking it may cause a rich state.
I have not tried to disconect the EGR valve. Not exactly sure what it looks like or what it does on my van.

[Wildthings]

Not sure how important the ground strap for the moving plate in the distributor is when you have an electronic module installed. Have you checked all the pins in the plugs that plug into the AFM and the ECU.

Maybe the coil is failing or maybe one of the relays in the double relay is getting weak?

[dlieffering]

[scubaseas]

The petronixs pick up shouldn't need a ground strap to work but if your breaker plate is loose that could give your symptoms.

If you have access to one, try replacing the Ignition Control Module. Make sure to put heat sink grease on it if leaving it in permanently. Usually a bad ICM will have hard hot no start or not start at all. If you tried a known good coil, your rotor, cap and wires are OK, then that leaves the petronix or the ICM. Doubt if this is the issue but easy to rule out if you have access to another ICM.

You have either a spark problem or a fuel/mixture problem.

A bad decel valve is more likely suspect. You can simply pinch or block off the two big hoses and see if that has an effect.

You can find good info at www.ratwell.com . Does your system look like this? http://www.ratwell.com/technical/VacuumHoses/VacuumLines_to_76.5.jpg
_________________
Al

08/1970 T2a Westphalia owned since 1980

ASE Master certification. 50 years pushing a wrench
Retired

[skills@eurocarsplus]

there was a recent post where (depending on the pertronics you had there was a bad miss

turns out the module can't compensate for the #3 being slightly retarded and makes the unit throw fits

almost the bottom of the page here:

https://www.thesamba.com/vw/forum/viewtopic.php?t=...p;start=40
_________________

[Wildthings]

[bbrowncods]

I would pull the Pertronix and replace with points. Easy and cheap. That would eliminate the electronic Pertronix.

[scubaseas]

[Wildthings]

[Randy in Maine]

I assume that you also have a mechanical lifter camshaft?

When it is missing does it help to ground out the TSII?

[scubaseas]

[bbrowncods]

[dlieffering]

Great suggestions guys..
I am planning on working on the van in the next few days, it will be interesting to see what the culprit part is.
Stay tuned..

[furgo]

[Wildthings]

I would suspect but don't know that any distributors with a retarded #3 lobe would have been sold with non dog house Type 1 engines. Removing the oil cooler from the air flow path to the left bank of cylinders fixed the problem with burning the exhaust valve on the #3 cylinder and would have made a retarded spark on #3 unnecessary.

[SlowLane]