Ready to kill something, Car still bucking EFI issue with 1.8L Options

[qa1142]

Ok,
I have cleaned contacts, tested at computer connector

tested MAF,

checked head temp,

checked fuel pressure,

Did it with points, now have compufire, still does it

Changed coils

Cleaned grounds

Changed plugs

Tech tips 700 says throttle position switch on 1.7 and 2.0 can cause this. Could the one on a 1.8 do it? I have spair.

Someone help me (IMG:http://www.914world.com/bbs2/html/emoticons/icon8.gif)

[qa1142]

PS: I have a copy of Volkswagen USA Course manual 4.02

"Fuel injection AFC Air Flow Controlled"

Still cannot figure this out (IMG:http://www.914world.com/bbs2/html/emoticons/blink.gif)

[grantsfo]

No vacuum leaks anywhere, right? Oil cap sealing well too?

[qa1142]

Vacuum leaks fixed last year.

removed Decel valve.

all new hoses,

double checked with ether for leaks. all AOK

O yeh, tested thermo time valve, no leaks after the couple of seconds it takes to close

[scotty914]

when you tested the maf did you put an ohm meter on it and move it thru its range to check for a dead spot, then you might as well change check the tps ( i think it is just a wot switch but check it any way )

if the stumble is at one rpm i would check the dizzy to make sure it is not sticky in any spot

how violent is the bucking, a miss be it either no fuel or spark is violent. now if you are loosing fuel the l jet does all 4 cylinders at once for fuel so if it is fi it should be accross all 4 cylinders.

have you changed anything before this started like plugs or spark plug wires, you can have a bad plug wire and have it intermentant. also how is the rotor and cap.

[grantsfo]

I'm going for silly stuff. Fuel filter clean?

[qa1142]

Fuel pressure is good, so filter should be OK - new last year - cleaned screen in tank when it was out this winter

I did check the AFS at all steps. My course book gives rating at every step (position) and it tested fine.

[qa1142]

BTW

Fuel filter is not that silly, but I have learned that lesson on my 64 chevy in high school
(IMG:http://www.914world.com/bbs2/html/emoticons/ohmy.gif)

[qa1142]

Tach reading stays steady, so spark is still there

I think I am dropping all 4 injectors, sometimes just enough to buck, sometimes long enough for car to decelerate for 8-10 seconds.

First it happend once mid summer last year

Went weeks fine, slowly became more frequent as year went on.

Now it is every time I am out
(IMG:http://www.914world.com/bbs2/html/emoticons/sad.gif)

[JerryP]

Even sillyer.....I had the same symptom with my 2.0. Cleaned some crud out of the tank....no more bucking (IMG:http://www.914world.com/bbs2/html/emoticons/confused24.gif)

[lapuwali]

While we're into silly, make sure all of your injectors are plugged in securely. I had a single (1) injector connector come loose on a Golf a few years ago, and the car would randomly buck like someone was cutting off the ignition asthe connector would make and break the connection. I believe Nathan had the same thing happen to a D-Jet 914 awhile back. It would cut out in hard turns, where the connector was pulled away from the injector.

Does it only cut out while you're driving, or does it do it sitting in the driveway, too? Is it tied to load (does it more up a hill than down one)?

[qa1142]

does not die at idle and does not feel or sound like it is missing

Bucks accel, decel, and just crusing

goes days fine (not this year)

Then bucks every time I drive her.

Fine for few miles, bucks couple, fine again

Sometimes is non-stop where I worry if I'll make it home
(IMG:http://www.914world.com/bbs2/html/emoticons/sad.gif)

[ClayPerrine]

Check the dropping resistors. They are mounted to the chassis, and the harness connects to the engine. Because the engine moves a little bit relative to the chassis, the wiring in the resistor packs have a tendency to break. There is one common wire that feeds all the resistors. If it is flaky, you will get fuel cutout. I have seen this same thing.


Start the car, and wiggle the wiring on the dropping resistors.


Otherwise check the grounds under the intake plenum.

[914GT]

Check your timing for too much advance. Make sure the distributor advance mechanism is working properly, it may be worn out.

[elwood-914]

Check your F.I. contacts inside the distributor,mine was bucking and checked it and it was badly pitted. No more bucking.

[qa1142]

L-jet has not contact points

I'll check timing and for loose connectins toninght

(IMG:http://www.914world.com/bbs2/html/emoticons/sad.gif)

[redshift]

I have never owned a 74 1.8.

I recently had a somewhat similar problem with my 74 2.0, that went away when I cleaned, and reterminated wires in the harness connections under the passenger seat, and taped the seatbelt interlock rig together with better tape than the PO..

(IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif)

I dunno...


M

[Michael J]

My 1.7 did this when cruising at constant speed. Throttle at nuetral position. Under acceleration it was ok. Started fine, idled fine. I finally took the TPS switch apart and it was full of "crude". A technical term. Carefully cleaned all the contacts and reinstalled. Problem fixed.

Yours does sound like a broken or loose wire. Hard stuff to track down.

Good luck & keep the evaluation results coming.

[qa1142]

FYI
Head temp sender was bad, Thanks to Brad Mayer (914LTD) for the suggestion

She's purring (IMG:http://www.914world.com/bbs2/html/emoticons/smilie_pokal.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/wub.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/laugh.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/rolleyes.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/mueba.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/driving.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/aktion035.gif)

An then some

See you on the trails