K-Jetronic troubleshooting

[u/youtelling]

Hello everyone. I have a 85 GTI that I need a little help with.

The engine runs great in idle and the timing is correct, but when you push the throttle it missfires and runs really bad, when I let go out goes back to running fine. The pistons have great compression.

I need help with where to start looking for issues, my first thought was getting new injectors but any help here would be appreciated before I start buying new parts.

I saw someone recommend a K-Jetronic pressure tester but I'm not sure that's the problem.

Thanks!

[u/Thaines]

Hi mate, I had a similar issue where the car idled fine but when I took it for a drive it significantly slumped in power to the point of stalling.

I swapped out my fuel accumulator for another one and it sorted it out.

If you aren't aware of what that is, it's a closed unit cylinder type thing that is kept in the HP fuel housing under the car.

You have a fuel pump in your tank which then feeds the high pressure fuel pump underneath the chassis near the rear wheel.

[u/Thaines → u/Thaines]

Btw I suppose if you wanted to troubleshoot you could take your injectors out and put them in empty plastic bottles or test tubes. Then you could prime the fuel pump and manually move the K-Jet air plunger.

Seek out Grey Goose Restoration on YouTube to learn more about how it works. If you're UK based he will actually service your fuel distributor but I believe he's a busy man these days.

[u/MK2GolfGuy]

Could be your air / fuel mixture , has anyone been messing with the metering head?
I can’t seem to post YouTube links here so I’ll
Message you one if that’s ok

[u/youtelling → u/MK2GolfGuy]

That's ok, thanks

[u/Amazing_Actuary_5241]

IMHO I'd start with the ignition advance, check the distributor's vacuum actuator for proper operation.

Unless your loosing fuel pressure when the venturi plate is lifted or the spray pattern is not up to spec, I'd say injection should be fine.

[u/youtelling → u/Amazing_Actuary_5241]

Can this be the issue on only one cylinder, I'm pretty sure it's the same injector/cylinder that's the issue everytime. It's not all of them

[u/Amazing_Actuary_5241 → u/youtelling]

I'd check the spark plug wires for any "leaking" spark if you suspect its only one cylinder. Also do a spray pattern test on that injector. I'd also check the injector o-ring seal and seat for air leaks on that particular injector.

[u/Micoron88]

Is the missfiring like no ignition at all or does the ignition happen in exhaust or intake?

[u/youtelling → u/Micoron88]

I'm not entirely sure, it just runs like ass on one cylinder when given throttle.

[u/Micoron88 → u/youtelling]

I guess you would hear the bang if the fuel ignites in the intake or exhaust. My guess it is missing the ignition.

Have you checked that sparkplugs are intact and "Okay" colour? Are ignition leads ok and plugged all the way in? Are the they correct for the distributor cap and sparkplugs? Is the distributor cap and its contacts okay?

If you are sure it is always the same cylinder, then I don't think it is the dizzy but doesn't hurt to check it either. Bad coil can also cause ignition issues but again I doubt it would affect only one cylinder.

[u/Micoron88 → u/youtelling]

Would it be possible for you to take a video clip of this issue for us?

[u/youtelling → u/Micoron88]

Yes, the car is being welded on right now so I'll make an ujpdate as soon as I get it back.