Calling K-Jetronic Experts - Overfuelling/Rough 925

[ChasR]

For one reason for another a friend has asked for me to help him out with a 924 (probably to pass the blame on!). It is someone else's mess after all...

Basically it seems to run very very rich, to the point where the car is misfiring badly and will smoke blue from what I am assuming to be bore wash (hopefully not a shot engine!).

If the pipe is taken off between the metering head and the throttle body the smoke stops, as does the misfiring. Of course it is undriveable in this condition. As you can expect the spark plugs become very wet.

Furthermore there seems to evidence of a slight amount of fuel being present in the bottom of the airbox? I am assuming this should not be occuring.

He was going to turn the mixture down using the mixture screw, but with how rich it is running surely this would only compensate so far!

My question to you is, where would you start to look? To make matters worse the cold start injector wiring has been hacked around with (it has a dedicated feed for the earth)), in addition to there appearing to be a missing pipe on the the very lower back of the metering head (it looks as if it should have a bung present there; There has been some botchery in taping up the bung, and so it appears not to be leaking with an application of carb cleaner on it etc.).

[metroman]

I would start by investigating the wiring problems with the cold start mechanism first and foremost. If the system isn't correctly installed then no amount of tuning is going to solve the issue. The cold start should only operate for a very short amount of time injecting an extra charge of fuel. It is controlled a regulator and time switch. This video is well worth a look:



I hope that helps

James

[ChasR]

I am not going to lie, that video is making me wonder whether I should run for the hills! Many aspects of that car have been fiddled with the further you dig. The fuel pump looks new (and is insecure), the filter has been changed along with what seems to be a gas hose going from the filter to the metering head!

Still, it has given some food for thought.

[vitesseefi]

Best thing to do with the cold start injector (known trouble maker) is to disconnect it electrically and leave it disconnected. I've done this on all 3 K-Jet cars I've owned (early Golf GTI 2, and 2 x Audi 90s). They continue to start perfectly well summer or winter.

Given the hassles it may also be worth checking it's not dribbling/spraying the whole time even when disconnected as apparently this has been known. This then eliminates it as the source of excess fuel.

That was the easy bit....... if it's still messing about you are probably in for it. Actually not that complex a system, but hard to diagnose without the right gear. You can do some of it with a reasonable 0 - 120 psi gauge and the relevant adapters. Warm-up valve (usually mounted down on the block) can be troublesome. This varies the pressure applied to the top of the metering head piston which works in opposition to the input provided by the air metering flap. When cold, the pressure applied to the top of the piston is lower, allowing more movement of the piston and injecting more fuel. Warm up valve is pretty simple looking inside - heated bimetallic strip acting over a bleed orifice. It is possible to dismantle them, wash out any cack and re-assemble exactly as was resisting the urge to tweak anything!

Could also be bolloxed injectors. Fairly easy to check: Pull out injectors and place in jam jars. Frig fuel pump relay so pump runs. Should get a continuous fine cone shaped spray when the air flap is lifted increasing in volume the more it is lifted but near complete shut-off when the flap is on its stop. Dribbling, blobbing or behaving like a cheap water pistol means time to renew.

Cheers

Nick

[spandelly]

If your getting fuel in the air box then it sounds to me like the seal has gone in the metering head and its pulling fuel into the air system. The screw only adjusts the mix at idle so that's not going to help. This isn't going to be the easiest thing to get right but pull the air intake pipe off the top of the metering head and try manipulating it by hand.you will be able to see if there's petrol getting into the air intake, Also its free.

[ChasR]

I have already tried this (lifting up the flap that is). Fuel was dripping into the air intake. On the plus side, my hands got a clean...

[spandelly]

That might be it then. If you remove the intake pipe from the head then the fuel that's dripping onto your hand cant pull into the air intake and into the chamber.

[spandelly]

Another thing is the fuel pump might not be the right one and might be forcing fuel past the seals.

[ChasR]

Sorry, I should have been clearer. It was dripping before the flap and into the airbox (it seemed to be coming from the metering arm/plunger area within the head arrangement).

The fuel pump issue is a good point. It does not look to be installed too well. A pressure test (along with the above checks (cold injector check etc.) shall be done .

[Smiler]

You might find my website helpfull, click on the link in my sig and scroll down to the K-Jetronic Idiots guide. It won't give fault diagnosis but may help to make its operation simpler to understand and so help you make your own diagnosis.

[ChasR]

Cheers Smiler, it seems to be a guide for sure . Cheers for the tips everyone, and it is good to know what can happen .

I forgot to say in the description last time that the car will not run after a certain amount of time (from it seeming to overfuel; the Plugs are black and wet with the engine oil smelling of petrol to boot.

Regarding the car, I have done further investigation:

1) Cold Start Injector was checked : Zero fuel present with the engine running.
2) Auxiliary Air Valve; It was not a dead clear passage, but there was a slot in the disc present which did allow for an air gap. Upon putting on 12V the disc obsured the opening within minutes. The resistance was 43 Ohms, not the quoted 30 as per the manual. Should the opening within the valve be completely open?
3) Control Pressure Valve value was checked: Ohms seemed correct as per the book, along with there being a supply (6.5V) at the terminals.

After this point the car decided it would not fire up at all without the assistance of Easy Start:

4) Injector was pulled out and disconnected. Zero fuel came out despite the metering head being moved manually, but it did vary upon the injector being removed, and it filled a 300mm bottle with petrol fairly swiftly.

This is where it gets strange:

5) Fuel Pump Flow rate: Just before the pipe goes into the metering head, the flow rate was seen to be around 310cc (or ml) after 30 seconds, under half of what it should be.

My suspicions are now falling onto the 'new' fuel pump which is pretty much hanging off the car, along with the bodges this thing has seen (someone has checked the aux. air valve etc. judging by the loose screws (God knows why I assisted in helping a friend out!).

Many thanks for the suggestions and keep them coming. Forgive me if my investigative techniques are a little Heath Robinson, although it does not help when the chap in question is trying to get a forlorn car roadworthy for almost next to nothing (it hasn't had an MOT for quite some time and it was bought as part of a job lot).

Most of the time, my experience with K-Jets has been fine, with them requiring nothing more than a simple tweak or basic maintenance (metering head plate is full of curse word due to poor prior maintenance in addition to a curse word fuel pump or a duff relay if I was unlucky (I never bought new mind you, but did go with genuine secondhand parts which lasted for some time).

[spandelly]

The aux air valve should be open until the engine warms up.

[ChasR]

I would have said this was 1/3 to 1/2 open tops, it was by no means a clear passage. With 12v put onto it, it closed up within 5 minutes. If it should be fully open I guess it can be added to the list of things that can be an issue.

In other news, the 'fresh' fuel which was put in did not seem so fresh (although the car has been stood for some time previously) in addition to the the fuel pump pressure still not being quite up to scratch.

[vitesseefi]

Aux air valves don't have a clear passage through even when fully open. You will be able to see a shaped slot in the disc (slot shape and size varies by application to give the extra air that the engine needs).

If you put 12v on the terminals a heater heats a bimetallic strip and moves the whole disc across until the passage is completely blocked.

They are very reliable devices and if the heater coil is not blown and the thing is not gunked solid it will almost certainly be working. Use them on both my EFI conversions - the warm-up characteristic of a Mk1 Golf Gti valve matches my Vitesse perfectly!

Nick

Nick