MK1 CIS fuel supply

[Hilltop]

Hi, having problems getting my Mk1 Storm to run properly due to insufficient fuel supply. When restoring the car I renewed the filler neck, fuel pump (Bosch - however it had been in storage for a few years), filter and tank and cleaned out the pipes, however it runs poorly and is down on power. Read a bit about the k-jet injection system and had a look at the Haynes manual.

I fixed up a wire, with switch, to bypass the relay and wired in a multimeter. When running the pump was pulling 6.3 amps which is within spec. I also measured the electrical supply to the pump - it was 12 volts, 0.5 less that the battery. Then I detached the return pipe from metering head and measured the fuel that was being supplied from the pump in 30 seconds. It was 700ml, and Haynes say this should be a minimum of 900ml.

Can anyone suggest what's causing the fuel flow problem ? Also, why is the flow measured on the return to the tank and not on input ?

Thanks for any help and suggestions !

[james butler]

could be the pump has an internal leak?

[blakey]

Lack of use, dirt and moisture ingress are k-jet killers.

It's worth carefully removing the System Pressure Regulator in the fuel distributor, these can stick with dirt or corrosion from moisture in the fuel.

There's a lot of info on the web for K-jet, but this site has some good info and how to's half way down the page:

http://www.cabby-info.com/fuel.htm

Mine was stood around for years and the Warm Up Regulator had seized due to corrosion, so had the same control pressure hot or cold, this cause poor performance, economy and emissions.

[mark1gls]

Have you pulled out the fuel injectors and checked the spray pattern and how much fuel is coming out of each injector.
Injectors don’t last forever but there’s a few more things to check/test before just replacing parts...

[Hilltop]

Thanks for all the suggestions, lots of good info on link by blakey.

The below spec fuel supply must be a clue to the problem. To try and narrow things down what I'm trying work out is - could something in the metering head or incorrect system pressure be decreasing the amount of fuel returned to the tank or is it down to a problem with pump/accumulator or tank.

[mark1gls]

The accumulator can be tested by unscrewing the little screw on the back, if petrol comes out the hole then it’s shot. The accumulator holds the fuel pressure in the system so when faulty it’s takes some cranking of the engine when hot as the pressure need get back up.

A pressure test of the injection system is probably the easiest way to find/check for faults, you can buy a kit but it’s expensive, I’ve seen people make a home made kit search Bosch k-jet pressure kit...

[blakey]

I'd recommend getting a pressure test kit too. I bought a cheap one and had to modify a few bits to connect it to the metric connections on the metering head. You can check the condition of the pressure regulator in the metering head and also ensure that the plunger has free movement, and is clean not corroded or scored.
A word from experience, do not be tempted to split the two halves of the metering head, it is very hard to get it to seal again afterwards.
In fairness, the issue you have will likely be with the pump, fuel lines, pressure reg in metering head or the warm up valve.

Sent from my Moto Z2 Play using Tapatalk

[Hilltop]

Quick update on this. Left car for a few months and started fiddling again a few weeks ago. Emptied tank (found to be clean), renewed pump and cleaned out main pressure regulator - no change ! So then took advice and looked for a pressure gauge. Managed to get a proper Bosch one on an auction site and did the tests. With tap closed system pressure came up at 5 bar which is within spec, opened tap to get control pressure and no change ! Hot or cold there was no change in control pressure. I then removed the fuel line return from the warm up pressure regulator and no fuel came out and no change in pressure.

Although I had cleaned the WUR once before I tried again - but pressure results were the same. I was fairly sure the WUR was at fault now so I searched online and managed to find a NOS one which matched the original part number - was quite expensive but cheaper than refurb. This arrived and went straight on the car. I tested system pressure -5 bar and then with tap opened the pressure went down to 1.5 bar and rose steadily to 3.6 bar. I have yet to take the car out on the road but things are looking good ! Thanks for all the advice - indeed pressure gauges are the way to go if you have problems with k-jet.

[mark1gls]

Fingers crossed it worked.

The cost of buying the pressure gauge will probably be cheaper than just buying lots of new parts to throw at the k-jet system and hoping they work parts are getting expensive now..

Let us know how you get on.

[Hilltop]

Annoyingly the new WUR did not sort this problem. As before it starts well hot or cold and idles fine but there is no power (although slightly better when cold). It will hardly rev over 2500 under load even if my foot's on the floor. If I stop the engine and then restart it seems to go better for a while but gradually worsens. Last effort was changing the coil and rotor arm (leads, plugs and dizzy cap are new BOSCH) but still no better. I've spent a lot of time on this now and renewed various parts - a bit fed up with it really. Not sure what to try next - possibly the fuel distributor - but these cost £400 to get refurbished !

[blakey]

If you haven't done an injector test, I'd do one before changing the fuel distributor. Carefully remove all four and set them up to spray into a container to check the spray pattern and flow. You could also do a quantity test. There are quite a few Jetronic guides on the web that detail how to do both tests.

Are confident that the cam and ignition timing is correct and the ignition distributor advance is working?

Sent from my Moto Z2 Play using Tapatalk

[chopperoli]

There is sometimes a tiny filter inside the banjo bolt on the metering head fuel inlet, meant to be removed at the car's first service but often left in. Easy to check and remove if it's there.

Also are you really sure it's not some other electrical problem still? If not I'd plan for a metering head overhaul

[Hilltop]

Hello again, still trying to get the Mk1 to run properly !

Had the Metering Head refurbished by KMI. Came back looking like new. Car was slightly better but still was hesitation and lack of top end power. So new fuel injectors, seals and accumulator. Checked fuel supply on return again and it was 800ml in 30 mins. Fuel pressures were done and they were ok. There was an improvement but still not right.

Took car to local VW specialist who set the CO2 and checked ignition system with a Bosch FSA 560 machine - said everything looked very even (I did get a print out but not easily understood !). This again improved it slightly but the hesitiation / blind spot still there (garage called it a "hiccup") and feels down on power - I don't think it would manage to get past 75mph in 5th.

I then have checked cam timing and it looked a tooth out so moved it a 1 forward - does seem to have more torque but otherwise similar. Also checked cold start valve thinking this might be leaking and messing up the mixture but it worked fine. Also re-checked for air leaks but can't see anything amiss.Running out of ideas now..

So summarise I have replaced/ refurbished most parts of the fuel system (filler neck, tank, accumulator, pump x 2, filter x2, metering head, injectors) and had ignition system and timing checked and everything seems to be working correctly but the car runs poorly. Any suggestions greatly appreciated.

[chopperoli]

Please say you've already done a compression test on the engine!

Did your specialist do the ignition check under load? As that's where your problem seems to be occurring. If not, and your spark timing is definitely correct I would then be looking for faulty ignition components, like centrifugal advance, hall sensor, coil, ignition amplifier.

Btw, how old is the fuel?

[Hilltop]

Thanks for the reply.

Hi, yes compression test has been carried out - they were in the range of 165-175,

To be honest I don't know if they were tested under load (they were done with a diagnostic scope). They said all the results were very even and gave me a print out which refers to U-secondary, U combust, t- combust, Delta-N, N-analysis and Compression. Said the ignition timing gave slight error but the distributor could not be moved and did not think that would cause the symptoms.

I've added fuel 3 times in last 2 months and not travelled far at all, so it's fresh.