Zavolli system running lean/missing on BMW 4.4 V8

[Marcuspd]

Hi all, I wondered if anyone had any ideas on a running issue I've got.

I have a Zavoli system with 2 X vaporisers feeding 2 separate Matrix 4 pot injector blocks. It's been running fine for the last 10,000 miles after cleaning the injectors and replacing the worn foil strips in the injectors. All of a sudden it started missing on LPG and the BMW ECU is registering lean fueling on both banks of cylinders. The missing isn't always that noticeable until you turn the engine off and go to restart. On petrol then, it stalls straight away as the BMW ECU has changed all the trims to make it run way too rich, trying to correct the lean fueling on LPG.

I've had the injectors apart twice now in the last 500 miles and there are signs of an oily residue on the paddles (heavy ends?). These have been cleaned twice now and 2 more tanks of fuel have been ran through it. (I did wonder if I got a dirty tank of LPG from somewhere).

The injectors looked like this - you can just see the oily residue on them. I don't know if this is enough to make the injectors stick.





I've replaced the inline filters between the vaporisers and the injector blocks as these had done around 10,000 miles anyway, this doesn't seem to have helped. I think I've heard that there may be a filter on the liquid side at the bottom of this blue solenoid , does anyone know where I could get a replacement?



I've reset all adaptations in the BMW ECU and cleared all errors again. I then did an Autocalibrate of the LPG system with my Zavoli software. This is the screen shot of it running when on LPG...



Change over is set to 75 degrees C with a 2 second overlay. Has anyone got any pointers for me? P.S> The car runs fine on petrol.
Many thanks, Marcus

[rossko]

Have you considered why the petrol injector times are so different, one bank to the other? Does that difference persist when running on petrol, or is it a gas-only symptom?

[Marcuspd]

Yes, I did find that a bit odd. On petrol they are far more evenly matched at around 3.5ms all the time. The Petrol ECU is picking up that it runs lean on both banks when on LPG though.

I wondered if the oily deposit is enough to make the injector paddles stick occasionally, causing the misfire and lean fuelling errors. I just don't remember seeing this much oily deposit when I rebuilt them a year ago. If I clean them every 2 weeks now, there is an oily deposit on them again. Not a lot, but maybe enough. I think the best thing may be to clean them again and just hope that after 2 more tanks of fuel, that this oily stuff will be mainly gone now.

[rossko]

On petrol they are far more evenly matched at around 3.5ms all the time.

Bit of a clue then. Bearing in mind that you have only one pressure sensor, and probably have two semi-independent pressure feeds with a small bore linking tube, I'd be having a close look at pressure behaviour under load.

Oily coating over anything in contact with gas is perfectly normal. When it becomes sticky varnish or clagging wax, then it might cause a problem.

[Marcuspd]

Thanks Rossko. This was why I changed the gas side inline filters. I have not yet changed the liquid side filter, which I think is under the blue solenoid in the picture I posted.

Edit - I've cleaned it up and can see it's a Valtek Type 1 shut off valve, so have ordered a filter kit. The outer casing doesn't look like it's been apart for a few years and I've had the car for over 10,000 miles too, so it will be due a new filter anyway. Worth a try.

[Marcuspd]

I've replaced the liquid side filter in the solenoid/shut off valve between the tank and vaporisers and so far so good. It was a pain to get to buried down the side of the engine bay and needed the offside wheel and inner wheel arch removing to get to the nuts holding the retaining bolts in place!

Even blocking one end and blowing through it there is a noticeable difference between the old and new filters, so hopefully this will be why it sometimes runs lean on gas.

[Marcuspd]

Spoke too soon - I still get the Check Engine Light when driven on LPG. When I check the BMW ECU it comes back with errors that it has reached the limit of adaptation for correcting lean running, this happens at around 2750rpm, which is under load as it cruises at 85mph on a motorway at around 2500rpm. On petrol I don't see this error, doing the same journey.

I wondered what sort of fault a failing stop valve/solenoid would cause? Mine has a type 1 Valtek and it's fitted down the side of one of the banks of cylinders. They're not expensive and I now know how to replace it after taking it out to change the filter last weekend. My other option is to replace the paddles in the Zavoli XJ/XF type injectors. I had spares in a service kit, but didn't fit them because the rubber seats looked slightly different.

Worth a shot?

[Marcuspd]

Well, at least I have a hard fault now, after changing the coil on the solenoid. Not long after switching over to gas, it bleeps and switches back over to petrol. The Zavoli software shows an error for the water temp sensor. I've replaced the water temp sensor in the top of one of the reducers and watched the Zavoli software as the car warms up.

In the Zavoli software the temperature reaches 75 degrees as normal, which is what I set it to switch over, it switches to LPG and straight away it shows the reducer temp jump to 110 degrees. Soon after this the fault is logged. If I switch back to petrol, the reducer temp drops to normal again, at around 80-85 degrees. I can only assume a problem with the wiring so will have to check that out.

I just wondered if anyone had a similar experience? I did change the radiator recently so have taken the water temp sensor out from the top of the reducer to make sure there wasn't an air lock. Coolant was up to the hole.

[Gordonjcp]

So the temperature jumps instantly as soon as the solenoid is energised, and drops back as soon as you switch it off?

Sounds awfully like a bad earth somewhere. How is the solenoid and temperature sensor earthed?

[Marcuspd]

I reckon you're right Gordon. As soon as it switches over it jumps to its upper limit, switch to petrol and it immediately drops to a normal temp.

I had the harness connector off the Zavoli ECU and did resistance and continuity checks on the wires from the temp sensor and all seemed good. I then cleaned the contacts on the engine side solenoid valve and squeezed the spade connectors as the +12v one was loose.

So far, 10 miles in and the temp sensor error has stayed away. Fingers crossed!