1998 Jaguar XJ8 with Zavoli desplays restricted performance

[r1russ1]

Hi all,

My XJ8 has a Zavoli system wtih 4 Cil Emulators code 124 fitted. the problem i have is that the Jag goes into limp mode and desplays restricted performance if I do not get the car upto normal running temp before switching to gas. I want to leave the gas selected so that it changes onto gas automatically, I have played with the settings that control change over but end up at around 70 degrees c at the regulator which is fine in the summer but in the colder months the swith over to gas involves switching off the heater and pulling over to get to achieve that high switch over temp. Can anyone help? I read the forum about making an emulator with 8 injectors and relays but feel that this may be a step too far.

[tommo2009]

sounds as if you have coolant circulation problems (water pump) or it is plumbed in incorrectly to the heater pipes.

[r1russ1]

The regulator gets to temp ok and never ices up, I think it is more to do with Jags ECU and cold start rich running cycle that the emulators don't emulate properly.

[tommo2009]

so how quickly does the vap come up to temperature.
It doesn't sound like an LPG problem, more like an engine issue. If it is running as if it is on choke then it could be the engine coolant temperature sensor.
If you have the software for the gas you can see the petrol injector times. see what they are when the car is cold and then check to see if they reduce as the car warms up.
As said on this forum many times a car may seem to run fine on petrol and not very well on gas but the problem is down to the petrol side of things. Gas will show a fault more then petrol will.
From your post you say you need to turn the heater off to achieve that high a temperature. that shouldn't be like that.
Thermostat opens between 80 to 85 degrees, so acheiving a temp of 70 shouldn't be an issue wether the heater is on or not. ( that is assuming you have a thermostat in place) if not then getting up to temp will take longer and the car will fuel different. possibly giving the symptoms you have.

[MobileLPG]

Hi,


Have you read the fault code on the Jag ecu to see what is causing the limp mode?

This may or may not help but I serviced a Jag XK8 in Blackpool last week that had a similar problem.
This was fitted with an old Bigas system and also had the external 124 emulator units running in line to the ECU.
The problem he was having was the vehicle when on gas would every now and then go into limp mode, it never did it on petrol so was definitely a gas issue, I checked the fault code and it was showing a fault with injector 2.
The owner was very helpful as he had already tried checking all the wiring etc and he found that if he moved the wiring around the fault would go away for a while and then come back, but more importantly the fault would often appear after hitting a bump.
I unplugged the 124 units and the connectors looked fine but when looking at the units themselves they were heavily battered (they had been fitted after the conversion as they obviously weren't intended in the original layout of the conversion) because of this the emulators had been left lying and hanging down getting knocked over the years, every now and then one of the units would stop working which resulted in the ECU itself still taking care of the petrol injector turn off but the 124 would no longer fool the petrol ecu into thinking the petrol injector was firing.
The fault here was either one of the wires in the connector having a poor contact when moved, or the unit being faulty internally.

Edward.

[javers]

Hi folks,

Not sure if its related but I had a similar thing with my Oscar-N conversion on my '98 xjr. All the lpg ecu does is switch a 100ohm resistor in series with the petrol injectors to stop them firing. However this value is too high and the petrol ecu thinks there is an open circuit and starts flagging random "restricted performance" and also logs fault codes "P0201 – Injector Circuit Malfunction – Cylinder 1" up to "P0208 – Injector Circuit Malfunction – Cylinder 8". Solution was to solder a further set of resistors in parallel with the injector emulator wires of 47ohms (where the factor injector wiring has been cut into). The internal lpg ecu 100ohm and 47ohm resistors running in parallel gave a lower overall value (approx 32ohms). This worked well for me, low enough to stop the petrol ecu thiking there's open circuits and still high enough to stop the petrol injectors firing, and most importantly no more "restricted performance" nagging.

If you read your fault codes and it's P0201 - 208, I bet it'll be the same thing.

Cheers,

Jon

[r1russ1]

Jon,

I think you may be right, I have now looked at the fault codes and they range from P0201 to P0208 – Injector Circuit Malfunction. It is very intermitent and if I warm the car up to normal running temp befoire switching to gas there is no issue. It never happens on petrol. I'll have a look at the wiring to see if it's within my capabillity to solder in some resistors.

Thanks for all the help folks,

Russ.

P.S. Sorry for the delayed response but I was waiting for the OBD interface.

[Gilbertd]

There was another poster a while ago with the same problem and he found that the ECU was intelligent enought to reject a simple resistance, it needed to see a simulated injector before it was happy. After some experimentation with various resistor and inductor values, he hit on the simplest solution. He obtained a set of worn out injectors, put them in a plastic box and switched over to them when running on gas.

[tommo2009]

Had an XJ8 3.2 in today, Zavoli setup with AEB124 emulators fitted. temperature set to 40deg and it changes over without any issues.

The ECU should not have any issues with the cold start running cycle, it slaves off the petrol ECU, the car doesn't know it is on gas.

To me it sounds as if you have a temperature issue combined with the LPG system not being calibrated correctly

[rossko]

arr, but the P20x codes are saying it's definitely an emulator/wiring issue of some kind, whatever the connection with temperature. Maybe AEB124 are marginal in some circumstances, or go so with age.
Is it all the P20x or just four? May take time to build a full collection.

[tommo2009]

New AEB 124's are around £23 quid each, why not just replace them and see if the problem goes away.

[r1russ1]

Hi all,

It does seem to be all the codes. The temp thing is completly baffling as the car should not know it is on gas with the emulation. Where can I get a wiring diagram to check the injector wiring?

Russ

[tommo2009]

the car won't know it is on gas, that is what the emulators do. they fool the petrol ECU so that it does not know it is on gas.
They create a signal that is the same pulse width as the petrol ECU but the amplitude is different and therefore the petrol injectors don't fire.

some petrol injectors put in a few more pulses during the PWM, and this can cause problems with some emulation

[r1russ1]

The car runs fine without the emulators fitted when warm The wiring looks good to the eye with all the wire colours matching. they have spliced in to the injector loom in parallel. I have changed the emulators once with nil effect.

[rossko]

What's the history here, has it always done this?
I would play with the 'sequential changeover' option if available

I think you have a picky car, and may need to fit Pitagora emulators instead. That's a fairly extensive rewire job.

Or as you now have some spare AEB214 you could crack them open and experiment with adding some additional resistors in parallel.

[xj8user]

Hi,
Hope I can help I had a 2000 xj8 converted to LPG and had Limp home restricted performance which would come and go until got a set of pitagora emulators fitted this cured it and I then stupidly sold it.
I also looked at the option of fitting a spare set of injectors in a box which was tried by someone on this forum I think his handle was "mef"

[xj8user]

Hi r1russ1,
If you are having heating/cooling problems there are some issues that crop up; if the car is coming up to normal temp but little heat is coming out the vents it is probably the auxiliary heating pump. If the car is not coming up to normal temp it looks like a coolant issue or the thermostat. The v8 engine was designed to reach normal temp quickly by using a special valve arrangement to close off the block and allow the coolant within it to heat up before flowing through the rest of cooling system.
I can help talk you through both jobs if you need assistance or if you are near enough to bring your car? I am not in the trade just an enthusiastic amateur who found out the hard way that jags need lots of attention.