Petrol consumption high?

[v8vroom]

Hi all,

I've noticed that my car drinks a lot of petrol even though I am always running it on LPG mode. (2000 Jaguar XJ8 3.2)
£20 does not last me a lot. Maybe a few days, max. Maybe this is considered normal? I noticed this being a problem when my car has failed to start due to no petrol being in the tank.

On cold starts, I wait for the car to warm up which takes a LONG while.

[Brian_H]

It shouldn't use much, but it can depend on your settings for changeover temp as to how long it runs on petrol for. Any idea of the changeover temp (and does the indicated reading for it look accurate?)

It can be setup depending on ecu to use petrol under certain conditions (high load for example), this can be used to compensate for under specced components etc. A look at the settings should confirm that if you have access? Don't know what ECU your using, may help to mention that?

Could also be leaking somewhere.

Of course, £20 of petrol is not a lot anymore either, The last can of fuel I brought for the mower was around £9.

I've run through about 1/4 of a tank every 6 months as long as its set to run on gas all the time, and its got enough gas to run on of course!. But most of my journeys are long so very little is spent with a cold engine (switchover temp is 30 degrees on mine I think, and its only a 2.3 4 cylinder).

[v8vroom]

It shouldn't use much, but it can depend on your settings for changeover temp as to how long it runs on petrol for. Any idea of the changeover temp (and does the indicated reading for it look accurate?)

It can be setup depending on ecu to use petrol under certain conditions (high load for example), this can be used to compensate for under specced components etc. A look at the settings should confirm that if you have access? Don't know what ECU your using, may help to mention that?

Could also be leaking somewhere.

Of course, £20 of petrol is not a lot anymore either, The last can of fuel I brought for the mower was around £9.

I've run through about 1/4 of a tank every 6 months as long as its set to run on gas all the time, and its got enough gas to run on of course!. But most of my journeys are long so very little is spent with a cold engine (switchover temp is 30 degrees on mine I think, and its only a 2.3 4 cylinder).

I do not have access to the ECU - as in I do not have a cable. I run a Romana system with a Romana ECU.
The car switches around 40degrees but what is odd is that it is not consistent.

1. On a cold start, it can take a long while to switch over - 5-10mins.
2. When I stop the car and head off to shopping, I come back to the car which cools down to around 40 but the car still takes a while to switch over to LPG. The second I drive off, it will change to LPG.

My car is set to run to gas all the time - I just have to wait till it turns over.
My LPG specialist did say he could smell unburnt petrol and that I should change the sparkplugs (this was to troubleshoot the lack of power with my car)

[Gilbertd]

Thermostat failed open? Modern stats tend to fail open rather than closed like the older ones did. That will cause it to take a long time to get up to temperature. If it takes a long time to changeover if you aren't moving but changes over as soon as you start driving, that would suggest the reducer plumbing isn't ideal so it needs more flow than it gets at idle.

[Brian_H]

I'd start looking at the reducer plumbing, easy enough to check with your hand how warm the unit is. It may be possible to get a better flow through it, photos of the plumbing might help get you some advice?

[LPGC]

Romano AEB2568 (and if so what year ECU) or Romano Antonio?

Most can be set to run entirely on petrol below or above a specified (in software) petrol injector pulse duration and rpm.

Some can be set to switch back to petrol if gas vapour is below a certain temperature. In which case they may run on petrol all the time or a lot of the time if the gas temp sensor is dodgy.

Some can be set to run on a specified percentage of petrol at a certain absolute gas pressure (split fuelling 'facility'). In which case if reducer pressure is wrong or the pressure sensor is wrong the split fuelling may be triggered.

Some will run on petrol or give petrol addition (up to 100% petrol) when incorrectly interpreting 'petrol extra injection pulses'.

Those things said, I should probably remember or search the forum to find this info... but what's the make/model of car? Always keep some petrol in the tank... the petrol gauge on some models gives false reading when running on LPG (workaround fixes are usually possible). Also depending on make/model... make/model can dictate where (and how high) in the engine bay and how the reducer should best be plumbed in to the engine heater water circuit - no good if too high or if plumbed in such a way that the reducer sees no flow if the heater is turned off or it might not reach or maintain the 40degrees changeover temp. My own car switches at 20degC, in this weather I can start the engine, back off the drive and it has switched to LPG by the short time / distance of a few hundred yards I have reached the main road.

[v8vroom]

Thermostat failed open? Modern stats tend to fail open rather than closed like the older ones did. That will cause it to take a long time to get up to temperature. If it takes a long time to changeover if you aren't moving but changes over as soon as you start driving, that would suggest the reducer plumbing isn't ideal so it needs more flow than it gets at idle.

In the attached pic, the car was warm. I rev'd it a bit and it then switched to LPG. So hm, I will investigate what the reducer plumbing is and what I need to do.

[LPGC]

2568 then..

[Gilbertd]

Assuming your gauge is the same as most other JLR cars, it will be a compressed scale so will read cold until the engine is up to around 60-70 degrees. If that is the case, even though your change over temperature will be set at something like 40 degrees, so should change over long before then. Both my current cars run single point systems so can, and do, run on LPG from stone cold, a previous one I owned with a multipoint would change over as soon as the gauge started to move off the blue. Simon will be able to advise where the reducer needs to be plumbed in to get full flow as it sounds like you don't have full flow so it isn't getting as hot as it should.

[Brian_H]

Some photos of the bits under the bonnet would help to see where your reducer is being fed with coolant from?

[LPGC]

There might not even be a hardware issue, it could all be software settings related. Romano Antonio has been around for a few years and replaced the older Romano AEB2568 ECU's. Some of the older 2568's have default setting for switchover RPM at 1600RPM... On a V8 Jag 1600RPM might not be reached if just driving steady from setting off.

You could do with the interface cable and software to see what's going on. Check the swithchover RPM and switchover reducer temperature. Obviously if the reducer isn't getting warm until you rev it that will be the problem but will be evident in readings. Even without the software you can use the number1 temperature test (use your hand to feel the temp of the reducer).

I can remember the (unusual) heater water plumbing arrangement on classic, X and S (modern S) types but I'm struggling to remember it on some of the other model Jags. I'll have some pics and info somewhere but I'm in the thick of replying to emails/enquiries and will be straight into converting a Porsche Cayenne turbo in the morning. Edit - hang on, I've remembered the post classic V8 XJ plumbing... if that's what yours is? lol.

[v8vroom]

2568 then..

The system was installed in 2007