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Looking for a bit of a pointer in the right direction please….

My 2000 Thor has started running very poor on petrol particularly when cold but also when hot too. It can be almost cutting out when cold and no response to throttle now and then, I think I can hear popping fro exhaust when it’s playing up too.

When hot it’s sounding like it’s misfiring but nanocom says not, it’s running “lumpy”. The car shakes gently.

It runs perfectly on LPG. It also runs perfectly when I reset engine adaptations.

I get p0172 bank 1 mixture adaptation factor few signal too low and p0175 bank 2 as well.

Clearing makes no difference.

Today though resetting adaptations has made no difference….

I’ve changed the MAF for a new genuine Bosch one. Initially I thought it fixed it as it was ok for a while.

I also put a bottle of injector cleaner thru.

It has 2 new coil packs, new leads, new plugs, fresh oil, new air filter,

Where shall I look next? I have nanocom but don’t really understand the numbers!

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O2 sensors maybe?

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I’m no expert on this but I don’t think O2 sensors will modify the fuel enough to make it run that poorly. I think you could confirm it’s not the O2’s by disconnecting the plugs to the upstream sensors (downstream sensors don’t modify the fuel trim). The ECU should then go into open loop and run quite fine if the rest of the system is fine.

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Which are the up stream ones please?

What else could do this?

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Up stream are before the cat on the engine side.

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Update, disconnected the battery for about 4 hours yesterday while i replaced some coolant hoses that had gone hard and weeping. After reconnect, engine ran really well on petrol. Did 2 x 15mile journeys both from cold.

Will see how it is today. Weird though.

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I recently purchased P38 4.6 Thor that ran terribly, it would not go over 50mph and was just terrible. The previous owner had replaced the Lambda sensors with new after market ones that did not fix the problem. I took it to my local LR expert who diagnosed and replaced them again with genuine ones. After 20minutes of driving the car was back to new.

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for £80, i might just do them anyway. They are 21 years old after all!

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@harv, there's no downstream sensors on rest of world spec cars, only NAS.

I've not known them cause really bad running, but I do know if you run a GEMS with the lambda sensors disconnected, the ECU progressively weakens the mixture until it won't run at all. GEMS uses 5-0V sensors with 0V being rich, whereas Thor uses 0-1V sensors with 0V being lean so it could be richening the mixture sufficient for it to run badly. Although with a multipoint slave LPG system, it would run badly on LPG too.

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There’s a fairly experienced guy on Landroverforums who swears by leaving his lamba’s disconnected on his Disco 2 (Thor) all the time. I think it would work the same on a P38 Thor. Personally I wouldn’t recommend this other than for troubleshooting.

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Sorted the problem. Was LPG map causing the Thor ecu to learn incorrectly which is why when disconnecting the battery for a long time or resetting adaptations sorted it for a short while.

I didn’t change the lambda sensors because i thought the readings were within spec.

My LPG service place gave the system a service and upgraded the firmware and create a new LPG map for me.

All well now!

Now onto the next issue. Went thru a car wash today (rare, as I usually DIY), and got wet shoes. Water pouring in drivers side bulkhead somewhere!

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Wouldn't like to say ---- heater matrix 🙄🙄

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I missed this thread or I might have suggested the problem could be LPG calibration.

As mapping LPG systems go they don't get much simpler than on a P38... Was it the same firm you visited that messed up LPG calibration in the first place?

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It’s a new (to me) lpg place that sorted me out.

I think the previous map was set when the vehicle had problems and was over compensating.

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Symes wrote:

Wouldn't like to say ---- heater matrix 🙄🙄

No not the matrix, the water is pouring in on the other side, against the firewall/bulkhead. Probably thru the pollen filter.

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If you have a Prins LPG system, there is no map - it bases its LPG injector times on the petrol injector times. However, if the LPG installer has set the Rc wrongly, it will cause these sorts of problems - could be the adaptations were out when they set it up, but they didn't have a tool to reset them?

Good to hear you've got it sorted.

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GasMan wrote:

If you have a Prins LPG system, there is no map - it bases its LPG injector times on the petrol injector times. However, if the LPG installer has set the Rc wrongly, it will cause these sorts of problems - could be the adaptations were out when they set it up, but they didn't have a tool to reset them?

Good to hear you've got it sorted.

Just about every sequential LPG system you'll see these days bases it's ginj (gas injector pulse duration) on pinj (petrol injector pulse duration) but most have a map. Prins VSI1 is a bit of an exception because unlike most systems it doesn't have an easily visible map but there is still a map if unseen... because the combination of offset and multiplier mathematically describe the same kind of curved multiplier line that other systems have. Egas and some BRC systems are similar in only having a control for offset and multiplier.

Most Prins dealers don't realise this and mess up mapping on VSI2 systems or any other system they try to calibrate that isn't VSI1 or BRC... They don't realise that if they plot points on a graph for a given offset and multiplier they'll end up with a curved line, and if they attempt to calibrate a system that only has the multiplier line or only has a set of boxes for multiplier the positions of the points on the line (or the shape of change of numbers in the boxes) should also be curved.

The shape of the curve should depend on the spec of the engine, the spec of it's petrol fuel system, the reducer pressure and reference pressure, manifold pressure, the spec of the gas injectors which includes the opening time, closing time and flow rate (including partial flow rates when the injectors are partially open during opening and closing).

We can draw a line for any combination but some combinations won't work due to limitations of injectors and/or pressures. With only a couple of controls (offset and multiplier) the line won't necessarily match the ideal multiplier all the way along it's length.

VSI1 won't cut it on a lot of modern engines, which is one reason why they introduced VSI2. The points above hint at why Prins VSI1 installers are so inadept at getting good results when they try to fit VSI2 or any other modern system - bolt on guys not LPG conversion experts, main focus on nuts and bolts not the finer points of correct fuelling.

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Very interesting read!

Anyway, my p38 is running lovely now! Smooth imperceptible change over, same or maybe more power on LPG, petrol isn’t lumpy any more after running on gas for a while.

Very please and we’ll worth finding someone who understood VSI1 even if they were half a tank of gas away!