Getting to the point of gving up!

If the wiring with the LPG stuff has a problem, then switching one or two injectors might not be working.

How well have you checked the wiring to the LPG ECU and all injectors?

Do you know someone with a good ECU, who is willing to let you swap over?

Try and get another one from a breakers yard and see if the same fault develops.

Have you changed the lambdas again? Or tested them on another vehicle? Have you got a friendly garage who will plug them into someone elses car?

Unless you have independently verified each component as working on a working vehicle, you cannot be sure.

If you buy ONE new lambda sensor and install it on one bank, then see if there is a difference between the two banks. If there is no difference, then you have to look at the ECU again. There is nothing else left!

Did you check the continuity of the lambda sensor circuits from the plug that goes into the ECU? If the continuity is there, then it is either the lambda sensors (chemically knackered / reacted with something bad) or the ECU itself.

I've been running a VW on LPG for about 2,500 miles now - no problems whatsoever and the emissions and running are fine. I had to do the lambda sensor and temp sensor (only one of each), but that was because both were old (100k miles) - runs perfectly (not a dig, just a technical point about effect of running on gas).

Try ringing The ECU Doctor as a starting point, perhaps they have had a RR ECU with the same problem, with the lambda /closed loop mixture control circuit/chip failing.

Bugger lost my reply.

Swapping out the ECU is not a simple option only person within 50 miles that can do it is a main dealer, last time we used a mobile guy Dynachip who despite the fact they were coming to do another job anyway I was charged £250 for nothing job.

As for the LPG ECU wouldn't even know where the nearest Romano dealer is over in England I think.

The improvement in mpg is holding up did some 700 miles at the weekend 500 motorway and the rest rural roads and driving in traffic and still getting in the high teens, but the hesitation on LPG is getting worse and also now getting the odd backfire on 4 again only on LPG. This leads me to suspect that the two issues are unconnected and the LPG issue is either a poor spark or injector issue.

Bill

The importer for Romano systems is Autogas Worldwide, or MINT LPG. They have their main place at Newport. Their website is MintLPG - Autogas LPG Conversions by The Experts

It could be the LPG injector for cylinder 4 is failing / sticking. There is a filter in the LPG system that does need to be changed every one to two years, about 10,000 to 20,000 miles.

Have you changed the spark plug on No.4 cylinder? You can get rogue plugs.

Have you got an old lead that works that you can swap over on cylinder 4?

If you run it with one LPG injector not working properly, this will alter the fuel map and cause poor running on petrol as well. I think the Romano injectors can be rebuilt.

If you're almost down to 7 cylinders, it's not surprising that the fuel economy is being hit.

I know you have said that you have checked the wiring, but if cylinder 4 has a problem, there might be a dry soldered joint in the loom for that one cylinder, where the LPG system wiring has been spliced into the normal petrol loom.

You would need to resolder the joints, even if they looked/tested OK. I've done some electrical fault finding like that before, and sometimes you have to resolder even though everything says it's OK.

Dry joints can work, but give increased resistance. This would reduce the voltage that the injector would see. As the join gets vibration, it will get worse over time.

You need to concentrate on that cylinder 4.

The +18% fuel trim shift and still only managing to get to 0.35 on the lambda value does indicate a problem on one cylinder.

If you want to wait another 6 months, and drive another few thousand miles, the fault will probably develop to its terminal state of injector failure or wiring failure. You'll definitely know what's wrong then.

Raving man as has been stated the problem is the lambdas are not switching and sending a value to the ecu!
So how can a injector fault cause the problem?
As the gas system lights of the lambda sensor for a signal then in theory as Bill is running open loop then the gas will not be furling correctly and the same will be of the petrol system too!
Now as the petrol system is the primary controller and the gas is the slave but interrupting certain aspects of the petrol system and lifting signals of the petrol system
As it worked for a while then failed seems we need to look at either the gas ecu as it does send a few duff fooling signals to the petrol ecu or we do have a faulty petrol ecu again

Your logic is a bit skewed.

Lambda sensors do not switch. They provide a voltage output depending on the O2 concentration in the exhaust gases.

The ECU is detecting the voltage output that the lambda sensors are generating - 0.35, lean, and as the fuel trims are +28%, it cannot get enough fuel to get the mixture richer, to get the voltage over 0.5, which would then allow the ECU to say the mixture is too rich, to then reduce the amount of fuel, which when burnt will give exhaust gases with more O2, dropping the voltage that the lambda sensor output that the ECU sees.

If you have got an injector that is not working, whether it is the injectors themselves, the LPG ECU, which has got a problem, not giving the injectors full voltage, or the main fuel ECU injector driver circuit, you will get the same problem.

The fuel mixture will always be lean and the lambda sensors will be working, but the fuel trims will be to maximum richness and you will never get the thing to switch (go closed loop), except by restricting the airflow.

You would get a similar problem if the fuel filter was blocked - high in the rev range, or if the fuel pressure regulator was not giving full fuel pressure you would get exactly the same problem all over the rev range.

There might be a filter in the LPG regulator, or the regulator itself not giving high enough pressure.

It might be an earth wire for the ECU and not the ECU itself.

If you have several injectors working off the same lambda signal, one injector going wrong will start to give misfires on that cylinder first, if there is a limitation as to how well the LPG can work down to very lean mixtures, it burns very easily, but even LPG has a limit as to what mixture strength will fire.

If all wiring has been checked for continuity and correct voltage profile at injectors - you need an oscilloscope to do this, then you get to a mechanical problem with the injectors.

If you cannot check the voltage profile at all injectors and check that they are all the same and with spec, you're going to have a long hard slog.

The ECU might tell you what it is doing, but if you cannot check that it is showing the same at the injectors themselves, then you're struggling, except by changing/reconditioning/testing every part, injectors, ECUs, etc separately.

Once you have checked the voltage profile at the injectors and if you find any discrepancy, you need to work back to the voltage output and earth, both the +ve voltage side and earth 0V side to work out where the voltage is being dropped, or if the ECU wasn't providing it in the first place.

I cannot stress this enough, you need an oscilloscope, where you can read at such high frequencies and see every bit of detail of the voltage profile.

Thanks for your thoughts.

I solved the fuel consumption problem a few weeks ago by disconnecting the lambdas and I have now solved the hesitation problem by replacing the coil packs, goes like a rocket ship now. May have to strip it down again as number 5 lead is too tight and pops off!

Alright it still not going closed loop but hey you can't have everything.

it's a LR V8.. it will make you smile then kick you in the nuts.. repeatedly..

enjoy the smiling enough and you don't feel the nut swipe..

Mogwyth said:

Thanks for your thoughts.

I solved the fuel consumption problem a few weeks ago by disconnecting the lambdas and I have now solved the hesitation problem by replacing the coil packs, goes like a rocket ship now. May have to strip it down again as number 5 lead is too tight and pops off!

Alright it still not going closed loop but hey you can't have everything.

Click to expand...

Glad you got it sorted! and you were saying something about giving up eh:doh:

Out of curiosity what spark plugs are you using Bill?

Ngk pfr6n-11

Mogwyth said:

Ngk pfr6n-11

Click to expand...

OK, just that I had issues with mine running rough, misfiring, refusing to go closed loop etc.Traced the problem with aid of Faultmate to the reccomended LR platenum Champion plugs, new set lasted just 8k miles & they went down one by one, replaced with Bosch Supers that originally came with car & now all is well again!

Glad to hear you've got it almost sorted.

Just a small point, did you have any diagnostic results that told you the coils were failing? Or was it only swapping them that showed that they weren't working properly?

Have you tried reconnecting the lambdas since doing the coils packs?

Poor combustion is a good way to give the lambdas a hard time trying to go closed-loop.
Perhaps the mixture was being pushed rich because of the poor combustion, showing unburnt fuel, which would prevent the right signal from ever being seen.

Closed-loop is dependent on almost complete combustion occuring.

If you have high O2 levels with a rich mixture, perhaps it might hit an instability and still have high O2 levels, even with lots of fuel.

This was one of the reasons I suggested a rolling road run at the start, or even getting the car hooked up to another lambda sensor / exhaust gas analyser.

If you ever get high O2 and high HC, CO, then it can be a misfire / incomplete combustion, but insufficient fuel (too lean) shows the same thing.