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1996 Range Rover P38A
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Discussion Starter #1
This is a long standing problem that is irritating to say the least, but i can't trace the source of the problem.

On a cold start it's clearly over fuelling, the idle is rough and it stinks of fuel. As soon as we're on to closed loop it settles down and it's fine.

On a hot start it will still apply chock and it stinks even worse, but again it will settle down and will be fine.

There are no codes on nanocom, the ecu temperature sender is working perfectly, the injectors have been out and checked.

The motor never fails to start off the key, it just over fuels.

I thought i found the problem when i found the fuel pressure regulator dumping fuel down the vacuum pipe. I replaced the fuel pressure regulator with an aftermarket adjustable one and set the pressure to 38psi at the fuel rail.

No difference.

The only clue i have is that the long term fuel trims are way out at -160 and the air intake says -6C when the outside temp is 20C and i don't know why. I did replace AIT sensor but it made no difference. The voltage to the sensor is good at 5V and i can't find any fault with the loom.

For something to do i kept dialling down the fuel pressure until i got the fuel trims to 0, this all but cured the starting over fuelling but then wouldn't hot start at all, classic symptom of low fuel pressure.

What is telling the engine to add fuel when it's not needed? And why are my fuel trims so far out?

This over fuelling only occurs on open loop, once we get feedback from the o2 sensors it'll settle down.

But on a hot start the nanocom will say we're on closed loop because the engines warm, but we're still on chock for at least 60 seconds, and you can see the o2 sensors maxed out until they've bought the mixture down, and then they start to cycle as they should.

I did blame the LPG messing with the fuel trims for many years, but i've been off LPG for over 1500 miles, still no change.

Anybody got any idea's?

Many thanks.
Andy Rudge
 

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IAT sensors almost always read low for some reason even though yours does seem to be reading very low. However, according to the GEMS ECU documentation, the IAT sensor only has an effect when the intake temperature exceeds 50C so reading low just means it would need to get very hot indeed for it to do anything. I suppose it could be affecting it, one way to check would be to disconnect it and short the two wires together, that should make it think it is very hot.

Assuming it is GEMS, you could always try changing the engine setting to 4.0 litre instead of 4.6.
 

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1996 Range Rover P38A
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Discussion Starter #4
Assuming it is GEMS, you could always try changing the engine setting to 4.0 litre instead of 4.6.
Sorry, it is indeed Gems.

I had shorted the IAT before and it showed 130C, i didn't run the engine on it thinking i could do some damage but i'll certainly try it.

I'll also try changing the engine map to 4.0, i certainly hadn't thought of that.

Thanks.
 

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1996 Range Rover P38A
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Discussion Starter #5
Did LPG installers alter fuelling to account for LPG ?
The LPG is the fully sequential variety made by Tartarini, it has it's own fuel map which piggybacks the petrol map. The LPG map is programmable and adjustable through software which i have.
I have had issues with the software because some of the displayed values are jumping all over the place and won't settle down, i suspect a dodgy connection, but i haven't found it yet. Subsequently i havn't been able to do a successful recalibration because of what i presume is a communication error.
The LPG installation was done by Autogas 2000 about 12 years ago, and in fairness it runs well on the LPG, its just the starting.
 

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If I understand correctly, if the IAT sees a temperature of greater than 50C, it causes the ignition timing to be retarded, so give it a try with it shorted and then maybe try with a resistor (1k Ohm for starters) and see if you can get it displaying something sensible. Are you still using it on LPG? Older Tartarini is probably a rebadged AEB 2568 controller with their hardware. You will have a vacuum hose from plenum to MAP sensor (which on a really old AEB is housed inside the controller) or reducer or both. If there's a hose from the reducer and the diaphragm is starting to show it's age, then gas can leak into the inlet manifold after you turn off the engine. Switching over to petrol before turning the engine off will use up the residual gas in the reducer if that is the case and starting again will be normal.
 

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You say you're not using the LPG system, but have you reset the adaptive values? Those sequential systems that piggyback of the petrol ECU can be a PITA. If not tuned to perfection, they have a tendency to get the petrol trims maxed out, causing poor runing on petrol. It's fundamentally a flawed system, both ECU's try to learn and end up fighting each other, unless everything is perfectly balanced.
Once in closed loop, the feedback will be enough to compensate for the faulty long term trims, so it runs better.

Filip
 
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1996 Range Rover P38A
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Discussion Starter #8
You say you're not using the LPG system, but have you reset the adaptive values? Those sequential systems that piggyback of the petrol ECU can be a PITA. If not tuned to perfection, they have a tendency to get the petrol trims maxed out, causing poor runing on petrol. It's fundamentally a flawed system, both ECU's try to learn and end up fighting each other, unless everything is perfectly balanced.
Once in closed loop, the feedback will be enough to compensate for the faulty long term trims, so it runs better.

Filip
Hello Filip
The adaptive values should adapt themselves over time, but yes, i have reset the adaptive values several times with no joy.
The way you describe the function of the LPG is how i understood it, as i said in my post i blamed the LPG for messing with my fuel trims for years, but that's not how it works. The LPG ECU is not a learning ECU in my application. You can wire the 02 sensors in for the LPG and flag the LPG software to use adaptive values but that is not my application, i have tried it and i couldn't get it to work.
Mine piggybacks off the Petrol ECU, the LPG is calibrated to the petrol at idle and that's just about it, you can fine tune the LPG with road testing but i've never needed to do it, i don't have the software dongle that allows me to access the LPG map anyway, i can only recalibrate, reset errors, which i've never had, and make basic changes.

Richard is on to something by changing the petrol ECU from 4.6 to 4.0, i shall reply in full to his post when i've stopped shouting WTF to myself outload. There are some very strange goings on here and i need to do some more digging.

14 years i've owned this truck, it's never run right.
 

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1996 Range Rover P38A
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Discussion Starter #9
Assuming it is GEMS, you could always try changing the engine setting to 4.0 litre instead of 4.6.
I did this first because it was quick and easy to do. The effects were almost immediate, the idle was more stable for a start. The idle wasn't that bad but it did swim around bit, not what you would expect from a V8.

After a few short journeys my long term fuel trim dropped to just -1.5 and sat there. The drivability was much the same but many have said that GEMS is very good at adapting to whatever it needs to.

Before anybody suggests i've got a 4.0 engine, i'm only the second keeper of this truck. I had the engine out 2 years ago for a refresh, it was clearly marked 46D, although i confess i never checked the crank stroke.

I've no idea what is going on here, but it's clearly better.

I can't find fault with any of the vacuum lines running from the LPG evaporators, but i will spend more time checking the system and identifying exactly what LPG model i have.

I'll run it for a while with no other changes, see how we get on.
 

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I was going to suggest you might have a 4.0 litre in there as the only immediately obvious indication is the number on the plenum top and, as they are otherwise identical, can be swapped over. I know of at least two cars that have 4.6 motors but the plenum says 4.0. However, if you've owned it that long, it's pretty unlikely that it was changed before you got it and the engine number shows it to be a 4.6. Can't explain why it was over fuelling but if by changing the engine size in the ECU cures the problem, then leave it at that. Easiest way to identify the LPG system is to look at the label on the ECU. If it is a Tartarini badged AEB unit it will have AEB 2568 then a letter signifying the exact model engraved in the metal casing.
 

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1996 Range Rover P38A
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Discussion Starter #11
I spoke to soon.

The truck runs well, the idle is still more stable and hot starting is fairly trouble free, but it's decided to trim back to -156.

I'm beginning to think this is a global problem, that means to say a single issue is affecting everything. I think i may have a slight voltage problem.

I have 14.00 V at the alternator and the battery, the cables were replaced two years ago. I understand 14.00 is a tad low, and nanocom is saying 13.74V. This value is at idle but doesn't change when i raise the RPM. I think I need to address this voltage issue first.

Attached is a pic of my LPG ecu, if anybody recognises it. Obviously, there are two evaporators and two injector blocks. 20200605_181040.jpg 20200605_181130.jpg 20200605_181153.jpg 20200605_181118.jpg
 

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What year is the car? Early ones had a lower set point on the alternator than later ones and 13.7V at idle would be right for an early car. If you rev it and it doesn't rise, that just means the battery is good, If you load the electrical system (headlights on, heater blowers on high) and it still achieves 13.7V with a few revs, there's nothing wrong with that. About the only thing that is common to both banks is the MAF sensor, what airflow does the Nanocom show for that?

The LPG ECU has the label on the front but the important information is on the back of it. The reducers look very similar to Tomassetti Alaska while the injectors are Matrix XJ544, one of the best you can get.
 

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I think the alternator voltage thing is a red herring... Have you cleaned/ reset the IACV? As Richard says, IAT probably doesn't have much impact here, but you can search for one of my posts here which details a shunt you can wire in if you want. Maybe post up some nanocom diagnostics so we have the full picture? My over-fuelling seemed to get sorted when I had the injectors cleaned, but you've already covered that. Have you checked the spark on all cylinders? May also be something to do with EGR (beyond my pay grade)
 

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Has it trimmed back while running solely on petrol or when running on gas? The map programmed into the LPG controller adjusts the pulse length for the injectors. If the LPG map is wrong and it is applying too much additional length to each pulse, then the engine will be running rich, the lambda sensors will report it is running rich and the trims will go negative to correct. Think of it this way. If for a given revs and load the petrol injectors need to be open for 10mS and at the same revs and load the LPG injectors need to be open for 13mS, the LPG controller is programmed to add an additional 3mS to the pulse length (as the petrol injectors are disconnected and the pulses from the petrol ECU are used to fire the LPG injectors instead). If the LPG map is wrong and is actually adding 5mS, then the engine will be running rich, the lambda sensors will report this to the petrol ECU and it will adjust the trims negative to drop the injector pulse length to 8mS to give a total opening time of the required 13mS.

However, if it has trimmed back to -156 while running solely on petrol and you aren't using the LPG system at all, then something else is causing it to initially run rich and the trims are altering to keep the mixture correct. About the only thing common to both banks that would affect it is the MAF sensor.

Not sure what EGR has to do with it, they are only used on diesels, unless it was a typo and you meant something else?
 

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  1. Just asking a silly question but has anyone put green injectors in it ? My gems got yellow yet my Thor got green ( same as my 300hp 940 Volvo) just wondering if changed ?????
 

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Good point Richard, for EGR I was really meaning the V8 emissions control, but used the diesel acronym.
 

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That's true, it could be dumping petrol vapour into the manifold from the purge valve (which is what you obviously meant). Simple way to check that is to unplug the purge valve (or junk the whole lot, we managed perfectly OK for years with just a vented petrol cap....)..
 

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1996 Range Rover P38A
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Discussion Starter #18
What year is the car?

About the only thing that is common to both banks is the MAF sensor, what airflow does the Nanocom show for that?
1996.
  1. Please see images for airflow and associated values. These values were after 5 miles, ambient temp 11C, AIT -6C when engine was started.
    286889
    286890
    286891
 

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1996 Range Rover P38A
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Discussion Starter #19
Has it trimmed back while running solely on petrol or when running on gas?

About the only thing common to both banks that would affect it is the MAF sensor.

Not sure what EGR has to do with it, they are only used on diesels, unless it was a typo and you meant something else?
We are running purely on petrol. Considering your last comments about diaphragm leaking gas I'll physically disconnect the LPG to eliminate that possibility.

I'd wondered about the MAF but was restricted to cleaning it by removing the electronic part from the body of the MAF using electrical cleaner and an artist's brush.

I'd also tested the functionality of the purge valve because there is no vacuum when you release the fuel cap, so I suspected the valve may be stuck open, but I could find no fault. But as suggested, I'll remove it and blank off the port. If I simply pull the plug off it, it throws a code.
 

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Discussion Starter #20
  1. Just asking a silly question but has anyone put green injectors in it ? My gems got yellow yet my Thor got green ( same as my 300hp 940 Volvo) just wondering if changed ?????
No idea mate.
 
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