P38A 1999 Range Rover P38 4.6 Thor

I'm guessing you would have spotted this when pulling the rocker covers, but could it be a massive vacuum leak. It will run rich on start up then massively lean out after a couple of seconds if you have a leak.
Just out of interest, what happens if you unplug the MAF sensor before starting?
I'm trying to think if the idle control valve could cause this issue, but whatever it's doing, I would have thought the MAF would allow the ECU to compensate for it anyway.

Quesntion:
If the idle control valve fully closes, do you get any air to the engine on these cars? Could it be worth cracking the throttle body open slight (assume you've tried this).

Montyjohn said:

I'm guessing you would have spotted this when pulling the rocker covers, but could it be a massive vacuum leak. It will run rich on start up then massively lean out after a couple of seconds if you have a leak.
Just out of interest, what happens if you unplug the MAF sensor before starting?
I'm trying to think if the idle control valve could cause this issue, but whatever it's doing, I would have thought the MAF would allow the ECU to compensate for it anyway.

Quesntion:
If the idle control valve fully closes, do you get any air to the engine on these cars? Could it be worth cracking the throttle body open slight (assume you've tried this).

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The rocker cover gaskets we split in places but the covers themselves are in good condition as are the pipes coming from them.

i have unplugged the MAF and tried to start it and it just won’t start but I did read somewhere the the Bosch engines won’t start with the MAF unplugged. I haven’t tried propping the throttle body open slightly to see if it will run but I can tell you that the IAC vibrates heavily when the ignition is on. Could this be indicative of a fault?

It will start and run with the maf unplugged, it falls back to defaults, which could further suggest trims are a long way out

IAC should hum/vibrate with ignition on

kermit_rr said:

It will start and run with the maf unplugged, it falls back to defaults, which could further suggest trims are a long way out

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Another spanner thrown into the mix. I have reset the adaptions prior to this with my Hawkeye and it is reading trim 1.00:1?

If it is the fuel trim (I had no idea they could go so far off that it wouldn't run) but if they can, it would seem it's running too rich. My reasoning being that unplugging the MAF should make it run richer, so if unplugging the MAF makes it worse, and assuming it's a trim issue, then it's probably running rich.

Assuming you don't have a nanocom, you could test this by introducing a vacuum leak downstream of the MAF. Slacken off a jubilee clip, and wedge somehting in there that's impossible to accidently slip inside. Coat hanger maybe.

Another thing I would try is whacking a timing light on one of the leads, and see if it still lights up as it dying. It wouldn't prove you have a strong enough spark under compression, but would eliminate somehting daft like the immobiliser doing something it shouldn't.

Or, could you try spraying easy start and continue spraying. Does this keep it running?

normally things run better with no MAF, pointing to a MAF problem. if its worse/not running with no MAF, ie on default values then.. erm..
can't be an air/vacuum leak after the MAF
are you sure the O2 sensors are working properly? could try unplugging them and the MAF, see if that runs? beyond that you need to see injector pulse times. could there be a short somewhere causing the injectors to stick open?

kermit_rr said:

are you sure the O2 sensors are working properly? could try unplugging them and the MAF, see if that runs? beyond that you need to see injector pulse times. could there be a short somewhere causing the injectors to stick open?

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Can the O2 sensors ever be so bad it won't run. I figured the ECU wouldn't allow it to go that far off.

Am I right that to fit LPG they splice into the injector harness? Could be a failure point worth checking.
It's a shame the injectors are so hidden, would be interesting to stick one in a bottle, fire it up and see how it behaves, especially when dying.

I wonder if the garage really did monitor the fuel pressure as it was dying.

Montyjohn said:

Am I right that to fit LPG they splice into the injector harness? Could be a failure point worth checking.

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newer ones, yes, they are spliced 'inline' with petrol injectors so there is no emulator signal, this also means petrol fuel trims can be pushed way out if the lpg map isnt correct. I can across this when i was setting up mine, it would run fine on LPG because it has its own fuel trim, but distorted the petrol trims so it barely ran at idle. thats why i asked earlier if we're sure the LPG is set correctly

kermit_rr said:

normally things run better with no MAF, pointing to a MAF problem. if its worse/not running with no MAF, ie on default values then.. erm..
can't be an air/vacuum leak after the MAF
are you sure the O2 sensors are working properly? could try unplugging them and the MAF, see if that runs? beyond that you need to see injector pulse times. could there be a short somewhere causing the injectors to stick open?

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I will give this a go and see if it makes a difference, I’m assuming I should start by un plugging them before the cats first and then after? Or does it not matter

kermit_rr said:

newer ones, yes, they are spliced 'inline' with petrol injectors so there is no emulator signal, this also means petrol fuel trims can be pushed way out if the lpg map isnt correct. I can across this when i was setting up mine, it would run fine on LPG because it has its own fuel trim, but distorted the petrol trims so it barely ran at idle. thats why i asked earlier if we're sure the LPG is set correctly

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My system is fitted with an emulator pack just to the right of the engine. When the LPG tech was out he believed it to all be working. Do you think it’s worth getting him back out to inspect it and see?

its the older type of lpg system if it has an emulator. it could be broken and sending gas and petrol at the same time? or doing who knows what

kermit_rr said:

its the older type of lpg system if it has an emulator. it could be broken and sending gas and petrol at the same time? or doing who knows what

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okay, I will see how to isolate the LPG system and see if that makes a difference. Fingers crossed. I checked for a healthy spark from the plugs and they all seem to be sparking well and right up until the engine stalls. At a lose really now spent nearly 600£ in the last couple of weeks replacing things as advised by garages who don’t seem to know what they’re doing. Shame there’s no folk round my way that are savvy with these cars

The simple way, disconnect the solenoid so it can't open the gas supply, then undo the low pressure pipes to the lpg filters, there shouldn't be much gas to let out. Then you can rule out lpg
Just be sure to reconnect the filters after the test, you don't want any leaks

Double check all the LPG pipes to inlet manifold are good with no air leaks. Another way to block the gas, is to unplug the LPG injectors.

Did exactly this when I was firing up my project after engine rebuild & LPG system deactivated. In my case the Prins ECU was connected, but without any 12V power. I'm guessing the ECU uses relays to pass the petrol injector wiring through ?

kermit_rr said:

the exhaust joins to a single centre muffler, then splits again, so the pipes at the rear dont reflect whats happening on a particular bank.
if theres nothing coming out of one side, there could be a restriction in the rear muffler on that side

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Not unusual for the baffle to fail or indeed the cats. When the cats failed on MrGorsky's I had a hell of a job getting it to keep running. Feathering the throttle I gradually got it up to the red-line, plated my foot and as it hit the rev-limiter there was a pop and fragments of catalyst blew all over my back garden!

Grrrrrr said:

Not unusual for the baffle to fail or indeed the cats. When the cats failed on MrGorsky's I had a hell of a job getting it to keep running. Feathering the throttle I gradually got it up to the red-line, plated my foot and as it hit the rev-limiter there was a pop and fragments of catalyst blew all over my back garden!

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I had the same on an S reg 4.6.....just would not rev, blocked baffles was the cause too....

Hi all, sorry for going AWOL been a busy week. So I have the car back up and running, I took a known to work MAF and placed it on and she seems to be running near perfect however she still has a slight rough idle to her. I have looked at the live day and the O2 sensor values on the DS don’t seem to be doing much if that makes sense. Both values seem to hover between 0.018 and 0.040 with bank 1 momentarily reading 0.444. Does this indicate that both sensors are intact goosed? I don’t think cats are blocked as there is a steady flow of visible smoke coming from the exhausts.

If the lambda values are changing then they must be doing something.