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Discussion Starter · #1 ·
Hi

Ihave a 1996 4.6 hse which has a brc autogas sequential system fitted and have only been able to cover 40 miles in the last 5 months because of running problems.
It started with what i can only describe as a pinking noise from the drivers side bank of cylinders, so i took it to a so called expert who replaced leads and plugs, which i had already done and said the car was ok. i picked up the car and on the way home it was still pinking.
i had to park the car for 5 weeks and tried to start it only to find it was not running on all cylinders and popping back through the exhaust i got about 1/4 of a mile before it stopped. so back to the expert for some rovacom diagnostics and more leads and plugs, fuse box,2 x fuel pump relays, fuel filter, crank sensor, airflow meter,altenator, nad a bill for nearly £1000 it had taken 3 weeks before this i had replaced the valley gasket in a bid to cure the pinking as it seemed to be drawing water from the rear waterway into the rear cylinder on the driverside bank , so i picked up the car and it started ok but on the journey home it was missing between 2000-3000 rpm and the expert assured me it was some stale fuel even though he had put £40 worth of fresh fuel in after draining the tank. i then took the car for a mot test and had to replace the middle exhaust section but the emmisions were through the roof on both gas and petrol so the mot station replaced the lambda sensor and then it started playing up again not starting or when it did it would not rev more than 1500, so new coils were fitted but were no good so a second set were fitted and it was running again unfortunatly it rained and it reverted back to not revving more than 1500 rpm which results in the car popping back through the exhaust and coming to a stop after 3 or 4 minuits. i did a compression test and it read 175 on all cylinders dry but the car is now sitting on the drive again and has cost me a total of £2700 for approx 40 miles has anyone any ideas the mot station think its the ecu but im not convinced.I have also replaced the battery last week as the old one had a cell down.
 

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Hi,
Just a thought,the wiring for the coil pack runs across the rear corner of the inlet manifold A bank side.I have had several with misfires where this wiring has been trapped by the coil pack bracket.It may be worth a look.
I'm in West Sussex,if you have no luck,let me know if i can help.
Mick.
 

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If you have been experiencing pinking you are running too lean. Check the stepper motor, clean thoughly the throttle body and set the base idle. Have you checked if the fuel temperature sensor is working properly.
Another possibility is a faulty fuel pressure regulator (you haven't mentioned it in your post). The fuel pressure regulator maintains proper fuel pressure to the fuel injectors. Problems with this device will likely result in a fuel starved engine thus it will stall.
Another thing to check is the idle air bypass valve.
Good luck.
 

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What LPG system do you have?Can you start and run on gas,if so undo the hose clip on the air flow meter and seperate the afm from the plenum pipework and try it like this. If not start on petrol switch over to gas then remove the afm.Why?,Without the afm the ecu will put out a default set of values,the lpg system should take care of the fueling with the exception of the throttle position switch which the lpg will need.if it runs better the next step is a lil long winded
 

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Discussion Starter · #5 ·
scoobymick said:
Hi,
Just a thought,the wiring for the coil pack runs across the rear corner of the inlet manifold A bank side.I have had several with misfires where this wiring has been trapped by the coil pack bracket.It may be worth a look.
I'm in West Sussex,if you have no luck,let me know if i can help.
Mick.
Thanks for the suggestion, The wiring all looks ok, I have since fitted a new coolant temputure sensor but its still the same, i refitted the old air flow meter and it runs exactly the same. it will start after about 4 or 5 turns of the key and will tick over roughly but any attempt to give it the trottle results in it stalling or if i feather the trottle it will rev to approx 1500 not on all cylinders and then start hunting before stalling. I have also isolated the gas system but no improvement, im now wondering if its the cam shaft position sensor.
Thanks Steve
 

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Discussion Starter · #6 ·
shiftech said:
What LPG system do you have?Can you start and run on gas,if so undo the hose clip on the air flow meter and seperate the afm from the plenum pipework and try it like this. If not start on petrol switch over to gas then remove the afm.Why?,Without the afm the ecu will put out a default set of values,the lpg system should take care of the fueling with the exception of the throttle position switch which the lpg will need.if it runs better the next step is a lil long winded
Hi
Its got a brc gas system which has individual injection tapped into the inlet manifold which is controlled by its own ecu, i have disconnected the gas sytem completly and its still the same.Unfortunatly it wont start on gas and with the backfiring at the moment im a bit reluctant to try, I did disconnect the wiring to the afm yesterday and it didnt make any differance it still ran the same, i dont know if this is a good or bad sign ? when i was able to drive the car it used to pink on gas and petrol on the drivers bank of cylinders.
Thanks Steve
 

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Discussion Starter · #7 ·
Hi
At the moment i cant get the car to rev high enough to see if its still pinking and the weird thing is it looks really rich on the plugs which if i try to rev the motor results in wet plugs , where is the fuel temputure sensor located?? i did try a new coolant temp sensor yesterday but its exactly the same. I will check the idle air bypass valve today, and according to the garage that attempted to fix the car the fuel pressure is correct, i have also cleaned all the trottle body assembly, do you think it could be the cam shaft position sensor ???
Thanks Steve
 

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Quote, "Then it rained again"
from your info it is running to rich,If it passed the MOT with a new lamda then this is a good place to start,put a test meter on the lambda sensor,it should cycle 0to5 then 5 to 0 and so on as the ECU controls the mixture.Then check the wiring .and the engine earths.If unsure of the earth points run new ones to eliminate.The wiring on the P38's is SHite,the insulation goes hard and brittle then cracks,so far on my own I have had problems with the coil pack,auto g/box lambda,s and axle faults,all through cheap cables :dunno:
The eletrics are like a woman,wired up wrong and youll never make sense of it :)
 

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Discussion Starter · #9 ·
Still not running right !!!!

UPDATE:

The car now starts and ticks over although not very well, I have removed the engine management loom and repaired a few nicks in the coil and ecm wires.
I have cleaned and checked the air purge valve seems to be working ok.
I checked the trottle position sensor and although i have no measurements
it does vary the resistance when moved open and shut. I did find one of the new plug leads was arcing against the head and replaced this.
The fuel pressure when running varys between 30---35 psi again i dont know if this is correct and the altenator seems to be putting out between 13.6---15.01 volts when running.
I also had a auto electrician spend an hour testing various sensors etc and he wants to strip out the wiring from the ecm to the gas ecu to isolate the gas system from the circuit, i am tempted to do this myself as it looks like spaggetti junction.
Any ideas anyone ?????
 

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Hmmm! Just a thought, but are you running on low octane fuel? If so, change to high octane, this could be your problem. With regards to the fuel pressure, your within range, so is your volt reading.
 

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Try this.undo the clips on the rubber hose that connects onto the AFM and loosen joint.Start car when idleing split the joint and move the AFM up out of line so that the airflow is not going through the AFM.Then gently try and rev the engine.It should cut out like it is starving of fuel ,releasing the throttle should bring it back to idle.Diconnecting the gas ECU shouldnt prove to difficult as long as you mark up all the wires and where they go.
 

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Discussion Starter · #13 ·
????

shiftech said:
Try this.undo the clips on the rubber hose that connects onto the AFM and loosen joint.Start car when idleing split the joint and move the AFM up out of line so that the airflow is not going through the AFM.Then gently try and rev the engine.It should cut out like it is starving of fuel ,releasing the throttle should bring it back to idle.Diconnecting the gas ECU shouldnt prove to difficult as long as you mark up all the wires and where they go.
Hi
I did as you said, and the tickover stayed the same, when i revved the engine it got to 2000 rpm and then cut out. and as usual it took about 5 or 6 turns of the key to get it started again. when i rev it above tickover it will get to about 1500---2000 rpm and then the revs drop and it starts hunting before cutting out. Also when its running the dash lights flicker and im wondering could the solenoid for the gas system be cutting off the fuel it normally changes from petrol to gas at 2000rpm but then i have taken the main fuse out of the gas system.. ive never had such a problem with a car all the signs keep contradicting what would make sence...
Thanks
Steve
 

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I wonder if during the course of fitting your motor up with the gas conversion, someone at the workshop hasn't fiddled with the idle control valve. Have you checked the ICV? Your problem could also be caused by an injector sticking open. Your O2 sensor sees a rich mixture and compensates with a leaner fuel mixture which causes your idle to fall, and, the Idle control valve compensates by trying to increase the idle speed. This would explain the revs 'hunting'. Have all your injectors checked to make sure they are all firing a uniform stream of fuel, one of them may be the culprit.
 

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Discussion Starter · #15 ·
Thanks

Hi

Thanks for the suggestion, the original garage reckoned they checked the injectors but like everything else they said they did its probally worth checking again. The icv seems to be working ok. I have done 80000 miles with the gas conversion ands its never been a problem until recently, but everyone who has looked at the car seems daunted by the fact it has a gas conversion and when they havent been able to sort out the problem the gas conversion gets the blame.

Thanks
Steve
 

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4.6 man said:
Hi
I did as you said, and the tickover stayed the same, when i revved the engine it got to 2000 rpm and then cut out. and as usual it took about 5 or 6 turns of the key to get it started again. when i rev it above tickover it will get to about 1500---2000 rpm and then the revs drop and it starts hunting before cutting out. Also when its running the dash lights flicker and im wondering could the solenoid for the gas system be cutting off the fuel it normally changes from petrol to gas at 2000rpm but then i have taken the main fuse out of the gas system.. ive never had such a problem with a car all the signs keep contradicting what would make sence...
Thanks
Steve
Hi steve,
The engine should run at idle with the AFM disconected.The ECU only looks for feedback after approx 550 rpm then it should go out of range and the engine cut out.not familliar with your LPG system,most dont rely on the AFM,only the lambda.So with the AFM disconected from the plenum the only thing that could happen is a loud bang.Try removing the fuse for the petrol pump,then running on gas.Killing 2 birds with 1 stone,fuse ensures your not supplying both LPG and petrol at the same time.If it runs then it looks like the AFM.
Or substitute The AFM for a known good 1
 
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