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1995-2002 Range Rover P38A
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Discussion Starter #1
I have been a P38 owner for 12 years and recently picked up another 1998 Range Rover P38 4.6 that was running but throwing exhaust gases from the head gasket when I bought it. I was able to drive it home at freeway speeds with reasonable power. About a week later I drove it from my home to my mechanic, about 1 mile away, where it started to lose power and I assumed it was running low on fuel. My mechanic replaced the head gasket, did a valve job, and put it back together. From that moment on it has had the same persistent problem. It will idle reasonably well with a little bit of fluctuation, but then when the accelerator is pressed it will start to knock, choke, hesitate,idle poorly, and will rarely go over 3000 RPM and is eventually accompanied by a strange foul smell. Upon further investigation I discovered that one of the catalytic converters had been melted so they've been replaced with an exhaust system from a previously known running vehicle and appear to be breathing fine. After clearing 9 fault codes I am still getting both P1509 and P0340 no matter how many times I clear the faults and then run the vehicle. The ignition wires and plugs are new. I have replaced the camshaft position sensor with with a new one with no difference. The idle air control valve, fuel rail and injectors, have all been replaced with ones from a vehicle that was known to run well before. I would appreciate any suggestions!
 

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1995-2002 Range Rover P38A
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250 Posts
P1509 Is "IACV stepper motor short circuit" and P0340 is for the camshaft position sensor "A" circuit. (writing them down for my own reference). Have you put a gauge on the fuel rail to test the pressure when driving? Some initial thoughts of mine are that it's giving enough pressure when the engine is at idle but is struggling to maintain line pressure with higher revs. Those two codes don't give me a warm and fuzzy though and should be investigated. Probably worth a double check to make sure they are plugged in all the way and also the wiring all the way back to the ECM. Also, double check that the grounds are all good and tightened.
 

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1995-2002 Range Rover P38A
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134 Posts
The codes should be investigated, probably a wiring issue. I think it's a red herring for your car running poorly, but it may be an indication of wiring loom problems. If you had a melted cat, unburnt fuel was getting into the exhaust. In general, this could happen due to either ignition problems or overfuelling on that side of the motor. What are the fuel trims from the ECU? Does it think that you are running lean or rich? Not sure if GEMS stores adaptations, but it probably does. You need to clear them, your ECU has "learned" a bunch of things about your engine that are no longer true after you did gaskets and exhaust.

The old rule of thumb is to rule out ignition issues prior to messing with fuel system. I'd pull the plugs and read them. They can tell if a cylinder is running lean or rich. The ECU may or may not detect a misfire, but spark plugs don't lie. Install new plugs, double check that the plug wires are connected correctly (they were incorrectly connected on my truck when I got it). Check the wiring to the coils, if you have other wiring issues it's possible that wiring to the coils is bad. If you ahve noid lights you could throw them on to check that the ignition is firing correctly. It could be a bad coil that craps out at higher RPMs because it needs to fire more times per second. You will easily see that with noid lights.

Once you are confident that ignition is ok, start looking at the fuel system. You could have a wiring issue with the injectors too, just like you would with ignition. I believe that the ECU opens the injectors by completing the ground circuit. if you have spurious ground due to damaged insulation, you could have an injector that fires when the damaged wire grounds itself, not when the ECU tells it to. You can use noid lights to troubleshoot electrical issues with injectors wiring. If they seem to be firing correctly, I would get a set of known good injectors. You could have a sticky injector or two flooding cylinders and causing a misfire. That would explain the cat damage. They could be sticking at higher RPMs and working ok-ish at idle.
 

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1995-2002 Range Rover P38A
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Discussion Starter #4
All great advice. Over the week I'll start going through and trying to rule out each idea. Especially the coils, which I haven't thought about.
 
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