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1995-2002 Range Rover P38A
4,216 Posts
Discussion Starter #1 (Edited)
Hi all,

Have an interesting, random issue with my 2001 Vogue... only has happened on a couple of trips, once she's been up and running for a fairly long time - both times after over an hour of solid, hassle free driving. Both journeys where I've experienced this were mostly high speed motorway driving (70mph - 2500rpm on the clock), and both journey's I've had this happen were at times when I was at cruising speed on the motorway, not on cruise control though.

So... The problem:

About 50 odd miles into the trip home (about 145 miles) cruising on the motorway I felt slight jolt out of the vehicle. Felt a bit like a 'hiccup' almost as if you sharply lifted and re-applied your foot to the throttle. I had been at 70mph for a good half hour or so, 2500rpm on the clock when it happened. Was running on Petrol at the time as the LPG was getting low. Happened a couple more times - one was a fairly fierce jolt.

Only happened a couple of times on LPG, but not as violent, and I wondered if it was because the gas pressure was getting low.. Anyway... Made it another 60 odd miles to the services that had LPG for sale – and had about 3 or 4 more ‘hiccups’ along the way. The petrol level was low too, so filled both petrol and LPG at the services (35L of petrol, about 45L of LPG). Got the Nanocom out whilst stopped, and read codes from engine ECU.. P0172 and P0175 running rich both banks. As you may know from my other thread last year, I have had these since owning the vehicle, and think it's down to the LPG system running a bit lean, so when on petrol it ends up running rich. I reset the adaptive values at the services (in case the fuel trims being at max were having an effect) and causing something weird.

Get out the services and a few miles down the road it happens again on petrol - fairly sharp jerk at 70mph. No noticeable change/blip on the tacho though (any of the times this has happened) – still reading 2500rpm. Switch to LPG, and run rest of the way home on gas, and seemed ok...

I initially thought maybe fuel pump - but I can sink my foot to the carpet, and she'll happily rev and accelerate without hesitation from a standing start. If it was a fuel delivery issue then I would have thought that it would be apparent under hard acceleration where a lot of fuel is required quickly! Also, as it has happened on LPG a couple of times which has nothing to do with the petrol pump, confuses me a bit.

Also wondered if it could be the Autobox slipping? It seems to have a bit of a weird hard shift in between 3rd-4th gear anyway sometimes.. fluid and filter is to be changed soon - when the weather lets me! Also, in the nanocom all of the shift pressure/speed ranges you can look at are at 0 apart from one value (can’t remember which, but it was in the upper gear ranges) was at 253.. seemed a bit out of place, but I’ve never had any other values to compare it to..

Any other ideas? In the past the TPS, Crank sensor and MAF have been changed as mentioned in the other thread.

Around town, and when engine is under load, she seems to pull OK, and doesn't falter on petrol or LPG. I didn't notice the issue when driving to London the other night, or from London to my destination - but then these weren't as long single stretches on the motorway as the return journey as I was coming back in one trip, not stopping overnight half way.

I am confused as to whether it's an engine issue - as it feels like a sudden drop in power, followed by a sharp restoration in power - but as mentioned - the tacho doesn't waver from it's indicated rpm. If it was a falter in the engine, wouldn't the rpm briefly dip before restoring? (like when I had rough idle issues)

I have an aftermarket MAF, which seems to have been running fine - but would a sudden spike/drop in MAF reading cause this? I would have thought that the ECU would just revert to OPEN LOOP mode, like it does if you plant your boot, or if the MAF is disconnected?

Could it be something momentarily slipping in the gear box, due to heat from running for a long period of time at speed? As mentioned above, I have fluid and filter to replace in the autobox, but every time I am at home, it's p**sing with rain, and I don't have anywhere undercover to work. It's top of the list as soon as there's a ray of sunshine though...

Could it be something in the transfer case? I'm pretty sure my VC is seized - though I don't see how it would have any affect like this. I have a second-hand replacement VC to fit (which I'm planning on doing along with the transfer case fluid when I get the weather to do the autobox service). I have some drivetrain whine still (probably from the second-hand 4 pin diff I put in the front a year ago or from the transfer chain) but if it was an issue with the chain in the transfer case, then surely I would get the 'machine gun' popping under heavy acceleration... she might whine a bit, but definitely no machine gun sounds from anywhere on the vehicle...

Has anyone else had any similar symptoms or issues such as this?

Just to recap - ONLY seems to have happened whilst cruising at speed, on the motorway after a fairly long period of driving. Around town is fine, and I can put my boot to the floor from a standing start and get to 70mph on petrol and LPG (motorway onramp... not hooning around town!) without any hesitation, or weird effects from the engine I would expect from a fuel delivery problem. There were no misfire codes stored when I hooked the diagnostics up, no CEL, MIL etc.


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