I went on a 60 mile round trip over the North Yorkshire moors yesterday to pick a bath up. The roads are really nice and you can see for miles. There's loads of uphill, downhill though and i noticed i definitely have a power/performance problem.

Car was really struggling up hills. The acceleration was really slow and when i put my foot down, it changed gear no problem, the revs went up, but we didn't seem to gain much more momentum. Obviously we gained a little bit of speed but it was horribly slow. On the flat, it's fine. From time to time i could hear and feel a low droning/whirring noise. I could liken the noise to a microlight aeroplane overhead. One of those with the big fan on the back or perhaps similar to a dishwasher on a wash cycle. If i recall, it was usually as we were going down a hill and i'd taken my foot off. So basically coasting or over run. whichever the correct term is. Speed was generally 40-60mph most of the way.

Temperature is fine. never moved from the middle. Coolant level is fine. Engine oil level is good. Checked both diffs and levels are fine. Have no fault codes.

On a day to day basis, i'm usually on flat roads with not really any hills so i haven't noticed this as much although i have mentioned in previous posts about thinking the car is a bit under powered. I sold my other p38 yesterday but i drove it before i did, and it went like an F1 car in comparison.

Did you switch to petrol when going uphill, just for comparision?

Could the droning noise just be the air suspension pump firing up?

Shouldn't be, it wouldn't run all the time (in fact, once up to height it shouldn't need to run at all) and the only time you can hear it is when the washers on the mounting studs are on upside down. Normally the only way you can tell if your EAS pump is running is by putting your hand on it.

If it's on the over run I'd suggest a noisy diff but that wouldn't cause it to be gutless.

Switched between lpg and petrol and didn't really notice much of a difference. Perhaps a slight one but we're talking significant slowness here. I know they're not a sports car, but a 4.6 V8 should really be able to fly up and down moor roads. Felt like i was driving a 1litre Micra at times. no poke at all.

Just drove home from my mums which is pretty flat all the way and theres no probs with acceleration. Seems to be when its asked to go up a hill that it's struggling for power. changes down gear and revs go up but no immediate increase in speed. As though the extra power is not being transferred to the wheels. Do the same on the flat and you're off. Had i have not had another p38 i probably wouldn't know the difference but this being my second, i know that there's definitely a problem.

Out of interest Richard, which way do the washers go on? dome side up?

Bottom ones go dome side up, top ones go dome side down so it's only the very centre that is in contact with the metal insert in the mounts.

i don't recall 6 washers on mine when i replaced the mounts. i'll have a look tomorrow.

Any thoughts on the performance issue?

Have i read correctly that if there were an engine misfire, then when the torque converter locks up, the misfire will be more pronounced?

When i saw Simon, he thought that there was a misfire on number 6. I've not had this investigated yet as i want to gather as much evidence as possible to try and correctly diagnose the issue without blindly throwing money at random items. No point only going in as far as an injector, if the problem is further inside, so to speak. Or perhaps i have more than 1 problem. Could the misfire account for the poor acceleration up hill and not be as noticeable on the flat as the engine is under more load on a hill? Although, that doesn't explain the drony/whirring that appears at approx 40-50mph on over-run. Doesn't happen below that speed.

Drone at 40-50 mph definitely sounds like a diff, dropping one or other propshaft off will identify which end. Just make sure you put at least a couple of nuts on the parking brake drum when you test it. The little countersunk screw may look like it's holding it on but it soon works loose and it'll make quite a mess as it makes a bid for freedom from under the car. Still can't offer much help on the lack of grunt though, although running on petrol for a while to make the adaptives reset may give a clue.

Ran it on petrol to rest adaptives when Simon did the LPG. Further investigation required then!

But if you've been running on LPG since then and it still isn't correct, they will have drifted off again.

Don't see how. it's not running like sh**e like it used to before Simon set it up. My idles are pretty consistent on both petrol and lpg.

The old car developed an underpowered issue at one point. Would hesitate to change down when you put your boot down and then when it did, would hesitate to pick up. Turned out to be a 5mm split in the exhaust at the Y branch. Fixed it and it was a completely different.

This however feels a bit different to that. I did ask when i took it for MOT about an exhaust blow but the guy reckoned it sealed up ok for the emissions so i've kind of discounted that theory on trust that he's right. Sorting that stainless exhaust today so i'll be checking it again.