stevieb wrote: Mandrake wrote:
stevieb wrote:PS is your car an auto or manual ?
Mine's manual, which helps me suss out power/mpg issues with the onboard computer. I rarely see anything as low as 20mpg though (apart from booting it, ahem). Just recently I was getting mid-30's mpg over 1000 mixed miles which isn't bad for the 3-litre monster. Mid-40's is easily achievable on long 70mph journeys
The mpg improved the most after I'd had the Terraclean treatment last year - that made a HUGE difference.
Lucky bugger. I wish mine was a manual...
The highest I've seen was 32.8Mpg on an 800 mile holiday trip with 4 people and luggage, but that was back before I had the first symptoms of trouble. On high octane petrol doing mixed driving but mostly 30mph I was seeing up to 23mpg for a while but now I'm back to really short (3 minute) trips again during the week it has dropped to 20mpg.
I'd love to recommend a few tests you could do for comparison's sake, but the lack of an onboard computer hampers things, nevermind the silkiness of the auto box hiding other tell-tale signs.
It's a shame they never fitted a trip computer on the Xantia - I've been told that the trip computer from a 406 V6 (D8) can be fitted to the Xantia relatively easy - just finding somewhere to mount it and running a few wires including one to the engine ECU - the code is still in the ECU to drive the missing trip computer but the wire is missing in the wiring loom.
I don't know about silkiness - the torque converter clutch on my gearbox is pretty worn so although gear changes are fine the transition from unlocked to locked is not exactly the smoothest sometimes. This manifests particularly when you're coasting at slow speeds - the gearbox will often unlock the torque converter to let the engine idle while coasting to reduce engine braking, when you put your foot down suddenly it tries to lock up quickly but with a slight delay then a bit of a jolt. Can't do much about it - I thought the gearbox was on deaths door nearly 5000 miles ago but after a few oil changes and some lubegard it is still going and apart from the torque converter lock up being a bit abrupt sometimes it still seems to be working ok - no clutch slip of the gears or other misbehaviour even under full acceleration, so any extra mileage it does is a bonus.
The auto adaptive gearbox really does muddy the waters though when trying to judge the engine performance, because both the gear change thresholds and the torque converter lock-up strategies change with both gearbox temperature and driving style, and whether the torque converter is locked or unlocked makes a big difference to the apparent performance and responsiveness of the engine.
For example it tends to stay unlocked a lot when the gearbox is really cold to warm it up quickly, (especially the first few minutes) for mid temperatures it has a mixed locked/unlocked strategy and over about 105 degrees it starts to strongly favour lock up - so after a really long spirited drive with a hot gearbox it will tend to keep the torque converter locked up even when you're down at 1200-1500 rpm pulling up a hill in 3rd for example which can curtail low rpm pickup a lot compared to it being unlocked. These variations in behaviour make it hard to judge performance.
What is really obvious though is lock up behaviour in 2nd gear when the engine performs well and when it doesn't. When accelerating through first and second it will start off unlocked but if your driving speed keeps you in 2nd gear with moderate acceleration and rpm for more than 2-3 seconds it will start transitioning from open to lock up.
When this happens the torque converter lock up places a lot more load on the engine - by trying to reduce the slip you're trying to accelerate the car but at the same time the reduced slip reduces the torque multiplication effect, hence it places a lot more torque load on the engine. When this happens there are two possibilities - the engine rpm holds steady and the car accelerates as the converter locks up, or the car stays at the same speed and the engine rpm sags.
When the engine is running badly (poor low rpm torque) as the converter locks up the car doesn't accelerate any faster and the engine revs just sag like its a cream pudding driving the car not a V6
You can clearly see the speedo staying the same and the rpm dropping 500 rpm or so.
When the engine is running well the reverse happens - as it transitions to lock up the engine revs stay roughly constant or increase slightly while the speedo shows the car accelerating rapidly, once the lock up transition is completed acceleration continues but engine rpm starts rising as well.
I can always tell by the performance in 2nd gear during torque converter lock up transition whether things are well or not.
In mine I've found that backing right off the throttle on a downhill stretch of road, engine braking and using the footbrake if need be to maintain speed, should see my real-time mpg climb quickly - a steep downhill road with a drop down to 4th usually sees 999.9mpg showing on the display within two or three seconds. However, when it's misbehaving the engine braking effect is a lot stronger and louder (this effect is also directly proportional to the extent of the problem) and that magical 999.9mpg takes a lot longer to reach, if it even manages it. It's a long-winded thing to describe, but an instant giveaway that there's a problem...
The 999mpg reading will be because the injectors are being cut off completely. What rpm is the car doing at that point ? If the rpm is above 1400 rpm and the throttle is at idle the injectors will be cut off. As you slow down and the rpm drops to 1100 rpm injection will be re-instated, it will not be cut off again unless the rpm increases to 1400 with the throttle still at idle. A Lexia will also show whether the injectors are in coasting cut off mode or not.
What I've noticed on mine recently is that sometimes the injection cut-off is not working when coasting despite being well above 1400 rpm - usually this happens to me in 1st gear at 2000-3000 rpm when I'm slowing down with my foot right off the throttle, instead of coasting smoothly with engine breaking it will lurch back and forth a bit as if I'm tapping the throttle and the injection is cutting off and coming back on again - since I'm well above 1400 rpm I'm assuming that either it thinks I'm touching the throttle slightly (TPS zeroing not quite right) or perhaps the MAP sensor is showing a lower than normal vacuum making it think the throttle is open slightly. (I am suspicious of a slight vacuum leak somewhere on mine as the ICV is closed too far to get correct idle)
Following up today's test-runs I can confirm the problem has to be ignition-related. My trip to Rotherham, straight after the installation of the factory-fit coilpack was smooth, refined, and VERY quiet (I have a stainless exhaust which isn't very forgiving when the engine is making unwanted noises). It was a huge improvement over this morning's trip out. I also managed the magical 50+mpg @ 50mph on the flat which is the sign that things are healthy. However, my return journey was a little louder and less refined - only slightly, but noticeable - so although this evening's journeys haven't shown much more deterioration I'm expecting it to hit me in the next few days, especially as I've regained the 2500-3000rpm drone
Either the disturbance of the ignition leads created a temporary cure (I'm unsure about this one, as right now my leads are all tightly bound with insulating tape and cable-tied away from the sources of earthing, at least in the areas I'd disturbed - unless of course the core is breaking down), or both my coilpacks are past their best and the problems are being revealed by the harsh engine bay environment. The engine runs better after cold starts than warm(er) starts which would reinforce this theory, and I've read online about electrical coils of various sorts suffering in hot environments, so maybe, just maybe...
Now, do I stump up for a brand new coilpack and leads which should solve the problem, or just the leads...? Hmmm...
If you've already replaced the coil pack once, I wouldn't do it again, at least not without strong evidence. Some cracks can be cosmetic only. Are the cracks in the epoxy resin on the top side or just around the sides of the black casing near the bottom ?
If its a crack right across the yellow resin in the top I'd be suspicious of it, but a good bead of epoxy glue should in theory fix that. If its just a bit of cracking around the sides of the black housing its not necessarily a problem - only if the crack goes deep enough into the epoxy potting would it necessarily cause a problem. As cracked as the black casing is on my original coil pack the epoxy is fine and I don't think there is actually anything wrong with it...
It's also possible for heat to cause one of the windings to short inside the coil pack, but its hard to prove conclusively if that is happening, since lots of things in the engine bay are warming up. You could swap a cold coil pack into a hot engine (ruling out heating of other things in the engine) but if the ignition leads are dodgy just the act of swapping it will introduce additional variables.
The engine note "loudness" will change with both timing advance and misfiring. If the engine is down on power but unusually quiet and smooth when accelerating (doesn't sound throaty like a V6 at all) then it can mean the timing is retarded. If you unplug the knock sensor and go for a drive you'll see what I mean - the ECU will log a knock sensor fault and drop the timing back 6-10 degrees which results in a VERY quiet, smooth sounding and smooth running engine with very lacking performance.
On the other hand if the engine is down on power but louder and raspier (rougher) sounding than normal particularly under hard acceleration then that's a misfire. When mine was misfiring badly I was reluctant to rev it over 4000 as it just sounded so rough and raspy.
On the ES9J4 you have the added complication that its a waste spark system so SOME causes of ignition misfire will take out two cylinders at a time - two cylinders that are on opposite sides of the timing cycle, so while you'd get a massive power loss from a two cylinder misfire if they're opposite cylinders it wont be as rough and raspy sounding as a single cylinder misfire. (In theory. Hard to test!) Any primary side ignition fault is likely to take out a pair of cylinders, while spark plug leads will generally only affect the rear cylinders.
Given that you've already changed the coil pack once but not the leads, I would suggest you try the leads rather than spending any money on a new coil pack. The last set of leads I took out (which were less than a year old) looked absolutely perfect but there was something wrong with them, so just because they look ok doesn't mean they are - especially when they're factory originals, like yours. Spark plug leads do have a limited life. A set of leads is also 1/2 to 1/3 of the price of a coil pack.
If you do change the leads be very careful fitting them, its easy to snag the insulation on the teeth in the guides and I managed to damage one set by doing so.
Engine still performing perfectly by the way!
That's nearly a week with no change now, even with a dodgy oxygen sensor.