Missing MPG, Strange Engine Noise When Tank Is Low.

[mondeoman]

I'm hoping someone might recognise the symptoms in the thread title, which afflicted my CRv about a month ago, and started pretty much instantly. I also have a nagging feeling that it is just hunting for power a bit a low speeds, town driving, accelerating away from junctions etc. It seems to change down a gear when I'm sure it never used to.

My journey pattern hasn't changed, driving style isn't different. I've filled the tank (49l toroidal which fills with 42.5 - 43l from empty, or the "beep") from different pumps to make sure it's filling properly. About six weeks ago I noticed a hollow growl from the engine when accelerating once the tank was within the last ten miles or so of what I'd expect. the growl disappears when you switch to petrol and returns when back on LPG. It is not there when the tank is full, only when on "the dregs". Then a couple of weeks later the range of a tank full dropped about 15 miles, or 8%. It has always been remarkably consistant between 178 - 182 miles per tank, but suddenly it has dropped to 165 +/- a couple. The flashlube seems to be working normally.

I filled it whilst out this morning, at the moment it's cooling down in the driveway then it's going to get a full service (oil, filters, plugs, valve clearances, LPG filters), and a remap. I'll see if that solves the issues. After that, the next step will be to strip the reducer and make sure that's working OK, anything else anyone can suggest.

I have been contemplating having the valve seats replaced for the last six months or so, I've mot previously had any concerns about them but it is likely I'll keep this car for a while now so thought it might be owrthwhile "future proofing" the valve train, again, any thoughts? The only reasons I haven't had it done is i) finding the time and ii) finding someone I trust to do it. Specialist engineering firms, once common in these parts are now about like rocking horse poo!

Honda CRv 2.0 VTEC 2004, 140k 150BHP (when new, maybe!!!!)
Stag 300 Premium with EOBD support
Tomasetto Artic Reducer
OMVL Fast Injectors
Flashlube electronic single point injection

Thanks for your time, as always it is appreciated.

[rich r]

Interestingly, in my 2004 CRV 2.0 automatic with similar mileage to yours, I get about 210 miles to around 42 litres of LPG. That could just be the difference in the roads we drive though, I'm mainly doing A-roads with little to no stop/start town driving.

If the valve seats are worn and can't be recut, then it's probably cheaper and easier just to stick a second hand head on. There are lots of relatively low mileage K20A4 engines around. But check the clearances, they might not be as bad as you think.

[mondeoman]

I do above average short journeys, and town driving, so MPG isn't good. It's always been very consistant though so I take that as a good sign. Having completed the service, two of the plugs were loose, not even hand tight with oil vapour collecting on one of the coils so that may well be the cause. I haven't done the valve clearances today as I did them on the last service, if the work I've done doesn't return the MPG then I'll investigate further.

I'm not sure that would be the cause of the grumbling on a low tank though, but we'll see in about another 150 miles. I'll remap it tomorrow just to be on the safe side.

The idea of having the seats replaced was to try and future proof the head and remove the need for lube.

[LPGC]

Well done with the description but 'grumbling' could still mean many things.

One interpretation of what you've said could be lean running under load, hearing induction roar but not getting the power or exhaust note to go with it... Lean running under load could be due to setting too low a reducer pressure combined with too low a 'change back to petrol' pressure. Would be most likely to happen on a low tank after a bit of foot down driving.

Along the same lines, a problem with the Vtec system (running the longer effective cam duration at lower rpms) could make a similar noise.

Or a grumbling noise might be coming from the reducer.

Nothing wrong with tank pickup pipe or pipe feeds?

If it idles just the same as before I wouldn't think clearances would be much to do with it.

Only maybe related but worth saying... Whenever the weather changes, particularly hot or cold spell, I always see a bit of an increase in the number of repairs (servicing as most customers like to call it ). Usually due to temperature correction affecting the system. If you take your car out with the laptop connected, give it a few boot-fulls and then park up on a hot day, your gas temp is going to read hot. This would have the effect, particularly on a system with linear gas temp correction like Stag, of over richening the mixture when you next momentarily boot it. I like to set temp correction so it mins out at about -5c and maxes out at about 65c - realistic temps for the gas in the pipes to actually be at, rather than the temp sensor getting heated by under bonnet temps. Particularly with an auto the engine will run with near atmospheric manifold pressure quite often and under those conditions may run open loop.. check mixture but don't adjust your map that you know has worked well, adjust temp correction instead if the above seems to apply.

Simon

[mondeoman]

Firstly, many apologies for not updating this sooner. I have been a tad off colour recently, had a bit of a funny turn. Doing anything non essential has been off the radar!

The car got it's full service and the missing mpg has returned. Each tankful since has produced 180m plus. The strange noise on a nearly empty tank is still apparent though. As per your suggestion Simon I have not looked at the mapping. I have a day off tomorrow so subject to being able to move when I wake up tomorrow then I'll plug the lap top in and take it for a ride. The current Mrs Mondeoman can keep an eye on what is happening for me and I'll check the temp settings etc and see what they look like.

[LPGC]

With a funny turn lasting 3 weeks you might want to visit a doctor mate Can't remember the last time I went to the doctors but good luck with that

Don't bother stripping the reducer... They can make noise at one pressure setting due to the diaghpram vibrating at certain frequencies with a certain load and pressure setting. Usual easiest cure is to slightly adjust the pressure setting, also ideally move the reducer away from the firewall if that's where it's fitted.

Does it feel as torquey at low rpm (maybe only on petrol) while 'grumbly'?

Have in the past got the girlfriend to read and adjust stuff on the laptop while I'm driving. Problem is they aren't usually the best at understanding calibration instructions and don't necessarily like the full throttle acceleration setup bit in high powered vehicles (when you might need them most). Particularly when this equates to getting to 160 in no time in high powered vehicles. Not on the A1 near me at 3am, obviously all on private roads etc...

Simon