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Author Topic: LPG and fuel trims  (Read 9503 times)

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Lazydocker

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Re: LPG and fuel trims
« Reply #15 on: 07 June 2010, 15:38:30 »
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It seems that the maps drift more than I expected over time... I had mine spot on last time and when I looked the other day the LPG map had drifted North a little... Still well within the 10% deviation line but had drifted none the less.

I think it's not an exact science mapping against the measurements in the LPG ECU. Different weather, road conditions, etc. during calibration will affect it.

Also, if you rely on the petrol curve that has built up over time that will have mostly been collected during warmup and, probably over the little bit of pottering around you do after each startup before hitting the open road, so it's always a good idea to clear that, do a run on petrol and then lock the petrol curve before looking at the LPG curve.

Also - you are mapping in 2 dimensions only. Injector duration versus manifold vacuum.

I suspect that, for each combination of the two, there are several driving conditions that can reproduce them, with slightly different calibration requirements which is where you are relying on the main ECU to trim the fuel.

I will have to look at mine sometime. At the lakes if not before. Mine literally hasn't been touched since a couple of weeks after I converted it. :-X

All I know is that the fuel trims have stayed within reasonable limits, so it can't be that bad.

Kevin

I must confess, mine never seems to drift too far unless I've been messing about with parameters etc to try and get rid of the lag. Much better with lower pressure but I may have to up it slightly if I get a repeat performance of the cutting out ::)

Think it was just down to being very hot... But we'll see ;)
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Kevin Wood

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Re: LPG and fuel trims
« Reply #16 on: 07 June 2010, 15:51:41 »
When you say an "early switchover" are you taking about switching over to LPG too early after a startup or switching back to petrol before tank is empty?

On the former, I've set mine up to switch over after 30 seconds / 20 degrees C. In this weather it's on LPG by the time I get to the end of my road and it pulls happily when I hoof it out of the T junction. ::)

I have never experienced the latter at all. Then again, I'm running 1.25 bar IIRC. What do you have the "switch to petrol" pressure set to? I wonder if it needs to be lower, with a lower pressure setting?

There is probably some further diagnostics we can do with these running issues but we need better tools than the datalogs we can get out of a tech 2 or the LPG software.

I wonder if we could jury rig a car for some better monitoring of a few of the signals? Hmmm. Need a nice data acquisition card in a laptop, I think. Failing that a scope in the passenger footwell.

Kevin
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Lazydocker

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Re: LPG and fuel trims
« Reply #17 on: 07 June 2010, 16:49:37 »
Think I may need to set mine back to 30 seconds... IIRCC it's currently 10 secs and it's too soon in this weather... The car's ECU is still bunging a load of (unnecessary with LPG) enrichment in ::)

I think I had to do the same last year too... I wonder if 20 seconds is enough

Switch back pressure automatically adjusts when you adjust the Vap pressure and re-calibrate IIRCC
« Last Edit: 07 June 2010, 16:50:29 by Lazydocker »
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TheBoy

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Re: LPG and fuel trims
« Reply #18 on: 07 June 2010, 18:15:04 »
In the hot weather last week, I pulled out of my parking space, went to hoof it out of carpark, and it bogged down. Mine set to 10s iirc :o. Might up it to 30s ;D


As to gearbox changes and hesitations - mine has only done it once or twice (one may have been me confusing gearbox with erratic throttle ::)), not sure how to provoke it? 
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Lazydocker

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Re: LPG and fuel trims
« Reply #19 on: 07 June 2010, 19:20:22 »
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As to gearbox changes and hesitations - mine has only done it once or twice (one may have been me confusing gearbox with erratic throttle ::)), not sure how to provoke it? 

ISTR that we set your pressure to about 1.06 BAR, which seems to be about the most reliable pressure. As for provoking it... It only seems to happen when changing gear over 5200ish RPM but is ok if taken right to the red line with the pedal buried. Can also be provoked if you come off the throttle and back on again in quick succession at very high RPM.

You checked the oil pressure on the silver bullet yet?
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TheBoy

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Re: LPG and fuel trims
« Reply #20 on: 07 June 2010, 20:03:35 »
I shall try to provoke it tomorrow.

Oil pressure? Was I supposed to do something ::)
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Re: LPG and fuel trims
« Reply #21 on: 07 June 2010, 20:26:57 »
yeah, see, i was doing well until we started talking about mapping, locking curves, and tweaking, no idea with all that.

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When you say an "early switchover" are you taking about switching over to LPG too early after a startup or switching back to petrol before tank is empty?

in my case, it was switching over too early that caused the problem, due to the higher air temps lately. Usually its a couple of minutes until gas clicks in, well down the main road, but this time it must have clicked in just as i pressed the pedal, and bogged instantly leaving me sat on the white line going nowhere.

I haven't had it switch back to petrol for a while, until its empty of course. ::)
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Lazydocker

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Re: LPG and fuel trims
« Reply #22 on: 07 June 2010, 20:27:11 »
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I shall try to provoke it tomorrow.

Oil pressure? Was I supposed to do something ::)

Come on... Is it all healthy again or still having to be treated gently? I may well have missed something during the last few weeks as my time on here has been incredibly limited :'(
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Lazydocker

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Re: LPG and fuel trims
« Reply #23 on: 07 June 2010, 20:28:44 »
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yeah, see, i was doing well until we started talking about mapping, locking curves, and tweaking, no idea with all that.

Quote
When you say an "early switchover" are you taking about switching over to LPG too early after a startup or switching back to petrol before tank is empty?

in my case, it was switching over too early that caused the problem, due to the higher air temps lately. Usually its a couple of minutes until gas clicks in, well down the main road, but this time it must have clicked in just as i pressed the pedal, and bogged instantly leaving me sat on the white line going nowhere.

I haven't had it switch back to petrol for a while, until its empty of course. ::)

At least it looks like we may have cured one problem then! Up the changeover time to 30s as Kevin says and see what happens... I'll be doing the same :y
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Re: LPG and fuel trims
« Reply #24 on: 07 June 2010, 21:48:12 »
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I shall try to provoke it tomorrow.

Oil pressure? Was I supposed to do something ::)

Come on... Is it all healthy again or still having to be treated gently? I may well have missed something during the last few weeks as my time on here has been incredibly limited :'(
Was I supposed to be treating it gently ::)
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Lazydocker

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Re: LPG and fuel trims
« Reply #25 on: 07 June 2010, 21:53:51 »
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I shall try to provoke it tomorrow.

Oil pressure? Was I supposed to do something ::)

Come on... Is it all healthy again or still having to be treated gently? I may well have missed something during the last few weeks as my time on here has been incredibly limited :'(
Was I supposed to be treating it gently ::)

Guess that means it's OK now then? Did you get to the bottom of the problem or did it just need another oil and filter change?
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TheBoy

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Re: LPG and fuel trims
« Reply #26 on: 07 June 2010, 23:03:56 »
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I shall try to provoke it tomorrow.

Oil pressure? Was I supposed to do something ::)

Come on... Is it all healthy again or still having to be treated gently? I may well have missed something during the last few weeks as my time on here has been incredibly limited :'(
Was I supposed to be treating it gently ::)

Guess that means it's OK now then? Did you get to the bottom of the problem or did it just need another oil and filter change?
Errr, uhmmm, yes, I was going to change the oil, wasn't I.  Job for the weekend methinks ::)


Apart from normal weekly checks, not even sure the bonnet has been opened  :-[
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TheBoy

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Re: LPG and fuel trims
« Reply #27 on: 08 June 2010, 18:12:25 »
Hmmm....

KW/LD, do you remember when we were calibrating my car on one of the high speed runs, it got grumpy, and KW saying "better slow down, something don't look right"?

Happened again today, similar speed, mucho grumpiness. As it happened, traffic forced me to slow down just as I manually went back to petrol.
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Lazydocker

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Re: LPG and fuel trims
« Reply #28 on: 08 June 2010, 20:35:29 »
Remember it... Yep.

So, it all got noisy again?

Don't think it's a LPG related problem... Still think it's oil thinning too much/starvation due to relief valve sticking etc?

Time to get a pressure gauge on I think :-/
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TheBoy

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Re: LPG and fuel trims
« Reply #29 on: 08 June 2010, 20:38:24 »
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Remember it... Yep.

So, it all got noisy again?

Don't think it's a LPG related problem... Still think it's oil thinning too much/starvation due to relief valve sticking etc?

Time to get a pressure gauge on I think :-/
I think its fuelling. Suspect it won't happen on petrol.  Possibly reaching the limits of single hole tank at, errr, 70mph.

Think the lifter issue is unrelated to that....
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