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 Post subject: Hunting Leo.........
PostPosted: Mon Jun 20, 2016 7:21 pm 
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Hi All,

got what i consider a "weird one" on two of my Leo 175 equipped vehicles but is probably easily (and painlessly!) solved so hoping someone can point me in the right direction?

Here's the "problem" :

I have fuel cut-off set at 1300rpm which equates to a cold fast idle (throttle closed) or about 28-30mph when driving, depending which car i'm in. When travelling at 30 ish, it's obviously a very light throttle but not closed so the TPS value shouldn't be the same as a closed throttle.

In both cases this is causing "hunting". Dropping either car into "3" instead of "D" at 30mph gets round the problem while driving but i can't alter the fast idle and dropping into "3" is a nuisance as it defeats the point (or most of the point) of having an auto.

I could alter the fuel cut-off point to a higher rpm but i suspect this will just shift the problem to 40 or 50mph or more, i did wonder about altering the TPS Hysteresis but can't see this would benefit the problem. :?

I haven't used the temperature sender input on either, i suppose using this and setting it to not switch to gas until after it had warmed up enough to prevent the cold idle hunting might work but it would be dependent on the vehicle OE sensor - whether that would be compatible with the Leo is another matter! It would also mean warming up on petrol. :(

Anyone else had this, found a solution or shed any light on getting round this please? :roll: :? :wink: :D

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 Post subject: Re: Hunting Leo.........
PostPosted: Mon Jun 20, 2016 8:02 pm 
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Forget the temp sender input, it's irrelevant. You need to reduce the TPS hysteresis figure (under the Optional Config tab, TPS). By default it is set at 0.14V, so if at idle your TPS is showing 0.5V, it still thinks it is at idle, so the fuel is still cutting off, when the throttle is open very slightly and the TPS is below 0.64V. Drop it down to 0.05V.

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'96 Saab 900XS, AEB Leo, sold
'93 Range Rover 4.2 LSE, Lovato LovEco, sold
'98 Ex-Police Range Rover 4.0, Singlepoint AEB Leo, my daily motor
'97 Range Rover 4.0SE, eGas multipoint, a project.....

Proud to be a member of the YCHJCYA2PDTHFH club.


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 Post subject: Re: Hunting Leo.........
PostPosted: Mon Jun 20, 2016 8:17 pm 
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Thanks Richard - i didn't think the temp input would have much effect!

I'll drop the TPS Hysteresis value to 50mV as suggested and report back. I can live (sort of) with the fast idle hunting as it's only temporary for a couple of minutes (less in warm weather) on either car so if it doesn't help that it's not so much of a problem.
The throttle butterfly remains closed at fast idle on both the Jeep and the Rover as the fast idle air is provided by the EICV (electronic idle control valve) and also a supplementary water heated idle valve on the Rover.

Originally i thought the fault was "Jeep-specific" but as the Rover does it too, it has to be the Leo.

Will let you know how it goes! :wink: :D

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 Post subject: Re: Hunting Leo.........
PostPosted: Mon Jun 20, 2016 9:09 pm 
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If it's doing it at a closed throttle while the idle is raised, then altering the TPS hysteresis won't have any effect as the TPS voltage will still be showing it as at idle. The only thing you can do is up the cut off threshold up to say 1,700 rpm. I doubt it will be revving that high on a closed throttle, so the TPS will be showing the throttle as open so no cut off. I've got my cut off at 1,700 rpm. I found that if it was too low and I was coasting up to a roundabout so the fuel was cut off and a gap in the traffic appeared, it came back in with a bit of a jolt as it went from cut off to a wider throttle opening. That's on a low revving V8 too, so your higher revving V6 would show it up even more.

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'96 Saab 900XS, AEB Leo, sold
'93 Range Rover 4.2 LSE, Lovato LovEco, sold
'98 Ex-Police Range Rover 4.0, Singlepoint AEB Leo, my daily motor
'97 Range Rover 4.0SE, eGas multipoint, a project.....

Proud to be a member of the YCHJCYA2PDTHFH club.


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 Post subject: Re: Hunting Leo.........
PostPosted: Mon Jun 20, 2016 10:52 pm 
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Well i have a 95% success story to report from setting the TPS hysteresis to 0.05V - it stopped almost all of the hunting on the Rover.

The only bit it didn't stop was downhill on a (now) warm engine at 30mph on a trailing throttle. I doubt this can be tuned out due to the characteristics of the autobox - on a trailing throttle, it cycles the torque converter lock-up, the brake bands etc to increase engine braking.

In doing this it first brings one brake band in, then a second, the T/C lock-up all of which bring the revs up in stages then drop them again. This confuses the Leo slightly - the revs are up, the throttle is closed so fuel cut-off happens. Then the box lets go of the brake bands and T/C so the revs drop again.

All of this causes a bit of hunting which i doubt can be tuned out without losing engine braking which would force the box to try and brake harder which would no doubt exacerbate the hunting! :roll:

In fairness, this is much less obvious than the cold hunting so can be lived with and the 30mph hunting is now gone. The TPS hysteresis was set at something like 0.38V before - it was previously used on a V8 Range Rover (hot wire) apparently.

If this has almost entirely eliminated it on the Rover, it should completely cure it on the Jeep as not only is the Jeep much lower revving (about the same as a Range Rover V8 - 30mph/1000rpm in top, obviously due to T/C slip at 30mph it needs 12-1500rpm to attain 30mph though as lock-up doesn't happen until about 45-50mph) but the fast idle is also lower.

As an aside, i also increased the changeover delay to 0.7s from 0.4s to improve the cold change to gas on the Rover which worked wonders too.

Thanks for your help again Richard - very much appreciated! :wink: :D

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 Post subject: Re: Hunting Leo.........
PostPosted: Tue Jun 21, 2016 3:58 pm 
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You should be able to get rid of the hunting. What opening have you got the actuator set at on cut off? What idle limits have you got set? Going downhill on a closed throttle, the petrol injectors will be shut off until the revs drop below a certain point where they start pulsing again to stop the engine from stalling. Exactly the same will happen with the Leo. If the revs are above your cut off threshold, then the actuator will close down to whatever you've got it set at (mine is at 30 with a default of around 95, so roughly 30% open), as the revs drop the cut off will cancel so the actuator will open up to default but that would only be to stop the engine from stalling if the revs drop further, it shouldn't start to accelerate again, it will just be running at idle so you won't notice the difference whether it is cut off or not.

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'96 Saab 900XS, AEB Leo, sold
'93 Range Rover 4.2 LSE, Lovato LovEco, sold
'98 Ex-Police Range Rover 4.0, Singlepoint AEB Leo, my daily motor
'97 Range Rover 4.0SE, eGas multipoint, a project.....

Proud to be a member of the YCHJCYA2PDTHFH club.


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 Post subject: Re: Hunting Leo.........
PostPosted: Tue Jun 21, 2016 8:09 pm 
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The default is 79 currently and the cut-off position is 20 with the "in idle" limits of +25/-20 if memory serves correctly.

I think the hunting is because of how the gearbox behaves during engine braking, it normally communicates with the PGM-Fi (engine management) ECU during petrol operation so the injectors will cut off above 1200rpm normally but during engine braking they obviously only let enough fuel through for idle if below 1200rpm. I'll see how it goes for a day or so, it may well settle itself down a bit more.
It may have been the engine was colder than i thought and still partly on fast idle last night when it happened, i'll double check again tonight.

It would indeed be nice to get rid of all the hunting, one way or t'other! :wink: :D

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 Post subject: Re: Hunting Leo.........
PostPosted: Tue Jun 21, 2016 10:08 pm 
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Hunting has now gone Richard - i suspect last night was either "sorting itself out" after tweaking the TPS Hysteresis or maybe just a glitch - all good now though! :wink: :D

Thanks for the pointer in the right direction!

Just got to sort the fuel gauge now............. :roll: :? :(

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 Post subject: Re: Hunting Leo.........
PostPosted: Thu Jun 23, 2016 8:23 pm 
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Fuel Gauge sorted! Seems to show "all or nothing" but at least it's an indication. :D

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 Post subject: Re: Hunting Leo.........
PostPosted: Wed Jul 20, 2016 10:53 pm 
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Partial update/partial conclusion on this.

Finally twigged the hunting when cold problem and increased the open loop time to 420 seconds from 5 as the Lambdas on min are single wire and take a while to warm up and become responsive.
It seems to have done the trick anyway!

Think i have also sussed the hiccup/holding back under hard acceleration (this may have been on another thread but can't remember just now) and the out of idle closing steps were set at 100 while i was doing the setting up. Because the mixer is a bit small (i think) it's going quite rich while hoofing it and the actuator is diving for zero which cuts the gas until the Lambdas respond with a then lean mix and it opens up again. I've set it to 30 for the clsoing steps below default now and all seems well.
Need to enlarge the venturi somehow or fit a different mixer methinks!

As for the fuel gauge - come to the conclusion the float is sticking in the tank. Last fill up it was showing full even though i got 40L into the tank then dropped to zero within seconds of restarting after filling. Once i know what it's doing to the tankful i'll just use the tripmeter and fill up before it's likely to run out.

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 Post subject: Re: Hunting Leo.........
PostPosted: Thu Jul 21, 2016 7:18 am 
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Earlier you said you though the mixer was too big, which is it? What size is in there at the moment and what is the bhp figure for your engine, that should allow you to get close by comparing with others for specific engines. You said previously that the actuator doesn't stay in the same place but alters with revs and load. That isn't right as you don't know what the default should be, in fact, the default will alter depending on whether you are cruising at high speed or just pootling around. What fuel gauge sender have you fitted, how have you wired it (as the wiring is different with different senders) and what have you set in software? Does the gauge on the tank read normally? If the float was sticking it would stay at empty when full, it wouldn't sink to the bottom when the tank had a liquid in it.

PS, where's my HT leads?

_________________
'96 Saab 900XS, AEB Leo, sold
'93 Range Rover 4.2 LSE, Lovato LovEco, sold
'98 Ex-Police Range Rover 4.0, Singlepoint AEB Leo, my daily motor
'97 Range Rover 4.0SE, eGas multipoint, a project.....

Proud to be a member of the YCHJCYA2PDTHFH club.


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 Post subject: Re: Hunting Leo.........
PostPosted: Thu Jul 21, 2016 9:24 am 
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Joined: Sun Aug 09, 2015 12:45 am
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I'm pretty sure it's too small - i don't know what size the venturi is in it but will in a few days time. Currently i have nothing to measure it with as my digital vernier internal jaws aren't long enough so have bought a pair of internal calipers from ebay - when they arrive i can measure it and report back.
As for the bhp, with the cat it's 169bhp, without it's 193bhp (Rovers figures) and i've fitted a genuine Rover decat box (basically a straight through silencer) so on paper it should be 193bhp.

The default is currently 81, it was previously 79 before i fitted the decat box and always idles spot on at the default value. I get what you're saying that it shouldn't alter too much during driving, however there is a "lean spot" between 1500-2000rpm as it changes over from idle to bias on the vap. This lean spot may have been what made me think at one point the mixer was too big but if it's going seriously rich at higher revs then it would seem it's too small.

I have another mixer sat here that i bought on ebay, apparently it was fitted to an 827 for 15 years and ran with no problems. The venturi is much larger but it looks almost as if the original venturi was chain-drilled out and all that's left is a 12mm (ish) hole that comes straight from the vapour feed elbow. The closest i can get to measuring the venturi in this second mixer is 42mm. Here's a link to the original listing :

http://www.ebay.co.uk/itm/291752654319? ... EBIDX%3AIT

If i get time i might swap it over just to see if things improve but i'm pretty busy for the next couple of weeks.

Thanks for the reminder on the HT leads, i had in all honesty forgotten :oops: them, sorry about that! As mentioned above, i'm pretty busy for the next couple of weeks but i will try to get the bits organised and if possible get them made for you. If not it will be ASAP after that if that's ok?

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Dave


Somewhere in Suffolk with a Jeep, 2 Rovers and a V6 Volvo

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