Grand Cherokee with nasty mpg on LPG

[Gilbertd]

The mixer is generally held on with some grub screws and sealant. However if that sealant happens to be tiger seal you may be pissing in the wind.

A blowlamp usually sorts that out, smells a bit but softens it up nicely. Although make sure the Throttle body and mixer are off the car, well away from any petrol and LPG and held in a vice preferably.

[Mdizzal]

Hi Toby thanks for that I will try alter the tps setting if I still have fluctuating revs, Okay Richard so your saying I have to use the blow lamp whilst the throttle is still on the car and preferably with the LPG system running?? Okay I'm off to that now Be back in a moment once it's off (hahah only jokin) Yeah I get what your saying Richard I'll make sure I'm out of harms reach when I do it, I think it is on with some sort of seal and I do have some tiger seal to hand so at least I can reseal it, can't see any grub screws

Cheers guys my new tb should be here tomorrow


Thanks again guys

[Mdizzal]

Right well the throttle is now all sorted and I managed not to blow myself up, I now have my rpm about as steady as I would image it is on any jeep (650 - 700 rpm) I have a had a twiddle with the idle bleed screw but still under any situation it makes no difference to anything so I just have it closed for now and I have adjusted the bias so that my actuator is sort of below the default (default is 75 but actuator is going from around 59 up to 84) has anyone ever heard of an actuator going faulty and always moving up and down like this or could my vapouriser be faulty as the idle bleed screw has no affect on anything?

Thanks

Mark

[Gilbertd]

How quickly is the lambda flip flopping? If the lambda sensor is getting tired they can slow down so it will take longer to go from one state to the other. If that is the case the actuator will move around quite a bit as it goes from one extreme to the other. It is recommended by OMVL that the idle bleed screw should be fully screwed in on the R90e. If you were to screw the main bias in until it was about to stall, then there is insufficient suck at idle to overcome the spring behind the diapragm then the idle bleed screw would do something.

[Mdizzal]

Thanks Richard, I have managed to upload a video here is the link

http://www.youtube.com/watch?v=lA8Vmgt_ ... ata_player

The lambda does not move very fast actually as you will see, I actually bought another jeep today (4L 6 cylinder) as it was too cheap to resist and i may fit a cheap single point unit it that one and get rid of this problematic v8

Also this link shows the lambda a bit more but it's a grainy image

http://www.youtube.com/watch?v=lA8Vmgt_ ... ata_player

Thanks
Mark

[rossko]

The speed of lambda sensor flipping from min to max looks okay, I would not suspect coking-up or coldness there.

The excursions of the stepper motor look maybe more than average, but not excessively so to me.
If it were a BRC I'd slow down the allowed rate of step change, but I don't think you can do that on AEB systems. So a long time delay in the overall closed-loop between stepper and sensor would cause excess variation and noticeable brum-brumming.

Is your stepper motor at the wrong end of a long dangly hose? Mixer far from the throttle? The closer the working parts are to the engine the better (the shorter the loop delay).
But mostly I'd say that's as good at it'll get on this V8 and refer to my first post "I wouldn't expect brilliant results from a singlepoint system"

You may be able to reduce the effect a bit as follows:
Tweak your main adjuster to 'leanness' and allow the system to find a new default 2500rpm step position that is significantly bigger - in the 160 league (but less than 200)
You might need to tweak the idle screw again afterwards to get an idle default close to the same number.
The effect of this should be to reduce the effect of each step percentage wise. So that as the system takes one step, it has half the effect it had in default 80 terms.
That's akin to slowing down the reaction time to match the external loop.

If you can't achieve a default in the 160 area at all, then maybe the mixer is slightly undersized or maybe the reducer is life expired (they tend to richness with wear)

----

How about putting this singlepoint on the straight 6 (which will thrive on any gas system) and treating the V8 to a cheapo injection front end?
It's not your fault if someone put something unsuitable on, but no amount of tickling can overcome that.

[Gilbertd]

Ross has made a very good point or two. How far from the throttle body is the mixer? Is it attached to it or down the trunking somewhere? How close to the mixer is the actuator? Mine is a close as is possible, no more than 3 inches of pipe separate them. Although on your video you don't show the actuator movement and lambda at the same time, it does appear that the actuator may still be opening up when the lambda has gone well into the red. That could well mean that there is lag in the system, the engine is running on that big dollop of gas that went in before the lambda told it there was too much. Moving the default is also a good point, I always try to get somewhere around 120-160 so the actuator is working in the middle of it's range (the 117 that my P38 is at is about as low as i would want to see it). If you get the car running and get your assistant to hold the revs up at around 2,500-3,000 rpm, you should then be able to screw the idle bleed in fully and start screwing the main bias screw in until the actuator starts to climb. Stop when it gets to around 150-160. You may need to open out the limits to achieve this. Then you may find it dies at idle (or at least the actuator screams upwards) but you should be able to sort that with the idle bleed.

Initially it may run very rough during the open loop running where the actuator sits at the default until the lambda sensor has warmed up. Although the default will learn and set itself correctly over time, you can change the default start point by going into the Optional Settings menu, select Actuator and tick the default lock box. Type in whatever default you want, hit enter so it saves it and then untick the default lock box. This will set the start point for it to fine tune and learn from there.

[Mdizzal]

Hi Ross and Richard

Thanks for the advice, my mixer is bolted directly to the inlet and then there is about 150cm of gas pipe from the mixer to the vapouriser and the actuator is in the middle of that pipe so about 75cm away from both the mixer and the vapouriser, not sure if that is an acceptable set up but I will be trying to lift my default as instructed to a higher level of 100-150 and I'll let you know how I get on

Thanks again
Mark

[Gilbertd]

I hope there's a decimal point in the wrong place, 150 cm is about 5 feet and 75 cm is fractionally under 2 and a half feet! Although if there is and you mean 15 cm (6 inches) 7.5 cm (3 inches) that should be fine. Distance between vaporiser and actuator isn't that important but distance between mixer and actuator wants to be as short as is practical.

[Mdizzal]

Hi just measured the pipe from the mixer to vapouriser is actually 85cm (sorry about the poor estimate earlier) the actuator is sited halfway (42cm ish) ??? Thanks

Mark

[Gilbertd]

That's why the response is so slow and the actuator is wandering up and down. Move the actuator to as close as you can manage to the mixer, ideally within 10cm (4 inches), less if there is space. Think about it, the actuator allows gas through, the lambda says it is too rich so the actuator starts to close. But in the meantime, the engine is still running on the gas that is in the hose so the lambda still says it's rich, the lambda closes further until the mixture is too weak but it takes a few seconds for the weak mixture to arrive and for the lambda to respond to it.

[Mdizzal]

Ahh right I see Richard, that would make sense basically there is a delay in the time taken when the jeep asking for more/less fuel and it actually getting it, so I will now see if I can put it closer but I suspect I shall need some hose so I'll have ago after the bank holiday unless I can some how find a way to just join out the where the actuator is now and then cut it in further up toward the mixer.

Thanks
Mark

[Gilbertd]

Standard 15mm copper water pipe and a couple of Jubilee clips will work fine as a temporary measure.

[rossko]

I should point out, if getting new hose later, you need the correct LPG type - propane eats regular 'water' hose.

[Mdizzal]

Hi guys just a quick update, I haven't moved the actuator yet but intend to do so, I did a quick check on my fuel consumption after the remapping/wireing in the lambda and getting my idle down and sure enough my lpg economy is very much improved (up by around 30%) so I am well happy and can't thanks you guys enough for all your help, I've now got my eye out for a cheap used kit to fit to my other jeep which is a 4.0 straight six on a 1999

Thanks again
Mark

[Tubbs]

Dont go cheap on the lambda controller. Something like a leo is dead good in this kind of application. As you well know the single point systems are pretty bullet proof on the jeep. I dont count them as worthy of an injection system because they run so flawlessly on a mixer.
A new system isnt out there price wise, couple of hundred for the back end and maybe a bit more up the front. its the little petrol tanks that are the killer £250 ish. The mixer is a DV 140, Bigas M84 and a Bigas pegaso (re badged leo) oh and an emulator. Thats about it bar a few bits of hose and some pipe.

[simonp]

ill second Tubbs on the lambda cost there. From back in my (petrol) performance tuning days having a good quality lambda sensor and WBo2 controller was a high priority. Some of the cheaper widebands just didnt cut the mustard, so to speak. Id imagine the same holds true in the LPG world!

[kalross]

Interesting. I have a Millennium on a 95 Shogun 3.0 V6 which idles a little rough and seems to drop 100 rpm lower than spec only while the stepper is closing. Lag would be an excellent explanation as the stepper is half way down the pipe in this case...I would need to extend the harness to put it closer to the intake though. Where can I get pipe?

Cheers.

Kal

p.s. Tubbs! You're everywhere!

[Tubbs]

Kal, im like an omnipitent lpg being
Tinley tech ? Or any local lpg installer will probarbly have a bit of vapour hose gathering dust in the corner. Altenatively, a bit of 15mm copper as a joiner and a couple of jubbly clips ?