Nissanclubman

My 91 4Runner auto has been converted to gas by previous owner. It runs great on both petrol and LPG, great mileage and power. Can swap between the two and can hardly tell the difference. Also idle perfect on both and starts from cold on both as you would expect.

On Petrol:
When I slow down the car goes through its gears as normal as it reaches its change down speed gates and engine revs adjust accordingly and are always above 1500 or so then as the car comes to rest it drops to idle as you expect. All good.

On LPG
When I slow down on LPG all seems fine until I get to 50kph. Shortly after it seems as through the change down hasn't happened and the engine revs start dropping away and continue until the engine stalls. If I keep dabbing the throttle to avoid it stalling until the car is below 20kph then it seems to be happy and will drop revs as the car slows normally and then idle like a kitten.. as it does on petrol. I've been chasing this ever since I've owned the car and honestly feel it is to do with the LPG kit. But how is it linked to slowing down has everyone stumped.

UPDATE:
The problem not only is triggered once I get below 50kph but also at higher speeds IF I touch the brake when decelerating. If I don't touch the brake then it is triggered once I get to 50kph. Also if I have O/D disabled it hardly ever does it regardless if I get to 50kph or if I touch the brake peddle. So it seems the ECU gets a signal from the brake circuit or 50kph speed but only if NOT in O/D. and ONLY with LPG... This is really one for the Runner techo's who know the ECU and electronics inside out.

I know the stalling issue has been discuss heaps of places on the net and not confined to 4Runners but I've not found anyone who has solved it on any other forums. Why only on LPG is the real kicker. Toyota specialists are stumped and LPG guys are also struggling. Any thoughts would be appreciated.

Nissanclubman

Anyone got any ideas? anything at all...

eisenfaust73

Very similar happened to me on 22RE. The mixture of gas and air was not right and around that time I just changed air filter. When I shifted between gears rpm started to drop down and on stop light engine just died. On petrol fine. Check it out with someone who instals LPG.

Nissanclubman

Thanks for your feedback. I have a wide band O2 sensor that I can install to keep an eye on the AFR as I decelerate. I can then compare it with what happens when on petrol. Will be interesting to see the difference.
Is your 22r an auto?
Do you know what your LPG tuner did to fix the problem?

eisenfaust73

Manual. Well, I'm noob for most stuff but his job was quite easy and took him like 15 min or so. Check on computer and some adjusting on valves under the hood... that was it. Hope yours will be the same. But I think it should be only due to LPG since youre doing fine on petrol

Nissanclubman

Thanks again and will be sure to update my findings. I'm sure you're right and that it will be something small and relatively straight forward. Just finding it is the challenge..

eisenfaust73

Sure, let us know how everything goes. Good luck

Nissanclubman

AFR readings:
Idle:
Petrol: 13.8 -15.2 is Ok. Set at 14.2. Below 13 and above 16 iles rough.
LPG: Set at 14.2

Driving:
Petrol: 15.8 - 16.8
LPG: 15.3 - 16.4

Decelerations: (Car moving)
Petrol: Above 2000 AFR is 20.00. Below 2000 down to idle 20.00 - 14.2
LPG: Above 2000AFR is 20.00. Below 2000 down to idle 20.00 - 20.00 then engine stalls. This does not happen if car is stationary and I just play with the revs. Car has to be moving.

LPG: below 2000 then switch across to petrol at 500. 20.00 all the way to 500rpm and about to stall then switch to petrol and AFR goes 14.2 and motor continues to run.

OK it seems the LPG system fails to enrich the AFR as the car slow down and revs drop to idle and the motor simply stalls because no LPG. This is not what happens on Petrol and motor continues to run.

Will need to get an LPG expert in on this.. Will let you know how I go.

Nissanclubman

UPDATE:

Ok problem is now solved... Yahooo.. What a frustrating 4 months.

The issue was primarily with the LPG gas regulator "Sensitivity" adjustment.

Here is how to tune it for an OMVL regulator but I assume many are similar.

The regulator has two adjustment screws 8mm (top and 10mm bottom) The Service manual says to tune the regulator you must turn the top 8mm screw in fully then and adjust the 10mm (bottom) screw so that you find the best idle speed/smoothness by screwing it in (lean off) until it starts to run rough then out until again it idles rough then find the center of the two.

However....

In the instance where the car dies when decelerating off load and stalls rather than idles then the sensitivity of regulator is out of balance.

Before proceeding remove the Auto tuning pulse valve from the hose that connects the regulator outlet and venture. Replace it with an open tube for this setup. Otherwise the LPG ECU will try to adjust the AFR as you setup op the Gas Regulator and you will be chasing your tail.

To set this correctly you must screw the 10mm screw fully in (Lean) (AFR 18.5) then unscrew the the 8mm top screw (enrich) to the point it is idling very rough (AFR 11.2). Then unscrew the 10mm (bottom) screw until the idle starts to get worse. Then go back to the top screw (8mm) and very slowly screw it in until it just idles smoothly (13.2). The 8mm screw is a very course and a very small adjustment makes a big difference. You also have to wait 5-10 sec for the change to settle down.

Once done return the the Auto Pulse tuning valve on the Gas hose and you are done...

Hope this make sense and goes some way to helping others with the same issue..

Thanks eisenfaust73 for pointing me in the right direction..and yes it only took the LPG guy 10 minutes to explain over the phone what to do.

Other information.... My car has a forward pointing Snorkel and this also causes a real issue with the tuning on open roads at speed.. The forced air was upsetting the air suction over the venture. I had to place a down facing elbow to solve this issue.

eisenfaust73

Glad to hear that everything is ok. I've heard about those screws but since I'm noob didn't want to mess with it, moreover because the LPG instalation was brand new.

Slowey23

glad you got it sorted and great tuning info, what sort of kms do you get out of a tank of lpg and what size tank? Im running an impco converter and mixer and only getting 200km from 55l, i love the way it runs but think it could be more economical

eisenfaust73

I manage to drive around 400 km with lpg tank. It's 75 liter tank but I fill it with 62-64 l. Consumption is around 15 liter of LPG per 100 kms. Careful driving, on road, even less. Mounted where spare tire was

Slowey23

thats awesome, might be time for me to ditch the impco sys and invest in a new computer controlled system

Nissanclubman

Yes the 3vze seems a thirsty beast. Love the way it runs but got to feed it with fuel. I have looked at ways to improve the economy adn was getting 220km on 41lts (5.3k/l) before I re-tuned the regulator. I am now running an AFR of around 15.5. If I run it much leaner (High 16s)then it starts to miss fire and I certainly don't want to run the risk of a backfire that could destroy the Air Flow Meter. Already done that once. Will check my consumption and let you know if it has improved.