10yr old PRINS system on 4.0 Jeep - Cutting out at speed

[strange_days]

Hi All,

Fairly new to the site. I need help from anyone with experience please, I drive a Jeep Grand Cherokee Orvis 4.0. The car has a single point Prins LPG kit fitted, which was put on the car back in 1999 by an authorised dealer.

The car will idle on gas perfectly, no problems. Then I drive off, and once I get to 30 mph it just cuts out then flicks over to petrol. It does it every time without fail. I can drive faster on petrol, say 50 mph, then flick to gas and it runs on gas at that speed fine, but after 10 seconds or so will cut and flick back to petrol. I am not sure if there might be an electrical fault.

I have already spent money with a specialist, he took the reducer apart and cleaned it etc, he said there was muck in there which he cleaned out. He said the gas filter was in good condition.

I am desperate not to waste any more money on investigations and parts/services that don't fix the issue.

Can anyone help??

[rossko]

You need to find a Prins specialist who can borrow the appropriate test gear for the AFS system. Prins UK used to hold one such textbox, but it was lost last time I enquired.

[strange_days]

You need to find a Prins specialist who can borrow the appropriate test gear for the AFS system. Prins UK used to hold one such textbox, but it was lost last time I enquired.

Thank you for your help

Are there any bits that are easy to eliminate, and quick checks I can do to rule out solonoids or anything like that? Do you think it sounds like an electrical thing? Do you think it is something that is possible to fix?

I drove it at 70 mph yesterday, and put it onto gas and it worked fine with power in reserve, but as before after about 10-15 seconds it just cuts out and flicks back to petrol

[rossko]

I drove it at 70 mph yesterday, and put it onto gas and it worked fine with power in reserve

That seems to rule out sticking solenoids, squashed pipes etc etc.

but as before after about 10-15 seconds it just cuts out and flicks back to petrol

If it is truly an AFS system, I don't think it has any pressure checking. I can't think of much to make it failsafe back to petrol apart from lack of lambda switching. That might be something silly like the wire has fallen off, or something more roundabout like a sticking stepper motor.

I'm sure it could be mended, but finding the resource to do it may be difficult. Have you found Prins agents yet? Bear in mind that while they can call on Prins assistance, many won't ever have seen an AFS.

You might take a view about the cost-effectiveness of repair. As a ten year old now, it may require more attention in future. It'll only get more difficult to support it, frankly a rare oddball in the UK now. If you're expecting to keep it, repair by replacement with a modern lambda-control singlepoint system (Leonardo etc.) and vap to suit may be a better bet.

The longer you leave it, the more it costs you in fuel.

[strange_days]

Thanks again Rossko

Yes I am seriously thinking on a replacement kit. I presume I could utilise the existing underslung tank and hoses, just relpacing the components under the hood.

[Gilbertd]

You could retain the existing mixer and vaporiser (if it isn't life expired), it's the controller and stepper that are the important bits.

[Tubbs]

You could fit a leonardo for example as the lambda controller and see how the vap copes. It wouldnt take long to do as all the inputs you need would be there, biggest pain would be fitting a new switch. I dont know this because its been many a moon since ive fitted anything prins, i used to a lot back in the early days, but on an italian system it would point at the rev sens from the coil causing that kind of thing, its the safety wire so to speak, if its loosing its feed from the coil the ecu sees that as the engine not running and will switch back to petrol and turn off the solenoids so its not chucking gas down the inlet with no spark or running engine ? just a thought.
Where are you, i would be happy to quote you for such a job if you arnet far from me. If you are it probably would be more cost effective to find someone closer, especially as you are on petrol !

[strange_days]

You could fit a leonardo for example as the lambda controller and see how the vap copes. It wouldnt take long to do as all the inputs you need would be there, biggest pain would be fitting a new switch. I dont know this because its been many a moon since ive fitted anything prins, i used to a lot back in the early days, but on an italian system it would point at the rev sens from the coil causing that kind of thing, its the safety wire so to speak, if its loosing its feed from the coil the ecu sees that as the engine not running and will switch back to petrol and turn off the solenoids so its not chucking gas down the inlet with no spark or running engine ? just a thought.
Where are you, i would be happy to quote you for such a job if you arnet far from me. If you are it probably would be more cost effective to find someone closer, especially as you are on petrol !

I'm in Crodon

Thank you for all the info though, it's hugely appreciated!

[mat_fenwick]

Yes I am seriously thinking on a replacement kit. I presume I could utilise the existing underslung tank and hoses, just relpacing the components under the hood.

Tanks have a 10 year certification, so chances are a fitter would suggest replacing it (as getting someone to test it would likely be similar to a new tank price). Obviously they don't suddenly become dangerous as soon as 10 years is up, but it would perhaps be a 'get out' route for an (LPG knowledgable) insurance company to use if the worst did happen...

[Tubbs]

You could fit a leonardo for example as the lambda controller and see how the vap copes. It wouldnt take long to do as all the inputs you need would be there, biggest pain would be fitting a new switch. I dont know this because its been many a moon since ive fitted anything prins, i used to a lot back in the early days, but on an italian system it would point at the rev sens from the coil causing that kind of thing, its the safety wire so to speak, if its loosing its feed from the coil the ecu sees that as the engine not running and will switch back to petrol and turn off the solenoids so its not chucking gas down the inlet with no spark or running engine ? just a thought.
Where are you, i would be happy to quote you for such a job if you arnet far from me. If you are it probably would be more cost effective to find someone closer, especially as you are on petrol !

I'm in Crodon

Thank you for all the info though, it's hugely appreciated!

As in Croydon ? By any chance.

[strange_days]

Sorry for the typo, yes I'm in Croydon.

The other thing I have noticed is this. When I got the car I filled the tank to maximum, and the 4 green LED's are all lit up on the switch unit. When the system flicks over to petrol as I have descibed, the lights all go out and then blink/flash, before going off altogether and then sporadically lighting up in 1's and 2's.

I'm at my wit's end here, I really can't afford to spend money on this and a new system or costly investigations are gonna hurt me bad

[rossko]

I'm at my wit's end here, I really can't afford to spend money on this and a new system or costly investigations are gonna hurt me bad

Then you'll have to run on expensive petrol instead. It might well not be worth fixing if you don't do many miles.

Extra info always helps the guessing game; maybe there is a bad power or earth connection. Check fuseholders, check gas system earth wire.

[strange_days]

I'm at my wit's end here, I really can't afford to spend money on this and a new system or costly investigations are gonna hurt me bad

Then you'll have to run on expensive petrol instead. It might well not be worth fixing if you don't do many miles.

Extra info always helps the guessing game; maybe there is a bad power or earth connection. Check fuseholders, check gas system earth wire.

I really appreciate your input thanks.

I have just replaced the HT leads and new plugs, and it has definitely improved. I can now drive up to 35/36 mph, and hover round there on and off throttle with no problems, but it still seems to be switching back once at higher speed.

I've not done well here. I didn't realise there was a problem with the system when I bought the car, my bad obviously.

[Gilbertd]

The previous owner probably did, which is why he sold it. The flashing lights do suggest an electrical problem somewhere. As Rossko says, check all of the connections and fuseholders. Spade type fuseholders can go high resistance. Sometimes simply taking the fuse out and putting it back in will clean them up, otherwise a squirt of contact cleaner, particularly if there are any signs of green deposits on them.

[strange_days]

The previous owner probably did, which is why he sold it. The flashing lights do suggest an electrical problem somewhere. As Rossko says, check all of the connections and fuseholders. Spade type fuseholders can go high resistance. Sometimes simply taking the fuse out and putting it back in will clean them up, otherwise a squirt of contact cleaner, particularly if there are any signs of green deposits on them.

Thank you. My mate is a mechanic and we're going to spend some time at his work tonight after hours. We're gonna go to town on the electrical system.

[rossko]

I can now drive up to 35/36 mph, and hover round there on and off throttle with no problems, but it still seems to be switching back once at higher speed.

I think that rules out simple electrical dodginess. Back to guessing bad stepper motor or vapouriser ... is it a Poliauto unit? Do confirm both of the car's lambda sensors are actually working properly on petrol.

[strange_days]

I can now drive up to 35/36 mph, and hover round there on and off throttle with no problems, but it still seems to be switching back once at higher speed.

I think that rules out simple electrical dodginess. Back to guessing bad stepper motor or vapouriser ... is it a Poliauto unit? Do confirm both of the car's lambda sensors are actually working properly on petrol.

Good morning Rossko

I've checked and cleaned the live and earth, and checked fuses. Still no joy, if anything it's worse again this morning ffs!

Vapouriser is Poliatuo yes, as mentioned I already had that stripped and cleaned by an lpg specialist, he reported that he cleaned it out and he confirmed it is working ok.

What's the stepper motor? Yes I must take a look at the lambda's, I'll ask my mechanic if there's a simple way to check..

[rossko]

I already had that stripped and cleaned by an lpg specialist, he reported that he cleaned it out and he confirmed it is working ok.

mm, but then again your car doesn't work.
Personally I wouldn't even have opened up a ten year old vap for fear of disaster, unless I was already certain it was broke and had nothing to lose.

Stepper is the motorised valve between Poliauto and engine intake. No real test, apart from substitution, or observation of its effectiveness using the test gear. Substitution can be a temporary manual adjuster for test purposes.

Also worth checking the innards of the venturi at the engine intake haven't come adrift.

[strange_days]

Rossko - I have as slight feeling the pressure/gas level sendor could be at fault on the tank ? Is it an eternal unit?

When I picked up the car, it had been standing a long time with an empty tank. I filled it up for a long drive home, literally as much as it could take. When the system fails over to petrol, the led's always flash then go to blank. Do you think the sensor might be struggling with a full tank ?

I drove it hard throttle up a hill this morning, got to 45 odd mph no problems, then off throttle cruising it will cut back.

[rossko]

I have as slight feeling the pressure/gas level sendor could be at fault on the tank ? Is it an eternal unit?

There is no pressure sensor in this system.
There is a level sender on the tank. I do not think the AFS can be set up to failback to petrol on 'empty' signal (though some can).
Change it if you like, it's your car.

When I picked up the car, it had been standing a long time with an empty tank.

And a flat battery? Sloowly we get the story. The AFS may simply have lost its software settings, in which case parts changing fixes nothing and the only cure is to set up from scratch using the right test box.

I'm sure its mendable but you are blind without the box and a knowledgeable operator.