VZ with liquid gas stalling problems

**cranky** · 09-10-10, 12:03 PM

Hi,

we have a 2004 VZ Lumina wagon that we've had on gas for approx. 65,000km's. About a month ago it started stalling when warm with no warning, nothing, just stopped. We've had it back to installer twice, no computer code errors found, new spark plugs (due to be done), gas filter and two oxygen sensors (car idles rough on petrol and this was thought to be the problem but didn't fix) replaced and the problem is still there. Installers are thinking it now could be the converter? But we're not jumping at spending another $500 to fix something that might not be a problem? There's no pattern as to when this happens except most of the time the car is warm (although has happened a couple of times when cold) seems to happen mostly when just changed over from petrol to gas and with around town driving. I have to travel 30 mins (highway km's) for work and it's never happened here but as soon as I stop and start in town it tends to start. Sometimes the alarm starts to sound (warning alarm) but more often than not it just stops.

We'd really appreciate any feedback, ideas, suggestions.

I am planning on driving it Tuesday morning until it stalls and then taking back to installer/mechanic to check it out then as to date, it hasn't done it for them. Hopefully if they hook it up to the computer then, it might, just hopefully might show the problem....

thanks in advance,

cranky

**Godzilla** · 09-10-10, 05:15 PM

Ive just been through the same thing but on a BA XR6 on LPG.

What i would do.

Drop your catalytic converter and take a look at it. Especially if you may have had a Oxygen sensor problem as you just replaced them.

The factory cats are ceramic and burn out, block and or crumble.

Yesterday i took a look at one of the family cars and it was holding back under power and surging, sometimes it was stalling.

Dropped the cat and thought i was going to find it blocked....guess what i found? (bloody thing had totally destroyed the ceramic substrate and left me with just a empty shell LOL)

Anyway after realizing the cat destroyed its self and totally burnt out the ceramic substrate i fitted a 300 cell high flow metal substrate cat.

The problem is that the extra heat generated by running LPG destroys the factory ceramic catalytic converters, replacing them with Metal substrate cats (preferably high flow for power gains) does the job.

Welded the new one on, replaced the O2 sensor as a safety measure and reset the ECU by disconnecting the battery and let the car relearn all its mixture settings.

So in a nutshell, take out your cat, inspect it for blockage, cracks and damage, if its damaged replace it, reset your ECU and let the car relearn and see how you go.

If you need a Metal cat, i have them for Commodores on ebay.

If your cat checks out OK still reset your ECU and see how you go.

If that fails wash your airflow meter probe with CRC contact cleaner, sometimes the probes get dirty and they dont measure air flow correctly and may cause it to stall.

If that fails, take it to a LPG installer who knows your injected gas system as the Gas ECU settings may need tweaking, ive heard some people are having LPG injectors fail too.

If that fails he will most likely try a recod gas converter.

Its a process of elimination, most of what ive mentioned costs nothing to check the cat, reset the ECU and clean the airflow meter, a LPG pro should not charge much to check the LPG ECU adjustments but a recod or new converter is not cheap, hopefully he is good enough to open your old one and take a look and throw some new gaskets in.

**cranky** · 10-10-10, 07:41 PM

Thanks Godzilla. We've not long replaced those so that eliminates that off the list

but I really appreciate your reply.

**Godzilla** · 10-10-10, 10:19 PM

Follow the rest of the list then, reset the ecu, check and clean your airflow meter, then leave it with a LPG tech to check the mixtures and if that fails to check your LPG converter.

**Mgoldbe1** · 11-10-10, 07:57 AM

So you removed your cat expecting it be blocked and it was totally high flowed...hahah I love it!!...I'll have to remember that trick...

You make a good point Godzilla. I friend of mine had his 4 year old Focus running shit...loss of power under load etc, His Mechanic did all the usual things - Change fuel filter, check fuel pump, check plugs, coils and leads...turned out to be blocked up Cat!...this is a relatively new petrol car too...

**Godzilla** · 11-10-10, 08:12 AM

Well thats the funny thing, a decat (or burnt out straight through cat) is a pretty good hint that your O2 sensor is also fried.

Took the car out last night for a test, pulls hard on LPG with no surging or holding back now and no longer stalls.

My son agreed that it pulls the same if not better with the high flow cat and new O2 sensor due the the mixtures being right now and the cat being high flow is not restricting the exhaust.

**cranky** · 11-10-10, 08:30 AM

Thanks Godzilla. The only thing from your recommendations we are yet to try is the air flow meter.

The car is now stalling as soon as it changes to gas with no warnings whatsoever so here's hoping it is something as simple as the airflow meter.

The installer isn't completely confident to this point that it is the converter so therefore, if it's not the airflow meter we then risk spending the money on a converter to 'see' if it will fix the problem. They've also told us that the converters; once pulled apart don't go back together as good as original condition so probably best to just replace.

Tomorrow is D Day.......

**cranky** · 11-10-10, 08:38 AM

Thanks Godzilla. The only thing from your recommendations we are yet to try is the air flow meter.

The car is now stalling as soon as it changes to gas with no warnings whatsoever so here's hoping it is something as simple as the airflow meter.

The installer isn't completely confident to this point that it is the converter so therefore, if it's not the airflow meter we then risk spending the money on a converter to 'see' if it will fix the problem. They've also told us that the converters; once pulled apart don't go back together as good as original condition so probably best to just replace.

Tomorrow is D Day.......

**Godzilla** · 11-10-10, 08:40 AM

Thats true about some converters, ive heard that the impco converter is popular because its one of the few that can safely be repaired.

I had one on my last car and it was easy to throw a gasket kit through it.

While talking about petrol to gas and back switch overs ive heard that the timing is programed by the LPG installer and if its wrong the car will stall.

Too much fuel it will run rough due to running rich, a moment of too little and it will stall due to no fuel, the installer has to get the switch over timing perfect via his progamming.

Maybe try a LPG fitter who has more experience and confidence with your system if the airflow meter clean does nothing.

**cranky** · 11-10-10, 06:07 PM

Godzilla,

airflow meter cleaned and still playing up. You seem to know your stuff so can you tell me, do they need to take the converter out to see if it's stuffed or when it's hooked up to the computer will that detect it now that we can get it to stall at the mechanics/installer?

thanks again,

cranky

**Godzilla** · 11-10-10, 07:32 PM

They will assume after all tests have been extinguished that it may be the converter.

Dont forget there are many test and adjustment to perform, the timing for switchover is critical and adjustable.

After all has failed the only way they will know for sure if it is the converter is to put another one in.

Hopefully they will exhaust all other possibilities first.

There is one other thing that comes to mind.
Your converter could be full of sludge from a bad batch of gas and need draining.

On some converters LPG specialists know that you need to have the engine warm and undo the plugs under the converter to let the sludge out.

There is also a idle valve on some that needs to be removed and cleaned.

Leave this to the LPG Pro, he should be going for these points first, hopefully he wont sting you for a converter because he is too lazy to clean out your current one.

Normally its a waxy sludge from Shell and Caltex servos, personally i use BP and have never had a converter clog up.

**cranky** · 14-10-10, 08:57 AM

Just updating.. still in limbo... after contacting supplier of kit; they're thinking the installers computer disk is faulty if not maybe our gas ecu? Although my other half dropped in and her gas mech. say it's the converter?

And so are the days of our lives...... (and god I hate that show LOL)

**Tradesman** · 14-10-10, 10:33 AM

godzilla , maybe a silly question but would an old fashioned vacuum guage be able to show up a blocked exhaust system of some kind?. i remember somewhere that watching how the needle behaves could be a way of diagnosing blocked exhausts.

**Godzilla** · 14-10-10, 10:47 AM

Im leaning towards a converter that needs draining/servicing or a ECU tweak to adjust the settings after the results so far.

@Tradesman ive never seen or heard of this but to some degree i could understand where your coming from, if a pressure gauge was put into the exhaust line before the cat, theoretically a pressure should be readable, never thought about it before but it makes sense. I however dont 100% understand how having a vacuum gauge on the intake side could produce a understandable result.

**Tradesman** · 14-10-10, 12:35 PM

i guess you could remove the oxy sensor and substitute it with a pressure guage to look for excess backpressure , if you knew what a unblocked system was reading.
i dont know how a vacuum guage would find a backpressure problem either , i remember an old book showing how to interpret vacuum guage readings , but that was for carby cars , prolly for the intake side.

**Aids** · 19-10-10, 04:13 PM

Read the title wrong.. thought it said "Liquid gas stealing problems"

I was going to advise you wait in your house with an intimidating mask and a meat cleaver

**cranky** · 25-10-10, 09:09 PM

We have officially been driving on gas again for the past week! Thank goodness! It turned out to be the gas system ECU, since they've replaced it, the car has never run better on gas. As for the supplier of the gas system, they only started to become helpful when it was mentioned I was thinking consumer affairs! GRRRRRR! But a huge thanks to all here for your advice, now here's hoping to some safe, problem free km's for this VZ!

**Godzilla** · 25-10-10, 09:53 PM

Good to see you sorted.

I took one of my cars in for its first mixer ring LPG free service after the conversion last Wednesday.

By Friday the Mrs mentioned it wants to stall when stopped at lights.

Popped the bonnet, screwed in the 8mm mixture screw 1/16th of a turn in to lean it out a little on idle and it idles perfectly now.

Called the installer today and mentioned his mixtures were out, mentioned i turned the screw in and he tells me yes it needed richening a little.

Couldnt be bothered telling him that i actually leaned it, not richened the mixture, needless to say i wont be back there again.

**Tradesman** · 26-10-10, 09:12 AM

Originally Posted by Godzilla

Called the installer today and mentioned his mixtures were out, mentioned i turned the screw in and he tells me yes it needed richening a little.

i wouldnt have told him you played with it, he may see it as a way of voiding your warranty.

**Godzilla** · 26-10-10, 11:16 AM

Nah he cant touch me for moving a mixture adjustment to make the car drivable again when he got the mixtures wrong and the car was on the verge of needing a tow truck to take it back to him.

If anything i saved him some warranty work and he was grateful for the work i saved him.

Id rather tell him the truth so he understands what happened, and ask if he wanted the car back to look at it, he was fine with what i did to get it running again.