While using LPG, the petrol gauge slowly drops. Not always, but more often than not. When it does this, it can run really rough on gas to at idle... We're thinking maybe the injectors need to be cleaned/replaced?

The driver prior to me seemed to have driven the car mostly on gas for around 20,000km. I alternate between petrol and gas often.

If we do something about the injectors, how much we looking at for a clean or replacements?


Car: KF Xi 3.5L. Aspirated gas system under 2 years old. 175,000km on the clock.

Thankyou.

Mine starts on Petrol but runs 95% of the time on LPG, the past week it was running rough on start(petrol) so I ran it on Petrol for a while and "blew" the cobwebs out .... now it seems fine.

Have you checked that the sender is actually functioning correctly? These in magnas fail quite often. You can check that it is running properly with a multimeter. Instructions should be in the service manual.

Also I have heard of some lpg systems having a fault where the solenoid doesn't fully shut off the fuel supply and a injector is still pushing fuel into the engine, albeit slowly. However this was diagnosed after they were having serious performance issues.

I know with mixer system in my car, that it automatically starts on petrol and quickly switches over to lpg so I do loose a good 1-2Ls per week as I live in the suburbs and start the car quite often a few times a day. With modern day injected systems they often switch over to petrol when the car is being driven harder to avoid a drop in performance. The process is seemless and you'd barely notice the change.

Also if you are running lpg often then its worth considering that petrol does also evaporate a bit as well. I know from comparing the amount of petrol ive used compared to the amount that my car has said ive used, that there is a discrepency.

Sender is working correctly, aye.

I use LPG more than petrol, but I do use petrol every week to look after the system. System does use petrol on start and under heavy load.

I'm just trying to track down the rough idle(much worse with LPG, happens a bit on petrol but not much. seems worse in hot weather and once engine is at op temp.) and possible solutions. Only things left really is looking at the coil/dizzy or possible injector issues. Performance wise, its great. Gas eco is utter crap though. 330km per 63litres, consistantly (approx 19l/100km). I'm a rather conservative driver too.

Just an idea... :(

Well at least the sender is working fine. We can rule that out.

You're lpg economy is terrible! I'm NOT a conservative driver and I barely use over 15L/100km on lpg. Bit more if I really push it. My dad's 1700kg falcon ute with a 4L engine lugging 500kgs of tools doesn't use that much and he drives in the city. There is a problem

With the rough idle when the car is warmed up suggests that you may have a O2 sensor and/or ISC problem.

The first thing would be clean up your throttle body and isc. Easy job to do. Use some carby cleaner and a rag. Be sure to replace the gaskets and the isc o-ring. That should hopefully help how your car is running.

Second would be to take off the dizzy rotor cap and check it out. It should be clean with no rust, corrosion or oil. Sometimes they stuff up and look fine but most of the time you can visually see that they're not in good condition. Thankfully these are really bolt on/bolt off and don't require the car to be at TDC.

Then you might need to check the O2 sensor, if it hasn't been replaced yet. They seem to kick it around 150-200km for petrol cars, and earlier for lpg cars. Touch wood, I haven't had a problem but it's very common with magna's. You can test their operation with a multimeter but best is to replace it. It's a serviceable item anyway. Usual culprit for bad economy and performance issues. Can be purchased for cheap from ebay or Rockauto in the US.

I'm guessing your spark plugs have been replaced before? I used IridiumIX plugs that are colder by 1 degree and smaller gapped (0.7mm vs. 0.9mm factory) and I've no real issues. Didn't have any problems with the factory plugs either but I just replaced them for good measure (pretty much a given with lpg installations) I also replaced the leads but that was only due to one of mine being destroyed by oil from hardened leaking spark plug tube seals. Stock were fine before they were destroyed by the oil, but I know other's haven't been so lucky.

Otherwise, lastly it's probably off to an lpg specialist to check out the vapouriser. It may be dirty and needs a bit of a clean up and a tune.

Yeah, I've replaced:

-Sparkplugs with iridium (i think, expensive buggers)
-New leads (standard though for gas, boash)
-New rotor button and cap
-O2 sensor, however.. Im not sure if the wires are around the right way.. Ill take a pick tomorrow as that might be the issue too!
-Ill clean out the TB again...

Oil does leak around dizzy though, need to fix that.

And thankyou for your help :)

You've definitely replaced all the usual culprits of bad lpg and/or petrol performance problems.

I was going to use Bosch leads but was then told to avoid them as their quality was no where on par. In the end I went with NGK's from supercheap auto for around $70. I'm very happy with the performance. Apparently genuine ones are also fine for lpg (was for me except NGK's were cheaper to replace).

Like I said I used smaller gapped and colder plugs. Still, standard iridiumIX's should be fine.

I would've thought a badly installed O2 sensor would throw up a CEL light.

Clean out the TB/ISC for sure. They can get super dirty quickly. Makes a difference for mixer lpg as that is where lpg is being thrown into the engine. Apparently the o-ring on the ISC is important to avoid rough idle's.

Could definitely be your dizzy mate if you've got oil leaking on it. I know had a nasty rough idle when the oil from the back rocker cover soaked my dizzy. Replaced with a working second hand one and it's been a lot better. It's still a bit rough on petrol but great on lpg. I think I'm going to clean out the injectors with some Injector flush or remove them and clean them on the bench using circuit to simulate them being used as they would in the car and run some carby cleaner through them.

Happy to help mate.

Let us know how you go.

Tomorrow I'll be investigating the O2 sensor, make sure it's wired correctly and be replacing the dizzy and oil seal and see how that goes. If not much change... Im at a loss! But ill cross that bridge when I get there :)

Thankyou for your replies MagnaP.I. Ill post updates.

Also if you are running lpg often then its worth considering that petrol does also evaporate a bit as well. I know from comparing the amount of petrol ive used compared to the amount that my car has said ive used, that there is a discrepency.
How big the discrepency? You might want to check your filler cap if so, mine is always and has always been within 0.1L, it's usually spot on.

Yawn. Just lost many minutes I will never get back with those essays........

Op just get a leakdown test done as I have seen this many times with LPG cars. Other test is unplug fuel pump for a few days if your car runs on gas all the time if symptom goes away then there is your issue. There are many systems out there where the fuel pump runs even when switched to lpg

Oh and only to clean injectors is properly. Bottle in tank does sfa

Replaced dizzy today. No more rough idle on petrol at all... Gas on the other hand didn't change much, but it has improved.

Removing the relay for the fuel pump is something we were going to do, hehe. Going to see how things go for a little before I do anything else though. Might see about getting the LPG system looked at first (mixtures etc.)

What's the best way to tune a gas converter system? The converter in my car is a Zavoli branded unit.

From what I've been reading you rev the car at 2,500-3,000rpm, screw in the idle adjustment screw all the way then screw out the other screw (sensitivity?) until it drops down then do a 1/4 turn in... for a rough tune. Thoughts?

Depending on how successful it is, I'll probably get it tuned somewhere. Can anyone recommend someone in Adelaide? :)

Thankyou.