LPG Misfire

[zen]

started while on hols,thought it was at first lpg ecu holding the petrol injectors on for a few secs after change over causing over fueling and bogging down..

but its got worse and obviously (now) is ignition related..

(lpg by the way takes twice(ish) the voltage across plug before it fires, thus putting more strain on the ignition bits.)

its really bad when switching over to lpg from petrol,maybe running on 4-6 cylinders, it gets better as it warms up and will/maybe clear itself after time...

so..changed the plugs (cos i had some).no change.
.....swapped out a lead at a time..no change.
.....swapped out coils with a good one..no change.
.....checked and cleaned rotor arms and dizzy caps..no change.

so what next??

have ordered new rotor arms and dizzy caps..
have ordered set of magnecor leads..
the leads on it by the way are oe and only 4 months old..

but my money is on the leads..strange though that its perfect on petrol.its so bad on gas(when cold) that i would have thought it would miss on petrol.?

can anything else be breaking down?cant see the ignitors being the problem...

what you recon then??

 

[cribbj]

Also make sure your earthing is good, and you're getting a solid +12 (hopefully higher) everywhere it should be for ignition. You may have loose or worn battery leads.

Remember that a low primary voltage at your coils will result in a very weak secondary.

 

[zen]

voltage is fine...spark is fine..ie pull a lead off and it jumps 20mm or so to earth...

i still recon its the leads breaking down,though you cant see any obvious external sparks or damage to them...

wondering about the noise suppressor cap, but thats on the +12 rail to coils,so i dought it..

or maybe an ignitor playing up with the extra load put on it by the coil having to work harder to spark though the lpg/air mixture compared to the petrol/air mixture...

i dont have a new lead set yet to try though..2 weeks for delivery!! and not paying another £180 for oe ones,(just to have them fail in 2 months?)

 

[BigKriss]

Not using a resistor lead AND a resistor plug together are you ? A simple mistake made by many with serious mess you around results..

 

[zen]

well i guess i am..standard plugs(now different heat range ) and oe leads...both resistive as standard to lexus..

 

[zen]

ok..its not the rotors or dizzy caps...

so to the leads..when they turn up...

 

[zen]

this is now really f***ing me off..

not the plugs..dizzy caps..rotor arms...coils...ignitors...leads..bugger..


so maybe its the lpg sytem...but it so much "feels" like the ignition...

oooooohhhhh...long day..

 

[Zuffen]

Look on the bright side.

At least you now know the ignition system is in top shape.

When you start looking into the LPG side at least you'll know you're on the rigtht track.

 

[cribbj]

Ditto to what Zuffen said. If your sure your ignition is now solid, and the car runs fine on petrol, then it's time to look at the LPG side. Are you running a vapor injection system, or one of the old carb setups?

I would look at the vaporisers first. LPG doesn't need or like extremely hot water going through the vaporisers in order to vaporise. In fact, too hot water will tend to fractionate the LPG and you'll wind up with vaporisers full of heavies, or even paraffins. "Over cooking" the LPG was such a problem years ago that a company came out with a thermostat that would bypass the coolant to the vaporiser if it was too hot.

Do you have a fuel pressure gauge on your rail(s) where you can confirm the vaporisers are working well, and the fuel pressure is OK?

Also check for clogged filters after the vaporisers and before the rails.

Do you have a wideband you can use to check your AFR's? You'll have to convert from petrol AFR's to LPG, but that's not difficult. I've got a conversion table if you need it.

 

[samsdad]

Odds on the regulator(s) are full of crud and need a clean out along with new diaphragms. Common enough problem...

As you say it runs fine on petrol so that is really all it can be...But...

Having said that I've seen some that run fine on petrol and horribly on gas and found the air flow meter to be the problem yet not firing any DTCs. In these instances the big burn from a backfire on the air filter was a bit of a give away so it may pay to check that too


Note in some places the vaporizers are called mixers. To help those with a lesser understanding the system from the rear of the car to the front has 3 basic components. Tank (obviously) leading to regulator(s) (some systems have 2), And lastly Mixers (vaporizers) which can either be in the form of a fitting( to dumb down the description a bit, think of it like the gas ring in a BBQ) in the air intake or some higher end systems use injectors.

 

[cribbj]

Note in some places the vaporizers are called mixers. To help those with a lesser understanding the system from the rear of the car to the front has 3 basic components. Tank (obviously) leading to regulator(s) (some systems have 2), And lastly Mixers (vaporizers) which can either be in the form of a fitting( to dumb down the description a bit, think of it like the gas ring in a BBQ) in the air intake or some higher end systems use injectors.

Hmm, well, I haven't heard of a vaporiser being called a mixer before, but then I don't profess to know everything about LPG power. I always thought "mixers" were the gas carby bits sold by Impco, OHG, etc. And as you say, those gas rings type sold by Amos and the eastern Europeans

Depending on the manufacturer, they may call their vaporisers vaporisers, or regs, or evaporators because that is, after all, what they do. First they vaporise or evaporate the liquid propane to gaseous propane, then they regulate the gas pressure to the rail (or to the mixer/carby/gas ring thingy). The pics below show a few examples of vaporisers from Prins, Teleflex, Technocarb, etc.

As you say, perhaps those who have a lesser understanding of these systems might refer to a vaporiser as a mixer.....

BTW, it was Technocarb in Canada that made the thermostatic control unit for their vaporiser. Pics of it below also.

Cheers!

 

[zen]

well digging into lpg system now...(sequential zavoli)

pressure sensor(fuel)..temp sensor..map all reading ok on the diagnostics

infact everything is..

changed liquid and vapour filters..recalibrated system...still the same..but after running awhile of running seems to be a ok...

now i am expecting that tomorrow morning it will be missing again...i am now pointing my finger at lazy/intermittent/dirty? injector rails..but at £250 per rail i wont just be swapping these out!

been told by russian who owns local lpg garage that it is the injectors..he pointed at a box of dead ones..says you can strip and clean them out.50% will then be ok..he had 4 high end motors being converted with zavoli sytems there..he may well be right..cant see that the filters would cause a miss,just lack of power..

we shall see..

 

[cribbj]

IMO, Prins (Keihin) injectors are the best but they're $$$$$. They're "real" injectors, designed & built to run on CNG and LPG.

Many of the cheap systems from Italy use little more than converted solenoid valves that aren't really up to the duty. I took apart an OMVL "Dream" rail a couple of years ago and was shocked how cheaply built it was.

 

[zen]

doing more reaserch on system...

it appears from reading various lpg forums that the zavoli matrix injectors (which i have) cause big time misfires when they get dirty..but they can be serviced...info appears to be reliable as appeared on more than one site and posted by lpg professionals..

i wish i had known this before spending ££££££££'s on ignition..oh well

 

[zen]

well alll sorted

cost of repair that did it £10..bugger,,after fitting £300 of ignition bits!!

still live and learn..

zavoli matrix injectors do come apart easy..proper gas injection units..no real moving parts,abit like an automotive relay,has 8 solenoids per 4 injectors..just cleaned it all with carby cleaner..(not that they looked dirty)

no more misfire...