Passat 2.0 LPG conversion down 9 MPG!!!

[BYD1380]

HI all,

I have recently got my VW Passat 2.0 (8valve 115bhp) converted to LPG. Before the conversion I was getting 36mpg on petrol, I record this tank to tank, I drive the same steady 100 miles a day, on A or B roads, car doesn't really get above 60mph.

I got the car converted over just before Christmas, I have about 1500 miles on it now and have consistently got 27mpg on LPG. At that rate it will take a serious time to pay itself off.

The system is KME and it uses OMVL injectors. This is my 4th car I have had converted and wasn't expecting such a big drop.
I have the software for KME and the LPG map seems fine. I have tried adjusting it a few times, but sitting pretty much with the petrol map.

Any ideas? Are those injectors not great for economy? The car seems to drive a bit better on petrol, I know i will lose a bit of power, but its the economy I'm worried about. I have access to VAGCOM aswell, nothing really wrong. Are there any better plugs I should try maybe?

Thanks in advance

Ivan

[Tubbs]

That's terrible !
What's the fuel trim data telling you ?

[BYD1380]

Fuel trim in VAGCOM? or on the LPG ECU? They seem ok, if it was really out (10% or more) i'd get a engine light on.
I was running 1.1bar on the LPG gas pressure and it kept added fuel, up to 10% when driving. I'm currently running 1.2 bar and letting it take 10% of the fuel away, just to try. I'm quite lucky that I have the same drive everyday and it's quiet at the time I go to/from work so the journey doesn't vary much, will just have to play with stuff.

I'm also getting at misfire/hesitation when accelerating under very light load, maybe 40mph up to a 60mph, just rolling on in 5th (I don't mean I only get the fault in 5th gear just an example when it happens) I bought the car from my brother it had plugs recently but the ignition leads look like they are a pain to change and look like they have been there a while.

Ivan

[classicswede]

I'm also getting at misfire/hesitation when accelerating under very light load, maybe 40mph up to a 60mph, just rolling on in 5th (I don't mean I only get the fault in 5th gear just an example when it happens) I bought the car from my brother it had plugs recently but the ignition leads look like they are a pain to change and look like they have been there a while.

Ivan

Think you might have just answered your own question

[LPGC]

The system is KME and it uses OMVL injectors. This is my 4th car I have had converted and wasn't expecting such a big drop.
I have the software for KME and the LPG map seems fine. I have tried adjusting it a few times, but sitting pretty much with the petrol map.

Any ideas? Are those injectors not great for economy? The car seems to drive a bit better on petrol, I know i will lose a bit of power, but its the economy I'm worried about. I have access to VAGCOM aswell, nothing really wrong. Are there any better plugs I should try maybe?

Ivan

Regarding injectors: Different spec injectors have different properties such as how quickly they can open and close and how much peak flow they can give. In simple terms, if injectors are working within (read above) there minimum pulse duration then each injector on the rail should flow almost exactly the same amount regardless of make of injectors. Petrol injectors need to have the correct spray pattern etc, LPG injectors only have to flow gas. If fuel trims are correct then under cruise conditions it is unlikely changing injectors would make any difference.

If car seems to drive a bit better on petrol? This is telling.. Should drive the same.

Getting a misfire on acceleration etc? Either not calibrated properly, not installed properly, ignition system problems or a combination of these issues.

I'm also getting at misfire/hesitation when accelerating under very light load, maybe 40mph up to a 60mph, just rolling on in 5th (I don't mean I only get the fault in 5th gear just an example when it happens) I bought the car from my brother it had plugs recently but the ignition leads look like they are a pain to change and look like they have been there a while.

Ivan

Think you might have just answered your own question

You upped the pressure and adjusted the calibration...? Not much difference between 1.1 and 1.2 bar but I'm wondering just a bit, OMVL SL injectors are usually supplied with nozzles that I'd usually run at a bit higher pressure on a 500cc cylinder (or preferably fit bigger nozzles). Without seeing your setup I don't think it would run to full throttle at max rpm without injector full duty issues, but I doubt this problem would be realised on your steady run to work. It is possible your map or install is wrong but far more likely it's your ignition system.

Simon
Lpgc

[BYD1380]

Sorry, maybe misfire is describing it incorrectly, more a hesitation or jolt, but a single occurrence, like when you would run out of LPG and switch onto petrol. Meaning i can't find it at a certain rpm and hold it there missing. If you know what I mean.

Ivan

[andy evans autogas]

Sounds to me like too much pressure and too small a nozzle ... Also check that the petrol /gas injectors aren't out of phase .... When you say it's a KME , is it Nevo 4 ??

[BYD1380]

Thanks for the replies guys. Yeah it's Nevo 4. Can I just unscrew the nozzles as per magicjet? Thats the ones used in the past. I will also by new leads and plugs and try that too.

Should I just buy standard plug/standard gaps or run one range cooler and tighter gap?

Cheers

Ivan

[BYD1380]

Update:

I had a MAP sensor go dead, it is a double sensor type measuring LPG pressure and MAP pressure. The car would hardly run on lpg as when it was accelerating the LPG pressure would rise instead on going down. Rang Peter (Alternative fuel company), he gave me a new one, so that fixed that. Have put ANOTHER full tank of gas through it since then and still doing 27.6mpg..... I did a full re-calibration of the system after it was fitted and when looking at the Model/Map in the software it looks pretty spot on to me. I'm still having the hesitation when lightly accelerating, next step is new leads they are on order and should be here today.

What plugs would be best for LPG? Would like to change them too.

Ivan

[BYD1380]

Update:

I installed new plugs and leads, the leads were a nightmare to change, and a few looked dodgy, and seemed original with VAG part numbers. I also fitted NGK BKUR6ET-10 as per spec. Car seems to be driving better, have about 400 miles on it since then, still getting 27.9 as a max mpg, filled up twice.

A question on the map. I looked at the LPG map tonight after driving home, it looked like it was running rich, I leaned it off slightly and then instantly got a lean error on VAGCOM. I cleared it and adjusted the idle until the Lambda value looked good.

What nozzles size should be in the injectors for a 2000cc petrol?
I'm still getting the hesitation, I would call it a hiccup, If you have been off the throttle ie. coming into a roundabout, then accelerating in maybe 3rd or 4th gear, just a single blip occurs.

Any ideas

Thanks

Ivan

[lukechris]

Hi mate

I've got a Golf with the same engine converted professionally with a KME Nevo system, I've just bought a cable so I can do some tweaking myself but the issue I'm facing is with misfiring (I don't get this on petrol). I've changed plugs, tried some decent leads, brand new coilpack etc. Did you get to the bottom of this?

Cheers,

[BYD1380]

no, not yet....

Update, since fitting the new plugs leads etc, still the hesitation and poor mpg. I have been playing with the LPG pressure, currently at 1.25 bar, misfire pretty much gone, although last fill up indicated 24mpg!!! My last 3 LPG cars have had magicjet injectors fitted, I'm wondering if it is to do with the OMVL's. They're really cheap compared to other brands, there has to be a reason for this.

I'm away for a weeks holiday tomorrow so won't get much done. Next step it to borrow the magicjets of my missus's Scoob.

Ivan