Outer Limits 4x4 Board

My 4.4 V8 is running dual fuel atm. The gas system i am using was originally fitted to the motor when I had the 3.5 so I'm not sure about its specs. I have some photos of the the converter and mixer which i will post when the pics are back up.

Anyway, after i installed the 4.4 i took it to a gas place and told them to set it up to suit the 4.4. The bloke put a new mixer ring on it and said it should be fine. I'm finding though that above 4000rpm the motor does not rev any harder and doesn't have any more poke. On petrol it goes really well up to 5500rpm (and even then its underfueled!)

I assume that its undergassed, but what can be done to solve this? Is the mixer ring wrong or is the converter not good enough?

TIA

Could possibly be ignition as gas requires better spark

Maybe blocked filter in convertor. (waxed)

Bazzle

bazzle wrote:Maybe blocked filter in convertor. (waxed)

Bazzle

Was my first thought too
Winter always seperates the good from the not working well

Kingy

Thanks guys, on the ignition front I believe all the components are up to scratch although the timing is still TDC, I understand with gas this can be advanced significantly? Although would this affect top end?

As far as the converter goes, I'll pull it apart and have a look at it today. I assume its a servicable part?

yep they are a servicable part

Just be careful of the rubber diaphragms that are inside ..... they tear easilly if ya not switched on.

The "wax" will have built up in a lower section ( gravity rules here ) and usually this buildup prevents the diaphragm form moving its full throw thus limiting the flow of the LPG

Kingy

The closer the timing is to TDC the more bottom end you get the further away the more top end but you need to check total advance it shoud be around 33-36 degrees. Around 8-12 initial will be a good starting point if you don't know how much advance is in the dizzy.

TuffRR wrote:I'm finding though that above 4000rpm the motor does not rev any harder and doesn't have any more poke. On petrol it goes really well up to 5500rpm (and even then its underfueled!)

Geez,
Didn't know they rev that hard. I don't think I have taken my 4.4 past 4000.

A couple of other tips.
Is the main fuel line from the tank large enough diameter,early kits were only 6mm or 1/4",not big enough to feed a V8.
If you have tried everything else,some of the larger engines used to run 2
regulators to cope with demand.
This was more often on CNG than LPG but if your reg is too small another
cheap small reg from a wrecker may fix your starving.
When she starves is she leaning out? An easy check is to put a tempory
restrictor over your air intake and see if it changes the performance.
Bring your timing up 5 degrees and always run on super petrol.
J Top

J Top wrote:A couple of other tips.
Is the main fuel line from the tank large enough diameter,early kits were only 6mm or 1/4",not big enough to feed a V8.
If you have tried everything else,some of the larger engines used to run 2
regulators to cope with demand.

J Top

The lines sold for all the kits I have had are 6mm and they are more than enough for my 3.9V8, and introducing two regulators would add a fair amount of complexity I would think. I know from my experience with gas on a 3.5V8 carby that the flow rates to the carbies had to be identical otherwise one would suck the gas out of the other.

A couple of things to think about, find out if the converter you are using using is up to the job, if it is the one I am thinking of I am sure it is - but ring up someone like sprint gas and see what they say.

The way that I have been told to tune is to set the main screw in the gas line on the way to the mixer first then do you other settings. Rev it engine to around 3500 rpm and then turn the screw in till the revs start to fall then back it out at around 1/2 a turn,

then use the larger of the two screws on the converter to set the flow of gas under acceleration i.e. make sure the motor can freely pick up revs with the gas that is supplied under load - I switch to petrol and try it then back to gas and compare.

Then set our idle with the smallest screw on the converter.

Some things to consider,

1. is the tap on the tank all the way open

2. is the gas filter clean

3. are you sure it is leaning out and not flooding (I am in the process of fitting oxygen sensors to my rangie so I can use them to tune it up more accurately - for a really basic setup but two from the wreckers from a commodore and the $59 monitor from jaycar with the digital read out - of course you can get a mate to smell the exhaust where it flattens out and guess from there)

4. Check your air filter for the engine if the flow is restriced (which would really take a lot of dirt and crap to do) it can bugger up the lpg

Just some ramblings good luck with it all

Tom

just simply , check / adjust your air / fuel ( gas ) mixture

had a gas system on my chev in a 4runner
put motor into my old hotrod.....on petrol
then put it on gas.......using same components from 4runner
they set it up wayyyyy lean.......it wouldnt rev past about 2800
**an they did this doing a test run in the car for the mixture settings**

once it was re-adjusted an richened , the motor went back to revving to 6500rpm or so everyday like it did on petrol

Looks like I'll be busy, thanks for the advice, I'll let you know how i go.