Thread: Running rough on fuel

Originally Posted by Baggy

Hi All

The 92 Rangie I've purchased on LPG / petrol is running rough on petrol.

Previously it would run fine on both but now when switching to petrol she will after a short period maybe 2minutes has a noticeable misfire and the idle at the lights would vairy enough for it to almost stall.

Ive changed the plugs less than a 1000 km ago and been running it more on LPG since it's stated to do this but I'm still on the same tank of LPG.

As a test was running it on gas in the carport it runs smoothly with the revs steady.
I then switch it to petrol after two minutes it starts to misfire very badly and there is alot of sooty smoke from the exhaust. She wouldn't idle smoothly and I have to keep the revs up otherwise she would stall.

I pulled out the plugs and they were all sooty ....I cleaned them and reset to bee utey's specification's started her and she runs and drives smoothly.

Since I had her I've deliberately ran her more on petrol using 98 octane but have changed it to 91 octane as bee utey and others advise it's just wasting $$$ and no additional benefit.

Ive heard people mention the stepper valve could it be this?
It does on initial start up rev very high then drop down to normal idle

I unfortunately saw a post that someone just posted about their P38 on gas and bee utey mentioned about blue plug leads ......bugger my leads are blue

Where should I start to sort this out

Baggy

The running too rich could be a failed temperature sender for the petrol system. It is behind the thermostat, next to the temp sender for the dash gauge and has a 2 wire plug like an injector plug. Hot it should read around 300 ohms or less.

Check that the fuel pressure regulator vacuum hose is still connected to its nipple on the back of the inlet manifold. Replace it if it's gone soft. Check that there's no petrol dripping out of the hose.

The stepper doesn't make it run rich. Unscrew it and squirt MAF cleaner into its guts to clean it out. Throw away the flat washer between the stepper and the body it screws into, this will limit the high idle. You can adjust the base idle screw with a 3/16" Allen key in the top of the manifold.

Blue leads of a certain brand are fine on petrol, and also this car runs a distributor not a coil pack, so they should not cause any dramas.

Is it only one plug that is black ? It could be a leaky injector too. Oh, I'd check the fuel pressure too. If the fuel pressure regulator has died and is allowing extreme pressures it will overfuel (I had this once with one of my other cars .... when I fitted a fuel pressure gauge it wound around and nailed itself against the back of the zero stop as soon as I started the car ).

seeya,
shane L.

Hi bee utey and double Chevron

Thank you for your advice.

I'll work through those items and see how it goes.
It's not my daily driver ....took it out tonight and she drives great on gas.

Using your advice bee utey I only run her on petrol ( switch from gas to petrol )when she is at operating temperature and for a few minutes each day.

Tonight I switched it over and she ran fine on petrol and didn't falter although it was cold (6 degrees) tonight which for Perth is cold.

One other thought ......could it be a dirty fuel filter ..... haven't changed that we yet but is on the list of things to do.

Cheers

Baggy

Hi Shane

To answer your question all the plugs were sooty ....

Me being electronically challenged I take it bee utey was referring to use a multimeter
to check the ohms on the temperature sender

Cheers

Baggy