Jts Low Mpg & Black Soot On Exhaust Tips

[SpoiledGT 0]

Hi all first post here and have a few niggles which I hope someone here can help with.

 

I've had my 2004 gt jts since November 2014 and the mpg has always been low..about 20 around town and 30ish on motorway runs.

I was getting a few error codes(1131, 1151, 1175 and 0303) at first

and since then I've repaired a split intake hose, replaced maf, had oil and filter change, changed coil pack on cylinder 3 and all sparks and had a new exhaust flexipipe and back box fitted but although i've solved almost all mcsfs I'm still getting the poor mpg as well as sooty exhaust. The oil has also gone dark very quickly too.

 

The car has had a full service history and 51,000 miles on the clock. I have been taking it on a motorway runs every couple of weeks to clear the cobwebs and it does drive fine with no flat spots etc.

 

The 0303 code does pop up when cold starting every so often but the mcsf self clears and it runs fine. Is there any reason for these niggles or are they just traits of the jts engine?

Edited March 30, 2015 by SpoiledGT

[SpoiledGT 0]

Forgot to mention I've already cleaned up the 2 large electrical connection blocks at the rear of engine bay plus all 4 lambda and maf connectors. I've looked at output graphs for lambdas & maf sensors and all look normal apart from slightly slow response from post cat bank 1 sensor.

[Smaky 73]

The most likely cause of the P0303 is the #3 coil pack connector, funny enough on cold days mine does the same, you just keep the revs up for a minute or so and then there is no more issues for the day, the soot is normal, it's burning a fossil fuel so what else would you expect??? low consumption?? Those figures are about normal, around town you sit in low gears requiring more fuel per mile, if you go over 56mph then as drag on the car increases more energy is required to push through the air so more fuel per mile is burnt, 56mph being accepted as the most economic speed of the car on a level road at constant speed. Accelerating and braking always has an adverse effect.

[SpoiledGT 0]

Thanks for that Smaky thought it might have been overfuelling and maybe harming the cats. Never known an exhaust to get so sooty though I have to clean it off twice a week.

[Smaky 73]

It may have the clogged injector problem that these all suffer, more expensive to resolve than the cost of fuel.

[SpoiledGT 0]

Surely not at 51k? I've been using premium fuels exclusively since I got it and have ran a few cans of bg44k through it to keep the demons at bay.

[Smaky 73]

Wouldn't really matter, the JTS wears so quickly that oil being burnt is the problem, it's this residue which clogs up the injectors.

[SpoiledGT 0]

So would frequent oil changes minimise wear?

[Smaky 73]

In my experience with these engines it doesn't matter, the problem is the piston design, the oil rings are too close together and they inherently allow excessive movement of the piston.

[SpoiledGT 0]

Sounds like my best option is to trade it in for a v6 then ðŸ˜