4jg2 using heaps of fuel

[claypot75]

Hi all, i have a 92 Jackaroo 3.1 here, 400,000k on the engine, recently replaced head (cracked), head gasket, valves, turbo, rebuilt injectors and pump, and all of the fuel delivery system, amongst many other minor bits n pieces. Problem I have been having since the rebuild is one of excess fuel usage.

Before rebuild the vehicle was using around 13-13.5 litres/100km. Not fantastic i know, but good considering the accessories attached.

Since the rebuild, its using 17-18L/100km and I am at a loss as to how or what may be causing this. It hasnt had any extra weight added, tyres are still the same size.

The rest of the vehicle is in very good mechanical working order, and if anything needs attention it is sorted out straight away.

Any ideas?

Thanks

[dubdubdub]

Thats allot of diesel... im not to flash on diesels but is the pump timing right?? at that rate big clouds of black smoke would be following you every time you push right foot... try get a boost gauge and see if boost level is correct...

[claypot75]

Only a tiny puff of black smoke under load, and boost is at 12psi. It has been in to the injector pump place twice now, still no change

[geeves]

leaking diesel pump
Auto or manual?
Driving differently due to the new found power?
Economy checked on a different route or traffic conditions
Someone stealing fuel?

[claypot75]

Pump and fuel lines all dry, no leaks anywhere, from tank to injectors

Manual

Driving the same, before engine rebuild, after pump rebuild and after pump repair. Definitely not changed driving style

Vehicle only gets used for 4wd trips, so travelling to the destination, 4wding, and return trip. Always, no mater how i drove it before rebuild it would return 13L/100k.

If anyone was able to steal fuel while i was travelling down the highway, then they can have it, as that would be an impressive feat!

[claypot75]

Its got me stumped, but not losing too much sleep over it as its not my daily driver. Thinking I'll just take it back to injector pump place and see if what they come up with.

[Roderunner]

My 93 jack uses 10 (hyway)-13(mixed hyway/town) litres per 100K, never gone over 13.5 per 100 from memory. I would be looking at the cam timing to make sure it is correct, the other possibility that comes to mind is the new head. Some of the import replacement diesel engine heads have the wrong pre-chamber volume, which results in high emissions, sluggish performance, and excessive fuel use. The only 100% accurate way to tell if this is your problem is to pull the head off and have the chamber c.c.'d, and you will need your old head to verify the correct displacement (and the correct prechamber cups). Maybe a compression test will help you to decide if this could be the problem, generally speaking a smaller size prechamber gives better bottom end power while a larger chamber will favour the top end, has the powerband changed at all compared to the previous engine? I'm not saying that this is your problem, but it's one of the possibilities....have you checked the exhaust pipe for blockages?

[claypot75]

Very interesting information there Roderunner.

Not too sure the cam timing will be out, as the cam itself hasnt been touched,

The prechamber thing, very interesting, was very careful to select the correct head (apparently two types), but obviously no way to tell unless i go down the head off path, again. Maybe a comp test is in order.

Powerband is the same as before.

Exhaust doesnt sound blocked, and it is only three years old, but it has been suggested that maybe it could be blocked. If i get a chance i'll pull the muffler section off and see how it goes.

Fuel consumption has always been up around the 13/100 mark since ive had it, that said, i run 33" tyres, 3" lift and loads of gear. But as i said before, none of that stuff has changed since before the rebuild.

[Roderunner]

The prechamber thing, very interesting, was very careful to select the correct head (apparently two types), but obviously no way to tell unless i go down the head off path, again. Maybe a comp test is in order.

Powerband is the same as before..

Apparently there are 4 versions of the 4jg2 engine worldwide, according to an engineer who specialised in precup replacement parts whom I exchanged a few emails with some time ago. Still, this is only one of the possibilities, so I would leave the inspection as a last resort. I honestly can't think of any other problem, other than injection timing way too early or late, but black/white smoke and overheating should accompany a dodgy pump tune with that kind of fuel use I would have thought!

[claypot75]

Yeah, only thing ive noticed of late is a little puff of black smoke under heavy load. No other smoke except for a small puff of grey on startup. Engine temp all normal, egt seems fine too

[geeves]

over what length run did you measure it? How many litres.
A common trap is to do a ecconomy reading over too small a distance and it only takes the car to of been on a lean for the before fill then the other way for the after to add litres or more to the fuel usage even though this wasnt the case

[claypot75]

Hi Geeves

Yeah, 3-4 tanks between 115 litres and 125 litre (long range main replacement tank of 135L max), each tank running at around the 680k mark, hence the 17-18L/100k 'economy'. The truck only does distance, no short running around the suburbs. Last trip was melbourne to bathurst, a round trip of around 1700k including some wheeling up there.

[geeves]

what speed do you drive at?

[claypot75]

Always have driven at the speed limit, or just a little below, so anything from 80 - 100kph. But again, driving habits haven't changed since the rebuild