[Donkey]

I’ve been driving a 98 coily Sierra which seems to have been well looked after (regularly serviced, never 4wd) and have been enjoying it though I was pretty disappointed with fuel efficiency which I have thought was normal cause it’s an old car, though I’ve seen ppl on this site saying their range is 350-400km per a tank. The car isles high, cole sits at 2-25k and warm is 1.5k. I’ve done a general service which included change fluids, filters, plugs, leads, distributor cap, rotor and run a fair fee tanks with Carey cleaner though it hasn’t helped this problem. Also it might be worth noting that the car hasn’t been drivin for a few months when I got it. What could the issue be?

[fordem]

Compare fuel consumption in "real" numbers only, either miles per gallon, or, liters per hundred kilometers - 350~400 km per tank tells you distance, but not fuel used. You also need to consider driving conditions, as an example, my 98GV returns anywhere from as low as 14 mpg, to as high as 28 mpg, and this is all on tar, no low range involved.

I also want to suggest you "re-read" your posts before clicking submit, try to make sure that what you're telling us is clear.

[HarryHoudini]

Donkey wrote:

I’ve been driving a 98 coily Sierra which seems to have been well looked after (regularly serviced, never 4wd) and have been enjoying it though I was pretty disappointed with fuel efficiency which I have thought was normal cause it’s an old car, ...

Ours is a 98 Coily.180,000 K's, and get the same MPG,around 200k's on a Tank,standard carby was stuffed so we fitted a Weber which only improved fuel consumption a bit but idles a lot smoother.
This is on short trips around Town 20 MPG,12-14 L per 100K,improves to about 25 MPG on the H/way but needs a heavy foot to cruise at 100 KPH even in 5th.
Ours is well tuned,new timing belt,plugs etc. so we are stuck with high fuel use until we fit a new motor i guess.

[Gwagensteve]

Confirm ignition timing.
Confirm the catalytic hasn't collapsed and is blocking the exhaust

Then, baseline the carby, by taking all adjustments back to factory specs. It's clearly out of adjustment as isle speed is high and choke is incorrectly adjusted.

Confirm the car has factory sized tyres on it and that the speedo is reading accurately.

Car should consume around 10l/100km in general road use.

[alien]

How are you driving it too?? Sierras like to rev. Mine's got a 1.6 in it, but the 1.3 was the same. They love sitting around 3000rpm. Anything under 2,500rpm is useless and you'll chew through fuel labouring the engine. That said, I also drive mine like I stole it, so fuel economy for me is about 13L/100.. I'm also pushing big tyres/lift blah blah though.

[HarryHoudini]

Ours was checked over by a local mechanic,after we fitted the Weber,and timing,valve clearances etc were all Ok.The compression was down a bit,170 something PSI,should be closer to 200 apparently but he said that was normal for a 180,000 K motor.He also said the 1300cc motor can become thirsty as the wear kicks in and compression drops and clearance's go out of spec.
I purchased a 160,000 Coily motor,from a Forum member here,so it seems in good nick and will throw it in when the present one starts using oil which it doesn't do at the moment.

[fordem]

FSM spec on the G13BA has the compression at 199 psi with a lower limit of 156 psi, I would not be in the least bit concerned with numbers in the 170 psi region, mine ran well with as little as 120 psi, albeit whilst going through about a liter of oil every 5000km or so - the vehicle was daily driven at the time and fuel consumption was not significantly higher.