3B crappy fuel economy (1 Viewer)

[JTarnow]

I have a 1985 jdm bj73 with a 3b motor. It is the style with the rotary injection pump, which was just replaced for different reasons. My fuel economy seems real bad, I'm getting about 16mpg or 15 l/100k. Shouldn't a 3b do way better than that? It has been the same with both pumps and I believe the timing is correct. I don't drive it to hard, most of my driving is at about 95kph in 5th gear. Everything else is stock and feels normal. I was expecting closer to 25 mpg. Can anyone shine some light on this.

 

[roscoFJ73]

I would have thought 10-12litres/100klms the norm. My old 73 series with a 1HZ was getting low 12/100

How accurate is your speedo ?
What size tyres are you running?
How many klms has the engine done?
What was the issue with pumps,was the replacement rebuilt or used?
Does it have a roof rack(add 2-3 klm/100 in fuel usage if it does)?

 

[JTarnow]

Speedo is pretty accurate
Tires are 30x9.50's
About 176,000km
Pumps were the original and a used pump, neither were rebuilt. The injectors were done about ten years ago (not sure if they were rebuilt or replaced).
No roofrack or any other mods.
Yeah I expected in the 9-10 per 100 range.

 

[JTarnow]

Oh the reason the pump was replaced was we were going to have the seals replaced in the original and ups lost it.

 

[gerg]

My first thought is injection timing... too much or too little. Lining up the marks doesn't count, it has to be properly timed by a shop. 10-11L/100k is more realistic unless you drive 50mph all the time, then its possible.
Merry christmas!
g

 

[JTarnow]

I have the tool and the timing is adjusted. Economy was the same with the old pump which hadn't been out of the truck to my knowledge. It wasn't driven much before the last couple months but apparently it used to get better mileage.

 

[Deny]

Just throwing this out there, injectors?

 

[roscoFJ73]

Speedo is pretty accurate
Tires are 30x9.50's
About 176,000km
Pumps were the original and a used pump, neither were rebuilt. The injectors were done about ten years ago (not sure if they were rebuilt or replaced).
No roofrack or any other mods.
Yeah I expected in the 9-10 per 100 range.

Sorry ,I should have said odometer. With 31x10.5x15,my odo was out by 10%

What kind of rpms are you pulling at 95kph?

Whats your tyre pressure?


On a 3B,176000 is barely run in.

I would do the injectors as you need to start with everything up to scratch.

 

[crushers]

that is really s***ty mileage
compression?
injectors?
timing?

 

[JTarnow]

What causes injectors to go wrong? They were done about ten years ago after which it was driven maybe a thousand km. I believe it was getting better mileage back then. After that it was put into storage and run a little every few months. Just a few months ago we started driving it again and the economy has been pretty consistent since then.

 

[JTarnow]

Stock tyres are 29 or 30 so the odo can't be that far off. The tach doesn't work but the gear calculator I found says it should be about 2230 rpm. Tyre pressure is 30-35 psi.

 

[crushers]

get them tested ... cheap and then you know for sure.

 

[JTarnow]

I'll have them checked, any other oddball things to look for?

 

[roscoFJ73]

What causes injectors to go wrong? They were done about ten years ago after which it was driven maybe a thousand km. I believe it was getting better mileage back then. After that it was put into storage and run a little every few months. Just a few months ago we started driving it again and the economy has been pretty consistent since then.

The friction of high pressure fuel being forced through the tips and the springs lose their tension.
But if its done little work since they should be fine,assuming they were done correctly.

 

[JTarnow]

The weird thing is the injectors were rebuilt less than 10,000 km ago and we have gotten better economy out of them. It seems whatever went wrong happened while it was in storage not being run that often.

 

[DEADSALT]

Hmmmm.... are you blowing black smoke, does your tank leak, do you have an edic, is it overinjecting, when you fill up, do you get diesel on your boots?

 

[DEADSALT]

... cause thats' really poor mpg's.

 

[crushers]

have you run a new tank of fuel?

 

[JTarnow]

New fuel, no leaking, no smoke of any kind, nothing else abnormal. It doesn't have an edic motor, it has a solenoid if that's what you're asking.

 

[crushers]

compression?