Poor Gas Mileage - '77 280Z

[SilverSurfer]

 

yanked the whole thing, harness and all and swapped in a set of su's with sm needles and i'm consistently hitting 22-25 mpg and i'm driving it like a lunatic most of the time.

old school just plain works.

 

Sorry, but I am dense. What is a "set of su's with sm needles"?

[rossiz]

carbs.

an unmentionable word in this area of the forum...

[SilverSurfer]

carbs.

an unmentionable word in this area of the forum...

 

Thanks. I have heard about people doing this. However, even if I end up doing a lot more work, I'd like to see if I can get my Z to get better gas mileage with the injectors. If not ... well ... I am definitely open to suggestions.

[hr369]

 

 

 

 

 

 

78 epa rating for a NEW datsun. We also have ethenol now so these figures are probably better than the best tuned car out there.

 

[SilverSurfer]

78-280z-epa.jpg

 

 

 

 

 

 

78 epa rating for a NEW datsun. We also have ethenol now so these figures are probably better than the best tuned car out there.

 

Right. So, since I am getting 11-12 city and 17 hwy, I need to find out what's going on.

[gundee]

It's been a while, but I wanted to add an update:

 

I drove the car for about 4 hours the other day (took 'er on a road trip, I did). My MPG ended up a little over 17 MPG on the highway. Not great, but better.

 

The speedometer is off by about 5-7 MPH depending on how fast I am going ... in this case, up in the 65-75 MPH range.

 

The tripometer appears to be working properly as I checked it against mile markers on the highway.

 

I will try to pull a spark plug and photo it tomorrow and post photos here.

 

Pull all 6 plugs, not just one.

Also run a compression test.

Report PSI of each cylinder.

[bartsscooterservice]

carbs.

an unmentionable word in this area of the forum...

 

It's funny because injection was invented for fuel economy, but they end up giving worse fuel economy than carbs ( if set up properly )

[Zed Head]

I think that emissions control was a big part of fuel injection development.  

 

With an adjustable FPR and some tricks I can get low 20's mileage on my engine.  But at the sacrifice of mid-range performance.  Tunability is the major benefit of carbs, compared to old EFI systems.  But the newer aftermarket tunable EFI will probably beat them both.

 

I get about 21 mpg mixed highway and city in the summer, and 18 in the cold of winter.  With things set for performance.

 

There are several parts that could cause low mileage, like out-of-spec. injectors, a coolant temp. sensor on the high end of the resistance range spec., an ECU on the high end of the injector open time spec., an AFM on the high end, stuff like that.  The easy way to increase mileage is to use an adjustable FPR.  Then you can move the whole fuel enrichment curve down.  The problem is finding an adjustable FPR that is as good as the stock ones.  They all leak down and cause a new aggravation.  I modified a $34 Bosch FPR but that takes some fabrication work.

 

Some of the California cars have an altitude switch that cuts enrichment by about 7% (I think).  If I had a CA car and it was rich, I'd short that switch and put the ECU in lean-mode.  Just one possibility.

 

Overall though, carb tuning is probably easier and quicker.

[siteunseen]

When I put the potinometer on the coolant sensor wire and got it adjusted and running really good my MPG went up. Maybe the ECUs drifting out of spec over the years make them less efficient?

[gundee]

Download the Factory 280Z FI Manual. Its excellent.

Will give you the full understanding of how your system works.

We found 280's are even running around with plugged up exhausts.

A definite mileage problem. Honda's and Toyota's are famous for the same thing.