So I heard these cars are rated to 27mpg highway?

[osirus9]

14 is mixed suburb driving and highway during last summer/autumn on nice days. If it was city or I was making short trips then yea, 14's not a big deal, but I was not.

 

So I tried pressurizing the system and then clamping off both fuel lines leaving the fuel pressure gauge in the little section of fuel rail I closed off from the rest of the system. Sure enough My pressure dropped right off with the lines clamped, so I definitely have a leaking injector. I poured a bottle of seafoam in the tank and let her idle for a few minutes until she got all warmed up and revved her a few times. Maybe the seafoam will do something but I kinda doubt it. I want to at least give it a chance before pulling the rail off though so I'll use most of this tank of gas then see if the injector is still leaking.

[Tony D]

Cold, you did it cold, right?

 

I like to block off the return so the engine stalls at fuel pump bypass pressure (around 60) then clamp the inlet. The FPR is open fully then and all pressure is absolutely being held by the clamps. 

 

It dropped off to zero, that is odd. I'd let the fuel tank get real low, like 5 gallons and 'superbatch it'... 

 

I take a can of Seafoam, and one of those truck-sized cans of Techron (enough for 20 gallons of fuel as I recall) and then run the hell out of the car until it's down to almost empty, then fill up again and repeat but this time with a full tank. 

 

Usually by the end of the first 5 gallons, it's purring like a kitten. The only thing that will make an injector 'leak' is dirt in the pintile. And chances are good between and intake manifold treatment with Seafoam, and the circulation of it through the injectors themselves it can be  cleaned out.

 

If you've got a stimulator, you can rig up your fuel rail backwards to clamp the pintile end in the fuel rail, hook up your injectors, and stim the box to induce the firing of the injectors, and reverse-flow pure seafoam and techron through the injectors. It's an amazing cleaning technique for the house-hobby dude.

[osirus9]

Yea I did it cold.

 

I'm gonna give the seafoam a chance and then pull the rail and swap out whichever injector(s) are leaking with spare ones I have. I don't have a stimulator, but that sounds pretty cool.

 

The thing is, I've got a perfect idle at like 800rpms and she revvs cleanly, so the only way to tell my injectors are leaking is shitty mileage and fuel pressure drop after shutdown. So I'll have to fart around with it some more then report back.

[Six_Shooter]

I guess no one has thought about pulling the rail and having it sit on some cardboard to find a leaky injector?

[osirus9]

 I think the next thing I'm going to do is pull the rail off and put a paper towel under the injectors and just lay them on the manifold but still hooked up to the fuel lines, then unplug the starter signal wire and pressurize the system. If an injector is leaking I'll be able to see it on the towel. If I get no leaks then I'll know I need a new fuel pump.

 

 

I guess no one has thought about pulling the rail and having it sit on some cardboard to find a leaky injector?

 

That's what I'm going to try next if this seafoam business doesn't work out.

[Spooler]

I do not see what year car you have. Anyhoo, If you have the 5 speed tranny, you should get 28mpg on the highway no matter how you drive. Most common part failure that would cause this issue is the head temp sensor or Head temp sensor harness. It depends on what year you have to where the head temp sensor is located. Early year models are in the thermostat housing and the older year models are between plug 5 and 6 on the head, passenger side.

Another thing to check is you injector harnesses. If they are corroded and green, get some replacements ends and splice them in.

[richie2619]

Before I swapped to the V8, My '78 was getting a consistent 23MPG on a 225,000 mile engine. Ironically, it got about the same with the 8, if I could keep the back half of the carb closed. Someone mentioned the possibility of the injectors having inconsistent flow due to carbon deposits. You may need to check the spring tension of the air flow meter. I've heard of people trying to richen up the fuel by altering the spring.

[richie2619]

Premium fuel is a waste of money on a low compression engine. Higher octane only raises the flash point to help prevent detonation in high compression applications 10.5:1 or higher. I think the 78 was 8.5:1.

The lower octane also helps prevent hard starts because it ignites more easily. Premium fuel being (better), is a misnomer. It's only better for High compression engines.

[NewZed]

I purchased my 78 280z 5 speed about two months ago. Drove it 100 miles home when I bought it, it gave me 26mpg. It idles great and starts up right away. I was doing about 75-80 the whole way.

How do you calculate mpg from 100 miles?

 

Now seems like the right time - http://www.mycyclonefuelsaver.com/howitworks.html

[Tony D]

" Anyhoo, If you have the 5 speed tranny, you should get 28mpg on the highway no matter how you drive."

 

Not on a California Emissions Spec you won't, no way, no how!

[osirus9]

Before I swapped to the V8, My '78 was getting a consistent 23MPG on a 225,000 mile engine. Ironically, it got about the same with the 8, if I could keep the back half of the carb closed. Someone mentioned the possibility of the injectors having inconsistent flow due to carbon deposits. You may need to check the spring tension of the air flow meter. I've heard of people trying to richen up the fuel by altering the spring.

 

The weird thing is that I have another AFM and all the resistances check out, and the I tested the spring tension on it and that checks out too. If I put that in the car it runs like total garbage, it will hesitate and barely rev. The one I have in there now has totally different resistances than what the FSM specifies, but the car runs way better with it.

Does anybody know if there were different AFMs and ECUs between 280Z years? I know my ECU was replaced at some point, but it was from a 77 automatic, I have a 78 Manual.

 

Also I put like 70 miles on the car since I added seafoam. I can tell that there is a difference, but I don't know if it is just the valve adjustment I did or what. The car feels *SLIGHTLY* faster from the butt dyno, but I still have to give it ~80% throttle to keep up with normal acceleration of other cars. I still lose fuel pressure after letting the car sit too. 

Edited June 26, 2014 by osirus9

[NewZed]

huh, well I know my timing is fine, I already checked that. I'm using some unknown injectors though. You'd think they would flow less over time instead of more though?

 

Any options to check them without having to send them away?

This is one of those threads that could ramble around for weeks, but just for curiosity what is unknown about the injectors?  Do you have a part number?  Are they the stock injectors for the engine you're using?  Turbo injectors?  Or truly unknown?

 

If you have the wrong injectors for the EFI system you're wasting money buying Seafoam.

[osirus9]

This is one of those threads that could ramble around for weeks, but just for curiosity what is unknown about the injectors?  Do you have a part number?  Are they the stock injectors for the engine you're using?  Turbo injectors?  Or truly unknown?

 

If you have the wrong injectors for the EFI system you're wasting money buying Seafoam.

Unknown as in they are the right injectors as far as I can tell for the engine, but they did not come off a running car. I have all 3 colors of injectors, green, tan, and white.

[Milenko2121]

So I installed my innovate lc-2 wideband today. Cruise/Idle AFR's are between 14.4 and 15.1 decently steady around 14.7.

 

Any ideas as to why I'm only getting 16mpg?

 

Also,

I use a 3.54 rear end with the S13 trans gearing.

I cruise 70 around 2700rpm on freeway and 45 around 2100

Edited July 8, 2014 by Milenko2121

[Tony D]

Any ideas as to why I'm only getting 16mpg?

 

Also,

I use a 3.54 rear end with the S13 trans gearing.

What does that mean? Is your odometer accurate for your gearing changes? Have you run a full tank out cruising on flat level ground at that 2,700 rpms and 15:1 AFR?

 

I'd bet you get 22mpg at least. Driving at altitude can change mix 7% leaner with the altitude switch -- is yours functional? Driving in hills will kill mileage for sure.

 

Fill to a set point inside your filler neck, then take a run out US50, refill to the same point in Fallon-note your miles and gallons added. Drive back. Refill to the same point inside the filler neck again and note miles/gallons used again. It helps to use the same fuel stations.

 

If you have a GPS, use it to verify miles driven against odometer, as well as speed.

 

My bro-in-law complained of terrible mileage which was nothing but odo error. Added a 4.57 gearset to get his mudder so back to 3.70 and his mileage "miraculously" returned!

 

This usually comes down to calculation error. Go take a drive out to NAS Fallon and back...then see what you get... Steady speed...steady foot!

Edited July 8, 2014 by Tony D

[osirus9]

So after I did my EFI adjustments I was up to 17.6mpg! Still losing fuel pressure though.

 

So I popped my fuel rail off and pressurized the fuel system. Apparently ALL my injectors leak? How could they all leak!?

 

pics of the test setup and results:

This picture was taken after about a half hour of letting the system sit and depressurize.

So I took my extra set of injectors, looked them over, and none of them look that great. I'm going to send them off to get cleaned and be done with this mess...

[Tony D]

I found the mileage to be pretty darned linear. 

I got 27 mpg at 55-60, and it tapered down to 19 at 100 consistently on the freeway.

 

You can't drive in the city and expect these kind of mileages. In town, 17 is about right.

[osirus9]

17 is like 50/50 highway at about 70 and rural/suburban driving mostly cruising at about 45mph. I don't think it will improve much more than that and that's fine. But in case anyone was wondering all the EFI adjustments i did were free or nearly free and just cost some time with a multimeter and some research. I think that's totally worth 3mpg.

[Phantom]

FWIW - I have over 101,000 miles of carefully computed fuel economy calculations for my 1977 280Z with the L28 engine.

Each time I filled up I would fill the tank until I could see fuel in the opening just below the cap. I then recorded my total mileage and the miles on the tripometer that I reset each time I filled up. Fuel used was entered to the nearest tenth of a gallon and economy was then calculated to the nearest tenth of an MPG.

My driving was a combination of in-town and interstate in the Dallas-Fort Worth area. Initially the car had the stock 4-spd with a 3.54:1 differential.

The first year (about 12,000 miles) the car got anywhere from 17.6 to 25.0 MPG. The 23.9 was achieved on a road trip that was nearly all interstate at 70-75 MPH.

The second year it averaged 18.0 to 20.6 MPG over about 11,000 miles. .

The third year it averaged 17.9 to 21.5 MPG over about 6,000 miles.

The fourth year it averaged 17.1-21.4 MPG over about 7,000 miles.

The fifth year it averaged 17.4-20.5 MPG over about 10,000 miles.

The sixth year it had a drivetrain change in mid year when I installed an '82ZX 5-sod and the 3:90:1 differential. The first part of that year it averaged 16.1 - 20.1 MPG over about 4,000 miles. The second half of the year it averaged 17.0 - 20.4 over about 5,000 miles.

The seventh year it averaged 18.3 - 24.5 MPG over about 11,000 miles.

The eighth year it averaged 16.8 - 21.1 over about 10,000 miles.

The ninth year it averaged 17.5 - 22.9 MPG over about 10,000 miles.

By then engine had right at 200,000 miles on it

The tenth year the car averaged 16.5 - 22.8 MPG over about 9,000 miles and that was the year that I installed the LS1 with the T56 and the 3.70:1 R200 LSD

The eleventh year with the LS1 the car averaged 16.3 - 26.3 MPG over about 11,000 miles. Mostly it was in the 18-19 MPG range. Pretty much the same as the L28.

So there you go. 9 1/2 years and 100,000 miles of mileage data on an L28.

Edited July 28, 2014 by Phantom

[osirus9]

That's awesome info phantom. looks like my car is just about even with yours even with my wider tires and a 3.7 diff with a '78 5spd (yes I changed the speedo gear, it is right).

Edited July 28, 2014 by osirus9