Ok sense I've gotten my motor rebuilt my MPG has been really poor lately, around 15MPG at best And I'm wondering why...

No fuel in the oil, the oil is clean, spark plugs are a healthy color, Fuel filter is new, No injectors leaking, no fuel leaks anywhere that I can see, the engine is running smoothly, and the valves and TPS are adjust to the specs noted in the FSM

Any idea why my MPG sucks? Oh and I wanted to ask if having a broken charcoal canister would cause this? The Smaller ported vacuum line snapped off and I can get it glued back on so I just capped the line, leaving the other 2 lines attached.

 

I don't know if this would have any effect, but are you using premium gas or regular?

 

Timing...
Spark plug gap...
Tire pressure....
Vacuum leaks...

 

Gas quality and how heavy is your foot??

 

Premium, Using what the owners manual says lol

Timing at 10*
Spark plug gap at 1mm
Tire pressure at 32PSI on all 4 corners
And no Vacuum leaks!

Been using 91 from Mavrick and I've been driving it the same way sense I got the Z but only sense after the rebuild as the MPG gone down.

 

Are you sure it's not running rich? Is it an Auto or a 5-speed?

 

Its a 5 speed. and I honestly have no idea. Doesn't smell like it and my plugs are a good healthy color so I'm just assuming its not rich.

 

I bet it's going to turn out to be something thats more referred to with its acronym then its actual name like the psu, ecu, tsu, o2 or something similar lol

 

... Hmm... That reminded me of the AFM... Tomorrow I'll do an OMH and Volt Test from the ECU plug and see if theres something wrong there

Oh heres something else thats interesting.

Before rebuilt I got high 20s or low 30s MPG, after the rebuild I got around 20mpg then I put the new fuel pump in and now its around 15MPG max. That kinda seems backwards, shouldn't it get better with better/newer parts?

And I have NO idea how to tell if the ECU is fine, this one oddly doesn't have an LED check light, course, it doesn't have an O2 Either.

 

Ok now I'm even more confused. Everything tested to the correct ohm and volt specs in the FSM.

Why the hell is my MPG getting so bad...

 

Maybe you miscalculated the mpg?

Have you looked at the plug tips to see if it's running rich?
Have you checked the CHTS?

 

Miles you drove divided by the total fuel you put in, correct?

And I said before, the plugs are a healthy color.
And the CHTS was part of the ohm test and it was at the proper spec.

Maybe my speedometer broke or something and its not keeping proper count of the miles.... As far as I can tell theres nothing mechanically or electrically wrong.

 

you DEF miscalculated... I average 17-20mpg on EVERY NA L28 I have EVER owned.

 

I got 17mpg last tank full. And that is having a a cylinder that doesn't burn all the fuel it is given. So if I didn't have that problem, I would be probably getting 20mpg or more.

Okay when you have the AFM open. Barely push on the device that floats up and down. If your car bogs, when you push it a little. You are at the right fuel/air mixture there. If not just move it a few teeth, about 2 or 3 at a time. (clockwise to lean it) Make sure you mark the tooth, before you move it. Another thing, is play with your TPS. Loosen it, and barely move it counter-clockwise, which is the rich side. Then keep the engine at a steady throttle. And slowly move it, until it runs a irregular idle. If that happens, you are to lean. So slowly put it back clockwise. (to the right) Until it smooths out on a steady idle. Hope that helps, and keep us updated.

 

I didn't miscalculate! I know I didn't, been using the same gas station, same pump (if I can) and I divide the miles I drove by the gallons I used. Isn't that how you're suposto do it?

And wildman, What thing that floats up and down? you mean the sweeper on the track?

 

what about a gas leak? what size rims/tire you running? what diff and color cog?

 

Yeah I think that is what it is. lol If you barely push it downward, while the car is running. And it bogs a little. The A/F mixture is correct on it. Then you would do the test on the TPS.

 

No Gas leak, that was the first thing I looked for. I don;t know what cog is in the trans right now but I have a 3.90

Ah ok If I can get the damn cover off I'll check that out

 

Use a sharp knife, or razor blade. And gently go around the black cover, to get the glue off. Then it should come open. Then when you are ready to put the cover back on. You can drill a hole in one of the corners, and put the cover back on with a screw. Or reglue it, or tape it shut. lol It is all up to you, good luck man.

Here is the link to rebuilding the AFM. It will show you how to get it apart, and even adjust the track inside.
https://www.zdriver.com/forums/240z-280zxt-s30-s130-tech-tips-275/js-how-rebuild-your-afm-15277/

 

Ah I know how to get the cover off as I've done it before with quite a few AFMs but this one just does not want to open like the others. this weekend I'll toy with it to get it open

Maybe I'll just finish my modded turbo afm and install it lol

 

Wait a second...you're talking about running premium in a non-turbo 1980 ZX, right? Wasting your money if so...it was designed to run on 87 & it does just fine on it. I started using 91 in my '82, switched to 87 & got BETTER mpg & no issues. One thing a lot of people forget is the ethanol in gasoline from November-March...nets you about 8-10% less mpg as well.

 

I was just wondering about the ethanol thing myself the other day when I filled up as there was a new label on that pump I never saw before that said "May contain up to 10% Ethanol"

And I read the owners booklet and it says premium fuel. Sooo ya Maybe I'll check again.

 

eh, they don't need it, I'd only put premium in the turbo datsuns. All my NA's got regular and they ran like a champ. but still man, I'm telling you, you will get 17-20 mpg on these cars.

 

I know what I will get! Cuz I had really good MPG before! The issue is that I'm loosing MPG for no reason at all. Can drag in a transmission cause this much MPG loss?

 

What all you do to your engine in your rebuild??