Getting around 11 MPG, running rich, need help

[Z Tyler Z]

So I've been daily driving my 1976 280z for about a year now and I'm getting around 11 mpg city 15 highway.

I've already replaced the coolest temp sensor and plugged off the cold start valve (thought it could be leaky).

Yesterday i picked up anther AFM, figuring mine could be bad and now it runs a lot smoother but still runs very rich. When I let up on the gas I hear a lot of popping from the exhaust.

When driving it feels like it has a vaccum leak somewhere but I've yet to find one. My idle will sometimes drop very low (600 range) and my car will become very gutless. other times it'll run great. My bccd doesn't turn on all the time only sometimes, when it does do it's job my car runs fine other times it won't turn on and that's generally when my car is gutless.

I'll go through he EFI bible next time I get a chance to work on my car. Till then is then any ideas?

[Zed Head]

Fuel pressure is key. It affects everything.

[GreenZZZ]

Bad wiring to or a failed O2 sensor will do that.

[Z Tyler Z]

No o2 sensor on my car, I'll check the fuel pressure next time I get a chance, pretty sure I even have anther fuel pressure regulator lying around somewhere.

[twsutt]

If your pressure is too low, how will that affect the car's mileage? Just curious. I haven't tested mine, but I suspect that it's low.

Edited September 30, 2010 by twsutt

[Zed Head]

If your pressure is too low, how will that affect the car's mileage? Just curious. I haven't tested mine, but I suspect that it's low.

The FPR can fail open (low pressure) or it can fail (clog) closed (high pressure). The stock fuel pumps have a bypass that kicks in at 43 psi. So you can have a clog in a return line or a failed (clogged) FPR and the car will still run, just really rich.

If you have an aftermarket fuel pump, you could get some very high fuel pressures, since many don't have a pressure bypass.

[Zed Head]

There is one other possibility for high pressure. It might be that some of the aftermarket fuel pumps push too much fuel for the stock regulator to handle. I realized that I have had three stock regulators give high pressure using aftermarket pumps. Two were with a new Carter fuel pump, giving 43 and 40 psi on two different regulators, on a 78 engine. The other was with an Airtex E8312 on a 76, giving variable high pressure depending on temperature.

Just a possibility. I tried to experiment with a 6 volt dry cell to compare but it couldn't put out the juice. I don't have any way to confirm and can't find any data on flow rates.

More and more aftermarket pumps are ending up on the Zs because they are quite a bit cheaper and that's what the auto parts stores sell. I wonder if it's one more reason that so many people have the "running rich" problem.

[Z Tyler Z]

Yesterday Dave (Zs ondabrain) and I installed anther fuel pressure regulator I had laying around. We also replaced a couple of the replaceable fuel line hoses and the vaccum line going tot he fuel pressure regulator (mine was hard as rock and has a few small cracks).

A day before that when it was running awful I double checked the AFM and noticed it wasn't in all the way :stupid: . It ran much smoother after that. Does anyone know where I can get the clip the goes on the connector for the AFM?

I'll know what kind of gas mileage I get tomorrow after work. Have to drive to Issaquah and back which is like 80 miles round trip or something. Lets hope for 20+ freeway.

[jthill3]

I've replaced every hose and sensor known to man in my car and only get

18.5 mpg on the highway.

[Z train]

Note to all:Go to your local speed emporium and get a 60lb FP guage and install it between the filter and the rail.It will help immensly in trouble shooting things.

[Zed Head]

I was getting about 18 also before I put an aftermarket regulator on. Now I get a consistent 20 (at least 6 fill-ups calculated since I put it on). I have a 76.

jthill3 - Just for my own personal interest, what fuel pump and regulator are you using? I'm still wondering about these high rate, high pressure pumps that the auto stores sell as replacement pumps for the Z cars.

Edit - I agree on FP measurements. A little disappointed that Z Tyler Z didn't measure before replacing parts but good luck to him.

Edited October 2, 2010 by Zed Head

[Z train]

FWIW:My DD is a 77 810 Goon.L-24E/auto/3.54s & 160,000 on the clock.I get about 19 MPG with a mixture of driving.