1977 280z running rich, troubleshooting help

[tdcrenshaw]

Hey guys (and gals), I'm the new proud owner of a 1977 280z. I don't know a ton about cars, but I'm mechanically handy and I have downloaded and read through the FSM and the FIB for the car. When I first got the car, it had been sitting for a year and wouldn't run at all. After replacing the fuel pump, it starts and runs, but very very rich. It fouls all 6 spark plugs in short order and idles very rough, occasionally dying. I first suspected the CSV, so I disconnected it with no success, though the engine still started fine so I have left it disconncted. Then I pulled the CSV to see if it was leaking fuel, but it was fine as well. Next I checked the water temperature sensor and air temperature sensor, which reported 2520 ohms and 2260 ohms at the ECU in around 68 degree weather. Finally, I ran through most of the ECU checks in the Fuel Injection Bible and while the air regulator circuit failed, it would result in an overly lean fuel air mixture, right?

I rented a fuel pressure gauge, at idle between the fuel filter and the rail it was around 32 PSI, which I know is slightly low. Since it's a new fuel pump, this makes me think that the fuel pressure regulator is suspect. Would a messed up FPR cause a low fuel pressure and make the car run rich? I checked the fuel return line to the tank by blowing in it and after momentary resistance, I could blow through. I also put the fuel pressure gauge between the rail and the fuel return line. There it indicated no pressure. I then pulled the line while the engine was running and very little to no fuel was being returned at idle.

I pulled the cover off the AFM, all the contacts look good, the flap moves freely, and the glue blobs all appear untampered with. At idle, the flap moves about 1cm back, though if I finger it to the lean side, the car runs much smoother. I've considered tweaking it a few teeth toward the lean side, but I would rather get to the root of the problem.

A few other things I've tried: adjusting the idle screw with no real change, pulled the oil cap while idling and felt vacuum resistance plus it ran worse, visually inspected all vacuum lines and tightened hose clamps, and examined the electrical connections. I'm sure I've tried a few other things and forgotten to write them down, but please suggest any boneheaded thing I may have missed.

I feel like my problem is with the FPR, but most of the threads I've read on it say your car will run leaner when the FPR fails. I've also considered replacing my water temp sensor even though it tested fine at room temperature since it seems to be a likely candidate. I know I probably need to check my vacuum pressure next, but I wanted to consult the gurus here before I spend any more money.

[siteunseen]

Auto parts stores should have a loaner vacuum gauge. Have you checked the Throttle Position Switch on the drivers side of the throttle body, small black plastic box you can pop the cover off and make sure it moves from contact to contact. You could clean all the grounds and the coolant temp bullet connections. Here's a few links that will help. Also could be a clogged up air filter or housing, maybe both.

Cleaning the brass,http://atlanticz.ca/zclub/techtips/e...ons/index.html

TPS switch, http://atlanticz.ca/zclub/techtips/tps/index.html

Everything else on a '77, Tech Tips

You'll get it figured out on here.

[siteunseen]

Second new member from T'town! Post #8, http://www.classiczcars.com/forums/i...ingham-al.html

[tdcrenshaw]

I have checked the TPS and it does move from contact to contact. I definitely do need to clean all the contacts and grounds and I'll check the air filter. Those tech tips are definitely a great resource! That's where I got the idea to finger the AFM haha.

I'm confident I'll get it up and running soon!

[tdcrenshaw]

I have checked the TPS and it does move from contact to contact. I definitely do need to clean all the contacts and grounds and I'll check the air filter. Those tech tips are definitely a great resource! That's where I got the idea to finger the AFM haha.

I'm confident I'll get it up and running soon!

[Zed Head]

32 psi is not low for idle. It's actually a little bit high. Maybe not because of the FPR or pump, but because intake vacuum is low due to poor running. The FPR drops pressure to offset intake vacuum. Disconnect the vacuum line from the bottom of the FPR when measuring base fuel pressure. you should get ~36-37 psi.

The engine probably keeps running with the filler cap off because it's running rich. On the TPS test, make sure that the TPS isn't indicating full throttle all of the time. There's a test in the FSM. You can do it at the ECU connection. Set your probes and move the throttle blade. For 77 there are three state - idle, WOT, and neither of those. You might be stuck on WOT.

Then there's the basics of a tune-up - ignition timing, valve lash, air filter. Each little thing will make it run better. If the engine has been neglected, the small things can add up.

[tdcrenshaw]

It's good to know my fuel pressure is ok. I think in my haste to check it I only scanned the relevant section of the FSM, saw 36 psi listed, then assumed something was wrong when I only saw ~32psi

I checked the idle throttle switch and full throttle switch at the ECU, both tested ok. I also pulled the cover off the TPS and visually checked it while moving the throttle linkage.

I haven't checked the timing with a timing light, but I have twisted the distributor cap back and forth. It runs best right in the middle, though it could be so far off twisting the distributor doesn't help.

[Zed Head]

Replay with Quote seems to be broken now also.

You're at opposite ends of the "way to do things" spectrum.

Good end - I checked the idle throttle switch and full throttle switch at the ECU

Not so good - I haven't checked the timing with a timing light, but I have twisted the distributor cap back and forth

You might spend a lot of time tuning the engine only to find that it's worn out. That's what I did with my first engine. The valve seals were bad and it sucked a lot of oil and generated a lot of blow-by. But I knew a lot by the time I got through trying to perfect it.

You can't go wrong by giving the engine a complete tune-up. The first item in the chapter is valve lash. It doesn't change much over time, but when it's off it has a big effect.