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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.
I had the "hot start" problem return this fall. The fuel pressure also dissipates over a few hours after shut-off. The PO removed the stock fuel rail "trombone" pipes and replaced them with a single billet rail. There is a Summit Racing pressure guage on the rail. With engine started and running, there is approx. 29-30 psi. Without vacuum to the FPR- approx 36 psi. I knew that the loss of fuel pressure, over time, can be (a) leaking: - check valve in the fuel pump - cold start valve - FPR - injectors The pump is fairly new, so I added a Parker check valve down stream, between filter outlet and rail inlet. No change. The CSV was original, so I replaced it. No change. The FPR was for a '77-without the stock fuel pipes, there was a blocked off inlet. I found one online for $45, so I replaced it with a'78 model FPR. Tidier. No change. The injectors were original, though they had been refurbed/ flow-tested by an injector service in the last few years, the connectors were getting brittle, so I replaced with new- not reman- Bosch units. No change. The pressure still drops to zero after a few hours. So where else can the fuel go if it can't flow backwards to the tank/pump (check valve) and it can't return through the FPR and the CSV/ injectors are brand new? I'm stumped. The "hot start" issue- engine stumbles and seems to run rich for a few minutes after a 10-20 shutdown having come to full temperature (180) is slightly improved. Before the work done, it was a b*tch to start and keep running for several minutes. Now it starts okay ,just runs a little rough. So there is some improvement. The CTS/ thermotime switches are new, all connectors and grounds have been cleaned and protected ( Caig De-oxit/ dielectric grease, where appropriate). The AAR was removed by PO. Vacuum is within specs, AFM checks out (Atlantic Z bulletins). I welcome any suggestions/ thoughts. Thanks for reading.