gv78280

car starts and idles wierd. its amlost different every time i start it. the ig. timing is correct, idle speed is correct. just replaced fuel pump.

car runs up to normal running temp and will stay there for a while, then sputters and dies. have read past posts but none have actual solution. any suggestions.

any help is much appreciated

BoulderZ

I had a previous '78 (not my current one) that had a dies-when-hot problem. In that case it was a dying alternator that, when the engine/bay was warmed up to operating temp would no longer trip the 'safety feature' relay which cuts power to the fuel pump if the alternator isn't pumping out full charge power. It's supposed to keep the fuel pump from running if you wreck the car. At any rate, an easy test is to put an in-line fuel pressure gauge in the line from the filter to the fuel rail. Start and run the car, and watch the pressure as it warms up. If, as the car reaches operating temperature, the pressure starts to fall off, then you know your fuel pump is getting it's power cut off. Test your fuel pump relays (mounted near the right front shock tower in a black metal housing). If those are working okay, then it means your alternator is dead (those are the 3 relays controlling power to the fuel pump).
If it doesn't drop off, then you know one of the sensors is bad and giving bogus info to the ECU. Probably the water temp, but there are a couple of possible culprits. Descriptions of testing those are best had from the Factory Manual, or sometimes the Haynes/Chilton manuals (has some nice sections). If you don't have any of those, I'd be happy to relay some quicky tests for those, if that turns out to be necessary. Hope this helps!
Dave

gv78280

thanx dave will check it out

gv78280

chilton/haynes has crap on the sensors. dont have factory man.

tips on checking sensors would be great

thanks dave

BoulderZ

Sorry this took so long. I was gone all last week. Anyway, here are the coolant temps and resistance values you should see for the temp sensor test, which is a good one to try after the fuel pressure test (which you should really do first). Obviously, you'll need a thermometer and a multimeter. If you plan on doing much work with this stuff, I'd *highly* recommend getting hold of a factory manual. With the manual, the Bosch L-Jetronic fuel injection on the Z car is incredibly easy to work on. As you've noticed, when push comes to shove, the Chilton/Haynes things don't measure up on the real detail stuff like this. Some other people on here have managed to find some hard copy factory manuals from a variety of sources. I use the CD ROM version from Courtesy Nissan and I've been *very* happy with it. Hope this helps!
Dave
deg. F (deg C) Resistance (in k-Ohms)
-30 (-22) 20.3 to 33.0
-10 (14) 7.6 to 10.8
10 (50) 3.25 to 4.15
20 (68) 2.25 to 2.75
50 (122) 0.74 to 0.94
80 (176) 0.29 to 0.36