78 280z barely running

[ransomnotes]

hi, i'm new to z's and not much of a mechanic besides basic stuff, but i have a friend helping me who knows a lot more than i do. we've been working on this car for several days. the car isn't some rust bucket that's been sitting in a field for years....well kept black pearl. the previous owner kept it in a garage when he wasn't driving it. claimed he rebuilt the engine along with a lot of other work and drove it daily for two years. then it was garaged for a short time after he got a Z28. not long enough for me to think the tank is in that bad of shape, but you never can fully trust someone your buying a car from.

i've been through so many forums and threads searching for answers, and have downloaded pretty much every manual on the car and have the chilton. some of it's just foreign to me but i'm pretty confident that if i had some key points to start testing/repairing on the car then i can figure it out.

sometimes it will start right up while other times it just cranks.

if it does start, it revs up to 2000 and back down to 500 before dying. the longest i've had it running is probably a minute or two while giving it gas at the times it dropped down to 500, and i'm getting misfires? out of the intake. a popping sound like it's out of time but it's not (used a timing light and adjusted as necessary).

i know it's getting gas pass the fuel filter but it won't stay running long enough to test the pressure. didn't want to start hardly at all using the pressure gauge.

i've tried to test the injectors with a stethascope but couldn't hear any clicking other than the normal sounds of the engine (how fast is the click usually?). plus it makes it hard for me to finally start it, jump out, and hope it doesn't die before i can see what the fuel pressure gauge says or put my ear to the injectors (my friend can't be here every time i get the urge to work on it).

we've put in new plugs (ngk), wires, rotor, dist. cap, fuel pump, fuel filter, various hoses replaced that were obviously bad, fusible links, cleaned injector contacts, replaced all fuses, and attempted a seafoam treatment.

there wasn't any nastiness when we put in the new fuel pump so i figured the tank was in good shape.

the new plugs became fouled (black) very quickly from gas.

if we spray carb cleaner up into intake it will run at 1500 to 2000.

there are some vacuum lines and a ground off the distributer that aren't hooked up. i have no idea where they go. we replaced a lot of the smaller ones, but there are still some of them that don't seem to go anywhere.

we're stumped yet again and if i don't get it running in about a week and a half i will have to tow it to the inspection station since it's an out of state car and i'm reaching my time limit before they start fining me. not that big of a deal but still a pain. + i'm really itching to finally drive this car.

any help is greatly appreciated.

[Neumeier]

You need to check the fuel pressure. Might be a bad fuel pump. For a fuel injected car to start and run well, you need over 30 psi (check manual on exact number). It should even hold that pressure when the motor is turned off.

Good Luck!

[sblake01]

Do you have the factory service manual. It's the best manual when it comes to dealing with these cars. You can download one at http://www.xenons30.com/reference.html. Other than that, it does sound like a fuel pressure issue to me also. Many variables there. Tank, pressure regulator, fuel pump, etc. My car had those same syptoms when I bought it in 1997 and it tank was the main culprit.

[ransomnotes]

hey thanks for the replies. i blew out lines with a compressor and nothing but clean gas came out. checked fuel pressure between filter and injectors again....still showing about 5psi. then from fuel pump and after damper. both times i was only getting 10psi max.

the fuel pump is new and i'm not seeing much sediment at all. there was a tiny bit that came out of the line from the tank, but i didn't think it was enough to be concerned with....just very tiny sand like particles. but like i said, it was a very tiny bit that i almost didn't even notice in the bucket. how do i test if the fuel pump is bad or weak? it's definitely working.

should my next test be the fuel pressure regulator? i really, really don't want to pull the tank....but i guess i'll have to if i can't figure anything else out. is there an easier way to check the tank?

[grantf]

I had the exact same problem as you, the exact same symptems allmost word for word, what you discribe, and I just got my 78 running great after much $$$ in fuel pumps clearing out the lines, ect what it ended up being was rust in the fuel tank, what I did is a temporary solution: drop the tank (it's really not that hard to do) look inside with a small flashlight to asses the condition on the inside, in my case i used medium sized gravel (motor cycle trick, or use a lenth of chain)to dislodge rust then followed it up with a few flushings with gas and compressed air through the outlet tube. last after reinstalling the tank I put a small inline filter about 3 to 4 inches after the outlet leading to the fule pump. now no backfiring no sputerring and I get alittle under 40 psi after the main filter under the hood.

Edited October 21, 2008 by grantf

[ransomnotes]

hey thanks a lot for the help and here's an update.

it ended up being the tank. even though it didn't look so bad, there was still some blockage. dropped and cleaned it, and it's been running with good consistent fuel pressure ever since.

but....after replacing the thermostat and flushing the radiator, my performance went out the window. it's like my horsepower was cut in half, and it gets worse the longer i drive it. it's not overheating though. it starts out with a good normal idle but that drops to about 4 to 500 once it heats up. it doesn't die but comes really close.

i'm stumped again because we went through so many diagnostic tests on this car less than a month ago and everything seemed to work just fine. went through all the ecu tests with no problem. now i'm back to checking and cleaning connections again but haven't found the problem. my fuel pressure is still good but i still need to run ecu tests again. gonna do that this weekend.

does anyone have any other ideas? why would this start happening right after replacing a thermostat? or could it be just a coincidence?

[sblake01]

Likely a coincidence. Running worse as it warms up and losing power sounds like it could be the temperature sensor or the connection at the temperature sensor not allowing the car to lean out enough to run properly when it reaches operating temperature.

[ransomnotes]

Running worse as it warms up and losing power sounds like it could be the temperature sensor or the connection at the temperature sensor not allowing the car to lean out enough to run properly when it reaches operating temperature.

that's what i was thinking initially. there was some coolant spilled in that area while changing the thermostat and upper radiator hose, so i checked and cleaned the temp sensor connector and it's good, but i haven't checked the actual sensor yet.

[sblake01]

Be sure you haven't switched the connectors between the Thermotime switch and the temperature sensor. I've seen people do that before. At the connection above the manifold, the thermotime switch wires connect to the green wires and the temp sensor wires connect to the black wires. Originally there was a red indicator on both sides of the thermotime connection and none on the temp sensor connection. They're usually long gone after 30+ years.

[ransomnotes]

actually i did have them switched after i put the new temp sensor in and figured out what i did pretty quickly.

i've got a bit more pep back but still running sluggish after heating up. i'm not positive that it helped much because it's been getting damn cold out for the past couple days, so it may just be that it's taking longer to build up to temp. still idling very low when stopped after the car heats up so i've had to open up the idle speed almost all the way. does nothing for the performance but keeps the car from dying at a stop sign at least.

another thing to mention is my spark plugs are white on the end now, so i'm running lean?

and this is the water temp switch? mine doesn't have one. it has everything but this. do the 78's not have this or am i missing something important?

Edited November 16, 2008 by ransomnotes

[sblake01]

IIRC, only 75s have that, maybe 76s, but I've never seen one on a 77-78. What's your timing set at?

[ransomnotes]

you got it! after rechecking the timing we realized we did have it off a bit. so i got my power back now and i feel dumb for not checking something so obvious. kept thinking the problem was bigger than it was.

i'm still getting very low idle after getting it out on the highway for a few miles though, and this car has done this since i bought it. i have an exhaust leak towards the rear of the exhaust manifold from a broken bolt, so my theory is that it's heating up the fuel rail and causing a sort of vapor lock. sound like a legitimate theory?

the po sloppily pieced together the fuel rail with parts from a 77 and it needs some attention. luckily my mom has two 77 parts cars so i plan on taking a complete fuel rail and exhaust manifold from them.

i've thought about an aftermarket header but i've heard some mixed things about using them. a lot of people seem to think stock is the best route to go. i would like to keep about everything under the hood stock, but a header is tempting.