78 280Z Troubles

[Znut]

Any advise would be appreciated.

I've just joined your forum and I've done some searching in the archives, but have to say I couldn't find anything that specifically addressed my situation. Below I've provided a description of my problem and would very much appreciate any guidance you may be able to provide.

My 78 Datsun 280Z seems to have a bit of a problem in handling its fuel. I have checked the fuel pump pressure which meets spec and I've ran fuel injector cleaner through it a number of times with little to no results. I've also changed the spark plugs, fuel filter, fuel regulator and clean the fuel tank.

Here's what it's doing....

When preparing to start the car I normally need to leave the key in the on position for several minutes before the car will even attempt to start. Once started it will run fine for a few minutes and then it will start to spit and sputter. When I try to accellerate sometimes it's fine it smooths out and other times it attempts to die.

The oddest thing of all is that when I have the key in the on position without the car running I can hear a gurggling in the gas tank - I have no idea what that could be, but I'd bet it has something to do with my problem.

Znut

[Virto]

You might have a plug somewhere in the fuel line, or a damaged line. Leaving the key "on" is forcing the fuel pump to push fuel to the engine...if there's a blockage or restriction, that could explain why it takes several minutes for enough fuel to reach the injectors to combust.

Maybe the pressure from the pump is OK, but it could be having trouble maintaining the pressure over time, hence the start/sputter/die thing. Replacing the fuel pump might still be viable path to follow.

[Znut]

Virto,

Thanks a million for the for the feedback it is very much appreciated. Any ideas about the gurgling in the gas tank? At one point I did integrate a pressure gauge in the fuel line just past the fuel filter and it seemed to maintain good pressure - not sure this is an absolute way of determining if the pump is good though.

Znut

[Fun_in_my_z]

I would look at the pump first. Thats what is sounds like to me. the gurgling sound is probably the pump droping gas back in the tank. Of it could have alot of air in it.

Bill

[DatsunZsRule]

Sounds to me like the pump is working fine and trying to do it's job. What it sounds like to me is maybe the Thermotime Switch went haywire. Have you tested that? The Thermotime Switch is what provides ground for the Cold Start Valve when the coolant temp is below a certain degrees. Once the engine coolant temp goes ABOVE a certain degree, the Thermotime Switch will break the ground for the Cold Start valve which then obviously kills the Cold Start Valve. The Cold Start Valve is only suppose to operate during cranking and when coolant is below a certain degrees (sorry can't remember off the top of my head what the exact temp. degree is) My guess is the Thermotime Switch isn't breaking the ground for the Cold Start Valve when it's suppose to and it's injecting the extra fuel when it's not needed which will cause your symptoms above because it's getting way to much fuel when it's warmed up and causing it to flood severely. That would be my guess

Best of luck

[hls30.com]

The gurgling in the fuel tank should stop when the car is off, or almost immediately. You should hear gurgling whenyou turn the key on with the starter soloniod disconnected for between 5 and 15 seconds, than it should stop-there is a circuit running through the afm that controls the fuel pump and stops it if no air is flowing into the engine. this control circuit is bypassed on a timer immediately at startup-which is what gives the engine gas before it is running.

I would connect a mechanical fuel pressure gage to the fuel line in the the injector side of the filter, and check fuel pressure through out the rpm range. I would also check for a vacuum leak by having the car at idle and spraying wd40 all around the intake. If the idle gets faster, you have a leak, and at speed this could cause your stumbling, fix the leak, and that problem should go byebye!

I would also check for a voltage drop from the engine block to the negative battery terminal(with the car at idle)-use a digital multimeter to read voltage putthe negative lead on the negative terminal of the battery, and the posative lead on a clean metal surface on the block or intake-any fluctuation over .25 volts, add a 10 gage ground wire between the block and the chassis or negative battery terminal, and test again.

Will

[First Gen Z]

No one has mentioned something as simple as a plugged fuel filter.

[hls30.com]

That would show up with the fpg on the engine side of the fuel filter...

Will

[sblake01]

Didn't you ask about this in another thread? I recall mentioning a malfunctioning fuel pump check valve and even inserting an attachment. From what you describe coupled with my experience with these cars, that would be a place where I'd look. The thermotime switch/cold start valve problem would make your car run quite rich but it would start. You'd notice the black smoke and you've made no mention of that happening. A plug in the fuel line? No that would show up in your fuel pressure test. Clogged fuel filter? No, same thing, it would show up in your fuel pressure test. Check the check valve. If it's bad, it won't allow the fuel system to hold pressure and evertime you try to start it, it has to fill the fuel lines, fuel rail, etc. causing it to be hard to start.

[Znut]

To all who've replied,

Thank you very much for your inputs they are all greatly appreciated. I have a little time this evening so I'm going to attempt to perform some of the tests that have been recommended and I'll report back with my findings in the event that it can be used to assist someone else with similar troubles.

Znut

[DatsunZsRule]

Good luck man. Yeah, let us know how you come out

[sblake01]

When you test the fuel pressure, turn the car off and see if the pressure goes away, it shouldn't. If it does than my theory of the check valve being bad is correct.