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Another EFI problem


EdMo

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Somewhat similar to the one posted a few days ago, I still can not find my problem. I have a 1978 280z w/EFI and have replaced pretty much everything in the fuel flow, except for the Pressure regulator and Dampener. It starts no problem, runs for 15-20 minutes no problem, then starts to putter and enventually stalls at idle. It's then difficult to start unless you let it sit for 20 minutes or so, then starts easy and the same scenario all over again. I'm thinking it's the fuel pressure regulator .... does anyone have opinions on this?

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After the car has sputtered and died, pull off the vacuum hose from the fuel pressure regulator. It should be dry, but if the FPR has developed a leak, it most likely will have gas in it.

Another possibility is that your fuel pickup screen is getting clogged up. That would make sense considering it takes about 20 minutes to do this, whereas a bad FPR would be a non stop sort of thing (lack of power, fuel in oil).

FWIW

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Got ya, I'll check the vaccum hose on the FPR tonight. As for the fuel pickup screen, not sure what you are referring to or where, I've put in a new filter, pump, all fuel injectors and sensors are new as well. Thanks for your response. Now I did not replace the connectors that go to the new fuel injector temp sensors and cold start temp sensor....thinking of ordering.

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That sounds like a fuel filter clogging up to me. I know you say that you replaced it, BUT after I read "I am the original owner of my 1978 280z, though set it to rest in 1996 and started restoring it last year in March of 2007. It's been fun and still on going..." This tells me that it sat for 11 yrs. so what more than likely happened is during its "rest" that gas in the tank got very old and crappy, plus possibly a little rust inside the tank with moisture so even though you replace the filter and clean the lines, this "crud" in the tank is breaking loose and constantly clogging stuff up and creating this issue your having. It just makes all too much sence. Then once you have the car off for X number of minutes, she is fine again because the junk has settled, but once the flow stirrs stuff up again when the car is running, then it starts blocking the flow up again which results in poor idling, or killing the motor.

Sounds like a new fuel tank is in order, or have it professionally cleaned internally. Just simply draining out the old fuel doesn't cut it.

As for that additional fuel filter, it's a small one located at the inlet side of the fuel pump. For sure replace that as well. Hopefully the crap hasn't clogged the injectors :ermm:

Anyway those are my thoughts.

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DatsunZs Rule...your absolutely right. What I meant about it sitting 11 years, it did untouched. I did not start restoring it until this last year March before breaking it all down, I did get the tank professionally cleaned with new pump and had a problem starting until I replaced the FI sensors and got it started. It was amazing that it ran pretty good, but I new I wanted to do a restore and rebuild, we just wanted to make sure we could get it to run before the tear down. Since, I had the motor rebuilt all new fuel injectors and sensors and a whole lot more to list all. I do need to check this small inline filter, is it closer to the tank or filter? Thanks.

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Have you tested the cold start, thermotime, and water temp sensor? Maybe one is telling the efi that it is cold and thus too much fuel is being injected once the car warms up? Do something to trick the system into forcing the sensors to read hot. I don't have my fsm as I am traveling and I forget whether the sensors are on or off when cold/hot.

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I probably will not be able to check the inline filter until Saturday .... but I will....oh I did check the Fuel Reg. after it bogged at the vaccum hose and it was dry (suggested in a previous post-thx). As for the sensors, I did replace the FI temp sensor and water temp sensor, I did not see in Blackdragon or Motorsport catalogue of a cold start sensor available or mentioned to order.... so I did not replace it, thinking it starts fine at cold, though it does make sense of getting to much gas after warm up. Also the connectors that wire up to them are old and tried to clean but still not sure if making good contact. Do you know whether the cold start sensor is the same as the FI temp sensor and where I might be able to find the mating connectors? Also, after warm up you can here the fuel pump humming (this is the second pump acting the same) and can smell gas, so it almost seems like its choking itself.

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Have you tested the cold start, thermotime, and water temp sensor? Maybe one is telling the efi that it is cold and thus too much fuel is being injected once the car warms up? Do something to trick the system into forcing the sensors to read hot. I don't have my fsm as I am traveling and I forget whether the sensors are on or off when cold/hot.
Sounds to me like you need to read the FSM a little more to understand the function of the components you mention. They don't 'tell' the system anything. They're much simpler than that as it the system. No need to 'trick' the system into doing anything. Even if you accomplished that, what have you really accomplished? A problem would still exist. Check each of the mentioned components as per the FSM. There is a test procedure for each one as well as the rest of the components in Section EF.
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The temp sensor is a thermister which decreases in resistance as the water temperature rises. The lower the resistance the richer the fuel mixture and vice versa. The thermotime switch is a bimetal contact that reacts to water temperature and a heater that reacts to electrical current that comes from the start signal. It sends a signal to the cold start valve while cranking when the water temp is below 72 deg. F but only for a maximum duration of 9 seconds due to the heater to prevent flooding. The cold start valve, which is basically an injector, can malfunction like a leaking fuel injector or dispense fuel because of a malfunctioning thermotime switch. The 'brain' as you call it doesn't do anything except patch signals through from one area of the system to another based on the signals it receives, or doesn't receive from the components of the system, generating a fuel injection pulse. It's not a brain, as such, compared to the modern fuel injection systems in that it makes no adjustments, calculations, etc. It's just three integrated circuits on a board in a box.

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