1978 280Z - Getting TOO MUCH Fuel or Not enough? Im stumped - HELP!!!

[UndefinedUser]

Hello all,

I have a 1978 280Z and it will only start after sitting for a few days. After sitting for a couple days It will run until I turn it off, then I cannot start it again until it sits for two more days give or take. I tried another ignition coil. I changed all the spark plugs. Tried a new rotor. It has a newly remanufactured distributor.

Sounds like it's flooded maybe?

It IS getting a good blue spark

It is getting the spark, at the right time (took valve cover off, made sure position of dist in relation to cam lobes on #1)

Before the mandatory two day wait after last run, It WILL NOT start if I introduce Starting Fluid into the engine.

It will NOT start if I introduce fresh gasoline into the cylinders. (Again, there is a blue spark and I'm sure it is at the right time)

Took the plugs out and cranked the motor over, fuel mist comes out as expected. I can hear the fuel pump running and fuel circulating in the fuel lines.

However, if I just wait two days without trying to start it...BAM! It starts right up. ONE time.

Could possibly be a spark that is too weak to overcome compression suppression?

Never seen anything quite like this. It defies the rule that says....

If you give a healthy and properly adjusted motor good fuel, air and adequate ignition all at the correct time, it MUST start....because it has all 3 and still won't.

I'm stumped.

HELP!!!!!!

Edited June 12, 2014 by UndefinedUser

[Zed Head]

Is this a car sitting in the driveway running for a few minutes, or are you driving it around then turning it off? Are there high RPM involved?

The ECU's have been known to go bad, though it's not common, and typically die by dumping too much fuel. Either cracked solder joints, or bad injector transistors.

[240260280z]

Ignition switch can wear and cause intermittent spark on start.

What are plugs like?

[rcb280z]

Yeah, take pics of the plugs condition a post them. Start with that so you will know if you are getting spark or not and if you are rich or lean.

[UndefinedUser]

Is this a car sitting in the driveway running for a few minutes, or are you driving it around then turning it off? Are there high RPM involved?

The ECU's have been known to go bad, though it's not common, and typically die by dumping too much fuel. Either cracked solder joints, or bad injector transistors.

Sitting in the driveway. No high rpm's involved. maybe 2,500 - 3,000 tops.

Maybe I should try another ECU. All I see on this vehicle is a Transistor module approx 4 x 5 on the passenger side at the feet. Is that the ECU for this car?

[UndefinedUser]

Ignition switch can wear and cause intermittent spark on start.

What are plugs like?

OK. Can I jumper the connections to check that? The plugs are new and do not seem to be overly wet when I remove them.

[rossiz]

i'm guessing it's your efi relay or a bad ground or corroded connection

[SteveJ]

Sitting in the driveway. No high rpm's involved. maybe 2,500 - 3,000 tops.

Maybe I should try another ECU. All I see on this vehicle is a Transistor module approx 4 x 5 on the passenger side at the feet. Is that the ECU for this car?

The transistor unit is for the ignition. Look up 280Z ECU on Google and look at the images. Also, refer to the FSM. That will give you a better idea of where to look. If that fails, bribe me to come over. Diet Mountain Dew usually works.

[Zed Head]

Sitting in the driveway. No high rpm's involved. maybe 2,500 - 3,000 tops.

Maybe I should try another ECU. All I see on this vehicle is a Transistor module approx 4 x 5 on the passenger side at the feet. Is that the ECU for this car?

You've given some good details but not the big picture. Is this car new to you, maybe just arrived, sitting in the driveway and you're trying to get it running? It's never run right for you, or you've had it for a while and this is a new problem?

It could be flooding due to coolant temperature sensor circuit problems. When it's cold, the extra fuel is good for starting. Then it runs for a little while until the engine is too hot to use the fuel. Then there's too much fuel on the restart since the engine is warm.

There are some tricks that you could probably try with your fuel pump relay, or pinching the fuel supply line, but the best thing to do is the standard advice of "get the FSM and a meter and do some testing". If you have a meter and download the manual, many people here can run you through the circuits to test. IT's not that hard and you'll learn a lot. Test before starting after the two day wait, then test when it won't restart. Something will show up. Unfortunately, the parts are so inter-connected that it's easy to get mis-led. It's rare that someone's first guess is the right one.

Fuel pressure testing is also important. FPR's have been known to be affected by heat.

[UndefinedUser]

The transistor unit is for the ignition. Look up 280Z ECU on Google and look at the images. Also, refer to the FSM. That will give you a better idea of where to look. If that fails, bribe me to come over. Diet Mountain Dew usually works.

Hey, I just might take you up on that offer Steve.

[UndefinedUser]

You've given some good details but not the big picture. Is this car new to you, maybe just arrived, sitting in the driveway and you're trying to get it running? It's never run right for you, or you've had it for a while and this is a new problem?

It could be flooding due to coolant temperature sensor circuit problems. When it's cold, the extra fuel is good for starting. Then it runs for a little while until the engine is too hot to use the fuel. Then there's too much fuel on the restart since the engine is warm.

There are some tricks that you could probably try with your fuel pump relay, or pinching the fuel supply line, but the best thing to do is the standard advice of "get the FSM and a meter and do some testing". If you have a meter and download the manual, many people here can run you through the circuits to test. IT's not that hard and you'll learn a lot. Test before starting after the two day wait, then test when it won't restart. Something will show up. Unfortunately, the parts are so inter-connected that it's easy to get mis-led. It's rare that someone's first guess is the right one.

Fuel pressure testing is also important. FPR's have been known to be affected by heat.

Ok...very informative reply. Thanks.

[superlen]

Undefined,

What you called the transistor unit is in fact the ECU. (Drivers side kickplate) What Datsun calls the ignition module, but is could be called the transistor module, is much smaller and is tucked up under/behind the glove compartment. If you have spark when it's not firing, you can ignore it and focus on the fuel delivery side of the equation.

You've probably figured this out already.

Len