Diagnosing fuel system issue

[the_tool_man]

Hi all:

First post, so go easy on me. I don't own a Z yet. But I'm going to look at one (a '77 280) that may become available for sale. Current owner says he let the car sit for a couple of years, and the fuel went bad. He drained the tank and refilled with good gas. The car will start, but won't run for long before shutting off. He says it starts right back up and then dies again.

He and I discussed, and theorize that there is crud (probably rust) in the tank getting sucked into the tank outlet screen and clogging it.  If that theory is right, I assume the tank needs to be cleaned out, and maybe coated to prevent rust.  I'm only beginning to learn about these cars.  So I don't know what else to look for.  It seems that the fuel pump works, and the engine otherwise has spark, or it wouldn't start at all.

I'm going to look at the car on Saturday. I plan to take a fuel pressure gauge, starting fluid and a spare fuel filter. What else could be wrong that can be tested without too much trouble?  I'm hoping for an easy fix if he decides to sell it to me.

Thanks in advance,

John.

Edited February 3, 2016 by the_tool_man

[siteunseen]

For sure put the new fuel filter on and see how long it runs. If it stays running you can bet the fuel turned to "varnish" and is causing the intermittent running. You should use that as a bargaining point  if he's not a close friend.

Once you get the car you should install a fram g3 clear filter right out of the tanks supply hose, before the pump. You can see if it gets crudded up fairly quick. Maybe running some new gas a few times through the system will clean it out without dropping the tank. 

After installing the new filter check the pressure first with the car sitting still. Something I would do is check the air filter for derbies such as acorns, damn squirrels and other rodents love to get in these cars, as much as I do! Look for broken vacuum hoses or ones that may have come off completely. Lots of help here on a '77. I've got one myself. Good luck and stay positive in your post. Nobody here likes a smarta**.

[EuroDat]

Hi and welcome to the club.

If you have a gauge you can test the system easily.

Fit the gauge between the fuel filter and the line that goes to the fuel injectors. What you describe sounds line its running out of fuel directly after starting.

That coud be caused by several things. just to name a threw:

1. Fuel tank full of rust and gunk blocking the fuel pickup.

2. Gunk in the pump inlet filter or in the pump if the filter has been removed. See photo.

3. Fuel filter is blocked.

4. It could be running on fuel from the cold start valve, but the injectors are clogged up and not supplying enough fuel to keep running. 

I would start with those simple things first.

[EuroDat]

If you check out the download section, you will find the workshop manual and fuel injection supplement for the 77 280Z. A lot of helpfull information in there.

[Zed Head]

33 minutes ago, the_tool_man said:

The car will start, but won't run for long before shutting off. He says it starts right back up and then dies again.

Sounds a lot like the AFM fuel pump relay contact switch.  You can jump the switch under the AFM black cover with an alligator clip or just holding it closed with your finger.  Clean it first with a match book striker or similar.  I'd try that first, just to make sure the pump is staying running.  It's the easiest.  Posted  a link with a picture.   I wouldn't do the other stuff it shows at this time.

http://www.atlanticz.ca/zclub/techtips/afm/index.html

[Patcon]

the_tool_man

I live in Spartanburg, I can probably help you if you need advise or parts. 280's are not my forte but I would be glad to help if you need it...

Charles 

[siteunseen]

32 minutes ago, Patcon said:

the_tool_man

I live in Spartanburg, I can probably help you if you need advise or parts. 280's are not my forte but I would be glad to help if you need it...

Charles 

Can I claim that as Southern Hospitality?  or are the Carolinas too far?

Just playing, those guys from the West are pretty darn helpful also! Great guys here.

Cliff

[Patcon]

15 minutes ago, siteunseen said:

Can I claim that as Southern Hospitality?  or are the Carolinas too far?

Just playing, those guys from the West are pretty darn helpful also! Great guys here.

Cliff

Cliff,

Remember it doesn't get any more southern than South Carolina. The buckle on the belt and the first to start a fight...

[EuroDat]

8 hours ago, Zed Head said:

Sounds a lot like the AFM fuel pump relay contact switch.  You can jump the switch under the AFM black cover with an alligator clip or just holding it closed with your finger.  Clean it first with a match book striker or similar.  I'd try that first, just to make sure the pump is staying running.  It's the easiest.  Posted  a link with a picture.   I wouldn't do the other stuff it shows at this time.

http://www.atlanticz.ca/zclub/techtips/afm/index.html

Good point.

I find the easiest way to test this is with the handle end of a screwdriver via the aircleaner. Remove the air cleaner filter, turn the key On and push the flap open with the handle end of the screwdriver. It takes a bit of fiddling and the right size screwdriver. You should hear the pump run and pressure up the system. You might even hear fuel sissing through the FPR (fuel pressure regulator.

Now that is assuming its the early 77 with the switch in the AFM. The later versions had it in the oil switch. The oil switch type has two wires going to the oil sender unit. If it only has a yellow wire with black stripes, its the AFM type.

[the_tool_man]

Thanks for the help, guys!  That gives me a few things to check.

For the record, I'm used to late model cars.  So it'll take time for me to figure out a car that doesn't use a MAF, IAC valve and OBDII trouble codes, lol.  I have a lot of reading to do.

Thanks again.

Regards,

John.

Edited February 4, 2016 by the_tool_man

[the_tool_man]

BTW, I take it from the photos there isn't a Schrader valve for the fuel pressure gauge?  What diameter fuel hose should I take?  Thanks.

[Zed Head]

No Schrader valve.  The hose is 5/16".  Get high pressure EFI hose, although plain old hose would probably work for the short time you'll be testing.  Take some extra hose clamps.

If the guy doesn't mind, it's actually easiest to just cut the hose between the filter and the fuel rail and slip the pressure gauge T-fitting in there.  You'll have a heck of time trying to get the old hose off of the metal tube ends.  Probably bend and maybe break things.

Test the AFM switch first thing though.  EuroDat's method, or mine, with the key On, will tell you if the switch is dirty or not.  Then, if the switch works, do the same while starting the engine to see if there's enough air flow to keep the switch closed.  Sometimes the idle speed will be so low or there's an air leak, and the switch will open and kill power to the pump.  Air has to flow through the AFM to keep the switch closed.