Jump to content
the_tool_man

Diagnosing fuel system issue

Recommended Posts

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 by the_tool_man

Share this post


Link to post
Share on other sites

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**. LOL

Share this post


Link to post
Share on other sites

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.

FuelPumpTest.jpg

IMG_1237.JPG

  • Like 1

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites
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

  • Like 1

Share this post


Link to post
Share on other sites

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 

Share this post


Link to post
Share on other sites
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? LOL

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

Cliff

Share this post


Link to post
Share on other sites
15 minutes ago, siteunseen said:

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

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...;)

  • Like 1

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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 by the_tool_man

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

It's the style of valve that's used for wheels/tires.  They make them for fuel systems too.  And rerigeration, AC systems.  Seals one way, with a little pin inside to open the valve to allow flow or  release pressure.

Share this post


Link to post
Share on other sites
14 minutes ago, Zed Head said:

It's the style of valve that's used for wheels/tires.  They make them for fuel systems too.  And rerigeration, AC systems.  Seals one way, with a little pin inside to open the valve to allow flow or  release pressure.

Yep. See photo. My fuel pressure gauge is fitted with a female socket to thread onto a Schrader valve.  Glad to know that won't work in time to get a different one.

fuel schrader valve.JPG

Edited by the_tool_man

Share this post


Link to post
Share on other sites

Thanks, I learnt something today. Here they are just called autoventiel or A/C ventiel etc. Schrader is a brand name, a bit like Xerox is to photo copying or Hoover to vacuuming.

 

Share this post


Link to post
Share on other sites
10 minutes ago, EuroDat said:

Thanks, I learnt something today. Here they are just called autoventiel or A/C ventiel etc. Schrader is a brand name, a bit like Xerox is to photo copying or Hoover to vacuuming.

 

In the US the same type of valve, when used on car and some bicycle tires, is universally called a Schrader valve.  Because the ones on fuel lines and a/c lines work exactly the same way, I call them the same thing.  I can't say whether the term, when used outside of tire valves, is standard or not.  I'm belying my US bias here.  Apologies if my use of the term confused the issue.

Share this post


Link to post
Share on other sites
59 minutes ago, the_tool_man said:

  Glad to know that won't work in time to get a different one.

If you have access to a wrecking yard I've found that mid to late 90's Honda Passports and Isuzu Rodeos have a valve on a metal T on the front of the engine.  They can be removed with some side-cutters, then cleaned up with a tubing cutter.  Cheap and solid.  I have one permanently mounted on my engine and a couple in the garage for whenever.

 

  • Like 1

Share this post


Link to post
Share on other sites

I want to start by saying thank you to everyone who helped.  The suggestion of checking the AFM was spot on.  There's a long story that belongs in its own thread.  But basically, I evaluated the car enough to convince myself of its condition, and that the engine was likely in good condition (i.e. test starting, verifying oil pressure, etc.).  I didn't attempt to further diagnose the issue.  Instead, I bought the car at a low price, since it wasn't running, and trailered it home.  When I got it home, we removed the air cleaner, and pushed open the AFM flap with a piece of wire.  The engine started and idled smoothly.  I was able to get it to run well enough to back it off the trailer and into my workshop.  I'll get to work cleaning the AFM and go from there.  I'm excited to finally be a Z owner (see pic), and glad to have found you guys.  Thanks again.

IMG_20160206_123407070_HDR.jpg

  • Like 2

Share this post


Link to post
Share on other sites

Concrates. Looks like a nice find going by the photo. Same color mine was, light blue metalic color code 305. It looks like a mid year 77 with the accordeon bumpers and the AFM fuel switch. In 77 they made a lot of changes through the year. A good idea to note the year and month in your signiture. It helps others giving advice.

From your description, it sounds like someone has been tempering with the AFM spring or a sticking flap. If that is what has been adjusted, it's generally a last resort at fixing fuel mixture issues and almost always a remedy to a symptom. You will learn that as you go along. Part of the experience of owning one of these cars.

The link Zed Head posted to Atlanticz is great for information and how to do a lot of fault finding. A good idea to read through the site. Also shows how to calibrate the AFM.

 

What are your plans for her?

Share this post


Link to post
Share on other sites
6 hours ago, EuroDat said:

What are your plans for her?

For now, I just want to clean it up, get it running and enjoy it as is.  I'll explore minor mods to improve engine performance while retaining the FI.  I'd like to swap over to 240 bumpers pretty soon.  Long term, I'd like to remove the sunroof and the body side molding.  But that'll have to wait for a full repaint.  It's funny; while I was searching I was thinking about lots of mods to modernize and customize one (lowered, triple webbers, custom interior, etc.).  But this car is so original, I feel a bit of obligation to preserve its originality.  So I'm going to have to consider my options for a while.  I have an introductory thread linked below which might be a more appropriate place for this discussion:

http://www.classiczcars.com/topic/53262-new-owner-of-77-280z-from-upstate-sc/

Share this post


Link to post
Share on other sites

If you are thinking of changjng to the 240Z bumper style, I did (or should say doing) that to mine. Here is the thread on it. 

 

  • Like 1

Share this post


Link to post
Share on other sites
21 hours ago, EuroDat said:

If you are thinking of changjng to the 240Z bumper style, I did (or should say doing) that to mine. Here is the thread on it. 

 

Wow. That's a lot more work than I had imagined.  I never noticed how different the 240 and 280 front ends were.  Thanks for sharing.

Share this post


Link to post
Share on other sites

you can do the bumper swap on a saturday with little drama - it's the valence and grill work that take the time & effort. i did just the bumpers and will one day do the valence/grill but for now just the brightwork makes such a big difference visually it's worth it. 

i do hate eurodat's thread though, because his work is so amazing that it's pushing me out of my complacency.... ;)

  • Like 1

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.