Jump to content

IGNORED

Engine rough running - at wits end


the_tool_man

Recommended Posts

Hi all:

1977 280z. Stock with 90k miles. Bought a year ago not running (I know, stupid). It would start, but die immediately.

The long version is detailed in my intro thread if you want to read it. http://www.classiczcars.com/index.php?/topic/53262-New-owner-of-'77-280z-from-Upstate-SC

The short version. Replaced fuel filter and lines, fuel pressure regulator, injectors, AFM, coil, plugs, plug wires and coolant temp sensor. Cleaned and verified coolant temp circuit function at ECU. Air gap between reluctor and pickup set to 0.012. Timing set to 10 degrees BTDC. All of this was done in response to various symptoms, such as low fuel pressure, misfire, etc. over the past year of off-and-on repairs interrupted by health problems.

Now it will idle roughly when cold. If I rev the engine it backfires and then revs okay. But it still runs roughly. Once the engine starts to warm up, it won't stay idling more than 15 seconds or so before sputtering to a stop. New plugs don't read yet. Old ones were sooty, even when fuel pressure was low.

I don't know what to do next.

Sent from my QTAQZ3 using Classic Zcar Club mobile


Link to comment
Share on other sites


JSM asked a good question.  Can you keep the engine running at all, or are you focusing on just idling?  Not clear if it's a running problem, or and idling problem.  Also can't tell if it backfires just once then everything is okay, or if it backfires once every time you rev it.  And is this when it's cold, or when it's hot, or both?

Seems like you're making progress.  Have you had it out for a drive yet?  Maybe it needs a slight thrashing.

Link to comment
Share on other sites

I adjusted the idle screw. But it didn't really help. It backfires every time I try to rev it, cold or hot. I haven't replaced the CSV or unplugged it. I'm wondering if that's leaking all the time, causing a rich condition that worsens as the engine warms up? If that's the case, I'd need to disconnect it from the fuel line, not unplug it (or maybe that's what you meant).

Sent from my XT1254 using Classic Zcar Club mobile

Link to comment
Share on other sites

Are you positive that your plug wires are installed correctly?  153624 counterclockwise.  The engine will start and run with them installed clockwise.  Strange but true.

Backfiring is usually caused by spark happening at the wrong time or lean fuel-air mixture.  I've seen bad front-fires from exhaust valves staying closed due to bad cam lobes.  Is it popping through the intake manifold or out the tail-pipe?  Easy to get back and front mixed, description-wise.

Link to comment
Share on other sites

^^^ you beat me to it!!

Not a knock on you as I have done this, are you 110% sure your plug wires are on the right cylinders? Also curious if it runs better at least at idle with the AFM u plugged? 

Seems like the only thing that you haven't swapped is the ECU? What is the number on your ECU?

Edited by JSM
Link to comment
Share on other sites

10 minutes ago, Zed Head said:

Are you positive that your plug wires are installed correctly?  153624 counterclockwise.  The engine will start and run with them installed clockwise.  Strange but true.

Backfiring is usually caused by spark happening at the wrong time or lean fuel-air mixture.  I've seen bad front-fires from exhaust valves staying closed due to bad cam lobes.  Is it popping through the intake manifold or out the tail-pipe?  Easy to get back and front mixed, description-wise.

Oh that's another good point. Have you checked your valve clearance yet?

Link to comment
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
  • Recently Browsing   0 members

    • No registered users viewing this page.
  • Who's Online   0 Members, 0 Anonymous, 184 Guests (See full list)

    • There are no registered users currently online
×
×
  • Create New...

Important Information

By using this site, you agree to our Privacy Policy and Guidelines. 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.