Engine rough running - at wits end

[the_tool_man]

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.

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[the_tool_man]

Double post.

[JSM]

Have you adjusted the throttle body screw to increase the idle once it warms up to help to see if it would run ok once warmed up? Also have you unplugged the cold start valve and tried?

[siteunseen]

If you haven't spent a small fortune already you might consider swapping over to carbs.  Seems like quite a few have done it recently and are happy with their cars again.  If I had to do my tail chasing over, my '77 would be a bigger 240. 8^)

[Zed Head]

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.

[the_tool_man]

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).

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[the_tool_man]

I'll swap to aftermarket EFI before I'll swap to carbs, .

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[Zed Head]

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.

[JSM]

^^^ 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 February 6, 2017 by JSM

[the_tool_man]

It's popping in the intake, not out the tailpipe. I double and triple checked the firing order. And when I replaced the plug wires I did them one at a time.

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[JSM]

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?

[the_tool_man]

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

No. That sounds like fun.

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