Engine rough running - at wits end

[Zed Head]

9 minutes ago, the_tool_man said:

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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That's often from running lean.  If you wanted to get tricky you could disconnect the coolant temperature sensor, either at the sensor itself or unplug one of the bullet connectors in the harness over the manifold.  That will make it super-rich but it might run right for a while until it gets warm.  A clue.

You can get fouled plugs from lean misfires.  You're kind of in a search for cause/effect right now.  If you can make something change reproducibly it will give you a direction to go in.

[the_tool_man]

That's often from running lean.  If you wanted to get tricky you could disconnect the coolant temperature sensor, either at the sensor itself or unplug one of the bullet connectors in the harness over the manifold.  That will make it super-rich but it might run right for a while until it gets warm.  A clue.
You can get fouled plugs from lean misfires.  You're kind of in a search for cause/effect right now.  If you can make something change reproducibly it will give you a direction to go in.

Early on, the CTS circuit read super high resistance. It may as well have been unplugged. When I corrected it (new sensor and cleaned bullet connectors), it didn't noticably change anything. But I was having fuel delivery issues at the time (bad AFM contacts), so that might have masked the issue. It's something to try.

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[JSM]

Also was the AFM you replaced another used one or a rebuilt one?

[the_tool_man]

Used from a running car.

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[JSM]

I'm running out of ideas for things to check.  Have you checked for vacuum leaks? Are you sure the intake/exhaust gasket is good? Torn /hole / crack in the AFM to TB boot? Check valve is good to the brake booster? What is vacuum reading when you can get it to idle?

Not to beat a dead horse but when you did the plug wires you said you did that one at a time, but maybe the Original owner did them wrong. So to confirm yours looks like this:

[charliekwin]

Just to throw more ideas out there...any chance a previous owner screwed up the timing chain? Obviously, keep checking the easier stuff first.

[Chickenman]

 

 

^ Above comment about timing chain is very valid. Check the Chain timing and make sure it is correct. If it is, carry on testing. In addition to the above suggestions.  

1: Do a compression test ASAP and post up the figures here. You want all cylinders within 15 PSI of each other.  It will tell you a lot about the condition of the engine. 

Engine to operating temp. Disconnect primary leads at terminal  connector on fender. That will disable injectors and ignition. Jam Throttle body wide open while cranking. Battery must be fully charged and ideally connected to a battery charger.

2: Do you still have a EGR valve on your engine?  EGR valves are supposed to be fully closed at idle.  A partially stuck open EGR valve can cause very rough running and sooty plugs. It doesn't take much for the EGR to cause rough running and spit back through the carbs. Old EGR valves tend to carbon up and won't seat closed all the way. It creates havoc with idle and low speed running. Even disconnecting the vacuum hose won't help if the shaft is stuck. The carbon and varnish buildup can physically prevent the valve from seating. Test the EGR valve off the car with a Mighty Vac.

 A block off plate for testing, temporarily eliminates the problem of a stuck EGR valve. EGR valves are useful though. They reduce emissions and reduce cylinder temps allowing more timing to be run at cruise. ( increases MPG while reducing chance of pinging ) But they must function properly. 

[siteunseen]

Have you looked under the intake manifold at the EGR or BPT tube connect?  Mine had rotted a big hole, golf ball size, into the aluminum intake.  The recall vin#s are 350001 through 410516.  Mine wasn't fixed and ran that way until it was parked by the PO.  I wound up with the car and it's problem, put a new intake on there and got rid of the emissions stuff.  If the recall work was done they were to put a sticker under the hood next to the emission information sticker.

My '77 was what I've heard called a "transition year" car, the EGR and all that crap was added as well as more problems.  Good luck!

 

 

Edited February 6, 2017 by siteunseen

[the_tool_man]

Have you looked under the intake manifold at the EGR or BPT tube connect?  Mine had rotted a big hole, golf ball size, into the aluminum intake.  

 

 

What's a BPT tube? Found pics of what you're talking about in your reply to G3BOWSKY's thread on popping noise. Thanks!

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[siteunseen]

It's the EGR tube that rotted mine out.  The recall I read in the How To Restore book says BPT though.  BPT is the flying saucer looking thing with two vacuum hoses on top.  It's closer to the valve cover.  The EGR mounts to the intake closer to the brake reservoirs.  

The male end of this tube screws into the hole under the EGR mount on the intake, 2nd picture.  It's exhaust and it ate up my intake causing a vacuum leak that I couldn't find for nothing.  I'm going to stop now, I feel like I might be confusing the issue with "alternate facts". 

 

[the_tool_man]

I didn't have much time to work on the car tonight. But I had a few minutes to poke around. The EGR/BPT recall has been done on my car (see photo of sticker). I used a mirror and looked under the intake. I didn't see any holes; not even any surface corrosion.

I picked up a remote starting switch, too. It'll come in handy for compression testing.



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[JSM]

10 minutes ago, the_tool_man said:

I didn't have much time to work on the car tonight. But I had a few minutes to poke around. The EGR/BPT recall has been done on my car (see photo of sticker). I used a mirror and looked under the intake. I didn't see any holes; not even any surface corrosion.

I picked up a remote starting switch, too. It'll come in handy for compression testing.

 

Keep in mind that does not guarantee that the EGR valve is not stuck.