78 country squire engine misfire

HELP!,,
I have a weird misfire situation. Good compression, 62,000 original miles.
I am 90% certain it is an ignition issue.. I have replaced dist cap, rotor, plugs, plug wires. I even rebuilt the carburator, as a last resort. But..... Still misses..
Doesn't do it under acceleration. Only at an idle or when cruising with a light load on the engine.
It has the electronic ignition, which I believe is the Duraspark II with the ignition control module. Non California.
I am stumped.
Even worse???
I seems to come and go. Sometimes it idles smooth, then it will start this miss fire. Same with cruising down the road.
Acts like it is just stalls for a nanosecond. Not enough to identify what the problem is.
I don't want to start replacing the distributor and ICM without first determining if it is just a waste of money.
Surely, someone out there has experienced the same problem.
Thanks,
T

 

I once had that feeling with my 1970 Caprice coupe. Once moving, I rarely felt it, but when just idling it would miss and want to stall. One time it actually did stall and I could not restart it. Long story short, it turned out to be a vacuum leak. Once that was figured out and repaired, problem disappeared.

 

Hmmm.
Checked the vacuum lines and intake with stating fluid. No sign what so ever of a leak.
Thinking it might be a power valve. I put on a remanufactured carburator. But, thinking it still points to a power valve.
I will replace it and see what happens.
Still... I am open to any other experiences.
T-Dawg

 

There was an issue with the current from one plug wire causing an "induced" current in an adjacent wire of a cylinder that was also consecutive in the firing order causing a misfire. The cure was to separate the wires in the loom on the valve cover. What engine does it have? Depending on the firing order determines which wires have to be separated.

 

These all came stock with the 351 Cleveland M code engines. That is what is in mine.
The plug wires have separators on the valve covers, but I am interested in hearing more.
I love a challenge!
T

 

First thing to do is verify the firing order. These Fords used eccentric firing orders and they will run and drive okay with 2 plugs crossed. One time, on a 302 I had 4 plugs crossed up and it still ran! No, I was not the one who installed the new wires. If the wires are getting old or dirty, this on a new set. Accel wires are not expensive. When looking for vacuum leaks, I use a propane blow torch, unlit and turned low. It does the job well.

 

If it wasn't so low miles I might suggest a new timing chain.
Maybe a timing adjustment? Have you got a timing light and a vacuum gauge?

 

seems vacuum leak. could be power valve. I have seen in recent years brand new carbs/ rebuilds be bad. Check the vacuum advance too(the vacuum canister the line hooks to) from behind where the shaft goes into the distributor with juice. OR simply unhook it and use a vacuum pump or you can take off distributor cap and move the deck the pick up sits on, and hold your finger tightly over the vacuum intake port and release the deck. See if it is holding pressure. diaphragm could be leaking and sometimes you forget to check that.

 

351w/351c/351m/400 1-3-7-2-6-5-4-8, so 5 + 6 should not be next
to each other

429/460 1-5-4-2-6-3-7-8, so 7 + 8 should be separated

Another issue was the EGR spacer plate under the carb. Original factory pieces were aluminum, would corrode out and cause an exhaust leak into the carb. (There was a recall for this back in the day). Also, if the EGR valve is dirty and can't close completely, this will cause drivability problems.

 

Ok..... Update.
Check firing order and it is wired correctly. Checked for vacuum leaks and all is tight.
PCV valve is fine.
Going to work on idle screw adjustments. What a pain in the butt!
How do I get to the driver side metering screw without removing the distributor cap each time? Is this one of fords better ideas?
Is there a specific tool that will allow adjusting this while the engine is running?
Some special flexible screw driver with an end that will snap on over the metering screw?
Yes....I'm have a vacuum gauge and timing light.
Haven't gone into the the EGR yet. Sure are a lot of vacuum lines and devices for the emissions!
Wa that thanks to Nader?
T

 

Yes, there's a flex carb adjuster with different tips; a small-diameter long-shaft screwdriver also works if the screws are slotted. You should go ahead and do the gaskets for the EGR spacer. There are two different gaskets for this, but they are still available, so be sure to get both. Then take the spacer to a machine shop and have them cold-tank it to remove the carbon and smooth the bottom on the platen grinder.

 

I was a parts manager at a Ford dealership in the late 70s, and I assure you, EGR spacers leaking were a major problem. However, double check your vacuum lines. Clamp off each one with a pair of needle nose pliers with engine running. Listen for change in RPM or smoothness. Safer than starting fluid. I have had 2 cars with a hard to find miss. One was an '81 Malibu with a 350. The vacuum "tree" behind the carb was cracked. The other was a '74 Dart Sport with a 318. The power brake booster's plastic one way valve (hose from intake) was broken on the bottom sucking air.

 

I would think there should be one available. Although a GM product I still have a flexible cable adjustment tool specifically for a 250 inline with the integral head and you needed that specialty tool for adjusting the carb so I would think(?) there must ne something out there for your problem. Try to find a old school guy behind the parts counter next time you are at the parts store.


EDIT...... I missed there was a page 2, to this.... your question has been answered

 

I have always used a fairly short, thin flat head screw driver. The best is one that was in a nest of screwdrivers, and the second largest fit in like it was made for the job. Don't ask me where to get anything like that, as the one in have was my great-grandfather's, so is well over 100 years old.

 

Hello again!
Been a while since I have updated my thread.
Soooooo...... I pulled the EGR Valve and sucked on the vacuum line coming out of it. I could not pull a vacuum, but could hear the air as I sucked. Next I placed a vacuum pump on it. Still no vacuum. Figured I had a bad EGR? So ordered a new one. After I received it I wanted to make sure it was ok before I installed it. Did the same test and got the same results. Could not pull a vacuum, but could hear the air leaking.
Ordered another one..... Same thing!
Is there something that I am missing? Everything I read about testing an EGR says to check that the diaphragm is good and that the shaft moves when you pull a vacuum.
Is this different for my 1978 Country Squire.... 400M???
T