My '97, manual transmission, 2.3L engine w/235,000 miles, will occasionally misfire and run rough (usually when down shifting to decellerate). The condition is temporary, and engine will run fine again after a while. The CEL illuminates with a "#1 cylinder misfire" code. CEL can be cleared and won't come back on until next event.

1) Plugs and wires are brand new and of a good quality. Changing them helped overall running performance, but did not repair this problem.
2) The two coil packs are not new, but recent (10,000 miles ago). I'm suspicious that the #1 coil on one of them might be faulty. If that's the case, is there any way to narrow down which pack might be the culprit?
3) Would a fuel injector cause such an intermittent problem (especially when downshifting to decellerate)?
4) The only other thing I can think of is a valve problem of some sort. Compression is excellent in all cylinders - - approximately 155-psi in each.

Any thoughts? Thanks!

 

In this spark setup both spark plugs in a cylinder fire at the same time, they do not alternate.
The exhaust side coil pack is the only active coil when starter motor is engaged, this allows for a hotter spark on cold starts, when battery voltage drops below 10volts.
Above 300RPM the intake side coil pack starts working.

Each coil pack only has 2 coils inside, not 4
So each coil in the pack fires two spark plugs at the same time
When a piston is at TDC(top dead center) it gets a spark
To balance a 4 cylinder engine 2 pistons are at TDC at the same time, 1 and 4, and then 2 and 3
So when 1 is at TDC, then 2 and 3 are at BDC(bottom dead center), and 4 is at TDC
When 2 and 3 are at TDC then 1 and 4 are at BDC

So 1 and 4 share a coil in each coil pack, and 2 and 3 share the other coil in the coil packs
Thats the "firing order" you see on the coil packs
Could be 1 4, or 4 1, doesn't matter
or 2 3 or 3 2, as long as they are on the same coil firing order is correct.

So now you know how it works

You can disconnect the 3 wire connector on the intake side coil pack and start engine and see if you are getting more misfires, so exhaust side coil pack would be questionable, or wires and spark plugs.

And after engine is started you could disconnect 3 wire connector on Exhaust side coil pack for the same test

"NEW" just means NEVER TESTED, it used to mean "tested and working" but not any more, labor for Quality Control is too expensive now, so companies now employ YOU to test products for them, employ is the wrong word, lol, no pay involve, but they do replace the bad parts with no charge, warranty
So.........."new spark plugs and wires" means...........never tested spark plugs and wires



Misfires codes are generated 2 ways, one way is rotational timing, computer has a crank sensor and cam sensor, both send data to computer on rotational speed, when a cylinder fires it "adds" speed if it misfires it doesn't, computer can "see" that, down to the millisecond.

Second way is Coil pack feedback, 1997 has ICM(ignition control module) inside the computer, 1995 and up did, with new EEC-V computers
An ignition coil works by powering it up and then cutting the power, cutting the power generates the high voltage low amp spark
When a coil packs power is cut the ICM expects some feedback voltage, and when it is powered back up it expects a certain draw, if this is out of spec it can also set a misfire code

Flashing CEL means dangerous misfire, engine damage could occur, so lay off the gas if that ever happens.

Deceleration misfires are unique, because generally you wouldn't "feel" them
I would check TPS(throttle position sensor) voltage
Key on engine off, use a sewing needle to pierce a wire
Center wire voltage should be under 1 volt, .69-.99v is spec, this tells computer your foot is off the gas pedal
Open throttle all the way and you should now see above 4.5volts, 4.5-4.9v is spec

Fuel injection save gasoline by turning off fuel injectors when you are coasting, if engine is above about 1,300RPM and TPS voltage is under 1 volt, then computer shuts of fuel until RPMs get to about 1,100 then it starts them back up at idle level.
So when going down a hill do not coast in Neutral to save gas, that carb thinking, with fuel injection coast in gear with foot off the gas pedal and RPMs above 1,300 that save gas

Anyway, if TPS is above 1 volt throttle closed then that could cause misfires
The is an anti-diesel screw on the throttle linkage, looks like an "idle screw" but fuel injection can't use an idle screw, so it ain't an idle screw, lol.
But it can be use to fine tune TPS voltage, and someone may have adjusted this screw without knowing what they were doing

 

My goodness! You should be an instructor at a tech school! Thank you for all of that...

One question re: the coil packs, to clear up my understanding: If, as you say, there are only two coils in each pack -- 1 & 4 fire together, then 2 & 3 fire together -- that means one of those pair of sparks are doing nothing because that cylinder is not on a compression stroke... it fires, but into a cylinder that's venting itself at the time. Is that correct?

I'm betting the TPS voltage is a very likely possibility. I changed the TPS a while back but knew nothing of the voltage readings to be checked and adjusted, if necessary.

Thank you, Ron. Happy New Year to you!