93 2.3l ranger miss @ idle

[black_demon69]

OK misses @ idle
I have replaced all 8 plugs (had 4 different kinds of plugs in it)
Replaced wires (all miss matched)
Replaced coil pack for intake side plugs
Compression is @ about 70psi dry 95psi wet on all 4 cylinders
Fuel pressure is @ 35psi and 40psi with fpr disconnected (fuel pressure drops like a rock when key is off) (I will be replacing pump soon)
Timing marks line up

A couple of notes
Spark plugs have a nice brown coloring
And it does pop through exhaust
CEL is off a d no codes

Thoughts suggestions? Where to proceed from here?

 

[RonD]

1993 2.3l Lima has 9.2:1 ratio, so should be running 165psi cold/dry compression, so did you forget a "1" in front of the 70 and 95?
Any engine running under 110psi is pretty much a lawn mower

Running compression is about 50% of static compression so maybe gauge you used was incorrect, because with those numbers it would be very hard to start and have little power not just a misfire at idle

So skip that part
If all cylinders test within 10% of each other then not a valve or ring issue

Is it a steady misfire, same cylinder, or random misfire?
And does misfire seem to go away at higher RPM?
And does it come and go under load or is it steady misfire under load?

The popping would be the unburned air/fuel from the misfire being ignited in the exhaust manifold by the next firing cylinders hot exhaust
So there is fuel in the misfiring cylinder, so probably not an injector issue

With the dual plug setup you can test if a spark plug, new or not, is OK
With engine running you can unplug one coil pack and engine will stay running(lower idle) on just the 4 spark plugs, but if there is a steady miss now then one of the spark plugs on the coil pack is bad
Repeat on the other coil pack

This also tests the ICM in case it is only running one coil pack
ICMs were a weak point on the 1989 to 1994 2.3l engines

On the 1989 to 1994 only the exhaust side coil pack works when starting, intake side should start working above 400rpm or so, engine started

 

[black_demon69]

Was suspecting gauge was off because if compression was that low then plug would be black or fouled would also be very hard to start...
Misfire is random and seems to go away @ higher rpms and doesn't seem to miss under load only returns when back @ idle

I will run the coil pack test and let you know

Engine does start right up after key is cycled 1 time and stumbles for a second until the fuel pressure comes up...
Could fuel pump be contributing to this problem?

 

[RonD]

I would doubt fuel pump or pressure, that would usually show up more as demand, engine load, increases

What's voltage like at idle, any headlight dimming issues?

 

[black_demon69]

OK truck dies when intake side coil pack is disconnected and no change when exhaust side coil pack is disconnected.

Voltage is @ 14.5@ startup and there is no headlight dimming whatsoever drops to 13.5 after it warms up.

 

[RonD]

Good alternator test, looks perfect

So only the intake side spark plugs are working

Check that the exhaust side coil pack's Red wire(center) has full 12volt(battery voltage) with key on, same as intake sides Red wire

If so then you are down to ICM issue or wiring

ICM is autonomous for spark
Crank sensor hooks to ICM, coil packs hook to ICM
It can spark without being hooked up to engine computer
Computer hook up is for "vacuum advance" spark timing, nothing more

ICM can be tested at most autoparts stores, but not sure on confidence level of the test, lol.
If the coil pack has the 12volts then I would say replace the ICM on speculation, it would be odd for both ground wires between ICM and one coil pack to be bad, but could happen

 

[black_demon69]

Wil test after I get home (wife wants to go to out) or maybe tomorrow
I will post results

FYI I pulled wires 1@ a time and had idle change on all intake plugs but not on exhaust plugs....

 

[RonD]

With only one coil pack working the engine will run like a 1988 and earlier model 2.3l, less power

And the chamber shape on the dual spark plug head may cause the random misfires at idle with only the one spark plug firing, above my pay grade, lol

 

[black_demon69]

I have 12v and grounds @ both coils exhaust side coil pack is now sparking but still has a miss. Grrrrrr! I am thinking bad connection to the exhaust coil is reason it wasn't sparking before....

Thinking gonna replace fuel pump and see where I am @

I also checked for vacuum leaks and found none
It does have exhaust leaks though.. And CAT is hollow (previous owner must have done it) so no exhaust restrictions

 

[RonD]

So with only the exhaust side coil working it has a steady miss or random?

And with only intake side working it doesn't, or still does?

 

[black_demon69]

Both coils working still has random mis

 

[black_demon69]

Still dies when intake coil is unplugged no change when exhaust coil is unplugged

 

[RonD]

Then exhaust coil is not working, if it has 12v then problem is most likely ICM

It should run on either coil

 

[black_demon69]

Just an update
I have ordered a fuel pump and I am going to install it and see what happens I will post results

 

[black_demon69]

Ok got and installed fuel pump and miss is still there but not quite as bad. I pulled out the original fuel pump and it had a small leak @ the rubber hose that attached the pump to the sending unit...