I have a 1997 Ranger 2.3 5-speed with 175k miles that misses at low RPM. When I put a timing light on it I see that I have between 10% and 50% misfires depending on the spar plug wire. The idle is slightly rough, and the engine will noticeably miss sometimes when I'm taking off. It also bucks REALLY hard at low RPM in gear if I try to accelerate (i.e. 25 MPH in fourth).

This problem surfaced after I changed the plugs and wires (with motocraft) and the timing belt. The intake plugs were worn down to tiny needles at the electrodes, and the exhaust plugs looked like they had been changed once. Since then I have:
~ checked for vacuum leaks (none currently exist)
~ replaced EGR valve
~ replaced PCV valve and associated vacuum tube
~ replaced breather tube from valve cover to intake
~ replaced IAC
~ cleaned intake and throttle body
~ replaced short vacuum hose from throttle body to intake
~ replaced CPS and repaired wires to CPS
~ cleaned MAF
~ replaced air filter
~ replaced oil and oil filter (oil was more like sludge than oil!!)

The CPS was pretty dirty, but made no difference when changed. Could there be dirt around the crank pulley that would confuse the ignition signal? Anything else I should look at?

Thanks,
Camelman

 

If timing light is missing pulses then problem will be spark related, not fuel injectors, as you have surmised.

1997 won't have a separate ICM(Ignition Control Module) like older 2.3l's, it is part of the computer(PCM) now.

Since your problem started after changing plugs and wires I would start there.
New no longer means "it works".
New now means "it has never been tested".

A spark pulse is generated by the ICM and coil but it won't show on a timing light if plug or wire doesn't pass the spark.
Ford uses a Waste Spark system, which means two spark plugs are "fired" at the same time, and are wired in series, +......spark plug...(head).....spark plug..... -
This means a bad spark plug or wire(or connection) can effect 2 cylinders.
Spark plugs are not pre-gapped when made, they may appear that way but they all need to be gapped before installing, when accelerating you are adding more fuel which can drown the spark, so no spark at plug or on timing light.
Coil wiring
3 1
2 4

4 2
1 3
front

Firing order is 1 3 4 2
Spark plugs 1 and 4 fire at the same time
And spark plugs 2 and 3 fire at the same time

Make sure coil spark plug wires are correct and the coil's 3 wire connectors are clean, dry and tight
And double check that all wire boots are pushed down all the way, on coil and spark plugs.

Needle tip spark plugs are made that way, NGK uses that shape, and a few others.
It is the gap that is important.

CPS(cam position sensor) is located near the oil pump gear driven by timing belt
CKP(crank position) sensor is located on the crank shaft

CKP sensor generates a pulse which sets base spark timing and 'tells' computer to start spark and fuel.
If this was not working or intermittent engine would not start or would stall, and CEL would come on.

CPS is used to time fuel injectors, for sequential injection, and it is used to advance spark timing, engine can run fine without this sensor, it would switch to Batch fire injection and advance spark timing would be done based on CKP sensor pulses only, but MPG would be less, if CPS and CKP do not "match" timing pulses the CEL would come on.

I wouldn't look at either of these to cause the misfires you describe.

 

RonD,

Thanks for the info. The other work I did was specific to operational issues I observed, but I'm 100% sure there is an ignition problem. I checked my plug wire connections today, and they all checked out. The issue doesn't get worse when it is raining, and holding the plug wires far away from each other doesn't reduce misfires, so I don't think the wires are arcing. I think the issue occurs prior to the coil packs. The postal service should deliver an OBD2 bluetooth module for me tomorrow, so I'll check out codes, etc. and report back.

BTW, the electrode that was down to a needle was the ground (outer) electrode. There was only about 1/8" left on them and they still fired!! I gotta admit... I'm impressed!

 

Today I found that pushing hard on the plugs where they snap onto the coil packs dramatically reduced misfires. I also noticed the wires didn't fit into the coil packs very well. I ordered a warranty replacement set through O'Reilly. Will report back in a few days on the result of new wires.

 

I replaced the plug wires today with a better set of Motorcraft wires. This set has the handles for the rear three plugs on the intake side... the previous set did not. This set seems better made too, and the truck runs marginally better. I found out my cat is broken internally and the core is rattling around in the shell. I imagine a broken cat will cause a rough idle on its own. I'm ready to stop with the fixing and just drive. Maybe find a replacement cat later.

 

I bought a bluetooth OBD2 unit and installed Torque on my spare tablet. It is such a cool app!

A couple things I noticed with the Torque app:
~ Engine temp is fairly steady at 195-202F, but occasionally drops to 140F or -20F for a split second. Strange?!
~ sub 190F idle: 800... over 195F idle: 720. Cold when sitting still after warming up, warm whenever moving or after stopping. I saw the idle drop to 0 momentarily when the engine stumbled once.
~ fuel mileage is back up to 25+mpg. I think the EGR valve was the biggest culprit
~ the strange idle stumble and low RPM issues are still there
~ Fuel trim is below 12.

Camelman

 

RPM signal for computer is from CKP(Crank Position) sensor, if it's pulse is dropping out then spark would stop until CKP pulse was seen again.
Since there is an actual stumble in RPMs when this occurs it is not a simple communications error with OBD II.

Temperature dropping momentarily, along with above drop would have me unhook battery and remove computers connector and check connections for corrosion.
Also inspect wiring in engine bay, from CKP sensor and ECT sensor.

Computer tries to keep 0 fuel trim, that's the target, and that is set by Factory data for engine size and MAF data.
The + and - trim is the dwell for the fuel injectors, dwell is the time an injector is open.
If Factory dwell time is 100(0) and O2 reports Rich then computer will try 95(-5) trim, if O2 reports Lean computer will try 105(+5).
At idle fuel trim will always be +5 to +10, idle is suppose to be rich.
But while driving you should see between -5 and +5, and numbers should be switching very fast.
O2 Bank 1, sensor 2 is behind the Cat Converter and will change slower, it doesn't play much of a roll in engine performance, it is there to check if Cat Converter is cleaning up the exhaust.

Now there are a few things that effect trims but not MPG, as fuel systems get older the pressure will drop, that is normal, lower pressure means longer dwell time so high + numbers, but you are injecting the correct amount of fuel.
Same with injectors getting dirty, they pass slightly less fuel than they did new, so computer needs longer dwell to set best mixture.
So while +12 long term trim is high it could be "normal"

Computer will report Lean or Rich condition at below and above -20 or +20, computer is limited to about -25 to +25

 

Fuel trim varies between -.5 and 3.0 while idling.

I changed the coolant temp sensor (engine side, not gauge side) today and checked the wiring for the CKP and CTS. All wiring looked good. I also checked all engine connections I could find (had to unbolt a couple), and they all looked clean.

I tried to access the Cam Position Sensor, but could only reach my hand around the power steering pump bracket. The CPS is covered in oil, but not sure where it is coming from. The engine runs slightly worse after prodding the CPS, and it has a slight surge going uphill at low RPM in first gear now. Timing at idle varies between 8 degrees and 10.5 degrees BTDC, but will also hang out at 20-31 degrees BTDC anywhere from idle to 1500 RPM.

Not sure what to do now.

 

I pulled the power steering pump/bracket off, and cleaned the area. It was just power steering fluid from the pump failure. Since I was in there I replaced the CPS. The truck ran a little smoother after doing so.

I replaced the throttle position sensor afterwards, which made the truck MUCH more drivable. The stutter at low RPM is almost 100% gone, the idle is steadier, and power comes on MUCH more smoothly.

The following issues have now shown up. Engine idle hangs and then comes down slowly. Idle is silky smooth when it first comes down, but gets rougher after 30 seconds of sitting at idle. Any ideas?

I also get an oil leak that hits the exhaust only when going uphill. Any ideas? I replaced the valve cover gasket and cannot find an oil leak when I feel around it after driving.

 

Woohoo! I found a vacuum leak that I must have created during the last repair. The engine runs like a champ now (except the ABS light is back on again). I'll clean the engine and look for the oil leak this weekend, but I think I'm mostly done with this engine repair.

I'm not sure what's up with the ABS light yet, but I'll start with a brake fluid flush... it's the original fluid!!!

Thanks for the help!!

 

Good work

My '94 ABS light came on a month or so ago..........was just a fuse in cab fuse panel, replaced it and no problems since, so not sure why it blew.