Misfire and Rough Idle from p0301 and p0303 code Please Help

[markandkilo]

Im new here so thanks in advance for any and all help
I have a 1998 2.5l manual Ranger the codes I get are p0303 and along with the codes come the misfire and really rough idle.
Heres what I have done
fuel filter
wires
plugs and they're platinum so im thinking of going back and putting in motorcraft
both coil packs
the injector in 1
checked and cleaned both maf and egr
fuel pressure test
compression test and it also help pressure for at least 20 minutes on 1 & 3
I also changed another sensor but I forget the name I think it was dpfe
Dont know what to do next Ive searched the net and all Ive done seems to be as far as anyone else has gone.
Any help or suggestions would be greatly appreciated

 

[RonD]

Does the engine run ok at higher rpms?

Yes, go to motorcraft plugs.
Double check spark plug wires, I know, but it just takes a second.

Clogged up exhaust can often cause misfiring but usually not cylinder specific, and while it can be cause for rough idle it is usually more of an issue at higher rpm as too much back pressure builds up, sluggish performance.

There is an interesting mod some have done, this mod basically changes the system to a dual spark, no tools needed.
http://www.therangerstation.com/forums/showthread.php?t=119047

Just wondering if the PCM(computer) or wiring from PCM is causing the main coil to not spark.
Each of the two coils have two coils inside, there are three wires connected to the coil, one 12v wire(has power when key is on) and two ground wires, the PCM controls the ground wires, a coil is grounded to power up then ungrounded to spark.
Because of this "pack" setup the coil sparks two cylinders at the same time, 1 and 4 and then 2 and 3 spark at the same time, waste spark system.
That's in one coil "pack".

The second "pack" is for emissions, it sparks in the same manner, but on the exhaust stroke instead of the power stroke, this helps lower emissions by burning any unburnt fuel.

The above mod changes the "exhaust coil pack" into a second "power coil pack", so double spark on power stroke.
If the mod helps then it could mean the PCM is not firing the main coil at the right time or not firing it at all sometimes.

The PCM gets a steady signal from the Camshaft position sensor when the engine is running, this tells it where the valves are in the 4 strokes of each cylinder, so it can adjust the spark and injectors to fire at the best time for engine speed.
A problem with the camshaft position sensor, or its wiring, could cause the PCM to misfire coils or injectors.

 

[markandkilo]

It does run better at higher rpms but still the misfire. Double and triple checked the wires. I have read that the after market coilpacks have a different order but have yet to find it so I have stayed with how its supposed to be. I just tried the mod and no change. I also have a question both coilpacks are new I just tested the first one with the multimeter at 200 ohms and it read 1.9 is this ok or is this my problem

 

[RonD]

Yes, that is high OHMs for the primary, .3-1.0 ohms at 200 scale would be expected.

Center pin on each of these style coils should be the +(12v) pin, then Ground pin on either side, one for each coil.
So if the OHMs between center pin and either of the ground pins is above 1.0 ohms then I would suspect the coil......or the ohm meter.

If both coil packs are new and all 4 "coils" test at 1.9ohms then I would suspect the ohm meter.

 

[markandkilo]

I just bought the multimeter i guess ill go out and buy another. Is there anything else I should be checking?

 

[markandkilo]

ok new multimeter .8

 

[RonD]

That's better........

But problem still remains.

I would unhook the negative battery cable for 5 minutes to reset the computer.
This also causes the computer to relearn engine settings for some sensors.
See how long it takes for CEL to come back on, then check codes again.

Also when engine is first started cold, the O2 sensors are off line so can not be used by the computer, computer also runs engine rich with advanced timing until it warms up.
Does engine miss cold or only after it warms up for 2 or 3 minutes?

 

[markandkilo]

It will miss from the very start. Should I just erase the codes or disconnect the battery?

 

[RonD]

I would disconnect the battery or "reset" the computer, same thing.

Erasing the history doesn't make the computer relearn anything.
The computers in cars learn how the engine sensors change over time, if you replace something the computer may be running old data tables based on previous learned data.

Missing from first startup means there is a mechanical problem, spark, fuel or compression.
You tested the compression, should be above 140psi on each cylinder, below that is where problems with missing start.

If you have a timing light you could watch the spark on #1, or #3 and make sure it is consistent, not dropping during a miss.

They make "noid" lights for injectors, these are like timing lights, they go in line with an injector wire and light up when injector is fired, so you could see if injector is dropping out when engine is missing.
You can use a small hose as a stethoscope on an injector and listen to its "click" as it opens and closes, if the "click" is stopping then it could be the issue.

Fuel and spark are controlled by the computer so any erratic behavior could be the computer not the coil or injector, reset might help, but hard to test computers.
There is also the Cam position sensor that feeds the computer info on when to fire coils and injectors, but a fault in that sensor would usually set a code.

Long shot would be to remove the valve cover and inspect the cam and rocker arms for #1 and #3, could be an issue where the valves are not opening all the way all the time because of worn or broken rockers.
Because of the OHC it wouldn't always make that tell tale clicking noise of a bad valve train.

 

[markandkilo]

I removed the battery cable like you said. I also ran some seafoam and im going to change the injectors to motorcraft in about an hour and see if that changes anything. Thanks for the help youve been great. After i make thenext changes i'll keepyou posted

 

[markandkilo]

Ok so I changed the plugs to motorcraft no change. I also did that timing light test and the erratic ones are 1 and 2 the other seem fine

 

[RonD]

Not a steady spark on #1 and #2, that's closing in on something, not sure what yet.
If coils are new, and assumed good, then could be a wiring issue between coil and computer, or computer itself.

Just to be clear, by erratic you mean the timing light didn't do a steady beat, it wasn't lighting up, so we assume no spark at that time, and engine also missed at that time.

On #1 do the timing light on the main pulley and see if it is steady on 10deg, or drifts around, when its working.