All cylinders randomly miss.

Hey Folks,

So here's my tale of woe.

I have a 1998 Ex Sport with the 4.0 SOHC engine in it and it's 4wd. I bought it because it had issues and the deal was good not great but good.
So far I've repaired some of the problems but the random multiple misses are driving me nuts.

I have spent the last week plowing through older threads but couldn't find anything that address this specifically.

I have up to this time replace the MAF, cleaned the IAC twice, replace the coil pack and wires, replace the upper and lower intake gaskets. It gets good vacuum 19 on the OBD2 analyzer.

It will not miss at idle or when cold. It will at times stop missing (CEL stops flashing) while rolling down the road at 60+ mph. Although you can feel the engine missing at times there seems to be no lack of power from a dead start or kicking to passing gear and accelerating.

So my question to y'all is do you have any thoughts on what could be giving this very nice truck the fits?

Thank you for any help you can provide.

Doc

camshaft position sensor... trying cleaning, reseating connector

Hey Budwich,

Replaced the sensor still getting misses. I'm stumped thought it was the crankshaft position sensor but everyone here says if it was that then it wouldn't start at all.
I've never seen an engine miss like this and still have power.

Thank you for the suggestion though.

Doc

clean crankshaft position sensor

Random misfires with a flashing CEL are good indications of an intermittent crankshaft position sensor. It may be nothing more than a bad connection. As budwich posted about the camshaft position sensor, remove, clean and reconnect the connector. Engine vibration under load or from road surfaces could be jarring the contacts loose.

The engine will not start with no crankshaft position signal because the PCM disables the fuel pump after a few seconds for safety reasons. Once the engine is running the PCM computes and predicts the firing of each plug and injector. If the PCM loses the crankshaft position signal it attempts to keep the engine running based on its latest information.

Engine misfire procedure

camshaft is "responsible" for help with "fuel duration" ... which with your "randomness" seems to be a possibility. So let's be sure here... I am talking CAMSHAFT and NOT CRANKSHAFT. Yes, the crankshaft sensor might be an issue but probably as mentioned more with not starting.

Hey Bud,

Yes I understood what you were saying and took care of the camshaft postion sensor.

I have checked the connection for the crankshaft position sensor but haven't replaced it yet as I can't figure out how to get to the bolts without disassembling the front of the truck.
Thank you both for the help.
Doc

Camshaft position sensor function

I think the sole function of the camshaft position sensor is to let the PCM determine if piston #1 when at TDC is on the compression stroke or the exhaust stroke. I think all fuel injector energizing timing and spark plug ignition timing is based on information provided by the crankshaft position sensor.

Many members have accessed the crankshaft position sensor from underneath the vehicle. You might just see if disconnecting and reconnecting the electrical connector makes a difference.

Probably go back to the start.... what dtc codes are you having? That might actually help narrow things down a bit.

Since we last met

Well folks thank you for the replys but I'm still having the same issue. I even returned my Autozone coil and picked up a Motorcraft one just in case it was the coil.

I've been at this car stuff for a long time and this one is the worst I've ever been stumped on.

As to codes it is random miss fires on all cylinders the only thing I haven't replaced is the IAC (cleaned it though) and the Crankshaft Position sensor.

If this were an old school pre-computer engine I would say it acts more like the timing is off than actually missing.

Thanks again,
Doc

time to break out the compression tester and check the mechanicals for any differences.

Nothing points to mechnical problems. No loss of power, no hesitation, no back fires and the gas milage is reasonable considering she spends most of her time in a closed loop.

Like I said its all 6 cylinders oh and the higher the rpm the less you notice it, plus at highway speeds it actually stops missing.

Going to try the CPS its cheap but not easy to get too.

Thanks again,

Doc