01 misfires on startup?

[whammy]

i had this problem in my 90 with the 4.0 when i would started it it would idle like crap but when you heard it from the exhaust it would miss almost constantly. turned out my crank sensor was melting from my exhaust manifold and that also helped shorten the long starting cranks. after that my problems went away.

 

[Talyn]

Hot soak TSB: http://www.wjjeeps.com/tsb/tsb_wj_1803103.pdf

Cold start rough idle TSB: http://www.wjjeeps.com/tsb/tsb_wj_1801301.pdf

 

[kastein]

There was a post very similar to this one about a week ago. E3's causing misfire codes. I haven't had a close look at an xj coil rail but I suspect they're like kastein said, 3 pairs of coils. If that's the case only half of the plugs fire electrode to ground. The other half fire ground to electrode. I suspect those fancy looking +10hp plugs don't like that much due to the weird ground shape.

While you're in there don't forget to clean the grit off your Tornado that the K&N let through.

Don't think I said that... but it's probably true.

Just curious. How does one go to ground and the other to the electrode? Usually you have good explanations and I want to learn more.

Not sure, but my bet is that the coils are "double ended" i.e. one long secondary winding, grounded at the center, and a standard primary coil. So one "arcs from the ground" and the other "arcs from the tip" because one coil gets a high voltage negative spike while the other gets a high voltage positive spike. I can see how this would cause crappy performance on half the cylinders with snake oil spark plugs installed due to the multiple ground electrode points.

 

[birchlakeXJ]

I'd sure want to see some fuel pressure numbers (with a gauge) if it were mine. It is easy to hook up a gauge at the schrader valve on the fuel rail and I do so whenever I see that pesky P0300 random misfire code. As well as inspect closely for a vacuum leak.

You want 49.2 psi of fuel pressure at idle, plus or minus 5 psi for the 97+ newer XJ.

Sure it could be something else but troubleshooting is a process of elimination and basics first.....

 

[nochance9]

I'd sure want to see some fuel pressure numbers (with a gauge) if it were mine. It is easy to hook up a gauge at the schrader valve on the fuel rail and I do so whenever I see that pesky P0300 random misfire code. As well as inspect closely for a vacuum leak.

You want 49.2 psi of fuel pressure at idle, plus or minus 5 psi for the 97+ newer XJ.

Sure it could be something else but troubleshooting is a process of elimination and basics first.....

How much and how exactly would one hook up a gauge to the fuel rail? I haven't ever dabbled with any of that stuff and don't even know what the Schrader valve is... But it could be useful if something lake this happens again.

 

[joe_peters]

Schrader valve looks like a metal tire valve, might have a cap on it, might not.

 

[JJacobs]

Regarding waste spark ignition and positive/ negative ignition voltage (kV)

http://diagnosticnews.com/tech/waveform-2/

 

[nochance9]

Hey, i know it's been a while but I finally tracked down the problem. After aligning the crank-cam sensor, new plugs, seafoam, and injector cleaner, i had to track down the service records and i found out that all the TSB reflashes had been made i was lost.. I then talked to my neighbor, who owns a shop, who was testing emissions and saftey on my 89. And he said that when the spark plugs wear down and the gap increases the coils have to up the voltage in order for the spark to arc, putting a lot of strain on the coils. The gap on the first plugs we pulled were gigantic! So we replaced the coil rail and she's runnin smooth as glass. I kept the E3's in there cause i'm cheap lol, but i'm glad i did because now my entire ignition system is under warranty.

On the up side, i learned a lot from this little problem and i thank all you guys for your ideas and knowledge.


Chance

PS: For anyone looking for a coil rail, the best deal i found was at Checker/O'riley $100 and a lifetime warranty. They'll regret that!

 

[Talyn]

Glad you fixed it. I wouldn't have thought of that.

 

[nochance9]

Glad you fixed it. I wouldn't have thought of that.

Me neither! My mechanic friend says it's very common and that he had replaced two coil rails that day. So if your spark plugs are gaped too wide when you pull them, expect to replace the coil rail soon.