PDA

View Full Version : Generic random misfires check engine codes


jtkratzer
July 23rd, 2010, 15:08
I'm getting a rough idle, noticeable decrease in power, and a very rough ride and sound. CEL is on.

To start off, this issue has been sporadic and strange. It used to happen only when the rain was extremely heavy and the vehicle sat outside in it or when I was driving through heavy rain and deeper water and the water splashed heavily into the undercarriage.

In the past, it would do this for maybe 15-20 minutes and then stop and the light would go off before I had a chance to get the codes pulled.

Today was the anomaly. It did this during a hot, dry day and we haven't had rain in several days. Last time I drove it, no problem, for several days.

I stop at a Pep Boys (it was close to where I was at the time to get the codes pulled). Codes are P0300 and P0301. I know those are random misfires and misfires on cylinder one.

1996 XJ, 4.0, 5 speed, 230,000 miles. Stock except for a replacement K&N air filter.

I changed the crankshaft position sensor today, what a PITA that was to get to. Not only that, I paid for the one that came up for the 1996 model and got home and the plugs are different. Ended up matching the 1997 sensor although it was a bit short and had to zip tie it so it wasn't laying on the intake manifold.

I'll pull the plugs tomorrow and check them and the wires, but the plugs and wires are only about 40,000 miles old. Rotor button and distributor cap were changed about 8,000 miles ago. Oil change yesterday. It has no problems starting whatsoever. I've read about the heat soak issue on others and those "symptoms" aren't the same. I'm going to check for moisture in the distributor cap as well and see how the contacts look inside. It doesn't seem to be a fuel delivery issue, although I haven't measured the pressure from the fuel pump or checked the injectors. I say it doesn't sound like the fuel because it's perfectly fine almost every other time I drive it.

Any thoughts or other suggestions?

Digger87xj
July 23rd, 2010, 15:27
plugs and plug wires. the comment about the rain gives it away. on a 96 plugs should be changed every 30 k... try those first, then replace the wires if need be. Do check the terminals on the cap for each wire too... they can corrode.

jtkratzer
July 23rd, 2010, 15:32
plugs and plug wires. the comment about the rain gives it away. on a 96 plugs should be changed every 30 k... try those first, then replace the wires if need be. Do check the terminals on the cap for each wire too... they can corrode.

Thanks. Would have been nice for the parts guy at Pep Boys to tell me that before spending $70 and the time plus a second trip since they sold me the wrong part. I'll check those tomorrow.

joe_peters
July 23rd, 2010, 21:02
And take another look at the cap--aluminum contacts, then replace it with a better cap with brass contacts.

With the engine running and in shade, use a kitchen spray bottle with water to "mist" the plug wires, cap, coil--sometimes you can get a real fun electric light show!

Wayne Sihler
July 24th, 2010, 06:16
When my 96 started doing this,there was a tell-tale sound from the distributor a tick-tick-tick. The shaft/housing had worn allowing the rotor and cap terminals to contact each other.
A NAPA cap has the brass/copper terminals--or did have--who knows now...

Wayne

hubs97xj
July 24th, 2010, 07:49
The NAPA/Echlin cap still has brass; the rotor, I think, is stainless.

ECH MO30, and MO31 respectively.

jtkratzer
July 24th, 2010, 09:11
I pulled the plugs on the first two cylinders, 1 is far worse than 2, but 1 is the cylinder I'm getting a code for misfires on, so I'm sure that's accelerated the fouling process. The contacts on the inside of the distributor cap aren't terrible, but there is some white corrosion on the contacts.

The wires are still snug and "pop" on and off. Should I replace them as well at 40,000 miles with the plugs, or leave them? I guess I could pick up all the parts (plugs, wires, cap, and button) and just start with the plugs and see how much I need to replace before I get everything running smoothly again.

I went to the gym this morning and until I got home and pulled the plugs, I missed NAPA by about 15 minutes. I'll have to wait until Monday to pick up parts from them. I guess that's an excuse to ride the motorcycle more now until then. :rof:

joe_peters
July 24th, 2010, 09:20
Standard cheapo plug wires about 30k and change them.

What kind of fouling on the plugs? Reading plugs: http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp

Bad plug makes the job of sparking a cylinder harder on all of the components--the plug wire, the cap contact, etc.

I would change all of them.

jtkratzer
July 24th, 2010, 09:45
Standard cheapo plug wires about 30k and change them.

What kind of fouling on the plugs? Reading plugs: http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp

Bad plug makes the job of sparking a cylinder harder on all of the components--the plug wire, the cap contact, etc.

I would change all of them.

Some brown and black on the insulator nose, like it's burnt, but the lead isn't corroded or eroded.

joe_peters
July 24th, 2010, 11:18
I would just change the plugs, wires, cap and rotor and see if the code returns. You could have a poorly performing injector on #1, but go with the basic tune up stuff first.

Make sure to check the plug gaps, most plugs are pre-gaped but you don't know how they have been handled in shipment.