2000 XJ problem

[Eagle]

This is a technical problem, but it's outside the MJ years so I'm posting in The Pub.

 

2000 XJ Sport has started throwing OBD-II codes: P0303, P1294, and P1494. It runs fine with the check engine light on, and the fuel mileage doesn't appear to be affected.

 

My reference says code P0303 is "Cyl 3 misfire." The 2000 XJ has the coil rail ignition rather than a conventional coil and distributor. I hope this doesn't mean I have to replace the coil rail assembly, but I'm afraid it might. Does anyone have access to a better explanation of what these codes are supposed to signify?

[89 MJ]

I looked it up quickly, and if it’s a coil, you’d need the whole rail. Could do the Viper coil mod though. 

Not sure on all of the codes. 

Did you check the plug and plug wire? Are you sure that injector is firing?

[Chad R]

I had a similar codes on one of my 2001 wranglers.  It ran fine and I kept clearing the code. That worked for awhile till the coils died and it was running on 3 cylinders. Replaced the coil rail and plugs and ran fine after.  It had 93k on it.

[derf]

1 hour ago, 89 MJ said:

I looked it up quickly, and if it’s a coil, you’d need the whole rail. Could do the Viper coil mod though. 

Not sure on all of the codes. 

Did you check the plug and plug wire? Are you sure that injector is firing?

No wires, it's coil on plug.

 

Once the coil packs start to go, you have to replace the whole assembly.  Personally I'd go with whatever is cheaper, the viper mod or factory replacement coil pack.

[89 MJ]

4 minutes ago, derf said:

No wires, it's coil on plug.

 

Once the coil packs start to go, you have to replace the whole assembly.  Personally I'd go with whatever is cheaper, the viper mod or factory replacement coil pack.

I see. I’ll stick with Renix haha

[derf]

4 minutes ago, 89 MJ said:

I see. I’ll stick with Renix haha

The coil on plug was only for 2000-2001 XJs (2000-04 TJ and WJ).  Before that it was still remote coil and distributor.

[Eagle]

What's the Viper mod y'all are mentioning?

[89 MJ]

Basically it replaces the coil on plug stuff with a Viper coil. It’s a coil with 6 terminals for your plug wires. 
 

Here is a video on it:

 

[Eagle]

Looks interesting. Thanks.

 

Now I just need to figure out if the coil rail is actually the problem.

[gogmorgo]

The coil rails are cheap enough online.  But I’ve also had a couple vehicles recently with misfire codes where there was just a bit of corrosion on the tip of the coil where it connects to the spark plug, and it just took a squirt of electronics cleaner to take care of it and they’re running fine again.
 

The problem with misfire codes is that you just have the knock sensor telling you the cylinder isn’t firing, without much else in the way to say what’s going on. Could be literally anything, from a fouled spark plug to a hole through the piston. But usually they’re ignition related. 
Usually for diagnosis I start with a visual inspection to make sure everything’s plugged in, then I’ll pull the coil and swap it to another hole if I can (don’t think that’s an option here) to see if the misfire follows. Then pull the spark plug. Usually a visual inspection of the plug is enough to diagnose but you can also swap them between cylinders to see if the misfire follows it. If a new plug and coil don’t solve it, then you’re looking at something deeper in the engine, stuck valves or whatnot.
 

1294 is an idle speed thing that I would expect will go away when you solve the misfire.

1494 is evap related. It indicates an issue with the leak detection pump. I don’t know if there’s anything super specific in the code itself, seems like it could be a circuit failure, or an actual leak somewhere. But it’s probably not related to the misfire. 

[pizzaman09]

22 hours ago, gogmorgo said:

The coil rails are cheap enough online.  But I’ve also had a couple vehicles recently with misfire codes where there was just a bit of corrosion on the tip of the coil where it connects to the spark plug, and it just took a squirt of electronics cleaner to take care of it and they’re running fine again.
 

The problem with misfire codes is that you just have the knock sensor telling you the cylinder isn’t firing, without much else in the way to say what’s going on. Could be literally anything, from a fouled spark plug to a hole through the piston. But usually they’re ignition related. 
Usually for diagnosis I start with a visual inspection to make sure everything’s plugged in, then I’ll pull the coil and swap it to another hole if I can (don’t think that’s an option here) to see if the misfire follows. Then pull the spark plug. Usually a visual inspection of the plug is enough to diagnose but you can also swap them between cylinders to see if the misfire follows it. If a new plug and coil don’t solve it, then you’re looking at something deeper in the engine, stuck valves or whatnot.
 

1294 is an idle speed thing that I would expect will go away when you solve the misfire.

1494 is evap related. It indicates an issue with the leak detection pump. I don’t know if there’s anything super specific in the code itself, seems like it could be a circuit failure, or an actual leak somewhere. But it’s probably not related to the misfire. 

All excellent suggestions.  Another easy one to check that has caused miss fires for me is engine ground.  Make sure the block actually has a good ground.

[75sv1]

I also have a 2000 XJ. Mine does have misfires. One thing to check is the Injectors. I'd put a Noid light in the #3 injector plug. Also, maybe switch injectors around. It could also be in the EMC. And check the Camshaft Position Sensor. 

[Eagle]

On 12/6/2024 at 11:36 AM, gogmorgo said:

The problem with misfire codes is that you just have the knock sensor telling you the cylinder isn’t firing, without much else in the way to say what’s going on. Could be literally anything, from a fouled spark plug to a hole through the piston. But usually they’re ignition related

 

No knock sensor.