2001 S-Type 3.0 w/ 70k miles.

Recently started running terribly with some bad misses and started blowing ignition fuses. It seemed an obvious fix, so I just replaced all six coils and plugs, and it ran around the block just fine w/ no misses at all. Nice and smooth. A few hours later, I drove about a 1/4 mile away and it started to stutter, then the ignition fuse blew again. Any new fuse blows as soon as the key is turned.

Any suggestions? Am I missing a component or am I just going to have to play find the bad wire.

 

To be more specific, the fuse in question is #12 in the Engine Compartment Fuse Box, Coil on Plugs.

 

Trace the wires. Sounds to me like it's shorting out on something. Also, check for water or oil in the pug recesses.

 

Fuses blowing - very uncommon on here, so probably a wire that's rubbed through or corroded or maybe a corroded connector.

If you don't have the workshop manual get it!! (ebay $10)
Then you'll know about which wire is meant o be connected to what BUT be a bit careful:
1. the diagrams may be 99% rather than 100%
2. do not use multimeter on airbag circuits

 

i would wait till night time, unplug the hood light if it hasone, and headlights.. go in garage with a buddy and you get your head under the hood and replace the fuse each time you he turns it over and watch for arching under the hood and you may find the problem this way....I had to do that with my heavily modded 81 rx7.. the wire harness that came from haltech...I saw a wire aching to the wheel well which otherwise looked brand new (it actually was but had a tiny pinhole or crack barely visible to the eye)

 

There's the problem right there. The jag operates on pug power and they're being over worked. Just take them out, feed them, play ball, and rub their bellies. They'll treat you well then.

sorry...couldn't resist.

 

My 2005 model operates on greyhound power....

 

Hi Jon,

Like this one?

 

Great picture, Mike....

No, not quite like that one. More like our nearly 6-year-old Greyhound, "Flyer". He's a 100-pound hoss who has more energy than a Border Collie. My wife's 3-year-old English Cocker Spaniel "Mickey" can't come close to keeping up with him, and our nearly 14-year-old Gordon Setter "Nellie" is smart enough to not even try....

 

Great one....I usually proof read...

That's what I get for posting before downing the first cup!

 

Thanks for the responses. Rubbing it's belly did not solve the problem. However...

I'm almost certain that I've found the offending wire. The Brown White (NW) supply on coil 2/3. What's the easiest way to reach the PCM to test the other end of that wire?

 

I found the location of the chaffing. That steel ring that protects the fuel rail disconnect. There is a joint in the cable sleeve there, and it had ground the insulation off of no fewer than three wires. I taped them up and, and while it's not registering a short to ground anymore, it's running like it's missing a cylinder.

 

Is it very possible that a short bad enough to blow a fuse was bad enough to burn out a coil? That's where I would start..

 

Has to be worth disconnecting the battery for 5 mins, then touch the disconnected ends together to discharge any tiny power left, then re-connect battery. That will clear the KAM (keep alive memory), which is where the learned stuff is. Then start car and let it idle for a few mins. The idle should smooth out as it relearns. Then drive and see. It should relearn more and more. Ideally follow the jag stuff about adaptions and drive cycles, which includes coast-down(s). If it stays like it's missing then you DO still have something to fix, sorry.

The point of coast-downs is that the PCM can see the tiny details of the signals it uses to detect misfires. Er, but ideally you'd not have it trying to learn with an engine that's misfiring LOL

JTIS includes some details of the PCM and its connectors. There are really FAT bundles of wires. I think there may be a big connector (split 3 ways on your era car, I think) on the PCM and another inside the engine bay but no idea how accessible any of them are.

You MIGHT get a DTC (code) for which cyl is misfiring (if it's a misfire) but most likely after two cold-to-hot engine cycles.

 

Huzzah! Blown coil.

I did jagv8's battery disconnect, and that cleared the codes, but I was still down a cylinder. I will, however, drive nice as was suggested for the computer to re-adapt. I also took the opportunity to clean the battery terminals.

JOsworth was correct that the coil was now good and blown. I swapped it with one of the old coils and all is well. I do find it odd that the new coil failed. It's been my experience that electronic components fail almost straight away (as in this case), but then again, it was in the position that contained the short to ground. Regardless, the problem appears to be solved.

Thanks to everyone for their inputs and help.

Oh, and the PCM is (for all intents and purposes) impossible to get to. It sits under the glove-box, but the connectors are in the engine bay. Fortunately, once the bad spot was found it was all too obvious.

 

On the newer cars there are 2 sets of PCM connectors - one set on the PCM and the other I think is through the firewall, with about 130 wires going between them (PCM is 134-pin but not every pin has a wire). The pre-facelift (2002/3) cars have a PCM with what looks like 3 groups of connectors and I guess the wires from them will also go through the firewall. Not that you care any more - good (overall) result!

Yeah, let it re-learn, it won't take long. Coast-downs are without braking from 50+mph to as close to zero as you can manage, so empty safe straight road. It'll learn any way but best to help it.