Jeep Update II: Exhaust Header & Ignition Wiring

Shiny new exhaust header

The 4.0L six-cylinder engine as found in many Jeeps – including mine – has a tendency to run hot. They seem more prone to this as they age, although there certainly can be different factors at play.

My engine doesn’t usually run too hot. Once the outside temperatures reach the 90s or so, at freeway speeds the water temperature needle will rise from it’s regular 190º. It then peaks somewhere 220º and doesn’t go any further. Slow, steep mountain roads have a similar effect if I zip up them. I did briefly have some overheating issues about two years ago, which was traced to problems with a replacement radiator. Luckily that was quickly sorted out.

Whatever the reason, maybe three years ago, the factory exhaust header cracked. I took the opportunity to “upgrade” to a lighter, stainless steel Edelbrock header. It eventually cracked, was re-welded, then cracked again (although the latter was predicted.) After waiting a long time for a replacement to become available under the warranty, I finally opted to purchase another aftermarket header, this time made by Gibson. It too cracked, which brings us to this last week, where it was replaced under warranty.

So what’s up with these headers? I suspect there are a couple of issues involved, including the tendency of the 4.0L engine to run hot, and perhaps also the relatively lightweight tubing on the aftermarket headers. I’d love to make the rounds of one of the big offroad shows and pick all of the experts’ brains on this, and see if my conclusions – and those of my very experienced Jeep shop – are at fully justified. Until then, fingers crossed that this header remains intact to a ripe old age.

In its death spasms, the header also created a gap between itself and the block, allowing hot gasses to vent upwards and melt up a lot of the injector wiring. The Jeep ran rough as a result of this, but between putting off repairs until I could afford them, and the three weeks of phone calls to get the header warrantied, there wasn’t much I could do. When the header was replaced, it also took my shop hours to clean and replace the melted tangle of wire.

Rat’s nest of cut-out injector wiring

Closeup of melted, fried wiring

This mess also resulted in some damage to the engine computer, which will get replaced next week, and then everything should be wonderful in Jeep Land.

*fingers crossed*

Engine computer with cover removed

New wiring in place, tested, and secured!

Images link to larger (600×800) versions.