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| North American Grand Cherokee Association | ||
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4.0L Leach Header Installation
My catalytic converter was broken, and had to be replaced. I knew that the exhaust manifold on the ZJ was prone to cracking, and since you cannot have too much power anyway, I decided to replace the whole system. This is what I ordered from Kolak:
The first thing we needed to do was to remove the old exhaust manifold. That doesn't sound too difficult, does it? Well, maybe not, but it took time. We first had to remove the air filter and the power steering pump, which are in the way. Then we carefully removed all electrical connections on the intake manifold and the throttle body. I marked these with some adhesive tape, to make sure I'd remember in what order they would go when it was time to reattach them. The vacuum hoses went next. I didn't mark these, since they could really only fit one way. The cables on the throttle body were quite easily dismounted, and the mounting bracket was possible to remove, too, although one of the bolts is quite awkward to reach.
Now we had reached the first major obstacle: the fuel line. The instructions said that a special tool was required for removing it, but some experienced jeepers on the ILoveJeeps.com forum told me I could do it without one. First, there is a bracket securing the fuel line. That is just a snap-on, which was removed by brute force. Then we discovered three tiny tabs inside the end of the fuel line. With three very small screwdrivers, lots of patience, and some cooperation, we managed to remove the fuel line. I had put a wad of paper under the fuel line, which soaked up the surprisingly large amount of gas that spilled out when it was disconnected. The fuel rail and the injectors went next, without any problems, then the connector to the O2 sensor.
Now the only things still attached were the intake and exhaust manifolds. There are a number of 14 mm (9/16") bolts holding these two parts attached to the cylinder head. Most of them are fairly easy to get to, but the lower ones are a real PITA. Luckily my friend has smaller hands than I have, and he was able to reach them. A little over two hours after we started, we were able to remove the intake manifold. I used this opportunity to clean out the throttle body, too. Two bolts were holding the exhaust manifold in place. One was very easy, the other one was not. It's located at the back of the engine, close to the firewall. The problem is that the dipstick for the 42RH automatic transmission is very much in the way here, and it took forever to loosen this bolt. (The dipstick for the 42RE is on the other side of the engine, so it should be easier on those models.)
When we at last could remove the exhaust manifold we could clearly see why I'd had some performance problems lately, and why my mileage was so low; a big crack in one of the welds on the manifold!
After removing the gasket, we cleaned off the remains from the cylinder head, being careful not to let any dirt enter the open channels. We then did the same thing to the intake manifold, before putting the new gasket in place on the cylinder head. I can recommend that you use this opportunity to inspect the engine mount, which has been known to crack.
We
then lowered the new headers into position, something that requires
some precision, and fastened the two bolts that don't affect the
intake manifold. We cleaned the headers with alcohol, to remove any
grease from our fingers that can cause discoloration when the pipes
get hot. Not that it really matters, since none of it is visible
anyway, when everything is put back together. That's too bad, really,
because they look very good. Then it was a matter of reattaching
everything in the reverse order. Mount the new O2 sensor
first, and don't forget to reattach the connector. I forgot, and it's
not easy to put it back when everything else is in place.
The bolts for the intake manifold are very awkward to reach. The instructions noted this, too, and said to "be patient." That's when I shredded the instructions and threw them away. Since these bolts will be virtually impossible to reach once everything is reattached, it's very important that you tighten them as well as you can at this point.
If you have marked all hoses and electrical connectors properly, there should be no major problems reattaching everything.
We disconnected the battery now, since it was time to start welding. My friend welded the down-pipe to the elbow that comes with the headers (there are two of them, but unless you're connecting the Leach headers to a stock down-pipe, you can use either one). He also welded the down-pipe to the inlet of the cat. Another short section of pipe was used to connect the cat to the muffler, but here we used U-bolts, in case I'd have to take the system apart some day. We cut the hanger from the old down-pipe and welded it to the new down-pipe.
If your ZJ is a '96 or newer, the stock down-pipe is already 2.5", and there is no reason to replace it. Just cut it off along the center line of the tranny oil pan, and weld it to the elbow. On my '95, the stock pipe is a measly 2.0", so it had to be replaced.
The mandrel bent tail pipe from Mike Leach/Mopar Performance attaches to the outlet from the muffler. Again, we used U-bolts. The tail pipe consists of two segments; one that goes over the rear axle, and one final tail pipe. That last pipe has a hanger on it, which fits into the same rubber bushing as the stock hanger. For some reason, the hanger on my new tail pipe was facing the opposite direction compared to the stock one. This prevented us from installing the exhaust tip, since it would have protruded six inches behind the bumper. We will cut this hanger off and weld it back facing the other way soon, but we ran out of time that weekend.
Now came the moment of truth. I reconnected the battery and turned the ignition key. With a growl, the engine came to life. It was loud, but not overly so. As I drove away from there, it felt like having a new engine. It felt like there was a down-hill when I was on flat ground! The performance gain was incredible. Experts have estimated that the engine with these modifications puts out about 220 hp. Low-end torque has suffered a little bit, due to the larger-diameter exhaust pipe, but it is negligible.
On the highway, there was quite a loud droning noise. When I pushed
the throttle it became really loud. I'm far too old to appreciate that
kind of loudness, but I thought I'd learn to live with it. A couple of
days later, I re-tightened everything I could reach - manifold bolts,
elbow bolts, U-bolts. After a hundred miles or so, the ECU had learned
the new parameters and the performance gain was even more noticeable.
At the same time, carbon residue had built up in the exhaust system,
making it much more quiet. In fact, it is now about the same as the
stock system, except when I really step on it. At idle, there is a
nice, deep, growling rumble. In fact, the technician at the annual
vehicle inspection thought that I had a V8 until he popped the hood!
Mileage has improved, too, but it's useless to quote exact numbers since the old system was cracked. Besides, my 31" tires don't exactly help keeping fuel consumption down.
To summarize, this is a fairly expensive modification, but in my opinion it's worth it. Especially if you want to have larger-than-stock tires, the Leach headers can alleviate the performance loss. The Flowmaster 70 is a good choice if you don't want a loud truck. I know many people prefer the 50 series, because they think the 70 series is just too quiet, but for me, it's perfect. Sweden has strict laws on how loud an exhaust system can be, and I didn't want to push it.
The whole installation took us over six hours. Most of the time is spent on loosening and tightening the bolts holding the intake manifolds and the headers, and it's not much you can do about it.
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