Exhaust Manifold and Fuel Injectors
|2004: By the Spring of 2004 I realized I had joined the ranks of many other Jeep 4.0L owners, and had a crack in the manifold. Officially, Daimler-Chrysler never acknowledged it as a problem yet they redesigned the manifolds for the XJ Cherokee in 2000, and the TJ Wrangler redesign showed up around 1999 as well.
After looking at it again, I realized I also had a leaky fuel injector on at least the #4 cylinder, and a few others that looked suspicious. At 170,000 miles, they were tired and could use some upgrade, but more importantly I needed to address the leak ASAP. In the last two months, I have read about three different Cherokee fires, and one theory postulated was that the cracked exhaust allowed the underhood temperatures to rise to the point that they either cracked a fuel line or otherwise caused the fire. Somehow that didn't appeal to me, and when I have my kiddos in the Jeep I certainly don't need that kind of problem.
I ordered six of the F5TE-24lb injectors from Fiveomotorsport.com. Service was fast and I had an email confirmation of my order very soon after placing it; the injectors themselves arrived shortly afterward by USPS Priority Mail. Unfortunately my plans weren't quite as speedy as it took me almost a month to get enough time and garage space to make the swap.
Leaky injector residue on the intake manifold. Yes, those stains are from leaky gas.
2008: Four years later, and here I was, ready to swap out the exhaust manifold again. However, this time I also decided to change out the intake to a '99 manifold, and I'm using what I believe to be a 2000 exhaust manifold...the seller wasn't entirely positive about it.
The manifold I put in four years earlier was ready to break. One of the cracks around the #4 collector was over 50% around the tube. Combined with the other two large cracks in the manifold, it's amazing that exhaust gas got out the back of the Jeep at all.
- New Exhaust manifold or header
- Replacement Fuel Injectors (F5TE-24lb in my case)
- PB Blaster or Valvoline Synthetic spray lube
- Replacement intake/exhaust manifold
- "Kopper-kote" spray gasket coating
- The usual assortment of hand tools (SAE and Metric)
- Torque wrench
To the left is the stock exhaust; there are actually three good-sized cracks in the manifold:
The wet look around the mounting surface is from a righteous solvent we used to remove the bolts. It's a Valvoline Synthetic brand that did wonders to loosen the eleven manifold bolts.
- Near where the last three cylinders match up to the collector
- On the backside of the same section
- On the backside where the front three cylinders come into the collector
I haven't seen it in the stores in quite awhile though but PB Blaster is another excellent penetrant you can use. WD-40 isn't a penetrating oil...don't waste your time.
The second manifold is from a '99 and was ceramic-coated but never installed by the previous owner. Yes, it's the same design as the original one, but it's also 170,000 miles younger. I have a feeling it will last longer than the engine.
Update Dec 2005...I was wrong on this one! I've already got cracks in the new manifold, and they are of course in the same places as the old one. Looks like I'm going to start saving up for an aftermarket header this time...
I delayed the start of the fuel injector swap until I had time to replace the exhaust manifold as well. Knowing I'd be working in that area anyway made it seem logical to do both at the same time.
Disassembly - Injectors
Removal of the fuel rail was pretty straightforward; since I was replacing the exhaust manifold as well, many of the steps for each procedure are intertwined in this writeup; use your head when trying to follow this procedure.
Disconnect the battery for safety first of course.
The throttle cable and cruise control assembly has to come off, there are three bolts holding that in place. It will lay over the valve cover out of the way
Label the electric connector for each injector and tuck it safely out of the way - WARNING! Don't screw up the numbering - #1 is at the front and #6 at the rear. The injector wires have to be put back in the same cylinder as they started or you will have all sorts of problems running.
If you haven't already done it, depressurize the fuel system by holding a rag on the pressure fitting and using a tool to push it. This really should be done with a non-sparking (wood, plastic, brass, etc) tool since you are prying on metal while soaking the area in gas. There are four bolts holding the fuel rail to the manifold and injectors; remove those and gently lift the rail off the injectors. There are o-rings holding the six injectors in place so it may need to be wiggled a tad as you pull straight out. Since it is still connected to the Jeep by the fuel line, place it off to the side carefully. I found that laying it over the top of the radiator kept the line unkinked and kept the fuel rail out of the way.
Remove the clip holding each injector to the fuel rail and store safely aside. Gently pull each of the six injectors out of the intake manifold; again they are retained only by o-rings and the fuel rail so they need a straight pull to remove each.
Disassembly - Manifold
I wish I could bring you pictures of the actual removal and installation of the new parts, but I was busy wrenching. Let me just point out that it's going to take most of a day to do, and that's even with help. The FSM has a procedure to follow, and it is correct. trying to take shortcuts around the steps outlined in the FSM actually cost us more time. Start off by removing the auxiliary fan, intake air hose and airbox. Take a couple pictures or tag parts as you remove them and unplug the lines and sensors.
Use a couple Ziploc bags or margarine tubs to store removed bolts in, and keep them separated into groups
DO NOT bend the fuel supply line. It's a flexible plastic piece, but take care not to flip it around too much or you may pinch the line.
The plastic fuel supply line runs through the rubber hose highlghted in this photo.
DON'T bend it too wildly
Once the fuel line and aux fan are out of the way, the power steering pump has to come off (on most models). There are three long bolts holding the pump and reservoir to the manifold; remove them after the airbox is out of the Jeep so the pump has some room to be out of your way.
Disconnect the exhaust downpipe from the exhaust manifold; there are two nuts on the exhaust side that are probably rusted in place. Soak them with PB Blaster early on and try it again now before pulling the manifolds off.
Now you've got room to access the bolts holding the exhaust and intake manifolds in place. If you haven't already noticed it, the intake and exhaust manifold share a common gasket. The intake and engine exhaust manifolds on the 4.0L engine must be removed and installed together. The two manifolds use a common gasket at the cylinder head.
Clean up the manifold sealing surfaces; if you are so inclined this would be a perfect time to upgrade the stock 4.0L HO intake for the much larger one found on the 99+ Cherokee, WJ Grand Cherokee and TJ Wrangler. See yet another great writeup from GoJeep for more info on this swap.
Reinstallation - Manifolds
Coat both sides of the new intake/exhaust gasket with a spray of Kopper-Kote - follow the directions on the can for proper application procedures. The Kopper-Kote helps seal the gasket by filling in any low spots on the gasket surface, and is capable of withstanding the high temperatures at the head. Set the gasket on the mounting studs on the cylinder head.
Position the exhaust manifold on the mounting studs as well and hold in place with a finger-tight nut on bolt #3 (below)
Install the intake manifold and fasteners, finger-tight. Once everything is in place, begin tightening and torquing the bolts in the sequence shown below. It's always a good idea to initially torque all bolts to a value lower than the final figure and then retorque everything once the first set has been finished.
Reinstallation - tighten the bolts in this sequence to ensure a proper seal
Reconnect the exhaust at the downpipe.
Reinstallation - Injectors
Once the intake is in place again, it's time to address the fuel injectors. Each injector is held in place by the fuel rail, and pressurized fuel is held in by the use of two o-rings per injector. Use the old injectors as a reference, but the basic idea is to lube the o-ring to prevent tearing and then install on each injector. We used the Valvoline Synth lube, but a small dish of clean motor oil is recommended. Make sure the injectors are inserted the correct direction with the electric connector facing up.
Reconnect the fuel rail, and replace the clips on the injectors. Reconnect the injector harness, making sure the injectors are connected to the properly-numbered wires.
Reconnect all sensors, power steering, air intake, and everything else that was removed.
That's all I've got for now; when I first completed this page eight months after installation I had noticed a reduction in underhood temperatures as well as reduced noise - the exhaust now goes out through the back like it's supposed to instead of venting in the engine bay. However, as I re-wrote it in mid-December 2005 I added the info about the new cracks in my new manifold...it's time to research replacements again. This time, I'm going aftermarket for something that had better last longer than a year.
Update - Aug 2008
I've left the crack (and updates to this site) alone for far too long now as other things have taken priority. I suddenly found myself in possession of two potential replacement exhaust manifolds (one from a TJ, and one unknown aftermarket), and will be installing those along with a '99 intake manifold...sometime soon.
Notice how the TJ Manifold has bellows in the #1 and #6 runners. This fix was never added to the XJ to the best of my knowledge, although both vehicles shared the same problem with cracks.
I have no idea what this manifold is; I have some cracks in it that I need to weld if this is the design I'm going with.
OEM Fuel Injector Identification
The following chart is based off information provided by Dino "Dr Dyno" Saava on NAXJA
OEM Fuel Injector Identification
|Model Year 4.0L
||OEM Part Number