Description
Premium Exhaust Manifold for Jeep 4.0L — End Cracked Manifold Problems Forever
The factory exhaust manifold on Jeep 4.0L engines is notorious for cracking, warping, and leaking — especially at the collector. The iFJF 4.0L Exhaust Manifold solves this problem with a tubular stainless steel design that not only lasts longer but also improves exhaust flow for better performance. Constructed from thick 16-gauge 304 stainless steel with TIG-welded joints and CNC-machined 3/8-inch flanges, this manifold is built to withstand the extreme heat cycling that destroys factory cast iron manifolds. It's a direct bolt-on replacement — no cutting, welding, or modification required.
Key Features
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304 Stainless Steel Construction — 16-gauge (1.5mm) thick tubing far more durable than factory cast iron
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Tubular Manifold Design — Better exhaust flow than restrictive factory log-style manifold
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Equal-Length Runner Design — Balanced exhaust reversion for smoother power delivery
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TIG Welded Joints — Gold brass-style welds prevent cracking at stress points
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3/8" CNC Laser-Cut Flanges — Hydraulic press-flattened for leak-free sealing
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Chrome-Plated Flanges — Added corrosion resistance at mounting surfaces
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Polished Finish — Rust-resistant surface with show-quality appearance
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Direct Bolt-On Replacement — No cutting, welding, or fabrication needed
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Complete Hardware Kit — Includes all gaskets, bolts, and mounting hardware
Vehicle Compatibility
| Vehicle |
Engine |
Years |
| Jeep Wrangler YJ |
4.0L L6 |
1991–1995 |
| Jeep Wrangler TJ |
4.0L L6 |
1997–2001 |
| Jeep Cherokee XJ |
4.0L L6 |
1993–2001 |
| Jeep Grand Cherokee ZJ |
4.0L L6 |
1991–1992 |
Fits ALL 1991–2003 Jeep vehicles equipped with the 4.0L inline-6 engine.
Technical Specifications
| Spec |
Detail |
| Primary Tube Diameter |
1-1/2" (38mm) |
| Collector Diameter |
2" (51mm) |
| Head Flange Thickness |
3/8" (9.5mm) |
| Pipe Thickness |
16 gauge (1.5mm) |
| Material |
304 Stainless Steel |
| Welding Method |
TIG Brass-Style |
Common Symptoms of a Cracked Jeep 4.0L Manifold
- Loud ticking or tapping noise from the engine bay (especially on cold start)
- Exhaust smell in the cabin
- Check Engine Light with lean condition codes (P0171, P0174)
- Decreased fuel economy
- Loss of low-end torque and throttle response
- Visible cracks at the collector junction (most common failure point)
Frequently Asked Questions
Q: Will this fit my 1997 Jeep Wrangler TJ with 4.0L?
A: Yes! This manifold is a direct bolt-on replacement for 1997–2001 Wrangler TJ models with the 4.0L inline-6 engine. All gaskets and hardware included.
Q: Is this better than the factory cast iron manifold?
A: Significantly better. The tubular stainless design eliminates the cracking issue of factory manifolds, improves exhaust flow, and the TIG-welded 304 stainless construction lasts far longer.
Q: Will this improve performance?
A: Yes — the equal-length tubular runner design improves exhaust scavenging, resulting in better top-end power and slightly improved fuel economy compared to the restrictive factory manifold.
Q: Do I need to replace my exhaust downpipe too?
A: No — this manifold is designed to bolt directly to your factory exhaust downpipe at the collector flange.
Q: Is professional installation required?
A: While possible for experienced DIYers, professional installation is recommended. Manifold bolts can be challenging to access and may require penetrating oil for removal of the rusted factory manifold.
Related Products
Complete your build with these complementary iFJF products:
Frequently Asked Questions
Q: Will these headers fit my 91-03 Jeep Cherokee/Grand Cherokee/Wrangler?
A: Check the compatibility details above. These headers are designed for 91-03 Jeep Cherokee/Grand Cherokee/Wrangler with the 4.0L engine. Always verify your specific year, make, model, and submodel before ordering.
Q: Are these headers CARB compliant / street legal?
A: These performance exhaust headers are intended for OFF-ROAD / COMPETITION USE ONLY. They may not be street-legal in all 50 states. Check your local emissions regulations before installation.
Q: What material are these made from?
A: Constructed from T-304 or T-409 stainless steel with mandrel-bent tubing for maximum flow and durability. Stainless steel resists corrosion and maintains its appearance far longer than painted mild steel headers.
Q: Do I need a tune after installing headers?
A: While not strictly required, an ECU tune is recommended to maximize performance gains. A proper tune adjusts fuel trims and timing for the increased exhaust flow, potentially yielding 10-25 additional horsepower.
Q: How do these compare to the OEM exhaust manifold?
A: Factory cast-iron manifolds are restrictive, heavy, and prone to cracking. Our stainless steel headers feature mandrel-bent primaries that reduce backpressure, improve scavenging, and increase horsepower while shedding weight.
Q: What gaskets and hardware are included?
A: Each kit includes the header(s), exhaust manifold gaskets, and mounting hardware unless otherwise specified. We recommend using new OEM or multi-layer steel (MLS) gaskets for the best seal.
Q: What is the warranty?
A: iFJF products come with a 1-year warranty against manufacturing defects. Contact support@ifjf.net with your order number for warranty claims.
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