According to Au7o's analysis of 400+ owner reports, the 1990-1992 Jeep Comanche has 3 documented known issues, with 1 rated critical. The most serious is Floor Pan and Frame Rust-Through ($300-$4,000 repair). The most commonly reported issue is Floor Pan and Frame Rust-Through with 220 owner reports. Across all issues with published estimates, repair costs range from $150 to $4,000. DIY maintenance guides at au7o.io.
The Jeep Comanche (MJ platform) is extremely susceptible to floor pan and frame rust, especially in salt-belt states. The driver and passenger foot wells, rear cab corners, and bed floor are the primary rust-through areas. The unibody construction means that floor pan rust is structural and affects vehicle safety. Water intrusion through deteriorated door and window seals accelerates the corrosion. Many surviving Comanches have been lost to rust rather than mechanical failure. Rust repair requires cutting out affected sections and welding in new metal patches.
Common Symptoms
Visible rust holes in floor pans
Water intrusion into cabin during rain
Soft or spongy floor when pressed
Rust bubbling under paint on cab corners and rocker panels
Structural weakness visible during inspection
How to Fix
Inspect the entire cab floor, rocker panels, cab corners, rear frame sections, leaf-spring/shackle mounts, and bed supports by removing carpet and undercoating, then probe all suspect areas with a pick or hammer to identify thin metal and hidden perforation. Any rust-through or heavily scaled structural metal should be cut back to solid steel and repaired with welded replacement floor pans, patch panels, or fabricated 16-18 gauge steel sections; treat surrounding areas with rust converter or epoxy primer, seam sealer, cavity wax, and replace leaking door/window seals to stop future water intrusion. If the frame rails, spring mounts, or major unibody sections are severely compromised, professional structural repair or donor-section replacement is required, and some trucks may be uneconomical to save. Typical costs range from about $500-$1,500 for localized patch repairs to $3,000-$8,000+ for extensive floor, cab corner, and structural rust restoration.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
Key Parts Comanche cab floor pan, driver side
OEMKey Parts 0482-227
Mapped driver-side cab-floor corrosion on a 1990-1992 Comanche where the repair boundary matches the stamped panel Fitment/availability: 0482-227 explicitly fits the 1986-1992 Comanche and is the left/driver cab floor.
Mapped passenger-side cab-floor corrosion on a 1990-1992 Comanche where the repair boundary matches the stamped panel Fitment/availability: 0482-228 explicitly fits the 1986-1992 Comanche and is the right/passenger cab floor.
High Confidence220 owner reportsLast reported by owners Feb 2026Reviewed Feb 2026
Community reported
180 owners
The cast iron exhaust manifold on the 4.0L AMC/Jeep inline-6 engine is prone to cracking from thermal stress cycling. The manifold design does not accommodate thermal expansion well, and cracks develop between the exhaust ports, typically between cylinders 3-4 or 5-6. Cracked manifolds cause exhaust leaks that are loudest on cold startup and may quiet down as the manifold expands when hot. The exhaust leak can cause a ticking or hissing sound that is often mistaken for a lifter or valve issue. Broken exhaust manifold bolts are extremely common and can complicate the repair.
Ticking or hissing exhaust leak noise, loudest on cold startup
Exhaust smell in engine bay or cabin
Reduced engine performance
Check engine light with catalyst efficiency codes
Noise diminishes as engine warms up
How to Fix
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
Dorman Renix 4.0L exhaust-manifold kit
OEMDorman 674-170 / ATP 101111
A confirmed cracked/leaking exhaust manifold on a 1990 Comanche 4.0L retaining its Renix emissions and sensor configuration Fitment/availability: 674-170 is explicitly listed for the 1990 Comanche 4.0L and interchanges ATP 101111/OE 5300…
Dorman High Output 4.0L tubular exhaust-manifold kit
OEMDorman 674-196 / OE 4883385
A confirmed cracked/leaking exhaust manifold on a 1991-1992 Comanche 4.0L High Output engine Fitment/availability: 674-196 explicitly fits 1991-1992 Comanche 4.0L and includes manifold, gasket, flange and hardware.
High Confidence180 owner reportsLast reported by owners Feb 2026Reviewed Feb 2026
The 1990 Comanche with the 4.0L uses the Renix (Renault/Bendix) fuel injection system, which is less reliable than the later Chrysler MPFI system used from 1991+. The Renix system relies on several sensors that fail with age: the coolant temperature sensor (CTS), throttle position sensor (TPS), and manifold absolute pressure (MAP) sensor. Failed sensors cause hard starting, rough idle, poor fuel economy, and stalling. The wiring harness connectors also corrode, causing intermittent issues that mimic sensor failure.
Common Symptoms
Hard starting especially when cold
Rough or hunting idle
Stalling when coming to a stop
Poor fuel economy (under 15 mpg)
Hesitation or stumble during acceleration
Check engine light intermittently
How to Fix
Replace the CTS, TPS, and MAP sensors as a set — they are inexpensive and the labor overlaps. Clean all wiring harness connectors with electrical contact cleaner and apply dielectric grease. For 1990 models, consider upgrading to the 1991+ Chrysler MPFI system (often called a "Renix to HO swap") which uses a more reliable ECU and simplified sensor array. Replace the O2 sensor at the same time.
SERVICE BRAKES, HYDRAULIC:FOUNDATION COMPONENTS:DISC:ROTOR
VEHICLE DESCRIPTION: PASSENGER AND MULTI-PURPOSE VEHICLES ORIGINALLY SOLD OR CURRENTLY REGISTERED IN THE STATES OF CONNECTICUT, ILLINOIS, INDIANA, MAINE, MARYLAND, MASSACHUSETTS, MICHIGAN, NEW HAMPSHIRE, NEW JERSEY, NEW YORK, OHIO, PENNSYLVANIA, RHODE ISLAND, VERMONT, OR WISCONSIN, AND THE DISTRICT OF COLUMBIA. THE FRONT DISC BRAKE ROTORS CAN EXPERIENCE SEVERE CORROSION IF OPERATED FOR AN EXTENSIVE PERIOD IN THE "SALT BELT." IF THE ROTORS ARE NOT REPLACED, THE CORROSION CAN EVENTUALLY COMPROMISE THE STRUCTURAL INTEGRITY OF THE STAMPED STEEL CENTER HUB SECTION OF THE ROTOR.
Campaign #98V00500012/01/1998
VEHICLE SPEED CONTROL:CRUISE CONTROL
MALFUNCTION OF FUEL INJECTION SYSTEM THROTTLE POSTITION SENSOR COULD CAUSE INTERMITTENT HIGH ENGINE IDLE SPEED IMMEDIATELY AFTER STARTING ENGINE.
Campaign #90V17700002/10/1990
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According to Au7o's analysis of 400+ owner reports, the 1990-1992 Jeep Comanche has 3 documented issues. The most frequently reported are: Floor Pan and Frame Rust-Through, 4.0L Inline-6 Exhaust Manifold Cracking, Renix Fuel Injection System Sensor Failures. Of these, 1 is rated critical and should be addressed promptly.
Is the Jeep Comanche reliable?
The 1990-1992 Jeep Comanche has 3 known issues documented across 400+ owner reports. 1 issue is rated critical: Floor Pan and Frame Rust-Through. Prospective buyers should inspect for these issues and factor potential repair costs into their purchase decision. Regular maintenance following the manufacturer's schedule helps prevent many common problems.
How much does it cost to fix common Jeep Comanche problems?
Repair costs for known Jeep Comanche issues range from $150 to $4,000, depending on the specific problem and whether you choose DIY or professional repair. The most critical issue, Floor Pan and Frame Rust-Through, typically costs $300-$4,000 to repair. Au7o provides step-by-step DIY maintenance guides that can help reduce repair costs.
What is the 1990-1992 Jeep Comanche Floor Pan and Frame Rust-Through?
The Jeep Comanche (MJ platform) is extremely susceptible to floor pan and frame rust, especially in salt-belt states. The driver and passenger foot wells, rear cab corners, and bed floor are the primary rust-through areas. The unibody construction means that floor pan rust is str… Repairs typically run $300-$4,000. Severity: high.
What is the 1990-1992 Jeep Comanche 4.0L Inline-6 Exhaust Manifold Cracking?
The cast iron exhaust manifold on the 4.0L AMC/Jeep inline-6 engine is prone to cracking from thermal stress cycling. The manifold design does not accommodate thermal expansion well, and cracks develop between the exhaust ports, typically between cylinders 3-4 or 5-6. Cracked man… Repairs typically run $200-$700. Severity: medium.
What is the 1990-1992 Jeep Comanche Renix Fuel Injection System Sensor Failures?
The 1990 Comanche with the 4.0L uses the Renix (Renault/Bendix) fuel injection system, which is less reliable than the later Chrysler MPFI system used from 1991+. The Renix system relies on several sensors that fail with age: the coolant temperature sensor (CTS), throttle positio… Repairs typically run $150-$500. Severity: medium.
Content on this page was compiled with AI assistance using NHTSA complaints, TSBs, owner reports, and public automotive data. While we strive for accuracy, this information may contain errors. Always verify repair procedures and specifications with your vehicle's service manual or a qualified mechanic.
