Jeep 4.0L firing order and spark plug gap (plus the 2.5L)
10 Verified3 Single source1 Not yet verified
Short answerShow me the answer
The Jeep 4.0L six fires 1-5-3-6-2-4, with cylinders numbered 1 to 6 from the front (radiator end) [1][2][5][8]. The 2.5L four fires 1-3-4-2 [1][3][5][8]. Gap the spark plugs to 0.035 in (0.89 mm) on both engines [1][4][6][7][8]. The factory plug is a Champion RC12LYC on 1993–97 trucks and an RC12ECC on 1999–2001 [1][3][6][8][10]. Tighten plugs to 27 ft-lb (37 N·m) [6][9].
| 4.0L firing order | 1-5-3-6-2-4, cylinder 1 at the front [1][2][5][8] |
|---|---|
| 2.5L firing order | 1-3-4-2 [1][3][5][8] |
| Plug gap (2.5L and 4.0L) | 0.035 in (0.89 mm) [1][4][6][7][8] |
| Plug torque | 27 ft-lb (37 N·m) [6][9] |
| 2000–01 4.0L ignition | Coil rail with three coils, no distributor [3][4][7][8] |
Firing order and cylinder numbers
The 4.0L straight six fires 1-5-3-6-2-4.[1][2][5][8] The factory manual numbers the cylinders 1 to 6 from front to rear, so cylinder 1 is nearest the radiator.[1][2][8] On trucks with a distributor (1999 and earlier), the factory figures show the rotor turning clockwise; only the factory manual shows this, so it sits in the “Not yet verified” table.
The 2.5L four fires 1-3-4-2, numbered 1 to 4 from the front.[1][3][5][8]
Spark plug gap and type
- Gap: 0.035 in (0.89 mm) on both the 2.5L and the 4.0L.[1][4][6][7][8]
- Plug: Champion RC12LYC on 1993–97 trucks; RC12ECC on 1999–2001.[1][3][6][8][10] If your truck is a 1998, or you’re not sure what’s fitted, read the number off the plug you take out.
- Torque: 27 ft-lb (37 N·m).[6][9] The factory ignition chapter allows 26–30 ft-lb, which is why you’ll see 30 ft-lb quoted too. Our 4.0L torque page explains the difference.
2000–01 4.0L: coil rail instead of a distributor
From 2000 the 4.0L has no distributor. A one-piece coil rail with three coils sits on top of the plugs.[3][4][7][8] The factory manual says each coil fires two cylinders at once (1 and 6, 2 and 5, 3 and 4), one on its compression stroke and one on exhaust.[3][4] That pairing is factory-only so far, so it’s in the “Not yet verified” table below.
No spark at any cylinder on a 2000–01 truck? Work through the crank-no-start guide and the crankshaft position sensor first.
Verified values
Each row is from the factory service manual plus at least one independent source.
Not yet verified
| Item | Value | Applies to | Sources | Status |
|---|---|---|---|---|
| Coil rail pairing, 2000–01 4.0L | Cylinders 1 and 6, 2 and 5, 3 and 4 share a coil (waste spark) | 2000 and 2001 factory manuals | Sources (2) | Single source |
| Distributor rotation, 1999 and earlier | Clockwise | 1994 and 1999 factory manuals (firing order figures) | Sources (2) | Single source |
| NGK cross-references | FR5-1 (distributor trucks), ZFR5N (coil-rail trucks) | ExtremeTerrain only | Report this value | Single source |
| Factory spark plug, 1987–92 4.0L | Champion RC12LYC (retailer listing only) | 1987–92 (ExtremeTerrain lists RC12LYC for 1987–99 distributor trucks) | Report this value | Not yet verified |
FAQ
What is the firing order for a Jeep 4.0L engine?
What is the spark plug gap on a Jeep 4.0?
What is the correct spark plug gap for a 1999 Jeep Cherokee 4.0L?
Is the firing order the same on a 1996 or 2001 Cherokee 4.0?
What spark plugs does a Jeep Cherokee 4.0 take?
Sources (10)
- 1994 Jeep Cherokee and Wrangler Service Manual (Chrysler publication 81-370-4146), Groups 8D and 9, archive.org scan
- 1999 Jeep Cherokee Electronic Service Manual (Chrysler publication 81-370-9146), Groups 8D and 9, archive.org scan
- 2001 Jeep Cherokee (XJ) Service Manual, Groups 8D and 9, archive.org scan
- 2000 Jeep Cherokee (XJ) Service Manual, Group 8D Ignition System (reproduced by johnmeister.com)
- 1993 Cherokee service data, engine performance theory (third-party; the archive.org item is titled "Factory Service Manual" but is not a Chrysler publication)
- 1993 Jeep Cherokee Specifications article (spark plugs and torque), third-party service data (reproduced by johnmeister.com)
- 2001 Cherokee SE 4WD, Engine Controls Service & Adjustment Specifications, Spark Plugs, alloemmanuals.com
- Jeep Cherokee XJ Spark Plug Specifications (1984–2001) tech guide, ExtremeTerrain
- 2000 Jeep Cherokee (XJ) Service Manual, Group 9 Engine, 4.0L section (reproduced by johnmeister.com)
- 1997 Jeep Cherokee (XJ) Factory Service Manual, Group 8D (hosted by xjjeeps.com)
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