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What P0304 means for your Jeep Grand Cherokee
Your Grand Cherokee dropped cyl 4. On the 5.7L Hemi, cyl 4 is one of the four MDS-active cylinders (along with 1, 6, 7). Chrysler's Multi-Displacement System deactivates these four under cruise, and the MDS lifters on these cylinders are the most common Hemi failure - they collapse, bend a pushrod, and damage the cam lobe. P0304 + a metallic tick = MDS lifter, almost guaranteed. On the 3.6L Pentastar, cyl 4 is bank 2 (right side) - watch for the W77 head valve-seat issue.
Top Causes of P0304 on the Jeep Grand Cherokee
50%
#1 CAUSE
Collapsed MDS Lifter (5.7L Hemi cyl 4)
Cyl 4 is a Hemi MDS cylinder. The MDS lifter on cyl 4 collapses and stays collapsed, bending a pushrod and often damaging the cam lobe. Symptoms: P0304 + metallic tick at idle + rough cold start. Once a pushrod bends, you need the head off. ALWAYS do an MDS delete during the lifter job because cyls 1, 6, 7 share the same flawed hardware.
Lifter + Pushrod
$1,800-$3,500
MDS Delete Kit
$650-$1,300
Cam if damaged
$2,500-$5,500
25%
#2 CAUSE
W77 Right-Bank Head Valve Seat Erosion (3.6L Pentastar)
On the 3.6L Pentastar, cyl 4 is bank 2 (right). The pre-2014 W77 right-bank head has documented valve-seat erosion causing bank-2 misfires (cyls 2, 4, 6). Chrysler TSB 09-001-13 extends the warranty to 10 yr/150k mi for the right head. CHECK YOUR VIN FIRST - this could be free.
Head Under Warranty
$0 (TSB 09-001-13)
Out of Warranty
$1,800-$2,800
New W77 Head
$1,200-$1,800
15%
#3 CAUSE
Cylinder 4 COP Coil Failure
Mopar 56028394AB (Hemi) or 4606824AC (Pentastar). Cyl 4 on a Hemi is rear-bank passenger side - moderate access. Swap-test with coil 6.
OEM Coil
$70-$120
Aftermarket
$28-$55
w/Labor
$140-$240
Most Affected Grand Cherokee Model Years
| Year | Engine | Primary Cause | Typical Mileage | Notes |
|---|---|---|---|---|
| 2011-2013 | 3.6L Pentastar V6 | W77 head | 60k-130k | TSB 09-001-13 free head |
| 2011-2018 | 5.7L Hemi (MDS) | MDS lifter | 60k-160k | Cyl 4 is MDS-active |
| 2019-2024 | 5.7L Hemi eTorque / 3.6L Pentastar | MDS lifter / coil | 40k-120k | eTorque adds 48V hybrid |
| 2015-2024 | 6.4L 392 Hemi | Coil pack #4 | 60k-140k | No MDS - clean coil job |
TSB info: Chrysler TSB 09-001-15 (Hemi MDS lifter inspection - cyls 1, 4, 6, 7); TSB 09-001-13 (Pentastar W77 right-bank head warranty extension); aftermarket MDS delete kits remain the de-facto Hemi fix.
How to Diagnose P0304 on a Jeep Grand Cherokee
- On a 5.7L Hemi, LISTEN at idle. Tick + P0304 = MDS lifter collapse - skip the coil test, pull the valve cover and check the cyl 4 pushrod for bend.
- On a 3.6L Pentastar, check VIN against TSB 09-001-13 FIRST. If the right-bank head qualifies, the repair is FREE at a Chrysler dealer.
- If no tick (Hemi) and not TSB-covered (Pentastar), swap coil 4 with coil 6 and drive 20 miles. If code follows, replace the coil. Cheapest fix first.
Want a step-by-step walkthrough specific to your Jeep Grand Cherokee? Run a $5.99 AI diagnosis report - we narrow the cause to your year, engine, and symptoms.
P0304 Jeep Grand Cherokee FAQs
How do I know if it's an MDS lifter or just a coil on a Hemi?
Listen at idle. Bad coil = silent. Collapsed MDS lifter = ticking sound (like a louder injector tick). A coil swap takes 5 minutes and rules it out. Tick + P0304 = open the valve cover.
Should I do an MDS delete during a lifter repair?
Absolutely. Cyls 1, 4, 6, 7 all share the same flawed MDS hardware - one failure means more are coming. Adding the delete to a lifter job costs $650-$1,300 extra and prevents three more $2,500 repairs.
Is the W77 head fix really free?
If your VIN is 2011-2013 3.6L Pentastar and right-bank compression is low, yes - Chrysler TSB 09-001-13 extended the warranty to 10 yr / 150k mi. Bring it to a Mopar dealer with the codes BEFORE you pay anyone.
Will premium gas help my Hemi run smoother?
The 5.7L Hemi is tuned for 89 octane (mid-grade). Running premium gives marginal smoothness but no real power. Octane will not fix an MDS lifter or W77 head - those are mechanical failures.