AKA009

Issue: Coolant Loss

Vehicle: 2004 Grand Cherokee Overland / 4.7HO, 123,000 miles.

Maintenance History: Unknown, recently purchased.


I hooked up my auto scanner (AutoEnginuity) to check fuel trims, while it was idling it started misfiring on cylinder 8.
Drove it around and it doesn't misfire, only while idling.

Looked it up and its apparently common issue. It threw a code which is the P0308, but it cleared itself after driving it around some.
Still misfires while idling.

Noticed coolant reservoir empty, just recently topped it off shortly after purchased a few days prior.

Did a combustion leak test (Uview 560000) and the blue turned green, not exactly yellow. Did this twice, with it off and warm and while running, both same greenish color.

Did radiator pressure test to 18lbs, dropped to 16lbs after 10 minutes. Could see on water pump one of the hose connections barely seeping water, but not enough to drip. Looks like clamp just needs to be replaced with band one. No other leaks, though radiator cap doesn't hold pressure either. Used MotorRad MT-300 Pressure Tester.

Compression test, cylinder 4 ejected water. Cylinder 4 spark plug looks bad (pictures attached), all others look same.

Compression on cylinder 4 was higher than others at 196-205, while all the rest are 175-185. Left it on cylinder 4 and its holding at 196 from last test.


Not sure what this means, but my guess is lower intake manifold is leaking into cylinder?


Looking at oil I can't tell if coolant is in it, it looks very new and clean, but nothing milky and jeep doesn't smoke.


Any ideas?

Willys55

these cylinder heads are prone to cracking