Cylinder 7 misfire only while running on cng

MARKSHOFFIT

MEMBER
2014 TOYOTA TUNDRA
5.7L
V8
2WD
AUTOMATIC
36,000 MILES

I bought a new Tundra and added a CNG system immediately. The truck ran fine for about 25k miles until the check engine light appeared. It checked out perfectly at dealership. They would only check it while running on gasoline. Took it to CNG installer and he ended up replacing entire CNG system with no luck in getting light to stay off. CNG installer even moved coil to see if misfire would move. It didn't move. Cylinder 7 is the only culprit. I believe that something is going on in cylinder 7 that has no effect while on gas, but causes a light while running on CNG. The check engine light usually stays solid, but occasionally blinks at which time I turn off truck and turn it back on and light goes solid again. The CNG installer did make the CNG fuel leaner which did make the engine light mainly stay solid. Before this adjustment the light would start blinking with very regular annoyance.

1 Reply

HMAC300

MECHANIC
48,601 POSTS

Check the injector for resistance it may be leaking or leaning out on propane as it's a gas not a solid. Also check compression. Misfires are extremely hard to diagnose and on propane it may be even harder or some type of cylinder leakage that while on fuel is fine but a gas may not be. Resistance shold be 11.6-12.4 ohms. Maybe trying some injector cleaner when on gas may straighten it out. Also in pic here are causes for your problem.

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