# Hello. I need help diagnosing a misfire code P0303 on a 2004 izuzu rodeo **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [March 4, 2019, 6:20pm UTC](https://community.cartalk.com/t/hello-i-need-help-diagnosing-a-misfire-code-p0303-on-a-2004-izuzu-rodeo/135773 "2019-03-04T18:20:27Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![Robert\_Wolf](https://avatars.discourse-cdn.com/v4/letter/r/41988e/32.png) [@Robert\_Wolf](https://community.cartalk.com/u/Robert_Wolf)\ **Post date:** [March 4, 2019, 6:20pm UTC](https://community.cartalk.com/t/hello-i-need-help-diagnosing-a-misfire-code-p0303-on-a-2004-izuzu-rodeo/135773/1 "2019-03-04T18:20:27Z")
I’m having trouble diagnosing a misfire on cylinder 3 on my Isuzu Rodeo. I’m getting spark, new coil pack and new plug. Cylinder compression dry test is 150 psi. Which is within Specs. OBD freeze frame data for the p0303 trouble code show a 10% positive change in the LTFT bank 1 and 5% positive change in the STFT bank 1. The trouble code is being recorded only when the engine is under load at about 30mph Fuel pressure is being reported bank 2 fuel trims are -.08%. I do have a leaky valve cover gasket on the left side of the engine. I have a 3.5l engine. Direct injection. This has happened before, I fixed the misfire before by pulling the injectors and manually cleaning them, I also replaced the valve cover gasket and plug seals at that time. Intake and exhaust Valves were cleaned thoroughly. What could be the problem? Should I just replace all of the injectors on that side? and the valve cover gasket, I don’t want to keep throwing money at it. I’m not sure why the valve cover is leaking again. It was replaced only 4 years ago. ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [March 4, 2019, 6:39pm UTC](https://community.cartalk.com/t/hello-i-need-help-diagnosing-a-misfire-code-p0303-on-a-2004-izuzu-rodeo/135773/2 "2019-03-04T18:39:38Z")
The problem might be caused by dirty intake valves. Since direct injection doesn’t allow fuel to come in contact with the intake valves, carbon deposits can form on the intake valves. ![](https://global.discourse-cdn.com/cartalk/original/2X/a/a8efcffb2d6fcbe752efc5de7e43876923c119e3.jpeg) Seafoam makes a product that addresses this problem. > **[Sea Foam Spray | Intake Valve and Top Engine Cleaner and Lubricant](https://seafoamsales.com/product/sea-foam-spray-intake-valve-top-engine-cleaner/)** > > Sea Foam Spray Top Engine Cleaner & Lube works through an engine’s upper intake to clean harmful deposits from intake valves and chamber areas. Tester ---
**Author:** ![Robert\_Wolf](https://avatars.discourse-cdn.com/v4/letter/r/41988e/32.png) [@Robert\_Wolf](https://community.cartalk.com/u/Robert_Wolf)\ **Post date:** [March 4, 2019, 6:44pm UTC](https://community.cartalk.com/t/hello-i-need-help-diagnosing-a-misfire-code-p0303-on-a-2004-izuzu-rodeo/135773/3 "2019-03-04T18:44:12Z")
I did an inline fuel injection cleaning with GM top engine cleaner to clean the injectors and put some techron fuel system clean in the tank. But I will try cleaning the valves with the seafoam to see if that is the issue. ---
**Author:** ![Robert\_Wolf](https://avatars.discourse-cdn.com/v4/letter/r/41988e/32.png) [@Robert\_Wolf](https://community.cartalk.com/u/Robert_Wolf)\ **Post date:** [March 4, 2019, 7:59pm UTC](https://community.cartalk.com/t/hello-i-need-help-diagnosing-a-misfire-code-p0303-on-a-2004-izuzu-rodeo/135773/4 "2019-03-04T19:59:04Z")
Could fouled oxygen sensors cause a lean misfire condition? I’m not getting a code for the O2 sensors. ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [March 4, 2019, 8:04pm UTC](https://community.cartalk.com/t/hello-i-need-help-diagnosing-a-misfire-code-p0303-on-a-2004-izuzu-rodeo/135773/5 "2019-03-04T20:04:32Z")
No. If there were a problem with the O2 sensors, there would be a code indicating so. Tester ---
**Author:** ![Robert\_Wolf](https://avatars.discourse-cdn.com/v4/letter/r/41988e/32.png) [@Robert\_Wolf](https://community.cartalk.com/u/Robert_Wolf)\ **Post date:** [March 4, 2019, 11:46pm UTC](https://community.cartalk.com/t/hello-i-need-help-diagnosing-a-misfire-code-p0303-on-a-2004-izuzu-rodeo/135773/6 "2019-03-04T23:46:32Z")
Sea-foam made no difference. Would a severe leak in the valve cover gasket cause a misfire? There is no oil leaking onto the spark plug tube, but it drips from the gasket onto the exhaust manifold. It has worked well for a few years since being replaced in 2016, but is leaking again. ---
**Author:** ![shanonia](https://avatars.discourse-cdn.com/v4/letter/s/9de053/32.png) [@shanonia](https://community.cartalk.com/u/shanonia)\ **Post date:** [March 4, 2019, 11:53pm UTC](https://community.cartalk.com/t/hello-i-need-help-diagnosing-a-misfire-code-p0303-on-a-2004-izuzu-rodeo/135773/7 "2019-03-04T23:53:25Z")
What are the useful fixes for the valve problems on some of the DI engines? ---
**Author:** ![Robert\_Wolf](https://avatars.discourse-cdn.com/v4/letter/r/41988e/32.png) [@Robert\_Wolf](https://community.cartalk.com/u/Robert_Wolf)\ **Post date:** [March 5, 2019, 12:03am UTC](https://community.cartalk.com/t/hello-i-need-help-diagnosing-a-misfire-code-p0303-on-a-2004-izuzu-rodeo/135773/8 "2019-03-05T00:03:12Z")
Oh In case it matters, the misfire makes the check engine light blink. ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [March 5, 2019, 12:07am UTC](https://community.cartalk.com/t/hello-i-need-help-diagnosing-a-misfire-code-p0303-on-a-2004-izuzu-rodeo/135773/9 "2019-03-05T00:07:21Z")
Stop driving the vehicle. A blinking Check Engine light indicates a major misfire is occurring. Which can damage the engine and/or the catalytic converter(s). > **[Flashing check engine light - CarMD](https://www.carmd.com/wp/flashing-check-engine-light/)** > > A flashing CEL (Check Engine Light) is something serious to be concerned about. A flashing check engine light indicates engine misfires and can result in costly repairs Tester ---
**Author:** ![Robert\_Wolf](https://avatars.discourse-cdn.com/v4/letter/r/41988e/32.png) [@Robert\_Wolf](https://community.cartalk.com/u/Robert_Wolf)\ **Post date:** [March 5, 2019, 12:34am UTC](https://community.cartalk.com/t/hello-i-need-help-diagnosing-a-misfire-code-p0303-on-a-2004-izuzu-rodeo/135773/10 "2019-03-05T00:34:06Z")
Yep. I know. I’m still not any closer to a diagnosis though. Does anyone have any suggestions? ---
**Author:** ![rckyrmrz\_148946](https://avatars.discourse-cdn.com/v4/letter/r/a6a055/32.png) [@rckyrmrz\_148946](https://community.cartalk.com/u/rckyrmrz_148946)\ **Post date:** [March 5, 2019, 3:07am UTC](https://community.cartalk.com/t/hello-i-need-help-diagnosing-a-misfire-code-p0303-on-a-2004-izuzu-rodeo/135773/11 "2019-03-05T03:07:12Z")
Try moving your injector and coil to a different cylinder and see if the trouble code moves. ---
**Author:** ![Robert\_Wolf](https://avatars.discourse-cdn.com/v4/letter/r/41988e/32.png) [@Robert\_Wolf](https://community.cartalk.com/u/Robert_Wolf)\ **Post date:** [March 5, 2019, 3:15am UTC](https://community.cartalk.com/t/hello-i-need-help-diagnosing-a-misfire-code-p0303-on-a-2004-izuzu-rodeo/135773/12 "2019-03-05T03:15:49Z")
It’s got a new coil and plug. Moving the injector is a 2 hour job. 😕 ---
**Author:** ![rckyrmrz\_148946](https://avatars.discourse-cdn.com/v4/letter/r/a6a055/32.png) [@rckyrmrz\_148946](https://community.cartalk.com/u/rckyrmrz_148946)\ **Post date:** [March 5, 2019, 3:38am UTC](https://community.cartalk.com/t/hello-i-need-help-diagnosing-a-misfire-code-p0303-on-a-2004-izuzu-rodeo/135773/13 "2019-03-05T03:38:49Z")
If you have good compression, try moving the coil just to make sure is good…if the the problem does not change…you may need to replace you injector…you could have a weak injector, clogged or leaking. ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [March 5, 2019, 4:53am UTC](https://community.cartalk.com/t/hello-i-need-help-diagnosing-a-misfire-code-p0303-on-a-2004-izuzu-rodeo/135773/14 "2019-03-05T04:53:15Z")
Try some starter spray in areas where a vacuum leak to that cylinder could occur. If the engine rpm increases noticeably, you’ve found the leak. I have to say however that this sounds like a valve or piston ring problem of some kind, given everything you’ve already done. Might wanna try a cylinder leak-down test. What are the compressions in the other cylinders?