P0303 ONLY on hard accel 2.4l 2010
 

First post, think I read all the "read this first" postings. Let's see if I get this right. 2010 accord 4 door 2.4 4-cyl. 150k miles. Try to pass somebody with hard acceleration and after a few seconds it seems like I get some "stumble" (missing cyl?) and if I keep on the gas the car goes into limp mode. Turn off, turn on, keep going. If I back off before it limps, the CEL and VSA and the third light go on (normal failure mode, I believe) and on restarting the CEL stays on until cleared. The error is ALWAYS P0303 and ONLY that. plug 3 looked good, but changed COP, plug, injector, checked for intake leaks. Seemed to run about a week before it acted up again, but maybe I didn't try hard enough. I think I've ruled out the most likely causes but do I go after fuel pressure, fuel rail, intermittent wiring (or computer)? I hate using the shotgun approach to troubleshooting but I'm used to points/coil/condenser. I could handle that.

I really would not do a shotgun approach until you do some more diagnosing. Throwing parts can waste money, but I've seen where a new aftermarket part does not work out of the box and makes troubleshooting much harder, because now 2 problems exist.

Do you have an OBD2 scanner that can read live data? If not, then you can find some blue tooth connectors on amazon for pretty cheap, where you connect your phone to read live data. The bluedriver is a bit more expensive, but also works for diagnosing.

I'd recommend looking at short and long term fuel trims when the engine is at operating temperature and at idle. I'd also increase the rpm to ~2000 and see what happens to the short and long term fuel trim. Ideally, adding up the fuel trims should be zero (ideal air:fuel ratio). If the fuel trims are between -10 and 10, then you are ok. The next step will depend on your results.

Do you have a compression tester and/or a leak-down tester? They would test the mechanical part of cylinder 3 vs the other three cylinders.

Thanks, I'll check compression and see if the shop can read live data. They have a couple of OBD2 scanners. Don't remember them having a leakdown tester but I may be wrong.

Wouldn't you know it... I borrowed a friends Actron scanner and now the car is not acting up. The fuel trim readings you said to look at are o.k. but I'm waiting for it to act up. I did have a "check gas cap" display on the dash once, and the cap was tight.