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This one came in today with a check engine light on and a complaint of running rough and won't accelerate past 30MPH.

Checked the codes.

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Some misfire freeze frame.

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Reset and went for a test drive.

Codes P0300, P0302 and P0303 come back right away. scan data shows a constant misfire on cylinders 2 & 3. Engine doesn't actually run rough I think the customer confused the limp mode rev limiter with rough running.

Looking at Stuff

Coil #2 primary side.

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Looks OK.

Coil #3 shows the same.

Spark? looks good enough to me. Jumps a 30kV gap looks blue enough to rule out a secondary issue.

The car has around a 100k on it so maybe a valve is sticking?

MAP sensor voltage looks OK < .90v with the engine hot @ idle. Pretty much rules out a sticking valve or the valves being out of adjustment.

Fuel trims look OK live readings weren't far off from the freeze frame. No vacuum leaks, all hoses secure and accounted for.

How about engine compression? > 150psi on each cylinder

Plugs? Not exactly new but looked OK. Some minor oil varnish around the ceramic.

How about bad injectors? To be honest I didn't even bother checking. Injectors on these motors rarely fail.

Fuel pressure? Around 50psi, good enough for me.

So how about that Crank Position Sensor code?

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Looks OK to me. No drop outs. Signal looks clean. Connector is secure.

What about water intrusion? Seems to be the most likely. And it did snow a few days back.

Unfortunately by the time the car came in the connector was dry. Pins looked pretty clean hit it with some dielectric grease and plugged it back in.

What's the deal?

Before anyone says check the injectors, it's not the injectors.

I thought this would be a good problem for someone to think on.

Instead of just posting the solution I'll give someone else a chance to respond and be a hero.

Ben
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3 Answers3

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Spark? looks good enough to me. Jumps a 30kV gap looks blue enough to rule out a secondary issue.

Great.

MAP sensor voltage looks OK < .90v with the engine hot @ idle. Pretty much rules out a sticking valve or the valves being out of adjustment.

Concur, and just about rules out engine pumping problems. That and the good compression test.

Fuel trims look OK live readings weren't far off from the freeze frame. No vacuum leaks, all hoses secure and accounted for. How about engine compression? > 150psi on each cylinder.

This is a good result if it was closed throttle. I like to check compression WOT, if possible, which would give numbers more like 180+ psi.

Plugs? Not exactly new but looked OK. Some minor oil varnish around the ceramic. Cool. How about bad injectors? To be honest I didn't even bother checking. Injectors on these motors rarely fail.

Concur, we have never had a problem with any of these.

Fuel pressure? Around 50psi, good enough for me. Great. So how about that Crank Position Sensor code? Looks OK to me. No drop outs. Signal looks clean. Connector is secure.

Nice graph, looks normal.

What about water intrusion? Seems to be the most likely. And it did snow a few days back.

Possible, but you saw none and it usually does not dry out on its own.

Having ruled out actual misfire and seeing no current failure of the crank sensor a different approach is needed.

My next move is to check and replace battery, repair any voltage loss to starter as needed to resolve the slow cranking problem. Then reflash per TSB 09-050. Perform crank relearn. Then retest.

I chose this route because you stated the engine was not running rough which I take to mean there is no actual misfire felt or seen in scan data while running. And the codes set immediately after the start. which is the condition covered by the reflash. I see nothing particularly unusual in the freeze frame data. Looks like most Hondas of this era 8 seconds after start.

Community
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Fred Wilson
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Ok guys I got the same problem with a 08 honda accord 4 cylinder I work as a mechanic in L.A. this is what I did the car was brought in with misfire problem on cylinder # 2 and 3 plus p0339 the consumer had change the crank sensor but still same problem so when the car got here I erase all codes and when for road test at soon i went around the block check engine start flashing code p0302 and p0303 back limp mode no acceleration. When back to shop start reading everything on Google. So this is what fix the problem to me check the battery I was good with everything off one's I put ignition on battery goes to 12.3v so i when end took my battery out my car that o have just bought put it on do a crank sensor re learn won't my cheap scanner and that fix my problem no more check engine no more misfire o but the way 218$ dollars on Amazon for the sccaner

Moises Mendez
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I also had numerous misfire codes. Turns out I just needed to have a "relearn" done to the car's computer. That's it. Simple as that. Just had to find a shop to do it. Good luck.

Shubert
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