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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.

  • 1
    Would that I had more than just +1 to give. Great question! – cdunn Apr 6 '16 at 23:29
  • Looking at the freeze frame, some things don't make sense. The engine is cold (coolant = 84 deg F) and it was just started (run time = 8 sec). For an '09 Honda I bet that means the current idle RPM would be about 1500, which is what is displayed. So why are the throttle positions saying that the pedal is somewhat depressed, and the calculated load is 40+%? That and the Fuel System 1 says Open Loop Fault. Since the pressure is actually good, is there a sensor for fuel pressure that's not right? Seems like a sensor issue and not a mechanical issue. Beyond fuel, not sure which sensor – cdunn Apr 6 '16 at 23:46
  • @cdunn Regarding the TPS/APP PIDs it's up to the manufacturer as to how it's displayed some cars never show 0% TPS1 and usually rest at 10% or so. As to the load I'd guess since it's on a fast idle and airflow is a parameter or calculated load if you did the math it'd end up working out. And the Open Loop Fault I'm unsure why it set. Without a closer look at what the O2/AFR sensor is doing it'd be hard to say. In this case it would be throwing you off as to why the engine was supposedly misfiring. – Ben Apr 7 '16 at 2:41
  • The only other thing I see that makes me pause is the -6 degrees of spark advance. Is it normal for an engine to be firing 6 degrees after TDC at idle when cold? The limited research I've done shows that at idle, the spark is still advanced, not retarded. So why would the ECU want to retard the spark so much. Does it work like fuel trim where an O2 says more fuel till it tops out? In this case some sensor telling it that it needs to keep retarding the spark until things don't run right. – cdunn Apr 7 '16 at 2:57
  • Thinking out loud again, misfire detection is generally the crank position sensor reports that the crank is not as advanced as it should be if the A/F mix had fired. If the spark is retarded to 6 degrees after TDC, then the crank may not be as far as it should because the spark is so late. Which makes the misfires a red herring, and the real problem is why is the ECU is commanding a -6 degrees of advance? (I'm reading -6 degrees of advance to mean 6 degrees retarded, I.E. after TDC). – cdunn Apr 7 '16 at 3:11
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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.

  • it's a little weird unlike gms when the pcm loses the crank pattern you don't feel any misfire. – Ben Apr 7 '16 at 10:00
  • TSB 09-050 is for cranking with a low battery. The voltage in the freeze frame is the output of the alternator so I'm not sure we know anything about battery state from the information we have here so far. Was the voltage of the battery measured when the car wasn't running? – cdunn Apr 7 '16 at 11:38
  • @cdunn i usually check battery condition anytime there are communication codes etc... in this case the battery had a good charge and the cold weather may have been a factor and/or the car was driven long enough for the battery to recharge. – Ben Apr 7 '16 at 13:27
  • I see the answer was accepted, was this in fact the issue? If so, was the actual problem? What part of this answer was the solution, the "reflash"? Does "reflash" mean rewrite the ECU flash memory with a factory fresh image? Is it possible for mere mortals (those not in the industry) to get the TSB's for their car? – cdunn Apr 7 '16 at 19:39
  • @cdunn "reflash" is jargon for an update to the PCM software; usually to solve a particular problem. In this case the crank sensor sees false misfires and sensor failure when the engine cranks too slowly due a some fault in the battery or starter. For TSB info try alldatadiy.com or most OEM's have short term subscriptions available. I know of no free source that has a comprehensive list. Even for pay professional level sites sometimes fail to have all the bulletins. – Fred Wilson Apr 9 '16 at 6:02
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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

  • Good to see you fixed it. Can you edit the answer so that the last section is readable? I had a hard time parsing the last few sentences. Also what scanner did you use to do the relearn? – Ben Jul 29 '17 at 21:28
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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.

  • update: This problem did not go away with the "relearn". One week later I got a crank sensor fault along with P0302, 0303, 0300. Installed a new crank sensor. This did not fix the problem immediately but clearing the codes several times, disconnecting battery, running A/C finally forced a relearn. Cars been running perfectly so far. We shall see...... – Shubert Oct 28 '17 at 3:06

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