99 Civic Misfire

Tiny
BIGBADSPOON
  • MEMBER
  • 1999 HONDA CIVIC
  • 4 CYL
  • FWD
  • MANUAL
  • 170 MILES
The misfire has been ongoing for over a year, but throws no codes and no engine light.

After cleaning the fuel injectors, checking for vacuum leaks, and resistance checking the injectors, I decided on a lark to hook up a timing light.

When hooked up to any of the spark wires, the timing light will strobe normally for several seconds, until it "misses" a beat, which I can hear as a misfire out of the exhaust. I'm guessing this means there is some sort of ignition issue here, but I can't find it.

After finding a failed coil and replacing it, nothing changed. Before that, over the last several weeks, I have also replaced the cap, rotor, plugs, and wires as well as run just about every diagnostic I could find including compression tests and just watching the streaming data on a scan tool.

The miss is very subtle, but at idle is just sounds like a very slight pop every 3-4 seconds (it's not cyclical, it's very random). At light loads up to 2000 rpm, I can feel it losing power, but after that it seems to behave pretty normally. My gas mileage is about 20% less than it was before this started, though.

I have also checked for vacuum leaks, both with propane and by simply putting a hand over the throttle plate (it dies instantly). The IAC is brand new, as I was having an idle issue a few weeks ago, so I know that's not causing anything. There is no EGR valve on the car either.

I'd love to hear your input on what might be going on here and how to test for it in some way other than throwing parts at it (as the local mechanics are wan to do).

Oh, it does this whether the engine is hot or cold, doesn't seem to matter. I checked the FIAC valve, ECT sensor, and IAT sensor just to make sure they were OK, and they all checked out within spec.
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Tuesday, January 11th, 2011 AT 11:19 PM

17 Replies

Tiny
KHLOW2008
  • EXPERT
Were the valve clearances checked?

Is streaming data within specs for :

1. O2 sensor.
2. Crankshaft position sensor.
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Wednesday, January 12th, 2011 AT 3:18 PM
Tiny
BIGBADSPOON
  • MEMBER
Yes, the primary O2 is fluctuating between.15 and.85, but my software doesn't show data on crosscounts.

No data is available for the crank sensor. Is there a way to manually test it?
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Wednesday, January 12th, 2011 AT 4:57 PM
Tiny
KHLOW2008
  • EXPERT
Usually when the sensor is bad, trouble codes would be stored.

Normal testing is the performed on the resistance.

I do not know which engine you have so I have included all the various models.

Did you check if the distributor has excessive side play, indicating a bad bearing.
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Thursday, January 13th, 2011 AT 12:31 PM
Tiny
BIGBADSPOON
  • MEMBER
It's the d16y8 motor. There are no trouble codes stored. The distributor feels pretty tight, too.

I will check the resistance tomorrow (my day off) and get back to you on where that sits.
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Thursday, January 13th, 2011 AT 4:46 PM
Tiny
KHLOW2008
  • EXPERT
Did you check/adjust the valve clearances? If any cylinder has too tight valve clearances, it can misfire and compression test would not show much drop in pressure.
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Thursday, January 13th, 2011 AT 6:21 PM
Tiny
BIGBADSPOON
  • MEMBER
I have never checked vale clearances, but would that cause my timing light to not fire when it's on any given cylinder? Doesn't seem like it would cause the same symptoms.

The main reason I believe this to be a sensor problem is because, when I have the timing light on any wire, it fires like normal until there is a misfire, at which point the light stays off for a brief instant, then strobes normally again.
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Friday, January 14th, 2011 AT 3:14 AM
Tiny
KHLOW2008
  • EXPERT
Timing light not firing could be due to misfiring which can be due to valve clearances faults. Could it be a fault with the timing light?

Since problem is intermittent and most likely to be electrical, I believe the distributor and ignition components such as rotor, ignition coil, spark plug wires or disteributor cap is more likely to be the cause. It could be wiring fault due to loose connections that is intermittently not working correctly.
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Friday, January 14th, 2011 AT 12:26 PM
Tiny
BIGBADSPOON
  • MEMBER
Well, the cap, rotor, plugs, wires, coil, and icm are all new. The timing light works well on every other car, just this one.

Air and fuel misfires don't cause ignition failures, do they? As long as the coil is good, I would think enough voltage would pass through the plug to make a spark regardless of the conditions inside the cylinder.

I will be checking the crank sensor resistance this weekend and will let you know what I find as soon as I do.
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Friday, January 14th, 2011 AT 8:23 PM
Tiny
KHLOW2008
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Recheck the ignition coil, is it OEM or after market?
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Saturday, January 15th, 2011 AT 12:33 PM
Tiny
BIGBADSPOON
  • MEMBER
I finally had a chance to sit down with the car and here are some values I measured for sensors on the ECU through the attachment you gave me as well as the coil.

The engine is the d16y8, so I used the 3rd diagram for the pins.
8 and 9: 521 ohms
20 and 21: 204.4 ohms
29 and 30: 299.4 ohms

coil pimary: 1 ohm
coil secondary: 20680 ohms
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Monday, January 17th, 2011 AT 9:39 PM
Tiny
KHLOW2008
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The ignition coil readings are out of specs. For secondary readings, it is neither here nor there whereas for primary it is completely out of range.
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Tuesday, January 18th, 2011 AT 12:13 AM
Tiny
BIGBADSPOON
  • MEMBER
Well, those specs are at 68 degrees, and I have to drive over to someone else's house to test, which raises resistance. The temp was prob around 200 degrees, at that point. I will try to let the engine cool down more next time I'm over there for a more accurate test.

I'm not convinced those readings are off far enough on a hot engine to be the cause.

Were the distributor sensors in spec?
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Tuesday, January 18th, 2011 AT 8:07 AM
Tiny
KHLOW2008
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Specification for those sensor resistance are 350 - 700 ohms.

The lower 2 are out of specs.
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Tuesday, January 18th, 2011 AT 1:25 PM
Tiny
BIGBADSPOON
  • MEMBER
Are both of those sensors located in the distributor?
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Tuesday, January 18th, 2011 AT 5:41 PM
Tiny
KHLOW2008
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Yes they are.
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Wednesday, January 19th, 2011 AT 5:11 PM
Tiny
BIGBADSPOON
  • MEMBER
Bought a new distributor, but before install traded coils just for fun and the misfire persisted. When I replaced the distributor, problem solved!

Thank you so much for helping me narrow that down. I have invested way too much time diagnosing this problem.
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Monday, January 24th, 2011 AT 1:35 AM
Tiny
KHLOW2008
  • EXPERT
Glad to know you have fixed the problem.

Have a nice day.
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Monday, January 24th, 2011 AT 2:47 PM

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