Engine is misfiring why?

Tiny
MONEYSAM
  • MEMBER
  • 1999 HONDA CIVIC
  • 180,000 MILES
A friend of mine had that pop up on a printout which shows the engine is misfiring?
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Monday, August 27th, 2012 AT 7:54 PM

34 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,606 POSTS
Check fuel pressure first then check ignition components. also check for a vacuum leak. This guide can help us fix it

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

Please run down this guide and report back.
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Monday, August 27th, 2012 AT 7:56 PM
Tiny
MONEYSAM
  • MEMBER
  • 173 POSTS
How do I check the fuel pressure and what should the reading b?
She says when she stops at a light it vibrates more than usual. How woul I check
The ignition components
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Monday, August 27th, 2012 AT 8:09 PM
Tiny
HMAC300
  • MECHANIC
  • 48,606 POSTS
Try this first, clean the throttle plate on both sides with choke or fuel injector spray cleaner. they get dirty on both sides and get all the gun k out. they get oily. check it out as you need a gauge to check the fuel pressure should be 47-52 psi.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

if lower you may need a new pump.
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Monday, August 27th, 2012 AT 8:41 PM
Tiny
MONEYSAM
  • MEMBER
  • 173 POSTS
I know all the ignition components and I know about cleanin the throttle body plate I jus dnt have a fuel pressure tester im thinkin I would have to hook it up to the shrader valve on the fuel rail
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Monday, August 27th, 2012 AT 8:49 PM
Tiny
HMAC300
  • MECHANIC
  • 48,606 POSTS
Ok then check with an auto parts store they may have one for a rental alot of them do that andthat would be wher eyou hook it up on the schrader valve.
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Monday, August 27th, 2012 AT 8:51 PM
Tiny
MONEYSAM
  • MEMBER
  • 173 POSTS
Ok, I did a fuel pressure test it was okay then I replaced eh distributor that worked perfect thanks for your help, this site rocks.
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Monday, August 27th, 2012 AT 8:53 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
Glad you could get it fixed, that kind of problem can be tough. Please use 2CarPros anytime we are here to help.
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Monday, August 27th, 2012 AT 9:50 PM
Tiny
LOPYLOBSTER
  • MEMBER
  • 2 POSTS
  • 1999 HONDA CIVIC
Engine Mechanical problem 4 cyl Front Wheel Drive Manual 91000 miles

Ok, my car is throwing codes p0300-p0304 and p1399, they are cylinder misfire 1-4 and random cylinder misfire. I've changed my distributor, spark plugs and wires, pcv valve, fuel filter, o2 sensor, ground wires, valves adjusted, valve cover gasket, compression test came out good, and injectors are firing. But I still keep getting these codes. The Car has no EGR because it's a SI model, and it's all the cylinders misfiring. Not sure where to go from here. Any ideas?
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Monday, January 4th, 2021 AT 12:42 PM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
A code P0300 follow these guides

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

and

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

and

https://www.2carpros.com/articles/repair-lean-mixture-codes-p0171-or-p0174-on-some-manufacturers

Diagram (below)
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Monday, January 4th, 2021 AT 12:42 PM (Merged)
Tiny
LOPYLOBSTER
  • MEMBER
  • 2 POSTS
Alrighty, couldn't find a vacuum leak, but you hit it on the money with the MAP sensor I replaced it and the problem was fixed!

I love this site thanks guys!
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Monday, January 4th, 2021 AT 12:42 PM (Merged)
Tiny
BIGBADSPOON
  • MEMBER
  • 9 POSTS
  • 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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Monday, January 4th, 2021 AT 12:44 PM (Merged)
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
Were the valve clearances checked?

Is streaming data within specs for :

1. O2 sensor.
2. Crankshaft position sensor.
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Monday, January 4th, 2021 AT 12:44 PM (Merged)
Tiny
BIGBADSPOON
  • MEMBER
  • 9 POSTS
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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Monday, January 4th, 2021 AT 12:44 PM (Merged)
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
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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Monday, January 4th, 2021 AT 12:44 PM (Merged)
Tiny
BIGBADSPOON
  • MEMBER
  • 9 POSTS
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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Monday, January 4th, 2021 AT 12:44 PM (Merged)
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
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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Monday, January 4th, 2021 AT 12:44 PM (Merged)
Tiny
BIGBADSPOON
  • MEMBER
  • 9 POSTS
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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Monday, January 4th, 2021 AT 12:44 PM (Merged)
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
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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Monday, January 4th, 2021 AT 12:44 PM (Merged)
Tiny
BIGBADSPOON
  • MEMBER
  • 9 POSTS
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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Monday, January 4th, 2021 AT 12:44 PM (Merged)
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
Recheck the ignition coil, is it OEM or after market?
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Monday, January 4th, 2021 AT 12:44 PM (Merged)

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