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  #1  
Old 07-26-2011, 10:39 AM
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Default Intermittent Misfire

I need suggestions... So I'm getting very frequent, but still not consistent, misfires at stop lights. I also have no guts when accelerating. Pretty much fine when engine's cold and when cruising.

I've changed:
-plugs
-plug wires
-Cleaned EGR valve
-PCV valve
-Fuel filter
-Fuel Pump (checked for any rust/crap in tank area)
-Gone down fuel lines and any wiring I could see for breaks or melting etc.

Every one of those things needed changing or cleaning.. but it's still happening and I'm running out of ideas. Any suggestions?
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Old 07-26-2011, 11:25 AM
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Which motor and model truck ? If it's an efi motor runing like that, it should have tripped a code(s).
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Old 07-26-2011, 05:24 PM
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Like Mr. Dragon said, check for codes, first. It could save you a tone of time and money. If you don't have a truck that will give you codes, it's time to do some good old fashion trouble shootin' and mechanicin'.

Could be any one of a number of other things...
Does your truck have a distributor? If so, Check the rotor, be sure it's getting a steady spark at each terminal.

No Distributor? Verify that each coil pack is firing every time.
Does the miss happen at idle and/or at speed? Under load, or not?

The last time I had an intermittent miss in one of my trucks it turned out to be a weak valve spring. Occasionally the valve wouldn't completely seal.
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Old 07-26-2011, 06:13 PM
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1991 C1500 2x4... 305ci 5.0L V8 103000miles
haha never owned a vehicle new enough for codes, I guess I should take a look under the steering column!

yes to distributor... I shall check rotor and cap and I guess ignition pack.

It doesn't happen at idle in park or neutral... only in drive with the brake on
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Old 07-26-2011, 07:06 PM
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That distributor might have vacuum advance, make sure the hoses are good and listen to the brake booster when you hit the brakes, does it hiss or make a whoosh ?
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Old 07-26-2011, 07:07 PM
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take a jumper wire to your obd1 port hook it to the a&b ports turn the truck on but not started
the service engine light will flash and then will flash 1-2 that means the computers working
then any other code will follow in a serious of numurous flashes
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Old 07-26-2011, 07:08 PM
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A bad o2 can also give you fits. I know they will suck power but I've never known them to cause a misfire.
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Old 07-26-2011, 07:21 PM
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Quote:
Originally Posted by MrDragon View Post
A bad o2 can also give you fits. I know they will suck power but I've never known them to cause a misfire.
i have my 05 crown vic needs all 4 o2 sensors replaced and it keeps throwing the number 1 cylinder missfire code every other day

but yes and 02 sensor will casue your truck to run like its about to die out on ya when you need it the most
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Old 07-26-2011, 08:34 PM
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I jumped A and B (the 2 top right pin holes) and it spit out 1-2 about 50 or 60 times...
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Old 07-26-2011, 08:38 PM
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Quote:
Originally Posted by MrDragon View Post
That distributor might have vacuum advance, make sure the hoses are good and listen to the brake booster when you hit the brakes, does it hiss or make a whoosh ?
I couldn't find one... In my last vehicle (80 camaro) there was one... this has an advance wire connected near the firewall. A week ago I checked the flywheel pull (has none, thank God) and the timing and had to remove the wire to do so... Is this wire the replacement for the advance vacuum hose?
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Old 07-26-2011, 08:38 PM
 
 
 
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2003, 53, blazer, chevrolet, chevy, diagram, iac, location, misfire, suburban, tahoe, tbi, truck, vacuum, valve

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