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Random misfires

Jaredthefail

Jaredthefail

New member
So when I start my car sometimes it misfires for the first mile or two. Not consistently just randomly. Three different cylenders have misfired while I scanned it today when it messed up.

It just drops in rpm and comes back at a higher rpm causing the car to jolt.

It doesn't just happen at idle. Throttle position and speed don't seem to help or hurt it but driving it for a while seems to make the problem stop.

After checking all plugs and wires my next guess is fuel pump as it's been whining recently and I read that's an indication that its on it's way out.

O'Riley's wants 250 for a fuel pump but I didn't want to pay that until I know for a fact it's the problem. I don't like to change parts I like to fix problems.

What else should I check before pulling the plug on the fuel pump?

Sent from my Moto G (5S) Plus using Tapatalk
 


The fuel pump being the culprit is a long shot. More than likely its the ICM or the coil packs. Are you running OEM coil packs? or MSD? How are the wires from the harness leading into the ICM? My wires were starting to come apart where they enter they ICM. You could see the copper wire. You could see it corroding and turning green. I would start there.
 
The coils and ICM are oem and the plug wires are Delco and about a year old. Is there an easy way to test the ICM?

I should also mention that it throws no codes at all
CHI2000GTP said:
The fuel pump being the culprit is a long shot. More than likely its the ICM or the coil packs. Are you running OEM coil packs? or MSD? How are the wires from the harness leading into the ICM? My wires were starting to come apart where they enter they ICM. You could see the copper wire. You could see it corroding and turning green. I would start there.
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Sent from my Moto G (5S) Plus using Tapatalk
 
What are you measuring the misfires with? I have seen a bunch of aeroforce guys that noticed misfires near startup, never a code or a true issue.

Is your ac running when the rpm are dipping?
 
BillBoost37 said:
What are you measuring the misfires with? I have seen a bunch of aeroforce guys that noticed misfires near startup, never a code or a true issue.

Is your ac running when the rpm are dipping?
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Tourque pro with a Bluetooth adapter. Usually the accounts is running but I turned it off and it still did it. I'm worndering now if it's a clogged cat??

Sent from my Moto G (5S) Plus using Tapatalk
 
I always start by checking long term and short term fuel trims. Scannerdanner on you tube has some good videos on using fuel trims to diagnose misfires.

Good example is misfire from vacuum leak. You can tell that from fuel trims then correct. You can even tell a weak fuel pump from them too.

If you have one, it wouldn't be a bad idea to check fuel pressure at key on engine off, running, and with fpr vacuum hose off.

Any other codes btw?

Oh, and if you suspect cat, you can remove the o2 sensor and check for backpressure.

If you haven't figured out yet, I'm very anti parts swapping! Lol
 


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