# Misfire issue? What else besides...?



## GulfCoast1102 (Dec 30, 2013)

My wife drives a 2004 Saturn Vue with a 2,2 liter GM Ecotec motor. Some times back, we had an issue with an intermittent misfire, which evolved into a continuous misfire. I changed the coil pack, and all was well, for about 3 days. The misfire came back, and I chased my tail for 3 weeks trying to find the problem. As it turned out, the coil pack I installed had failed, and was covered under warranty. Installed another coil pack, and the car ran great.

A few days after replacing the coil pack, the check engine light came back on. Car ran fine, but had the CEL. I put my computer on it, and it came up with a P0420 code, along with verbiage saying that the Catalytic converter was bad. After some research, it seemed that driving the car for 2-3 weeks with a misfire like we did had damaged the Cat. I added changing the Cat to my list of chit to do, but haven't changed it yet. The car ran fine otherwise...

Fast forward about 4 months or so, and we now have a misfire issue again. This time, the computer says it is a random misfire and not a cylinder specific misfire like we originally had. I immediately assumed that the coil pack was failing again, so I went back to the store, and swapped it out under warranty. No dice. Still running with a sporadic, random misfire. 

After some reading, i'm finding that potential causes of the misfire include coil pack, plugs/wires, cam shaft sensor, catalytic converter, O2 sensors, water temp sensor, and the price of tea in China.

A good friend of mine has all but sworn that the Cat has likely not failed. He insists that it would require very long periods (months/years) of driving with a steady misfire to damage a Cat. I don't know this to be true, but he suggested it...

He also suggested unplugging the O2 sensors and driving the car to see if the car would go into Limp Mode, and not rely on (potentially) faulty inputs from the O2 sensors. I tried this, and got no change in the run condition.

The last go'round of this stuff, I removed, cleaned, and tested each of the fuel injectors, and cleaned the fuel rail. Replaced the plugs and boots (this goofy thing doesn't have plug wires), replaced the coil pack and ignition module.

I'm now at a frustrated "*** do I do?!" moment. I hate to change the Cat to solve the misfire issue, not knowing if the Cat is now causing the issue that potentially caused the Cat to fail to begin with. 

Any other suggestions, guess, etc? I hate dealing with mechanics. Partly the cost, but it also robs me of the chance to learn something new.


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## Pocketfisherman (May 30, 2005)

The cat is not causing your misfire, but a cat can fail in a few days if run with a misfire. The unburned fuel from the misfiring cylinder lights off in the cat and overheats it ruining the platinum catalyst coating. A few things to check -
1) If the fuel filter has more than 50K miles on it, change it.
2) check the fuel pressure on the injector rail with the motor running at idle and make sure it meets spec for that motor. Low fuel pressure from a failing pump can cause your symptom.
3) Run a couple tanks of fuel through the motor using Chevron Premium and add a double dose of either Yamaha ring free or Sea Foam. This will clean the injector tips.
4) Replace spark plugs if they have more than 50K miles on them, or if the electrodes look like they are eroded.
As a last resort, 
5) Try replacing the spark plug wires and coil high voltage wire.

Check the engine ground cable attachment and battery cable clamps for tightness and corrosion working up under the crimp into the wire.

Chances are if the problem is not cylinder specific and you have already replaced the coil, then it is either fuel system related, or the coil high voltage wire.


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## GulfCoast1102 (Dec 30, 2013)

Pocketfisherman said:


> The cat is not causing your misfire, but a cat can fail in a few days if run with a misfire. The unburned fuel from the misfiring cylinder lights off in the cat and overheats it ruining the platinum catalyst coating. A few things to check -
> 1) If the fuel filter has more than 50K miles on it, change it.
> 2) check the fuel pressure on the injector rail with the motor running at idle and make sure it meets spec for that motor. Low fuel pressure from a failing pump can cause your symptom.
> 3) Run a couple tanks of fuel through the motor using Chevron Premium and add a double dose of either Yamaha ring free or Sea Foam. This will clean the injector tips.
> ...


Fuel filter is in the tank, as is the fuel pump. Filter is "supposed" to be a "lifetime" part, which seems like BS to me, but that's GM's word on it.

I do need to check fuel pressure. Everything related to spark is new, as in, brand new. Coil, ignition module, boots, and plugs (as i mentioned, the way this thing is built it does not have plug wires).

Injectors were all removed and cleaned, and tested. All performed properly. Nice clean stream of carb cleaner spraying through when energized.

I'm planning to replace the Cat, but I want to get the misfire issue fixed first, or i'm just pizzing in the wind changing the Cat.


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## ibtbone (Oct 7, 2013)

If you drive it like you stole it will the rpm's go to the red line? If the cat is restricted it will not build rpm's under a load, pull the plugs again and look at the ceramic, where the boot goes, google spark plug carbon tracking, look for that, the boots are replaceable , if any are carbon tracked replace the plug and the boot, a miss fire will cause a converter to go bad


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## MARK MACALUSO (Sep 29, 2010)

Did you ever do a compression check on the cylinder ? PO420 should be a cat efficiency code. How many miles are on the vehicle ?


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## redexpress (Apr 5, 2010)

Ground wire most likely loose is what I'm hearing from gearhead buddies with my PO300 misfire code. 
Haven't checked it yet though.
Chevy dealer said I just need to drive it more, and harder.


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## GulfCoast1102 (Dec 30, 2013)

MARK MACALUSO said:


> Did you ever do a compression check on the cylinder ? PO420 should be a cat efficiency code. How many miles are on the vehicle ?


Car has 180k miles. The Cat got damaged by driving with a really bad misfire for a stretch of about 2 weeks. This occurred 3-4 months ago.

Last night I cut the old cat out, and started welding a new one in. Ran out of time. Will finish today.

I'm replacing the cat, both O2 sensors, crankshaft position sensor (because it's cheap, and an easy thing to rule out), and taking the coil pack and boots back to the store under warranty and replacing with OEM instead of aftermarket.

Shotgun approach!


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## toyotapilot (Jun 11, 2004)

I know it is a different vehicle, but my Jeep kept throwing random misfire codes. It ended up being a crack in the exhaust manifold....


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## GulfCoast1102 (Dec 30, 2013)

toyotapilot said:


> I know it is a different vehicle, but my Jeep kept throwing random misfire codes. It ended up being a crack in the exhaust manifold....


Weird! I'll file that away in the back of my mind.

Anyhow, a few updates...

Over the weekend, I changed the catalytic converter because it needed done from the last misfire episode we had. While I was in there, I also changed both O2 sensors, and the crankshaft position sensor.

I replaced the existing Bosch coil pack and boots with AC Delco (OEM). The ignition module is still Bosch.

I ran a compression test, and all was well.

I checked fuel pressure, and although the pump does produce a steady 50-60 PSI, the check valve in the fuel pump is leaking, which allows fuel pressure to bleed down on the fuel rail once the key is turned off. Mechanic insists that this is relatively common, and will cause extended cranking time, but not a misfire.

Car is STILL misfiring. Not all the time, and not horrendously, but it is misfiring.

I pulled the fuel rail off, and left all wiring and injectors in place. Cranked the car, and watched all 4 injectors actuating and spitting fuel as they should. Shut the key off, and none of them leaked.

I don't know what the hell else to do with this thing. It is headed off to the mechanic this morning...


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## Pocketfisherman (May 30, 2005)

Please post up what they find, this has piqued my curiosity.


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## toyotapilot (Jun 11, 2004)

When I was having my misfire codes I took my Jeep to a Meineke Car Care Center and had them hook up there computer to it. They could turn individual injectors and coils off and on and stuff like that, but couldn't find anything wrong. It was after that when I found the cracked weld on the exhaust. It might be cheaper than changing a lot of stuff.


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## Y-Not (Sep 14, 2012)

Now that you have replaced the crankshaft sensor you'll need to do a crankshaft variation relearn. If not done it will give the impression of a misfire with no trouble codes found.


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## GulfCoast1102 (Dec 30, 2013)

Car is with the mechanic now. He says it's not misfiring at all, and he can't find anything wrong with it!

:headknock


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## GulfCoast1102 (Dec 30, 2013)

Mechanic drove the car twice, and checked codes with computer. Car is running like a top. No misfire. Don't know what to think.

My only guess, and this is nothing but a guess, is that the computer had to go through a "learn" cycle after I replaced the crankshaft position sensor. Normally, a computer is required to "force" the computer to "re-learn". This was what Y-Not suggested. 

Mechanic's guess was that possibly the ignition module starts heating up and malfunctioning after extended periods of driving. 

At this point, I'm happy that it is running good. Mechanic says I don't owe him anything because he couldn't find any problems.

Used cars are just about enough to drive a fella to drinkin...


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## MARK MACALUSO (Sep 29, 2010)

Next step i replace injector and harness. Make sure you replace the harness.. If not that then need to check ECM and wire lead for cylinder. Quit using that Bosch junk...


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## Pocketfisherman (May 30, 2005)

Some engine control systems detect misfires via feedback from the spark plugs, measuring the voltage where the spark initiates as it ramps up. Harley does this. The type of spark plug used is critical to this working correctly. Were the plugs changed to something different than originally installed?


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