The Great Misfire Mystery

"The Swedish Bandit" (swedishbandit) 08/02/2013 at 09:22 • Filed to: joy

0

10

Yesterday I took Joy for her first real "longer" drive. It was a 90 mile drive down to the sea and back. It all went pretty well and I had no major fluid losses during the trip... however. About halfway through, while I'm on an onramp to a short highway section I had to drive on, I accelerate pretty hard to get up to traffic speed and then something happens. She starts backfiring like crazy while at the same time giving me almost no power at full throttle. I let off the throttle and the backfires stop and I've got power again.

After the highway section, I pull over to see if there's something obviously wrong with her, but I find nothing. I then start her up again and listen carefully to the engine and yup, she's not quite running on all cylinders.

Both exhaust pipes are letting out quite a bit of smoke and the air coming out is lukewarm, probably due to unburnt fuel in the air coming out. This tells me that I have a misfire problem on both sides of the engine as the pipes are separate all the way from the engine. Now I didn't have any real equipment with me to fix this problem right away so I do what I can, which is take of the distributor cap off and look for moisture in it (which there were non), and then continue driving with probably only six cylinders functioning. Other than that the trip went pretty well and I gotta say for being an almost 40 year old muscle car with super worn bushings and dampers, the car handles terrifically well.

When I get back home, I let her cool down a bit and then get back to diagnosing the misfire issue. First thing I check is the sparkplug wires, and I immediately find one cylinders cause of not functioning. The wire was broken at that metal bit that connects to the sparkplug, meaning that the metal bit sat on the sparkplug and the wire lay loose inside the wireshoe. I replace the wire with an older one I had laying around and proceed by starting her up again. FUCK YEAH!, no more misfire on the right side of the engine.

On the left side however, I don't find anything obviously wrong with neither the sparkplug wires nor with the sparkplugs themselves. It's getting kinda late so I resort to the quick way of testing them, which is pulling the wires with the engine running. First one I pull, no difference in engine noise - meaning Bingo!, that's the one! I replace that one as well with an older one and then start her up. But this time, there's no real improvement. I'm thinking that it might just be the sparkplug that's a bit flooded from all the unburnt gas and call it a day, to let it dry out over night.

Earlier today I took her for a short test drive to see if the problem had been fixed, but alas no such luck. I'm now starting to run out of options and becoming seriously worried. Oh god I hope it's not a cam lobe that's been grinded down to nothing! I've still got a few more things I'm gonna test later on today but I wanted to see if you guys could have some ideas of what the problem might be.

TLDR: My engine isn't running on one cylinder and I need help sorting it out.

Slave2anMG > The Swedish Bandit 08/02/2013 at 09:28

0

Bad plug as in broken internally? Perhaps just heavily crudded up due to misfire and needs cleaning?

And are you sure you actually have spark at that plug?

Takuro Spirit > The Swedish Bandit 08/02/2013 at 09:30

0

I too hope its not a worn cam lobe. That's what killed my Firebird once. Ran low on oil (no light came on until it was too late) and wore off the #8 intake valve lobe smooth.

Did you pull the valve cover and check for a broken spring/bent rod/etc?

The Swedish Bandit > Slave2anMG 08/02/2013 at 09:32

0

The plug itself looks alright, a bit of sot on it but nothing to serious. But as you say it might be broken internally, which is the first thing I'm gonna test later on today.

The Swedish Bandit > Takuro Spirit 08/02/2013 at 09:39

0

If I can't find anything wrong with the sparkplug I'm gonna pull the valve covers and turn the engine by hand to see if all the rocker arms move up and down as they should.

My old cam had a worn lobe, so who's to say that it can't happen again. However this is on a completely different cylinder so I'm hopeful that it isn't that. But I gotta get me some gauges to monitor the engine better, having just a warning light for both the water temp and the oil pressure feels seriously sketchy.

Takuro Spirit > The Swedish Bandit 08/02/2013 at 09:41

1

First thing I did after having the cam replaced was buy a triple gauge pack. I never had the chance to hook it up, but I had the intentions of knowing exactly what was going on under the hood.

GRIVLET - Proud of Cobalt > Takuro Spirit 08/02/2013 at 09:45

0

"The road to the junkyard is paved with good intentions"

I think this is more applicable than the more popular quote relating to hell.

lolz.

Takuro Spirit > GRIVLET - Proud of Cobalt 08/02/2013 at 09:47

0

I wish I knew what happened to that car..... Can't track down the VIN and the DMV can't help me based off the license plate that was registered to it.

The Swedish Bandit > Takuro Spirit 08/02/2013 at 09:49

0

I'm thinking gauges and a real scoop is probably next on the agenda if thinks work out with the engine again. However if it turns out to be the cam, that probably means the my cam bearing replacement procedure wasn't successful, which basically means that I might as well start looking for my dream engine; the 455 right away.

Bruno Martini > The Swedish Bandit 08/02/2013 at 15:07

0

easy to test, ground it to the body and start the engine. If it sparks, you have fire. Although the plug could be broken internally and still fire under atmospheric conditions. I would honestly do at least wires and plugs. Cant be that expensive on a 350. If the cam ground itself to nothing then go junkyard hunting and buy either a 350 or parts out of a 350. Although sumit has the whole valvetrain for a 350 for cheap too. Your call, luckily even catastrophic failures are cheap to fix on a 350.

The Swedish Bandit > Bruno Martini 08/02/2013 at 16:45

0

Yeaaah about that... Forgot to mention that it's a Pontiac 350 and not the regular CSB we've got here. This results in that prices are a bit more expensive and parts being somewhat harder to come by.

But it's cool, I have everything under control now! Link

!!! UNKNOWN CONTENT TYPE !!!