Sudden random misfires..2.2l

[GaryC]

Been fighting a goofy problem for the last month. Had the dreaded ignition switch problems. Replace tumbler and housing, that took care of a bunch of no start/dash light issues. A problem that was happening in tandem with the ignition switch is "random misfires". That's the code it sets, when it does set the code (doesn't always). The engine starts misfiring, sputtering, back firing etc. You can shut it off and restart and it will be fine most of the time, other times it goes on like that then fixes itself and runs fine. Other than the ignition switch and housing , I've replaced the Ignition Control Module, which didn't help at all. Any ideas?

2002 Alero 2.2l 4, 5 speed.

Thanks, Gary

[[ion] C2]

What Causes a P0300 Code?

• Low Fuel Pressure
• Vacuum Leak
• EGR system malfunction
• Internal Engine Problems (such as low compression)

Less Common Causes

• Faulty Coil
• Faulty Spark Plugs and/or Wires
• Camshaft or Crankshaft sensors
• Ignition module
• Computer

http://www.myautorepairadvice.com/p0300.html



Only time I ever have random misfires is when I have a vacuum leak (or major head gasket leak). Vacuum leaks also tend to be my most commonly faced issue over the years with various hardware attached. I am currently fixing some this week, in fact.

Could also be bad upstream O2 sensor. Can test by electrically disconnecting the sensor. If problem goes away, that's what it is. I've also had bad O2 sensors.

[GaryC]

Originally Posted by [ion] C2

What Causes a P0300 Code?

• Low Fuel Pressure
• Vacuum Leak
• EGR system malfunction
• Internal Engine Problems (such as low compression)

Less Common Causes

• Faulty Coil
• Faulty Spark Plugs and/or Wires
• Camshaft or Crankshaft sensors
• Ignition module
• Computer

http://www.myautorepairadvice.com/p0300.html



Only time I ever have random misfires is when I have a vacuum leak (or major head gasket leak). Vacuum leaks also tend to be my most commonly faced issue over the years with various hardware attached. I am currently fixing some this week, in fact.

Could also be bad upstream O2 sensor. Can test by electrically disconnecting the sensor. If problem goes away, that's what it is. I've also had bad O2 sensors.

Thanks, I'll start with the vacuum leaks and work my way around.

[GaryC]

Originally Posted by GaryC

Thanks, I'll start with the vacuum leaks and work my way around.

\\

I've gone through and eliminated all except the computer. A trip to the GM dealer is next.

[[ion] C2]

No idea. Sorry

[03Alerosil]

It could be a camshaft solenoid. It could be going bad and then the computer won't know what the timing is. Heck it could even be a loose timing chain.

[GaryC]

Originally Posted by [ion] C2

No idea. Sorry

Here's something I found out tonight . I took a small wire and wrapped it around the braided ground strap on the engine (connects block to head) and the other end to the master cylinder. It sparks and gets hot if I keep it touched to the master cylinder. What the hell gives? Engine and body should be all grounded together I thought?

[[ion] C2]

There's a positive wire that looks like a ground on the 2.4L. I accidentally connected it to a grounded location once. Might be the case on the 2.2L as well. There shouldn't need to be a strap connecting the block to head since the head bolts and timing cover bolts etc. are connecting them pretty solidly.

Could just be a broken wire in a circuit somewhere. I would suggest the ICM wires just as a wild guess. I had an injector whose soldered connections broke and caused an intermittent open circuit causing a misfire on one cylinder recently. Anything relating to the spark or fuel will cause misfires. When it's random, it's got to be something that has the potential to affect all of them, so it's not going to be spark plug wires or an injector.

Could be a clogged fuel filter or faulty pump, but difficult to diagnose while driving, I know. If you lose fuel pressure intermittently it could cause a misfire across all cylinders.

@03Alerosil the camshafts don't have solenoid valves, lol. The sensor that detects pulses from the camshaft to determine its position/RPM could be faulty, though.

Hit up the dealer. I'd be very curious to see what it is. I'd be leaning toward a bad ground of some sort making it either difficult for the spark to occur or the fuel injectors to open. An air-fuel ratio gauge would help determine if when it's running rough it's lean or rich which would let us know whether the fuel or spark is having trouble.

When my injector 3 had an open circuit my AFRs were off the chart lean during the misfires. If the spark was at fault, it'd be richer than usual.

[GaryC]

OK, made some progress tonight. I took a meter and measured .10 to .20 volts between the engine and the body. I took jumper cables and jumped from the strap on the engine to the master cylinder. The misfiring stopped. I let it run for 10 minutes. It was normal. I removed the jumper, it ran for 6 minutes fine then started misfiring. I put the strap back in place, it ran normal again. It looks like I have a ground problem, broken wire as you suggested. I will run through it again tomorrow to reconfirm.

I'll keep this thread updated as I find things out. Thanks for your advice.

[[ion] C2]

Fascinating! I always wonder where grounding issues begin (where the electrical break actually is occurring).

[GaryC]

Originally Posted by [ion] C2

Fascinating! I always wonder where grounding issues begin (where the electrical break actually is occurring).

After placing a ground strap from the engine to the body I have had no further issues. Car has been running great. I have checked and re-tightened any ground straps I could find but they all seemed good. I thought maybe the mechanic who put my clutch in left something off when the transmission was out but I found nothing there. Obviously something is off/corroded somewhere. I will continue to look and report any findings.

Thanks all for the ideas and advice!

[Papa Rad17]

Good find! and good test! I recommend going ahead with some larger welding cable for a replacement. Heavy coating, oxygen free, and fine stranded.