Multiple Misfire: Not the one with Steven Seagal

So I bought an Aveo LS 5 speed. Last Weekend.

It drove great, during the test drive. Well - I liked it... Obviously.

It was low on gas, It had been sitting for a few months. I fill the tank with gas. - On the way home from picking it up.

Within a minute of that, I have a blinking CEL.

My OBD2 scanner says: P0300 - Multiple Random Misfire.

Well, that's just ... Well that's not desirable at all.

So I take it to a mechanic.

He charges a $110 + tax, says change the plugs, wires, and valve cover gasket. So I do that.

I kind of wanted the shop to do some vacuum tests, and leak down tests or something, not just point out the first most obvious thing. Maybe they couldn't. Who knows.
Is the timing OK I don't know. That's something I really wanted to know actually. Because that was how Sylvie Died but that's another story.

But the valve cover gasket along with plugs and wires - did not solve the issue. Granted it needed to be done, provided the engine is sound.

How do I know if this ignition system is working? I put new parts in, do the new parts work?

So I'm kind of short on money now, so I was following a thread, where much of the diagnostic process here begins with a vacuum test. How do I go about doing that?

Is there a specific line that I need to attach to?
Where do I get one of those gauges.

What about the timing? It should have been done by the owner before this owner. The car has 134000 KM or under 85000 miles on it. Do I just pull out the airbox, remove the cover and compare the marks? The belt should have been done at 100,000 KM.

I don't get the EGR - From my understanding if it's jammed closed, than I could have excess gasses building up in the engine causing a misfire?

The flashing light on the dash... Well if it was flashing for the previous owner, that would damage the Catalytic Converter, what would that damage look like? How would it effect the way the car drives?

I'm fairly used to driving mostly dead cars.
But this is perfectly springy lively little car.

I need to check fuel injectors. I thought it was driving just fine.
But I suppose it's one of the area's that I need to look into. You would be able to tell right? Maybe?

Worst case scenario: Burn't exaust valve - that sounds really bad. So that's not even in the head is it? that's part of the block, and that's when you toss the motor away and all that.

For scan tools, all I have to work with is torque pro.

Any Ideas?

I'm afraid that If I stick with this mechanic...

P0300 Random Multiple Misfire..., = "something, somewhere, may not be right with this engine, or some other part of the car, or maybe the road is bad, or some other thing, that prevents that thing from doing the other thing, eh?"

Now Replace these parts in this order:
Plugs,
Wires,
Coils,
Feul Injectors,
O2 Sensor,
EGR Valve,
ECM,
Replace every type and hose and gasket,
Camshaft/Crankshaft sensors..
And if that fails blame the problem on a burnt valve and buy a new car.

OK, sounds like you are getting in over your head, but will try to see what we can do.

First, a moderator needs to move this to the right section - this is a technical question, not an "Introduction"

Misfiring can be caused by a number of items; and the mechanic did truly point you towards the basics - plugs and associated components. These are usually considered the "cheap" items to fix. Valve cover gasket is important on these engines since it will allow the plug area to fill with oil.

You note that it has been sitting and was low on fuel - that's a great recipe for condensation and corrosion in the fuel tank, as well as varnishing in the system. You may have something as simple as a fouled/stuck injector; an application of your favorite flavor of in-tank injector cleaner may be a good start.

If you wanted to run a vacuum test, you can get a simple gauge at any parts store, and hook it to any available port on the intake - but I'm not sure that's going to tell you much at this point. Better option would be to run a compression test - that will rule out major failure items like valves. Speaking of valves - yes, the valves are in the head; but if you had a burnt valve, it would be running like total crap at this point. The engine just honestly isn't large enough displacement to mask a burnt valve among all the other cylinders.

If status of the timing belt is unknown, change it - plain and simple. If it fails, you will be pulling the head and replacing valves at a minimum.

O2 sensors, probably not a absolute need to change - they will typically throw a code if they start acting up.

EGR valve is a possibility, check other threads for more troubleshooting on that.

Check engine light flashing is simply telling you to get it scanned and fix the issue - if the only thing you have is a random misfire, then need to address the basics of fuel and spark first.

Cam and crank sensors are a possibility, if memory serves, there is a "relearn" procedure that needs to be done after changing one of those...

Whoever told you that a burnt valve means the block is garbage needs to have a good swift kick in the posterior - stop listening to that person...

So I know I have p0300

Torque allowed me to run some tests, I ran them twice.

Trying to collect some more info:


05 04 0A High Sensor Voltage For Switch Time Calculation 0.0000 to 7.9900 V 0.122 mv / bit

I wonder what this means? Test result value: 224

Rich to lean... Maybe an 02 sensor?

I did take your advice on the fuel injector cleaner.




Fresh DATA:

Test report:
------------------
TID:$04 CID:$60
- High sensor Voltage for switch time calculation
Max: 0
Test result value: 224
FAIL
----
TID:$07 CID:$4d
- Minimum sensor Voltage for test cycle(calculated)
Test incomplete or dependant test failed
--
TID:$0a CID:$03
- Sensor period(calculated)
Test incomplete or dependant test failed
--
TID:$0a CID:$05
- Sensor period(calculated)
Test incomplete or dependant test failed
--
TID:$0a CID:$06
- Sensor period(calculated)
Test incomplete or dependant test failed
--
TID:$0a CID:$42
- Sensor period(calculated)
Max: 32,768
Test result value: 32,768
PASS
----
TID:$0a CID:$48
- Sensor period(calculated)
Max: 32,768
Test result value: 32,768
PASS
----
TID:$04 CID:$60
- High sensor Voltage for switch time calculation
Max: 0
Test result value: 224
FAIL
----
TID:$07 CID:$4d
- Minimum sensor Voltage for test cycle(calculated)
Test incomplete or dependant test failed
--
TID:$0a CID:$03
- Sensor period(calculated)
Test incomplete or dependant test failed
--
TID:$0a CID:$05
- Sensor period(calculated)
Test incomplete or dependant test failed
--
TID:$0a CID:$06
- Sensor period(calculated)
Test incomplete or dependant test failed
--
TID:$0a CID:$42
- Sensor period(calculated)
Max: 32,768
Test result value: 32,768
PASS
----
TID:$0a CID:$48
- Sensor period(calculated)
Max: 32,768
Test result value: 32,768
PASS
----

End of report.

While Torque is a useful app (I have it myself for quick troubleshooting); it can provide some false alarms - depending on how long you had the car running, that particular failed test is to be expected.

A bad or failing O2 sensor typically won't cause a misfire; if anything, it will cause increased fuel consumption since it will put the engine into a "safe" mode to prevent leaning in out too much.

In your shoes, I'd be focusing on potential ignition issues first - pull the plugs, and check to see if any of them look abnormal. While the plugs are out, maybe a compression check just for good measure?