What is the more common reason for a missfire? Plugs? Wires?

Its missfireing on 8 @ 124 or so and on 1 @ 24 or so. I have not lost any power, and the only thing that I have noticed is when I'm decelerating my RPMs stay at 1500 and take a while (10-30seconds) to drop to when I come to a stop. My SCS light was flashing, but than stoped and then went off. It hasn't came back on for about 70 miles or so. Please help in anyway possible. Oh I have a m6 tranny if that helps

Thanks > Pete

 

Whats the firing order in a diagram from?
example

##
##
##
##

 

not sure about the firing order but try this, pull off one plug wire from the plug at a time and try and get it to arc on something. if they all arc pull out the problem plugs and make sure they are firing, if the dont look like they have been firing try to replace them and see what happens. this was my meathod to find out i had a wire that wasnt snaped all the way lol

 

Thanks

 

Checked and replaced plugs and wires. SCS light keeps flashing???? Why would it misfire at cold start, but not while driving? Light goes away after cars warms up. I dislike problems

More help please....

 

How do I get the wires to arch? Does the ignition have to be on? Should the car be started?

Can anyone else help out with some trouble shooting tips?

 

yeah u have to have someone sit in the car and turn it over, as soon as u see it arc shut it off. im wondering if u might have a bad coil, and this could cause it. let me know what it does after u do this

 

New news???

 

I had the top end cleaned with Top End Cleaner, and with no luck. All wires have juice too. Now A small missfire when car starts has turned into another troulbe code > P0507 Idle higher than it should be. What's the deal here? Changed plugs, wires, cleaned out the top end of the motor, and everything is getting juice. Anymore advice that is out there would be great on how to fix this.

 

im having troubles like this with my frineds, ill keep u posted on what we do.....

 

Firing order 1–8–7–2–6–5–4-3

 

I've got the firing order. Now I'm just trying to trouble shoot a missfire that only occurs during a cold start, and only lasts for 2-3mins. This really makes no sence. That cruise control feel when I'm driving is starting again as well.

Cold starts = missfire
Driving = car wont rev below 1800 RPMs and the car drives its self
Idle = Shooting p0507 idle to high

What would cause all these things to chain react?

 

From the GM diag worsheet...


MISFIRE

Abnormalities, such as severe cracking, bumps, or missing areas in the accessory drive belt

Abnormalities in the accessory drive system and/or components may cause engine RPM variations and lead to a misfire DTC. A misfire code may be present without an actual misfire condition.
Replace the drive belt. Refer to Drive Belt Replacement - Accessory .

Worn, damaged, or mis-aligned accessory drive components or excessive pulley runout and may lead to a misfire DTC.

A misfire code may be present without an actual misfire condition.
Inspect the components, and repair or replace as required.

Loose or improperly installed engine flywheel or crankshaft balancer

A misfire code may be present without an actual misfire condition.
Repair or replace the flywheel and/or balancer as required. Refer to Engine Flywheel Replacement or Crankshaft Balancer Replacement .

Restricted exhaust system

A severe restriction in the exhaust flow can cause significant loss of engine performance and may set a DTC. Possible causes of restrictions include collapsed or dented pipes or plugged mufflers and/or catalytic converters.
Repair or replace as required.

Improperly installed or damaged vacuum hoses
Repair or replace as required.

Improper sealing between the intake manifold and cylinder heads or throttle body.
Replace the intake manifold, gaskets, cylinder heads, and/or throttle body as required.

Improperly installed or damaged MAP sensor

The sealing grommet of the MAP sensor should not be torn or damaged.
Repair or replace the MAP sensor as required.

Damage to the MAP sensor housing and/or O-ring seal
Replace the intake manifold.

Worn or loose rocker arms

The rocker arm bearing end caps and/or needle bearings should be intact and in the proper position.
Replace the valve rocker arms as required.

Worn or bent pushrods
Replace the pushrods.

Inspect the top of the pistons for valve contact. If the top of the piston shows valve contact, replace the piston and pin assembly.

Stuck valves

Carbon buildup on the valve stem can cause the valve not to close properly.
Repair or replace as required.

Excessively worn or mis-aligned timing chain
Replace the timing chain and sprockets as required.


Worn camshaft lobes
Replace the camshaft and valve lifters.

Excessive oil pressure

A lubrication system with excessive oil pressure may lead to excessive valve lifter pump-up and loss of compression.
Perform an oil pressure test. Refer to Oil Pressure Diagnosis and Testing .
Repair or replace the oil pump as required.

Faulty cylinder head gaskets and/or cracking or other damage to the cylinder heads and engine block cooling system passages. Refer to Diagnostic Starting Point - Engine Cooling in Engine Cooling.

Coolant consumption may or may not cause the engine to overheat.
Inspect for spark plugs saturated by coolant. Refer to Spark Plug Inspection in Engine Controls.
Inspect the cylinder heads, engine block, and/or head gaskets.
Repair or replace as required.

Worn Piston Rings

Oil consumption may or may not cause the engine to misfire.
Inspect the spark plugs for oil deposits. Refer to Spark Plug Inspection in Engine Controls.
Inspect the cylinders for a loss of compression. Refer to Engine Compression Test .
Perform cylinder leak down and compression testing to identify the cause.
Repair or replace as required.

A damaged crankshaft reluctor wheel

A damaged crankshaft reluctor wheel can result in different symptoms depending on the severity and location of the damage.

Systems with electronic communications, DIS or coil per cylinder, and severe reluctor ring damage may exhibit periodic loss of crankshaft position, stop delivering a signal, and then re-sync the crankshaft position.
Systems with electronic communication, DIS or coil per cylinder, and slight reluctor ring damage may exhibit no loss of crankshaft position and no misfire may occur. However, a P0300 DTC may be set.
Systems with mechanical communications, high voltage switch, and severe reluctor ring damage may cause additional pulses and effect fuel and spark delivery to the point of generating a P0300 DTC or P0336.

 

How did you use the Top engine Cleaner? And what kind of information are you getting back from the IAC motor? Is the throttle blade returning fully to closed? Is it possible you left a vacuum hose off or accidentally knocked off another vacuum hose while using the TEC?

Cylinders 1 & 8 are consecutive in the firing order. There could be an issue with the 24x reluctor ring, since they are adjacent cylinders, provided you've checked all other potential sources of problems. You may want to find a buddy with access to a Tech 2 (don't know if any other tools will have this feature) and do a Crankshaft Position Variation Relearn procedure. Last resort if you can't get access to one for free since the dealer will charge 1 hour labor, and it's not likely the cause anyway.

You're not getting any other DTC's? Did you check the history? A misfire DTC may only be stored in the history, and not in the regular DTC memory. If you read the last lines of the diag info I posted above it mentioned DTC's for the reluctor ring and related components.

The first thing I'd probably do is check the coilpack connections, and swap some coils to different cylinders. Since the misfire is on 1 and 8, I doubt it's a coil problem but it's easy and free to try.

Also, are you getting any noises from the motor, like valvetrain or piston noises?

 

No I haven't heard any noises. But my IAC (i think that's what it was) was zero. The GM dealer ( my good friend ) told my that its very likely that I have a small vacum leak. I've sprayed carb cleaner everywhere possible and have found no sign of a leak from idle rpm. The only codes that have came up are:p0507,p0171,p0170, and the missfire code > and that was only 1 & 8. What's a reluctor ring anyway????

Thanks for all the help > one of these days my baby will be fixed!

 

Well I found part of the problem. The gasket between the intake manifold and heads was blown. Well I took everything apart and put it back together, and now the hose that connects to the brake booster is pinched behind the intake so I have to take it apart and fix it.