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Old 12-28-2010, 02:49 PM
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Help with 3.8L misfire

My 01 Regal (L67 3.8L) has been setting the cel the last couple of weeks and now has a misfire on cold starts.
First code was PO305 (missfire #5) and now is PO300 (random missfire).
1,3, and 5 wires and plugs look fine and are about 1yr old. Haven't looked at 2, 4, and 6 yet. Since the miss goes away with any throttle input and after the vehicle warms up, I'm not too sure the plugs/wires are the problem.

Looking for a little help troubleshooting this before I start throwing parts at it.
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Old 12-28-2010, 08:33 PM
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could be intake gaskets.
cold miss is pretty common with the plastic intakes and/or plastic intake gaskets with aluminum intakes.
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Old 12-28-2010, 08:42 PM
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Quote:
Originally Posted by Rhansen
My 01 Regal (L67 3.8L) has been setting the cel the last couple of weeks and now has a misfire on cold starts.
First code was PO305 (missfire #5) and now is PO300 (random missfire).
1,3, and 5 wires and plugs look fine and are about 1yr old. Haven't looked at 2, 4, and 6 yet. Since the miss goes away with any throttle input and after the vehicle warms up, I'm not too sure the plugs/wires are the problem.

Looking for a little help troubleshooting this before I start throwing parts at it.
I would check to be sure all the wires are clipped on tight. The back ones can be tough. There are several things that can cause misfires. As mentioned above the intake could be leaking, bad crank sensor, hanging EGR.
What brand plugs are in it. Bosch plugs are great for misfires.
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Old 12-29-2010, 03:05 PM
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Replaced plugs/wires today (old plugs were autolite platinum, wires unknown) new are ngk and some napa belden wires. All the old plugs/wires looked fine.
So far no codes but also no cold start to speak of.
Quote:
could be intake gaskets
I put aluminum LIM gaskets on about 1 1/2 yr ago and it doesn't use coolant atm.
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Old 12-30-2010, 07:32 AM
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On first start up this morning the car still misfires. Also had the idle speed hunt between 1000 and 1300 for maybe 30 sec. Checked for vac leaks but found none. Scanner had a PO300 code pending.
Any ideas? crusty egr?
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Old 12-30-2010, 07:51 AM
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Sticky EGR could do it, The upper intake may not be sealing well when cold but once it warms a little it may be sealing.
Those kind of problems can be tough to find.
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Old 12-30-2010, 08:00 AM
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miss fire

i don't know if u have a single coil pack for alll plugs or one for each.. depending on milage u most likely have a weak coil. my sons escape is doing the same thing and i'm gonna replace the 3 coil packs.. already did the front 3... he had the same codes as u.. i purchased all 6 (new) from uneeksupply in calif for $80 bucks including shipping (ebay). i've used them before on my truck and i'd deal with them again.. and this is NOT an advertisement for them.. just my op.. bill
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Old 12-30-2010, 08:04 AM
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misfire

Quote:
Originally Posted by Soul_Hunter
could be intake gaskets.
cold miss is pretty common with the plastic intakes and/or plastic intake gaskets with aluminum intakes.
thanks soulhunter for that info.. i didn't know about this and the plastic intakes.. but wondering if u use a special gasket or RTV ??? as i mentioned below i well be pulling it to replace the back coils on my sons car.. bill
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Old 12-31-2010, 01:09 PM
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back to the top
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Old 12-31-2010, 02:28 PM
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I would have to say dirty injectors. Put in a can of sea foam, but change your fuel filter first.
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Old 12-31-2010, 08:46 PM
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im not familiar with aluminum LIM gaskets. is LIM the brand name?
if they are like the metal gaskets from Fel-Pro, then i would say they should be ok.

sometimes a po300 can be a pain, especially on fords.
but with a GM if you have access to a scanner, you should be able to look at the misfire counters and see which cylinders are missing.
it should show both current and history misfires for each cylinder.

a EGR valve leaking when cold is possible, it is something i would check if nothing else showed up.
surging idle can be a sign of a vacuum or EGR leak.

valve deposits are another possibility.
i've had great luck using a product called 44K from BG products.
they also make some of the best spray throttle body cleaner i've ever seen.
the down side to BG, you can only find the BG line at auto repair shops that sell it.

this part is a little long.
a bad coil can cause cold random misfire, but normally you also get some warm misfire with heavy throttle with a bad coil, but not always.
the way i check DIS coils on a GM is by pulling both plug wires off each coil 1 at a time and then start the motor. the coil should fire between the towers only without a problem. if a coil is not firing between the towers, its bad.
next, using a very good quality pry bar with a perfectly intact and completely undamaged plastic handle, i hold the handle as far away from the metal part of the pry bar as possible and lay the metal part of the pry bar on some metal part of the motor and move the other end of the pry bar near the outside of the coil towers one at a time. the coil should continue to fire between the towers. if it doesn't on either tower and jumps to the pry bar, the coil is weak and shorting internally.
of course if you have the pry bar between the coil towers, the coil will fire to the pry bar.
a good, new GM DIS coil will fire between the towers even with the pry bar touching the outside of either one of the towers.
when you get within about 1/4 of an inch of either tower, some fire will jump to the pry bar, but the coil will still fire between the towers.
this does not work for the older type GM DIS, ford or Mopar DIS coils. for those systems you need to use 2 known good spark plugs and wires and use the pry bar to slowly lift each spark plug away from where the metal of the car you laid them.
if you try this with a cheap pry bar, or one with a wood or damaged handle, or touch or get near the metal of the part bar, you will regret doing it. i have a Snap-On pry bar that i bought specifically for doing this test only.
i also wouldn't do this type of test on COP systems. the risk of frying the electronics is too great.

im not a big fan of NGK plugs in a GM, A/C delco parts is all i would put in a customers' GM car when i did auto repair for a living.


Bill, on the O-ring type gaskets the only place i would use any sealant was around the water ports, and that was only if the surfaces were damaged and the customer either couldn't afford, or didn't want to repair or replace the damaged parts. when i did use sealant, i used very little.
if i had to use sealant, the customer knew before hand i wouldn't warranty the repair. if the damage was too bad, then they either had to repair or replace, or it didn't get put back together.
minor pitting of the parts i would always take care of with a good cleaning and some JB Weld.


i should also mention that using a spray like carb cleaner doesn't always work for finding a vacuum leak on port fuel injected motors.
i did use carb cleaner as one of my tools to check for leaks, mostly on a warm motor. but even a pretty minor leak can cause a cold start misfire.
the more minor the leak, the less likely a spray check would work.
i used a smoke machine to check for leaks, and even with it some leaks didn't show up and i had to take a leap of faith that a leak was the problem.

Last edited by Soul_Hunter; 12-31-2010 at 09:03 PM.
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Old 01-01-2011, 11:25 AM
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Quote:
Originally Posted by Soul_Hunter
im not familiar with aluminum LIM gaskets. is LIM the brand name?
LIM = lower intake manifold, 'upgrade' gasket I ordered from dealership. Car is factory supercharged.
I have a code reader but no scanner. Might be able to borrow a scanner, but not right away.
Today I got PO171 in addition to the PO300 and no surging idle. Maybe whatever is wrong will fail completely and reveal itself in the process.

Quote:
if you try this with a cheap pry bar, or one with a wood or damaged handle, or touch or get near the metal of the part bar, you will regret doing it
lol yes, these have a wee bit more juice than an HEI. Will have to check out the coils.
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Old 01-04-2011, 05:54 PM
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I borrowed a Solus scanner yesterday (after driving about 80 miles on the hwy) and all it showed were 4 or less missfires on cyl's 4, 5, and 6. My friend suggested that the O-rings around the injectors may need replaced.
Going to work this morning I got on it to pass and could smell fuel, it set the CEL w/a PO171 (bank 1 lean). I repeat and basically I smell gas if the blower makes any boost. Also not seeing the PO300 code any more.
This is making me think my friend is on to something, got a vac leak somewhere.
I'm working out of town now but will try to find it this weekend.
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Old 01-09-2011, 01:06 PM
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Found the problem, it's sucking air around the injectors.
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