endless misfires w 3800 V6

[lght1]

hi

I have a 1997 Olds LSS w/3800 "K" . This engine has about 182k mi on the clock.

Until I decided to install another set of NGK Iridiums, there never was a single instance of misfire.
Within 24 hrs, on cold starts, a SES (misfire #4) would occur.

I elected to install a new set of plugwires.
Again, withing 24hrs, another SES on #4. Thinking that I may have a bad plug on #4, I installed a new NGK. The "old" one looked fine

This time, I swapped in a new coil pack for the offending cylinder, but again, the next morning brought SES #4.

I used four bottles of Techron, one each tank full for the first two bottles and the final tankfull was with 2 bottles of Techron.
The next day seemed to bring relief, esp after a 460 mile drive. But the next morning after, another SES #4.

I then installed a new injector for #4, but still...the same SES #4.

Once the engine has been driven and underhood temps are up, all roughness seems to be virtually gone, and never a SES at load or warm operating temps.

The SES only occurs when the engine cools down, and you are ususally at idle. The roughness is apparent at this time.

Any help would be appreciated

[ April 15, 2005, 09:19 PM: Message edited by: lght1 ]

 

[theguru]

You sure you have the plug lead pushed all the way on?

Is it possible that you have a coolant leak into that cylinder?

Just a couple of random thoughts.

Good luck.

 

[lght1]

hi

I just had a UOA last week or so and it showed "0" coolant. I hardly ever need to top off the bottle so i dont think there is a coolant leak.

 

[theguru]

Was the problem evident before the UOA?

 

[lght1]

hi

no, its recent.
however, since its been evident, no loss of coolant.

I really dont believe its coolant esp since the 3800 leaks over near thew egr chimney.

the problem only occured after the new irridiums were installed.

 

[theguru]

I have the irridiums in my 3.8Ltr GM motor. Seem fine. Have you a standard plug to try? Still a little suspicious of the coolant. Doesn't take much of a leak to cause a misfire.

Have you checked all the electrical connectors around the motor that might have been moved during the change.? Any vacuum hoses loose? Have you tried fuel from another petrol station? Changed your fuel filter lately? Air cleaner (i assume clean) and air lines all tight?

Are the gaps on the plugs correct?

 

[lght1]

hi

the misfire started immediately after the new irridiums.

based on this, issuspect that it might possibly be carbon tracking on the old plugwire, transferred to the the new plug, which inturn , transferred it to the new plug wire, which again transferreed it to the new replacemetn irridium plug for #4.

another site has suggested that it is likely to be the ignition module.

the plug gaps were checked at .60
gas from many sources, even states.
filter was changed in early march as was air cleaner.
no leaks, or apparent vac leaks.

the problem seems to magically disappear with the rise in temps... that is the confusing thing.

for it to be a coolant leak, the leak would have had to occured within days of the last UOA as the dates were very clsoe.
since then, i've driven 4100 miles without a drop in coolant.

 

[Cutehumor]

in the GM 2.2 sunfire, I changed the plugs to Bosch platinums for the car. immediate notice! the engine started to shake erratically at idle. drove fine only at idle would the engine idle erratically. it triggered a check engine light after a few stops. note there was no problems with the engine before putting the brand new bosch platinum plugs. changed out the new bosch plugs for new OEM ac delco plugs, the check engine light went off and everything was back to normal. this was 25k miles ago and no problem since.

 

[theguru]

When you said new irridiums I assumed you had them in before. If not, then change out the plugs for the standard NGK's. Some engines just don't like them.

 

[Elroy the Unique]

If you want a performance plug, go with AC Delco Platinum Rapidfires. These are a GM premium Plug that are the best choice for the car.

Also, the Rapidfires have a 30-day money-back guarantee, so it would be easy to replace them in and see if that fixes your problem. If not, you could return them.

Did you try Dielectric Grease on the Spark Plug Wire boot, too?

http://www.acdelco.com/html/pi_plugs_rap_reason.htm

 

[lght1]

hi

the car had the same plugs last 2yrs for over 100k mi with no ill effect.

once i installed their replacements using the same plug wires the orig irridiums had, the #4 issue started and nothing i've done since has eliminated it.

 

[eljefino]

If it's anything like Saturns there isn't a direct way of telling #4 is out. The computer just guesses based on an inductive kickback through the plug wires so it's sensitive to non-stock situations. I'd try ordinary stock equivalent plugs and wires.

 

[brianl703]

A bad plug can make a good wire bad. A bad wire can make a good plug bad.

If I'm not mistaken, it looks like you haven't replaced BOTH the plugs and wires at the same time. Check your sparkplug socket for crud buildup, too.

 

[JohnBrowning]

Some year of 3.8 called for Iridiums and AC/Delco made some Iridiums for it so I think we can rule out the elctrode material. For this short of a cycle it would not mater if they were copper,iridium or platnium and most people taht had the iridiums replace them with platnium any ways. lets list what has been changed.

1)Plugs #4 twice
2) Plug Wires
3) Coil for #4 wich if it were bad would ahve made the other cyclinder feed by this coil misfire as well.
4) #4 injector and asumeing o-rings too.

What do we have left that is well know to case misfire on these engine.

1)Ignition Module
2)Piece of Sh!t Dupont Nylon 33(see plastic)upper intake manifold!
3)Cam and Crank sensor (unlike if isolated to one cylinder)
4)PCM ( unlikely if isolated to one cylinder)

THe EGR and IAC can cause rough idle but would not cause a miss on one cylinder.


I am thinking that it is either the ignition module or the upper intake manifold. It does not have to leak coolant into the engine the leak can be external as well. It can also cause a miss if any of the bolts holding it down losen up or if the sealing surface warps and allows air to leak in!

 

[brianl703]

If the problem were the ignition module, I'd expect it to cause the other cylinder paired with #4 to misfire, as well. Unless there's some way where it fails that it provides a proper drive signal to the coil primary for those two cylinders only every 2nd time...

 

[lght1]

Hi

This morning before i left for work, idid the following:

Swapped the wires 2-4 around. I could still feel some misfire/roughness, but it never set a code today in over 230 miles. Temps were mid 60's/dry conditions.

Later this afternoon, I replaced both plugs 2-4 with irridiums, and replaced all wires with a AC Delco set.

In 75 miles, no SES, but unless engine is at operational temps, like the 75 mi drive, then it wont misfire anyways.

I had a UOA done just a few days before I first installed irridiums, and no coolant in sample.

BTW, I installed the orig set of irridiums 2 yrs ago, with 100k of no issues. On the 4th ofthis month, I installed the next set of same plug, drove 300 miles that day with no issues.

I had Tues (April 5th) off, didnt drive until that evening to go to wally, and then the misfire. Since then, it has been present.

Update: I just went outside to start it. It idles rough, and if you put it in gear, the idle drops precariously enough to dim the dash lights somewhat. it recovers quickly but you can influence the diming and normalization by shifting from park to gear and back again.

The car has a tach, and it looks like the rpms drop maybe 200 before getting back to where 1000. The engine had cooled off at this time. Usually idles about 800 or so under normal oper/temp.

[ April 16, 2005, 11:19 PM: Message edited by: lght1 ]

 

[lght1]

Hi

Just another thought, could I have had two issues running at same time?

It seems that today, there was ample time to set a SES if it was indeed misfiring.

If it is a intake leak , could engine heat from highway miles seals the leak even temp? Once this thing has been run on the highway or even driven for 20 min or more around town, all seems much better.

Could it instead be a malfunctioning IAC which hates cold but functions somewhat after it warms up?

Where is the IAC located?

[ April 16, 2005, 11:37 PM: Message edited by: lght1 ]

 

[chas3]

i have iridiums in my 3800. runs fine with them.

you seem to have tried everything else. try swapping the coil pack. this would be a better test and swapping the posts.

also, #4 can be hard to replace. is it fully seated in the block? engine gets hot, expands and seals cylinder.

[ April 17, 2005, 09:38 AM: Message edited by: chas3 ]

 

[lght1]

hi

the coil to #4 has already been replaced with a new one.

no effect.

i will try cleaning the ign module, and coils tomorrow. i had a valve cover leak which may have spread down to module, etc.

 

[outrun]

Flow Chart:

I had the same problem, higher the letter, higher the chance it is not that...and more labor wasted for diagnosis

A) Plug

B) Wire

C) DIS Coil Pack

D) IGNITIONAL MODULE

E) Injector/Loop Circuit


Side note...I did see a AC Delco Iridium Plug for my car. Interesting it was stamped made by NGK in Japan

Will have to do more research, do not want any problems if I switch out my AC Platinum RapidFires for any Iridium problems.