CHECK ENGINE LIGHT-RANDOM MISFIRE

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JAM25

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Hey Bob Oil Gang,

In my 1999 Olds Cutlass I have my check engine light. I went to AAP so they can scan the car and it got a code. I dont remember the code but the guy told me it was a random misfire. I had told him what could the problem be? He said its mainly Spark Plugs and Wires. Now. I dont think thats the problem.becausr i had just replaced them little over a month. OEM models. AC Delco wires and Plugs. The car starts right up and idles smooth, not rough. What could cause this random misfire? Ive also noticed that my gas mileage is horrible i get like 12-13MPG city and like 20-22 MPG highway. When its estimated at 17 city and 28 highway. Ive also noticed a loss of power when trying to speed up. Ive asked my dad since hr passed tbis car to me. If he had ever had any problems with it, he said nothing major just simple quick fixes.

I asked him if he has ever replaced the o2 sensor, fuel filter and he said no. Now ima try snd buy the fuel filter this weekend and replace it. O2 maybe in the next couple weeks. Since its darn expensive.

Now again. What can cause a misfire? Will me replacing what i me.tioned help fix it? If not what could i do in regards to looking for other parts that could have cause this. All i do is mainly city driving so stop and go short trips. I do live in chicago. Hopefully is nothing major because imnalso trying to.learn automotive technology now that ive graduated and received my law enforcement degree.

Any help is appreciated.
 
I had a random misfire on 2 cylinders a few weeks ago, turned out to be 2 coils that both went out at the same time. Better check those first
 
How would i check them though??
Originally Posted By: renegade_987
I had a random misfire on 2 cylinders a few weeks ago, turned out to be 2 coils that both went out at the same time. Better check those first
 
If it were a single misfire or 2 misfires (like P0301, P0302), you could go after items specific to that cyl like coils, plugs, injector, etc. But you stated random misfire (P0300) which effects all cyls at once, so you looking for a "global" event. For me, that was a vacuum leak combined with some needed fuel system/combustion cleanup. To answer your question, the upstream A/F o2 sensor CAN cause random misfires setting fuel trim too rich. A symptom of a Lazy o2 is a drop in gas mileage over time.

For a random misfire, clearing the ECU after repair may be required. Unlike other CEL's, misfire codes take MANY cycles before they are tripped off, MANY cycles for them to go away.
 
Bad gas or water separation in the fuel can also cause random misfires or temporarily trigger the CEL.
 
Originally Posted By: 147_Grain
Bad gas or water separation in the fuel can also cause random misfires or temporarily trigger the CEL.

The "seafoamers" don't realize the 20% IPA in Seafoam can do that. So they add even more, then finally appear in a forum stumped.
 
Thats what I get for bringing it up... Claims that somehow 50% Pale oil, 30% Naphtha, 20% IPA does magical things in a combustion engine.
 
You need to get the actual code. P300 is random. Did you have problems before you changed the plugs?? Make sure that your plug wires are kept separated, cross firing will also cause this. The AC Delco plugs should be a double platinum, were yours, and did you carefully check the gap.
 
Originally Posted By: LeakySeals
Thats what I get for bringing it up... Claims that somehow 50% Pale oil, 30% Naphtha, 20% IPA does magical things in a combustion engine.

Sorry....who am I to let my experience contradict your statement
 
Based on that configuration, if you had a dead coil two out of six cylinders would misfire if a coil were dead. If they line up with the markings on a coil, I'd say you have your culprit.

I've seen faulty wires cause a random cylinder misfire code before, but it manifested first as a transmission code issue on a 2003 Impala.

If I recall there were some contradictions in literature during that model year for GM V-6 engines WITH the Eaton Supercharger. If your engine falls in line with that, you have more research to do. If not, you have lots of troubleshooting ahead.
 
Originally Posted By: JAM25
Hey Bob Oil Gang,

In my 1999 Olds Cutlass I have my check engine light. I went to AAP so they can scan the car and it got a code. I dont remember the code but the guy told me it was a random misfire. I had told him what could the problem be? He said its mainly Spark Plugs and Wires. Now. I dont think thats the problem.becausr i had just replaced them little over a month. OEM models. AC Delco wires and Plugs. The car starts right up and idles smooth, not rough. What could cause this random misfire? Ive also noticed that my gas mileage is horrible i get like 12-13MPG city and like 20-22 MPG highway. When its estimated at 17 city and 28 highway. Ive also noticed a loss of power when trying to speed up. Ive asked my dad since hr passed tbis car to me. If he had ever had any problems with it, he said nothing major just simple quick fixes.

I asked him if he has ever replaced the o2 sensor, fuel filter and he said no. Now ima try snd buy the fuel filter this weekend and replace it. O2 maybe in the next couple weeks. Since its darn expensive.

Now again. What can cause a misfire? Will me replacing what i me.tioned help fix it? If not what could i do in regards to looking for other parts that could have cause this. All i do is mainly city driving so stop and go short trips. I do live in chicago. Hopefully is nothing major because imnalso trying to.learn automotive technology now that ive graduated and received my law enforcement degree.

Any help is appreciated.


Check all the electrical connections you possibly can .

Check all the vacuum connections and hoses you possibly can .

Look under the hood , at night , with the engine running . Any sparks or glow from the spark plug wires ?

Again , get the codes . I eventually bought a $ 50 code reader / eraser . Got tired of going down to the auto parts store . Finally cleared the codes ( CEL no longer coming on ) on 2 Checys .

Oh , also , make sure the spark plug wires are secure plugged in at both ends .

God bless
Wyr
 
Originally Posted By: jam25
I dont think thats the problem.becausr i had just replaced them little over a month. OEM models. AC Delco wires and Plugs.

Did it start this right after doing this work? IIRC this uses wast spark ignition with 3 coils?

Make sure the plug wires are going to the correct terminals you may have a crossed wire.
 
I recall a friend of mine who had their vehicle tuned up once who had a couple of spark plugs fail. Basically the center electrode was not bonded properly to the porcelain which caused it to ground to the heads during driving. That came back as a random misfire code along with cylinder 4 (yours may vary).
 
Originally Posted By: Trav
Originally Posted By: jam25
I dont think thats the problem.becausr i had just replaced them little over a month. OEM models. AC Delco wires and Plugs.

Did it start this right after doing this work? IIRC this uses wast spark ignition with 3 coils?

Make sure the plug wires are going to the correct terminals you may have a crossed wire.


Ha, seen this one on a Cavalier years ago.

Was a bit tricky to figure out...
 
we may help you once you give us trouble code...
After this we can check code in database of check engine code site
 
A random multiple cylinder misfire is usually code P0300. You need to get a spark tester and start checking for spark. You could have a bad Coil Pack or a bad Ignition Control Module. You won't know which one unless you do a spark check.
 
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