2003 Oldsmobile Silhouette engine miss

Tiny
JBLASKI13
  • MEMBER
  • 2003 OLDSMOBILE SILHOUETTE
  • 3.4L
  • V6
  • FWD
  • AUTOMATIC
  • 203,200 MILES
Have a 2003 Oldsmobile Silhouette 3.4L that has recently started to misfire badly. I know the design of these engines is susceptible to head gasket leaks, but the temp remains well within the normal range and it does not appear to be losing coolant as you would expect with a leaky head gasket. With the trans in P or N, the engine will idle roughly, but if you give it enough gas to increase rpm to 1500 & above, it smoothes out & appears to run just fine. In gear, however, the miss is almost always present. It will intermittently disappear if the engine isn't under too much load, but for the most part, a misfire in 1 cylinder (sometimes 2) is always obvious. The codes I was able to retrieve are: O2 sensor (2X), Bank 2 Lean, Fuel System Pressure, and Random Multiple Misfire (2X). Then the same code sequence repeats. I have checked the coil packs, wires & plugs. All check out ok. The underside of the oil fill cap will occasionally have a very slight tinge of evidence of coolant mixing, but the oil on the dipstick looks normal. Not what you would expect to see if there were a head gasket leak large enough to cause a bad misfire, and again, the coolant level has not dropped, and the exhaust doesn't have the "white smoke" appearance usually seen with a blown head gasket. Am I too easily dismissing a possible head gasket o problem? Could a bad O2 sensor cause that kind of misfiring? Or where should I look next?
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Tuesday, February 24th, 2015 AT 6:45 PM

14 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
IF you see a slight discoloration under the oil fill cap, chances are that is just from condensation. Maybe the PCV isn't working properly.

Since you have a lean code / O2 sensor, I have to question a vacuum leak rather than a head gasket or low fuel pressure. Have you checked for any of those issues?
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Tuesday, February 24th, 2015 AT 6:54 PM
Tiny
JBLASKI13
  • MEMBER
No, I started first trying to rule out electrical / ignition issues. I'm honestly not that familiar with O2 sensor issues, so when that code showed up twice, it got me thinking. My next step was to check for vacuum leaks. I considered the possibility of a bad EGR too, but wasn't sure the symptoms matched. I didn't want to just start replacing parts. None of those are terribly expensive or difficult to replace, but why fix what ain't broken, you know?
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Tuesday, February 24th, 2015 AT 7:11 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Start with fuel pump pressure. See if that is in spec. If it is, then I would start searching out vacuum leaks. When there is a lean mixture issue, usually it is a vacuum leak.
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Tuesday, February 24th, 2015 AT 7:38 PM
Tiny
JBLASKI13
  • MEMBER
Also, a detail I left out inadvertently. Upon initially starting the engine and until the engine begins to warm up, there is a strong smell of gasoline. After the engine begins to warm up, the smell dissipates.
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Tuesday, February 24th, 2015 AT 7:48 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Are you certain there are no leaks? Also, if you smell gas, I'm now question the coolant temp sensor as a problem. If it tells the computer it is colder than it actually is, the computer will compensate by making the fuel / air mixture too rich. However, that doesn't add up with a lean code.
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Wednesday, February 25th, 2015 AT 3:41 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Do me a favor, check to make sure none of the injectors are leaking both the rail and where they go into the engine. You may have a bad o-ring allowing a leak when cold. When it gets warm, the steel expands and may be stopping the leak. (Just a thought)
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Wednesday, February 25th, 2015 AT 3:42 PM
Tiny
JBLASKI13
  • MEMBER
Ok. I'm truly at a loss now. Maybe.
Vacuum ok, fuel pressure ok. Still misfiring but no longer getting Bank 2 Lean code. Here are the codes I have now:
P0128 Coolant system - possibly thermostat or faulty sensor
P0132, P0134, P0135, P0141. All 4 are O2 sensor codes.
P0440 Evaporative Emission control system
P0300 Random Multiple Misfire.
So now I'm a little lost, but thinking maybe bad EGR or plugged catalytic converter.
What do you think?
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Saturday, February 28th, 2015 AT 11:29 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Does the engine warm up to a normal operating temp?
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Saturday, February 28th, 2015 AT 11:48 AM
Tiny
JBLASKI13
  • MEMBER
Yes. And it runs very rough until it begins to warm up
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Saturday, February 28th, 2015 AT 11:51 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
I could be wrong, but I THINK the coolant temp sensor is sending the wrong info to the PCM. The result could be an extremely rich or lean air / fuel ratio. The PCM will compensate for outside temps. For example, if the engine coolant is 100 degrees and the sensor tells the PCM it is -40 degrees, the PCM will allow the injectors to stay open longer so the engine gets more gas to run under those conditions. The result then could be a lean, rich, O2 sensor readings and allow the engine to run poorly.
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Saturday, February 28th, 2015 AT 11:58 AM
Tiny
JBLASKI13
  • MEMBER
Ok so I changed the ect sensor & the harness. Still having the same issue.
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Saturday, February 28th, 2015 AT 1:00 PM
Tiny
JBLASKI13
  • MEMBER
Question. If I were to hit a huge pothole & somehow the catalytic converter happened to get snagged & fall off, would the O2 sensor mess up the fuel air ratio even more? There is unfortunately an aft sensor on this vehicle.
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Saturday, February 28th, 2015 AT 1:06 PM
Tiny
JBLASKI13
  • MEMBER
I noticed something this afternoon. The harness to the EGR was unplugged. I must not have plugged it back in when I checked the wires a couple days ago. Here's the thing: with it plugged in or not plugged in. Still runs the same. Rough idle, loss of power, etc. So you think the EGR could be bad?
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Saturday, February 28th, 2015 AT 7:51 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Yes, a missing catalytic converter will cause O2 sensor issues. As far as the EGR, it could be. However, before just replacing it, I would recommend that you have it checked.
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Monday, March 2nd, 2015 AT 8:47 AM

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