Oldsmobile Silhouette

[oilythumb]

Hello ALL, having an intermittent problem with this van > Its a 99 Silhouette, V6 3.4L engine that has 138853 miles on it . It has a misfiring problem BUT only seems to occur

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[Trcustoms719]

1

[Matt]

Hey bud. I would start with a good visual inspection of the ignition system. It sounds like you are getting a misfire at the no. 4 cylinder when it happens. When was the last time you tuned the van up? Plugs, wires, etc. You might also do a power balance test to help check for poor ignition:

http://www.youtube.com/watch?v=bAOmUjAjNjE

For the system lean code, I would check for vacuum leaks. The 3.1/3.4 v6’s are notorious for failing lower intake manifold gaskets. You could also pressure test the cooling system which might help identify a leak at the LIG.

Vacuum leaks:

http://www.youtube.com/watch?v=9CPqbaSgcok

Cooling system diagnosis (which should include pressure testing)

http://www.youtube.com/watch?v=hUzOTnsWImI

And for your heated o2 sensor concern, the most likely cause is that the sensor is failing. But you should check your fuses, and if you can, check the circuit integrity for the heater circuit for the o2 sensor. The thing about that circuit is that even if the heater isn’t working, the o2 sensor will get heated by the exhaust gasses and function normally, it just takes a couple minutes longer. If you have access to a scan tool, then you should watch that o2 sensor, and it should fluctuate rapidly between .1 and .9 volts. The fact that you have both a heater circuit code and a lean code may both be related to the o2 sensor failing though. Good luck, and keep us posted.

[EricTheCarGuy]

+1 on Beefy’s post as that covers the basics that should get you started.

[oilythumb]

Thank you all for your input and taking the the time to answer my problem, I will be doing a tune up very soon, I have a question… I did take out the MAP sensor and ssprayed it clean as one of the codes had something to do with it, could the MAP sensor cause misfiring? .How would you check power on this engine (mainly the back three plugs).
Once again thanks in advance.

[dreamer2355]

MAP = manifold Absolute Pressure.

You can test these with a DVOM and a hand held vacuum pump. You would back probe the SGN RTN and GRND.

And what do you mean by ‘check power on this engine’?. Spark test?

[oilythumb]

SORRY power balance test

[EricTheCarGuy]

You should never ‘clean’ a MAP sensor that way you can damage it. MAP sensor readings are actually effected by misfires but don’t often cause them in other words if you have a misfire it may set a code for the MAP since it gets it’s readings from intake vacuum which would be effected by a misfire.

[oilythumb]

UPDATE: finally the problem occurred long enough for me to do some checks and found the culprit …. the spark plug.
NOW the KEY PASS light is lit on the dashboard but van still starts and drive, can anyone help me with this key pass light

[oilythumb]

UPDATE: finally the problem occurred long enough for me to do some checks and found the culprit …. the spark plug.
NOW the KEY PASS light is lit on the dashboard but van still starts and drive, can anyone help me with this key pass light

[EricTheCarGuy]

Not sure on that one, I think the dealer would be the only ones to have access to that system since it’s antitheft related. Someone on the forum might have some better input for you.

[EricTheCarGuy]

Not sure on that one, I think the dealer would be the only ones to have access to that system since it’s antitheft related. Someone on the forum might have some better input for you.

[Author]

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