I have a 2002 Buick PA (not ultra) that is giving me fits. It sputters and hesitates during acceleration but only when going forward. I can back up as fast as I want and it never sputters or hesitates. The SES light is not on and there are no codes in the computer.

My mechanic noticed the car runs right when the MAF and AIT sensors are unplugged even though the SES light come on. So he changed those along with the TPS but no luck. Since the problem was still there he reinstalled my original parts, charged me nothing and suggested I take the car to the dealer.

The dealer charged me $1500 to change the MAF, TPS, IAT, AIT and MAP sensors but no difference in how it runs. I was surprised that they asked for $1500 without telling me the car wasn’t fixed. I took it back to the dealer and they now want to change the PCM but they won’t give a guarantee changing the computer will fix the car. I sense their plan is to change parts at my expense until the car works or I run out of money.

I bought a cable and some software thinking I could compare the readings from my 1999 Alero 3.5 with those of the Buick and perhaps get a clue to a sensor or something that isn’t functioning normally.

What I noticed is that my spark advance is all over the place during acceleration (see below). I then compared to the spark advance with the MAF and IAT sensors disconnected and believe my problem definitely has to do with the spark advance.

My questions to you fine people are what do you see in these graphs? What sensors effect or impact the spark advance?

This is the chart with the sensors connected IE.. car messing up.



Here is the chart with the sensors unplugged which means the SES light is on but the ICM is controlling the spark.

Can you scan for something called Knock retard? Or KR. You may have a bad knock sensor.

Those pictures look hard to read and I don't see an edit button so here is another stab at the graphs.

Sensors connected



Sensors unconnected

Yes, I can try that tomorrow evening. I think I saw two knock PID'* in the software.

Any idea how I can post a better picture of the graphs? Is it photobucket or this site?

The pictures look fine to me. Also change your MAF scan to hz instead of lb/min. Put the KR scan in the same area as timing as they are interconnected, as KR goes up, timing goes down.

These are image shack...

Connected

<a href="http://img829.imageshack.us/i/buickconnected.jpg/" target="_blank"><img src="http://img829.imageshack.us/img829/4491/buickconnected.th.jpg" border="0"/></a>

Unconnected

<a href="http://img24.imageshack.us/i/buickunconnected.jpg/" target="_blank"><img src="http://img24.imageshack.us/img24/6315/buickunconnected.th.jpg" border="0"/></a>

Oh, then I guess it'* my cheap computer. It is hard for me to see the posted pictures but the ones on my machine are very readable. I guess I'm done uploading shots now...

I'm wid Dan. We need more info, but it'* looking good so far.

Let me begin by saying I added knock retard and it appears to be responding to the conditions taking place and not necessarily the cause. I say that because it never seems to indicate anything until the problem is occurring and never simultaneously or before. However, I don’t know what the difference is between this “knock retard” measurement and what the actual sensors are up to.

I also did some reading and tried to focus the measurements around the PCM, Fuel and ICM signals. I suspect I have a bad wire since at times this thing runs great and at other times I'm afraid the motor is going to fall out. Today was a fairly good day and it wasn’t noticeable taking off from a start but you could feel a few chugs when asking it to accelerate. It also seem to smooth out quickly today.

The left side of today’* graph you can see my take off was fairly smooth (not too noticeable) but I let it calm down a bit a tried to accelerate and you can see a little chugging. I guess intermittent problems never surface when you want them to, just at the worst possible moments in our lives. I drove for about an hour and this was as bad as it got.

Here are my observations, the 18x signal seems to peak at 1668 RPM’* and that’* when the whole darn thing goes buck wild. Is that normal for it to peak like that? I am just curios why it doesn’t continue to rise like the engine and 3x RPM???

I also find it strange that the IAC valve seems to be stepping during all of this?

Lastly my fuel rail pressure and CAM signal doesn’t seem to be registering. I don’t know if that’* just the software I’m using or could that be indicating a problem since I obviously have both.

What do you all see in the graph? I bought a multi meter but what wires should I be checking?