1998 Monte LS - Random Hesitation, Bucking
 

Alright, so my 98 Monte LS (3.1) s doing something strange. <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p>
If driving the car up an incline around 1600-2100 RPM, the car will start bucking or hesitating. If I give it the gas it will go away.<o:p></o:p>
I have replaced.<o:p></o:p>
All 3 Coil Packs along with the ignition module . All Brand new.<o:p></o:p>
The Spark Plug Wires<o:p></o:p>
The Spark Plugs<o:p></o:p>
My friend also told me that my car had thrown a code about the knock sensor. So I replaced that with a new one along with the connector and 1 foot of the wire to the connector.<o:p></o:p>
The car still does it and it is driving me crazy. What else could it possibly be?<o:p></o:p>
PS if my drive is on a relatively flat plane, it will not do it and it will drive like a champ. <o:p></o:p>

Do you have any codes? Knock sensor very rarely go bad. This sounds fuel realted, or fuel air mixture. Since you state this happens on an incline, does it buck going down a hill, or only up a hill?

I should have added, what level of gas in the tank, 1/2 full ect? Does it matter, does it at any tank level?

I have absolutely no codes whatsoever. No MIL light. I use Torque for Android and a BT ELM 327 with my car to check regularly if there are any pending and there are none .
I know Knock sensors normally don't go bad, but like I said my friend hooked his reader up to it at his shop and he said there was a pending Knock Sensor Code in it ( It has since left ). It sounded good and symptoms fit somewhat, but a new one w/ a new cable didnt fix it. I guessing that the knock sesor code must of been from all the bucking the one day when I was trying to make it up a 2 mile hill.

The tank level does not matter, I am currently running at 1/4 tank which I just filled a couple days ago w 93 Octane. No difference.

I had the car to 2 shops and no one can give me a straight answer at this point. THe Fuel pressure did check out yesterday. SO now I am wondring if it could be a Cat Converter or something.

I also have to make mention of one other thing.. During the trip up that 2 mile hill ( Last week ) , I did have my check engine light come on. It was for a misfire on cylinder 5 and only going up the hill and that is when the car was bucking real bad. By the time I got home later that evening ( 200 miles later ) the light went out.
In the morning I pulled the plug and checked for damage, and it was fine and the gap was still set. It never threw the misfire code again.

ANd to answer the other question.. This only happens uphill or at least a slight incline in the 1600-2000 RPM range

Its not throwing any other codes? to me this sounds like a TPS. Girlfriends car did almost the exact same thing at higher RPM and it ended up being that.

My take is fuel starvation on incline. I think there is trash floating around in the tank, and the suction side of the pump is picking it up on an incline.

I will look into it. Any other thoughts are appreciated as well

Well I replaced the TPS sensor on the car, It did not make a difference whatsoever. I am out of ideas. I think I am going to seafoam the intake and gas tank later on this weekend..

My take is fuel starvation on incline. I think there is trash floating around in the tank, and the suction side of the pump is picking it up on an incline.

If it wasn't tps I agree with the above its fuel. Take the filter off and smack it on the ground, if a lot of crap comes out then my advice is to flush or replace the tank and replace the filter

I am actually starting to narrow it down. "I think" . I have a BT Elm327 that I use with my phone and car. I have been driving around and looking for a constant that always happens when it is hesitatiing. The constant is, when I am driving around and the Vacuum pressure raises to -2 to -5 it strarts its acting up. I am guessing that I have a vacuum leak somewhere. Also when sitting at idle my Vac pressure is only -9.1 in/hG which stays constant. I believe it is supposed to be higher than that, like -17 to -21

It was an EGR Valve, issue is all resolved. Once I was able to narrow it down to a Vacuum issue and I brought it to my mechanic. He said that EGR valves can show as a massive vacuum leak.. IT has been replaced and is running great now.