Hello,

My name is Livan and I have a question regarding my mother's 95 Gran Prix SE with the 3.1L V6.
We are having a horrible problem with hesitation and/or chugging at freeway speeds under light to medium throttle inputs. Both my father and I are certified mechanics and we have both tossed our hands up.[sm=headbang.gif]

Some additional history: The problem began as a light to almost intermittent chuggle under light throttle at freeway speeds. The problem then evolved to turning on the check engine light. The scanner indicated an EGR problem (sorry can't remember code of the top of my head).
1. The EGR was changed, slight improvement but still illuminated the check engine light and reported the same code.
2. Checked all hose and wiring, replaced all vacuum hoses, no change.
3. Took the intake plenum off -- thoroughly cleaned the plenum and throttle body, as well as the EGR pipe and all EGR portals and of course replaced the gaskets, check engine light no longer illuminates and no codes are stored, hesitation and chuggle still persist. Please help![sm=dontgetit.gif]


Anxiously waiting reply,

Livan

wow it sounds like most of the bases are covered....tough one[:@]

I forgot to mention that we also replaced the ECM. [:'(]

What do you think about the Crank position sensor?

could be CPS, MAP sensor....

if it was a CPS, it would have starting issues.

Well the mystery is solved. It was the CPS, the car runs perfectly now! [sm=gears.gif]

Although I need to perform a lerning procedure assuring proper allignment of the CPS and Crankshaft. Does anyone know how to perform this procedure? [sm=nerd.gif]

wow..everytme that i have heard of a bad GM CPs, the car wouldnt start...

Well this car is something else. The problem is back but not as severe. [:'(]

I took the car to a friend who has a Tech 2 scanner for GM cars but to both of our amazement the car does not have the learn mode capabilities. So no adjustment or sync is necessary. [sm=dontgetit.gif]

I then decided it might be a ground issue so I cleaned some of the contacts as this being a MN car there is some although insignificant corrosion (wire has slightly green, whitish powder on it) on the battery to chassis connector. This believe it or not made a big difference in the light lummens (brightness), window operations (up/down speeds), and yes it improved but still continues with a minor stumble, ONLY at freeway speeds. I no longer can simulate the problem under brake load.

Tomorrow I will check all other ground points and TCC.

Stay tune for the SAGA of the coughing Prix! Robitussin anyone!!! ;)

i am intrgued...

I don't know if I am on base here but have you check you cat-convertor for plugging.
Seems to me that if you are at freeway speeds you car will not run well if it does not have full exhaust flow????