Tech Tips: Miscellaneous by Christopher Sass...

The Noise That Annoys

After 13 years of having Fiero's around, I think we sometimes assume everyone knows some of the more common maladies. I also tend to think that if I've managed to discover the cause of a problem on my Fiero by myself, then every other Fiero owner must already possess this knowledge. The inaccuracies of these statements were brought to light at a recent meeting when one of our members, who has considerable knowledge regarding Fiero's, complained about an annoying squeak emanating from outside his car when the car is in motion; particularly over bumps. Immediately every other member sitting around the table diagnosed his car's problem without hesitation. It's the exhaust system!

The exhaust system on the 2.5L and the 2.8L are similar in the respect that they use hangars and springs to keep them in place. The 2.5L has two hangars and ten springs. The 2.8L also has two hangars and ten springs. The four cylinder's have two types of hangars. One is an inverted "L" shaped piece of steel with a U-bolt to undersling the exhaust pipe. It is located on the passenger side behind the cradle front cross member. The shorter leg of the "L" has a rubber isolating pad attached to it. This pad, which faces down towards the ground when the hangar is in place, rests on the top side of a transverse frame rail. The problem I experienced with this hangar is that, due to minimal clearance, the factory only installed one nut on the U-bolt. Consequently, after years of driving, this hangar became loose and rotated 180 degrees so that it was dragging on the pavement. The fix was simple. I reinstalled the hangar in position and installed a new nut on the U-bolt. The difficult part, and I suspect the reason the factory didn't install the second nut, is that when the hangar is in place, there is not enough clearance to get the closed end of a box wrench over the end of the U-bolt and therefore you must use the open end. Clearance to the sides is at a premium, allowing only a quarter turn of the wrench before you must remove it, turn it over, place it back on the nut and turn another 90 degrees.

The other hangar is at the rear of the car in front of the exhaust tip(s). The 2.5L has one of these and the 2.8L has two of these, one for each exhaust. These hangars are steel "U"-shaped hangars with a rubber strip fastened to one end. The rubber strip acts as a shock absorber to compensate for vibrations.

There are also various springs to keep everything in place, and while Pontiac thankfully chose to give us stainless steel exhausts, these springs are mild steel and therefore will corrode and disappear long before our cars are used up. The 2.5L has ten springs, three on each end of the muffler, that hang off of brackets attached to the frame, two springs from the exhaust to the left front corner of the cradle, and two from the exhaust to the right corner of the cradle. The 2.8L has ten springs, two from the exhaust to the left front corner of the cradle, two from the exhaust to the right front corner of the cradle, and three on each side of the muffler.

If any of these pieces are missing, damaged or broken, you may experience a squeak or chirping noise as you negotiate bumps in the road. After the meeting, we went outside and pushed on each of the tailpipes of the car and sure enough, one of the pipes moved easily and recreated the telltale sign that something was amiss with the exhaust system.

If you have any questions or concerns, or if you've solve a problem that you think is specific to your car or that "everybody must know about", let us know anyway. What seems like common knowledge may be news to someone else; what you consider unique to your car may be a common problem for many. Send a letter, E-mail or call.

Some Good News From the Repair Front

In a recent issue of Fiero Focus, Byron told the tale of his repair woes. Although he did finally receive satisfaction, his experience is becoming too common. The more people I talk to, the more I here about various garages that are unwilling or unhappy to work on Fiero's. I don't really understand this mentality because Fiero's are not really that difficult to repair.

I recently have had a good experience which I want to share with the membership. I needed some work performed on my car and I notified the nearest Pontiac dealer which happens to be Currie Motors in Elgin, Illinois. Currie Motors is listed in every issue of Fiero Focus. Currie will give NIFE members a 25% discount on parts and a 10% discount on labor. More importantly however, they welcome Fiero's. I dealt with Greg Dubas who is professional and interested in taking care of his customers. Currie Motors has a technician, David Grens, who actually doesn't mind working on Fiero's and is an excellent trouble shooter. I diagnosed my problems myself and asked them to perform certain work. David Grens, in turn, looked the car over and decided that some of the work I requested was not necessary and he suggested other work that should be performed. They also had no problem with selling me the necessary parts for the work they diagnosed which I felt I could perform myself.

Greg Dubas was very good about keeping me updated on the status of the work since the car couldn't be finished within the agreed upon time frame due to the necessity of having to order parts. (Obviously having cars which are as old as thirteen years old means parts unique to the Fiero are most likely not going to be in stock.) As an added nicety, they called about two weeks later to inquire whether I was pleased with the service and the repairs. This is the first time in twelve years and three Pontiac dealerships (including the dealership I purchased the car from) that a Pontiac dealer followed up with me!

Throttle Position Sensor Equality

Are all Throttle Position Sensors equal? Yes and no. There are two types of Throttle Position Sensors (TPS) used in Fiero's - adjustable and non-adjustable versions. The 2.5L TPS from General Motors is non-adjustable. Some aftermarket versions are adjustable. The same goes with the TPS for the 2.8L. Both types function within an upper and lower limit. The non-adjustable TPS has narrow parameters which obviously can not be modified. The adjustable TPS functions within parameters which can be "slid" up and down. The adjustable TPS can be identified by the slots in it. This adjustment must be performed using a voltage meter. The adjustment is not a simple "cause and effect" modification because whatever parameters are set are interpreted by the ECM which modifies other controls.

Additionally, the parameters may vary from TPS to TPS due to manufacturing tolerances and the affects of other components. So my original TPS, which eventually failed and was removed, provided a faster cold and warm idle and better throttle response, (which also uses more fuel) than the new identical TPS. Presumably, the car will use less fuel but it provides less satisfactory throttle response when cold. The throttle response when warm appears satisfactory.

Other differences are the heat shield which should be in place to protect the TPS from manifold heat. One shield attaches at the EGR valve; the other at the TPS. It is unclear which was used when, but Elmer Schild reports they can not physically both be installed. Elmer also feels that the shield connected to the EGR may be better because you don't necessarily want a metal heat shield, which conducts heat, being attached to the part it is shielding from heat.

So are they all equal? Yes and no, but they are close enough that they perform the intended function and vary enough to produce noticeable changes in performance. Besides, if you have a 2.5L, there is nothing you can do about it short of changing out the TPS until it produces performance that is satisfactory.

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