Help...any ideas on what's wrong with my fiero?


jwright777
03-06-2009, 10:11 PM
I have a 1985 Pontiac Fiero, 2.8L V6. Last winter going into spring, it began to accelerate more slowly on warmer days and the car had a whining sound when trying to accelerate hard. I cleared out the catalytic converter with a screw driver because I thought that it being clogged was the problem. In this past winter, it ran fine, but on warmer days, it has the same problem that it did last year. It seems to be running rich with gasoline and in 60 degree weather will not even start. I'm thinking it's a sensor dealing with the fuel-air mixture but am not entirely sure what all of the sensors are, which ones would be affected by outside temperature and not engine temperature, and which ones it most likely is. Any help is very much appreciated. Thanks

Ragtop_Renegade
03-07-2009, 12:10 AM
The engine coolant temperature sensor has a lot to do with fuel mixture, especially cold start up. The sensor has to be pretty far off (like telling the ECM engine temp is -40 or 400 F) to warrant a check engine light. A slight glitch could report temps 15 - 20 degrees below what they really are, enough to cause a somewhat rich condition and rather poor fuel economy in chilly weather, but easily flood the engine when temps get a bit warmer. Once the engine is warmed up, it may or may not improve, depending on how far off readings are. Once the engine is at operating temperature, the system enters "closed loop" and the oxygen sensor is what primarily dictates fuel mixture. If the CTS is too far off, however, this may never happen.

Here's a quick way to test for a overly rich fuel mixture:
On a warmer day when the engine doesn't want to start, turn the key to off, hold the accelerator ALL THE WAY to the floor, and crank again. If your fuel mixture is rich, the engine will fire a few times, then catch, sputtering at first then smoothing out a bit. At this point you can play with the pedal a bit, and depending on how far the fuel mixture is off, you may be able to keep it going well enough to drive. If all of the above occur, you're defiantly rich, and perhaps in need of a CTS. (most common cause) Make sure that the pedal is all the way to the floor before turning the key on, and keep it held there until the engine is running!!! (badly or otherwise, just as long as it's keeping itself turning) Changing the throttle position with the engine not yet running will create an even richer mixture and only make things worse.

By the way, this is called "clear flood mode" and it's not a trick, hack or glitch. The ECM is programmed to look at throttle position before doing anything when cranking begins. As part of the program, if the ECM sees wide-open throttle when cranking begins, it will not fire the fuel injectors during cranking. This allows excess fuel to clear the combustion chambers and brings more air in. It effectively leans out the mixture in the cylinders until it is balanced enough to ignite. It's a neat feature and has served me well many, many times. FYI, this exists on just about every GM built gasoline powered vehicle with electronic fuel injection, from the very early 80's on up.

jwright777
03-07-2009, 11:52 AM
I should have also mentioned the check engine codes that I got:
24-Vehicle Speed Sensor (irrelevent)
32-EGR Circuit (probably also irrelevent because the hoses are all worn out)
35-Idle Speed Error (not surprising)

Last year when it had this problem, it also had Code 33-Manifold Absolute Pressure Sensor (high voltage). I checked the MAP sensor and that was working fine, so I thought that the low pressure in the chamber was caused by the clogged catalytic converter. I thought that I had fixed it when Code 33 went away, but the car is having the same symptoms as last year but without Code 33.

Ragtop_Renegade
03-09-2009, 01:38 AM
While it's probably not causing your problem, the EGR system is critical to a healthy engine. A malfunctioning EGR system can eventually lead to serious mechanical damage, such as burnt valves. Some will eliminate the EGR, which is fine, but realize the potential problems do not go away. A custom PROM should be ordered with adjusted fuel and spark curves to compensate.


Check for vacuum leaks! While they normally cause lean conditions, a vacuum leak in the right place can confuse the MAP and miss-represent engine load. Give the ECM bad data, get a bad fuel mixture.

A lack of a code does not rule out a coolant temperature sensor. In fact, most of the time the ECM can't even tell the CTS is malfunctioning. As far as the fuel curve is concerned, the ECM simply believes the current engine temp is -10 (though it's 65 outside) and richens the fuel mixture to allow a cold start. Test your CTS to know for sure.

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