One of the tools you will...
One of the tools you will need is a good volt-ohm meter. An older Pontiac can get by with an analog style, while a digital one is required for ECM circuits.
Poor Grounds
Symptoms: Any Electrical Problem That Does Not Make Sense
A poor ground circuit in a Pontiac can wreak all kinds of havoc. This is especially true with a newer EFI version, but it's just as important on an older model.
The only accurate method to check a ground is a voltage drop test using a voltmeter. This simple test measures the amount of electrons caught in a traffic jam because they can't pass through the poor ground.
To perform this test, connect the positive end of the voltmeter to the ground in question and the negative lead to the battery negative terminal; then power up (turn on) the circuit.
The voltage drop on the ground should be no more than 2/10 of a volt. If it's higher, the ground is faulty and usually just needs a cleaning. A visual inspection will show the reason it failed the voltage drop test.
Don't assume the manifold...
Don't assume the manifold bolts are all tight. Confirm this with a wrench. A minor air leak can influence engine performance.
Manifold Vacuum Leaks
Symptoms: Rough Idle, Slight Pinging
An intake manifold vacuum leak that only affects one cylinder will act differently than a major leak that impacts all the bores. An intermittent miss or roughness that may feel like a bad spark plug or even very light detonation is the result of the mixture being too lean, but only in the offending bore(s).
All that is usually required is a good snugging of the bolts with a wrench to cure this condition. It is very common with an aluminum intake manifold and a cast iron cylinder head due to the varied expansion rates.
Idle Air Control (IAC) Motor
Symptom: Stalls on deceleration
GM EFI systems, both TBI and port designs, use an idle air control (IAC) motor as a controlled air leak around the throttle plate. It works in similar fashion to an old carburetor dashpot but without moving the throttle plate. The throttle plate, and in turn, the IAC pintle are prone to getting carboned up from gasoline fumes and the exhaust gas that is introduced into the manifold. When this occurs, the engine may stall or undershoot and struggle to idle when the throttle is released quickly, such as when coming to a stop sign.
To remedy this situation, clean the throttle plates with throttle body cleaner and do the same with the IAC pintle.The IAC will need to be removed to clean its pintle. Reinstall everything and take the Pontiac for a ride. On some early TBI EFI models ('82-'84), the idle may stay high for a few miles until the system reteaches itself. After a few miles and one ignition key cycle on and off, everything will be fine.
Trouble Codes
Symptom: Many Misunderstand Them
A common misconception when using a scan tool to access ECM troubles codes is the assumption that the failure is in the sensor. GM makes it very clear that a trouble code identifies the circuit that is being affected. The problem can be due to wiring; a mechanical issue, such as a jumped timing chain, which would impact engine vacuum; or some other malady. For this reason, when a code is set, it's imperative that you follow the Pontiac shop manual instructions, and not just replace the sensor. If the engine does not run properly due to a mechanical or ignition issue, there may be no codes set, since the failure is not with an engine management circuit.
Further Considerations
Don't forget the basics such as performing a compression and vacuum test. Examine each spark plug electrode and insulator--they shouldn't have oil or fuel on them. To determine if a problem is fuel or ignition related, try richening the mixture temporarily by choking the carburetor slightly with your hand. If the engine responds even slightly in a positive manner, there is a good chance that the problem is fuel related. When diagnosing driveability issues, determine if the condition is impacted by speed, rpm, etc., with a test drive.
Here are few quick diagnostic tips.
Editor's note: Special thanks to our lead photo/cover models, Eric Orban and Kevin Clarkin, for participating in our photo shoot and for having a good sense of humor about it.
Often an engine may misfire...
Often an engine may misfire after new spark plugs are installed. This is due to a piece of carbon flaking from the combustion chamber and bridging the electrode gap.
The carbon button under the...
The carbon button under the coil in an HEI and needs to be examined for wear. A misfire at high rpm or engine load can occur if it is worn.
The TPI system is very prone...
The TPI system is very prone to throttle plate and IAC coking since the EGR is introduced right behind the butterflies.
Proper float level is essential...
Proper float level is essential for the carburetor to work correctly and should be high on your list of priorities.
If the fuel system seems to...
If the fuel system seems to act up without reason and then corrects itself, it usually means there is dirt in the float bowl.
To check for an electrical...
To check for an electrical draw, connect a test light in series with the battery ground cable. If it illuminates, there is a draw. Keep pulling out fuses until you locate the circuit (the light will go off).