Having problems with your 1999 Pontiac Grand Prix ?

99 pontiac grand prix that is still mis firing even after we changed plugs and wires, not sure what to do now please help

Posted / edited by AnonymousUser on : 24-01-2022

Answers :

Misfires can be caused by several things including all the parts you have already replaced as well as faulty ignition coils, faulty injectors, vacuum leaks and engine mechanical problems such as low compression.
\012With the proper equipment, injector operation can be verified by performing injector balance tests, where the operation of the injectors in the misfiring cylinders is compared to the other cylinders that are not misfiring.
\012Also, engine mechanical failures such as bad piston rings or leaking/burnt valves can be diagnosed with a simple compression test.
\012An easy (and very inexpensive ) way to verify ignition coil operation is to swap the coil from the misfiring cylinder(s) with the coil(s) from the cylinder(s) that is(are) not misfiring. Then clear the fault codes and drive the vehicle. If the same cylinders are still misfiring, the coil is not the problem. If the misfire moves to the cylinder that you swapped with - replace the coil.
\012Sometimes, injectors can also be tested this way, but on most GM V-6 or V-8 engines, this is not practical due to the labor involved in "swapping" injectors.
Repair Help & Product Troubleshooting for 1999 Pontiac Grand Prix

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