QuestionThe engine in my '94 GV 3.3L was rebuilt twice. After each time the engine ran great for about two days then quit. It now backfires badly; will not rev up. Some obvious things (cp/cs sensors, coil pack, fuel delivery, sparkplug, chain, flexpate, injectors, wiring harness, etc) have been checked and still nothing. The rebuilder is baffled. Appreciate any ideas.
AnswerHi Tom,
That is frustrating, no doubt. I assume that the timing marks have been rechecked so that there is no issue with the valve timing and also that the ignition timing is o.k. because that is controlled by the crank sensor/controller.
It would be important to check the engine controller memory for any fault codes: on-off-on-off-on and leave on using the ignition key within an elapsed time of 5 seconds or less. Then count the check engine light flashes before each pause, group the numbers in pairs to form two digit fault codes, then look up the translation at: www.allpar.com/fix/codes.html
Other causes for backfiring: a vacuum leak or a malconnection/malfunction of the emission control system (check underhood sticker); egr valve stuck open (see if the stem moves when you change the throttle opening). It could also be a problem with the engine controller or a sensor that affects mixture (such as the MAP or the engine coolant sensor) that is off-value but not so much as to set a fault code. That could be diagnosed with a diagnoistic readout box that shows you some of the operating parametes, not just the codes.
Those are the standard item to check beyond all the ones you already have done. Let me know please when you find it or if some questions are still unresolved by my suggestions.
Roland
