Q: My 99gmc suburban backfires in the throttle body, won't start.

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It stalled but started & ran to the next light first: then would not idle unless accelerated, i made it home, from that point it hasnt started,if it did ,it was crazy erratic till it stalled.was throwing cam,crank sensor codes,I replaced both. The codes were gone but still not starting. Was told it was the fuel (spider) injectors, replaced it & still not starting. smoke & black sut in the throttle body. Days before any problem ,I did notice some rattling in the lower front of the engine while idling in park. Hope this gets me a correct diagnosis.

My car has 220000 miles.
My car has an automatic transmission.

If you were getting a rattling noise in the lower front of the motor then you engine may have jumped timing. The timing chain may have been so worn that it jumped ignition timing between the crankshaft and camshaft. That is why you had codes for the two sensors. You should do a compression test of the engine and you will find the engine compression to be low. If it is low then have the timing chain replaced.

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