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1999 GMC Sierra Hesitation - won't take gas

I have a V8 with bad hesitation to the extent it will not take gas (with backfire at time). It occurs when cold (sometimes) and when it restarts (sometimes) after a brief engine shutdown. We have changed the gas filter and replaced the fuel pump with no change in the symptoms. There is no error recorded in the computer. We have had it to a GMC and a Chevy dealer and they both are unable to find the problem. It is happening more frequently as time goes along. Any ideas?


*Faulty emissions systems
*Faulty secondary ignition system (cracked spark plug insulator or faulty plug wires)
*Fuel injection system not functioning properly
*Vacuum leak at throttle body, intake manifold or vacuum hoses or possible sticking valves.

What say you bmerrill?

Have any luck?

My 1999 GMC Sierra does the same thing… mostly in the morning when it’s cold here in Maine… wait, it’s always cold in the morning here in Maine… (this is where you guys are yucking it up!) It feels like it’s not running on all 8 cylinders and when you step on the pedal, it seems like I’m just crowding the engine. Then it might backfire and the transmission will wind to 5000rpm… whereupon I back off the accelerator and give it a minute, then the other cylinders seem to catch up and go and all is fine for the rest of the day. I took it to the dealer that said it’s time for it’s 100,000 mile tuneup and they put in new plugs… I asked them to check the spark plugs wires and they say they couldn’t find anything “wrong” with the wires… but the truck still hesitates even after the “tuneup”. (Friends have advised that I change the wires anyway, since they have 100,000 miles on them.) Since it backfires, I presume the injectors are functioning. What think ye? How does one “check” the spark plug wires? PS> I love my truck… I hope to have it for another 100,000!

No luck - same problem. The check engine light used to come on occasionally but no code in the computer. Now the check engine light is on all the time. I have an appointment to check it out - perhaps now I’ll have a failure code.

If you really like messing with machinery. I hate giving bad advice (so often) but here we go again. Change the channel quick; this is sounding like The Dragon King. Why isn’t Caspar Van Dien in that? I had this 85 Caddy, see… When my problem happened I disconnected the battery for a few seconds and reconnected. The computer rebooted and the problem went away for a couple days. I changed the computer and the problem never returned. Oh, if everybody could be so lucky, I would do the same thing on every GM car. If only you had the right car. Too bad I can’t pass the luck to everybody else. I hope nobody reads this.

One sensor that is key to off idle, transition, and acceleration is the Throttle Position Sensor. During transitions the ECM goes to open loop to forestall driveability problems. Thus, it is not using the oxygen sensor in its fuel calculation and using the TPS to select tabled data for the enrichment. Once the ECM sees steady conditions it switches back to closed loop for emissions and economy.