Each Morning when I first start my 2007 3.8 Sorento (127k miles) it misses like it has a weak cylinder. You can literally count 1001 to 1018 and the engine clears and runs fine. Rarely does it set a code. No matter how many times the engine is started during the day there are no more problems, even if the engine is left off for 6-8 hours. Replaced spark plugs, still no joy. Placed dry gas in tank still does it. Checked PCV valve, hoses, wires for leaks and bad spots, all look good. At 18 seconds the engine runs normal and goes through the warm up cycle. My diagnostic tool shows that everything is within the limits on live feed. The rpm is around 1500 when started and reduces at what seems to be the normal rate for the weather. I've had this vehicle since it was new. The only thing I can add would be every couple of years when I would start it up it would miss and buck like crazy, Shutting the engine off and restarting would solve the problem and it wouldn't disappear for several years. Once the problem clears there is no bulking at acceleration, no misses, runs great. What could it be?
fisco
Things I would check,
- Are you losing coolant ?
- Pressure test cooling system when cold..
- Pressure drop the injectors before first start,
- check in cylinder with borescope, look for fuel/coolant contamination..
Perhaps a bad coil? As it warms up the connections come back together and all is good until next time...
Did you do the plugs or a shop. If you over tighten a plug, sometimes the ceramic insulator will crack. Again, when cold its open and as it warms up, the short closes off and the plug works. Since this repeats only on cold start, then goes away, it is going to be a tough one to run to the ground. You may have to leave it over night at a trusted mechanic to look at whilst in the garage, hooked up to some diagnostic equipment....Or, since it goes away in short order, live with it.
Keep us in the loop please as you discover what's going on!!
Did you do the plugs or a shop. If you over tighten a plug, sometimes the ceramic insulator will crack. Again, when cold its open and as it warms up, the short closes off and the plug works. Since this repeats only on cold start, then goes away, it is going to be a tough one to run to the ground. You may have to leave it over night at a trusted mechanic to look at whilst in the garage, hooked up to some diagnostic equipment....Or, since it goes away in short order, live with it.
Keep us in the loop please as you discover what's going on!!
Well that would be easy and quick to check, connect an amp clamp and scope to a fused shunt on the coil circuit, the resulting waveform will tell you all you need to know.
Thank you for the response. The problem started before I changed the plugs. I just pulled the plugs checked the gap and inspected them. They looked fine. I am not losing coolant. my coolant is clean, no evidence of blowby. My next plan is to replace the coil packs or take it to the dealer for a diagnostic. I don't have a scope. I have a hard time taking it to a dealer because I have always done all repairs even up to replacing and rebuilding motors. However, I may end up there. One thing I noticed on the live data what seems like a lot of ignition advance when it is cold. Does anyone know what the advance should be cold?
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