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1998 Chevy Tahoe LT 4x4 4-door, 5.7L, 125,000 miles, "service

engine soon light." I drove...
1998 Chevy Tahoe LT 4x4 4-door, 5.7L, 125,000 miles, "service engine soon light." I drove a little less than 300 miles on the freeway two weeks ago. The last 30 miles of the trip are over a mountain pass with increased road grade and decreased temperatures. The temperatures were in the 60s until reaching the mountain where they were in the 50s. I set the cruise control to 70 MPH for the whole trip and the engine stayed at about 2000 RPM. Upon reaching the mountain and climbing the hill the transmission shifted down a gear as expected to maintain 70 MPH. As a result the engine sped up to about 3000 RPM as expected. After less than a minute the service engine soon light came on and flashed. I slowed down and the light remained on steady without flashing. The engine felt as though it was running smoothly except for one slight stutter at the beginning of the hill climb. All gauges read in the normal range. I drove the vehicle back with what seemed like no problems other than the light staying on. After about 100 miles the light shut off and did not come back on. A week later my mechanic read the diagnostic code, which indicated cylinder #7 was misfiring. Based on how the engine ran (smoothly) before and after the trip I did not feel as though the engine had a misfire. A couple months ago I had major service on the vehicle including changing all spark plugs, filters, and drive train fluids for a few hundred dollars. My mechanic thought the spark plug wire was possibly the problem so he replaced the set for another $125. I made the same road trip yesterday under the same conditions. As I reached the mountain the transmission shifted down a gear again and revved up to 3000 RPM again. After about 10 seconds the service engine soon light came back on flashing. I left the cruise control on and maintained 70 MPH. The light stopped flashing when the transmission shifter up to OD and the RPMs dropped back to 2000. There were no stutters or hesitation this time. I drove back home as I did last time but this time the light stayed on and remains on now. Based on this information, what do you believe might be the problem causing this to occur?
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Answered in 6 hours by:
9/6/2010
Tim's Auto Repair
Category: Chevy
Satisfied Customers: 16,170
Experience: Have owned a repair shop for 25 yrs.
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hi

get me the code..if you have no scanner..auto zone and most parts stores will scan it and give you the codes for free..the code for #7 miss fire is p0307....if this is the case..you may just need to regap the spark plugs.the gap is to be at .060..if the plug gap isn't right it may give this code

thanks

 

 

Tim's Auto Repair
Category: Chevy
Satisfied Customers: 16,170
Experience: Have owned a repair shop for 25 yrs.
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Customer reply replied 7 years ago
the plug was only a couple months old when this occured two weeks ago. The #7 platinum spark plug looked fine when the mechanic was diagnosing the problem but he replaced it a few days ago when he changed all of the plug wires just to eliminate it as a problem. The light finally went out on its own this afternoon. I took the Tahoe to the mechanic later today after I told him the problem had repeated itself. He plugged in the diagnostic computer and told me it again said the #7 cylinder was misfiring. I sent him a message asking for the actual code number but I have not heard back from him yet.

hi

it will be p0307..

sense you have had a tune up.....check the compression on the #7 and compare it to the compression on the other cylinders..if that is fine,,again check the plugs,sense this started after the tune up...the other possibility would be a bad poppet injector on the fuel meter body[spider]

thanks

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