1999 Chevy Silverado 4.8 l V-8 mileage 136,000

JUKBX69

MEMBER
1999 CHEVROLET TRUCK

Truck misses when ambient temp. Is below 45 degrees. It runs very rough until engine temp is warm, then runs perfectly. When ambient temp is above 50 upon start-up, there are no problems.

The fuel pump reads 59 to 65 psi, the injectors balance within 1/2 pd of each other, replaced O2 sensors, cleaned throttle intake and bore, installed new plugs and wires, and installed a new 2-wire temp sensor next to the number 1 cylinder. Also installed new fuel filter.

There are no codes from the scanner and all parimeters seem to read within normal range.

What can be done to fix this problem!

Thanks you for any help you can provide.

James

2 Replies

BLACKOP555

MECHANIC
10,371 POSTS

Clean your MAF or AIS, they are known to get dirty enough to malfunction but not enough to throw a code!

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Tuesday, November 27th, 2007 AT 9:03 PM

PEAR69

MECHANIC
1,482 POSTS

THERE ARE TWO COOLANT SENSORS
There is a sensor called the I.A.T. Sensor--Intake Air Temperature. It's mounted on your or in your intake duct by the air cleaner. There is also an E.C.T. Sensor--Engine coolant Temperature. This sensor is located in the front, top of the engine or front of the lower intake manifold. Both of these sensors work the same. They both are resistors which vary in resistance according to temperature. This resistance varying resistance tells the injectors how much fuel to let into the engine. One or both of these sensors are probably the cause of your problem. The problem is, it is difficult and time consuming to test these sensors for proper operation. I very rarely suggest this but it's easier to just change these sensors than to struggle with testing them.
The coolant sensor you changed has nothing to do with fuel injector performance. This coolant sensor is the one that is connected to the gauge in your dash.