Engine Performance problem
1989 Chevy Cheyenne 6 cyl Two Wheel Drive Automatic 161300 miles
Here is the problem: Truck runs high idle at start up, and sometimes it will go down as it warms up. When in idling in park before it is warm there is occasional misses (spit and spatter). When it warms up still in idle it misses even worse and will surge from high to low idle and at times has stalled. When driving there is a noticable loss of power because it constantly wants to stall. The missing and sputtering happens at all speeds. There is a distinct rich exhaust smell. Here is what we have done so far: First we scanned the computer and it read it was the O2 sensor running rich. We replaced it and gave it a tune up. In the quest to eliminate further possiblities we also replaced the MAP sensor, cap and rotor, ignition control module, electronic spark control, TPS, EGR valve and gasket, IAC, engine coolant temp sensor. In addition we have checked the timing with a timing light. Also we have had 3 different throttle bodies and the problem has never changed. We also put another distributer in, no change. We changed the fuel filters (both internal and external) last year due to another problem. Fuel pump was also replaced. After all this and scan still says running rich! After the open loop closes there is a distinct difference in the operating. What else is there? Please help!
Temp sensor replaced was it CTS located by thermostat? If yes check for 5v on yellow wire key on no start. If present use small wire ie. Paper clip and jumper yellow to black on connector. Run is there improvement? If yes CTS faulty if no need to OHM check black wire to ECM connector D terminal #2.
Let me know results
Thanks for donate
June, 14, 2010 AT 11:48 AM
We checked the CTS the way you said to, and that was not the problem. The wire read 5v. The black wire to the ECM, it's continiuty was good. Is this a possibility that the ECM is bad, or are there other tests you think we should do? The black wire that goes to the ECM is also shared by the TPS, is that normal? What else there to do? Let me know thanks!
June, 14, 2010 AT 12:03 PM
Was code 45? Disconnect wire from O2 place DVOM pos lead to O2 groung black. With engine at op. Temp. What is voltage?
June, 16, 2010 AT 12:32 PM
Ok, we had a slight issue with the starter, but we finally got to check the voltage and it is running between 1 and 4 volts. It is constantly fluctuating.
June, 16, 2010 AT 1:05 PM
You disconnected O2 at connector put POS lead on wire to sensor and grounded and got 1-4 v that is not possible max output on O2 is 1V try millivolt scale
June, 16, 2010 AT 1:38 PM
Ok, checked it again it says 1v. This is what is happeneing; when the open loop closes the truck spits sputters and chugs, and reads rich on the O2 sensor then something happens and the truck goes into high idle and will then go back to normal back and forth rich/lean reading according to the scanner, however idle remains high. As soon as we go to drive it, it wants to chug and stall.
June, 17, 2010 AT 3:17 PM
1v tells computer at extreme rich condition so ECM cuts inje ctor pulse adj. Timing to get to correct ratio. O2 is contaminated need to replace