|Username||Post: 88 K3500 7.4L no knock sensor, no ESC Module|
02-14-12 11:40 PM - Post#2190813
Here's the story. I bought this truck cheap...$500, the previous owner had destroyed the motor by continuing to drive it down the freeway when one of the oil cooler lines burst. I had the motor rebuilt, replacing most of the external components (temp and oil pressure sensors, fan clutch, radiator (because of the bearing bits in the oil), water pump, oil cooler lines, etc.), fired it up and let it run for a half-hour, changed the oil and fired it back up again. It was idling pretty high (1200 RPMs) and it never kicked back down. I didn't even think there was a big issue until I took it to get smogged. The techs left it running for 30 minutes in their shop thinking I hadn't let it warm up enough (I wasn't paying attention..that'll learn me) where it sat and overheated (melting the little do-dads that let my engine builder know it's been overheated, voiding my warranty) but they neglected to tell me this happened until later.
So I was....rather upset at this point, and I took it to the dealer. They said the knock sensor was "Sending a Flag" and was causing the ECM to retard the timing causing the high temp. Charge $150. I took it home and I looked and looked but could not find the knock sensor. I checked my book and found where it should be...the hole is plugged and no connector/wire. I saw on the diagram it should be connected to an ESC module...I have no ESC module or connectors/wires/mounting bracket for such a thing. I found the diagram online for the 1227747 ECM module and dug the module out of the glove box to find that I have no wire connected to the terminal where it should be (B7). I split the harness open to see if the wire was there but had the ends cut off....nope. I took the truck back to the dealer where I informed the service manager that he gave me faulty information because the vehicle does not have a knock sensor. He replied that every fuel injected vehicle ever produced has a knock sensor. I asked him to show me where it was on my truck....20 minutes later and 3 GM technicians could not show me where I had a knock sensor. He said that even though they couldn't find it, it was there because it was sending flags. Won't be going back there again.
Hopefully somebody is still with me here. Is it possible to buy a "Knock sensor kit" (comes with ESC module, knock sensor, and wiring harness) and add it to a no-knock-sensor-having vehicle?
It looks like one end of that cable plugs into the ESC and it has the connector for the knock sensor itself, does anybody know what the other end connects to? I see no matching connector on my engine harness, and since there is no wire connected to B7 on my ECM would it do me any good anyway?
The electrical diagram in the Haynes manual shows the knock sensor connecting directly to the ECM, could I just stick one in and wire it directly without the ESC module?
edit: It didn't pass smog...way too much VOCs at idle. Also I have no trouble codes, and the light is functional.