Electronic Spark Control

vzfox · March 21, 2007

My ECM keeps throwing a code of 43 once you get above 60mph, which says it is ESC issues. Where is the ESC on my truck, should I immediately jump to replacing it, or should I look for other possible problems?

Also, at speeds between 30-40mph the transmission shifts up and down really fast until you get above 40mph. Are all these problems connected?

rodeoron · March 30, 2007

I believe that would be the knock sensor that controls the timing when "knocking or pinging" is detected. It is located on my 91 on the left side of the engine block approx 6" under the heads in the center of the left side of the block. The knock sensor is screwed into the coolant passages, hence, you gonna get wet, when you take it out (from the anti-freeze). It can be a bit challenging getting it out as if it hasnt been unscrewed at all. I use an anti-seize compund and Permatex when I replace it or when I want to fully drain the block of coolant. Hope it helps.

I cant help with the tranny question. Good luck.

vzfox · March 31, 2007

I found the Knock Sensor and found its problem.......the DK BlUE wire coming off of it is broken. My only problem is, I cant find another end of a wire to reconnect it to. The only wire close to its location is a PURPLE wire with a single connector (similar to the connection for the O2 sensor). Does the DK BLUE wire from my knock sensor plug into the PURPLE wire?

vzfox · March 31, 2007

I found the other end of the wire. It connects to the ESC module next to the TBI (DK BLUE wire). Now, why is there a purple wire hanging just above the bell housing unconnected, I dont know.

rodeoron · April 2, 2007

Could the purple wire lead to the oxygen sensor located on the left exhaust manifold? On my '91 truck, there is a purple wire leading to the oxygen sensor...dont know if that the one. I am sure there are more than one purple wire in the engine bay vacinity however.

Glad to hear you located the wire problem leading to the knock sensor. Good luck with the purple wire.

vzfox · April 3, 2007

My O2 sensor is already plugged in to another purple wire, and yes it is in the same vacinity. Thanx for your assist and let me know if you find the other purple wire on your truck and what it might go to. Again, the wire I am talking about is hanging by the firewall next to the tranny dipstick tube.

rodeoron · April 4, 2007

If I get time tommorrow, I'll see if I can locate it on my truck...

rodeoron · April 7, 2007

The only purple wire that I could come up with on my '91 in about that location, is a slightly heavier guage wire that goes to the starter soleniod (not the real heavy guage/high amperage one). It comes from the location and goes to the starter. Thats about all I could locate on mine. Good luck with it.

vzfox · April 21, 2007

Just thought I would let you guys know that I sold my truck. My new toy is a 1983 Camaro Berlinetta. It's a 5spd with the V6 motor....ughhhhh, I know, but anyway.....I am sure I will be posting many a many questions about it to come, but obviously in a different room/forum. thanx for all your help guys.