89 K2500 Code #43...

A friend of mine has an 89 K2500 with a 350 in it, and recently it developed a code 43, which the book says something about low voltage to the ignition or something like that.
When it WILL start, he cant get anymore than 1500 rpms out of it, and it wants to just die. Sometimes it wont even start.
One person suggested a bad crank position sensor, or a bad ignition module.

Any ideas???

How about checking those two things?

Code 43 is a knock sensor code. The knock sensor sends a signal to the esc(electronic spark control module)when it senses a ping or knock. the esc then retards the timing until the knock goes away. Also it will sense rod knock when you trash a rod bearing. Commonly code 43 shows up when the plug comes off the knock sensor or the knock sensor fails. The knock sensor is in front of the starter in the threaded hole in the water jacket which before knock sensors had a pipe plug in it. Often the plug or sensor is damaged when the starter is replaced. It is fairly fragile and easily broken. The esc could also be bad. The knock sensor is about 35-40 bucks and the esc about 100-125. It is not a crank position sensor which this truck doesn't have. However it could be a combination of the ignition module (Under the dist. cap) and the esc module( mounted above the pass. side valve cover-- about half a inch thick and 2 and a half by 3 inches square. I keep a spare good one of each on hand to test with when I have problems with my 88 K3500.

We have replaced the ignition module, the ESC, and the knock sensor, and it still doesnt run right. My friend who owns this truck is ready to get rid of the tbi and put a carb on it. He is so frustrated.

Any other thoughts??

assuming that you don't have an internal engine problem (rod,bearing, etc.), I would reccomend you trace the wiring from the knock senor to the esc and the wires coming out of the esc. The wire to the knock sensor runs right next to the exhaust manifold, so its easily burnt. Code 43 states there is no signal being received from the knock senor, so since you have replaced these parts, I would focus on the wiring harness between the esc and the sensor