Mystery Engine Light

**cchas14** · 02-15-2008, 03:20 PM

I hope someone can help with this one. After I warm the truck up and start driving it. After a short distance if I press on the gas to speed up (on a flat surface) I hear a noise like the valves are knocking. Then the noise will stop it is about 30 seconds and after the engine light comes on. But the truck will run fine with the light on, the light stays on until I turn off the motor.

Any guesses?

Charles

**TahoeFever** · 02-15-2008, 05:25 PM

did you have someone run an engine code reader on your truck yet?
basically the engine trouble light is basically telling you what the problem is

**cchas14** · 02-15-2008, 06:28 PM

Not yet, I was hoping that someone might have an answer.

**cchas14** · 02-22-2008, 03:42 PM

Went to AutoZone and they can up with a 43 code. In the book it said that it woud be a TPS out of adjustment. But it also said it was a knock sensor. How would you adjust the TPS?

**MrShorty** · 02-22-2008, 06:56 PM

Year? Engine?

**cchas14** · 02-22-2008, 09:41 PM

Originally Posted by MrShorty

Year? Engine?

1991, 5.7 K engine, That I know of I am the third owner. The motor was replaced with a crated one at 60K.

**GaryL** · 02-25-2008, 10:00 AM

If the code is telling you knock sensor and you are hearing a knock, I would start with that. If the tps was bad it would run lousy and have a hesitation on acceleration.

**MrShorty** · 02-25-2008, 01:01 PM

Originally Posted by cchas14

Went to AutoZone and they can up with a 43 code. In the book it said that it woud be a TPS out of adjustment. But it also said it was a knock sensor. How would you adjust the TPS?

I looked at www.troublecodes.net, and according to their list, 43 refers to the knock sensor on a '91 5.7. I don't know where Autozone got TPS, maybe looking at a list for a different GM application, or BAT auto's list needs updated (though BAT's Ford code list is pretty good, so I think they do a good job).

Do you have access to a real manual (Motor, Mitchell, Helm, other)? I'm not familiar with GM's OBD-1 diagnostic procedures, so the first thing I would probably do in your shoes would be to find some good information. Many public libraries carry good manuals in the reference section.

Another good first check would be to check the wiring between the PCM and the knock sensor to make sure there are no obvious wiring problems.

**cchas14** · 02-25-2008, 10:44 PM

Well, I did waste $30.00 on a TPS Sensor and the problem is still there. But I can say that the engine idles nicer. The thing I do not understand is why when I am driving say 45 MPH and I want to increase my speed to say 50 MPH. When I press on the gas, slightly mind you, the motor will knock badly for 3 seconds then nothing. The Check Engine like comes on about 6 seconds after, but the motor runs fine.

**MrShorty** · 02-25-2008, 11:24 PM

I'm not an expert on the TBI set up, which is why I recommended going to a library and finding a good manual. A 43 seems to point to no knock sensor signal. So, the engine pings when accelerating, because the PCM isn't getting the KS signal to retard the timing to prevent the pinging. Once the PCM recognizes that the KS signal is missing, it "defaults" to a safe value for timing advance, and the CEL comes on. The bahavior you describe sounds pretty normal for the faut code described. I would still start by looking into the knock sensor circuit and see what's wrong.