TBI 454 to TBI 350 head scratcher code 43

I just read recently purchased a 93 TBI 1 ton Chevy, that bad headgaskets. The previous owner told me that the truck had been converted from a 454 TBI to a 350 TBI before he got it.

Once the head gaskets have been replaced, the truck now runs fine, until fully warmed up then it sets a check engine light for a code 43. The knock sensor looks like it has been changed with a new wiring pigtail. From the little bit I've been able to gather online I am wondering if the wiring is the same from the 350 to the 454? I can't imagine this truck still has a 454 ECM as I would not think the fuel rates or curve would be the same. Can anyone verify for me that the knock sensor wire coming into the ECM would be the same on both the 350 and 454 versions of the 93? The truck is a five-speed stick shift.

Thanks a bunch!

Pin should be the same. Do you know what brand of sensor is in there? Could just be Chinesium junk.

i believe IAC and TPS plugs are different between SB n BB. Knock sensor should be the same as well. Check the VIN and see if indeed was a BB. Im looking for one, and while finding some, see many saying that the truck was a big block converted to small block but yet has the light duty rear lol. Umm, don't think so lol...

The VIN on this model checks out as a 454 cab and chassis truck from 1993. Has the heavy 14 bolt full floater axle. I have so far today swapped out ECM swap with an 88 GMC that I knew to be good, same code still set. On one other site I noticed they said on a big block truck the knock sensor wire went directly to the ECM, while small block trucks did not. I traced the knock sensor wire to the electronic spark control module, then it goes out into two other wires from there. I am not however getting 5 volts current at the knock sensor

Adam Courtney said:

The VIN on this model checks out as a 454 cab and chassis truck from 1993. Has the heavy 14 bolt full floater axle. I have so far today swapped out ECM swap with an 88 GMC that I knew to be good, same code still set. On one other site I noticed they said on a big block truck the knock sensor wire went directly to the ECM, while small block trucks did not. I traced the knock sensor wire to the electronic spark control module, then it goes out into two other wires from there. I am not however getting 5 volts current at the knock sensor

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As I understand it you shouldn't. The sensor generates the signal.

Is the knock sensor from the 454? It needs to be for a 350 and match the ESC module. Also, do you have any loose exhaust pipes or anything else that may rattle? The KC can pick those up too.

PlayingWithTBI said:

Is the knock sensor from the 454? It needs to be for a 350 and match the ESC module.

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Beat me to it. That was first on my mind as I was reading "converted from 454 to 350" - the knock sensor applications are very specific.

Richard

someotherguy said:

Beat me to it. That was first on my mind as I was reading "converted from 454 to 350" - the knock sensor applications are very specific.

Richard

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Not if you buy from the parts stores, at least for the ICMs. That's why I'm curious what's in there.

ECM is different from 93 to 88. 88 is 7747, not sure what the newer ones are, but they control the 4l80, 88 didn't have those yet. Might not make a difference...

The ecm in this truck is the same one as the one in my 88. I just tested the connections on the knock sensor, the wire test good, the sensor ohms out the same as the knock sensor on my 88, the electronic spark control unit has the same input and output voltages as my 88. Also swapped over the complete electronic spark control unit from the 88 truck and has not made a difference. Only thing I can figure at this point is where the engine harness mates to the ECM harness there is a difference on the truck side between The Junction at the firewall and the ECM. However I do not have a schematic to know what that difference could be.

Since I do not know what your of donor engine was put into this 93, I can only assume it is an earlier 88 or 89 going off the ECM.