scoogie_scott

Hello all,

I have a 2003 Tahoe VIN Z. This vehicle came with the Flex Fuel Motor. I have since put in a standard motor (non Flex Fuel). Engine seems to run great with no problems at all; however, I have a check engine light blinking at me saying multiple cylinder misfire when I get above 2500 RPM's or so. I'm using vehicle's original wiring harness. The plugs on the fuel injectors for the standard motor and the flex motor are different; therefore, I had to reuse the injectors that were on the flex fuel motor. From a little internet searching, I have found that the flex fuel injectors are rated at 35lb while the standard injectors are rated at 26lb. Might this be the reason I am getting an error code with multiple cylinder misfire? My thinking is that maybe it's injecting too much fuel or something at the higher RPM's. I'm trying to find some fuel injector wiring harness plugs with pigtails from a junkyard that will fit the fuel injectors that came with the replacement standard motor. My hope is that once I change the plugs and put the proper injectors in there, the misfire error code will go away. If I do this, is this going to require a replacement of the ECM as well? Any thoughts?

Thanks

tech2

if its injecting to much fuel the fuel trim % would be negative as it would be trying to cut fuel. Check the fuel trim with a scan tool.

did you do a crank position sensor learn when the engine was swapped?

scoogie_scott

I will have to check the fuel trim % later this evening. How do you do a crank position sensor learn?

tech2

you will need a full function scan tool to initiate this procedure. If this is not done you will get false misfire codes setting at higher rpms.

scoogie_scott

Ok I will see if I can get my local GM dealer to do the relearn for me. Do you think there would be any issues with me using the 35lb flex fuel injectors instead of the 26lb injectors that came on the replacement motor?

tech2

I don't think there will be an issue. The ecm should adapt.

Injector resistance is the issue I would be concerned with when swapping injectors. They must be correct resistance or the ecm driver will fail.

scoogie_scott

Well I had the computer reprogrammed, but that didn't solve the problem. I'm thinking of removing those flex fuel injectors and making the modifications to the wiring harness so I can use the standard fuel injectors. Also, any idea if the computer is the same for flex motor and standard motor? Just wondering if that would have to be swapped.

tech2

you did a ecm reprogram or a crankshaft sensor variation relearn? 2 completely different procedures.

scoogie_scott

I told them to do a computer reprogram. I guess for some reason I assumed it was one in the same and didn't realize it was two different procedures.

tech2

there is slight variation in signal output from each crankshaft sensor. If the signal differences are not learned by the ecm; at high speeds the ecm will think a misfire condition (determined by crankshaft speed) is occuring, when its really not. This will cause false misfire codes to set.