I have a '67 Bronco that I swapped a '02 5.3L & NV4500 into. I just got it out of the exhaust shop last night, stopped off for gas, and it wouldn't start. It was cranking away but it was not starting. I pulled a P1336 (Crank position re-learn needed) & P0178 (Flex Fuel Sensor) codes. So I reset the codes and it did start but barely, and ran poorly the rest of the way home. Later I cleared the codes again and it took forever to start but eventually did and ran like crap, just enough for me to pull it into the garage. Now I'm suspecting either the crank or cam sensor went south but need help on how to diagnose these sensors. I spoke with the dealer they said that neither of these codes would prevent the vehicle from starting so I think I have a faulty sensor. The motor has always had some issues starting, but always ran decent albeit some hesitation under harder throttle. Any help is appreciated.

Most starting problem are fuel related. So check the fuel system. And might do a crank relean as well. Just google it.

The flex fuel one is weird. What PCM do you have and who tuned it?

Most starting problem are fuel related. So check the fuel system. And might do a crank relean as well. Just google it.

The flex fuel one is weird. What PCM do you have and who tuned it?

The fuel system should be fine but I'll triple check. I've been digging into the crank relearn since I saw the code last night, all I can find is that it can only be done through a Tech2 or tuning software? My buddy has a pulled 5.3 so I am going to take his crank & cam sensor and swap them out tomorrow and see if that takes care of it. I realize I'll need a relearn either way.

The PCM that I have is a custom one (not the original one that came with the motor) and was tuned by spareECM. I made sure that abuse mode and everything was removed.

I was told that in my '02 5.3 the flex fuel sensor is actually the O2s. I also am pulling a code for bank 1 sensor 1, so I'm guessing/hoping that it's just a bad O2. Either way, I don't think that has any effect on the starting of the motor so it's a lower priority right now.

HPtuner or efi live will do the crank relean. I would see if anyone locally can do it. The GM dealer will want an arm and a leg. You might talk to them if all else fails as it only takes 2min!

I don't think that will cause the starting issue. Could be fuel pump, colged fuel filter or even a leak in the intake. Hows the fuel system setup ie return or return less


Sounds like a bad O2, but I believe those had a third O2 (composition senor) for the E85. Wierd as I thought 03 or 04 was first year for flex-fuel. What year is the PCM and whats the service number??

I went home after work last night and decided even though the fuel filter was brand new (less than 5 miles) I had mixed old gas with new gas, so I figured it was a nice and cheap place to start and it did take care of the starting issue. I also swapped banks on the O2s to see if the problem followed and the code went away so I'm guessing it was either a bad connection or just the bad gas throwing off the O2.

I do not know what year the PCM is, I will have to look into that. Is the flex fuel sensor code a hard code, i.e. CEL code, or just a soft code that doesn't cause limp mode?

My buddy works at the local GM dealer so hopefully he can hook me up on the re-learn. Thanks for your help as always.

I went home after work last night and decided even though the fuel filter was brand new (less than 5 miles) I had mixed old gas with new gas, so I figured it was a nice and cheap place to start and it did take care of the starting issue. I also swapped banks on the O2s to see if the problem followed and the code went away so I'm guessing it was either a bad connection or just the bad gas throwing off the O2.

I do not know what year the PCM is, I will have to look into that. Is the flex fuel sensor code a hard code, i.e. CEL code, or just a soft code that doesn't cause limp mode?

My buddy works at the local GM dealer so hopefully he can hook me up on the re-learn. Thanks for your help as always.Gas is really shit now days. Change it every 10,000 miles at least.

I would by new Bosch O2 be worth it if they are the original ones.
It's should be a soft code meaning it will default to regular gas mode I believe.

is the harness your using for an 02 or a newer motor?You shouldnt be gettin a FF code unless its a newer computer and your tuner doesnt know his ass from a hole i the ground.There is a big difference between the 02 and 03-07 OS (operating systems) in the ecm's.If your runnin a a flexfuel tune in a motor thats not setup for it,it'll run like crap.The FF motors have bigger injectors and different fueling.
I think most of your problems (aside from needing a relearn) are in the tune.