5.3 swap done on a 70 feels rough

[camaney]

I finished the engine swap from 03 pickup on my 70 and im having a terrible mpgs . Before The swap I change the knock sensors and everything that need it to change new but the injectors.. The truck idles good , runs good at times, no noise or knocks but there is times that it feels like missfire lack of power or tranny kinda hard to shift, i got the check engine light with 4 codes fist it n/a (i guess not avalable) po332 po327 and po332 again(knock sensors)its a new haness from painless ,auto trans.. Any idea what could it be? Should I get new sensors? Engine has 80k miles supposedly thanks for any input

[Oldtruckfanatic]

With those codes your pcm is reverting to 4 degrees btdc at wide open throttle. There are a few things to check. First check the plug at the back of the intake and make sure there is no corrosion or bent or pushed out pins. 2nd check to make sure your block is grounded well. There is a service bulletin for replacing the sensors in regards to procedure for using silicone to keep moisture out of the sensor bosses. Check to make sure the harness didnt get pinched or chaffed when installing the manifold. Also there have been numerous accounts of parts store and ebay or similar knock sensors being faulty. We always use gm sensors and replace the harnesses with them. I have read things like low fuel pressure causing the code etc. But i have never personally experienced that. When its both sensors its almost always a sensor or wiring issue.

[Oldtruckfanatic]

Almost forgot. Never put anything on the threads. The sensors need to be grounded And they dont thread into any fluid passages. All teflon tape or thread sealant etc. Will do is prevent a good ground.

[camaney]

Ok thats what I did, I bought tge sensors on ebay .so I will buy them from dealer or napa just to not be cheap this time and hope they work..will that take care of my terrible millege? Mileage its realy bad, like 5mpgs or less

[Nitis]

Fwiw I did run accross an ad on CL the other day for a shop out off fruitridge that claimed to be LS specialists and offering swaps. Maybe talk to them?

[camaney]

Yeah thanks. I already talk to him he says that he thinks is that but he is not sure, that he never had any issues like that

[Oldtruckfanatic]

As the above said if you arent comfortable looking up the test procedure for diagnosing the sensors etc. Try giving a reputable shop a call. You can do a search of those codes and get the diagnosric procedures. Its best to do that before just throwing money at it and when you do have no doubt you will find several forum threads on getting bad non gm sensors. Lots of guys have used aftermarket sensors with success i just personally chased a problem on a 53 chevy with a 5.3 for about a week and after we switched to gm sensors and harnesses the engine light never came back on. I still diagnose before I go replacing soneones new parts and charging them I was just giving you suggestions on where to start looking. Yes the knock sensors causing the pcm to default to a base timing setting will cause poor mileage and drivability concerns. But so will a bunch of other things so dont just replace parts because aftermarket knock sensors have been a problem before. It can get costly to just throw parts at it and find out there was another issue. I just gave you information I have experience with as a place to start looking. Hope you get it figured out. Sucks to pull that intake off after having it off to avoid this issue in the first place.

[Oldtruckfanatic]

Also as a general rule on all efi engine swaps and for me even oem replacements I ALWAYS start my diagnostics with checking the grounds.

[camaney]

Thanks for helping, I know what you mean by wasting money and time trying to figure out my self, been there before and learn from it to pay someone that knows and coming ahead at the end