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2009bert

1992 5.0 To 5.7 Swap, Running Rough, No Power

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I tried this same post earlier today and it appears it didn't upload properly... as it came up blank in the forum.

 

Anyways I will try this again. I have a 1992 GMC Sierra 5.0L TBI with about 300k on it.

 

I got my hands on a gently used 5.7L (from a 93 GMC Sierra TBI) and just got finished with the swap. I used the TBI off my original motor. It started up right away, but is idling really rough and has no power. I have done a lot of reading on forums and found lots of conflicting info on this. I have not yet changed my ECM, but from what I read it could be the problem? The problem I have is that the ecm units for the 92 & 93 have different chips and wiring hook ups, so I cannot interchange.

 

Q1- Can I buy an ecm from a 92 Sierra SLE with a 5.7, and fix this problem?

Q2- Do I need the ecm or just the chip?

 

Also, I reused the knock sensor off the original 5.0L... as the one on the 5.7 broke when I removed it from the donar truck. I have read some info saying that I cannot interchange knocks b/w a 5.0 and 5.7L.

 

Q3- Can I use a knock sensor out of a 5.0L in a 5.7L?

Q4- Is there anything else that could be causing the problem?

 

I am new to the forum, and this is my first swap, so any help would be much appreciated.

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First off, welcome aboard.

 

Secondly, I believe that most of your problems will be solves with an ecm swap, although I cannot speak from experience. You should look to one that matches your vehicle, except one that has the 5.7L "K" code 350. It should also come with the chip attached. As far as the knock sensor, I would just put the one on for a 5.7 and run it correct. They are about $40 from the auto parts store....

--Mike

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You could always go back to the basics,check the timing,cap,rotor,firing order maybe the ignition module in the dist.How did this engine run while still in the donor truck?

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You could always go back to the basics,check the timing,cap,rotor,firing order maybe the ignition module in the dist.How did this engine run while still in the donor truck?

 

 

Thanks for your help guys. I am going to have a look at it again this weekend. I already reset the timing, and it helped... but it still seems to lack power. I am going to try an ECM from my year/body of truck, only for a 5.7... after I check the rest of the ignition/firing stuff. The motor ran fine in the donor truck.

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You could always go back to the basics,check the timing,cap,rotor,firing order maybe the ignition module in the dist.How did this engine run while still in the donor truck?

 

 

Thanks for your help guys. I am going to have a look at it again this weekend. I already reset the timing, and it helped... but it still seems to lack power. I am going to try an ECM from my year/body of truck, only for a 5.7... after I check the rest of the ignition/firing stuff. The motor ran fine in the donor truck.

 

 

 

A proper tune will help with power. But the other thing to take into account is that a 305 has smaller injectors than a 350. It's the same TBI unit but 305's run 55 lb/hr injectors and the 350's use 61 lb/hr's ( misconception in the past was 45 on a 305 and 55 on a 350). With proper fuel pressure and a proper tune the truck will run well. Even if you upped the fuel pressure with what you have right now you would probably notice a good increase in power. Stock the TBI chips are pretty conservative and a good custom tune, even on a stock engine will give a good jump over the proper original. Again though, an adjustable fuel pressure regulator should be added.

 

Apparently the knock sensors are calibrated differently from a 305 to a 350. This may cause the amount of timing to be pulled if the engine is knocking to be off. Getting a new 350 unit is probably a good start.

 

92 has the 6299 ECM, 93 and later is different and is 91 and earlier.

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