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Discussion Starter · #1 ·
Hi I have a 94 c1500 that I just swapped over to a 350TBI from a 4.3TBI. I used 350 knock sensors. throttle body, injectors, full distributor(with ICM and ETC) and PROM chip. When I put the PROM chip in it the ECM retards the timing rediculously. I put the 4.3 PROM chip back in it and it runs 10 times better. I mean of course it doesnt have the power or that a 350 should and it surges a little due to the fact that its all running on the 4.3 chip, but even so it still runs tons more power than when I run the 350 chip. I don't know what else to do. Any ideas whats causing it to retard the timing so bad when I put the 350 PROM in?
 

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khaos88gt said:
Hi I have a 94 c1500 that I just swapped over to a 350TBI from a 4.3TBI. I used 350 knock sensors. throttle body, injectors, full distributor(with ICM and ETC) and PROM chip. When I put the PROM chip in it the ECM retards the timing rediculously. I put the 4.3 PROM chip back in it and it runs 10 times better. I mean of course it doesnt have the power or that a 350 should and it surges a little due to the fact that its all running on the 4.3 chip, but even so it still runs tons more power than when I run the 350 chip. I don't know what else to do. Any ideas whats causing it to retard the timing so bad when I put the 350 PROM in?
Which ECM number and which chip number did you use. There are bunches of choices, your 94 uses several and other years use even other selections.

This assumes all the external parts are working correctly and the wire bundle circuits are compatible.

Bogie
 

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Discussion Starter · #9 ·
timing light

today I had a chance to use the timing light to get a little more accurate description of the problem. I put the 350 PROM in and set base timing to 0 degrees with ETC wire unplugged. At idle on start-up it idles just fine sits around 6-8 degrees advanced. As soon as you give it any gas the timing retards to -2.
 

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I had a GM truck in the shop years ago that had an issue like this. It had the positive bat cable running to close to the knock sensor wire and when you would crank it the bat cables amperage would cause enough blead over to pull timing out of it.

The next thing is are any of your plug wires near any of the est wires it will cause the same issues with bleed over from the ing system.


Mike
 
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