LT1 4-7 swap
06-12-2010, 10:38 PM
#16
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Join Date: Jan 2005
Posts: 11
just switching the two injector wires will make the computer freak out. if 4 and 7 are swapped and 4 is running lean, the computer will sense that bank is lean and try to make 4 rich to compensate. not knowing 4 is now 7, seven now runs rich and the computer tries to lean seven, which is now four. you see what i mean?
06-13-2010, 08:03 AM
#17
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Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
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But with the stock two bank configuration it knows if the left bank (normally containing #7) is running lean, and will add fuel to 1/3/5/7. If injector wire #7 has been switched by injector wire #4, a lean condition on the left bank would result in extra fuel being added to the right bank via the injector wire for #7 being attached to injector #4. The left bank O2 sensor is not controlling 1/3/5/4 and the right bank O2 sensor is now controlling 2/7/6/8.
09-23-2010, 07:53 PM
#18
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Join Date: Nov 2003
Location: Mishawaka, IN
Posts: 1,770
Just swap the ignition wires and leave the injector connectors where they're at. It's not like carbureted engines had injector timing, and they ran fine as far as performance is concerned.
You could try swapping the injector connectors too if you want and see what happens. Might **** off the o2 sensors- most people never realize this but "narrow"-band o2 sensors switch from slightly rich to lean rapidly, giving the ecm a very accurate ability to control fuel trim and monitor system performance. As this ability is controlled by the ecm's fuel injector pulsewidth and also the o2 sensor's response time, swapping things around will probably eliminate that function.
You could also try using one o2 sensor to send a signal for both but the ecm might get upset with that too, since it won't be seeing a proper signal response on one bank. Since an o2 sensor's switching speed degrades with time, and no two o2 sensors have exactly the same speed, they will never be in sync with each other. Each bank runs independently of the other after the injector and any interference between the two will throw things off. (Some mercedes and bmw v12s actually use completely different ecms on each bank, to the point that the engine will still run even with one ecm unplugged- obviously lacking a little power though)
I'd have to agree with the previous posters about the 4-7 swap in general though; even professional builders with a lot of tuning experience sometimes get mixed results from this swap, and it certainly isn't worth the effort in a street engine.
You could try swapping the injector connectors too if you want and see what happens. Might **** off the o2 sensors- most people never realize this but "narrow"-band o2 sensors switch from slightly rich to lean rapidly, giving the ecm a very accurate ability to control fuel trim and monitor system performance. As this ability is controlled by the ecm's fuel injector pulsewidth and also the o2 sensor's response time, swapping things around will probably eliminate that function.
You could also try using one o2 sensor to send a signal for both but the ecm might get upset with that too, since it won't be seeing a proper signal response on one bank. Since an o2 sensor's switching speed degrades with time, and no two o2 sensors have exactly the same speed, they will never be in sync with each other. Each bank runs independently of the other after the injector and any interference between the two will throw things off. (Some mercedes and bmw v12s actually use completely different ecms on each bank, to the point that the engine will still run even with one ecm unplugged- obviously lacking a little power though)
I'd have to agree with the previous posters about the 4-7 swap in general though; even professional builders with a lot of tuning experience sometimes get mixed results from this swap, and it certainly isn't worth the effort in a street engine.
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