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Old 05-16-2012, 05:02 PM
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Vortec 454 retarding timing

Hey i have a 97 vortec 454, falls all over itself accelerating from stop, if u really get into the throttle when trying it it shakes and sputters but goes, chased mass airflow wasnt the cause. Bank 1 at 25% long fuel trim flushed injectors and have good gas. But i found that when looking at cylinder #1 advance its 25*. But when getting on the throttle it retards to as low as 2*. Unplugged knock sensors to eliminate the possibility of the vcm seeing detonation. The cmp retard offset is 1*. Running out of ideas appreciate any help. Comp cam that is supposed to run with stock factory injection. Honed cylinders and knurled pistons. Decked heads.003. Valve job.
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Old 05-17-2012, 05:03 PM
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Quote:
Originally Posted by Preston Husker
Hey i have a 97 vortec 454, falls all over itself accelerating from stop, if u really get into the throttle when trying it it shakes and sputters but goes, chased mass airflow wasnt the cause. Bank 1 at 25% long fuel trim flushed injectors and have good gas. But i found that when looking at cylinder #1 advance its 25*. But when getting on the throttle it retards to as low as 2*. Unplugged knock sensors to eliminate the possibility of the vcm seeing detonation. The cmp retard offset is 1*. Running out of ideas appreciate any help. Comp cam that is supposed to run with stock factory injection. Honed cylinders and knurled pistons. Decked heads.003. Valve job.
The timing dropping back when you accelerate is normal, ignore it.What it is doing is dropping back so the engine doesnt knock under load as it is at low rpm. As rpm builds , so will timing advance.
Bank one adding 25 % enrichment is something.Sounds like a fuel starvation issue, like failing injector, or injectors on one side of motor. Dont overlook the fact it can be a vacuum leak, intake leak or any other source of unmetered air.
Unmetered air means air entering into engine that is not measure by the Mass air flow sensor, basically an air leak, which is not suppose to be.
CMP offset 1 degree... ignore it, thats normal -OK.
I would be checking for any air leaks, intake leaks,etc.
I would also check the fuel pressure. Those are very sensitive to even a few pounds difference from there specification.
Checking the injectors for spray and pattern will be a task, we can talk about that later. Check this stuff first.

didnt know anyone knurled pistons anymore, new ones are so cheap. Good luck.
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Old 05-18-2012, 05:24 PM
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Running fuel pressure is right on spec, 61 psi. Volume also good im not worried about the pump it's brand new as is filter. Injectors are not leaking holds pressure after turned off, no vacuum leak i propaned around the intake and used a fog machine on whole system. Plus the iac count is at 20. I set the cmp offset that wasnt a concern, i know they should retard timing a little but i cant get over going from 25 to nothing, especially all ranges of the tp, WOT or barely pushing down on the pedal. This was a swap project the pickup is originally a 95 throttle body 350 but i changed everything to the vortec setup. Gonna pull the vin # out of the vcm and make sure its the right one, other than that i dont have any leads. Haha as for knurling the pistons the walls measured really straight i just honed them a little, hard to bore too much out of that year the water jackets are right there!
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Old 05-18-2012, 06:18 PM
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Quote:
Originally Posted by Preston Husker
Running fuel pressure is right on spec, 61 psi. Volume also good im not worried about the pump it's brand new as is filter. Injectors are not leaking holds pressure after turned off, no vacuum leak i propaned around the intake and used a fog machine on whole system. Plus the iac count is at 20. I set the cmp offset that wasnt a concern, i know they should retard timing a little but i cant get over going from 25 to nothing, especially all ranges of the tp, WOT or barely pushing down on the pedal. This was a swap project the pickup is originally a 95 throttle body 350 but i changed everything to the vortec setup. Gonna pull the vin # out of the vcm and make sure its the right one, other than that i dont have any leads. Haha as for knurling the pistons the walls measured really straight i just honed them a little, hard to bore too much out of that year the water jackets are right there!

IAC count being at 20 is a good sign,pretty indicative of no umetered air getting in.
Injectors can hold pressure and not leak, but can also spray a poor pattern or not spray enough fuel to run the engine correctly.
The OE style "poppet" injectors are prone spraying a poor pattern and causing plenty of driveability trouble.If you have replaced them with the upgraded non poppet style injectors then this would not apply.
Having one side of the engine s fuel trim maxed out at 25 % and the other side at normal can only be about 4 things...lean AFR on that side, such as caused by injectors plugged or not spraying correctly, messed up O2 sensor , corrupt flash in ECM , or wacked ecm.
If you think the timing is the issue, you can disconnect the Bypass wire, then set timing at 4 degrees , and leave the bypass unhooked, then go drive it, see if that at least alleviates the stumbling bucking... whatever.It may not be a powerhouse running it that way , but it could give you an indication of which direction to go. If the problem is still there, then it would be indictive of a fuel delivery problem, be it injectors or ecm etc.
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Old 05-18-2012, 10:06 PM
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Quote:
Originally Posted by LATECH
IAC count being at 20 is a good sign,pretty indicative of no umetered air getting in.
Injectors can hold pressure and not leak, but can also spray a poor pattern or not spray enough fuel to run the engine correctly.
The OE style "poppet" injectors are prone spraying a poor pattern and causing plenty of driveability trouble.If you have replaced them with the upgraded non poppet style injectors then this would not apply.
Having one side of the engine s fuel trim maxed out at 25 % and the other side at normal can only be about 4 things...lean AFR on that side, such as caused by injectors plugged or not spraying correctly, messed up O2 sensor , corrupt flash in ECM , or wacked ecm.
If you think the timing is the issue, you can disconnect the Bypass wire, then set timing at 4 degrees , and leave the bypass unhooked, then go drive it, see if that at least alleviates the stumbling bucking... whatever.It may not be a powerhouse running it that way , but it could give you an indication of which direction to go. If the problem is still there, then it would be indictive of a fuel delivery problem, be it injectors or ecm etc.
I will have to wait until monday when i can get a tech 2 on it and check the 8th vin and make sure its a J. I dont have the 4L80E behind it yet, im just running the original 4L60E until i can find one which isnt as easy as i originally intended, and since gm never put a 60 behind the 454 i cant reprogram the vcm to run it, theres no parameters, and around here most places want 500-700 to custom tune, and beings as it is getting tired i dont want to dump the money on that route. But i wonder since i dont have the vss hooked up if it sees no speed and and increase in tp and air flow if it would retard itself for some reason? Highly doubtful but trying to eliminate everything that could be a possibility. I do know the suburbans had a problem with having a wire harness too close to a manifold and it would get too hot and hurt the vcm. I have all harnesses ran well and tucked away, but i only think about this because originally the communication wire from the vcm to the dlc was melting in areas causing too much resistance, so it wouldnt surprise me if when this set up was in its original pickup if it had the same problem. Worth checking out i suppose.
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