at a loss. replaced MAF

[454cid]

So issue is "only" happening going over bumps? Some wire is chaffed, a ground is losing contact or something in that realm,

I'd agree that sounds like a connection making intermittent contact.

if I had to guess. But don't guess. At some point I was going to say that the MAF also has the IAT sensor

The new MAF likely has an IAT in it, but I don't think it's being used. The 454 has a separate IAT in the intake tube. Unless the IAT harness also plugs into the new MAF?

OP, I'd recommend watching this video, and part 2

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[L31MaxExpress]

South Main auto is 2 and half hours from me. IDK if i am at that point yet.

I believe i had 2 issues. I believe my MAF was slowing failing (threw out of range and lean codes) and a bucking issue with bumps. after replacing the MAF, my power has significantly returned, but going over bumps still causes bucking and fuel enrichment on short term fuel bank 2. Unplugging the MAF seems to have cured the bucking problem, what I am trying to determine now is what sensors are removed from the equation when the maf is disconnected. I am hoping the 02 but IDK.

The MAF is the only thing removed from the equation other than the PCM defaulting max line pressure on the trans.

 

[Chevy Express]

The MAF is the only thing removed from the equation other than the PCM defaulting max line pressure on the trans.

Then why does the problem go away, if i disconnect it, but when connected bank 1 trims remain normal, yet bank 2 trims go rich instantly during the bucking?

The must be doing some other calculations now since the sensor is removed. since the maf affects both banks, i don't see how only 1 bank is being affected, and while the bouncing is occurring the MAF is still giving readings....

 

[L31MaxExpress]

Then why does the problem go away, if i disconnect it, but when connected bank 1 trims remain normal, yet bank 2 trims go rich instantly during the bucking?

The must be doing some other calculations now since the sensor is removed. since the maf affects both banks, i don't see how only 1 bank is being affected, and while the bouncing is occurring the MAF is still giving readings....

I cannot answer that one, but I tune the VE tables in those PCMs with the MAF disabled. Then tune the MAF tables.

 

[Chevy Express]

I cannot answer that one, but I tune the VE tables in those PCMs with the MAF disabled. Then tune the MAF tables.

so what does that mean? I'm not familiar enough to understand if thats some sort of answer

 

[Chevy Express]

so what does that mean? I'm not familiar enough to understand if thats some sort of answer

I cannot answer that one, but I tune the VE tables in those PCMs with the MAF disabled. Then tune the MAF tables.

actually let me ask this, how does it know the calculations for the VE table? is it taking 02 sensor input?

 

[L31MaxExpress]

so what does that mean? I'm not familiar enough to understand if thats some sort of answer

It means that when the MAF is disconnected it still goes into closed loop and uses the 02 sensor feedback.

 

[Chevy Express]

It means that when the MAF is disconnected it still goes into closed loop and uses the 02 sensor feedback.

what happens at WOT with MAF connected, is it still using sensor? or going to default tune?

 

[L31MaxExpress]

what happens at WOT with MAF connected, is it still using sensor? or going to default tune?

WOT it goes into power enrichment, similar to the power valve on a holley carb opening. Some engines have up to a 60 second delay on this. If the long term fuel trims are negative or zero it runs on the base programming. If the fuel trims are positive, it adds that much more fuel. So if its at +10%, the PCM adds 10% more fuel at all points at WOT. Either way at WOT the 02 sensors are ignored for fueling changes.

 

[Chevy Express]

is the MAF ignored as well? the FUEL TRIMS go to zero