at a loss. replaced MAF

[Chevy Express]

So I had a power performance issue with bucking, which got worse, finally threw a code for MAF out of range, and after watching Fuel trims LT+25, I pulled the sensor plug, and it restored all power and no bucking.

So i buy a new Delphi AF10057 MAF, install it, and now fuel trims are averaging -18 and it actually threw a bank 1 rich code. and it slightly stumbles now. This is on a 2000 454 express van cut off motorhome.

I am extremely confused as to how it can now swing completely the other way.

any thoughts.

 

[stutaeng]

That's because when you unplug the MAF sensor I'm pretty sure the ECU default to speed-density mode.

Does your scanner have live data? Or these are freeze frame readings you are getting?

Lean or rich conditions affecting only one bank are almost always going to be vacuum leak or fuel pressure regulator or injectors. But need to confirm.

What is the history with the van? Ran fine before?

 

[454cid]

So I had a power performance issue with bucking, which got worse, finally threw a code for MAF out of range, and after watching Fuel trims LT+25, I pulled the sensor plug, and it restored all power and no bucking.

So i buy a new Delphi AF10057 MAF, install it, and now fuel trims are averaging -18 and it actually threw a bank 1 rich code. and it slightly stumbles now. This is on a 2000 454 express van cut off motorhome.

I am extremely confused as to how it can now swing completely the other way.

any thoughts.

Multiple issues from the start, maybe? A MAF isn't going to affect only one bank. What are the o2's doing, have you checked for vacuum leaks? What about leaking injectors?

 

[ralmo94]

Any chance you are running parts store aftermarket o2 sensors? Did you unplug the battery when you installed the maf, that would reset fuel trims. Is this all stock? Also a manifold leak at the head can play with fuel trims quite a bit. There is nothing wrong with running speed density of you need to drive it before you figure it out.

 

[Chevy Express]

Both Banks have identical fuel trim readings. Motorhome sat for 5 years was given to me and would drive fine, then start bucking on hard pulls, initially was throwing lean codes, as FT were going +25. No idea on 02's originally, but i would say original.

it runs absolutely flawless with the MAF unplugged, and fuel trims are perfect, I almost fell like the delphi is not good? I don't have a scope and only a basic reader, I can get pids but not a ton.

this is a motorhome, nothing has been done outside of stock that I can tell.

it had problems with hot restart, which did lead me down injector paths, but unplugging the maf fixed it, and it starts perfect with the new one.

should i just buy the ac delco rebuilt? or do guys not have trouble with the delphi?

 

[454cid]

Oh, I read LT as left instead of long term, sorry.

You need to find out what the o2s are doing, map, and other sensors.....live data otherwise you're guessing.

 

[Nad_Yvalhosert]

What's the fuel pressure?

Motorhome sat for 5 years was given to me and would drive fine, then start bucking on hard pulls, initially was throwing lean codes,

Sounds like low pressure or low volume: runs out of fuel at high demand...

 

[stutaeng]

I also understood lean/rich was only one bank...

What are the MAF numbers? You can pretty much determine if MAF sensor is bad by looking at live data and accelerating the engine at multiple rpm ranges.

There's a way to test it with a DVOM with Hertz reading, but takes longer. Do you have a wrecking yard nearby? Popping in a MAF from there is probably cheaper.

Did you clean your old one? I've read if that little filament gets dirty it can produce numbers that are inaccurate.

 

[Nad_Yvalhosert]

but unplugging the maf fixed it, and it starts perfect with the new one.

Though I cant explain that, how does it drive with the new MAF?
And I mean at WOT...

 

[Chevy Express]

What's the fuel pressure?



Sounds like low pressure or low volume: runs out of fuel at high demand...

No its not low pressure. disconnecting the maf. I pull a long grade hill. its over a mile long straight up. with MAF connected barely 42. disconnected and floored Full power got to 72 mph at 10k weight. I thought it was pressure too, but it NEVER skipped a beat, and i had it buried the whole run, and trims were perfect.