Hello - this issue is occurring on a 2001 Blazer, 4.3 4x4.
A couple days ago, we were pulling out of a gas station and the truck nearly died when accelerating. Every time you slowed down to stop, it would nearly die and choked when accelerating.
I did some research and thought it could be the MAS - so I unplugged it and the issue seemed to go away.
I bought a new one (Well a Spectra - probably re-manufactured) and put it in yesterday. After that, I started the vehicle and went inside for a couple of minutes, came out and it had stalled. This happened a couple of times until I just unplugged the new unit and then it ran better - but still not perfect. (Obviously it throws the code for the MAS - but if you plug it back in and clear the code, there are no codes thrown.)
So, I'm debating if I got a bad unit I put in (don't want to chance another $100+). Just odd how when I put the new one in, everything went to hell and got worse. Not like it is hard to install, right? Was I supposed to do something to it before installing?
It has a new fuel pump and filter change plus just changed the fuel pressure regulator.
I'm taking it in to have the fuel pressure tested tomorrow.
I was just wondering if anybody here had any ideas on why swapping out the MAS would make things worse? I just pulled it out of the box and swapped it out with the old one.
Thanks for any ideas!

 

Any codes?

Do you have a scanner that can display fuel trims?

you need to verify the fuel pump repair by doing the entire fuel pressure test in the sticky.

When you unplug the MAF, the ECM goes back to open loop mode like when the engine is cold and ignores some of the sensors used to compute the air fuel ration and instead uses the hard programming in the ECM tables to use average fuel ratio values. Point being that it might not be the MAF.

George

 

Thanks for the reply!
Just took it into the shop, MAS was fine - I think. (But at least I replaced it which you should do once in a while anyway, right?)
Turns out they put in a bad Fuel Pressure Regulator a month ago - you could see the pressure going from low and then jumping sky high, so seems like it was sticking.
I'll post if the fuel pressure regulator was the culprit in the end or if it was something else.

 

I don’t know what the life expectancy of a MAF is, mine is original at 205,000 miles. There is always a risk of a replacement part having issues, especially if it not AC Delco in certAin cases. It may very well be that you had a bad MAF but it’s always better to confirm a failed part through diagnosis before replacing it and then verifying the fix afterwards. Disconnecting the MAF and the truck running better is an execellent piece of information but there can still be more than one thing wrong at that point.

parts swapping is one way to go and many people here prefer that approach but it can get expensive if the first couple of guesses are wrong.

George

 

Yeah - hindsight 20/20, right. The first thing they said at the shop was "where did you get the MAS" and then told me how they have problems with the non AC Delco parts. (Which I actually almost bought, but went with Spectra at the advice of somebody.) Regardless, it was a waste of time/money and hopefully not a mistake that will come back to haunt me later. Still learning here. Our '01 only has 98,600 miles on it, which is really low for one of these vehicles of that age, I'm sure.

 

No sweat. Your here for help and we're going to do exactly that. If I made a list of all the mistakes I made before I mastered something , we would be here for a while. Glad to see your figuring out how your truck works.

George

 

Thanks George for the kind words of encouragement. Still learning, but these are amazing vehicles aside from their minor shortcomings.
It did turn out to be the Fuel Pressure Regulator and thankfully we have good people here in Montana and they were honest and admitted that a bad one was installed. (Not their fault - a part purchased from CarQuest) so yeah - aftermarket stuff is like rolling the dice. After they swapped out the regulator the truck is running amazing.
I'm thinking the new MAS couldn't have hurt - but I could have just cleaned my old one off, right?
Anyway - looking forward to the next 100k on the truck and all the issues that might arise, so I'll surely be back.
Thanks again for the ideas on my issue!

 

There may not have been anything wrong with your MAF. When you unplugged it the engine control computer changes to a more primitive control mode that ignores some of the sensors. The screwed up regulator was probably causing havoc with the air fuel mixture and the O2 sensors were scrambling to maintain the ideal air/fuel mixture. They are ignored in this open loop mode. I could be wrong, there could have been more than one thing wrong at once but Occam’s Razor suggests probably not.

Glad your truck is running better

George