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Mass airflow sensor issue (engine shuts off)

 
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kolumbo38
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PostPosted: Sat Aug 18, 2012 11:11 am    Post subject:  Mass airflow sensor issue (engine shuts off) Reply with quote

A year before the engine kept shutting off (while driving) I installed a dual exhaust system- it was custom, leaving a bit of back pressure (at least, that's what the shop guy told me). He assured me my PCM wouldn't have to be reset or anything. It sounded good, especially when everything else was stock. It ran well until I began to lose torque (makes sense now, when removing backpressure). I took my car to my mechanic repeatedly, and assured me it was the mass airflow sensor. Replaced twice, the issue re-occured. Unfortunately, this led me to get rid of the car altogether (it was my dd).

So here's my question: by installing the new exhaust system (dual flowmasters with two magnaflow resonators- had to, drone on highway was unbearable). Did the change of exhaust flow mess up the m.a.s, or even, components in the engine? because I loved that car so much, I'd buy another one (definitely as a project car) but how do I avoid such a thing happening again? did this happen to anyone else here?

Any advice would be much appreciated!
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outonthetiles
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PostPosted: Sat Aug 18, 2012 11:37 am    Post subject:  Re: Mass airflow sensor issue (engine shuts off) Reply with quote

kolumbo38 wrote:


So here's my question: by installing the new exhaust system (dual flowmasters with two magnaflow resonators- had to, drone on highway was unbearable). Did the change of exhaust flow mess up the m.a.s, or even, components in the engine? because I loved that car so much, I'd buy another one (definitely as a project car) but how do I avoid such a thing happening again? did this happen to anyone else here?


No.

http://www.thumpertalk.com/top.....-the-myth/

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PostPosted: Sat Aug 18, 2012 12:26 pm    Post subject:  Re: Mass airflow sensor issue (engine shuts off) Reply with quote

kolumbo38 wrote:
I took my car to my mechanic repeatedly, and assured me it was the mass airflow sensor. Replaced twice, the issue re-occured.


kolumbo38 wrote:
but how do I avoid such a thing happening again?


kolumbo38 wrote:
Any advice would be much appreciated!


Find a new mechanic... seriously once he suggested the same repairs after it had already re-occured it was clear he didn't know what was going on.

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Lingenfelter
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PostPosted: Sat Aug 18, 2012 1:09 pm    Post subject:   Reply with quote

It sounds like you're implying your car has died or you sold it.

Where did the custom exhaust start? right behind the catalytic converter?

My first thought was that your cat was plugged. Of course, there's a lot of things that could need servicing by the time is 10 or so years old.

The money you spent on two dual exhaust systems, I'm sure you could have bought one of the popular dual exhaust kits on the market for our cars.

Magnaflow/GMPP
SLP(I think)
Borla
And I beleive one other, were all available at one time. They may be thinning out from production, though.

The GMPP kit doesn't exist as a kit anymore but it still sold separately (all Magnaflow parts) - it's pretty popular, minimum drone. Magnaflow suffers more drone. Borla is the best, but it's twice the price of the next best system (Magnaflow/GMPP).

And get a new mechanic, even if this guy is your uncle or your best friend. Clearly he dropped the ball when you trusted your car's maintenance to him.

You want as little backpressure as possible, while maintaining adequate velocity. The cole's notes version of the link posted above is that your exhaust needs to move fast enough to 'suck' the exhaust from your combustion chambers while the valves are open. Not enough 'suck', not enough exhaust pulled out of the chamber. That leaves less oxygen for the next combustion cycle in the chamber. Less oxygen=less power.

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00impala123
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PostPosted: Sat Aug 18, 2012 1:24 pm    Post subject:   Reply with quote

LOL the catback exhaust did not cause the problems.


You can completely remove the cat-back if you wanted to and still drive the car.

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kolumbo38
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PostPosted: Sat Aug 18, 2012 2:55 pm    Post subject:   Reply with quote

Lingenfelter wrote:
It sounds like you're implying your car has died or you sold it.


Yup, unfortunately, I did. I needed a car for school, and after the engine cut off at 120 km/h on the highway and left me with no brakes/steering, I figured it was time to get rid of it and get something else.

Lingenfelter wrote:
Where did the custom exhaust start? right behind the catalytic converter?


Indeed. Someone even suggested to me at one point to start right at the exhaust manifolds, but that's grey territory for me entirely.


Lingenfelter wrote:
The money you spent on two dual exhaust systems, I'm sure you could have bought one of the popular dual exhaust kits on the market for our cars.


I came really close to getting a GMPP kit, but the place I ordered it from screwed up my order, so I gave up. That is, until I discovered a shop that supposedly specialized in exhaust systems, so I had the catback installed there. The owner there assured me I still had some backpressure, though tbh I didn't really feel any difference in performance until about a few months later, when the sluggish acceleration became more apparent.

Lingenfelter wrote:
And get a new mechanic, even if this guy is your uncle or your best friend. Clearly he dropped the ball when you trusted your car's maintenance to him.


Honestly, I was baffled by his inability to figure it out. Though a many number of things could of happened to cause this, he was convinced it was the m.a.s, and it just wasn't.

Lingenfelter wrote:
You want as little backpressure as possible, while maintaining adequate velocity. The cole's notes version of the link posted above is that your exhaust needs to move fast enough to 'suck' the exhaust from your combustion chambers while the valves are open. Not enough 'suck', not enough exhaust pulled out of the chamber. That leaves less oxygen for the next combustion cycle in the chamber. Less oxygen=less power.


Well, it certainly makes sense to me now, because this wasn't an exhaust system specific to the Impala- the guy at the shop told me he left a bit of backpressure to avoid this negative effect, and all would be well, but perhaps he was just bsing me.

I plan on purchasing another LS of the same gen in the near future, just cause I really like the look and feel of this car. But I don't want to repeat the same mistakes. My mechanical knowledge only takes me so far, so other than 3800Performance and Cartuning, is there anybody else (especially here in Canada) that specializes in properly tuning W-bodies? (granted, if the car itself is in good shape to be modded in the first place)
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PostPosted: Sat Aug 18, 2012 3:31 pm    Post subject:   Reply with quote

kolumbo38 wrote:
My mechanical knowledge only takes me so far, so other than 3800Performance and Cartuning, is there anybody else (especially here in Canada) that specializes in properly tuning W-bodies? (granted, if the car itself is in good shape to be modded in the first place)


I never ended up getting a PCM tune, but Overkill is based out of Toronto. He seems to get good reviews, judging by the reading material around here.

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PostPosted: Sat Aug 18, 2012 6:29 pm    Post subject:   Reply with quote

#BackyardTech
If you think the MAF is bad, unplug it. If things improve, there's your problem.
Thousands of MAFs are ruined every year due to over-oiled K&N filters.
Midas Muffler isn't in the business of diag, they're in the business of doing fast dirty work for high profit. Just keep that in mind next time. Joe Pipebender doesn't need to know jack squat about engine controls to weld up exhaust.

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kolumbo38
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PostPosted: Sat Aug 18, 2012 11:24 pm    Post subject:   Reply with quote

Dan wrote:
#BackyardTech
If you think the MAF is bad, unplug it. If things improve, there's your problem.
Thousands of MAFs are ruined every year due to over-oiled K&N filters.


When I still had the car in and out of the shops (about a year ago or so) I did in fact unplug the MAF and the engine coughed back in. But doesn't the engine run at half capacity without it though?

Dan wrote:
Midas Muffler isn't in the business of diag, they're in the business of doing fast dirty work for high profit. Just keep that in mind next time. Joe Pipebender doesn't need to know jack squat about engine controls to weld up exhaust.


Amen to that, lol. The place I went to is called 'Hot Rod Scott's', located at Islington and Norseman St in Toronto. I should of taken the overconfidence in their 'muffler specialists' as a stern warning of things to come. And of course, the final bill, which at $1,100, swiftly ripped my balls through my wallet.
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PostPosted: Sat Aug 18, 2012 11:35 pm    Post subject:   Reply with quote

kolumbo38 wrote:
Dan wrote:
#BackyardTech
If you think the MAF is bad, unplug it. If things improve, there's your problem.
Thousands of MAFs are ruined every year due to over-oiled K&N filters.


When I still had the car in and out of the shops (about a year ago or so) I did in fact unplug the MAF and the engine coughed back in. But doesn't the engine run at half capacity without it though?


It doesn't run from the MAF tables (I think it goes to speed density or something like that). It usually feels like you are dragging a boat anchor, but it will usually make things dramatically better if the MAF is the problem. It's certainly not a long term solution, but if the problem goes away with the MAF unplugged, it's the sensor that's causing the issue.

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outonthetiles
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PostPosted: Sun Aug 19, 2012 6:32 am    Post subject:   Reply with quote

Yep, speed density mode. The pcm calculates how much air should be coming by using factors such as air temperature and engine rpms to determine fueling, as apposed to using the MAF sensor.

Some custom tunes rely solely on speed density, but its more sensitive to weather conditions and altitude.

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kolumbo38
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PostPosted: Sun Aug 19, 2012 6:43 pm    Post subject:   Reply with quote

outonthetiles wrote:
Yep, speed density mode. The pcm calculates how much air should be coming by using factors such as air temperature and engine rpms to determine fueling, as apposed to using the MAF sensor.

Some custom tunes rely solely on speed density, but its more sensitive to weather conditions and altitude.


So would an Overkill PCM use more or less of this mode? or that's completely unrelated? As I mentioned, the engine sputtered back into life when I removed the MAF, leading me, and my...confused mechanic, into believing it was the MAF. Replaced twice, made no difference, which again, leads me to believe there was something horribly wrong between the PCM and the catback.
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PostPosted: Sun Aug 19, 2012 7:39 pm    Post subject:   Reply with quote

I don't think overkill uses a speed density tune. The cat back would make no noticeable difference in performance whatsoever unless it was super restrictive.

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