Mass Air Flow Problems and PCM "Default Strategy"

[dogememe]

On a previous vehicle, a 97 Suburban, when I suspected I had a bad MAF sensor, it was simple to diagnose. I unplugged the MAF and the truck ran great. Check engine light was on, but no hesitation, rough idle, plenty of power, it shifted fine...

But I'm noticing something about Fords that bothers me... they rely too much on the MAF. When a bug got sucked into the MAF on my 2010 Escape (it shifted terribly and was overall unpleasant to drive until I replaced the MAF) it set a lean code but the PCM was happy with the MAF readings and that's why it shifted so badly.

Ever since I bought this 2008 Crown Vic I have had some weird shifting and I honestly was like, well, yay, I bought a car with transmission trouble. Fuel trims looked fine and no codes for rich/lean or MAF performance, so it's not my MAF, right? Wrong. Last night I experimented and tried to drive the car with the MAF sensor unplugged - it barely ran and I barely made it out of the parking lot before the wrench light went on and I lost power and had to pull over. Trying to restart it resulted in a long crank and then stall. So, I plugged it back in... again, OK, you'd think my MAF sensor is fine based on this test, right? Again, wrong. I replaced my MAF sensor today (even though the old one looks clean inside) and WOW, the car drives much better and my "transmission issue" is gone (I found it that's one of the reasons the previous owner decided to sell the car, I found his Facebook post asking about transmission problems a few weeks ago).

What I'm curious about is why do some cars run fine in "default strategy" (or whatever it's called when the PCM realizes the MAF sensor is dead/unplugged) and some don't? It seems like GM, at least in this case, does this better than Ford (although I'm compared an old vehicle with a real throttle cable to a modern vehicle with electronic throttle control, if that has anything to do with)... wouldn't there be some verification using other sensors (MAP, O2, etc) to notice that the MAF is wrong and causing problems (like in the case of both my Fords where the MAF sensor was bad but the vehicle either set no codes at all or a lean code)? Wouldn't they design it so that a dead/unplugged MAF would still let you get to your destination?

I'm just trying to understand how these engine management systems are designed, why it seems some manufacturers build in redundancy and some don't (since I'm sure a 2008 Crown Vic or a 2010 Escape has a much "smarter" PCM than a 1997 Suburban), and why they allow so many aspects of the car (transmission shifting, for example) to rely on one sensor that the PCM doesn't even know is correct.

Any thoughts or input appreciated.

 

[das_peikko]

Let me list some red flags for you:
1. OHC with camshaft phasors (because they want us to have 12 foot long chains and adjustable cam timing)
2. Direct Fuel Injection (never washes your valves clean)
3. Active Fuel Management (cylinder deactivation)
4. Fly By Wire throttle bodies (because a cable is too simple)

 

[clinebarger]

Ford's "In General" don't have a MAP sensor, Where just about all OBD2 GM vehicles have a MAP & MAF sensors & can default to "Speed Density" fueling with the MAF unplugged.

 

[StevieC]

Originally Posted by das_peikko
Let me list some red flags for you:
1. OHC with camshaft phasors (because they want us to have 12 foot long chains and adjustable cam timing)
2. Direct Fuel Injection (never washes your valves clean)
3. Active Fuel Management (cylinder deactivation)
4. Fly By Wire throttle bodies (because a cable is too simple)


1. Chrysler has miles of chain and VVT on Exhaust and Intake cams in a DOHC setup on their PentaStars and we have one in the family that has had 0 issues after 300K along with many others. It can be done, it's just GM does a [censored] poor job at everything usually or they choose poor quality economy chains.

2. While they don't wash the valves in the traditional sense there are work arounds like valve overlap, the way the injections are aimed, and keeping the valves at higher temperature all to combat deposits. Some Ford and Mazda engines are great examples of this working properly and later Hyundai/Kia models.

3. Chrysler's MDS on the Hemi's work flawlessly. My neighbour is on his 2nd one with this feature and the first one had a good amount of miles before it was in the accident. Far more reliable than Honda's VCM.

4. Fly by wire is being used because they can better control engine by modifying throttle response in certain conditions. It has also eliminated the need for an idle control valve in a lot of cases which makes the vehicle have one less thing to go wrong. It can be done properly with 0 issues.

 

[Skippy722]

I saw a video where they had bought a c6 corvette that was set up to run a MAP, but had the tuning was looking for a MAF so the PCM cranked the transmission line pressure to max and it was running so rich it wouldn't rev to redline

 

[eljefino]

My 91 volvo was so dumb that a small air leak in the tube between MAF and throttle body led to it idling slower and slower until it actually stalled out.

Nobody ever hard-coded it that it would always be, at a minimum, ingesting enough air to idle.

 

[clinebarger]

Originally Posted by Skippy722
I saw a video where they had bought a c6 corvette that was set up to run a MAP, but had the tuning was looking for a MAF so the PCM cranked the transmission line pressure to max and it was running so rich it wouldn't rev to redline


Probably had DTC's P0101, P0102, P0103 disabled in the tune, These DTC's must be active to force the PCM to run in Speed Density Mode.

 

[Colt45ws]

Originally Posted by clinebarger
Ford's "In General" don't have a MAP sensor, Where just about all OBD2 GM vehicles have a MAP & MAF sensors & can default to "Speed Density" fueling with the MAF unplugged.

When the ESM "EGR System Module" was added to the Crown Vic 4.6L in 2003 (probably other apps around that time) a MAP reading became available as instead of using a separate DPFE they now have a sensor built into the module, with the orifice between the EGR itself and the intake, so the DPFE sensor is measuring MAP on one side of it.
However I dont think they actually do anything with it. I know for sure the EEC-V cars definetly dont as they have a hard code 'Failed MAF' table. I wouldve hoped the later PPC cars would make actual use out of it but maybe not.

The problem is likely because its DBW. It may not have even gone into failed MAF mode with the amount it was run. Might take a second key cycle for it to realize the MAF _is_ dead and it needs to use a fail safe strategy. All three of my EEC-V Vics run great with the MAF unplugged. The only reason I figure it out is the trans shifts harder than normal. I actually had to drive my 2002 with it unplugged when I blew a spark plug out of the head, as it runs way worse with it plugged in and stalls more.

 

[dogememe]

Originally Posted by Colt45ws
Originally Posted by clinebarger
Ford's "In General" don't have a MAP sensor, Where just about all OBD2 GM vehicles have a MAP & MAF sensors & can default to "Speed Density" fueling with the MAF unplugged.

When the ESM "EGR System Module" was added to the Crown Vic 4.6L in 2003 (probably other apps around that time) a MAP reading became available as instead of using a separate DPFE they now have a sensor built into the module, with the orifice between the EGR itself and the intake, so the DPFE sensor is measuring MAP on one side of it.
However I dont think they actually do anything with it. I know for sure the EEC-V cars definetly dont as they have a hard code 'Failed MAF' table. I wouldve hoped the later PPC cars would make actual use out of it but maybe not.

The problem is likely because its DBW. It may not have even gone into failed MAF mode with the amount it was run. Might take a second key cycle for it to realize the MAF _is_ dead and it needs to use a fail safe strategy. All three of my EEC-V Vics run great with the MAF unplugged. The only reason I figure it out is the trans shifts harder than normal. I actually had to drive my 2002 with it unplugged when I blew a spark plug out of the head, as it runs way worse with it plugged in and stalls more.

I restarted it enough times before even leaving the parking lot for the check engine light to come on and for it to set codes (I checked with my scanner) for the MAF sensor. So the PCM better have known the sensor was no good. I thought this car has a MAP sensor, I do see that reading on the scanner, or perhaps it's calculated/estimated?

 

[clinebarger]

Originally Posted by Colt45ws
Originally Posted by clinebarger
Ford's "In General" don't have a MAP sensor, Where just about all OBD2 GM vehicles have a MAP & MAF sensors & can default to "Speed Density" fueling with the MAF unplugged.

When the ESM "EGR System Module" was added to the Crown Vic 4.6L in 2003 (probably other apps around that time) a MAP reading became available as instead of using a separate DPFE they now have a sensor built into the module, with the orifice between the EGR itself and the intake, so the DPFE sensor is measuring MAP on one side of it.
However I dont think they actually do anything with it. I know for sure the EEC-V cars definetly dont as they have a hard code 'Failed MAF' table. I wouldve hoped the later PPC cars would make actual use out of it but maybe not.

The problem is likely because its DBW. It may not have even gone into failed MAF mode with the amount it was run. Might take a second key cycle for it to realize the MAF _is_ dead and it needs to use a fail safe strategy. All three of my EEC-V Vics run great with the MAF unplugged. The only reason I figure it out is the trans shifts harder than normal. I actually had to drive my 2002 with it unplugged when I blew a spark plug out of the head, as it runs way worse with it plugged in and stalls more.


Yep.....I've seen the Ford "synthesized fail safe" MAF values with a completely dead MAF, Confused me a bit the first time I ran across that. The engine still seems to run like crap in fail safe.
Where GM has fully functional Speed Density fueling maps......When I was tuning my Camaro, The MAF scaling proved to be quite difficult & time consuming with the 90mm throttle blade vs a 76mm the MAF table was scaled to. Drove around for weeks with the MAF signal wire unpinned running solely on Speed Density. Ran so well I really considered leaving it SD! But my OCD wouldn't let me

 

[Colt45ws]

Originally Posted by dogememe
Originally Posted by Colt45ws
Originally Posted by clinebarger
Ford's "In General" don't have a MAP sensor, Where just about all OBD2 GM vehicles have a MAP & MAF sensors & can default to "Speed Density" fueling with the MAF unplugged.

When the ESM "EGR System Module" was added to the Crown Vic 4.6L in 2003 (probably other apps around that time) a MAP reading became available as instead of using a separate DPFE they now have a sensor built into the module, with the orifice between the EGR itself and the intake, so the DPFE sensor is measuring MAP on one side of it.
However I dont think they actually do anything with it. I know for sure the EEC-V cars definetly dont as they have a hard code 'Failed MAF' table. I wouldve hoped the later PPC cars would make actual use out of it but maybe not.

The problem is likely because its DBW. It may not have even gone into failed MAF mode with the amount it was run. Might take a second key cycle for it to realize the MAF _is_ dead and it needs to use a fail safe strategy. All three of my EEC-V Vics run great with the MAF unplugged. The only reason I figure it out is the trans shifts harder than normal. I actually had to drive my 2002 with it unplugged when I blew a spark plug out of the head, as it runs way worse with it plugged in and stalls more.

I restarted it enough times before even leaving the parking lot for the check engine light to come on and for it to set codes (I checked with my scanner) for the MAF sensor. So the PCM better have known the sensor was no good. I thought this car has a MAP sensor, I do see that reading on the scanner, or perhaps it's calculated/estimated?

No its getting MAP from the ESM so its real but it isnt programmed to do anything with it, and the torque calculations rely on MAF so much that without it it cannot figure out what throttle angle to run the engine to get your requested throttle input or even keep enough base torque so the engine doesnt stall.
Another reason 2004 is best year.