airworks-fc3s

guys, what are the symptoms of an S5 Tii beiing in limp mode??

1BADSP

iTrader: (4)

your omp is probably bad,symptoms are very little power,it was designed to just get you to a repair shop or home.

airworks-fc3s

ok! the problem is it's running quite fine but i checked the map sensor yesterday: pulled the hose, and pressurized it with about 7psi at idle, but the engine would not stall! but it should have! then i gave it extreme vacuum and it did have no impact in running. then i took out a map sensor of a friends S5 TII to check... but it was the same. now i think that my ECU is just not reacting on the map sensor, because normally if you have boost, the ECU will enrich your mixture! i thought that the ECU was in limp mode, because i have all the emissions removed! confused??

RotaryResurrection

iTrader: (8)

Boost sensor controls timing, not fuel. Afm and water thermosensor control fuel.

The only thing that should put it into limp mode would be the OMP. You would definitely have a CEL.

NZConvertible

Also the AFM.

RotaryResurrection

iTrader: (8)

I've never seen a bad AFM that would allow the engine to run in any resemblence of "normal". AFM's are either right, or wrong, without much in between, in my experience.

airworks-fc3s

thanks guys! ok so i think i'm fine... car runs great!

NZConvertible

Yeah, I just made it up for fun...

As per the S5 FSM, for error code 03 (AFM) the fail-safe function is "basic fuel injection amount and ignition timing fixed", i.e. limp mode. The same is true for codes 20 (OMP position sensor), 27 (OMP control system) and 37 (battery voltage).

RotaryResurrection

iTrader: (8)

You can quote from the manual all you want, while I quote from experience. I have seen more FC's than anyone on this forum I would wager. About 2 months ago I had an s5 car with a bad afm...it had gotten water and debris inside. The car did not throw any CEL or engine codes, but it was absolutely undriveable, and would barely even run no matter what was tried with the throttle.

This type of damage is the only way I have ever seen an AFM actually fail. That, or if someone has taken it apart and been dicking around with the internal spring settings.

NZConvertible

You've never experienced it so it can't be right? Mazda just put that in the FSM for a laugh? Are you saying the info is wrong, or can you admit that maybe you haven't experienced everything that can go wrong with a car?

The AFM doesn't have a water and debris sensor. Error codes don't mean "bad device", they mean "bad signal". The self-diagnosis system is looking for signals that are obviously a long way from normal, i.e. very low, very high or not there at all. A dirty sensor won't necessary fall into those categories but will still affect the signal enough to cause poor drivability.

A broken wire or a loose or disconnected plug are two obvious possible causes of an AFM error code. Internal sensor failure (i.e. loose or failed electrical connection) is also completely possible despite you not having seen it.

RotaryResurrection

iTrader: (8)

Yes, right after you admit that the manual does not cover every contingency of possible failures, and it does cover possibilities that almost never occur.

For instance, right now I am fighting an electrical problem on a car that the manual offers no help for. An emissions/engine harness had a bad section of wiring to the CAS, just a couple of inches away from the CAS connector the insulation was cracked and the wires almost broken, causing an intermittent lack of signal that would cause the car to run poorly until that section of wiring was jostled. Being a hard to find harness, I decided to simply splce on a new connector with a few inches of wiring, but when I was done the car no longer has ANY CAS signal at all.

EVERY SINGLE ELECTRICAL CHECK per the FSM related to the ignition/control system is perfect, yet I have no injector pulse and no ignition signal. Each of the CAS wires shows perfect continuity from the CAS plug to the ECU plug. I have tried different ecu's and different CAS's. It's a real head scratcher that the FSM provides no contingency for...according to the FSM, if the CAS shows good impedance and the CAS wire voltages at the ecu are below 1..0VDC then it should work, but low and behold it does not.

What does your almighty manual tell you about that?

This wasn't just a bad connection or a little debris keeping air from flowing through. It was a legitimately bad sensor, the plunger would no longer move freely and correctly, resulting in an incorrect signal and incorrect AFR to run the engine. Since the fuel injection was not sufficient, and the AFM is the deciding factor in fuel injection volume, we can assume that the AFM signal was incorrect versus the engine conditions. Then, according to you, the incorrect signal must have triggered an ECU code and a limp mode, yet it did not. There were no codes stored during or after the issue. Car ran perfectly with another AFM, but the codes and limp mode would never have led the average person to the problem.

YOU CANNOT DECIPHER EVERY PROBLEM WITH THESE CARS BY THE MANUAL. Many, yes. All, NO.

Again, I had an internal sensor failure and no codes or light. Why?

Could an AFM fail internally and trigger the light? I guess. I have I ever seen it, in the over 200 FC's I've worked on personally? No. Has anyone here sampled a larger group of FC's to make this comparison? Doubt it.

NZConvertible

I never claimed or implied anything different. I'm simply telling you what THE CAR does, and you seem to disagree for some reason. The FSM isn't really the topic of discussion here, but you seem to have a real hate on for it. To remind you, you said "the only thing that should put it into limp mode would be the OMP", and I simply pointed out there was one other thing that will do it. End of discussion. You learnt something you didn't know, so now you're just a little bit better off. I learn stuff from reading your posts all the time, and I'm sure you learn stuff from mine (not that I'm expecting that admission). I'm not sure why you think this deserves a diatribe against the FSM.

No, you're not understanding the self-diagnosis system. It's 20yo technology and way less complex than you seem to think. All the ECU can do is look at the signal voltages to see if they're within a normal range. It can't tell if the AFM signal doesn't perfectly match the engine conditions (and I never said it could). If you dirty AFM was sending out a signal that was wrong in relation to the airflow, but the signal was still in a roughly 1.0-4.5V range, then the ECU sees nothing wrong. You're expecting way too much ability from such an old device. You need to look at ECU's in cars from this century to get that sort of error reporting.

You say this as if it somehow changes the facts...

RotaryResurrection

iTrader: (8)

Don't get me wrong...I refer to the FSM almost daily, and it is great to have. But it only provides about half of the information that I need to know...the other half is derived from experience with the cars...what parts fail and what parts don't, and how best to deal with those failures.

But you guys sitting here quoting the FSM like it is your god have to realize that there is a lot of missing info that can only be made up for with experience.

I was simply saying that my experience has shown that AFM's do not trigger limp mode because they are either good, or bad enough that the car wont run. I had an AFM in bad enough shape that the car would not move under it's own power, but no code or limp mode. You say that we should not expect an AFM in this condition to throw a code because the computer is not that advanced. Okay, fine...so exactly how bad would the AFM need to be to actually cause limp mode? Wouldn't an AFM, in even worse condition, make limp mode a moot point, since the car couldn't be driven anyway? That is my point.

Perhaps I should have amended my wording to be more precise, just for the armchair FSM readers: "By the book, the AFM or the OMP could trigger limp mode, however in real life, the OMP is the only part that is actually likely to cause the limp mode per my experience".

There, happy now? <sigh>

Yeah, every once in a blue moon I learn something from yours or someone else's post. And vice versa. I also learn from wierd failures like the CAS issue I am having now. And when all is said and done, I will know something that probably no one else knows. Wanna know why I havent bothered asking about it here? Because I am sure no one is likely to have seen such an issue, so I will figure it out myself.

NZConvertible

No ****. You say that like it's some grand revelation that none of us know, but you couldn't be more wrong. You think all I know is stuff from the FSM? I've been playing with cars as a hobby for nearly 20 years, and most of that time was without the benefit of extensive manuals. Try owning and working on a car not sold new outside of Japan, with not even a Haynes available. Quoting the FSM like it's a god? Geez, what a drama queen...

Seriously, you need to accept that this is simply a limitation of your experience. That's not an insult in any way, it's simply a fact. You haven't been around nearly long enough to be making claims that if you haven't seen it, it doesn't happen.

You're still not getting how the system works. Like I said, the error code means the device's signal is bad, not necessarily the device itself. A loose, dirty or damaged connector or a bad wire on the harness are obvious possible causes of a bad signal, just like any of the other sensors. The AFM can be perfectly fine but an error code will still be generated if one of these occurs. On the flip side, if you pull off the filter, start the engine and start pushing the AFM cone in and out, it would be wrong to expect an error code despite causing an airflow signal that obviously isn't reflecting the actual airflow.

Who says it couldn't be driven? Limp mode is more correctly known as limp-home mode, i.e. if something goes wrong the ECU will limit engine performance by using a "basic fuel injection amount and ignition timing fixed", allowing you to get you to where you're going or at least let you stop the car somewhere safe rather than the car stopping dead in the middle of the road. As you pointed out, the AFM is one of the most important sensors, so if something happens to it (or its signal) it's advantageous to be able to keep the car drivable without it. Keep in mind we're only talking S5's here, and the S5 doesn't need the AFM to operate the fuel pump like the S4 does.

You can bang on about your experience all you want. If the ECU loses the AFM signal or sees an obviously out-of-range signal, it will go into limp mode. This is not open for discussion or interpretation based on your experience. It is a FACT. I'm sure it is uncommon, but that doesn't change anything. I'm baffled by your need to argue about it. Get over it and move on.

Wow, your modesty is impressive...