Limp Home Mode is just for a processor failure. It means the ecm is using the RFD (redundant fuel devise).

Fail Soft Mode, is when there is a failure of some sort like a Coolant temp sensor and the ecm is using a **default** value, and is running on that.

Period.

Might as well spread the word, so we all get to being on the same wave lenght.

 

If you dont mind, can you tell us what does work & what does not? I have studied the prints for my ecm (7730) & it appears that if the Processor shuts down it does not pet the watch dog (or something similar to this type of action) & the LHM takes over & starts to "run" the ECM. This being said, the car is going to run as well as it can for the LHM that is built into the Memcal. this means that if you have a bone stock L98 it will probably run OK, but for me with a superram & some cam, the motor is going to barely run. In other words the tuneup for the engine combination is in the Memcal & Ign module.

when in LHM, the ALDL, purge canister, EGR, AC, & other small stuff does not work, but the basic, timing, & Injectors does.(?) this is more of a quesiton than a statement.

when in FSM, the processor is actually running, but because of a failed component it has to assume some default value for that sensor. Using your CTS example, it will assume a coolant temp of 195 Deg F (for the sake of argument) & goes on with life using that defualt value. @ the same time it will set a code for the failed CTS, & flash the CEL.

I would expect that the rest of the engine systems would work as they ought to (egr, canister purge, AC etc), including the ALDL port (you would hope right?).

thank you mucho.
BW

 

Bruce, thanks for the enlightment on the differences between Limp Mode and Fail Safe Mode. I am sure that many otheres just refer to ANYTIME the SES light comes on, that they are in Limp Mode, and not Fail Safe.

I have not dived into the differences between the two that much, but I do see a lot of references to "Stay Alive". Is Stay Alive Mode also Fail Safe Mode or is this yet another "state" of the ECM that we DIY'ers should be more concerned about?

 

In fail soft, everything is working. Just a steady *on* engine light.
Flickering light is indicative of LHM.

LHM is fixed timing, ecm wise. The module does have some self advance in it, so there is some timing change, but not due to ecm control.
LHM is just that. On some applications, you will be lucky to get to the side of the road. On some ecms (ie the 165 with the 6E code), you wind up in an Alpha-N command system, and surprisingly good running.

 

Thanks again,

BW

 

Would an '89 IROC have the 165 ecm with the 6E code and would this "running in Alpha-N" be the reason why my friends MAF is uplugged and it doesn't change how the car is running?

If not, how is it that he can run with no MAF hooked up on his L98? The engine is completely stock except for bigger injectors, raised fuel pressure, and N2O. The chip is stock.

 

It's my understanding that w/ out the MAF, he'll be in limp home mode.

On sequential LT1's (94-97), this will "revert to batch fire & result in a major loss of economy & power"

If it's in limp home mode, it'll be running rich, so it might "feel good" but you'd be missing out on economy, spark curve (might not be too noticable) and other items...

 

NO.
Limp Home Mode is in case of PROCESSOR failure.

Running with a sensor disconnected, the ecm will use a set of default values, and FAIL SOFT.

 

It might not feel terribly different, but that is just showing what a lousy sensor the human body is.
The human body is easy to fool.
Drive and STS and you'll think your in a fast ol barge, break out the stopwatch, and you'll see your in a yawnmobile.

 

Maybe you should actually read the code to grasp it, rather then going on what you understand things to be.

Have you read the LT1 code?.
It doesn't seem to make sense to go to batch fire over loosing a MAF. Even without the MAF it can do a calculation based on the MAP.

BTW, in back to back tests my car runs better in batch fire rather then SEFI.

BTW, there's lots of nonsense being repeated as truth on the LT1s, and it seems some folks think because things are repeated so often makes them true.

 

Hey Bruce,

You had a big opinion of yourself on control arm discussion on gnttype.org years ago. I didn't get cocky about this, all I said was "it is my understanding that..."

If you care to correct, then you should post the correct information, not just flame.

The info that the LT1 goes to batch w/ MAF failure comes from the factory service manual, i.e. Helms. I can fully enjoy the fact that you dislike me, but I am regurgitating info directly from it, so retort to Uncle Helms, not me. I don't care if it "makes sense" to you for it to go batch, that's what factory documentation says that it does. Can Helms be wrong? Yes. Do I agree that reverting to batch doesn't make sense? Yes. Was that the point? No.

No, I have not slept with & had a relationship with LT1 code. Yet. Maybe after I've had all the experience you've had w/ code, I'll understand your bitterness. But, I was just trying to help. It's a bad habit of mine to refer to things as "limp home" when there can be further clarification made to a "fail soft" mode. So sue me.

Your attitude of "period." at the end of statements is deserved in some cases; you know an obscene amount of good stuff about our cars. But you're still capable of making assumptions and being wrong, just like the rest of us. Keep your ears & mind open. Even when you know it all, there's still more to learn.

Matthew

 

What a post about a arms has to do with the price of tea in china is pointless, and i fail to see the relationship with prom burning.

There is no bitterness in my posts, you're just reading things into it.

GM has been teaching stuff full of errors for years, and that doesn't make it right. If you quote something as being true, you're responsible for what you're saying.

Funny how when anyone gets corrected the immediate response is using the word flame.

Weither you like it or not, there is a difference from fail soft to limp home. If you want to continue to use the phase improperly, well, don't get upset about being corrected.

BTW, when I am corrected, I don't going hollering about being flamed. When I'm wrong, I admit it and just go on.

BTW, I don't try and remember everyone I write to, so my reply to you was minus any alledged attitude, from a thread from years ago.

ECM content,
Some people still think a 730 has two injector drivers in it. Yep, the accuracy of some training manuals is just wrong.

 

Just a continued pattern of you having been, being, and continuing to grumble like a 4bbl at cold start in your responses to those things you don't like to admit.

I am declaring, in your grand tradition of declaring, my own definition of bitter. And in your bitterness towards those who assume LT1 functions, you flamed me for a statement you believed to be false, when in fact it was and is, true.

Your annoyance at LT1 presumptions doesn't make it wrong, either. I stand by my statement that without MAF input, the 94-97 LT1's go to batch. I stand by the words I write here as true and I have no qualms about being responsible for my words.

Again, if you care to correct, you should post a correction, not just flame. If you had a valid reason to question the statement, that would be understandable, but your little tantrum about "nonsense being repeated about truth" in reference to an accurate statement was uncalled for.

Lumping someone into a category of those who spout "nonsense being repeated about truth" is a mite more than a mere correction.

I didn't even read your first post before replying to his in the first place. Get over it. I am.

I didn't disavow it. Drop your little hints that I'm whining all you want. I made a statement, you flamed me, I defended my statement, I stand by my statement, and I'm calling a flame, a flame.

I have a good memory. Get used to it. I'm not going anywhere. And I'm not going to lie down for your flames & tantrums.

Great shift of topic there. Go do some reading, of the LT1 code if you wish, and then, and only then do you need to reply to my post with an assumed correction. Until then, don't reply to something you do not understand, or are not familiar with. It's good policy to follow, and I attempt to do so.

Matthew

 

I've been trying not to get in the middle of this and I will continue to stay out but I just have to add a little 2 cents. Grumpy, your post did seem like a flame to me as well. You may have not intended it that way, but that's the way it came across. To two people not just one. I agree it's hard to tell a persons "attitude" when it's just words on a screen but I think "wording" of sentences and paragraphs go a long way and that same "wording" can have a lot of attitude in it, good or bad, intentional or not.

Ok, you two can go back to arguing now.

 

Grumpy did question my maf tables post.But I did'nt take it as a flame.I would have liked a response to mine though.I'm not calling you out grumpy but could you give me some detail as to what the counts in the maf tables stand for,please w/ vurtual sugar on top?I know how to change all the maf tables to get 128blms accross the boards.But I have not read the code so can't say the exact relationships the "counts" have.I just know how to use the current bin editors very well.If you dont want to answer then just give me a y or n if looking at the bua hak will help explain things(if I don't know assebly language)?I will say Grumpy is his name so what do you expect?I would like to say thanks Bruce for all you have done for diy-prom.I have read hours of your material its all very good.It's funny because I just had a fail soft mode occur today then I read this.

 

I'm not clear on what exactly your asking. Maybe a snippet of actual source code will explain it.

These values are what calibrate the MAF to convert the maf signal into a form for calculating the grm/sec at any given point in time.


*################
* FMTBL1 TABLE
* MASS FLOW TABLE 1 FOR FM AIR METER
* TABLE VALUE = GRAMS OF AIR/SECOND (9 VALUES)
* 0-22 Gms/sec
*################
*TBL2D,9,2,TBL25,1,'GM/SEC'
*EQU N=E*256/FMTBL1
FCB 142
FCB 142
FCB 142
FCB 142
FCB 142
FCB 142
FCB 165
FCB 195
FCB 231

 

You know something folks, this is getting rediculous. I once asked Bruce (Grumpy) why he continously repeats himself with to people. I mean, to the newbies, the same things. To the stubborn, the same things. To the trully undeserving, the same thing. He just repeats himself, saying the same things over and over. Why? He simply told me that he doesn't want anyone to follow or believe something that isn't true, no matter how many times he has to repeat himself. This is the reason for the "Final Answer" posts folks. It's not so that you can argue with him or call him arrogant or get upset because he corrected you and you took offense. The problem is people want to believe what's easier to believe. They want to hear that what they know is correct. They don't want to actually have to do anything to see if it works, they want someone to tell them, "yeah, that sounds like a great idea, that'll work." What are we doing on this forum if it isn't trying to learn something. And if everyone here told you exactly what to do, have you really learned anything? This virtual world of all reward and no work just isn't real. Grumpy isn't some maniacal school teacher trying to embarras you in front of the whole class, he just has his way of saying things. I bet you didn't mind learning anything from him as long as he told you what you wanted to hear but the second he asks you to do some "research" you get bent out of shape and start accusations of flaming on his part. This is an internet forum and the things you say on here can be seen by thousands of people and could be taken as fact and that is why he coorects folks when they say something incorrect. I hope all of us would do the same thing so as to not cause anyone to believe in false statements. And if you disagree with anything anyone has to say, then prove them wrong by doing something about it. And before this gets taken out of context, I am not singling anyone out. This is not a post about one person but rather a group of people that need to relax and come to their senses. No one here is out to get you so get over it! Spend your time trying to learn something instead!

 

I will say Grumpy has the right to slap me around anytime.He has done so much for diy-prom,by sharing what he has learned.The type of info the aftermarket company pays to hear.But Grumpy's final answers should'nt be in a message type post.Really they all need combined into one post then locked and sticky.That way emotion don't get involved with the facts.It puts a smoke screen over the truth and facts.Grumpy I will think about exactly my question.The source code helps solidify my question though.

 

If the prom is bad, doesn't it go to limp home mode?
I had a bunch of bad chips due to PP2 Software not working with WinXP Pro. Program looked like it was burning good chips, but wasn't.
I drove around for 6 weeks with a bad prom thinking the ECM wasn't working right. I did get my 305 to run a 14.7 @ 93mph without the prom functioning.

Car ran extrmemly rich and averaged less than 10mpg, but seemed to run very strong.

 

I think that's what was happening with me with my idle misfire (due to an excessively lean condition). I had a short circuit on the fuel injector circuit that I believe was damaging the ECM. I replaced the ECM a number of times (with wrecking yard units) before I located the problem. Each time, the car would run fine for a few minutes and then the misfire would start up again. AS soon as I got off idle, the misfire went away, but there was a lot of hesitation on throttle tip in (and sometimes a lean pop). However, no codes were registered and the scanner read out showed that all was just fine- sensor readouts were good, 128 BLMs, there was no indication of a problem save for the obvious misfire. As soon as I found the short and repaired it, then replaced the ECM, the problem went away. I'm assuming this was some sort of limp mode?

 

Yeah Grumpy,

I like the one about the 2 injector drivers in a 730!!
In the several 730s and 727s that I have opened up the second driver ( and the alternating bank injector fireing outlined in the GM FI and other manuals) is just vaporwhare. I guess i could solder the second driver parts on the board but I dont think it would make me feel any better.

You can enlighten me anytime!!!

Greg.