'97 850 problems after ecu reset

Post by **misha** » 28 Jan 2015, 15:13

I thought that it's a good idea to open a new thread about this problem.

So,every time i reset my ecu by disconnecting negative battery cable i have problems with air/fuel mixture and black smoke from the exhaust.I mean every time.

I know that ecu need time to gather new parameters and informations,but does it mean that car needs to run rich and that fuel consumption goes up for 50-60% for that time ?!

After i reset it again it's good for a day and then it goes again...and again...and again....untill somehow in some of 5-25 reset it learns good things and have normal air/fuel mixture.

You can change Maf,o2 sensors....what ever you think of and things are always the same,without improvement at all.

When i keep resetting it...after some time it gives good result,but untill it relearn good things and go back to normal there are a lot of disconnecting negative battery cable.

I read that with this relearning things are affected only Motronic 4.3 & 4.4 cars.All others don't have this kind of problem.

I tried with relearning procedure,but no improvements.It's just going worst & worst untill i reset it again.

Post by **misha** » 29 Jan 2015, 19:23

Advices?

Does ecu suppose to make engine run rich after reset?

Post by **Ozark Lee** » 29 Jan 2015, 20:19

I don't know that this is a problem to all Motronic 4.3 or 4.4 modules. Resetting the ECU sets all of the trims to their nominal values and it is supposed to tweak them from there to establish new trim offsets based on what it "learns". What it is learning is largely the manufacturing tolerances on the sensors. I have had stock ECUs that were slow learners but I've never had one that made increasingly wrong decisions when it was getting good input information.

I did beta test an audio processor for a radio station that touted a "neural network" that was supposed to learn and optimize its dynamics based on the dynamics of the music it was processing. The algorithm, however, had a couple of flaws that caused it to learn bad things. Over the course of a week it went from sounding very good to downright awful. It was a beta test and I suppose that is why things get tested in the real world before they are released. I don't think there is an inherent problem with the base algorithm in the Motronic ECUs however. There are many thousands of them and I've not heard of your problem before.

Has the ECU mapping ever been altered by the previous owner?

There are gobs of freeware programs to download and re-map your ECU. Armed with the program and a PC, some people think they can tune a 2.4 liter N/A into a 450 HP beast. If the engine mapping was significantly altered I suppose the algorithm could cascade into divergence rather than convergence when it comes to trimming things.

Do you have another ECU available to you to play with for a week or so? It would be interesting to see if the behavior follows the ECU or the car. What it troubling is that when you introduce a vacuum leak the car runs better and never lights the lambda light.

...Lee

Post by **misha** » 29 Jan 2015, 22:35

Ozark Lee wrote:...Has the ECU mapping ever been altered by the previous owner?

Do you have another ECU available to you to play with for a week or so? It would be interesting to see if the behavior follows the ECU or the car. What it troubling is that when you introduce a vacuum leak the car runs better and never lights the lambda light....Lee

No...i'm the only owner since 2000.Car was bought from a Dad's friend,maintained at stealership untill 2002.

The car is not actually run better with a vacuum leak.It runs very good with or without vacuum leak,but with vacuum leak introduced it doesn't run that much rich.Exhaust smell better with a vacuum leak.

You are not aware that there is a problem untill you see black smoke from exhaust.There are not a single point that something is wrong except rich running condition and high fuel consumption.

I'll see if i can find another Motronic 4.4 ecu to try it.I guess that it must be from a car with auto transmission because mine is an auto...Or just to find another ecu with a matching Bosch numbers will be enough?

Post by **erikv11** » 29 Jan 2015, 22:56

The ECU must be from another automatic.

Post by **jreed** » 30 Jan 2015, 05:04

I know this thread started life as part of another thread, where this question may already have been asked and answered... has the engine coolant temperature (ECT) and wiring been checked? I ask because the one time I've experienced my '97 855 running rich with black smoke especially at start up was when the resistance coming from the ECT was out of spec on the high side, sending a false signal to the ECU to make the mixture richer to compensate for cold temperature. When I replaced the ECT with a known good one, the engine ran a lot better with no black smoke.

Post by **misha** » 30 Jan 2015, 05:08

I know that must be from automatic,but how can i tell that ecu i need to find is for auto or manual transmission?

When i type Bosch numbers from my ecu,for example,it just say that it's Motronic 4.4.It's not saying what type of transmission is it for.

Post by **misha** » 30 Jan 2015, 05:13

jreed wrote:I know this thread started life as part of another thread, where this question may already have been asked and answered... has the engine coolant temperature (ECT) and wiring been checked? I ask because the one time I've experienced my '97 855 running rich with black smoke especially at start up was when the resistance coming from the ECT was out of spec on the high side, sending a false signal to the ECU to make the mixture richer to compensate for cold temperature. When I replaced the ECT with a known good one, the engine ran a lot better with no black smoke.

It's checked and it's ok.

Like i said before in previous thread....you can put in a new maf & new o2 sensors and reset ecu.....it acts the same.When i keep resetting ecu...somehow after some time...it comes back to normal but ONLY with introduced vacuum leak.

Post by **erikv11** » 30 Jan 2015, 08:07

I am also stuck on the ECT idea. How close are the resistance values to specification, are they perfect, within 10%?

About the ECU, Is your car a turbo or not? I can't tell if you have a 97 GLT (LPT) or a 97 NA. There is more information available about turbo ECUs. A few 97 NAs did come with 4.4. If you have a turbo, you may find helpful information over at http://support.turbo-tuner.co.uk/.

In general, it is the last three digits of the ECU number that matter. If you match the last three digits then it is a matching ECU, although it may have different emissions on it. The best way to know emissions (primarily SAS in this case) is to look at the car it came from. Another factor is whether or not the car had an immobilizer, there are ECU differences for that. But those differences will only determine whether or not a CEL is thrown, and/or whether or not the immobilizer works, you are on your own (no guarantees!) but I don't think putting in a different ECU will damage anything.

As you know, it is rare for the ECUs to be bad. But your car's behavior does sound unusual.

Post by **misha** » 30 Jan 2015, 15:28

It's non turbo GLT,but for european 850(s),GLT is a trim level.

To go back on problems....today i disconnected front o2 connector and i didn't got check engine at all.When i disconnected Maf and started the car i got check engine right away.

Anyway...i left o2 disconnected and reset ecu.Started the car with it disconnected and the car ran like champ.

Ecu didn't registered that it's disconnected.Test driving gave me normal exhaust smell and according to board comp ideal fuel consumption.

Parked the car and went for a drive.Soon...the idle and exhaust smell got bad.

I did a reset once more and car performed excellent,o2 still disconnected.Like the ecu doesn't see it at all,neither connected neither disconnected.

Came home and exhaust smell got rich again.I removed ecu,deleted sas delete,connected o2,reset ecu...started the car and exhaust smell is good again.

It will be good for a day or two and then all bad things will come back untill ecu is reset again.After god knows how many ecu reset it will eventually go back to normal.Had this bad experience many years ago and because of that i didn't disconnected battery since 2004.Yes 2004.I just kept the battery in excellent shape.

I wrote about this in one thread many years ago.

Before i disconnected battery and removed ecu because of sas delete last week,i didn't had this problem.