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Old 04-26-2011, 06:50 PM   #1
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What goes wrong or bad in a ECM Simply

An Ecm is just basically a EEPROM chipped module that controls by monitoring the inputs given to it.

Inputs to program to output.

All of the sensors are powered by the ECM except those requiring more power to function, these will have separate power supplies and most generally relays (Maf sensor, Maf burn off, fuel pump) The sensor input to the ECM will be in low voltage range or in pulse width modulation (counts)

So much for the inputs

The program
Think of it as what comes around WILL go around. Very simply, if the O2 sensor sends to the Ecm a high reading, that means too much air or too little fuel to the program, So the Ecm looks at the throttle position sensor which looks ok acording to the speed sensor, then the Ecm looks at the fuel pressure sensor which sends a low reading. The Ecm cannot do anything about this problem so it alerts you by energizing the CEL.

In this synario, the first thing to check is the fuel filter, if in doubt change it, second, fuel pressure is controlled by vaccum, which is another input to the ECM by the maf or map sensor depending on which car you have.
(Look for a vacuum leak before changing any sensors)

The outputs from an Ecm
There are 3 kinds;
analogue 0-12 volts
digital = on-off
pulse width = counts

Inside of an Ecm there is a bank of triacs (look like overgrown transistors) These are what do the output from the Ecm. They are like on-off switches, a volume control and a momentary switch. They will go bad over time.

Unfortunately the Ecm knows that it sent a signal out to lets say the maf sensor via the maf sensor relay and did not get a reading back. There are 3 components involved. One the maf sensor relay (coil could be bad or contacts worn out) Two (maf sensor itself, not likely) Three (triac that sent the on-off signal) This equates to a code 33 CEL

So what goes bad in a ECM, The triacs!

Last edited by red88tagta; 04-26-2011 at 06:52 PM. Reason: spelling
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Old 04-26-2011, 08:52 PM   #2
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Re: What goes wrong or bad in a ECM Simply

Quote:
Originally Posted by red88tagta View Post
An Ecm is just basically a EEPROM chipped module that controls by monitoring the inputs given to it.

Inputs to program to output.

All of the sensors are powered by the ECM except those requiring more power to function, these will have separate power supplies and most generally relays (Maf sensor, Maf burn off, fuel pump) The sensor input to the ECM will be in low voltage range or in pulse width modulation (counts)

So much for the inputs

The program
Think of it as what comes around WILL go around. Very simply, if the O2 sensor sends to the Ecm a high reading, that means too much air or too little fuel to the program, So the Ecm looks at the throttle position sensor which looks ok acording to the speed sensor, then the Ecm looks at the fuel pressure sensor which sends a low reading. The Ecm cannot do anything about this problem so it alerts you by energizing the CEL.

In this synario, the first thing to check is the fuel filter, if in doubt change it, second, fuel pressure is controlled by vaccum, which is another input to the ECM by the maf or map sensor depending on which car you have.
(Look for a vacuum leak before changing any sensors)

The outputs from an Ecm
There are 3 kinds;
analogue 0-12 volts
digital = on-off
pulse width = counts

Inside of an Ecm there is a bank of triacs (look like overgrown transistors) These are what do the output from the Ecm. They are like on-off switches, a volume control and a momentary switch. They will go bad over time.

Unfortunately the Ecm knows that it sent a signal out to lets say the maf sensor via the maf sensor relay and did not get a reading back. There are 3 components involved. One the maf sensor relay (coil could be bad or contacts worn out) Two (maf sensor itself, not likely) Three (triac that sent the on-off signal) This equates to a code 33 CEL

So what goes bad in a ECM, The triacs!
I am not sure of the reason for this post. I will say though, there are no Triacs in these ECMs. Traics are used for A/C current, of which there isn't any in our vehicles (other then internal to the alternator).

An O2 high reading is rich, not lean.

There are many reasons for an ECM to go bad. Which areas have the highest failure rate actually depends upon which ECM we are referring to.

I'm leaving the rest of the post go...

RBob.
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Old 04-27-2011, 11:53 AM   #3
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Re: What goes wrong or bad in a ECM Simply

The purpose of the post was an attempt to remove some of the mystery of an Ecm operation and failure of components for those who do not understand how they work.

I have finally chased down my mysterious code 33 problem to the Ecm. It was a failure of the Ecm to power the MAF burn off relay. I thought I would break down the Ecm operation to a more simplier format.

I was in error with the high o2 sensor reading. I was thinking of the percentage of o2 in the exhaust gases instead if the actual voltage output to the Ecm. The o2 sensor has a NGC (negative gas coefficient) which means if the o2 percentage is high in the exhaust gases the output voltage will be low.

As far as triacs being used in our cars, they are almost everywhere.
http://www.st.com/stonline/products/...re/an/5201.pdf

You might find this useful as well, this is the output circuitry of a 1227165 Ecm, note the circuitry of chip 16042368 #'s U3 and U6;
http://www.exatorq.com/ludis_obd1/1227165schematic.html

Most other Ecms can be found here;
http://www.exatorq.com/ludis_obd1/schematics.html

The Ecm triacs I was writing about (mine) are pictured here.
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Old 04-27-2011, 12:01 PM   #4
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Re: What goes wrong or bad in a ECM Simply

Those aren't triacs, they're monolithic output drivers. The actual internal circuitry in the final output stage varies depending on application, but there are no triacs that I'm aware of. For example, I believe the relay drivers are bipolar transistors and the injector drivers are MOSFETs.
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Old 04-27-2011, 12:10 PM   #5
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Re: What goes wrong or bad in a ECM Simply

Quote:
Originally Posted by Apeiron View Post
Those aren't triacs, they're monolithic output drivers. The actual internal circuitry in the final output stage varies depending on application, but there are no triacs that I'm aware of. For example, I believe the relay drivers are bipolar transistors and the injector drivers are MOSFETs.
English please!
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Old 04-27-2011, 12:19 PM   #6
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Re: What goes wrong or bad in a ECM Simply

How could you have read my post, analyzed the information and repost in just 8 minutes and come up with "that I am aware of" and "I believe"
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Old 04-27-2011, 12:47 PM   #7
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Re: What goes wrong or bad in a ECM Simply

Call it a few years of experience in engineering.

I did go back and look at your schematics, though. No triacs there, just BJTs and MOSFETs inside output driver packages.

There are lots of things inside an ECM that can fail. Sometimes it's an output driver, sometimes it's something else.
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Old 04-27-2011, 02:10 PM   #8
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Re: What goes wrong or bad in a ECM Simply

Quote:
Originally Posted by red88tagta View Post
The purpose of the post was an attempt to remove some of the mystery of an Ecm operation and failure of components for those who do not understand how they work.

The Ecm triacs I was writing about (mine) are pictured here.
The problem is that there is very little factual information in your post. A MAF sensor can't read and report manifold vacuum, there are no fuel pressure sensors, and there are no analog outputs from the ECM. Not to mention the total lack of Triacs in an ECM.

I've seen the schematics of your '165 ECM, along with those for the other ECMs Ludis made available.

As for types of failures, as I mentioned it depends upon the ECM. The C3 series the most prevalent failures are the quad drivers and the small transistor that drives the fuel pump relay.

For the P4 series of ECMs, which your '7165 is, the most prevalent failures are circuit board or trace cracking, and I/O on the various custom chips. Haven't seen a bad quad driver in one, but expect to someday.

As for your failed '7165, why do you think it was the driver? I have a '7730 here (a P4), that one of the two IAC outputs was dead. Wouldn't do a thing. The failure wasn't the IAC driver, it was the port on the custom CPU that wasn't doing anything.

And last but not least in the list of common failures is corrosion of the connector pins.

These ECMs are nothing more then a computer with custom I/O in them. There is a CPU, PROM, RAM (memory), an ADC unit, and custom I/O to handle the duties of engine control.

RBob.

Last edited by RBob; 04-27-2011 at 02:16 PM. Reason: spelling
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Old 04-27-2011, 03:15 PM   #9
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Re: What goes wrong or bad in a ECM Simply

Weren't you the moderator here:
http://www.thirdgen.org/techboard/df...ng-cranks.html (ECM not reading? Cranks, engine light not coming on)
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Old 04-27-2011, 04:36 PM   #10
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Re: What goes wrong or bad in a ECM Simply

Quote:
Originally Posted by red88tagta View Post
Yes, I moderate the DFI & ECM board,. What does this have to do with your thread? I can answer that for you: nothing. Other then the same attitude you have in the last post of that thread and the attitude in this thread.

You may want to re-read my posts in that thread. Mostly post #2 where I stated that I wasn't positive that the power feed I mentioned was used in the OP's car.

Very few know about the ECM & fuel pump using that feed. And the fuse fails on a regular basis from heat & vibration. Not sure why you told me to get the right schematic for my car, as I have the FSM for my car.

Since you want to air this in public, I'll state that your thread on selling the ECMs is in the wrong forum. Users have complained about it but I let it go. So you have been cut some slack.

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Old 04-27-2011, 05:29 PM   #11
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Re: What goes wrong or bad in a ECM Simply

The point being by bringing up this tread
http://www.thirdgen.org/techboard/df...ng-cranks.html (ECM not reading? Cranks, engine light not coming on)

Is that you did not know about that fuse being there on that model/year. Is it possible that you don't know everything about Ecms as well? I know I don't! Never proclaimed to!
I never asked you or told you to get the right schematic for your car. The point was for the readers to get the right schematic for their cars. You should re-read that one.
Just since I just happen to know a few things about these cars is not something to get huffy about. The only attitude coming across here is from the moderators jumping on me with both feet.

Seriously doubt if anyone complained about a sale of Ecms on the wrong board. If they did, Please forward any complaints that you have recieved.

All that aside, as a community, we are supposed to be helping one another with problems. If I have erred in my discussion of Ecms, you could have consulted with me by PM to correct the information.
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Old 04-27-2011, 05:49 PM   #12
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Re: What goes wrong or bad in a ECM Simply

Quote:
Originally Posted by red88tagta View Post
The point being by bringing up this tread
http://www.thirdgen.org/techboard/df...ng-cranks.html (ECM not reading? Cranks, engine light not coming on)

Is that you did not know about that fuse being there on that model/year. Is it possible that you don't know everything about Ecms as well? I know I don't! Never proclaimed to!
I never asked you or told you to get the right schematic for your car. The point was for the readers to get the right schematic for their cars. You should re-read that one.
Just since I just happen to know a few things about these cars is not something to get huffy about. The only attitude coming across here is from the moderators jumping on me with both feet.
I would trust what RBob says without hesitation, due to his work with the Delco ECMs, both C3 and P4. There is also a second highly regarded member that posted the same as RBob.

Quote:
Seriously doubt if anyone complained about a sale of Ecms on the wrong board. If they did, Please forward any complaints that you have recieved.
While I didn't make any formal complaints, I did find it odd that it was allowed to remain in this forum.

Quote:
All that aside, as a community, we are supposed to be helping one another with problems. If I have erred in my discussion of Ecms, you could have consulted with me by PM to correct the information.
If this thread is any indication, I'm sure that your response would have been much the same.

Yes, that same argument "that we as a community should help each other" also includes correcting when people "err."

Last edited by Six_Shooter; 04-27-2011 at 06:08 PM.
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Old 04-27-2011, 06:14 PM   #13
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Re: What goes wrong or bad in a ECM Simply

Hey Six_Shooter,
Not that I started one, But you don't have a dog in this fight.
You did not make a complaint.
When you correct someone in public it should be done nicely or take it in private.
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Old 04-27-2011, 07:10 PM   #14
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Re: What goes wrong or bad in a ECM Simply

Thread isn't going anywhere productive... Best to put it to rest...
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Old 04-27-2011, 07:10 PM
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