How can i test if my ecm is fried?
02-20-2001, 01:26 PM
#1
Member
Thread Starter
Join Date: Oct 2000
Location: pleasanton, ca usa
Posts: 489
Likes: 0
Received 0 Likes
on
0 Posts
How can i test if my ecm is fried?
I think i may have fried my ecm...i sure hope not but i just want to rule it out, because if i did fry my ecm im making the switch to tpi now. My computer reads codes off, but i dont know how else to tell if its working properly. Thanks
02-20-2001, 01:55 PM
#2
Senior Member
Join Date: Aug 1999
Location: Glendale, AZ
Posts: 611
Likes: 0
Received 0 Likes
on
0 Posts
One way to tell, run the engine, and hit the ecm, if your engine skips a beat, its bad.
------------------
Rob
'86 TA 305 TPI
Gutted MAF
Ported Plenum
TB Bypass
------------------
Rob
'86 TA 305 TPI
Gutted MAF
Ported Plenum
TB Bypass
02-20-2001, 03:50 PM
#3
TGO Supporter
i'd say if you can read codes it's a good sign it's working.
------------------
ICON Motorsports
1st & 3rd
------------------
ICON Motorsports
1st & 3rd
02-20-2001, 06:06 PM
#4
Member
Thread Starter
Join Date: Oct 2000
Location: pleasanton, ca usa
Posts: 489
Likes: 0
Received 0 Likes
on
0 Posts
Ok well first off, i cant run the car...thats the whole reason im trying to find out if the ecm is fried. But i can read error codes so im happy about that. Well even though i wanted to switch to tpi i dont have the money right now so its probably good its not fried 
02-20-2001, 06:59 PM
#5
Banned
Join Date: Jan 2001
Location: Belleville, IL USA
Posts: 1,429
Likes: 0
Received 0 Likes
on
0 Posts
I've seen tons of bad ECM's that were bad and would still read codes for other things.
Surprisingly enough I have also seen the ECM-beating method described above work. Smack the thing hard enough and the car would work great for a while. The story I've heard is that the circuit boards develop cracks from heat/cold and vibration.
I have never seen an ECM go bad and actually tell you (via code) that it was bad.
If I suspected one, the first thing I would do is borrow another just like it.
good luck
ODB
Surprisingly enough I have also seen the ECM-beating method described above work. Smack the thing hard enough and the car would work great for a while. The story I've heard is that the circuit boards develop cracks from heat/cold and vibration.
I have never seen an ECM go bad and actually tell you (via code) that it was bad.
If I suspected one, the first thing I would do is borrow another just like it.
good luck
ODB
02-20-2001, 07:43 PM
#6
Member
Thread Starter
Join Date: Oct 2000
Location: pleasanton, ca usa
Posts: 489
Likes: 0
Received 0 Likes
on
0 Posts
Ok well if thats the case...anybody around the san fransisco bay area have a 91 305 TBI they wanna bring by my house and let me try it out?? cmon guys...itll be fun.
02-20-2001, 08:34 PM
#7
Josh,
One quick check is to watch the MIL lamp before you turn the key. Insert the key and turn it to RUN, not START. The MIL lamp should turn on briefly, then off briefly, then back on continuously. This flash alerts you that the ECM has passed power up diagnostics and has a valid PROM and/or CALPAK installed. If you don't get the flash, there is something wrong with the ECM.
Another thing you can do is to insert a 3,900 ohm resistor between terminals 'A' and 'B' of the ALDL. This forces the ECM into Backup Fuel / Factory Diagnostics Mode, or Mode 1. This will force the ECM to use the lookup tables in the PROM for base fuel and spark curves.
You can try to force Mode 2, which is an I/O exercise. If the resistor is in place, and the transmission is in PARK/NEUTRAL or the clutch is depressed when the key is turned to RUN, you should be able to force Mode 2. This will force the ECM to scan for loads and inputs, then exercise the discrete outputs at about a 32Hz rate. You should hear the fuel pump relay buzzing rapidly, then the IAC stepping, then the injectors clicking open and shut, etc. If this is working, the ECM should at least be able to operate the engine in Backup Fuel (Limp Home) mode. If this doesn't work, your ECM may have an I/O problem.
------------------
Later,
Vader
------------------
"No matter how hard you try you can't stop us now..."
Adobe Acrobat Reader 4.0
One quick check is to watch the MIL lamp before you turn the key. Insert the key and turn it to RUN, not START. The MIL lamp should turn on briefly, then off briefly, then back on continuously. This flash alerts you that the ECM has passed power up diagnostics and has a valid PROM and/or CALPAK installed. If you don't get the flash, there is something wrong with the ECM.
Another thing you can do is to insert a 3,900 ohm resistor between terminals 'A' and 'B' of the ALDL. This forces the ECM into Backup Fuel / Factory Diagnostics Mode, or Mode 1. This will force the ECM to use the lookup tables in the PROM for base fuel and spark curves.
You can try to force Mode 2, which is an I/O exercise. If the resistor is in place, and the transmission is in PARK/NEUTRAL or the clutch is depressed when the key is turned to RUN, you should be able to force Mode 2. This will force the ECM to scan for loads and inputs, then exercise the discrete outputs at about a 32Hz rate. You should hear the fuel pump relay buzzing rapidly, then the IAC stepping, then the injectors clicking open and shut, etc. If this is working, the ECM should at least be able to operate the engine in Backup Fuel (Limp Home) mode. If this doesn't work, your ECM may have an I/O problem.
------------------
Later,
Vader
------------------
"No matter how hard you try you can't stop us now..."
Adobe Acrobat Reader 4.0
Last edited by Vader; 08-02-2023 at 06:23 AM.
The following users liked this post:
StratosFear1986 (06-22-2022)
Trending Topics
02-20-2001, 08:50 PM
#8
Josh,
If you find that the ECM is damaged, check this link from a familiar name:
http://cgi.ebay.com/ebaymotors/aw-cg...item=562535690
------------------
Later,
Vader
------------------
"No matter how hard you try you can't stop us now..."
Adobe Acrobat Reader 4.0
If you find that the ECM is damaged, check this link from a familiar name:
http://cgi.ebay.com/ebaymotors/aw-cg...item=562535690
------------------
Later,
Vader
------------------
"No matter how hard you try you can't stop us now..."
Adobe Acrobat Reader 4.0
02-20-2001, 08:52 PM
#9
Banned
Join Date: Jan 2001
Location: Belleville, IL USA
Posts: 1,429
Likes: 0
Received 0 Likes
on
0 Posts
Man I am truly impressed. Vader is the man and knows his ECM's.
much better tests than beating on the thing, though the beating is probably more fun.
The only time my ECM ever made me smile was when it hit the bottom of my trashcan.
hope you find your problem.
If you can't find it and it becomes too expensive or puts you into some form of therapy, then there is always the old carburetor. Six years of it was enough for me and I admit I had to give up. Difference was I didn't have connections to knowledgable people back then like you do now with Vader and others.
(ok I feel better now... breathe)
ODB
much better tests than beating on the thing, though the beating is probably more fun.
The only time my ECM ever made me smile was when it hit the bottom of my trashcan.
hope you find your problem.
If you can't find it and it becomes too expensive or puts you into some form of therapy, then there is always the old carburetor. Six years of it was enough for me and I admit I had to give up. Difference was I didn't have connections to knowledgable people back then like you do now with Vader and others.
(ok I feel better now... breathe)
ODB
07-27-2015, 07:36 PM
#11
Junior Member
Join Date: Nov 2013
Posts: 34
Received 0 Likes
on
0 Posts
Engine: 305 5.0 TBI
Transmission: 700-R4
Re: How can i test if my ecm is fried?
Josh,
One quick check is to watch the MIL lamp before you turn the key. Insert the key and turn it to RUN, not START. The MIL lamp should turn on briefly, then off briefly, then back on continuously. This flash alerts you that the ECM has passed power up diagnostics and has a valid PROM and/or CALPK installed. If you don't get teh flash, there is something wrong with the ECM.
Another thing you can do is to insert a 3,900 ohm resistor between terminals 'A' and 'B' of the ALDL. This forces the ECM into Backup Fuel / Factory Diagnostics Mode, or Mode 1. This will force the ECM to use the lookup tables in the PROM for base fuel and spark curves.
You can try to force Mode 2, which is an I/O excersize. If the resistor is in place, and the transmission is in PARK/NEUTRAL or the clutch is depressed when teh key is turned to RUN, you should be able to force Mode 2. This will force the ECM to scan for loads and inputs, then excersize the discrete outputs at about a 32Hz rate. You shoudl hear the fuel pump realy buzzing rapidly, then teh IAC stepping, then the injectors clicking open and shut, etc. If this is working, the ECM shoudl at least be able to operate the engine in Backup Fuel (Limp Home) mode. If this doesn't work, your ECM may have an I/O problem.
------------------
Later,
Vader
------------------
"No matter how hard you try you can't stop us now..."
Adobe Acrobat Reader 4.0
One quick check is to watch the MIL lamp before you turn the key. Insert the key and turn it to RUN, not START. The MIL lamp should turn on briefly, then off briefly, then back on continuously. This flash alerts you that the ECM has passed power up diagnostics and has a valid PROM and/or CALPK installed. If you don't get teh flash, there is something wrong with the ECM.
Another thing you can do is to insert a 3,900 ohm resistor between terminals 'A' and 'B' of the ALDL. This forces the ECM into Backup Fuel / Factory Diagnostics Mode, or Mode 1. This will force the ECM to use the lookup tables in the PROM for base fuel and spark curves.
You can try to force Mode 2, which is an I/O excersize. If the resistor is in place, and the transmission is in PARK/NEUTRAL or the clutch is depressed when teh key is turned to RUN, you should be able to force Mode 2. This will force the ECM to scan for loads and inputs, then excersize the discrete outputs at about a 32Hz rate. You shoudl hear the fuel pump realy buzzing rapidly, then teh IAC stepping, then the injectors clicking open and shut, etc. If this is working, the ECM shoudl at least be able to operate the engine in Backup Fuel (Limp Home) mode. If this doesn't work, your ECM may have an I/O problem.
------------------
Later,
Vader
------------------
"No matter how hard you try you can't stop us now..."
Adobe Acrobat Reader 4.0
02-03-2016, 04:44 PM
#12
Junior Member
Join Date: Feb 2016
Posts: 1
Likes: 0
Received 0 Likes
on
0 Posts
Re: How can i test if my ecm is fried?
So if I turn my key over to the run position the MIL lamp should flash and if it doesn't and it just stays lit up my ecm is bad? Sometimes if I let my truck set long enough when I turn the key it flashes 1 time then stays lit up until I start the truck... any ideas?? Ive been having some problems with my truck and cant figure out what the problem is and really don't want to go to a dealer and pay out the butt for a mechanic to look at it.... Starting to think the ecm is bad but want to make sure before I replace it and have it programmed.. its a 1996 Chevy k1500 Z71 5.7L auto trans
08-01-2023, 08:19 PM
#13
Junior Member
Join Date: Aug 2023
Posts: 7
Likes: 0
Received 0 Likes
on
0 Posts
08-02-2023, 06:33 AM
#14
Re: How can i test if my ecm is fried?
If tapping the ECM causes an interruption, there may be an intermittent or unreliable connection(s) inside or to/from the ECM. That can include the harness connectors, CALPAK and PROM socket, or any of numerous solder connections. The easy thing to do is remove, clean, and inspect the harness connectors. A new ECM will do no good if the connectors are contaminated or corroded. The same applies to the CALPAK, so it can be useful to remove the cover and inspect the plug-in connections for it. All of that would have to be done with a new ECM anyway.
Of course, it would be best to do that with the battery power removed.
If the connections are cleaned and reliable, there may be circuit connections within the ECM which are intermittent, requiring some electronics bench time ( or replacement ECM).
Of course, it would be best to do that with the battery power removed.
If the connections are cleaned and reliable, there may be circuit connections within the ECM which are intermittent, requiring some electronics bench time ( or replacement ECM).
Thread
Thread Starter
Forum
Replies
Last Post
