So on the way to work on Saturday. Car cut off about 5 times and I would just restart it and it would keep going down the road, but there was a burnt plastic smell all the way to work. Actually still stinks up the car. So I tracked the smell of the burnt part with my nose to the console. I removed the console and followed my nose to the ECM. I removed it and replaced it with another that didn't stink although had the same issue with not turning on the fuel pump. So I have temporarily hot wired the Fuel pump to a switch until I can get another ECM (the 3rd one)..
Here are the pics of the burnt FET inside the ECM. I thought you guys would want to see it.
Here is what the FET usually looks like
So from here I'm gonna try to replace it although I have no idea of it's value since it was a pile of dust after I took it off the board. I will just try one of the FET's I have already and see if it works. Worst comes to Worst i will replace my Oil Sending unit and run the Fuel pump off that circuit until I can find a good ECM that won't burn up.
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07:25 AM
PFF
System Bot
jaskispyder Member
Posts: 21510 From: Northern MI Registered: Jun 2002
Sounds like you have another issue besides the ECM. Did the other ECM burn up the same way?
Yea, could be something else but I don't even know where to look. What makes a FET burn?
Yes, both ECM's have the same symptoms, they both will run the Fpump only right after the key is turned OFF for a second. when you go to re-start it tries to start but won't. I will turn over and kick over a little but never fully start. Last time this happened I replaced the ECM with the 2nd one and still didn't fix the issue. Only when I added another Ground cable did the car start up again. This leads me to think it's a grounding issue. And it has ran fine for about 4 months now until last Saturday.
[This message has been edited by jwrape (edited 11-09-2011).]
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09:38 AM
phonedawgz Member
Posts: 17091 From: Green Bay, WI USA Registered: Dec 2009
The obvious is something that the ECM controls has a short on the wiring, or is taking too much current.
First thing to do is look at the INJ1 and INJ2 fuses and the ECM fuse and make sure they are of the correct size.
Next look for shorts/bad wiring on the fuel pump relay, A/C relay, injectors, and EGR control valve.
The main power to the ECM is via the quick disconnect right next to C500, and is not fused on the Fiero. I would take that apart and put an amp meter inline to see what is happening. Measuring the current there you should get no more than 3 amp.
The obvious is something that the ECM controls has a short on the wiring, or is taking too much current.
First thing to do is look at the INJ1 and INJ2 fuses and the ECM fuse and make sure they are of the correct size.
Next look for shorts/bad wiring on the fuel pump relay, A/C relay, injectors, and EGR control valve.
The main power to the ECM is via the quick disconnect right next to C500, and is not fused on the Fiero. I would take that apart and put an amp meter inline to see what is happening. Measuring the current there you should get no more than 3 amp.
I checked all the connections under the ECM. I pulled them apart, checked the pins for security and when I re-installed I pushed all pins from behind to make sure they were in good contact. There are a couple wires on harness there, that have SMALL slices in them where they were probed before. They do not look charged or even dangerous. They are so far away from anything and are mostly still insulated. I have checked all the Relays with their connectors multiple times (now and before) and also swapped them with 3 others that are on my Sport. I have already checked all my fuses for correct size and no burn't out fuses.
I will check the EGR connecter and the Injectors for bad connections and/or bad wiring, but I don't ever remember seeing any issues with them(I have been all over that motor, many times). I also think I will double check each and every wire in that harness for ANY place that might have been sliced for probing that maybe I missed.
The trouble IS, if it is a short or a bad ground I could potentially fix the issue by just moving things around and never find where the trouble actually is.
For instance, if a bare wire is leaning on a grounded area and I pull on the harness to check it and move it, I could easily moved it out of the way of danger and never find the issue. That is my largest concern. AND furthermore, i won't know if it's fixed until I put a fixed ECM in and wait for it to potentially burn again..... Scary for me and my extinguisher. LOL!
I am moving towards that 3800 conversion faster. I need to start collecting parts and the motor and tranny so I can make this thing more reliable. I am constantly afraid of this car stopping on the hwy with me where I can't fix her.
ECM is burn usually means something else is wrong... R68, Q5, Q6 & CR14 is the driver for fuel pump relay.
FP Relay or wires to relay likely is shorted.
If relay is fried too... then check pump, op sender, and all wire to them. also see my cave, Electric Motors in electrical section.
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
ECM is burn usually means something else is wrong... R68, Q5, Q6 & CR14 is the driver for fuel pump relay.
FP Relay or wires to relay likely is shorted.
If relay is fried too... then check pump, op sender, and all wire to them. also see my cave, Electric Motors in electrical section.
The Fuel Pump is brand new. The funny thing is that the wiring was not looped through the fire wall when I removed the tank to put the pump in. It was hanging below the hole around the firewall. I prolly need to look and see if it has any rubbing there. I routed it properly when i put the tank back in , although I didn't notice any damage, but it could have damage from previous installer.
The fuel pump would have nothing to do with damage to the ecm. If the wiring is all stock the ecm output only runs the FP relay so would seem the problem would have to be the FP relay or wiring in between. Possible some past owener had the problem and added some wiring somewhere?
The fuel pump would have nothing to do with damage to the ecm. If the wiring is all stock the ecm output only runs the FP relay so would seem the problem would have to be the FP relay or wiring in between. Possible some past owener had the problem and added some wiring somewhere?
No, no extra wiring. I actually love this car for that. All the wiring is original. Even the Radio is installed correctly. I love my unmolested wiring. :-)
The fuel pump would have nothing to do with damage to the ecm. If the wiring is all stock the ecm output only runs the FP relay so would seem the problem would have to be the FP relay or wiring in between. Possible some past owener had the problem and added some wiring somewhere?
No, no extra wiring. I actually love this car for that. All the wiring is original. Even the Radio is installed correctly. I love my unmolested wiring. :-)
I agree, I'm the same way. Hate to deal with mucked up wiring.
I'd sure replace the FP relay. Maybe something came loose inside and is shorting otherwise would almost have to be a wire rubbing somewhere.
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10:50 AM
Nov 12th, 2011
85 SE VIN 9 Member
Posts: 690 From: Harwood Heights, IL, USA Registered: Apr 2010
So from here I'm gonna try to replace it although I have no idea of it's value since it was a pile of dust after I took it off the board. I will just try one of the FET's I have already and see if it works. Worst comes to Worst i will replace my Oil Sending unit and run the Fuel pump off that circuit until I can find a good ECM that won't burn up.
If the wiring is stock and the fuel pump cutting out is one of the symptoms I would replace both the oil pressure sender and the fuel pump relay.
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06:06 PM
Nov 13th, 2011
Will Member
Posts: 14274 From: Where you least expect me Registered: Jun 2000
The high side of the fuel pump relay primary is switched by the ignition. The ECM provides the ground. Sounds like your relay has failed with a short on the primary circuit. That will pull too much current through the ECM AND cause the relay not to energize, which is why your fuel pump doesn't turn on.
Check for proper primary resistance on the relay before you toast another ECM.
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11:07 AM
phonedawgz Member
Posts: 17091 From: Green Bay, WI USA Registered: Dec 2009
To activate the relay the ECM provides power on the Green/White wire. The black wire of the fuel pump relay is attached to ground.
When the ECM is providing power to the relay, the relay will close (connect) the two contacts of the relay.
One of those contacts is connected to the Orange/Black wire - Power that is unswitched, ie always on, and comes from the FUEL fuse.
The other contact is connected to the Tan/White wire - that leads to the fuel pump itself.
The 'contact' side of the relay is supposed to be electrically isolated from the coil. While I have never heard of it, there is a possibility the relay failed in a manor that shorts the coil to the contacts.
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11:20 AM
Will Member
Posts: 14274 From: Where you least expect me Registered: Jun 2000
Woops... Went and checked the book... this is the *one* relay GM runs by switching the high side through the ECM...
So in addition to a shorted primary coil in the relay, potential failure modes would include a short to ground on the dark green/white wire from ECM pin C2-A1 to pin A on the relay connector. To check for this, unplug the ECM and the relay and measure resistance to ground at either (or both!) ends of this wire. They should be completely isolated from ground.
[This message has been edited by Will (edited 11-13-2011).]
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04:53 PM
Nov 14th, 2011
85 SE VIN 9 Member
Posts: 690 From: Harwood Heights, IL, USA Registered: Apr 2010
Is your wiring harness loose? On my no factory air car it has come loose from the motor mount stud to which it's supposed to be attached - twice. The harness has spent most of it's time in my possesion held up by a bungee of some sort. If not held up it might contact the fan belt pulley.
Also, are the wires to your oil pressure sender twisted, as in someone plugged it in, then tightened it?
I haven't looked at it since I installed a new FET that didn't work. I have been just driving it with a switch on the FP. I plan to replace the oil pressure sensor and the relay and see if it works again.
The way I see it, there are two circuits powering the FP. There is a connections from the ECM to the FP relay directly and a connection that is ran through the Oil Pressure Switch. I drew arrows for the two routes
ECM ONLY sees FP Relay Coil. You have major problems with relay or wires to relay to burn out ECM. If relay is fried too... then short wire, burn up FP, etc.... Burn out FP too? Easy to do with bad power or grounds... or both. see my cave, electric motor in general electrical section.
ECM can die on its own but check everything else or likely Fry Off a new ECM.
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
No... ECM ONLY sees FP Relay Coil. You have major problems with relay or wires to relay to burn out ECM. If relay is fried too... then short wire, burn up FP, etc.... Burn out FP too? Easy to do with bad power or grounds... or both. see my cave, electric motor in general electrical section.
ECM can die on its own but check everything else or likely Fry Off a new ECM.
No I'm not saying the FP Relay is fried. I only said I am replacing it, for good measure. It is still working, it's the signal from the ECM that i am not getting to turn on the relay and the FET on the ECM board burnt up. I have no other burnt items, or wires.
I have cleaned all the grounds AND added a secondary large Ground wire to the car. Not sure what the issue is really.
[This message has been edited by jwrape (edited 11-29-2011).]
ECM ONLY sees FP Relay Coil. You have major problems with relay or wires to relay to burn out ECM. If relay is fried too... then short wire, burn up FP, etc.... Burn out FP too? Easy to do with bad power or grounds... or both. see my cave, electric motor in general electrical section.
ECM can die on its own but check everything else or likely Fry Off a new ECM.
No I'm not saying the FP Relay is fried. I only said I am replacing it, for good measure. It is still working, it's the signal from the ECM that i am not getting to turn on the relay and the FET on the ECM board burnt up. I have no other burnt items, or wires.
I have cleaned all the grounds AND added a secondary large Ground wire to the car. Not sure what the issue is really.
You might want to depin the fuel pump relay signal wire (Green/White) from the ECM connector before you install the ECM. Then run it with the fuel pump switch for a bit and make sure the ECM doesn't fail. If the ECM lasts then put the Green/White wire back in (along with a new relay) and see if it still holds.
You also might want to replace the ECM reset connector with a weather resistant fuse holder. The ECM reset connector is right next to C500. GM didn't fuse the ECM, and thus if something gets shorted, the ECM fries instead of a fuse. You should be fine fusing the ECM at 10A.
Yes there is a fuse in the fuse box marked ECM, however that is only for the switched power to the ECM. The ECM only looks at that as an input, not as the power source. It's the unfused direct battery power that is the actual power input to the ECM.
Weather resistant fuse holder
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02:34 PM
Reallybig Member
Posts: 974 From: Calgary Alberta Canada Registered: Mar 2011
There are three wires coming from the (my) oil pressure sensor plug; tan, tan-white, and orange-black. ONE of them shorted to ground inside the op sensor and took out the 10amp FP fuse. I replaced it on the side of the road with the only fuse I had; 20amp. I put out the fire but could have burnt the car to the ground as the plastic op sensor plug caught fire! (thank God for 1L bottles of Pepsi!) Perhaps your problem is the same; a short to ground inside the op sensor...just not the same wire of the three that I had shorted. Someone online hear responded to my post with a write up on how poor these sensors are and that it is not an uncommon problem for them to short out.
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10:36 PM
Nov 30th, 2011
phonedawgz Member
Posts: 17091 From: Green Bay, WI USA Registered: Dec 2009
The Tan/White is the wire that runs to the fuel pump.
When you have oil pressure the oil pressure switch connects those two together and can also supply power to the fuel pump - just the same as the relay can do it. Yes, it is a little unclear as to why GM made two ways for the fuel pump relay to be powered.
The Tan wire runs to the oil pressure gauge.
--- But none of those wires run to or through the ECM. So there is no way that I can come up with that the oil pressure switch could possibly cause the ECM to fail.
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12:22 AM
Reallybig Member
Posts: 974 From: Calgary Alberta Canada Registered: Mar 2011
The Tan/White is the wire that runs to the fuel pump.
When you have oil pressure the oil pressure switch connects those two together and can also supply power to the fuel pump - just the same as the relay can do it. Yes, it is a little unclear as to why GM made two ways for the fuel pump relay to be powered.
The Tan wire runs to the oil pressure gauge.
--- But none of those wires run to or through the ECM. So there is no way that I can come up with that the oil pressure switch could possibly cause the ECM to fail.
Hey, makes sense to me...but as long as there is someone who sees a posible cause and effect, I'll throw them a bone to chew on.
There are three wires coming from the (my) oil pressure sensor plug; tan, tan-white, and orange-black. ONE of them shorted to ground inside the op sensor and took out the 10amp FP fuse. I replaced it on the side of the road with the only fuse I had; 20amp. I put out the fire but could have burnt the car to the ground as the plastic op sensor plug caught fire! (thank God for 1L bottles of Pepsi!) Perhaps your problem is the same; a short to ground inside the op sensor...just not the same wire of the three that I had shorted. Someone online hear responded to my post with a write up on how poor these sensors are and that it is not an uncommon problem for them to short out.
Yes, I think the reason it started going in and out the last time might have been cause of my Oil pressure sensor going bad. I think I have actually been running on that circuit for a long time now. I think the original circuit had failed a long time ago because I know once when I got low on oil the car quit. Now that's the first thing i check, but I am full on oil but the pressure sensor must have not only stopped reading correctly but isn't providing the secondary connection to the fuel pump.
The reason i think the Factory put two connections to the fuel pump was in case the first circuit failed the car wouldn't cut off in the middle of a intersection or something as mine did once. LOL!
[This message has been edited by jwrape (edited 11-30-2011).]
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06:08 AM
85 SE VIN 9 Member
Posts: 690 From: Harwood Heights, IL, USA Registered: Apr 2010
Yes, I think the reason it started going in and out the last time might have been cause of my Oil pressure sensor going bad. I think I have actually been running on that circuit for a long time now. I think the original circuit had failed a long time ago because I know once when I got low on oil the car quit. Now that's the first thing i check, but I am full on oil but the pressure sensor must have not only stopped reading correctly but isn't providing the secondary connection to the fuel pump.
The reason i think the Factory put two connections to the fuel pump was in case the first circuit failed the car wouldn't cut off in the middle of a intersection or something as mine did once. LOL!
It's well known that the oil pressure sender circuit won't last as the secondary to the fuel pump relay. The fuel pump relay is less than ten dollars. It's worth carrying a spare. I always turn the ignition on and wait for the relay to click off before starting cold. That way I know the relay is working. It saves the starter some effort too.
[This message has been edited by 85 SE VIN 9 (edited 11-30-2011).]
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05:44 PM
Dec 1st, 2011
Reallybig Member
Posts: 974 From: Calgary Alberta Canada Registered: Mar 2011
I replaced that bad transistor on the ECM that controls the fuel pump. It is a PNP , replaced with PN2907-Type Radio Shack #276-2023 and they actually do stock them. Been working fine for months in my '86 GT.
I replaced that bad transistor on the ECM that controls the fuel pump. It is a PNP , replaced with PN2907-Type Radio Shack #276-2023 and they actually do stock them. Been working fine for months in my '86 GT.
That's good info. Thanks. Mine was burnt so bad I couldn't identify the correct one. Now I will replace it with the one above. Thanks
No prob... Mine wasn't burnt but tested bad. I couldn't identify the type from the markings so I did a current read on the energized relay and got a pnp within range.
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10:20 AM
Feb 4th, 2012
deceler8 Member
Posts: 2139 From: Sioux City, Iowa USA Registered: Sep 1999
