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ECMB fuse kepps blowing
- Thread starter 91jimmy
- Start date
89yimmiJ
1/2 ton status
I had the same fuse on my '89 keep blowing. Sometimes it would go as soon as I put a new one in and sometimes it would let me drive 500 miles and it would blow. No matter where I looked I couldn't find a short anywhere and my wire harness was in perfect shape. One day I was changing the trans mount and I saw the wire that goes down on the drivers side to the top of the trans, not sure the actual wire name., had a wear spot from rubbing on the trans. I replaced that wire and the plastic loom and have never had a problem since. My friends would laugh at me as I probably had 15 hours into cutting the loom open and looking for that short before I gave up.
Check your injector wires sometimes they get pinched by air breather. Fuel pump relay runs off ecm B also I think.
k20
3/4 ton status
I had that blow when my fuel pump went bad. My buddy had that problem, found a shorted wire near the air cleaner, fixed it, it ran kinda....blah, then it blew again. Ended up being the oil pressure switch on the back of the manifold, go figure.
Big6ft6
1/2 ton status
I'm watching this post, please be sure to post your solution. It seems the ECM B fuse has quite a few possible reasons that it will blow and I don't see any single cause being more common.
Mine (89 Suburban 5.7 TBI) is blowing so much now I can't make it out of the driveway. What is interesting is lots of the posts I've found on this site and others this problem first show up when in reverse gear. Mine started to blow only when backing out of my driveway, but now it happens in all gears.
Anyway, looking foward to what you find. Here is a small summary of different causes I've read about.
1) Fuel Pump Bad
2) Fuel Pump Ground Bad
3) Wires melted to manifolds
4) Fuel Pump Relay
5) Oil Pressure Sender/Switch
6) Short in any wires connecting the above mentioned items
My wiring diagram says this fuse protects circuit with oil pressure sendor and fuel pump relay, all connected by an oragne wire..? I don't know enough to know if that is the only wire I have to check or if all other wires on this circuit could do it too?
Mine (89 Suburban 5.7 TBI) is blowing so much now I can't make it out of the driveway. What is interesting is lots of the posts I've found on this site and others this problem first show up when in reverse gear. Mine started to blow only when backing out of my driveway, but now it happens in all gears.
Anyway, looking foward to what you find. Here is a small summary of different causes I've read about.
1) Fuel Pump Bad
2) Fuel Pump Ground Bad
3) Wires melted to manifolds
4) Fuel Pump Relay
5) Oil Pressure Sender/Switch
6) Short in any wires connecting the above mentioned items
My wiring diagram says this fuse protects circuit with oil pressure sendor and fuel pump relay, all connected by an oragne wire..? I don't know enough to know if that is the only wire I have to check or if all other wires on this circuit could do it too?
Big6ft6
1/2 ton status
Correct me if I'm wrong, but on my wiring diagram the injectors are protected by the other ECM fuse (ECM-ign? I think is how the other is labeled on my fuse box) but I could be reading the diagram wrong..as I'm not an electrical engineer!
Big6ft6
1/2 ton status
Well I think I solved my ECM B fuse problem (I'm not the originator of this post, but might as well make this the "ECM B" post).
Seeing that the oil pressure switch and fuel pump relay are the main two components protected by this fuse, and they are cheap, I decided to replace these two items.
To do this I had to remove the distributor, which gave me very good access to most of the engine compartment wiring harness. So while I was in there I tried to inspect every visible inch of the wiring on this circuit just in case I saw something obvious. I cut away alot of the factory fabric tape so I could check every part of the orange wires powering this circuit. I replaced any tape I removed with new electrical tape. I didn't find any obvious shorts in the engine compartment wiring, but any suspicious looking areas I covered with electrical tape.
I also replaced the fuel pump relay ($8.99) and oil pressure switch ($22.99). After buttoning it all back up and firing the truck up I noticed I had resolved an old mystery with my truck!
After installing a rebuilt engine two years ago the oil pressure was almost always 60 psi, and sometimes when it was cold out when first getting underway, the oil pressure gauge would peg past 60psi and get stuck there for a few minutes. I called the engine rebuilder and they said it wasn't uncommon to see 60psi when firing up a new engine becuase the tolerances are so tight. They said it would come down after the engine was borken in and "loosen up".
Well... after two years the oil pressure had never come down. I was starting to wonder when the engine would "loosen up". Yesterday after replacing the oil pressure switch, whola! 40 psi...and it was much more steady.
Also my ECM B fuse wasn't blowing!! So these two things I'm hoping point to the oil pressure switch as being bad and causing the fuse to blow. I drove up and down the driveway, and finally had enough courage to go around the block and the fuse never blew. Only time will tell for sure ( I did wiggle a lot of wires), but the evidence gives me confidence I found the problem and it was the oil pressure switch.
Why the fusing blowing seemed to be related to going in reverse I'll never understand. The only thing I can think of is, usually I would be going into reverse was just after starting my truck. When you just start you vehicle the engine oil is cold and thick, so the pressure would be higher than after it warmed up and might've been putting the most pressure on the presure switch?
Seeing that the oil pressure switch and fuel pump relay are the main two components protected by this fuse, and they are cheap, I decided to replace these two items.
To do this I had to remove the distributor, which gave me very good access to most of the engine compartment wiring harness. So while I was in there I tried to inspect every visible inch of the wiring on this circuit just in case I saw something obvious. I cut away alot of the factory fabric tape so I could check every part of the orange wires powering this circuit. I replaced any tape I removed with new electrical tape. I didn't find any obvious shorts in the engine compartment wiring, but any suspicious looking areas I covered with electrical tape.
I also replaced the fuel pump relay ($8.99) and oil pressure switch ($22.99). After buttoning it all back up and firing the truck up I noticed I had resolved an old mystery with my truck!
After installing a rebuilt engine two years ago the oil pressure was almost always 60 psi, and sometimes when it was cold out when first getting underway, the oil pressure gauge would peg past 60psi and get stuck there for a few minutes. I called the engine rebuilder and they said it wasn't uncommon to see 60psi when firing up a new engine becuase the tolerances are so tight. They said it would come down after the engine was borken in and "loosen up".
Well... after two years the oil pressure had never come down. I was starting to wonder when the engine would "loosen up". Yesterday after replacing the oil pressure switch, whola! 40 psi...and it was much more steady.
Also my ECM B fuse wasn't blowing!! So these two things I'm hoping point to the oil pressure switch as being bad and causing the fuse to blow. I drove up and down the driveway, and finally had enough courage to go around the block and the fuse never blew. Only time will tell for sure ( I did wiggle a lot of wires), but the evidence gives me confidence I found the problem and it was the oil pressure switch.
Why the fusing blowing seemed to be related to going in reverse I'll never understand. The only thing I can think of is, usually I would be going into reverse was just after starting my truck. When you just start you vehicle the engine oil is cold and thick, so the pressure would be higher than after it warmed up and might've been putting the most pressure on the presure switch?
There is one way to tell, but it might be more trouble than you are willing to go to.
I would do it, but it would bug me forever if I didn't. Other folk are more forgiving.
Hook an air line, preferably with an adjustable regulator, to the sending unit, and an ohmmeter from the body to the terminal.
Slowly raise the pressure on the sending unit while you watch the meter.
Somewhere about 40 or so pounds, I'm betting you are going to see a dead short.
J.
I would do it, but it would bug me forever if I didn't. Other folk are more forgiving.
Hook an air line, preferably with an adjustable regulator, to the sending unit, and an ohmmeter from the body to the terminal.
Slowly raise the pressure on the sending unit while you watch the meter.
Somewhere about 40 or so pounds, I'm betting you are going to see a dead short.
J.
Big6ft6
1/2 ton status
Fordum,
I'd love to confirm that the oil pressure switch was the culprit. However mine has a 3 prong connection and I'm not sure how to test it? You mention grounding the body and testing the resistance between the body and the the "terminal". Which terminal should I use on a 3-prong switch?
Thanks!
I'd love to confirm that the oil pressure switch was the culprit. However mine has a 3 prong connection and I'm not sure how to test it? You mention grounding the body and testing the resistance between the body and the the "terminal". Which terminal should I use on a 3-prong switch?
Thanks!
Well, thats a good question. I was thinking that it was a single terminal.
What model and year is it?
I'll look up a schematic and see what the terminals do, unless someone here knows and chimes in.
I suspect one is the gauge, and it should have variable resistance to ground. And I suspect that the other two probably should not go to ground, but they are at a certain pressure.
I'll see if I can't find out for sure.
J.
What model and year is it?
I'll look up a schematic and see what the terminals do, unless someone here knows and chimes in.
I suspect one is the gauge, and it should have variable resistance to ground. And I suspect that the other two probably should not go to ground, but they are at a certain pressure.
I'll see if I can't find out for sure.
J.
sandypants
1/2 ton status
hey mine keeps blowing too, replaced my fuel pump worked for about 10 min then pop. sometimes it blows without the key being on. tough the fuse and boom baby! hmmmmm so sounds like if any wire is worn could lead to this problem....
well i will keep you posted
well i will keep you postedBig6ft6
1/2 ton status
sandy pants, I spent a lot of time starring at the wiring diagrams and and as far as I can tell you CAN limit your search to just the wires connecting the fuel pressure switch and fuel pump relay. Other issues would blow the ECM 1 fuse or simply cause an SES light to come on becuase it would give a bad sensor reading.
I never got an answer about whether this fuse really protects the pump itself or not. But even if you have to include the pump wires in your search there are only 2 wires going back along the frame rail to the pump and mine were inside plastic wiring tube, so unlikely they are grounding to the frame.
My fuse wouldn't blow unless I turned the key. Yours blows even with the key off? Did you mean to type as soon as you "touch" the fuse it blows? That is wierd, maybe something in the fuse box?
I never got an answer about whether this fuse really protects the pump itself or not. But even if you have to include the pump wires in your search there are only 2 wires going back along the frame rail to the pump and mine were inside plastic wiring tube, so unlikely they are grounding to the frame.
My fuse wouldn't blow unless I turned the key. Yours blows even with the key off? Did you mean to type as soon as you "touch" the fuse it blows? That is wierd, maybe something in the fuse box?
Big6ft6
1/2 ton status
Fordum...89 V2500 burb 5.7TBI. The haynes wiring diagram was worthless, the diagram available from autozone was much better, but only showed two wires going to the oil pressure sensor. Mine has 3 wires. The parts stores had all three types available for 1989 1-wire, 2-wire, and 3-wire.
Ok, I think I have it figured out.
If I am reading the Autozone schematic correctly, you should have an orange, gray and tan wire going to that switch.
Either the orange or gray wire should NEVER be connected to ground. Doing so will blow the ECM-B fuse.
I am pretty sure that a short to ground on the orange wire will blow it as soon as you turn on the truck, while a short to ground on the gray wire would blow after you crank it.
Also, the tan wire should be isolated from the other two. It should have variable resistance to ground depending on how much pressure it sees.
Use an ohmmeter and check the two terminals to the threaded fitting. If no short, try it with pressure.
The orange wire comes right off the fuse and goes to the fuel pump relay. The gray wire also goes to the fuel pump relay.
Since I do not have a schematic of the fuel pump relay, oil pressure switch or hot fuel module handy, a lot of this is educated guessing.
What is certain is, a short to ground on the orange wire will blow the fuse.
J.
If I am reading the Autozone schematic correctly, you should have an orange, gray and tan wire going to that switch.
Either the orange or gray wire should NEVER be connected to ground. Doing so will blow the ECM-B fuse.
I am pretty sure that a short to ground on the orange wire will blow it as soon as you turn on the truck, while a short to ground on the gray wire would blow after you crank it.
Also, the tan wire should be isolated from the other two. It should have variable resistance to ground depending on how much pressure it sees.
Use an ohmmeter and check the two terminals to the threaded fitting. If no short, try it with pressure.
The orange wire comes right off the fuse and goes to the fuel pump relay. The gray wire also goes to the fuel pump relay.
Since I do not have a schematic of the fuel pump relay, oil pressure switch or hot fuel module handy, a lot of this is educated guessing.
What is certain is, a short to ground on the orange wire will blow the fuse.
J.
acharlie13
Newbie
ECM 2 Fuse keeps blowing
After reading a few of the notes posted I was able to figure out why my ECM 2 fuse was blowing instantly as I changed " with the truck off" I found the Oil Pressure Sending Unit Wire on the exhaust manifold. As soon as I moved the wire off of the exhaust, the fuse did not blow , the truck started fine and is running perfectly. I cleaned off the wires the best I can so electrical tape would stick to it and I triple insulated the exsisting wires with the electrical tape and then zip tied the wire in a comfortable position , away from the exhaust . Thank to you all for you much appreciated input. Acharlie13 all smiles now
After reading a few of the notes posted I was able to figure out why my ECM 2 fuse was blowing instantly as I changed " with the truck off" I found the Oil Pressure Sending Unit Wire on the exhaust manifold. As soon as I moved the wire off of the exhaust, the fuse did not blow , the truck started fine and is running perfectly. I cleaned off the wires the best I can so electrical tape would stick to it and I triple insulated the exsisting wires with the electrical tape and then zip tied the wire in a comfortable position , away from the exhaust . Thank to you all for you much appreciated input. Acharlie13 all smiles now
Big6ft6
1/2 ton status
Congrats Acharlie! Isn't a grand feeling! Don't you love forums?? I think they are one of the greatest things to come from the internet, a group of people all working together and sharing...it is a beautiful thing. I can't imagine working on cars before forums...I'd still be trying to figure out my first engine install!!!
sandypants
1/2 ton status
Well i go home next month we will see. i will try everything you guys mentioned. sounds like it should work. thanx for all your help sandypants
sandypants
1/2 ton status
ok well i am finially back in the states, so i d/c the fuel pump at the connector and the fues still blew when i touched it to the fuse box at point ecmb...
though the wires are covered in clay and sand, so wayyyy dirty, they apear fine up to the point where they go to the plastic box on the fire wall. i am soo confused and just want my truck back!!!!
i will look for that oil unit mentioned above about the wire touching the header.
anything else i should look at and check while im here? belive me i am all ears
though the wires are covered in clay and sand, so wayyyy dirty, they apear fine up to the point where they go to the plastic box on the fire wall. i am soo confused and just want my truck back!!!!
i will look for that oil unit mentioned above about the wire touching the header.
anything else i should look at and check while im here? belive me i am all ears
Big6ft6
1/2 ton status
If I remember correctly the only other things on the ECMB fuse are the fuel pump relay (on the firewall above and to the passenger side of distributor) and the oil-pressure switch mentioned above. You can check the wiring to be sure it isn't melted on the header, but the switch itself can have a short inside it as mine did. I replaced the oil-pressure switch and problem solved.
My oil pressure gauge had been randomly spiking, especially when cold before I fixed this...so that was another symptom pointing to the switch itself.
My oil pressure gauge had been randomly spiking, especially when cold before I fixed this...so that was another symptom pointing to the switch itself.
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shovelbill80
1/2 ton status
you pretty much said it there........sounds like you guys are talkin about a spaceship here. is this what i got to look forward to on the '90 i just got? i'm just praying i don't break the O2 sensor when i change it this week......i miss my '75, or even the '86 for that matter
