Computer constant problem. PLEASE READ
Computer constant problem. PLEASE READ Hey guys I am having a problem with supplying too much amperage for the computer constant. I have it setup to take voltage from an auxilery fuse block I have to control the fuel pump relay and efans and stuff like that. But the problem is that it wont keep a fuse in it??? Every time it pops upon installing a new one. I have a 5 amp fuse in the inline holder and also a 5 amp fuse in the aux fuse block. Could this have anything to do with the resistance of the wire? I have 14 or 16 gauge coming from the fuse block, but on either end of the inline holder I have 10 gauge for a few inches. I am guessing this is what the problem is, but would like some more input. Also do you think putting a resistor inline would make any difference or would this be unneccesary??? BWT I have a 10 gauge wire supplying power to the aux fuse block, and from there 14 or 16 gauge wire supplying it......and the truck is a 6.0 swap. If anybody has any ideas please let me know asap.
Remington
Remington
Originally Posted by Remington H.
Hey guys I am having a problem with supplying too much amperage for the computer constant. I have it setup to take voltage from an auxilery fuse block I have to control the fuel pump relay and efans and stuff like that. But the problem is that it wont keep a fuse in it??? Every time it pops upon installing a new one. I have a 5 amp fuse in the inline holder and also a 5 amp fuse in the aux fuse block. Could this have anything to do with the resistance of the wire? I have 14 or 16 gauge coming from the fuse block, but on either end of the inline holder I have 10 gauge for a few inches. I am guessing this is what the problem is, but would like some more input. Also do you think putting a resistor inline would make any difference or would this be unneccesary??? BWT I have a 10 gauge wire supplying power to the aux fuse block, and from there 14 or 16 gauge wire supplying it......and the truck is a 6.0 swap. If anybody has any ideas please let me know asap.
Remington
Remington
It's not that you're supplying amperage, the circuit is drawing amperage. Current can only flow as the circuit dictates. E/R=I is how it works...given E (voltage) is dictated by the battery and alt voltage regulator, and R (resistance) is the net of the circuit, that means I (amperage) is a function of voltage and resistance. A dead short has a near-zero resistance (R), which creates a larger current flow (I) and smokes fuses.
The battery has enough juice on tap to smoke any wire in the car, all you need is a circuit drawing full current...like a short to ground as mentioned above. You could run 1ga wire to your fuse block, that wouldn't increase the net current draw of the circuit(s) it supplies.
You didn't specify which fuse is blowing. 5A isn't enough fuse for most fans I've seen, more like 20A for the typical GM fan. Mine are running a 30A fuse for each fan.
5A definitely isn't enough fuse for a Walbro 255 high pressure fuel pump, sucker draws over 7A generating 58psi. I fused mine at 15A.
So...either you're undersizing your fuse(s) or you have a short...sounds like the first one.
The battery has enough juice on tap to smoke any wire in the car, all you need is a circuit drawing full current...like a short to ground as mentioned above. You could run 1ga wire to your fuse block, that wouldn't increase the net current draw of the circuit(s) it supplies.
You didn't specify which fuse is blowing. 5A isn't enough fuse for most fans I've seen, more like 20A for the typical GM fan. Mine are running a 30A fuse for each fan.
5A definitely isn't enough fuse for a Walbro 255 high pressure fuel pump, sucker draws over 7A generating 58psi. I fused mine at 15A.
So...either you're undersizing your fuse(s) or you have a short...sounds like the first one.
yes I rewired it myself from a stock 6.0 harness, but then went back, tore it apart and redid the harness to tuck it under the fuel rails so it would look alot cleaner than the factory setup, the fuse I am having trouble with is a fuse for supplying the computer constant which should be 5 amps and hot at all times. Yeah I do have a 25 amp fuse for the fuel pump and a 30 for the fans. But it keeps wasting the 5 amp going to the computer for a constant. I am thinking that since this fuse keeps breaking, that there is a short in the computer constant lines somewhere???? Any ideas.
Remington
Remington
OK, I misunderstood your original post. 5A may still not be enough...I'm using a fusible link for my PCM constant-hot just sized to the wire gauge, no idea how many amps it smokes at.
Exerpt from John Bzdel's excellent writeup on his LS1 swap detailing problem he hit w/ the switched PCM feed fuse which may provide some clues:
08/19/01 My LS1 breathes it first air in a G-body!
Once the wiring was connected with the proper "hot & ignition on" for the PCM I turned the ignition key to only the "on" position, heard the fuel system & pump relay run for 2 seconds like it is supposed too, cranked the starter and NO START! I thought, what the heck is up with this?
I blew the 10 AMP Ignition/ECM fuse after I could hear the fuel pump prime the fuel system. I replaced the fuse several times and blew several more. Hmmmmmmmmmm.......very frustrating after getting the mechanical portion of the installation this far.
I consulted long distance with "Crazy Bill" (as he is affectionately know on the "Monte Mailing List" since he is a "Jedi Master", well seasoned TPI/LT1 G-body retrofitter) to explore my concerns regarding the LS1 PCM wiring and fuses and he suggested a 20 AMP fuse based on the LT1's. The PCM/ignition fuse in a G-body has only a 10 AMP OEM fuse for the L69 ECM and the LS1 PCM apparently needs a larger fuse too!
Installed a 20 AMP fuse and music to my ears!!!!!!!! The LS1 fired up and ran smooth as silk!
Exerpt from John Bzdel's excellent writeup on his LS1 swap detailing problem he hit w/ the switched PCM feed fuse which may provide some clues:
08/19/01 My LS1 breathes it first air in a G-body!
Once the wiring was connected with the proper "hot & ignition on" for the PCM I turned the ignition key to only the "on" position, heard the fuel system & pump relay run for 2 seconds like it is supposed too, cranked the starter and NO START! I thought, what the heck is up with this?
I blew the 10 AMP Ignition/ECM fuse after I could hear the fuel pump prime the fuel system. I replaced the fuse several times and blew several more. Hmmmmmmmmmm.......very frustrating after getting the mechanical portion of the installation this far.
I consulted long distance with "Crazy Bill" (as he is affectionately know on the "Monte Mailing List" since he is a "Jedi Master", well seasoned TPI/LT1 G-body retrofitter) to explore my concerns regarding the LS1 PCM wiring and fuses and he suggested a 20 AMP fuse based on the LT1's. The PCM/ignition fuse in a G-body has only a 10 AMP OEM fuse for the L69 ECM and the LS1 PCM apparently needs a larger fuse too!
Installed a 20 AMP fuse and music to my ears!!!!!!!! The LS1 fired up and ran smooth as silk!
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so you think I just dont have a big enough fuse for the computer constant????? Lets say I were to put a 20 amp fuse in, wouldnt that draw alot of power when its parked since it would be hot at all times??? Also is there a possibility of feeding too much power to the computer and frying it?
Remington
Remington
Last edited by Remington H.; Jul 7, 2005 at 09:15 AM.
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Verdad Gallardo The fuse doesn't regulate current in any way other than stopping at it's designed blow rating.
You could theoretically put a 100A fuse in there and it won't change how much current the PCM draws...again, circuits "pull" current, batteries don't "push" it.
Connect a big car battery via giant 1ga wire with a zillion-amp fuse on a tiny dash lightbulb to ground, it can still only pull as much current as the little lightbulb filament will allow to pass thru it to ground.
You size the fuse based on the combination of the components and wiring specs to prevent a fire or electrical damage, you want the fuse to be the weakest link in the chain so it can protect the circuit.
If you go up to a 20A fuse and it still smokes, you'll know for sure that you have a short.
Disconnecting the PCM at the red and blue connectors, and probing the constant feed wire to ground w/ your Ohm meter is a somewhat safer way to proceed. You can probe either from the PCM side or from the fuse output side. If you get infinity or any indication of continuity, you're shorted.
You could theoretically put a 100A fuse in there and it won't change how much current the PCM draws...again, circuits "pull" current, batteries don't "push" it.
Connect a big car battery via giant 1ga wire with a zillion-amp fuse on a tiny dash lightbulb to ground, it can still only pull as much current as the little lightbulb filament will allow to pass thru it to ground.
You size the fuse based on the combination of the components and wiring specs to prevent a fire or electrical damage, you want the fuse to be the weakest link in the chain so it can protect the circuit.
If you go up to a 20A fuse and it still smokes, you'll know for sure that you have a short.
Disconnecting the PCM at the red and blue connectors, and probing the constant feed wire to ground w/ your Ohm meter is a somewhat safer way to proceed. You can probe either from the PCM side or from the fuse output side. If you get infinity or any indication of continuity, you're shorted.
Last edited by crainholio; Jul 7, 2005 at 09:24 AM.
Joined: Sep 2004
Posts: 3,148
Likes: 12
From: Downers Grove, IL
Fuse too small I have a chiltons manual for 99-01 trucks in front of me and the diagram shows a 20 amp fuse for the ecm constant power. If I can figure out how to post the diagrams they will be in the stickies at the top.
edit: Can`t figure out how to post the pdf files so if you want a copy of the diagrams I can e-mail them to you. I found the chiltons manual at the library ISBN # 1-5639-2460-9, it has the engine wiring diagram and all of the engine related fuse sizes.
edit: Can`t figure out how to post the pdf files so if you want a copy of the diagrams I can e-mail them to you. I found the chiltons manual at the library ISBN # 1-5639-2460-9, it has the engine wiring diagram and all of the engine related fuse sizes.
Last edited by G-Body; Jul 7, 2005 at 11:31 AM.
Ok awesome, yeah I found out that there was a short in the line, that one of the wires was pinched and had a tear in the insulation. And I will be installing a 20 amp fuse to see what happens. Thanks for all the help crainholio and g-body.
Regards,
Remington
Regards,
Remington
