84 Electrical Fault "Fuse pops"
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Heel & Toe
Joined: Apr 2007
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84 Electrical Fault "Fuse pops"
Hi...i have an 84 which i have owned for over 12years...it always starts on the button and drives ok....just recently i took it for a spin and it died on me...engine was purring fine up until then....i tried to re-start and it just turned over but didn't fire. The recovery man checked everything he could at side of road then went to the fuse panel and found the ECM 5A fuse blown...changed that and away we went. I left it a week or so and went for a drive again and same thing happened...changed fuse and away we went. In total 3 times now the same fuse has blown. usually within about 5 miles of the house or 10 mins of driving...Any ideas anyone? Last night i waded thru the 84 shop manual and found something on "cold start modules" and "so many hours of engine run time before it pops a fuse" but that is all.(could this be it i thought!)
I am reluctant to tear it apart before i have an real lead to go on so any ideas or possible causes anyone may have wouyld be appreciated..
thanks
I am reluctant to tear it apart before i have an real lead to go on so any ideas or possible causes anyone may have wouyld be appreciated..
thanks
Race Director
Joined: Sep 2000
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From: The Top of Utah
Logic says if that fuse in blowing, the circuit it protects is becoming overloaded intermittantly. With your FSM see where the wire runs to, from the fuse and check for any worn insulation or possibility for shorts.
The way I read it, just checking quickly, that fuse feeds 12 volts from the ignition switch on circuit #439 to pin 16 of the 24 pin, (white) ECM connector and then on to pin B of the ESC. Maybe trouble shooting the ESC should be your first step. BTW, my FSM shows that should be a 3 amp, not a 5 amp fuse.
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The way I read it, just checking quickly, that fuse feeds 12 volts from the ignition switch on circuit #439 to pin 16 of the 24 pin, (white) ECM connector and then on to pin B of the ESC. Maybe trouble shooting the ESC should be your first step. BTW, my FSM shows that should be a 3 amp, not a 5 amp fuse.
RACE ON!!!
Thread Starter
Heel & Toe
Joined: Apr 2007
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Logic says if that fuse in blowing, the circuit it protects is becoming overloaded intermittantly. With your FSM see where the wire runs to, from the fuse and check for any worn insulation or possibility for shorts.
The way I read it, just checking quickly, that fuse feeds 12 volts from the ignition switch on circuit #439 to pin 16 of the 24 pin, (white) ECM connector and then on to pin B of the ESC. Maybe trouble shooting the ESC should be your first step. BTW, my FSM shows that should be a 3 amp, not a 5 amp fuse.
RACE ON!!!
The way I read it, just checking quickly, that fuse feeds 12 volts from the ignition switch on circuit #439 to pin 16 of the 24 pin, (white) ECM connector and then on to pin B of the ESC. Maybe trouble shooting the ESC should be your first step. BTW, my FSM shows that should be a 3 amp, not a 5 amp fuse.
RACE ON!!!
Thread Starter
Heel & Toe
Joined: Apr 2007
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Access to ECM
Ok...so i have read all i can on what to check for on the ecm ...now comes the hard part..How do you get at the ecm..i've removed the top dash pad...and the lower right panel(with the courtesy light in) but cant see how the carpeted knee pad come off...also thinking i could remove the box piece...i cant get near the bottom screws which look like they were screwed in from the bottom! and i can even get my 8 year olds arm up there...This is becoming a nightmare before i even work on the electrical fault...Is there an easy way anyone?
Race Director
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From: The Top of Utah
With the hush panel (lower right panel(with the courtesy light in)) off, it is fairly easy to stick a 10 mm socket on an extension up there to remove the two bolts. With the wiring harnesses out of the way it should slide out into your waiting hands. There was no need to remove the dash pad. Have you tried unplugging the ESC module to see if the fuse still blows?
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Thread Starter
Heel & Toe
Joined: Apr 2007
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With the hush panel (lower right panel(with the courtesy light in)) off, it is fairly easy to stick a 10 mm socket on an extension up there to remove the two bolts. With the wiring harnesses out of the way it should slide out into your waiting hands. There was no need to remove the dash pad. Have you tried unplugging the ESC module to see if the fuse still blows?
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I started the car yesterday and got it up to temp..engine was purring ok with no obvious signs that the ecm-ign fuse was going to pop!
This may be silly question but so far the fuse only blows when im driving after about 5 miles or so or 10 mins. I know my head is stuck with this right now but i keep reading about this Cold start module that pops a fuse after an "elapsed time" Have you any knowlege of this module?
Also i dont think i have every had the check engine light on at all. This means have no way of checking for fault codes..so have just worked thru chart A diagnosis when i back probe pin20 on wht connector the test light is very dim!. if i back probe pin16 test light is full on. pins 10 or 15 are also full on.....what would be reason for such a low glow to the test bulb when in pin20....earthing maybe? I checked up at the connector to the info ctr and the test bulb was dim there too (off brn/wht wire).... Any ideas please would be appreciated thanks
Last edited by SG84vette; Apr 16, 2007 at 08:14 AM. Reason: add more info
Race Director
Joined: Sep 2000
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From: The Top of Utah
Originally Posted by SG84vette
Silly question but will car still run with esc un-plugged?
Originally Posted by SG84vette
but i keep reading about this Cold start module that pops a fuse after an "elapsed time" Have you any knowlege of this module?
Originally Posted by SG84vette
Also i dont think i have every had the check engine light on at all. This means have no way of checking for fault codes..so have just worked thru chart A diagnosis when i back probe pin20 on wht connector the test light is very dim!. if i back probe pin16 test light is full on. pins 10 or 15 are also full on.....what would be reason for such a low glow to the test bulb when in pin20....earthing maybe? I checked up at the connector to the info ctr and the test bulb was dim there too (off brn/wht wire).... Any ideas please would be appreciated thanks
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Thread Starter
Heel & Toe
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I don't know. I suspect it would. I know it will run just fine with the knock sensor disconnected. Pull the plug and see what happens? Better yet trouble shoot the ESC to be sure it is operating properly.
My understanding of the L83 cold start module is that it was used for to keep the idle speed higher than normal when the car was new. After the break in period (a predetermined number of hours) the cold start module blows a fuse or otherwise "times out" and is no longer functional. Any 1984 would be WELL beyond any such period.
I don't see a "Chart A". What section of the book are you in? In chapter 6E2, I see charts "A1", "A2", etc. Pin 20 of the white ECM connector is for the check engine light. With the ignition on, engine off, is should read 0 volts, warmed up and running in closed loop, it should read battery voltage (14+). I don't know where you are going with your testing, or why. You can pull the codes to see if any have been set. Just because you didn't see the check engine light, doesn't mean that it didn't come on. After you record any codes, erase them and recheck for them after another incident. Your trouble sounds more like an intermittent short or circuit open rather than a failed component, the worst kind to try to trace.
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My understanding of the L83 cold start module is that it was used for to keep the idle speed higher than normal when the car was new. After the break in period (a predetermined number of hours) the cold start module blows a fuse or otherwise "times out" and is no longer functional. Any 1984 would be WELL beyond any such period.
I don't see a "Chart A". What section of the book are you in? In chapter 6E2, I see charts "A1", "A2", etc. Pin 20 of the white ECM connector is for the check engine light. With the ignition on, engine off, is should read 0 volts, warmed up and running in closed loop, it should read battery voltage (14+). I don't know where you are going with your testing, or why. You can pull the codes to see if any have been set. Just because you didn't see the check engine light, doesn't mean that it didn't come on. After you record any codes, erase them and recheck for them after another incident. Your trouble sounds more like an intermittent short or circuit open rather than a failed component, the worst kind to try to trace.
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Race Director
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From: The Top of Utah
Originally Posted by SG84vette
Any chance you could give me a proceedure to follow to check the ESC to see if it is doin its thing ok as sourses of parts are limited.
Originally Posted by SG84vette
As i started to read the manual to get a better insight into the ECM etc i have come to reaslise that my check engine light has never illuminated even prior to starting it doesn't(as it is supposed too)
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Thread Starter
Heel & Toe
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Code 43. Page 6E2-46, explains the way it function and Figure 44, page 6E2-47 has the trouble shooting chart. It would be silly of me to try to retype all of that, especially since you have the book in front of you. Regardless of the status of "sourses of parts" resist buying anything that you can't verify as bad.
You mentioned that in a previous post but I interpreted you to be saying, you hadn't received any faults, because you'd had no check engine light. I didn't read that carefully enough. Yes. The check engine light should come on when you turn the ignition to "On" before you start to crank the engine. Once running, the check engine light indicates a fault and a code being set. Fix the check engine light first, pages 6E2-14 and 15, chart 1A.
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You mentioned that in a previous post but I interpreted you to be saying, you hadn't received any faults, because you'd had no check engine light. I didn't read that carefully enough. Yes. The check engine light should come on when you turn the ignition to "On" before you start to crank the engine. Once running, the check engine light indicates a fault and a code being set. Fix the check engine light first, pages 6E2-14 and 15, chart 1A.
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Race Director
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From: The Top of Utah
Originally Posted by SG84vette
It was probably my poor typing but yes that is the case...i have no check engine light at all....but working the flow chart A1 6E215 on step1 with my test lead i get a dim light!(will check to see what voltage it is ) Chart says either on or off. Assuming light off....step 2 is full brightness, step 3 full brightness. Battery is at full charge so no probs there, the dim glow on test lead is a mystery at the moment... Will look at those pages you refer to later when i take the boy to school...regards
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Instructor
Joined: Nov 2006
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From: Madison WI
hey i have the same problem wiht my 85 vette it sometimes blows the fuse. i always had a code 55 ecm failure code so i replace the ecm and the car ran great. just today while driving in stop and go traffic i blew a 30a fuse (i know its suppose to be a 3). i replaced it and it blew another one in stop and go driving as well. you were talkin bout disconnecting the knock sensor which perks my interest because with my old ecm my motor would knock real bad. when i replaced the ecm the knock went away but maybe that is intermitent? what do u think? so my real question is how do u go about disconnecting the esc or troubleshooting it to see that it is faulty? thanks,
tyler
tyler
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From: The Top of Utah
Originally Posted by superboop
so my real question is how do u go about disconnecting the esc or troubleshooting it to see that it is faulty? thanks,
tyler
tyler
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Thread Starter
Heel & Toe
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When the "Chart says either on or off.", why do you assume, "a dim light!" to be a light that is off? The chart suggests if the test light is on, the first likely cause for the problem is a faulty "Check Engine" bulb. That is the first place I would go. While you have the bulb out, you can check for 12 volts TO the bulb with the ignition switch in the "On" position and also for zero ohms on the other side of the bulb socket, to ground.
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Based on the 6e2-15 for test light on i have continuity in ckt419 between pin17(chk eng harn)and 20 (wht conn) but not sure about repair to open IGN1 ckt! Where do i go from here
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From: The Top of Utah
Originally Posted by SG84vette
Ok...i have 12 v to the bulb...
but not sure about repair to open IGN1 ckt!
but not sure about repair to open IGN1 ckt!
Originally Posted by SG84vette
what i did notice though was that when back probing wht con 20 mt test bulb was glowing dim, my check engine light was on. It only comes on when the test light is included..that maybe as my test bulb has an earth the check engine light can come on.Is this suggesting that the ecm isn't grounding ckt419? Is it an internal grounding problem in the ECM?
If you were to connect an ohmmeter between the pin of the ECM that pin 20 of the white ECM connector connects to (with the connector disconnected from the ECM) and ground, it should read zero (or close to it) ohms. Although I almost never blame the ECM for problems, your tests are pointing that way.
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Safety Car
Joined: Sep 2004
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From: Mission Viejo CA
It's a pain to keep replacing fuses when you're looking for an intermittent overload or a short circuit. I made a gadget to help me know when the overload occurs. I took and old, burned out fuse, and wired the two terminals of the fuse to a headlight bulb. The headlight bulb has a very low resistance, so most circuits will work just fine with this thing plugged into the offending position in the fuse block. When an overload occurs, the headlight will come on brightly, but nothing will get burned out.
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Heel & Toe
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I think 12 volts to the bulb proves there is no "open" in IGN1 ckt.
When you are doing test 1 of Chart A-1, are you connecting the test light to 12 volts as instructed? The dim glowing and the Check Engine light coming on suggest you have the test light connected to a ground and that the test light is making the ground for the Check engine light, just as you suspect. If I am correct that you don't have the test light connected properly, redo your tests.
If you were to connect an ohmmeter between the pin of the ECM that pin 20 of the white ECM connector connects to (with the connector disconnected from the ECM) and ground, it should read zero (or close to it) ohms. Although I almost never blame the ECM for problems, your tests are pointing that way.
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When you are doing test 1 of Chart A-1, are you connecting the test light to 12 volts as instructed? The dim glowing and the Check Engine light coming on suggest you have the test light connected to a ground and that the test light is making the ground for the Check engine light, just as you suspect. If I am correct that you don't have the test light connected properly, redo your tests.
If you were to connect an ohmmeter between the pin of the ECM that pin 20 of the white ECM connector connects to (with the connector disconnected from the ECM) and ground, it should read zero (or close to it) ohms. Although I almost never blame the ECM for problems, your tests are pointing that way.
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Thread Starter
Heel & Toe
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It's a pain to keep replacing fuses when you're looking for an intermittent overload or a short circuit. I made a gadget to help me know when the overload occurs. I took and old, burned out fuse, and wired the two terminals of the fuse to a headlight bulb. The headlight bulb has a very low resistance, so most circuits will work just fine with this thing plugged into the offending position in the fuse block. When an overload occurs, the headlight will come on brightly, but nothing will get burned out.
Race Director
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From: The Top of Utah
Originally Posted by SG84vette
OK, just so i get this clear in my head, Disconnect wht connector...connect ohmeter onto corresponding pin where pin20 goes to. and ground other terminal and i should get zero ohms coming from it...I take it that if its zero then the internal switch inside the ECM isnt going to ground cause if it is then the ohometer will go off the scale! Have i got it this right?
However, back up a few steps. Did you understand what I said about how you were hooking up your test light for test 1 in Chart A-1? I really think you have conducted that test incorrectly.
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Instructor
Joined: Nov 2006
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From: Madison WI
I'm sorry i know this doesnt really relate but im wondering if i may be blaming the wrong problem on my ecm or esc. Along with popping fuses my car also oscillates, causing it to want to jump ahead at stop signs and even somtimes kill. i replaced the tps and set it to .54v. What can i do to fix this could this be the Idle Air Control sensor or something else. thanks for the help
tyler
tyler