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Hey yall. I have questions about the COR-VAF circuit. Do you have any PFD's describing locations, troubleshooting, etc. of 5th gen Toyotas? I have a 92 pickup4x4 that yota tech helped me with a few months ago regarding the starter. Before all of my problems occurred I drove the truck through salt water, and now after alternator, efi relay, and various other problems, the fuel pump is engaging intermittently. Sometimes dying on the road, sometimes at idle. Truck is totally dead right now.. I jumped the +b and Fp diag, I ran power to the pump itself (it works), I ran power to the Fp diag (it pumped fuel), I checked the +b and Fp while cranking the engine and the multi meter read no power. The ignition switch to on, but is not starting the pump. Classic COR circuit fault,corroded wires, any thoughts besides the obvious "dont be a dumb idiot and drive through salt water"?
Very Respectfully,
... I checked the +b and Fp while cranking the engine and the multi meter read no power. ...
With key-on, B+ should be at 12v to ground, through the EFI fuse and EFI Relay. With no B+, the COR/VAF has nothing to work with.
By the way, terminology helps. While I do have meters that measure power, you multimeter doesn't. If your multimeter read 100 ohms or 0.5volts or 12ma, say that. Power is not at all the same thing.
With key-on, B+ should be at 12v. If your multimeter read 100 ohms or 0.5volts or 12ma, say that. Power is not at all the same thing.
Roger.
I had 12v from the +b while the key was in the on pos. Then nothing while cranking. I took the cover off of the EFI relay while cranking and closed the switch with no effect or 12v. The EFI fuse was not damaged and was reading 12v. I recently replaced the EFI relay; after the the truck died on the hwy. It would intermittently start, idle, drive for a bit and die. The EFI relay was hot to the touch so I figured it was faulty, and after replacing it drove fine. There were a couple of stalling incidents that resloved themselves. Now, after having complete loss of fuel pressure, I'm thinking the problem is between the ignition switch and the EFI relay. Any step by step solutions to this? or more information needed. I was honestly considering running a switch in the cab from the battery to run the pump for now.
why would you think loss of fuel pressure is the ignition switch or efi relay? the mechanical fuel system (injectors, fuel rail, inlet/return lines, pulse damper, and fuel pressure regulator, vacuum lines) plays a role in fuel pressure. the relays serve to provide power to the fuel pump at different points in the starting/running/off cycle.
... I checked the +b and Fp while cranking the engine and the multi meter read no power. ...
Originally Posted by Jimmyjohn
...
I had 12v from the +b while the key was in the on pos. ....
Rrrrr ... 12v TO WHERE? Voltage is always between two points. Automotive electrics are so simple that we almost always measure voltage from point A TO GROUND, so if someone says "I had 12v at B+" we can usually assume the other point is ground.
But the way you describe it sounds almost like you're measuring between FP and B+. Because FP goes straight to the fuel pump, and the fuel pump is less than 10 ohms, FP is "at" ground. With key not in STArt, measuring from +12v (battery terminal) to FP would give 12v.
What happens when you turn the key to STArt? The COR closes, and shorts FP to B+ (to connect the 12v at B+ to the pump). If you are measuring BETWEEN FP and B+ when you do that, you're measuring voltage across a short. Which better be 0v.
[QUOTE] why would you think loss of fuel pressure is the ignition switch or efi relay? [QUOTE]
my reasoning is because the pump works when i provide battery power to it directly, or when i provide power to the Fp diagnostic port. I figured i could just jump the fuel pump with the +B to the fp, but that didnt work. No fuel came out of the line from the tank at all when I tried that. I dont think the pressure regulator, fuel rail, injectors, etc. Have anything to do with this issue. I could be wrong tho.
Rrrrr ... 12v TO WHERE? Voltage is always between two points. Automotive electrics are so simple that we almost always measure voltage from point A TO GROUND, so if someone says "I had 12v at B+" we can usually assume the other point is ground.
But the way you describe it sounds almost like you're measuring between FP and B+. Because FP goes straight to the fuel pump, and the fuel pump is less than 10 ohms, FP is "at" ground. With key not in STArt, measuring from +12v (battery terminal) to FP would give 12v.
What happens when you turn the key to STArt? The COR closes, and shorts FP to B+ (to connect the 12v at B+ to the pump). If you are measuring BETWEEN FP and B+ when you do that, you're measuring voltage across a short. Which better be 0v.
If that's the case then I think that its working fine. Key on: no volts at +B. Just to be clear this is the diagnostic port that i have been using.
why would you think loss of fuel pressure is the ignition switch or efi relay?
my reasoning is because the pump works when i provide battery power to it directly, or when i provide power to the Fp diagnostic port. I figured i could just jump the fuel pump with the +B to the fp, but that didnt work. No fuel came out of the line from the tank at all when I tried that. I dont think the pressure regulator, fuel rail, injectors, etc. Have anything to do with this issue. I could be wrong tho.
the point of the diagnostic port Fp to B+ jump is to bypass the AFM and COR portions of the fuel pump circuit. if the pump doesn't run with those ports jumped, there's something wrong in your wiring. to be clear, with the ports jumped, and the key in the "on" position, the fuel pump should run. it should remain operating if the key is put in the "start" position, too. it should stop when the key is turned to "acc" or "off".
Rrrrr ... 12v TO WHERE? Voltage is always between two points. ....
Originally Posted by Jimmyjohn
.... Key on: no volts at +B. ....
Either you're not reading what I posted, or you're messing with me. Either one is okay with me, but it's moving you away from a solution to your problem.
When you put the red lead of your multimeter on B+, where is the black lead? If it is on ground (or the negative terminal of the battery), and you're getting "no" (zero?) volts, then something is wrong in your ignition switch, EFI fuse, EFI relay, or the wiring between them. If the black lead is somewhere else (FP? your pocket?), then you're just not testing anything.
Either you're not reading what I posted, or you're messing with me. Either one is okay with me, but it's moving you away from a solution to your problem.
When you put the red lead of your multimeter on B+, where is the black lead? If it is on ground (or the negative terminal of the battery), and you're getting "no" (zero?) volts, then something is wrong in your ignition switch, EFI fuse, EFI relay, or the wiring between them. If the black lead is somewhere else (FP? your pocket?), then you're just not testing anything.
its the former not the latter. I'm confusing myself here. You see, i was using a tester "the kind that you hook up to your battery and it has one prong that tests v and can provide 12v from the battery" i never used a multi meter at all. The truck is at my house, im on 48hr duty ending tomorrow am, so i haven't had the truck in front of me. I'm recalling this from memory when i was running some tests before the tow truck picked me up. My bad Scope. As to the +B to Fp jumper, it does not run with the key in the on pos and +B jumped to Fp with a wire.. so that's bad right?
the point of the diagnostic port Fp to B+ jump is to bypass the AFM and COR portions of the fuel pump circuit. if the pump doesn't run with those ports jumped, there's something wrong in your wiring. to be clear, with the ports jumped, and the key in the "on" position, the fuel pump should run. it should remain operating if the key is put in the "start" position, too. it should stop when the key is turned to "acc" or "off".
yeah, so that means I have to check all the wiring w/ a multi meter and find where the fault is, right?
When you put the red lead of your multimeter on B+, where is the black lead? If it is on ground (or the negative terminal of the battery), and you're getting "no" (zero?) volts, then something is wrong in your ignition switch, EFI fuse, EFI relay, or the wiring between them.
when i get back to the truck I'll check the +B with my multi meter. I'll ground it to the battey and see if im getting 12v at +B ( i usually just ground it to whatever is closest) I'm pretty confident that it was not showing any voltz when i was using that test light. Running through it again in my head that would make sense since jumping Fp and +B did not run the pump. Must be like you said above about ign switch, efi fuse, relay or wiring. Thank you for your help! I'll update tomorrow when I can take a look at this beast.
So, this is what I have found out so far.
I can jump Fp straight from the battery and it does run (not the truck unfortunately just the pump). I also +B reads .17v with the multimeter. I had the ignition turned on, connected the black lead to the -Battery and checked the Diagnostic +B and that's what it read. It should be close to 12v right?
I'm going to start checking wiring at the EFI fuse, EFI relay, and ignition switch like you said
checking diag port whats this mean?
.
Just to be absolutely sure, touch your "red" lead to the + terminal of the battery. If THAT reads 0.17 volts, then your meter setup is wrong. You should be about 12.6v (depending on state of charge and temperature.)
So now you're making real progress; you know you're not getting voltage to B+. Start with the stupid-easy test; put your finger on the EFI relay, and have someone turn the key from off to on. You should be able to feel it click. I'll bet you won't (since B+ is only an inch or two away, it's less likely the problem is AFTER the EFI relay). Then check the EFI fuse AND the IGN fuse (IGN is in the driver's side kick panel).
Note that ATO fuses have a pair of recessed (but exposed) metal bits on top; use them to check for voltage on EACH SIDE of the fuse.
Just to be absolutely sure, touch your "red" lead to the + terminal of the battery. If THAT reads 0.17 volts, then your meter setup is wrong. You should be about 12.6v (depending on state of charge and temperature.)
So now you're making real progress; you know you're not getting voltage to B+. Start with the stupid-easy test; put your finger on the EFI relay, and have someone turn the key from off to on. You should be able to feel it click. I'll bet you won't (since B+ is only an inch or two away, it's less likely the problem is AFTER the EFI relay). Then check the EFI fuse AND the IGN fuse (IGN is in the driver's side kick panel).
Note that ATO fuses have a pair of recessed (but exposed) metal bits on top; use them to check for voltage on EACH SIDE of the fuse.
Everything you mentioned checked out except the EFI fuse has 11.65v on both sides of the fuse (probably a little lower than usual because I'm cranking over my engine with no start), the IGN. fuse has 11.65v, the Relay is not clicking when key is turned to "on", and the relay itself is reading proper continuity from 1-2, no continuity on 3-5.. and when I jump 1-2 with the battery it activates and passes 11.65v to 3-5. just like the pdf. for EFI relays says it should. I'm stuck.. key in on pos. does not power up the fuel pump or activate EFI relay, so something from the ignition switch is not operating properly would be my guess. I had ignition problems a while back, but replacing the EFI relay solved the problem. You helped me with that as I recall. What should I check next?
Pin 1 of the EFI relay goes back to the IGN fuse (pin 2 goes to ground). So with the relay out, check for voltage on pin 1 of the socket with key-on. If you're getting voltage, I would suspect a damaged relay socket, so that the relay is not making a connection. If no voltage, it should be a black-yellow wire back to connector EA1 (in the relay box), then straight onto the IGN fuse. You're only talking about an inch or two of wire between your got-voltage IGN fuse and working-but-not-closing relay.
You've done a great job of narrowing it down; just keep going.
I checked the pin 1 of the socket with the key on. it read .16v. I then checked the wires in the fuse/relay box underneath the EFI relay and saw no problems. I found the black-yellow wire and followed that to the IGN fuse,(there are two wires with Black-yellow but one looks like 10ga the other maybe 16ga) but its got to be over 5 ' of wire from the EFI realy, or fuse, to the IGN fuse. I don't see any damage in there.
you can see the black-yellow wire running from the EFI realy. Both blk-ylw wires drivers side fuse box. one in front looks like 10ga, one in back looks like the same as from the EFI relay
I checked the COR as per the manuals specs. It looks like the COR is working fine. I had a little trouble finding it, but the 1991 Toyota Truck Repair Manual came in handy (as you all know it does). So, my next spot is the Ign. Switch. Has anyone removed/inspected this before? My repair manual is for a 91 and my truck was built 12/91, so is there going to be a ton of stuff that is different? The guy I bought the truck from rolled the truck at one point. Some of the electrical is embarrassingly FUBAR. If it is the switch. ( I'm just going to use some gator clips and jump wire as per the diagram to test continuity with my ohm meter) Then how do you replace it? There are no nuts and bolts on the assembly with the tumbler and switch.
i'm not sure how to test continuity on multiple pins at once. the pig-tail is different than the diagram, but it is labeled.
04-26-2017, 01:31 PM
