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I finally got my carburetor fixed up, and all should be golden. However, when I hooked everything back up and turned the key to get the fuel pump goin... nothing. The relay under the hood for the fuel pump wont kick on unless the voltage regulator is unplugged. And when I do that, the fuel pump runs in reverse... (I tested the voltage at the black / red stripe and ground wires that connect to the fuel pump and got a neg. 12v) So obviously no fuel was entering the carb. My roommate and I started tracing down the problem last night and didn't come up with any concrete other than it appears that the voltage regulator isn't receiving juice when the key is turned to the "on" position. If I recall correctly, the white / green stripe or white / black stripe coming from the alternator is what is supposed to power the V.R. but i'm just spitballin. I'm getting 12 volts to the alternator through the large 10 gauge black wire, and I have continuity between the large black wire post and one of the wires coming out of the alternator plugin. (guessing that one of those supplies a 12 volt output to the rest of the system when the alternator's not spinning, and the other one supplies the voltage outputted from the alternator when running for the voltage regulator to tame down a bit for the rest of the system? )Does this sound familiar to any of you guys? Or have any experience with this that ya might aid with? Thanks!

Oh, yeah, this is for a '81 manual with auto wiring harness.

Let me address the fuel pump side of this issue:

The fuel pump gets no power until the motor is running or the key is in the start position. The idea is so the pump will not stay on in an accident and cause a fire. The pump will not come on with the key just turned to ON.



On the reg/alt:

To be honest I've never unplugged the reg to see what happens. I would not rely on your pump symptoms to say you've got a bad reg or alt though. As I recall it, the alt puts power out through the large gauge wire, the wires from the reg to the alt basically act as a switch to turn the charge circuit in the alt on/off . I'm sure we've got an electrician around here that can explain it better.

The black/red wire also feeds power to the coil. It is odd to be getting reverse voltage there. I'd suspect a short or something causing that, or you may be right on track looking at the regulator.

If it were me, I'd hook everything back up, and crank it over. If you get fuel to the carb while its cranking, then you know you've got other problems keeping it from firing up. The way those relays are set up, you get different behavior with the key on and not running, key to start, and with the key on and the motor running.

I didn't even think to try turning the engine over to see if the fuel pump works it's magic. In the past, before I replaced the entire wiring harness, the fuel pump would come on with the ignition in the "on" position, I will definately try that tonight when I get home from work and hope for the best. Thanks for your reply, I'll let ya know what I find out.

Well, that was it!! It's funny to me, because when my roommate and I were working on it the other night, we couldn't help but to think that we were overthinking the problem and that it was a simple answer.... We did NOT think at the time that it WAS working just fine, just needed to turn the engine over! doh! Now I know, another entry in my backyard mechanic journal.

Now I've got a new problem though, I got the truck started up and it idles HIGH, like the choke never goes off. The carb is one of those beloved Hitachi's, with an auto choke. It's been in about 3-4 peoples hands now, and I'm thinking that i'm having a combination of vacuum leaks and incorrect screw settings for the various throttle linkage screw stop points (and auto-choke rich / lean setting).
It's an '81 with a '79 engine, the header has 3 vacuum hose connections on the engine block side of the intake man. The one closest to the cab is connected just under the intake man to (what appears to be) a thermostat of some sorts. Can't see under there very well. The middle vac. line is connected to nothing, and the one closest to the front of the truck is connected to the vacuum advance line on the distributor. No catalytic convertor, and no vacuum canister. Probably all been removed from the previous owners. That takes care of the intake man., now on the carb, there are two vacuum lines next to eachother that come off of the side of the carb closest to the passenger tire. These lines are simply looped into eachother with a hose. (not a standard feature I'm guessing? hehe)

That's an accurate description of what's hooked up and what's not, hopefully someone knows what's required in the way of vacuum hose hookups in order for it to run smoothly? I've got the timing about dead on, and it starts well, but even with the idle screw turned all of the way out, it idles somewhere around 1700-2000rpm (I'm guessing, just by the sound compared to a roommates truck) If such a reference exists out there for the "recommended" settings for how far each of those screws on the linkage are supposed to be out, and the approximate rich / lean setting for the auto-choke mechanism... then I would be a happy happy luv'r. <G>
Thanks!

is there a vacuum line on the other side of your( drivers side) carb? mine was just as baffling but hooking that one to my dist advance works. of course if your timing it while the advance isn't capped off and there are leaks you'll need to time it again.good luck,keep at it.

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Dr. Frankenstein

Not on the carb itself, (that I can readily recall, I scoped it out pretty well last night but will check again) only on the intake manifold on the drivers side are the 3 vacuum line connections. Are all 3 of those vacuum lines coming off of the intake manifold the same? i.e. they open up to the same location inside the manifold? Because if they do, then that COULD be a problem that I'll have to test out with some carb cleaner when it's running to see if the idle changes. Do you see a problem with the two vac lines on the passenger side of the carb being looped into eachother? I just wanna get this thing running well enough that I can use it to drive down & pick up a 350 / tranny with.

the one that I found had a mystery hose w a screw capping it on mine and it was a b**** to figure out where it led and just as big a pain to attach a hose to. the other two you spoke of (I think) are for emissions stuff so if they're capped it should be o.k.

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Dr. Frankenstein

Oh yeah, if someone out there has a totally stock engine with emissions PLEASE make us a diagram!

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Dr. Frankenstein

So if I find something on the carb that's capped off on that side, then that's my timing advance you think? I'll just assume then for the time being (unless I hear otherwise) that I'll plug the timing advance hose from the distributor to the side vacuum line on driver side of the carb. Otherwise, if there is no available (or plugged) line on the carb, then I'll leave the timing advance plugged into the intake manifold and cap off the other vacuum line that goes to nothing. Will give me something to poke around with tonight when I get home from work. Along with figuring out why my dash lights come on when I press the brake...(key off, lights off) yeah, go figure.

yeah,but I'm no isuzu engineer. I think the lines that come out of the carb are the metered vacuum. I think one of the looped off lines you were talking about might also work to advance the timing.

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Dr. Frankenstein

Here is a rough run down:

Port on the carb, closest to the front of truck goes to distributor
rear port on carb goes to thermal switch screwed into front of intake manifold, which goes to EGR valve on the bottom of the intake, port on the EGR valve is way under the intake, toward the block, not visible at all)

(The 79 EGR system should have a backpressure transducer too, hooked to a small metal line that comes up from the EGR valve, it should be hooked up, but I don't have the diagram in front of me and it gets a little involved there. Plug off that metal line)

On the block side of the intake you have three ports. One of them is different looking. It goes to the little stub above and a bit forward of it on the valve cover. It is basically your PCV valve.

The other two on that side are basically interchangable as far as I recall. One is for the air cleaner (should hook to a tee and then to a deal on the bottom of the air cleaner and the flapper valve out in the nose of the air cleaner. The other port hooks to a hose that goes over to the other side of the motor and into a valve for the smog pump system. You can cap both of these off (I usually hook a hose between them) and the truck should still run right. Just don't expect to pass emissions testing like that.


The high idle could definitely be caused by how the vac lines are run, especially the ones on the carb. The distributor hooks to a specific port for a reason, and it could be throwing things off having it hooked to another port and/or having the disti port hooked into another port.

Just as an aside, you can cap off every port on the intake and carb without seriously affecting how it runs. Just don't hook the ports on the carb together to block them off. I'm not sure that makes a difference, but I can see how it might. Losing the EGR and the distributor lines will rob some power though. The disti advance kicks in under a load so removing it will cut acceleration/pulling hills, and the EGR helps control pinging/detonation which also crops up mostly under a load.


I'll work on getting my collection of hood sticker vac diagrams up someplace. I think I have one from every year 76-80 except for 78 and I might have one from an older truck laying around too.

800 you are my hero. I could feel it in my bones that I had it rigged up not right (amazing how well its working) sorry elijahe defer to the encyclopedia.

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Dr. Frankenstein

Wow, you're amazing... I can't wait to get home and go through the printout I've just made of what you've written. Thank you so much! Hope this information can make it's way to other people with the same issue... Thread got pretty well hijacked, but still.. awesome. Thanks a million to both of you for giving me direction. When I took the luv for a test drive yesterday, I did notice that it was a lot more gutless than I would have expected when going up a small hill by my house, going down hill (no load) it accelerated great, EGR and Dist. Advance are probably ALL fuggered up then the way it is now. I'll keep ya posted

hijacked? maybe so but if your truck works better tomorow then its a good thing (right?) I did my vac lines like 800 laid out just now (my timing was at 0 degrees!) tell us how it turns out elijahe

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Dr. Frankenstein

On that distributor advance one, someone here quite a while back mentioned that it needed to be hooked to "a ported vac source". That was how I learned that it really did make a difference. If you hang around here long enough you can't help but get smarter, I know it worked for me. If I recall they said something about if the motor speeds up with the advance hooked up, the source isn't ported. I'm still not completely sure what ported means, but I assume it means vac coming from in the carb (above the throttle plate?) rather than in the manifold. Whatever it means, it makes a difference.

Good luck and I will spend some time on those diagrams tonite. I know a lot of folks could use them, and they should be in the info section of luvtruck.com.

Here is a pic of my 79 Vac Diagram
Maybe it will help



Jim

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`79 LUV 2WD Stocky
`80 LUV 4WD Stocky

No fair! its like Bullwinkle drew the one for cali!

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Dr. Frankenstein

Well, got the vacuum hoses routed according to that fine writeup (thanks xl800!) and it ran a LOT better. I had a lot more pull going uphills, although it still seemed pretty gutless) managed to get it down to the gas station & fill er up. Just how gutless is the Luv going up steeper hills on highways? I found myself downshifting to 2nd when I was heading up a steep grade hill at 35 mph. My turn was shortly after I had to downshift, but it was falling off fast. The idle is still a WEE bit too high, but I think it's down to fine-tuning now, as when I sprayed around the carb with wd-40, I didn't notice any change in rpm's. Then again, when the engine is idling at 1700 or so, how much of an impact is wd-40 through a vac. leak really going to do? More tinkering. It did seem to run a little hot though. On my short trip down and back (all of about a mile and a half, maybe 2) the temp guage was sitting at about 2/3rds of the way to redline. I'll probably yank the thermostat tonight and check it for any obvious signs of corrosion / blockage.

Oh yeah, getting back to the subject of this thread on the fuel pump not kicking on. So before I had the truck running yesterday, the fuel pump wouldn't kick on until the truck was turning over and then when it was running. Now after taking it for a test spin, the fuel pump kicks on as soon as I turn the key to the ON position... I think the old Luv is becoming sentient, guess I'll have to get on it's good side quick.

I got a good shot of the vacuum routing diagram for the '81 luv down at the local Pull & Save. Stopped by yesterday to see what other parts I could confiscate from it and brought my camera just in case. I'll post it up tonight when I get home

800xl you are right. "Ported" is vacuum taken from just above the throttle plate. Full or manifold vacuum is from below the throttle plate or from the intake manifold itself. With ported you would have vacuum only when you open the throttle a little but none at idle. ----hope this helps.