Ok so I have a 1980 Toyota truck 20 R stock carb with most emissions gear in place. Intermittently it will run like crap, shuttering, shaking, trying to idle at less than 500 RPMs (it will ultimately die out if you don't keep on the gas). It seems to particularly happen after the truck is run hard, but not always.

After some research the other day in an inspired moment I jumped the idle fuel cut relay and the truck started running OK. Confident in my find I rewired the solenoid and away I drove, trying to get the truck to duplicate these symptoms.

Sure enough even with the fuel cut solenoid hard wired to the battery the truck started running like crap again.

This time I had to see if the solenoid itself was still working. So with one hand keeping the truck idling, I unplugged the idle cut solenoid from its jumper and replugged it back in (hoping the solenoid was weak or maybe sticking and might through my efforts become unstuck).

The problem still persisted, however, until I ultimately in a fit of frustration left the solenoid jumper off and walked around to turn the ignition off on the truck. As I walked away from the stumbling truck the idle suddenly straightened out - everything running like it should (except the idle cut solenoid should have been starving the engine for gas).

So I plugged the solenoid in - truck ran like crap. Unplugged it again - ran good. It's like the opposite of what is supposed to happen.



Does anybody have any thoughts on this? It seems to defy logic... I don't know enough about the Aisin carburetor to feel confident in the one theory I do have - that the vacuum actuated secondary venturi is somehow kicking in at idle intermittently after the truck experiences some major vaccuum load (i.e. it gets run hard).

I am definitely going to try investing in a carb rebuild kit anyway since the accelerator pump looks like it is developing a bit of a leak. I think I will also be trying a fuel pressure regulator to try and better regulate the ammount of fuel the carb is getting (i.e. perhaps fuel pressure is on the high side forcing fuel through the other fuel circuits when it is not needed). It would also explain why the truck will start OK after being allowed to sit for a few minutes.

Edit: also very strange but when the AAP diaphragm is unplugged the truck immediately dies again too. Not sure why. I am also going to test the choke pulloff because I think the diaphragm in it is leaking more than it should - the choke plate opens correctly when the truck is warm though.

 

As of now the problem (might) be fixed. On a hunch I decided to install an inline fuel pressure regulator and set it down to 5 PSI (kept guessing and checking until the truck ran good). Truck seems to run a little leaner and the fuel level is down a little bit in the sight glass. My sneaking hunch is that the running badly after being run hard (i.e. high RPM) may have been due to the fuel system developing too much pressure. Coming soon I will be checking the fuel return line from the pump to see if it might be clogged.

Time will tell. Today I also did the one front wheel bearing that needed replacing. After that I will fix the speedometer, and then on to the wiring gremlins. After that the truck will be as close to mechanically perfect as I think you can make a 30 year old truck with nearly 200,000 miles on it.

 

Let us know how it goes! I don't have advice for you but I've got a weird intermittent engine-dying issue that I haven't been able to figure out, too. This is with a rebuilt engine, new coil, ingitor, plugs, wires, distributer, fuel pump, fuel filter and rebuilt carb. I'm thinking either a vacuum leak, plugged fuel line issue, or you've got me thinking something electrical with the solenoid, so I'm interested to see what you find out!

 

http://www.toyotanation.com/forum/ar.../t-275556.html

Check this out. If you read all the responses, there's some good stuff in there. Since mine is intermittent..IF this is my issue...I'm thinking it's an electrical connection that's going bad. Sometimes it works sometimes not. I'm going to test my solenoid and if it checks out I'll see about soldering the area one of the lasts posts talks about..

 

Yes the problem was intermittent but not totally random - remember I said it seems to persist only after the truck is run really hard (I don't typically drill my vehicles but it is still a problem that needs resolving).

The post you quoted is one that I did use in my research. However, the 1980 has no emissions control computer so that is out as a solution. The choke pulloff on mine is not working correctly but I have it plugged off and the choke wired open for temporary (runs like crap when it's cold but straights right out).

I am basing my current diagnosis on the following:

1) The number 1 intake valve is very noisy. I think I am misdiagnosing the intake valve for fuel pump noise (i.e. the pump can't return fuel properly through the fuel return)

2) The fuel pump on the truck looked quite shiny on the truck when I got it, yet it crapped out a few weeks back (ruptured diaphragm). Again this could point to the fuel pressure being run too high (I wasn't thinking at the time and never checked the return line)

3) Since the 5 PSI fuel regulator mod, the truck has not misbehaved.

4) When the idle cut solenoid was disconnected, the truck would run OK again. This could point to high fuel pressure

5) When the idle cut solenoid was disconnected to test it out, the truck would not die right away. It would starve out and run really crappy. Theoretically the truck should have literally died out cold within 1 second...

 

Yeah, I was more talking about what mine was doing there. Yes, you're right, we don't have a computer. I didn't realize that's what he was talking about with the soldering there. I'm glad you already saw that thread. Hopefully it will help me out!

Seems like a fuel pump putting out too much pressure would cause the problem to always happen, not just happen intermittently, right?

 

Blowing out the fuel return line has solved my problem. In fact I took out the fuel pressure regulator because the truck starved for fuel with it on. Now the truck runs good - doesn't run super rich anymore (just a bit with altitude here in Flagstaff, AZ), and doesn't smoke black under heavy load.



The problem I was having was not intermittent exactly. It would only run like after having been run hard at high RPMs. While the clogged return line would seem to always make the truck run poorly, it would manifest itself severely after being run at high engine RPM as a mechanical fuel pump develops significantly more pressure as engine RPM increases. The truck would always start after sitting for a few minutes because it had time for the fuel pressure to bleed down a bit. Fiddling with the idle cut solenoid proved to be a major clue as restricting the flow of fuel to the idle circuit caused the idle to straighten out (as the solenoid was unable to overcome all of the excessive pressure buildup in the fuel system).

I will post back if the running condition of the truck changes, but I drove it significantly and even tried to almost beat the crap out of it for a few blocks running it hard (this used to alaywas cause the truck to misbehave on the first or second try). I think if it was going to revert to its old ways, it would have done so by now.


As I said, next on the agenda is the Speedometer, then I am almost home free as far as mechanical problems go with this old truck.

 

Wow i had almost the same problem. But that was only when i changed out the fuel filter. I got one from checkers that their system said to get and when i installed it, there was too much fuel going in and there was backfire. I went back to the old filter and the problem was gone.

Im interested to see how you get your speedometer working as mine is not working either. So is the tachometer. Good luck!

 

I will post back on the speedometer. I suspect it is the drive cable.

I am not for certain but I do believe that unlike the speedometer, the tachometer is electronically driven (most likely from the distributor). Maybe that helps. If you are unlucky you could have a bad head unit (i.e. the instrumet cluster itself is bad). For my part, I am hopeful that a new speedometer cable will fix my woes...

 

this makes me thing you may have found the solution to my intermittent stumbling idle issue..

for a speedo I have a 2WD 82-83 speedo/tach cluster (says 114K 'ish on odometer) someone can have, just pay shipping...in case your's turns out to be hosed

 

My tach actually did work once. Dont know how but it did. haha. So im guessing something rattled into the correct position for it to work.

 

So far the little truck continues to run well. Hoping the return line doesn't re-clog...

The tachometer (on mine) is electronic as I thought. Once in a while mine won't get a signal - you have to shut the engine off and restart and it will jump to life. Even if the tach did crap out on this truck I don't think I would fix it.

Getting to the speedometer cable today, I degreased part of the transmission so as to keep the cable clean. Turns out the cable was fine - the speedometer drive off the transmission is the problem. The transmission extension housing has major bulges and cracks in the casting (perhaps the transmission was struck against something).

Not sure what I'm going to do at this juncture. Part of me says I should buy the '81 for sale in town for 400 bucks that claims to need a clutch and rob the transmission out of it, then part it out. I could probalby break even or turn a (small) profit doing that. Then again old 2wd Toyota trucks don't seem to be that desireable so maybe I'd just be getting a bucket of old parts that I don't need and can't sell...

I could rebuild the transmission but I'm working out of the truck bed if I do. That is really gonna suck and I bet it's a 2 day job struggling with jackstands and doing this crap on my back. Even then the extension housing is probably tough to locate since that casting really ought to be discarded.

I could find a rebuild or junkyard transmission but that sucks almost as bad as rebuilding it myself and is probably 3 or 4 times more costly...

All I can say is that I will fix it one way or another. In the meantime I will continue driving the truck gently and hope that casting doesn't take a dump while it's going down the road...

 

The truck did begin acting up again today. However, this time I immediately pulled over, blew out the fuel return line again and got it going in no time. Hopefully the truck will do this less and less - otherwise I will have to figure out how to stop the fuel return from clogging. I did notice that it seemed like the gas cap vent was leaving a lot of fuel vapor trapped in the tank. I installed a new gas cap (cheap guess) and will have to investigate if there is anything else wrong (i.e. with the carbon canister or if there are other dedicated vent ports on the gas tank).

Closer inspection of the extension housing of the transmission reveals that what I first thought was a crack may simply be where the mould was broken on the casting.

 

I hope you have it figured out! That's an easy fix and I'm definitely going to try it.

Yeah the tach is gets it's signal from the coil, definitely electronic.

I've been meaning to just replace all my gas lines but haven't gotten around to it...maybe now's the time.

 

Hey, when "blowing out" a fuel line, what exactly are you doing? Do you disconnect it at both ends and blow compressed air through it, or should it be hooked up to the gas tank when you blow air through it? I'm hopefully going to see if this does anything for me this weekend but I'm not really sure exactly what I'm doing & don't want to damage anything.

 

OK so it is probably best to disconnect the line at both ends like you said but I did not do this - I don't have a lift and getting back under the gas tank is a pain and I didn't see any obvious way to do this.

Basically I just took compressed air and blew it through the fuel return line hose.

MAKE SURE YOU REMOVE THE GAS CAP WHEN YOU DO THIS.

Capitalized so you don't blow up your gas tank. Good luck!

 

Thanks. Did it over the weekend. Definitely didn't help with my stalling issue, but at least that's one more thing ruled out!

 

Well for your random stumbling issue spray some starter fluid around the base of the carburetor you might find your issue. My throttle shaft was loose in the rear of the carb and sucking in extra air at random times and making it stall or run like . Just anouther idea thats cheap-o

 

I did the carburetor rebuild on mine today and it runs even better. The problem I was having did re-emerge. I had gone through very carefully with carb cleaner around the intake manifold gaskets and such and found no leaks. I will try focusing on the throttle shaft too. I am also thinking that the plunger on my accelerator pump looked really worn out. My problem wasn't so much "random" as it would always occur after acceleration at or close to wide open throttle. Now typically that means the truck ran fine but once in a while it would be a problem. So I might have fixed it. I'm going to go test drive it now. At the very least I have a clean carb now...

As a side note, I found a possible engine swap candidate today. A guy is giving away a free Jeep Cherokee diesel that was Tboned and has no axles, and allegedly a transmission that has an output shaft going bad in it. The little toyota would probably respond well to such an engine swap, but we will see. I am going to take measurements tomorrow to see if it is possible to use it. If so, it might be my swap. Toyota turbo diesel trucks are hard to get ahold of and frequently horrendously overpriced. I think I could do a good quality engine swap for somewhere south of a grand, dependingi on how easily the engine will just fit in the engine compartment.

The Jeep diesel was built by Renault and was an OK design...

 

OK so... The truck seems fixed but I will post back within a week if it starts acting up again.

I used the GP Sorenson (spelling?) carb kit from Autozone to reubuild the carb because I could not locate the carburetor identification tag that the NAPA wanted to find out. The ID tag may be important when it comes to which gaskets you end up using on reassembly.

The Sorenson kit seemed OK. Some parts seemed kind of cheap. Not sure if the NAPA one would be better. There were two little oring type gaskets that the Sorenson kit didn't seem to have, so I reused the old ones. Didn't seem to be that big of a deal though. The gaskets were of good quality and worked excellent. Everything went pretty smoothly it seems for a carb kit that only cost $22 and the fact that I rebuilt the carb in a pan that I set on the tailgate of the truck.


I know some people sometimes ask about the Sorenson rebuild kit so I figured I'd post it up. I would be willing to bet that the NAPA kit is better but if you're careful and you have a good eye, this one worked fine for me.


The last thing to reset on the truck is the float level. It is set slightly too high at the moment and it causes the truck to stumble a bit off idle. Once I get it cranked down I think it's going to run great...