hesitation while cold (open loop) 3vze

[nicnmike]

I'm so close to having this thing running well (aside form the all the other stuff that needs to be addressed)!

The truck is a little hesitant to start sometimes. Right after starting, if you blip the throttle, it really stumbles. Trying to accelerate hard soon after starting (like getting out of the neighborhood, on the way to work) it hesitates/stumbles. After it fully warms up, the damn thing runs like a stuck pig, even for a 3vze which leads me to believe the issue lies in the open loop.

Is anyone aware of a thread, or discussion that explains what changes occur when things go from open loop to closed loop? I'm hoping it's just a vacuum leak.

I've not kept up with the build thread, but I've been messing with the truck for a few years now. rebuilt engine and lots of new parts....

 

[Bad_Vision]

First off I need to know if it's a manual or automatic?

 

[nicnmike]

First off I need to know if it's a manual or automatic?

Manual.

 

[Bad_Vision]

Check your dashpot if the check valve isn't opening and closing right it will cause delay after throttle open.

 

[nicnmike]

Check your dashpot if the check valve isn't opening and closing right it will cause delay after throttle open.

Dashpot is long gone. I don't remember a vacuum diaphragm associated with it like in the diagram you attached. It's a1990 3vze. Would the dashpot really affect the acceleration?

 

[Bad_Vision]

Yes, why was it removed?

 

[nicnmike]

Yes, why was it removed?

First of all, thank you for helping. This site has been awesome and I appreciate everyone who participates.

How? When accelerating, with the throttle held either in one position, or increasing, the dashpot shouldn't matter.

The test above is done after warm up. My 4runner runs fine after warming up.

Isn't it there just to keep the engine speed from decreasing too much between shifting?

 

[Bad_Vision]

If the valve isn't working or it's missing it's a vacuum leak. I don't know how you deleted yours.

Sense you seem to notice this when its cold I lean on vacuum leak. And commonly dashpot gets removed because some go happy dingbat takes it off thinking it's useless and winds up with the issue your having. And when you said you removed it then I suspect this.

Your defiantly getting vacuum leak when a engine is warm the seals swell and close you need to smoke the engine when it's cold to determine leak locations.
Look on YouTube for a instructional video on how to make one for cheap.

 

[nathan25]

Im having simular issue. Starts but wont stay running, will stay runing with gas then die

 

[flyinhawaiian01]

Well, I'd say to just read up on posts here that have similar problems and try some of their solutions. If that doesn't help, then it would probably be good to start a new thread with what year and model you have (including what engine you're running)the symptoms you're having and what you've done so far.

Its really all the same process for every one of these "issue" threads, before anything, do some basic tests first, these can be found in the online manual for your model, then go through the threads to see if anything sorta sounds like what you are experiencing, try what they've done, and if all that fails, then post up with a good list of what you have.

Having said that, I'll assume you have the 6 cylinder and you've already checked your intake and made sure its all together, right? If it starts then immediately dies, it could be the intake tube is not connected to the throttle body! And, without the above tests and more info, that's about as much as I would be able to guess.

 

[nicnmike]

If the valve isn't working or it's missing it's a vacuum leak. I don't know how you deleted yours.

Sense you seem to notice this when its cold I lean on vacuum leak. And commonly dashpot gets removed because some go happy dingbat takes it off thinking it's useless and winds up with the issue your having. And when you said you removed it then I suspect this.

Your defiantly getting vacuum leak when a engine is warm the seals swell and close you need to smoke the engine when it's cold to determine leak locations.
Look on YouTube for a instructional video on how to make one for cheap.

You had posted in someone else's thread about testing for vacuum leaks using water. I don't know if driving in the rain counts, but I was driving in the rain the other day and my idle dropped, when normally warm form about 900 rpm to 400/500 rpm. So I'm still thinking vacuum leak. I changed all the visible, smaller vacuum lines when I finished the rebuild. I guess I need to go over them again and make sure they're routed properly.

I haven't done anything with the charcoal canister. And the last couple of fuel ups, I haven't noticed the usual hissing when opening the gas cap.... Might need to run through that.

If you look up images for the dashpot for a 1990 3vze, you'll see that there's no vacuum actuated diaphragm associated with it. It was just a plastic thing with a cap on the back. No vacuum, no nothing.

On a side note, I just got back from 750 mile round trip drive. I hauled a golf cart on a trailer on the way back too. The truck ran great. Starting took longer than it should've when I stopped for gas, but I think once I pin point the vac leak, I should be golden. I actually got to use 4 wheel drive on this trip too! These are some handy little trucks.

 

[nicnmike]

I did the smoke test using this method: https://youtu.be/HRiK2HEA3QQ

There was smoke going in, but I didn't see any coming out. I ran it through the PCV port on the plenum. I also found a vac tester I had lying around (I'm a hoarder), so I'm not sure of its accuracy, but it measured above 20 in mg.

I have also noticed that when trying to set the timing, the indicator mark moved around a bit. Not a lot, but it didn't hold steady. So I replaced the distributor with a new Cardone Select. Now the mark hold steady and I seemed to have almost no hesitation this morning. I'll need a few more days of testing before I can come to any real conclusions. Here's hoping!

 

[nicnmike]

I feel the new distributor has solved the hesitation while cold problem, but not the hard start when hot problem. I was using the truck a lot this week cleaning up my mom's yard, so I did a lot of turning it on and off. After warm up, the starting took a little longer than when it was cold. Plus, now it's leaking some gas because you can smell it after one of the hard starts. After some research, I read that it could be the fuel damper. I need to re-do the valve cover gaskets, so I'll replace it while the plenum is off.

Now the brakes are starting to get soft, so there's that to contend with now too!

 

[flyinhawaiian01]

Could be, I've replaced mine and hard starts went away a while back. IIRC, it was easier to start if I cranked for 1 or 2 seconds, waited about 3 or 4 more seconds, then hit the starter again and it would fire up easily after that.

 

[nicnmike]

Could be, I've replaced mine and hard starts went away a while back. IIRC, it was easier to start if I cranked for 1 or 2 seconds, waited about 3 or 4 more seconds, then hit the starter again and it would fire up easily after that.

that's what I find too. They're supposed to be prone to leaks as well, so between that and the leaky valve cover gaskets, I feel like a ticking time bomb. Gah, freaking plenum.