96' hard to start after running A/C

After driving down the highway w/ a/c on in 95 plus heat today for 50 miles I pull into lumber yard, cut truck off, go get what I need. Get in to go it wont start, it try to fire off but wont(let sit with hood open for 5 min. it fires off). Truck does the same thing when idleing around the ranch with a/c on. Leave the a/c off in both above circumstances, no problem restarting.
Temp gauge from day 1 has never got over 1/2 way hot on stock guage. Week or so ago I replaced the fan clutch and temp sending unit, thought that had fixed it. I am thinking truck is running hotter than idiot guage is showing, mechanical going tomorrow. Weird thing is after I replaced temp sending unit, dash guage still acts thesame.

 

Hmm, kind of sounds like vapor lock to me. I believe the ign. coils were right above the exhaust manifold on those. Maybe they're getting too hot?

 

I dont know. It only happens when I have the a/c on, then shut down truck. I can literally run the truck for all day in the heat without a/c on, turn off and start at will. Run the a/c and I have a hard time restarting after cutting truck off. After restart with a/c on I catch a smell- like heat if that makes sense. Thing is there is no boiling radiator or anything like that.

 

Hmmm, barring strange and unusual circumstances, the only other things I can think of are a bypassing fuel pressure regulator, or a leaking check valve in the fuel line. That usually causes fuel pressure to bleed down, but not usually like this. Or also, try and see if the A/C switch has anything to do with it.

 

XB can you explain more on the fuel possibility... I dont smell fuel leaks/problems, just a hot motor smell after start up with a/c running. After running a/c and shutting truck off, and trying to restart, the motor turns, trys to fire. I give it gas @ pedal = instant shutdown, no start. I can pop the hood open for 5 min. or so and it will start. Thats why I was leaning more towards heat. I am at a loss on this. I dont get why I can I can run the truck all day with a/c off and have no problems, run the a/c on the hwy or at idle and have problems.Maybe after I hook up a real temp guage will help.... I dunno.

 

If the pressure regulator sticks open (low fuel pressure position) the pressure in the fuel rail would drop to zero psi, almost immediately after shutting the engine off. If you tried to start it with a stuck open regulator, it would try and run on maybe 10% of the required fuel pressure. You wouldn't smell fuel, because it would all drain back down the return hose and in to the tank.

One way to check this, is to attach an EFI fuel pressure gauge with the engine hot and running, with the A/C on, and check the pressure. Now shut off the engine, and see what the rest pressure is. If it drops a few psi and holds, that's normal. If it plummets to zero, or sinks slowly to zero, it indicates either a leaking fuel injector, check valve, or pressure regulator.

What's causing it to only happen when it's hot is hard to say. Maybe the regulator sticks when it's hot, and then closes once it cools off.

Another worthy mention about fuel injected vehicles. Since they no longer have accelerator pumps, or chokes; hitting the gas while cranking may cause it not to start. On most post-'96, OBD2 vehicles, cranking with the gas pedal past 80% will put the computer in to "Clear Flood" mode, and shut off the fuel injectors.

 

My 95.5 does the same thing, hard starting after a/c use. My guess is the extra heat as stated above and creating some sort of vapor lock somewhere. Maybe something to do with the location of the fuel filter under the intake manifold? It starts, but takes twice as long. Starts right up after sitting, though. Temp gauge reads the same whether a/c or no a/c use. Not gonna worry, but will look at this post if a solution is found.

 

Thanks XB for the breakdown, very helpful info. I learned something new here, thanks.

 

I was wondering if you ever found a resolution to this as my 95.5 does the same thing on warm days. Hadn't noticed the A/C vs. not, but what I did figure out is that if I unscrew the gas cap and let the pressure out of the tank, it seems to help it start up a lot faster than just waiting 10-20 minutes more.

Would love to hear if anyone knows why this might be.

 

Sounds to me like it is the alternator. An old alternator my be charging enough under normal circumstances, but with extra draw of the A/C, especially when the A/C has been running for some time, the alternator may not have enough output to overcome the a/c draw.

 

In my case its not an alternator problem or charging problem. I have no trouble with turning the motor over with the starter. Its a firing the motor off problem. I am leaning towards XB's explanation. We have had some very chilly weather here in S.Tx this winter.I have had no problem, since the cooler temps have hit us. I think its the fuel regulator to be honest. I'll replace the regulator when the problem comes back as the temps warm up.I keep a can of starting fluid in the truck and use it when it wont fire off. A couple weeks ago we got into the 80's and it would not fire up after I went into a store after pulling in off the hwy.

 

Years later I’m revisiting this to see if anyone ever found a solution to this because this is EXACTLY HAPPENING TO ME.

Only when the AC is on do I have a sluggish turn over when the truck sits for a short time

 

Try searching “hot no start”

IMO ac on/off doesn’t matter bc our 2RZ’s only have one fan

in my case, the issue was leaking injectors
lots of other causes thou…..

 

Control car

totally makes sense

yesterday the problem happpend again

only when I turn the AC on/ drive truck around town/turn off then turn back on after truck been sitting for a short time/ slow crank over.

beyond annoying lol

when I don’t turn on the AC the truck fires up no problem every time even after stopping at the store and returning truck back on.

I’m going to the crank position sensor and new plugs and spark plugs this weekend (verify the new plugs are properly gapped)
And a new distributor cap since I have one at my house already.

I’m hoping it’s not the injectors lol but if it’s ultimately the injectors then so be it lol ‍♂️

 

Thinking out loud here... in perfect A/C system and depending on pressures on the high side of the AC system the temperature/pressure chart shows that the AC condensor temp will be between 120 and 145 degrees. I am wondering if your AC condensor is clean and clear for proper airflow and if that superheated air from the condesor is the issue, like I said, thinking out loud.

 

interesting^^^^^

hmmmmm

more i think about it and after reading that altn or "firing of the motor power" was mentioned above......

ok on my 98 subaru race car i have a trunk mount battery
always had a hot no start issue
found from a GTO forum that i had to run a ground wire not just to chassis but also to engine
no issues for over a year
just recently, i was tooling around the town(45mins few stops), dropped by the house to pick up something....
and i was "stranded" in my garage........thank goodness
i thought a was clear of this issue
sometimes if im lucky.....i shut off radio/HVAC/lights and suddenly starts no problem

so back to searching for another solution

found this
https://painlessperformance.com/product/hot-shot-kit-part-no-30202/

so from searches.....read that many times on older vehicles the ignition cylinder starter signal wire becomes weak(bc of wear)
heat only makes the weak signal even weaker
this solenoid, takes the weak lock cyl signal wire and holds for full power to starter solenoid and bingo starts up np
seeing how both my car and your taco are 25 plus yrs old.....makes sense

i havent bought just yet.....literally discovered this last weekend

very interested to see Glamisman thinks of this electrical situation bc of his knowledge of the same!

 

Back in the day when I was spinning wrenches professionally, Porsche/Audi/Ferrari/Range Rover, I was the only tech to work on Audi Diesel/Turbo Diesels, anyway, same situation as your subi, battery far away from the starter and after years the battery cables would become questionable at best. Run new welding cables for power and grounds to the starter and subframe and that ALWAYS fixed a slow crank - hard start issue on the diesels.

As to the wire to the starter solinoid, a voltage drop test will either confirm or deny that is an issue or not.

 

HA! Glamisman
-5g wire (both) from batt terms to starter(+) and to engine/tranny(-) then to chassis in rear
-new SS ground cables from engine to frame rails

didnt think of my steel subframe thou......hmmmmm

but to clarify
when issue arises.....once key turned to start.....nothing
entire car getting power to lights/AC/radio/etc but once key turned to start.....silence

typical.....this occurs when im by myself or with kiddos(cant perf V drop test)
typical.....i even took a electrical friend with me for 2hrs of errand running.....never occurred

then re-wired with 5g wire as above and no issues.....until now

 

I broke down and bought/installed that Painless hot/hard start relay on the subie this weekend….not difficult, hardest part was locating the relay.

Typically, after 3-4 errands (multiple stops/starts) the issue arises
Anxious to see if this works


Crap
I forgot about the ground wire to subframe as Glamisman suggested. Will install the same.
HA
Perfect excuse NOT to go to grocery store tonite

 

Okay everyone
So after changing out the fuel injectors and CPS my truck hasn’t had no issue turning over even when the ac has been on and truck under load.
Looks like it was more the fuel injectors then anything else.
Couldn’t afford OEM Toyota ones and went with Echilin from Napa and verified they didn’t stay open and no issues since