OT Strange Automotive Prblem

-- Last Updated: Jul-09-07 4:58 PM EST --

When my '96 Toyota Tacoma motor (SR24 2.4 Liter) gets hot, and I cut it off, it is difficult to start unless I wait until the motor cools.

I notice this a lot more at altitudes over 7,000' level in the sierras.

PS. This problem started right after a major tune up. New plugs, O2 sensor, wires and distributor cap. I also added dual exhaust at that time.

I took it to a master diagnostic tech at Toyota,l but he had no real clue

hot gas doesn’t burn as well as cool
You probably know an old drag racer’s trick of running the gas line through a cooler filled with ice.

Don’t know if that’s what’s going on. But, I figured I may as well throw out the first of many theories of your problem.

It Doesn’t Happen in Winter
So you may be on to something

Years ago we always called this…

– Last Updated: Jul-09-07 5:08 PM EST –

... "vapor lock" whether we had any proof that it was or not. Seems like it used to be a very common problem that you don't see as much now for some reason (I've heard it said that the location of the fuel pump makes the difference, but with the old carbeurated engines, you didn't even need a working fuel pump for the first minute or so that the engine would run, so that doesn't make sense to me). In fact, I wonder if the trick of running the gas line through ice that Clarion mentions was just a vapor-lock prevention method since extreme heat is the order of the day on drag-race engines (fuel ignites more easily when hot, not the other way around, and so another thought is that perhaps the fuel was igniting before it was supposed to unless it was pre-cooled). Pre-cooling the air increases power at the extremes of an engine's working ability, but I didn't know they used to cool the fuel as well.

I guess I've not made much of a contribution here, but this stuff is interesting just the same.

Okay, based on your updated info, I'd bet that something about the electronic mixture control has changed, but don't ask me exactly "what" that might be. Seems like your mechanic should be willing to experiment a bit to figure this out, since this happens after all that tune-up work.

Vapor lock
What you’re experiencing does indeed sound like vapor lock. In modern day fuel injected cars, it’s indicative of the system not holding pressure when the engine has been shut down. This is usually caused by dirty/leaky injectors or a bad fuel accumulator.


cool fuel permits a higher comp. ratio

– Last Updated: Jul-09-07 5:15 PM EST –

Like you said, hot fuel ignites quicker. But, that's a problem, not a solution. I think we're saying the same thing ... essentially that you don't need bow/stern lines ; )

New exhaust system…

May be heating something up causing vapor lock.

Them’s fightin’ words
Don’t get me started on bow/stern lines (funny, I’ve actually never cared to get into that argument).

Oh, about the fuel, yeah, we were saying the same thing it seems.

Might not hurt, just for grins, to
replace the thermostat if you haven’t done so in a while.

Vapor lock plausible
Is your new exhaust running closer to the fuel line than the old one? The extra heat, coupled with the drop in atmospheric air pressure at higher elevations could be causing vapor lock. Just a thought.


Vapor Lock
Vapor Lock was specifically related to carbureted vehicles, but a lot of times it was a general syndrome like “ADD”

But this does sound exactly like “vapor Lock” in that the symtoms are exactly the same.

The dual exhaust thing is more of an art than a science.

Frankly I just couldn’t think of any other reason to send money on it. It may have been ill advised

California cars are different…
…at least they used to be. I brought one back in the 70s and I had to tell them when it was being worked on the it was from CA. My Subie is from SF but haven’t run into problems yet.

Vapor lock
Is highly unlikely in a EFI vehicle. My guess is something electronic, probably something related to the ignition.

Run it hard and get it hot so it wont start and then pull a spark plug, ground it and try to start it to see if you have spark.

not ignition

– Last Updated: Jul-10-07 12:45 AM EST –

Ray it shouldn't be ignition, because if it was, it would cut out while driving, not just have a hard time starting after being shut off.
What exactly do you mean by dual exhaust? Since we're talking 4 cylinder engine, dual exhaust makes no sense in any way except looks. Are we just talking about a muffler with one inlet and 2 outlets(which isn't really dual exhaust)?
Definetely sounds like a malfunction of either a sensor or a VSV(vacuum switching valve,screwed into intake manifold typically,switches vacuum flow depending on temperature).
This is all assuming you mean it'll crank over healthy but won't start. If it won't crank healthy it's probably starter contacts.

PS. This problem started right after a m
I would double check tune-up??

The exhaust is probally a cat back, wich will not cause this problem…

Where the o2 sensors o.e. or after market…should be 2 on that model.

are you getting a orange service engine light?

at all,ever,sometimes???

Dual exhaust is the first clue…
did you have the problem when the auto was new or prior to the work you just had done?

Does your new exhaust include new manifolds or is it just a split? Where did the O2 sensors go in the new exhaust systems? Make sure they are actually connected. A dealership tech should see error codes…they have the most specialized equipment for diagnostics.

You’ll find your problem in the new exhaust system and the O2 sensor arrangement. Modern car engine computers are designed for a stock engine. Your new exhaust and O2 sensor data is throwing the computer a curve outside it’s parameters and in return, your air/fuel mixture is mal-adjusted at altitude.

Vapor lock doesn’t “just happen”. It’s a symptom…there is a cause.

hard start when hot
typical culprits:

latest fuel formulation has a lower boiling point exacerbated by fuel lines in close contact with engine or exhaust pipes/manifold

starter gets hot from close contact with the exhaust pipes

a failing coil will work cold but breaksdown in the heat, works when cool

another biggy is if the timing/distributor advance weights/springs was messed with during the “tune-up”…go to someone you can trust and have them check the timing and advance

greyak may have something
I had this symptom in my subaru shortly before the catalytic converter became clogged and needed replacement.

Not Real Dual Exhaust
One pipe into the Cat and one into the Muffler, with two pipes out. Really just a splitter