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Toyota starts hard when hot

I have a 1995 Toyota Tacoma 2.4 liter 4 cylinder.

It won?t start when hot (must be over 90 degrees) outside. Starts fine when engine is cold. Drive for 10-15 minutes, let it sit for 10 minutes and it won?t restart. I can get it to start by either shooting a little starter fluid into intake or pinching off fuel return line.

Problem started three summers ago. Had to be boiling hot out. Over 90 degrees.

Things I have done.

Checked compression when very hot. I don?t remember exact compression but I think it was around 165 all across the board.

Replaced fuel filter

Last summer I messed with the fuel pressure regulator and the problem seemed to go away.

This summer the problem is back in force. I drove to California this spring and it was acting up out there when the outside temp was only about 80 or less.

I checked the valve lash. It was fine. A few were .001 loose but that was about it.

I replaced the spark plugs.

I performed a leakdown test on the cylinders. 45-50% cold. Most passing by the rings but some past the exhaust valves.

I ran bg44k thru it.

I noticed one day after filling up with gas that the problem did not occur when it should have since it happened only 15 minutes earlier. I have since removed the fuel cap while hot but it has not helped. This makes me believe it had something to do with the cold fuel that just went in the tank but maybe it was just a fluke. I buy supposedly good 85 octane gas.

I replaced the fuel pressure regulator when I discovered it would start if I blocked off the fuel return line.

I finally made an adapter to check fuel pressure at the banjo on the injector rail. All pressures were within the specs I have. I checked it cold and hot and the numbers did not change. 46 starting. 38 running. Held 36 for 5 minutes after stopping. I did notice when removing the pressure adapter that the fuel looked like it was boiling slightly in the bar. At that point the fuel is no longer under pressure of course. I also checked pressure when blocking the fuel return line. It went up to about 80 psi. It was failing to start after checking the fuel pressure hot and the pressure while trying to start was 46 psi.

I tried to keep cranking through the false starts as suggested by a Toyota mechanic. That did not work.

I wired in a toggle switch so I could run the fuel pump before trying to start it. I tried running it for about 10 seconds once. That did not help so the next time I ran it for about 30 seconds. That did not help. Center position is off.

I was told that diesel fuel has a higher boil point and a small amount may help. I put in about a quart. That may have helped a little but it still took some doing to get it to start and certainly didn?t solve the problem.

I performed a volume check on the fuel system cold and hot when it was failing to start. I removed the fuel return line just past the pressure regulator and installed a tube. Both cold and hot it delivered about 325cc?s in 20 seconds. However, when it was hot a lot of air was coming out with the fuel confirming again that this is a fuel boiling issue.

It has only been driven about 13,000 miles in the last two plus years. I have considered trying to move the fuel filter and insulate the fuel lines. I have also considered trying to install an adjustable fuel pressure regulator and raising the fuel pressure a bit. Keep in mind we are at 5000 feet elevation and vapor locking problems occur a bit differently here.

Is there something else that is making the problem more pronounced on this vehicle. A mechanical problem such as restricted injectors that could be replaced. Failing mass air sensor or any other electronic device that isn?t feeding it a bit more fuel when hot. Intake air leak causing a lean condition.

I did not notice anything about a coil or what passes for it in your car. They do tend to become heat sensitive.

Make sure the hot exhaust pipe is far enough away from the fuel lines. Are the exhaust pipe, or muffler, isn’t too close to the gas tank. Examine these area after making a run which would heat everything.
You have checked fuel pressure at idle; but, have you checked it when the engine is under load (acceleration, hill climbing). If this is an automatic transmission truck, you can simulate a load test by: connecting the fuel pressure tester with a long hose, run the engine in DRIVE, at 2,000 rpm for 3 minuets. The fuel pressure should hold. If not, fuel pump, or pressure regulator, right? If it has a manual shift transmission, do the fuel pressure test while driving at 30 to 50 mph.
Have you used a vacuum gauge to help determine if there might be a vacuum leak?

Once I get it to start with starter fluid it runs fine. The fuel line is on the other side of the engine from the exhaust. This truck is stock.