Heat Soak Problem?

So I've noticed my truck has been hard to start sometimes. It happens once I get it to operating temp. then turn my truck off and let it sit for about 30 mins or so. If I try to start it, it just cranks but does't actually start until after about a minute or two of cranking on and off. Once it starts it runs fine and has zero issues. It always starts great in the morning when the motor is cold. I noticed this problem correlates with the ambient temp. as well. Today was the warmest its been the past few weeks and it happened to me 3 times. It's as if something is getting heat soaked and needs to cool off before it can start again. I did some research and it seems like it could maybe be the engine coolant temperature sensor or possibly a leaky injector? How hard is it to replace the ECT sensor on the 3.4s? Does coolant leak everywhere once it is removed? Any input is greatly appreciated!

 

Bump.

 

I had this exact set of symptoms on a '93 prelude, it was a known issue with the model. The fuel pump relay became sensitive to heat as it aged and would stick in the off position. When the car was at temp and then parked, the under hood temperature actually rises a bit as heat moves from inside the engine to the rest of the engine bay. As soon as it cooled a bit everything was fine. Looks like the tacoma has a relay for the fuel pump in the relay cluster (with the fuses) under the hood, but I only did a quick search so i'm not sure.

The test in my case was to buy a new one and swap it out, took 2 minutes and was returnable if it didn't fix the problem. I literally did it in the parking lot of the dealer. It was $50 for a new relay 15 years ago, but that's for a prelude and probably irrelevant.

Good luck.

 

I'll look into that. Any other suggestions?

 

Check the EGR system is working correctly, too.

 

If it is not the relay, you will need to check the fuel pressure with a gauge. If it is low, it is either a weak fuel pump or regulator. The pressure has to be high enough to overcome "boiling fuel" in the system. In the old days, it was called "vapor lock".

 

I have seen this several times with multiple manufacturers. While there are a couple of different ideas, the most common (90%) that I have found is a diaphram in the fuel pressure regulator breaking. This allows the vacuum line that controls the fuel pressure regulator to draw in fuel directly into the vacuum port. When the engine is cold, this is not an issue, as the fuel has evaporated. It also is not an issue when the engine is running, because the fuel management system is capable of compensating for the additional fuel. What DOES happen, is after the engine has warmed up and you turn it off, residual fuel pressure, will force fuel up the vacuum line into the intake manifold. If there is not sufficient time for this raw fuel to vaporize AND evaporate, then when you key up two things will happen: 1: This extra fuel will flood the engine, preventing it from wanting to start. 1: Since the fuel pressure has leaked off into the intake, when the fuel pump energizes it can take a couple of seconds or even longer for the fuel pressure to build back up enough to start the engine. Sometimes it won't build up enough at ALL on the first crank.

To check for this get your engine up to operating temperature, and shut it off. Then disconnect the vacuum line to the fuel pressure regulator and check for ANY signs of fuel. There should be no "wetness" in the line, or at the regulator. If you see none, have someone start up the truck while you observe the nipple on the regulator for fuel. It may take a couple of seconds. Be careful, as this will be FLAMABLE.

 

I was hoping you'd chime in! I thought FPR also. I just went test it with the procedure you mentioned above and saw no fuel with the engine off at operating temp and running at operating temp. So I'm guessing it's ok? I should mention I did replace the ECT sensor earlier today. It was relatively cheap and easy to replace so I figured I'd give it a shot. I haven't driven it and started it enough yet to see if the problem is gone. If the problem persists even with the new ECT sensor, I plan on getting some gauges and testing fuel pressure. I'm just hoping its not a leaky injector.

 

That only tests the diaphram being ruptured or not. You COULD still have a bad FPR. So don't rule it out. Testing the actual fuel pressure, and looking for a significant rise when hot soaking is really the best way to check all components of the fuel system.

 

this is some great diagnostic advise. I've seen this problem on several vehicles. I'm really impressed it was traced down to the fuel system so fast. Usually (and I'm guilty too) most people want to think it's an ignition component that doesn't restart when already warm, but will continue to work after it gets warm. Distributor cap or something. I'll keep this in mind for the future

 

What exactly would I be checking for with a fuel gauge? Would I get the motor to operating temp. then shut it off and monitor the pressure from there to see what its doing? Thanks for the great replies!

 

First you want to check running pressure. Make sure it is within specs. Then when the engine is hot, shut off the truck and observe the gauge. A SLOW drop off of 5-10psi over 2-3 minutes is acceptable. A fast drop in pressure means that perhaps the fuel pressure regulator is bad, allowing the pressure to bleed back to the tank, OR that the check valve in the fuel pump is bad. A SLOW increase in pressure of no more than 5psi is acceptable, and is expected since hot fuel will expand slightly, increasing the line pressure. A significant pressure increase of 5-10 psi or more means that the fuel is boiling and that is bad. You may need to go to a different quality/brand of fuel, or perhaps insulate the fuel lines at the engine.

 

Just thought I'd update this thread as my problem seems to be fixed. I was trying to fix the issue before I installed my URD 7th injector kit. I installed a fuel pressure gauge under the hood and constantly checked the pressure for different scenarios. All seemed good. I really wanted to check it while I had the hard hot start problem but I could not make the problem happen during the time I had the gauge installed. I decided to go ahead and install my 7th injector kit. I also decided to replace my fuel pressure regulator while I had everything off. This would help eliminate that as being the problem. The 7th injector kit came with a new fuel pump, so that was replaced as well. After installing everything, the truck ran great! I also have not had a hard hot start problem yet. I'm 99% sure it's fixed. I cannot narrow it down to exactly what fixed the problem but it's between the fuel pressure regulator and fuel pump. So I would suggest anyone having this issue to check these two components. I would start with the fuel pressure regulator since it is easier to access. Hope this helps anyone experiencing this same problem.