2.7l Will not start when hot - ANY ideas?

1996 Toyota Tacoma 2.7l 4x4.

I got this truck in the spring and it has been running well. However, about a month and a half ago, I could not start it after I had driven it. After waiting for 10 minutes or so, it started and I had no problems with it for a couple of weeks. Then it happened again. I had driven it 20 miles and could not get it to start. I had to wait 10-20 minutes, and then it started.

In the two weeks it is happening more often. I notice a smell like old gas when it won't start. I have replaced the coil, the plugs, the plug wires, the rotor and the distributor cap because I thought it was spark related (because I was troubleshooting with a broken plug wire I found out).

When it turns over, it will sometimes ALMOST start. Once it is started it
runs fine. Waiting has always allowed me to start the vehicle, but sometimes I have to wait up to twenty minutes. It always starts when I first use the vehicle and the engine hasn't warmed up.

I did replace the head gasket and although I was very careful, I wondered if there was a head bolt that had loosened and when things expanded some coolant was getting in the engine. I have started monitoring the coolant level and have not noticed anything.

I know these are hard to diagnose at a distance, but if anyone has ANY ideas of what it MIGHT be, I would appreciate any thoughts. TIA.

 

Sounds like possibly a head gasket , Not sure but Its my best guess.

 

My guess: Check fuel pressure.

 

It hasn't reoccurred for a while, but I have done nothing since the last time it happened. It also hasn't been quite as hot. The coolant level appears to be staying the same, so it does not appear that I am losing coolant into the cylinder/head gasket problem.

 

I have a possibly blown head gasket on my '01 2.7 but with some different symptoms. A very experienced mechanic friend of mine said I should look for foam in the engine oil and check not just the coolant level--since that can potentially be deceiving--but check for different coloring of the coolant and seeing if there is indeed oil in it.
Among other things, my coolant is really dark (I haven't actually checked for oil yet, since I don't feel like losing sleep tonight over the thought of needing to replace my head gasket) and my engine is giving off a large amount of excessive heat

 

There is no coolant loss, so it isn't the head gasket. It is somehow related to heat. Hot days after the vehicle has run. I was able to try removing the gas cap to see if the vent was blocked, when it wouldn't start, but that did not help it to start. I am wondering about the igniter (ignition control module). It does seem to get quite warm.

 

One of my coworkers drives a 98 Honda Accord that wouldn't start when hot. Turned out to be a relay, and was common for that model year.

Another thing to consider might be crap gas. The engine runs rich in open loop mode when engine temps are low.

 

Plug in obd scanner and verify coolant temperature. A bad temp sensor could cause no start when engine is hot.

 

Yup!

 

I'm having the exact same problem with my 96 2.4L right now. Do a google search and you will see it's a common problem. I'm willing to bet if you unplug your air temp sensor (sticking into the air filter housing), the taco will start on the first try. This is how I have to do it if I've been driving it a while. Just got this truck a couple weeks ago so I'm hoping after summer it will fade away.

Seems to be an issue with the air temp sensor, the coolant sensor or the ecm, as these are all connected. I replaced the air temp sensor and that did not help. I don't feel like replacing the coolant sensor just yet (should be able to just test the current one), so I'm going to see what trouble codes show up when connected to the computer.

 

I have connected an obd2 to the vehicle and checked the coolant temp while running, and it was showing 88-90C, so that appears to be working. I will try unplugging the air temp sensor and see if that helps, next time it occurs.

I did try starting it last time it failed, and checked for spark. The spark *appeared* to be intermittent, but I was getting a stranger in the parking lot to crank the engine, and did not give it a good test.

 

I'm hooking mine up to an obd2 this weekend to see what codes pop up.

 

I know this is old, but this continues to be a problem for me and has me stumped.

The truck ran like a top all winter. Never had a problem. However, now that it is warm, when I run it on a hot day, it stutters and will not start properly after it has ran for at least ten minutes. It always starts from cold fine. When it won;t start easily, I can smell what smells like bad gas? too. I am not sure if this is due to an ignition problem, or a fuel problem, but I have replaced the plugs, wires, and coil.

Anyone have ANY ideas?

 

I have not had my tacoma for a couple months now but it started up every time through winter as well. I'm sure if I had it now it would be having trouble starting in this heat. I think it definitely has something to do with the intake air temp sensor, at least the way the computer is reading its signals. If I unplugged the sensor, if would always start, even a hot start. If left plugged in, I would have to crank it for 4-5 seconds and pump the gas before it started, or wait a minute before another attempt. I never found a solution, I looked online everywhere. We were all having the same problem over at this thread too:

http://community.cartalk.com/discussion/2143825/wont-re-start-when-hot-on-warm-days-95-toyota-tacoma

 

That is a good thread. It describes my symptoms exactly. I can't recall if I disconnected the temps sensor last year, but I will try that again next time there is a problem.

One little note that jumped out is that I do also have my heat shield off of my exhaust manifold. I took it off when I did my head gasket last year and did not put it back on...yet. I didn't think it could be relevant but it might be more relevant than I thought!

 

If you had a known good temp sensor, you can compart the signal of each(when the engine won't start). Disconnecting them is a recipie for engine failure. Replace the air temp and coolant temp sensors, and your problems should disappear.
Normally you'll have the symptoms you describe as the sensor starts to fail. Eventually, they may set a code, but not until they drive you nuts.

 

Disconnecting a sensor will not cause engine failure. And that thread discusses the need to disconnect the sensor just to start the vehicle and then replace it once it starts, as it will not start until it either cools down or you disconnect the sensor. And, as reported by numerous people in that thread, the sensor itself is not faulty and replacing it will not solve the problem.

I can report that disconnecting the sensor does seem to allow the vehicle to start. I will continue to monitor this and see if I can find the root of the problem. It is a major annoyance.

 

I have been reading all your posts, and I believe that your problem may be with the Computer's coolant sensor. You have two water temperature sensors, one is for the temperature gauge on your dash, and the other one is for the computer. It could be sending a conflicting temp to the ECM or computer and making the engine too rich. This may be something to check out next. Good Luck.

 

While I haven't tested it this year, I did get obd output last year iirc. That would be from the water temp, I believe, as the air temp sensor doesn't show on (my) obd. It seemed to be what I would expect it to be. I will take a look into it, and will probably replace both sensors (although the linked thread although the linked thread provided by ccs1676 seems to indicate that replacing them doesn't fix the problem. However, I am willing to try almost anything and will probably replace those sensors.

One thing that I did notice in one of those threads is that one persona happened to mention that their exhaust manifold heat shield was off. Mine is also off as I never put it back on when I replaced the head gasket. I think I will replace that today, before I do anything else.

I appreciate any and all input on this.

 

Further information:

Replacing the heat shield did not help. However, disconnecting the temp sensor at the airbox to start the vehicle does work each time I have tried it.