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2.7l Will not start when hot - ANY ideas?

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Old 02-02-2014, 03:49 PM   #81
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I have tried the coil, along with several different plugs. At one time I actually carried extra plugs in the truck so that when it fouled the ones in the engine I had a back up......it was a headache. Nothing seems to fix this ongoing issue.
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Old 02-13-2014, 09:26 AM   #82
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Quote:
Originally Posted by samwise View Post
I used to have a potentiometer(POT) in place of the the resistor and fiddled with it for about a year. After a while I got a pretty good idea of how much resistance I had to add to get it to start. I then took a measurement of the POT and replaced it with the switch and resistor. As for plugs, I did NOT use OEM plugs. I might give this a try. Has any replaced the ignition coil? Warn plugs have increased gaps, and increased gaps have more resistance. So a low high side voltage due to heat could cause a weak spark, just a theory. If I had access to an ignition scope, I would definitely check the hot and cold start voltage. I looked at a 98 and noticed that it no longer has the IAT sensor. They either moved it or combined it with the MAF sensor.
The IAT was combined with the MAF starting with either 97 or 98. I wonder if using an updated MAF from a 98 would also resolve this issue. Of course, you'd have to adapt the harness connector but that's not impossible.

I don't think the plugs would make enough of a difference to cause a start/no start problem. I'd also think if heat were affecting the coil, it would be most noticeable while running in the heat and under load. I havent replaced my coil but I've read plenty of threads in which people did (it didn't help). No one here seems to have a problem with the truck shutting down once it's running. It's only getting it restarted when warm.

From what I've read, the IAT is only used during open loop operations (i.e. at startup and immediately after startup). Once the engine warms up and the ECM goes into closed loop, the IAT is no longer in the equation and the ECM manages fuel based on the O2 sensor readings.
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Old 03-02-2014, 07:53 AM   #83
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Hey all, I'm having pretty much the same problem except for I have a 2001 Tacoma with the 3.4. My problem seems to be that once the engine is hot and then turned off and I try to crank it about 30-120 minutes later it's just hard to crank and takes an extra second or so. When it is cold it starts up just fine. I have tried everything. New fuel filter, cleaned the MAF, the TPS, the IAC (idle air control. ), the ignitor box and I just took off the whole throttle body yesterday and cleaned it and the upper pluneum completely. I out a new starter on last summer and also changed the plugs last summer. I do live in northern Florida and I feel that the heat issue has a lot to do with it. I've read everything that everyone has out on here and I've done most everything besides replacing sensors and all.
Like most are saying, nothing seems to completely fix this issue
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Old 03-02-2014, 08:07 PM   #84
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Anyone with a 98 2.7 in here that can post up the part number on the top of their MAF? Trying to track down the official denso part number with little luck.

Thanks
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Old 03-19-2014, 06:46 PM   #85
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I have a 96 2.7L 4X, and it's been doing this for years. Always in hot weather.

I've taken it to 3 shops, spent about $1800 at 3 different shops - they've pretty much replaced everything in the fuel pipeline, to no effect.

Last year I was at a Toy specialist in Denver for a different issue. I mentioned the hot start problem, and the tech says, "Oh yeah, we get that all the time - bad charcoal canister." It'll be around a grand to replace, which I don't have right now, so I can't say if it's worked or not.

Question is, how can the charcoal canister possibly cause this problem? Doesn't make any sense to me. Any thoughts?
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Old 03-19-2014, 09:07 PM   #86
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Interesting. The canister is only $300 from Rock Auto if anyone is feeling froggy.
https://www.rockauto.com/catalog/mor...661&cc=1317623
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Old 03-19-2014, 09:33 PM   #87
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My 2.7 dose this from time to time, First time stopped to get something to eat after high school football game. It turned over and tried to crank but it would not till I played with throttle then it started, still dose it from time to time. It developed a bad misfire don't know if its related. I think it is from worn rings and low compression. Gota do a test to see if it is rings or head so I can fix it.
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Old 03-20-2014, 03:17 PM   #88
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Quote:
Originally Posted by BonedaleToy View Post
I have a 96 2.7L 4X, and it's been doing this for years. Always in hot weather.

I've taken it to 3 shops, spent about $1800 at 3 different shops - they've pretty much replaced everything in the fuel pipeline, to no effect.

Last year I was at a Toy specialist in Denver for a different issue. I mentioned the hot start problem, and the tech says, "Oh yeah, we get that all the time - bad charcoal canister." It'll be around a grand to replace, which I don't have right now, so I can't say if it's worked or not.

Question is, how can the charcoal canister possibly cause this problem? Doesn't make any sense to me. Any thoughts?
I don't see how the charcoal canister could be related. This is definitely something to do with the IAT sensor. I've been having this problem again recently and my fix was to remove the IAT from the air box, hold the tip of the sensor between my fingers or leave it exposed in the engine compartment (still plugged in) with the hood up for a couple minutes. Once it cooled down, the truck started again within minutes. Worked every time.

With this is mind, what I did this past weekend was to remove the IAT and it's grommet from the air box. I sealed the hole with a bolt, nut, fender washers, and rubber washers then relocated the IAT to the bottom of the intake air duct elbow in the right fender. To do this, I needed to extend the wiring harness to the sensor.

My new theory is that the heat from the engine after shut down (especially from the hot exhaust manifold as well as internally through the intake manifold) is warming the IAT to a point it won't start. With the relocated sensor, it's not at the top of the engine compartment, in fact, it's not in the engine compartment at all and no longer subject to all that heat. It still measures intake temperature, just in a different location. I have yet to try it on a hot day to see how it does but I'm hoping for the best.

When I did some tests earlier, I saw my IAT temps rise from about 60 degrees to over 102 AFTER I shut down the engine. Outside temp was about 60 degrees and I read the data with my OBDII scanner. It took about 30 minutes to peak. The coolant temp, meanwhile only rose five degrees from 185 to 190 after shutdown then fell. Granted any vehicle should still start at 102, or even 120+, but perhaps this will be a work around that doesn't require any user interaction. I'll post my results after a few hot days have passed.
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Old 03-20-2014, 05:18 PM   #89
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Quote:
Originally Posted by BonedaleToy View Post
Question is, how can the charcoal canister possibly cause this problem? Doesn't make any sense to me. Any thoughts?
I think you might be onto something. The canister is used to prevent unfiltered vent fumes from the gas tank escaping to the atmosphere. This is the one area that I have not looked at. The canister described about has the electric valves on it which could be what fails.
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Old 03-20-2014, 05:20 PM   #90
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Quote:
Originally Posted by Rickalders View Post
I don't see how the charcoal canister could be related. This is definitely something to do with the IAT sensor.
I think the IAT mod is just compensating for another problem which may have to do with the vapor recovery system. There is a procedure in the service manual for testing the electric valves. I might just give this a peek.
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Old 03-20-2014, 07:16 PM   #91
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I googled charcoal canister and hot start issue. Seems it has happened before, though most threw a code.

Guy explained that some of the fuel in the lines turns into a gas when vehicle is hot and is supposed to be released through the canister, this making room for more fuel to enter the lines.
When the canister malfunctions, it creates a pressure issue. The gas can't escape, leaving fuel lines empty, thus creating a hard start. No idea if it's true or not, just what I gathered from his postings.
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Old 03-20-2014, 07:21 PM   #92
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Starter getting hot? I would've said timing too adv but some of you guys have coil pack trucks (cant adj a dizzy).

Fuel getting to hot or something? I dunno?
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Old 03-20-2014, 08:24 PM   #93
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Quote:
Originally Posted by samwise View Post
I think you might be onto something. The canister is used to prevent unfiltered vent fumes from the gas tank escaping to the atmosphere. This is the one area that I have not looked at. The canister described about has the electric valves on it which could be what fails.
I actually looked into this briefly but discounted it after I saw it was in the 5VZ-FE engine section. I bookmarked page EG-313 (for the V6) of the FSM. It describes the "fuel pressure control circuit".

What caught my eye was the description,

"The ECM turns on a VSV (Vacuum Switching Valve) to draw the air into the diaphragm chamber of the pressure regulator if it detects that the temperature of the engine coolant is too high during engine starting.
The air drawn into the chamber increases the fuel pressure to prevent fuel vapor lock at high engine temperature in order to help the engine start when it is warm.
Fuel pressure control ends approx. 120 sec after the engine is started".

Sounds exactly what could be happening with our problem but when I saw it was only under the V6, I wrote it off. FWIW, mine is a 2.4L and I'm having the same issue as you 2.7L guys. The charcoal canister is different and I believe the 2.4L only has the VSV for EVAP where the 2.7L has a VSV for EVAP and a VSV for Vapor Pressure Sensor (page EG-111 of FSM).
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Old 03-20-2014, 08:40 PM   #94
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Quote:
Originally Posted by samwise View Post
I think the IAT mod is just compensating for another problem which may have to do with the vapor recovery system. There is a procedure in the service manual for testing the electric valves. I might just give this a peek.
This thread mentions the same problem and the VSV: http://www.customtacos.com/forum/sho...d.php?t=153243

He also mentions a very high RPM with the A/C on. I have that same issue. With the A/C on, my engine idles at about 1200 or so RPM. It's way higher than it should be and enough to cause the truck to lurch forward at a stop and I have to apply more brake pressure to keep it stopped. Does anyone else have this high RPM with A/C on issue? I wonder if this could also be indicative of the failed VSV and therefore the starting problem.
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Old 03-21-2014, 05:29 AM   #95
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Quote:
Originally Posted by Rickalders View Post

When I did some tests earlier, I saw my IAT temps rise from about 60 degrees to over 102 AFTER I shut down the engine. Outside temp was about 60 degrees and I read the data with my OBDII scanner. It took about 30 minutes to peak. The coolant temp, meanwhile only rose five degrees from 185 to 190 after shutdown then fell. Granted any vehicle should still start at 102, or even 120+, but perhaps this will be a work around that doesn't require any user interaction. I'll post my results after a few hot days have passed.
That makes sense, a temp spike once the cooling system stops. That's when I notice the problem the most - about 5 mins after the engine is shut off and it won't restart until it cools down.

Re: the AC and revving - mine seems to do it under normal operations, with or without AC.
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Old 03-21-2014, 05:45 AM   #96
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Quote:
Originally Posted by Murrfk View Post
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.
If you disconnect the sensor the system will go full rich.
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Old 03-23-2014, 06:47 PM   #97
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Quote:
Originally Posted by samwise View Post
I think the IAT mod is just compensating for another problem which may have to do with the vapor recovery system. There is a procedure in the service manual for testing the electric valves. I might just give this a peek.
Ok, so I tested my VSV for EVAP (aka electric valve) and it functioned perfectly (see page EG-152).

I also tested my charcoal canister (page EG-114) and I'm not so convinced. When I blow "low pressure compressed air" through the tank line fitting (just me blowing through a vinyl hose), I had some resistance. The FSM says air should flow from the other lines "without resistance" but I wonder how much it would take to cause a problem. I was still able to blow through the line but it took a little effort. I'd liken it to the amount needed to blow up a balloon.

It wasn't as warm today (72F) as when I have problems but out of curiosity, before I tested everything I removed the tank line from the top of the canister and it released a little bit of pressure. In fact, I could hear a slight noise from the hose because of the pressure and that's what made me curious. I wonder if there's normally supposed to be any pressure there at all.

After some research I saw several sources (like this one http://www.epa.gov/donttopoff/ ) that mention topping off your tank can damage the charcoal canister. Admittedly, I do this ALL THE TIME. I round up to the nearest $.50. Although I don't think I caused it (I've only had the truck for 4 months and it was doing this the week I bought it), I wonder if the previous owner did the same thing. Apparently when the tank is super full, like after topping off, the liquid fuel can expand through the tank line and into the charcoal canister, causing damage.

So now the big question is whether or not to replace the charcoal canister. It would be nice to have a new one to compare it to. If I were sure that was the problem, I really wouldn't have an issue with dropping $250 but without knowing for sure...
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Old 03-23-2014, 09:07 PM   #98
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Quote:
Originally Posted by Rickalders View Post
So now the big question is whether or not to replace the charcoal canister. It would be nice to have a new one to compare it to. If I were sure that was the problem, I really wouldn't have an issue with dropping $250 but without knowing for sure...
I have removed them from motorcycles, but am not sure about removing it from my taco. My guess is that it could just be removed as an experiment. I cannot believe that they charge $250 for one. I believe this is because it is an emissions device.
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Old 03-23-2014, 11:15 PM   #99
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Interesting finds Rick. I read the same thing about "topping off". I never do it, but as I was filling up today I could hear the fuel almost filling up to the brim. More so then most other vehicles I've owned. Wonder if on some of the trucks (mainly the 2.7) the cutoff allows just a little too much, which would then flood the canister. Could explain why some have the issue and others don't. Or maybe I just never payed as much attention when filling up to notice on other vehicles.

There was a tacoma on CL that a guy was parting out. I might see if it's still there and try to score the canister and give it a go.
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Old 04-12-2014, 10:55 PM   #100
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I have a 97 dlx with similar problems. Is it ok to take out the air temperature sensor permanently ?
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