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2.7l Will not start when hot - ANY ideas?

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Old 09-09-2013, 08:57 PM   #41
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Someone mentioned the temp sensor. Only temp sensor I can locate in a book is the coolant temp sensor. Confused on how that would affect the engine starting.

Also, did a random search and people were saying the starter is getting too hot, from an exhaust leak, or other issue, causing the hard start issue. That make any sense to the more qualified mechanical people here?
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Old 09-10-2013, 11:53 AM   #42
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Throttle Body needs cleaned. That will take care of your issue.
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Old 09-10-2013, 06:12 PM   #43
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Wouldn't a dirty throttle body also effect the idle?

I'll give it a try once I get some free time. If that's it, best first post ever by MD51
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Old 09-11-2013, 02:16 AM   #44
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Quote:
Originally Posted by Murrfk View Post
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.
Check fuel injectors and wires maybe its time
to replace.
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Old 12-20-2013, 08:27 PM   #45
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My 96 Tacoma has been doing the same thing for awhile. It will cold start everytime but if i drive it for awhile and turn it off it has issues starting. Recently I removed the cylinder head to fix an unrelated problem. The intake side was sludged up pretty bad. I got the head resurfaced and had a valve job done. I had to clean the entire intake side of motor to remove sludge and debris. When I took the throttle body off and saw the problem. There is a gasket that basically keeps the port of egr valve air isolated from the rest of throttle body air system. The gasket was allowing the hot dirty exhaust Air into the intake manifold thus making quite a mess inside intake side of motor. Gonna put new egr valve and replace that gasket this weekend. Will keep you posted on final results
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Old 12-20-2013, 08:41 PM   #46
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Should clarify that when valve was functioning. Real problem is that gasket inside throttle body. I am replacing the egr valve just to
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Old 12-20-2013, 08:42 PM   #47
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Egr valve. Not when valve. Damn spellcheck
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Old 12-20-2013, 10:47 PM   #48
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Pics or diagram?
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Old 12-28-2013, 10:15 AM   #49
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New here, but looking for answers like everyone else. However I do have some information on this issue. I have a 96 2.7 backed by a 5spd. I've been fighting this issue for about 5 years, trying various things along the way. It had gotten to the point of whether the truck was going to be dependable. I had the engine rebuilt (by a very reputable engine builder) stuck it back in the truck ran fine, then all at once it began the aforementioned issue. When i would try to start the truck after sitting for a few minutes, the smell of raw fuel (as if it was flooded) when it would turn over. Sometimes if it was hit just right i guess it would fire up, run but stumble & smoke. I have replaced IAT sensor, cleaned everything that could be cleaned, coolant temp sensor, fuel pressure regulator it was clogged up & inoperable, everything that has to do with the ignition minus the key switch & igniter. Replaced vacuum hoses, checked with obd reader this morning to find I now have a crankshaft sensor code, fairly certain the only thing I haven't replaced. Repaired some questionable wiring going to sensors. Apologize for long post but. Anyone ever figure out the fix?
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Old 12-28-2013, 10:19 AM   #50
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Also I noticed several people made comments about unplugging the IAT sensor & it starting. When that sensor is in plugged it sends the computer into default mode of -40° adjusts the timing to compensate for the vast amount of fuel being delivered to start the engine. I pulled my injectors & had them tested supposedly in good condition.
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Old 12-28-2013, 10:27 AM   #51
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Old thread coming back, but many people do have a similar issue it seems.

For those who do not know this, there are TWO engine coolant sensors. One is for the gauge and scan tool data, the other is a direct input to the ECU. You won't find the second sensor data on a scan tool. The one for the gauge is the one that is located near the water inlet into the top of the engine, on the left side. The other sensor (the one for the ECU) is located on the back of the cylinder head.

One thing that has me interested here is the common "fuel odor" and stumbling. Since most have already checked sensors and such, I would suggest looking at the fuel line and fuel rail. If there is excessive heat after the engine has been running for a while, it can cause the fuel to "boil" in the line. This will cause a reduction in fuel flow when cranking. This is a common problem on engines that do not have an efficient fuel return. For instance a clogged or kinked return line will cause excessive fuel temp in the lines at the intake and injectors.
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Old 12-28-2013, 10:40 AM   #52
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Yea the one I replaced was on the back of the head. Thanks for the heads up though.
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Old 01-03-2014, 10:46 AM   #53
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Quote:
Originally Posted by basementbuilt View Post
...I now have a crankshaft sensor code, fairly certain the only thing I haven't replaced.
From all the posts I've seen related to this issue (all unresolved), I think you're certainly the closest to finding a resolution. I just recently started having this problem with my 96 2.4L and started diagnosing the issue. It seems very common on both the 2.4 and 2.7 but no one seems to positively resolve it.

So here's my theory...and let me start off by saying I believe in diagnosis rather than throwing a bunch of parts at a problem because that's super expensive and frustrating when it doesn't work. I'm sure there will be a bunch of people who shoot it down without any evidence but if so, then WHAT IS THE SOLUTION, NAYSAYER?

If you look at the EFI circuit, the crankshaft position sensor provides an input to the FUEL INJECTION SYSTEM. I read another post somewhere in which someone checked his injectors with a noid light during the no start condition and the injectors weren't opening. Everyone seems to go through and replace every component of the ignition system only to find the problem remains. Same with the IAT sensor; it doesn't solve the problem. No one who has this issue ever mentions replacing the crankshaft position sensor and the posts simply fade away. I've seen bad CPS on other vehicles cause a cranks-but-won't-start condition and think this mysterious issue is going to have the same cause on our Toyotas.

As far as the people who disconnect the IAT sensor and the truck starts, it's because disconnecting that sensor puts the truck into limp home mode and it bypasses that sensor and ALL the other sensors (including the CPS). Of course they think they've solved it and think it's the IAT sensor when it's only masking another problem.

Here's an overview of the crank and camshaft position sensors. Note the reference to the no-start condition and that heat is usually what kills these. I'm not promoting this brand or any other, it's just something I found while researching my problem and think its a good reference. http://www.standardbrand.com/upload/...FT-SENSORS.PDF

Here's another post in which the guy damaged his CPS while replacing the alternator (the sensor is just behind the alternator) and surprisingly he had a cranks but won't start condition: http://www.yotatech.com/f2/repair-re...77/?styleid=41

He says, "I recently removed and reinstalled my alternator after having it rebuilt. Afterwards, the truck wouldn't start. I cranked it and it kept turning over without running. Oh, what joy. I apparently tore out the wires from my crankshaft position sensor, which was located conveniently behind my alternator, exactly where I was trying to lever the bloody contraption back into place."
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Old 01-03-2014, 11:53 AM   #54
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I actually done a little bit of research, after adjusting the timing to see if just maybe it was off, and read about the code. It mentioned a few issues that would cause the CPS code to come up, one of which the "G" signal from the distributor, corresponds with the" NE" signal from the CPS, & if they do not match then the code will appear. So being that the timing was the only thing that I had changed, I gave it a shot & wa-la code disappeared. I have also read of cases where people are having the same issues, they are putting a timing light on any wire and revving the engine up, if the timing becomes erratic then they are replacing the distributor or coil.

I have checked my coil, after it was hot, to see what kind of resistance I had & it is within spec. Spoke with a fellow mechanic and he said that he has seen coils test good but then lose the ability to maintain a consistent spark when it is called upon.

I am having multiple issues from the hot start to stumbling on acceleration. The more aggravated I get the more I consider a v8 swap.
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Old 01-03-2014, 12:10 PM   #55
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My issue is just when I attempt a restart when the engine is hot, occasionally it will just crank but not start until it cools (usually about 5-10 mins with the hood open). It runs great once it starts and I have no other issues so I think it's going to just be the CPS.

I could see how the conflict with the cam position sensor could through the code on your vehicle. Mine has only happened about 3 times in the past couple months (and only lasts a few minutes) so it's a little hard to diagnose. I've scanned several times and been unable to retrieve any codes.

A couple days ago I cranked but no start, then cranked only 10 seconds later and it fired up just fine (so intermittent). Amazing how common this issue seems and without any conclusive solution. I've read so many posts where people have been dealing with is problem for years and that's so not cool. If a CPS solves these problems it would definitely be worth sharing so if there is anyone out there willing to give that a shot, I'm sure we'd love to hear about it. I think I'm going to go that route but want to do some more testing first.
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Old 01-03-2014, 12:16 PM   #56
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For what its worth to you, I have replace mine before with no luck. Thanks for sharing your thoughts. A friend of mine & me may take a look at mine this weekend, if we come up with something I'll be more than happy to share it.
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Old 01-03-2014, 12:29 PM   #57
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When yours threw a code was it P0335 or P0336? Per the FSM, P0335 is "malfunction" and P0336 is "range/performance". I may also do the resistance test but I have a feeling it will work just fine...except when it does work at all.
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Old 01-03-2014, 12:32 PM   #58
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335 when I replaced it, 336 when I adjusted the timing.
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Old 01-05-2014, 11:58 AM   #59
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Amazing that no one has found the actual cause for this. I am the guy that long ago posted the info about unplugging the IAT sensor to get it to start. This works but is a pain since you need to plug it back in once started due to the limp mode mentioned above. I have since come up with a somewhat better band aid that works just fine, but requires some soldering skills and a wiring diagram. So here is what I did.

1. Disconnect the battery.
2. Remove the glove compartment.
3. Locate the wire that comes from the IAT sensor as it enters the ECU.
4. Cut this wire leaving enough length so that you can re-solder it.
5. Solder/screw a switch in line.

At this point you now have a way to unplug the IAT from the ECU without having to open the hood, but we are not finished yet. On my Taco the wire was brown with a black stripe, but I CANNOT guarantee that this will be the same on you truck. Failure to cut the correct wire could cause damage to your truck!!!!!!

6. Solder a 470 Ohm resistor in parallel with the switch.
7. Heat shrink or tape(electrical) all exposed connections.

The reason for the 470 Ohm resistor is that the computer will see that the IAT is still installed which prevents the engine check light from coming on. This fools the ECU into thinking the air temp is cooler than it actually is.

So, to start, flip the switch to the open position which has the effect of adding 470 Ohms to the IAT circuit. Truck should start easily. Once running, switch the switch to the closed position which removes the 470 Ohm resistor. I have been using this for the last 4 years and it works just fine. No change is gas mileage and no engine check light.

Other things that I have tried to actually fix the problem.

1. Fuel pressure regulator.
2. New IAT
3. New plugs/wire/rotor/cap
4. Fuel pump relay
5. Checked TPS
6. Cleaned MAF sensor(This helps)

To Do:

Check the VSV's for EGR and fuel pressure
Check the EGR valve
Clean the Throttle body. It is very dirty.

Other symptoms:

Pinging
Erratic idle speed at times.

Here are some pics of the mod:
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2.7l Will not start when hot - ANY ideas?-p1020389.jpg   2.7l Will not start when hot - ANY ideas?-p1020390.jpg  
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Old 01-05-2014, 12:11 PM   #60
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Has anyone ever checked they wiring harness to see if pins at the ecu plug are corroded and shorting out one another, or worn insulation letting to wires touch? Reason I ask, I haven't done it either, but I have a 2005 Silverado and the weather pack going to the ecu wasn't installed at the factory properly & over time dirt, water got into the plug & shorted 2 pins out and would send the truck into limp home mode.
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