2.7l Will not start when hot - ANY ideas?

Ahh the old 2.7 curse. I have had this exact issue since I bought mine 2 years ago. Been troubleshooting ever since. Tries unplugging air temp sensor. No dice. Replaced coolant temp sensor. No dice. Replaced catalytic converter & o2 sensor. No dice. Replaced distributor, rotor, wired & plugs, & ignition coil. Nuthin. I'm convinced this is a fuel problem. Engines need 4 things, air, spark, timing & fuel. Air, check. Spark (replaced everything), check. Timing (runs like a champ once it starts), check. Gotta be fuel related.

Here's my current theory. (lemme know if I'm nuts yet). Maybe fuel return in fuel rail isn't returning fuel to the tank once shut off & keeping pressure behind injectors causing them to leak into the piston where fuel is puddling ontop of piston. Thus causing flooding issue? Huh? Whattya think? Please let me know if anyone thinks I'm on to something. Or if I'm bat shit crazy. Either one is fine I just wanna fix this problem cuz nobody seems to know what in the Sam hell is going on with these 2.7s.

 

Your logic is good, but I don't think that is it. You need pressure at the fuel rail for the injectors to work, and it has to be held there for the vehicle to be able to start cold (doesn't have to build up pressure...must be there). The injectors should not leak if they are working properly. There is an electrical pulse that opens them, then the pressure that is there pushes fuel into the cylinder.

However, the cold start injector could be a suspect. I too think that this is fuel related. I can smell fuel...like old fuel...when it doesn't start right away on a hot day. It could be too much pressure, that that would be a pressure releif valve problem. Try disconnecting the cold start injector, and let us know if that works. You shouldn't need it now!

 

This is my first post here and well I hope there are more people trying to figure this problem here since everywhere that i see people trying to figure this out the post eventually dies out with no more responses.

Anyways this is what I have tried on my 98 taco 2.7l 5 speed. I bought the truck about 10months ago and she runs great i get 19-24mpg doesnt make any weird noises shes just perfect except for that problem.

I changed the plugs, wires, pressure regulator, MAF, coolant temperature sensor, exhaust manifold(had a crack), cleaned Idle Air Control Valve (not sure if i did that good) and Circuit opening relay. Mine doesnt have the air temperature sensor on the air box like yours and instead its on the MAF so i changed that which rules both of those sensors out.

The way i get mine to start when i dont have time to wait is by doing a really quick shot of starting fluid down one of the vaccum lines going to the intake manifold and she will start but want to die down so i have to press the gas pedal to get it to stay on. I dont know too much about cars but if it was leaking fuel into the pistons then the truck wouldnt start with starting fluid so im sure that is ruled out there if its true.

From the troubleshooting i have done i keep thinking its something that is keeping the fuel injectors to open when hot so maybe a sensor that controls the pulsing of the injectors like the camshaft sensor or maybe even the ECU. What I do know is that im probably going to try the camshaft positioning sensor next since that sends the signal to the computer to about the position of the valves so it might think the valves are in the wrong place to open the injectors.

Ill post what i find as soon as i try this.

 

That seems to be big problem on the 4.0 jeep engine. Hope you get it fixed.

 

You might want to check out the VSV.

http://staticfrost.com/manual/90-94 UCF11 Manuals/Engine/Troubleshooting (EG)/eg-636.pdf

 

That sounds like that my be my problem, now my only question is which vsv is the one I need to check. I see one in between the intake manifold 2 by the charcoal caniter.

 

I really appreciate the link to that PDF. I'm gonna check it out when I get a chance. That sounds like it may be the problem. Thanks bro.

 

well i tested my vsv and it failed so i went to autozone, oreillys, advanced, napa, and carquest looking for a replacement but no one carried it. I went to a junkyard and all i found was one from a 93 4 runner which had the 3.0 but it looked the same and had the same resistance values as well as looked the same. The connecter was the same except for a small notch that didnt fit the connecter on my truck.

It didnt change anything once it got hot the truck wouldnt start and the junkyard vsv would not work when i checked it after i left the truck off for about 10min.

Im still going to try to buy a new vsv but got a 16hour drive this weekend so it will be a few weeks before i try a new one.

 

. Check the main relay. If not its a fuel pump issue

 

I have the same problem with my '08 2.7L. Although mine actually starts on its own after a few cranks. It starts a bit faster if I give it a little bump of the throttle. And when it finally does start it just kinda rumbles to life. This is a very strange issue and I have been looking everywhere for an answer. If I find one, or any info that helps I will pass it along.

 

Reaching out of the air for this one..... Try disconnecting the main battery leads, clean the battery terminals so they shine, next clean the cable ends where they contact the terminals. There is a nice male/female wire brush for this at automotive stores. Then make sure the cables are very securly tightened. Perhaps engine temps make the cable clamps expand loosing good contact and ability to pass high amperage for cranking. The terminals aren't as likely to expand because inside they are bathed in a mass of liquid acid and lead plates. Takes much longer for that to heat up and expand. If it doesn't solve your problem, its just one of those little maintenance 'might-as-wells' that should be performed from time to time anyway. Another thought, rust at a ground connection to the frame. My 1993 underside is very rusty, but no known ground issues. My starting issues were mechanical at the starter.

 

Just to clear up your information here... Engines need THREE things, not 4. Air - spark - fuel. Your timing has to do with spark. Air means air coming in, and proper compression, spark means a good spark at the right time, and fuel means the correct amount of fuel being supplied at the right time.

That being said, OP, it sounds as if when the engine gets hot you may be getting too much fuel, and are flooding your engine (I obviously can't be sure, but it is not uncommon). A good fuel pressure gauge to monitor fuel pressure would help. A blocked fuel return line would not allow enough pressure to get past an injector. Actually just the opposite, higher fuel pressure would help keep the injectors closed. An injector is just a solenoid that is energized by a PWM signal from the ECM. If you have access to a scan tool of some sort you can take down the data readings when you first try to restart the truck. Perhaps post all the data here for us to look at?

 

Looks like we got a hair splitter amongst us. Either way the engine needs to be in time for all of those things to work properly. I think you were agreeing with what I said, just trying to reword what I had already explained. Oh & you are right about pressure on injectors is what would keep them closed, If they were brand new. We are talking about 17 year old injectors. If there is any erosion of the nozzle surface or deposits on the nozzle surface then pressure, like I said, could possibly cause them to leak.

Let's focus on sharing advice rather than nit picking other peoples verbage. Bottom line is, you sad the same thing I did, just in your own words. That's not really, as you put it, "clearing it up". This forum is about helping one another with our common interest. Not talking down to others & trying to make them look like they have no clue what they are talking about. Try to remember that next time you reply to someone's post.

 

Wow. Well please forgive me for ruffling your feathers. I was simply trying to clarify things. Yes, older injectors could have some deposits on it, you are correct, however that is not what you said.

Your description is saying that the excess pressure is causing a leak, not deposits. I simply stated that excess pressure would not cause a leak. You yourself asked for a response, and when you get one, you act offended. If you don't want an opinion, then don't ask for one. We are all here to lend our help to those who ask. Don't get upset just because someone is trying to make sure someone else is getting the right information. I simply made sure that the OP understood the proper diagnosis of his issue with relation to what you said. Ask any auto tech out there, and they would say the same thing. Spark, fuel, air. To which I leave it at that.

OP, my apologies for the short-term Thread Jack.

 

Hmmm...crystal ball has a crack here, but you might consider a circuit board for electronic ignitioin has a crack. When warm, things expand and something looses contact.

Just 2 days ago I had to replace my starter. A Bendix was worn and only got the 'click-click' sound. Of course, I first bought a new battery, then 4 days later 'click-click'. Oh well, even a Toyota has an issue if one has it long enough.

 

It is summer, so I find that the problem is still occurring. In fact it seems to be happening at lower temperatures than it did previously. I can tell you that removing the air temp sensor connection at the air filter will allow the vehicle to start instantly, everytime. So that would suggest that the injectors are not the problem. I have monitored the air temp with an obd2 reader, and it will spike to 40c on a day when the actual temp is 20, and drop down to about 23c when driving ont a 20 degree day. I feel that the sensor is operating properly?

Someone on another forum suggested putting a 100ohm resistor inline to the air temp sensor, but there sure seem to be a lot of people having this problem with around 96 2.4 and 2.7l engines. Here is a sampling:

http://community.cartalk.com/discus...-start-when-hot-on-warm-days-95-toyota-tacoma

http://www.fixya.com/cars/t890232-1996_toyota_tacoma_wont_start_when

 

Had same peoblem on my 95 ranger, turned out to be a relay, the pcm relay

 

I'm having it too. Was suggested to try the temp sensor. Was going to do that today, and see what happens.

Just out of curiosity, how many people with this problem also have the Deck Plate Mod, or other intake mod?

 

Temperature related, for sure. Could be the solid lifters are needing more clearance from the tappets. When warm enough, they expand and omit the gap, thus the valves can't close completely. Have them checked. Typically, we are used to hydraulic lifters which aren't prone to the gap issue. I have a '93 with solid lifters, and have noticed an improvement in performance after the regap. Good luck.

 

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?