2.7l Will not start when hot - ANY ideas?

Samwise, because you have fuel-pressure testing abilities, would you (and anyone else who's capable) do a test for me? I'm curious to see how much, and for how long, the fuel system holds pressure after shutting down a running engine. So, if you install the pressure gauge and run the engine at operating temperature, then turn it off and wait, I'm wondering how long residual pressure remains in the fuel rail, lines, etc. See EG-125 item (r). This says 21 psi for 5 minutes but that's a minimum.

Reasoning is this: My issue behaves like vapor lock. Our fuel pumps have a check valve built into the pump outlet (see http://densoautoparts.com/fuel-pumps ). When the check valve wears, it allows the fuel pressure to bleed off after shutdown. With lower fuel pressure and warm ambient temps, fuel evaporates and vapors displace liquid fuel in the fuel rail and lines. The fact our fuel rail is the highest point of the fuel system doesn't help. The check valve is supposed to hold residual pressure after shutdown to keep pressure on the fuel and prevent evaporation. If the valve is failing, it should be detectable by keeping a pressure gauge on the fuel system and watching the residual pressure. If the pressure drops before the fuel cools, you get vapor lock. If the pressure is maintained until the fuel cools (and stops vaporizing), you're fine.

The term Reid Vapor Pressure (RVP) relates to the evaporative/volatility rating of fuels and can influence vapor lock, especially in high ambient temps with ethanol fuel additives. Interesting reading.

From http://www.astm.org/Standards/D323.htm "5.2*Vapor pressure is critically important for both automotive and aviation gasolines, affecting starting, warm-up, and tendency to vapor lock with high operating temperatures or high altitudes. Maximum vapor pressure limits for gasoline are legally mandated in some areas as a measure of air pollution control."

With all that said, I replaced my fuel pump this past weekend and now only need to wait for the heat to verify it works but thought it would still be nice to confirm the actual cause. I was thinking the pump was unable to create sufficient pressure when hot but now I'm leaning toward the failing check valve in the pump as the cause. Another possible solution might be to install an external fuel check valve after the fuel pump.

 

Hi all, FWIW, my excessive cranking when hot problem turned out to be my injectors. We battled for nearly 5 months to figure this out, see our thread here: https://www.tacomaworld.com/threads...p-3-4l-5vzfe-v6.354399/page-153#post-10234158

The injectors were passing on testing machines, but dripping in the cylinders when the truck was shut off from being up to full temp (our mechanic borescoped the cylinders and took video of it happening). He put a set of known good ones in to let us drive it for a bit to be totally sure this was the fix, and as of day 4 with the known goods, every single start has been normal. So we plan to buy a brand new set of Toyota injectors and have them put in a few days from now, and finally be done with this annoying problem!! We tried everything. Literally.

Donor known good parts tried: ECM; igniter; MAF; Charcoal Canister.
Parts serviced/cleaned/etc: TB/IAC; adding ground wire; servicing injectors and replacing failing ones with rebuilt.
Parts tested: everything but the tailgate
Parts replaced: TPS, ECT, Crank, Cam Sensors; Charcoal Canister; Fuel Pump; FPR; Fuel Filter; Starter; Battery; Fuses; Plugs; Plug Wires; Coil packs; Thermostat; Air Filter. Yep, we really replaced ALL of that.

Haven't totally kept up on this thread, so not sure if this is helpful to anyone, but hoping it might be. Best of luck to all suffering with the hard warm start issue!!

My advice would be consider asking your mechanic to borescope your intake manifold and see if your injectors are dripping! : )

 

Has any of your mechanics hooked up an OBDII reader to see what the sensors were reporting before they started throwing parts at it? The ECT should be reading the coolant temp correctly when your engine is hot. If it isn't then I would suspect that the sensor would be bad or the harness would be bad. I would measure the resistance of the sensor when hot just to make sure it was bad before replacing it.

Who replaced the engine? What were their qualifications on the engine replacement? Did the harness get tweaked at some point (maybe a sensor wasn't disconnected before the engine was pulled)?

 

We replaced the ECT, it wasn't that. It was being caused by our injectors dripping, even though they passed on the test machine. Our mechanic borescoped the intake manifold to see them dripping. Then he put his own injectors from his 4 Runner in and we drove it for a week and it's damn near perfect starts every time, hurray!! So he is putting in a brand new set of Toyota injectors for us now, and we are thrilled that someone finally figured this out for us so we can move on.

The engine people were not good and seriously overstated their qualifications in their initial sales pitch calls. Lots of careless, shoddy work and dishonesty, some big and some small stuff. I'm not comfortable saying their name right now, but eventually will, because I hate thinking of other Toyota fans dealing with what we did. It royally sucked bigtime. I think there may have been lots of sensors that were not disconnected before removing the engine, it was that bad.

 

I'm very glad you found the solution to your problem. I have been searching for this solution for a long time and have seen a lot of people refer to the injectors causing problems. the injectors were the second thing I went for (after replacing the IAC valve which needed replacing anyway). Unfortunately, even with replaced injectors I am still having the warm start issue BUT let me ask you this- is it possible that my refurbished fuel injectors are not living up to real new toyota injectors and are leaking as well? Hate to drop $600 on new ones but I guess I should have anyway!

 

I know, they are a lot of money!! It's tough to commit to such a giant chunk of change unless you are really sure it will fix it.

We were lucky, the dealer tech that helped us had identical injectors in his own 4Runner, so he went above and beyond and put his own in our truck to let us drive it for a week to be sure it'd be the fix before spending the $. If you can find someone willing to do that, that would be gold for you.

Also, he was able to prove our injectors were dripping in spite of them passing on the test machine by putting a borescope down the intake manifold right after the truck was shut off and video them dripping. If you can find someone to do that for you then that could help you be more sure.

After what we went through, I definitely DO think it's possible that your injectors are dripping even though they were replaced with refurbished ones, and that perhaps a set of truly NEW injectors (whether from a dealer or the aftermarket of your choice) could be the fix to your problem, assuming you had the same symptoms we did (excessive cranking ~30 min after shut off). Although, I am no expert - just another person that experienced the same frustrating problem.

Best of luck to you! I feel your frustration man, it's an annoying problem that's tough to solve! Hope you find your solution : )

 

Two things worth mentioning about lovemytacolots's problem/solution 1) She has a 5VZFE (V-6)...everyone else with this problem has either a 2RZ or 3RZ (the four cylinders are both more or less the same engine with a different stroke) and 2) many others before her have replaced fuel injectors to no avail. Her problem sounds different than ours.

Now don't get me wrong, I'm happy you found the solution to your problem but I seriously doubt it's the same issue as ours. Also, your issue started after an engine replacement (this is extremely significant). For the rest of us, this issue just started out of nowhere completely unrelated to an engine replacement. My engine is original and bone stock. Before everyone rushes out and buys four brand new injectors, keep these things in mind. Or buy the four brand new injectors and let us know how it works out if you want...whatever.

One last curiosity: What is the correlation between the ECT and a no start condition? Seems if you have an open or a short, the engine will start. Yet everyone seems to either suggest this or replace this component. Kinda LMAO at this. And for those who intend to argue their point there is some relation, please provide some reference.

 

Has anyone else besides me and someone with an FJ Cruiser on a different forum (her name was Jamie, or Jamers or something) replaced their injectors with brand NEW ones, or when you said "many other before have replaced fuel injectors to no avail" did you mean people who replaced with REBUILT injectors? Just curious.

 

ECT sensor tells the ECU how hot or cold the engine is at start up and when running. It tells the ECU the correct temp which is used as one of the variables to determine air/fuel mixture for optimum performance(in theory). If the ECT is bad it will tell the ECU that the engine is hotter or colder than it really is. This can cause an enriched fuel mixture which leads to a flooding condition or lean mixture that causes not enough fuel. Both will lead to a hard start issue. I replaced mine with know good injectors and it didn't fix my problem. I finally ended up replacing the fuel pump after some more fuel pressure investigation.

 

I understand the ECT provides data during engine startup and while running but I don't believe for a second it's as crucial to vehicle starting as some say. Just in this thread alone there are probably 10 people who replaced their ECT and it didn't solve the issue for a single one. Yet still, there seems to be some love affair with replacing this component. I'll bet if you disconnected it or shorted it, the vehicle would start the same. In fact, per the FSM, short of any ECT data the computer just reverts to its fail safe fuel mapping. Granted, your emissions would rise and fuel economy lower but it would still start.

 

Well...here's what happened to my 3rzfe and ECT issue. A shop was replacing the valve cover gasket. The truck drove fine during the road test and into the shop stall. After replacing the valve cover gasket, the engine would not fire. They pushed it out of the stall and told me the vehicle was ready to be picked up. Took me about a good hour to diagnose that the ECT was broken off when they replaced the valve cover gasket. Luckily I was able to pull the code (P0115, Engine Coolant Temperature Circuit) from my data logger (Car Chip) that showed the ECT was reporting a temp of -40.0°F in February here in Houston TX. The data log showed the proper temp of 51.8°F prior to them working on the valve cover gasket. Needless to say, the shop replaced the ECT for free after I told them the vehicle would not start in their lot and they admitted they pushed it out of the stall.

So in short...the engine will not start (without a lot of help aka starter fluid and the throttle wide open) with the ECT disconnected or broken/reporting the wrong temp outside of the ECU's working range. I do not know the full range of the ECU's ability to compensate for the coolant temp.

 

Per the Toyota FSM, if a 1996 Tacoma detects code P0115 the computer defaults to a coolant temp of 176 F. This should be well within normal operating range. Then again, if you have a short or an open you should also have a MIL illuminated (after the code being logged the required two times). Anyway, for our issue I think it's fuel related, either vapor lock or fuel delivery dependent on the IAT.

 

Vapor lock in a fuel injected engine is very rare.

 

As are a bunch of Toyota trucks that won't start because of weather conditions.

 

I forgot about this thread and posted my own which is retarded of me- I'll just stick to this one bec its the longest running and most informational. Lovemytacolots, I still have to get the boroscope done. Don't have anyone close with 4 injectors to try. BTW add this attempt to the list of things that didn't work:

Heat wrapped the fuel rail and any fuel line near the manifold in case vapor lock may have been the issue. Didn't work.

Can we publish this when we figure it all out? It'll make for a good movie perhaps.

 

Being a tech in a different industry (copiers) I can tell you that different issues may cause the same symptoms and troubleshooting is universal. I read every response in this thread and came up with a conclusion. This issue is either (1) an IAT sensor with the fix being either repositioning the sensor on the rubber housing or bypassing it with an on/off switch. (2) From my experience with a Mazda Miata I owned with the exact same start up issue. I threw parts at the damn thing an eventually took it to a mechanic. Where they diagnosed it to the Crank Shaft Sensor. (3) The canister issue makes sense to me because of all the emissions crap that you have to deal with. (4) I'd go for for vacuum hoses (on older vehicles) because heat will weaken their firmness over time. Eventually they either become brittle or dry rotted. Again, just troubleshooting. Finally (5) I'd look at injectors/fuel lines only because experience has shown me that other issues usually go hand in hand with fuel issues such as bad mileage & fuel odors. Good luck out there.

 

Anyone come across this thread?
http://www.yotatech.com/f2/1998-2-7-l-starting-issues-251560/index2.html

Ended up being the guys fuel pump and that fact that pressure dropped earlier in the fuel line then expected somewhere near the fuel filter.

 

Mine hasn't missed a beat since I replaced the fuel pump back it March.

 

Glad im not the only one, Anyone have any results? Mine just started acting up. Not too happy.

Symptoms: Charcoal Canister makes squeaking nosie once shut down. Wont start after a heat soak condition. Just started no starting in the cold.

Replace: Fuel Pump, Spark Plugs, Distributor cap and rotor.

 

Alright i think i fixed it!
So mine was an intermittent no spark no start condition. It was the igniter ground, its case grounded to the body. Its located right behind the air box. I just removed it and took a wire brush to the contacts then sprayed with brake clean. Truck now starts easier than ever. Will repost in 1 month if no problems continue.