Tacoma 4.0L hard to start when warm

I haven't checked in here for awhile, sucks you're still chasing this. Too bad guaranteed online solutions don't come with free parts, lol. I noticed you checked the ECT, CO and FP relays and cleaned the MAF, but has the MAF been tested (I think it requires a scanner)? MAF and ECT seem to be common culprits with these issues. I believe you said you already tried swapping the ECT with a known good unit, do you have the ability to do the same with the MAF? I wouldn't buy one, but if you have a friend that can swap... Hope you figure it out soon.

 

Wouldn't a bad MAF throw a code though?

 

It probably should, however in some other cases (non Tacoma) they've caused issues before they're bad enough to throw a code. From what I've read, the vehicles are basically flooding on warm start up because the computer is always trying to "cold start". ECT is more common than MAF, but I believe the ECT has already been ruled out in this case.

 

I don't have any way to swap the MAF. I did try unplugging it to see if that Mae a difference, but it didn't help

 

Something like this may be worth researching.
http://www.ebay.com/itm/Mini-VCI-Di...860966&hash=item1c7c6061cc:g:ltcAAOSwB-1YnT~W

 

There was no need to. I left the injectors alone and just replaced the fuel pump as I needed to.

 

Not necessarily. They will sometimes throw a code P0171 or P0174 or both which are lean bank 1 or 2 codes.

Sometimes the MAF's are bad enough to the point where they single handedly throw a specific MAF code to where you know without doing the sensor is NAD.

Itis possibly he is experiencing MAF issues. I can't tell you how many I've gone through in the last 80K. It's almost become such a routine problem sensor for me that I know when it is bad even when there is no code. Right now I am having intermittent hiccups or long start issues only when cold. Yep. Time for me to replace the MAF again.

 

How much does an OEM MAF cost for just the part? I heard they were pricey.

 

I don't know. I have been going with Denso MAF's but I am starting to believe that even the legendary Denso brand is now being outsourced to build in China also now though. I think I remember reading a part had stamped on it the dreaded words, "made in China." I believe OE is made in Japan.

 

Oh, I thought you said you replaced the injectors, figured you did that at the same time.

Am I correct in assuming that when you unplug the MAF and run the truck it just runs at the stock fuel trim levels? Do I need to reset the ECU after unplugging the MAF to get it to do this?

 

I replaced the injectors when I installed my supercharger hence the no longer need for smaller CC injectors that these have over the larger CC supercharger ones.

Normally what happens when you unplug any sensor (MAF included) is the computer assigns itself a known good parameter for whatever sensor is unplugged. Seeing that the MAF is a bit more dynamic in range and constantly switching it is a little bit more difficult to do so.

It is always a good idea to reset and zero out fuel trims after replacing the MAF or similar vital sensor. It helps restabilize operating condition and stop the computer from using excessive fuel it shouldn't while at idle and driving quicker.

 

Ok, that's what I thought on the MAF. I'm going to drive around a couple of days with it unplugged and see if it will affect anything.

I was just trying to get a timeline of when you replaced your injectors. I'm going to pull my rail and see if I can spot an injector leaking before I buy any new ones.

 

[QUOTE="Fike, post: 15818759, member: 2234
I'm going to pull my rail and see if I can spot an injector leaking before I buy any new ones.[/QUOTE]
When people say leaking injector I assumed they meant leaking into the cylinder. If you have a scope you can look into cylinder. I don't so I would pull one plug out at a time after it sat and have some one turn it over and see if any fuel shoots out the hole...just an idea

 

When people say leaking injector I assumed they meant leaking into the cylinder. If you have a scope you can look into cylinder. I don't so I would pull one plug out at a time after it sat and have some one turn it over and see if any fuel shoots out the hole...just an idea[/QUOTE]
I tried a buddies scope, but it was a cheap one, and I honestly couldn't tell anything with it. The images were very dark and blurry.

Good idea on pulling plugs and seeing if any fuel comes out. If I've got one bad injector I will probably replace them all.

 

When you cleaned your MAF, what did you clean? The IAT "bulb" and the fine MAF sensor wires down inside the tube? Maybe a dumb question, but then again...

Have you had your battery load tested anywhere in this process? Just because it cranks doesn't mean the ECM is getting good voltage while cranking.

Your leaking injector theory is also very likely, even if uncommon. I doubt you'll get fuel spraying out of a cylinder with a spark plug pulled though, more like the manifold is rich with fuel vapor (because the engine is hot), to the A/F ratio is too rich for ignition when you try to start hot.

I'd suggest pulling your fuel pump relay while the engine is running to shut the engine down when hot - the rail pressure will drop significantly, and the engine will die. Then shut the key off, re-insert the fuel pump relay, and try re-starting after 1/2 hour, or when your long crank normally happens. Repeat this test a few times to be sure of the results.

 

Yes, i cleaned the bulb and the wires in the tube with the can of CRC MAF cleaner. The MAF and Air Temp bulb were both extremely dirty when i first cleaned them. I also load tested the battery and everything checked out good.

I'll try to run the test you mentioned and pull the relays.

Also, does anyone know if Toyota changed injectors on the 4.0 during different model years? I am looking up replacements and finding several different OEM model numbers out there, but I thought it was the same injectors in all 4.0Ls. I'm not in a hurry to buy them as I am going to be sure that they are leaking before I purchase anything.

 

When people say leaking injector I assumed they meant leaking into the cylinder. If you have a scope you can look into cylinder. I don't so I would pull one plug out at a time after it sat and have some one turn it over and see if any fuel shoots out the hole...just an idea[/QUOTE]

So I pulled my fuel rail, and I definitely have one injector that was leaking. I cleaned all of my injectors with a can of carb cleaner and a bunch of fittings to create pressure. Then hooked it up to a 12v with a switch and cleaned all of them out.

After I determined the one that was leaking I spent the rest of the can of carb cleaner running through one end, and then backflushing it. It is no longer leaking. Not sure if something just got caught up in there or what. I'm going to reinstall and check, but the dude at O'Reilly's sold me the wrong orings, and the old ones are too loose to go back, so I'm stuck with my intake apart until my wife gets home and I can get new orings.

Hopefully this works, if not, I will be buying new injectors

 

Must have gotten a batch of bad gas. Which is why unless I'm absolutely desperate avoid fuel stations when the fill up rig is there. They dump in all the delivery fuel and disturb all the gunk settling at the bottom all the while you pump. Since they probably don't have many filters from their tanks to the pump itself you are more likely to get junk contaminated fuel.

Hopefully this solves it. Sounds like a freak incident.

 

Hoping for this to be the fix.

 

Just got it all back together, went and drove about 10 miles of interstate and several miles through the town to make sure I didn't have any leaks or forget any vacuum lines. Shut it down and now I'm waiting an hour to check startup

Fingers crossed