This is my first post so be nice.

I'm gonna weigh in on the 3.4L fuel injectors. Take it for what it's worth. I've been a lurker for years off an on and it's time I contributed. I've had a 99 4Runner SR5 for 16 years and have fixed things on and off since 2003. I'm now about to sell it and wouldn't ya know, it started acting up. Here's the story..

· Like others with a bad injector, it was "chugging" and had little power for acceleration and/or hills but mostly after it had warmed up.

· I checked the coils, plugs, and wires. The coils and plugs were OK but a couple of the wires were corroded at the coil interface so I replaced them with Densos. I thought I had it licked.

· It didn't fix it so I kept researching. An OBD2 scan said I might have a problem with the number 2 injector among other things such as wires, coils, and plugs which I already checked

. I used a vacuum hose "stethoscope" to listen to the #2 injector before and after it had warmed up and it seemed to be working fine. I looked at other causes but kept coming back to the injectors.

· I finally sucked it up and pulled the intake manifold & fuel rails off. I pulled the injectors one by one and cleaned them by spraying carb cleaner through them both directions while actuating them in quick pulses. They were pretty clean to start with and all sprayed well before and after cleaning. Then I measured their resistances. They all measured 14.5/14.6 ohms (at about 80°F) but one. #2 measured slightly more at 14.9 ohms but was still within spec. Now what? Remembering that the Runner worked pretty well until it warmed up, I decided to test #2 at temperature. I got my meter and a toaster oven and monitored the injector resistance while it heated up. I used an instant thermometer to monitor the oven internal air temp. The resistance started out at about 15 ohms and quickly ramped up as the injector heated up. During that time, the resistance was all over the map. Up, down, up again, down again. Then it shot up and eventually opened to infinite resistance. Then I did the same test on all the others. I waited for the resistance to stabilize before recording temperatures. (About 15 minutes.) All the rest of them SLOWLY ramped from about 14.6 ohms at 80°F to 16.8 - 17.0 ohms at 160°F. This was the smoking gun. Note that the bad injector was in spec at 80°F. (Photo of test setup below)

· I bought 6 new injectors (the seller assured me they weren’t refurbished) from Ebay just because I didn't want to do this again if another one died. When I received them, I ran the same tests on them after inspecting them. They looked almost exactly like the originals and came in Toyota packaging. They all performed “well” in my testing (as good as I could tell with my crude test facility). My only concern was that the spray holes weren’t always very aligned with the holes in the pintle caps. I put them all in and put everything back together. Unfortunately, there was a gas leak when I started it back up. It ran fine but left a (large) puddle of gas under the vehicle. So I pulled everything back off and removed the injectors. One injector had a damaged o-ring. That was the cause of the leak. Two of the injectors had the pintle caps remain in the engine upon removal. It was a PITA removing the caps from the engine and after I got them out I inspected them. The molding quality of the caps wasn’t as good as the originals with poor feature definition and a lot of flash. At that point I decided that I’d reuse 5 of the originals and use the best “new” one. I put it back together making sure ALL THE O-RINGS AND MATING SURFACES WERE WELL LUBRICATED WITH OIL before reassembly. Everything worked well and I have over 200 miles on the engine since then with no issues.

· Moral of the story? If you're buying "refurbished" injectors, ask yourself what are the chances the "refurbisher" tested them at temperature? Buyer beware. Maybe this is why many people have had issues with refurbished injectors. My injectors appeared to be Toyota seconds although I can't explain the pintle cap quality. They all ran fine when I put them in but I felt more comfortable with the old ones.

· In hindsight, I think I’d rather just buy a new Toyota injector from a local dealer if I was to do it again. However, I learned a LOT about injectors and wouldn’t hesitate to jump in and work on them if I was to run into an injector problem again.


I hope this helps others that run into this.



Test setup - injector is in the toaster oven with clips on connector pins.

 

Thanks for the great write up!

 

Great writeup - thank you!”

I’m still rolling along with my original injectors - at 439,000 miles...



Andreas

 

Watch some of those 'genuine Toyota injectors' from ebay- there are some very good fakes- the ones my husband bought (one of his injectors tested good cold but failed when warm, like the op's) looked identical to the ones that came out of the truck but for the red o-rings. When they said 'Genuine' they meant 'Leaky Sadness Injectors'.