Fuel Issue
 

Hi, longtime lurker, first post. I've been having a fuel issue and wonder what could be happening:

1987 4Runner EFI
Checked good:
- new O2 sensor
- ECU seems to know mixture is rich/lean when it is (Vf to E1 check)
- TPS set and check with meter
- AFM opened, cleaned, checked with meter
- FPR at least puts fuel out the return line, connected directly to engine vacuum (rather than VSV), no change
- injectors all work when connected to a battery and carb cleaner sprayed thru
- EGR blocked off to test, no change

2 years ago, I upgraded to flamethrower (advertised ~240cc?) injectors, computer seemed to be handling it fine for 2 years. Last week, started running super rich, engine stumbling, black smoke out the exhaust, etc. Replaced O2 sensor, TPS checks within specs as does AFM when I check with a meter. Vf to E1 shows 0.04V (lean condition) as I understand, ECU has settings of 0V, 1.25V, 2.5V, 3.75V, 5.0V from rich to lean, 0V indicates it is pegged and can't compensate by reducing pulse width any more. Pulled intake plenum and fuel rail to see if I had a giant leak somewhere. Didn't see anything major, rail holds pressure for a long time too... Replaced a few worn O-rings, re-assembled...

Now my problem is almost gone! Just from taking it apart and re-assembling. Thing runs mostly fine, but still a little rich (Vf to E1 shows 0.04V still) but it runs without stumbling, exhaust still smells like gas a bit, but seems just barely rich. I think, "OK, what if I swap back to stock injectors (195cc?), maybe that will get me back within range to where the ECU can control AFR". So today, I swapped back to the stock injectors, bench tested all of them with a battery and they at least flow... Now, the truck runs like $#!t and it's super LEAN (Vf to E1 shows 4.98V). What is happening? I have ordered a fitting to be able to check fuel pressure (should be here soon) so maybe that will give me another clue. My next move is possibly installing an aftermarket FPR to be able to reinstall the bigger flamethrower injectors and dial the pressure down a bit to where the ECU can control AFR. I also picked up a FPR from the junkyard from a 3.0L 3VZE (is it the same? maybe try this before spending $ on an aftermarket FPR?) Only other thing is I broke the connector to the coolant temp sensor today (will replace ASAP), but should it still run like crap at idle and under load? Wouldn't it just assume the engine is cold?

Just confused why the stock injectors don't work unless maybe sitting in my garage for 2 years one or more of them is a little clogged/faulty. Thanks in advance for your input!

Yes fuel injectors sitting like that can cause them to go bad. From Hurst Injector Service. He posts under the user name Trav at Bob Is the Oil Guy forums. https://hurstinjectorservice.com/index.html

What will cause injectors to go bad when not in use?

The internals of injectors are made of various steel alloys that will corrode and or rust when in the presence of moisture. Large parts of America contain enough moisture to cause corrosion/rust damage. Gum, varnish and other normal deposits can be removed by cleaning but once an injector dries out and the deposits hardened inside causing a pintle to get stuck to its seat, that injector will become inoperable and in most cases not possible to clean.

Injector Storage.

From time to time injectors need to be stored. Since corrosion is probably the injectors number one enemy it is important to make sure that injectors are cleaned properly and lubricated, inside and outside, with a good quality lubricant. The injectors should then be placed in a sealed plastic bag or container and stored in a cool dry place.

I have four Toyota factory 22RE injectors that have been sitting for two years next month. Luckily, I have not needed them...yet! They will go to Hurst for cleaning one of these days.

What snippits said is definitely a possibility.

Was the battery unhooked for at least a few minutes during the time you switched injectors? The ECU may need a reset as it was expecting the injectors to be putting out more fuel than they really were. It may take some time for the computer to relearn the fuel trims if it has not been reset.

Why were the "flamethrower" injectors installed to begin with? Does your engine require more fuel due to engine modifications?

:safari:

Yes, I made sure to unhook the battery to reset the ECU. It was unhooked the entire time I was disassembling and reassembling everything so that should be plenty of time.

I swapped in the bigger injectors somewhat by mistake/stupidity. I used to own an '88 pickup and when I got the '87 4Runner, it took me a while to remember to order '87 parts not '88. So I tried out the '88 injectors (bigger) and the computer seemed to be compensating for it fine so I left them. Wondering now if I was still running slightly richer than I should have been and now just notice it because I killed the cat? Removed my cat and you can see the grids are still there and not clogged, but may not be doing much... Doesn't run substantially different with/without the cat aside from noise. We will see when it's time to get an emissions test (thankfully I am good for at least a year).

Ordered a new set of balanced injectors for the '87 from LCE yesterday (checked fuel pressure 38psi so good) rather than have mine serviced because I need to have the truck up and running ASAP and would rather shell out some $ than have my old ones come back unserviceable. I'll send 'em in later for a clean though, thanks for the link! Hopefully that new set of injectors fixes the issue. Also ordered a new set of O-rings and grommets for the injectors because the dealership charged me like $45 for a set! (and the guy supposedly gave me the wholesale discount)! Good to have some extras on hand...

Edit: Weird, it used an account I used to have on here, but it's me, the OP

OK, update... So I swapped in brand new LCE injectors from the right model year rather than wait for mine to be serviced (plus I like having extra parts...) No leaks, everything looks good, but the thing still runs rich! Almost the same story as before with the larger injectors... If I rev the engine up and let it come back down to idle, I can get Vf-E1 to read 2.5V for a few sec, then 1.25V, then back to 0V after about 10sec... So the computer knows it's running rich but just can't compensate...

The truck runs alright (some stumbling at certain RPM, some slight exhaust smell, but otherwise ok). This isn't a huge pressing issue, but I don't want to run forever like this as gas on the cylinder walls could dilute the oil and eventually cause larger problems, not to mention worse gas mileage... I'm stumped. Any ideas? And why this could have come on so suddenly? One thing maybe to note is the rich running condition first started when I was driving at altitude (~10,000ft). I live in Golden, CO so 5,700ft

Spark; pick up coil, coil, igniter, plug wires, plugs?
Compression check?

Spark is good, all cylinders are doing the same thing (black sprak plugs) and it's not missing consistently on any cylinder so I'm 99% it's a fuel issue. Took it on a longer trip this weekend and ran out of gas :/ because it was still getting terrible (12mpg) mileage. I'm starting to suspect the eECU now because injectors are brand new, fuel pressure is right, and O2 sensor is sending the correct (full rich) signal to the ECU... Maybe the computer is getting the right inputs but not adjusting the injector pulses to be shorter? ECU problem is really the only thing I can think of left in this fuel system that I haven't made sure is operating correctly

I'm thinking about trying to get an oscilloscope I have at work hooked up and see if I can measure pulse width to the injectors. Any idea what the injector pulse width range should be? Like what is the shortest pulse width the ECU will send? Possibly could get a shop to diagnose this for me too with some fancy electronic tool, but that takes all the fun out of it huh?

https://cimg8.ibsrv.net/gimg/www.yot...c64e3baac.jpeg
VF1 voltage

Thanks for that about reading 0V at altitude. Makes sense... but now how is the computer supposed to compensate at 5,000ft? Can I figure out if the signal is correct? Or do i have to drive down to the beach... It definitely still runs rich (exhaust smell and terrible gas mileage).

I am pretty sure I didnt fry my ECU. The kit I bought when I initially put in the '88 fuel injectors had a resistor delete plug and I used it. When I swapped back to the '87 injectors I plugged back into the resistor bank. For the exact reason you mention, I was very careful to only connect the battery with/without the resistor bank at the correct time based on which injectors I had installed.

Have you checked you efi relay per fsm?
Id ohm that out per fsm.
Remove that drivers footwell fuse panel and check the back for corrosion while you’re there.
Maybe disconnect battery, pull efi fuse, pull efi relay, and completely disconnect the ecu from the harness just to be sure it definitely resets without any supplied voltage or ground sources.

I imagine it is in open loop above 5000 ft. You might be stuck in open loop

Might ohm out your coolant temp sensor and cold start timing switch per fsm as well.
A faulty coolant temp sensor can keep you in open loop.
Cold start timing switch I suppose could fail in a way that would cause incorrect operation of the cold start injector.
Either would result in a rich condition.
Just spit balling here, all of these are free quick checks.

Just an update on this...

After a few months of running rich (didn't drive much) all the sudden it would start right up and immediately die. Turned out I could fix this problem by opening the AFM flapper about halfway, meaning it was dying due to a lean condition.

Finally broke down and bought a used ECU off ebay and that fixed everything. Easy fix, after I had ruled everything else out in the whole EFI system basically. No obvious corrosion or damage to the old computer at all, looked mint on the inside, so I guess they can fail somehow without obvious damage.

Hope this saves someone else a headache. Would have been great to be able to swap a known good ECU in to test, but they are hard to find...

Hell yeah, glad you got it fixed! It’s rad you reported back!