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86-95 Trucks & 4Runners 2nd/3rd gen pickups, and 1st/2nd gen 4Runners with IFS

Fuel Issue

Old 07-09-2019, 10:15 PM
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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!

Last edited by TelefunkenU47; 07-09-2019 at 10:17 PM.
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Old 07-10-2019, 05:10 AM
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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.
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Old 07-10-2019, 05:17 AM
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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.
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Old 07-10-2019, 01:36 PM
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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?

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Old 07-11-2019, 12:25 PM
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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

Last edited by jaskotmb; 07-11-2019 at 12:27 PM.
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Old 07-19-2019, 11:07 AM
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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
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Old 07-19-2019, 08:34 PM
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Spark; pick up coil, coil, igniter, plug wires, plugs?
Compression check?
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