99 SC 4Runner Strange Lean/Rich problem
#1
Registered User
Thread Starter
99 SC 4Runner Strange Lean/Rich problem
On the freeway I can cruise at 60 mph with my narrowband AF Gauge "dittering" lean to rich as per normal for 100 miles. If for some reason I need to speed up or slow down for a bit, and then I go back to 60 and cruise again, it will show me running all the way at rich.
After I run all the way at rich for a period of time, say 20 miles to the nearest gas station, and I exit the freeway my 4runner will lean out a LOT and have zero throttle response. It even died on two occasions (after the tuner added 5% fuel at 0% throttle to try and fix the problem). The gauge will show all the way lean, and the 4runner will sputter when throttle is applied for a couple seconds, then back to normal.
This does NOT happen EVERY time I drive, but it does happen probably 50% or more of the time.
It does not often throw a code, but has a couple times thrown a P0171 [System Too Lean (Bank 1)] when it will be showing 100% rich on the AF Gauge, climbing a steep incline.
ANY HELP IS GREATLY APPRECIATED.
I am running:
2nd Gen TRD Supercharger
TRD Exhaust
315cc Supra Injectors
Split Second ESC1
APEXi SAFC
Split Second ARM1
Dyno Tuned
After I run all the way at rich for a period of time, say 20 miles to the nearest gas station, and I exit the freeway my 4runner will lean out a LOT and have zero throttle response. It even died on two occasions (after the tuner added 5% fuel at 0% throttle to try and fix the problem). The gauge will show all the way lean, and the 4runner will sputter when throttle is applied for a couple seconds, then back to normal.
This does NOT happen EVERY time I drive, but it does happen probably 50% or more of the time.
It does not often throw a code, but has a couple times thrown a P0171 [System Too Lean (Bank 1)] when it will be showing 100% rich on the AF Gauge, climbing a steep incline.
ANY HELP IS GREATLY APPRECIATED.
I am running:
2nd Gen TRD Supercharger
TRD Exhaust
315cc Supra Injectors
Split Second ESC1
APEXi SAFC
Split Second ARM1
Dyno Tuned
#3
Registered User
Thread Starter
Oh, and I don't mean to disregard what you've been saying at all by posting this, just wanted to see if anyone else has the same problem, or any new ideas.
#4
I had a similar issue & spent hundreds of dollars, new exhaust,new O2 sensor new plugs, new wires, dealer diagnosics 4 hours, changed MAF sensor, tried different computer, all one at a time with no avail. A small trouble shooting shop took it for a drive and said it was the crank sensor, I did not want to buy one so I got a used one to try and bingo, a 2 minute drive and he knew this, I wish that I went there first.
#5
Contributing Member
Crank sensor? Would not have guessed that but i have a similar problem just under different circumstances. 2 or 3 times a year it will act like you are describing, bog bad and misfire/sputter and even die.
Didn't have my wideband hooked up till till it happened a few days ago and noticed it was running lean, till then i was thinking something to do with spark.
To date i have not figured it out, it usually goes away by the next day so i don't worry about it, i can still drive the truck when it happens, just got to give it more gas.
What did your truck dyno BTW?
Didn't have my wideband hooked up till till it happened a few days ago and noticed it was running lean, till then i was thinking something to do with spark.
To date i have not figured it out, it usually goes away by the next day so i don't worry about it, i can still drive the truck when it happens, just got to give it more gas.
What did your truck dyno BTW?
#7
My '99, 4runner, sr5, 4.3 has same sort of problems.
I replaced plugs, wires, coils, map, cat con, added second cat con, 02 sensors, and throttle position sensor,...it ran better but still chugged, spit, backfired, and stalled....
I changed the coolant temp sensor and I thought that I had it ... but a day later it started again.....
I don't know what to do....
Its suckin back gas and running leaner all the time.
I replaced plugs, wires, coils, map, cat con, added second cat con, 02 sensors, and throttle position sensor,...it ran better but still chugged, spit, backfired, and stalled....
I changed the coolant temp sensor and I thought that I had it ... but a day later it started again.....
I don't know what to do....
Its suckin back gas and running leaner all the time.
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#10
#11
Contributing Member
Throwing parts at a problem rarely fixed it. Luckily up to now you have replaced basic tune up items so you are none the worse for wear.
Sadly don't have much of a suggestion for you either except possibly a bad ECU or wiring.
Sadly don't have much of a suggestion for you either except possibly a bad ECU or wiring.
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