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Hey everyone, I’m new to the site due to needing some serious help with my 3.4L.
I’ve had toyota mechanics try and help diagnose over the phone many time since I’m in the middle of the desert in AZ, but after 6 months of trying everything I still have the same issue. I am mechanical but by no means am I a mechanic. I am a fabricator by trade.

so here it goes, my issue seems to be a misfire or something fuel related I’m guessing. Truck starts and runs great, drives good. Problem is when the engine sees a load it instantly pulls timing and sputters. Watching my scanner it seems to be around 40% load the timing goes from 20deg to -2deg. It’s not RPM or speed related. I can drive around town shifting at low rpm with no issue but once I get on it the problem occurs every time.

Some info on the truck, it’s a 89 4x4 chassis with a 92 cab. Original power plant was from a 97 T100 auto 2wd. Its a off road race truck so nothing is factory. I built it 15yrs ago and it’s about to get its 3rd long block. The engine that’s currently in it came out of a 2000 4runner but still running the 97 T100 auto ecu and wiring harness. It does have TRD 2nd gen super charger with no fuel upgrades besides a walbro 255 fuel pump. 7th injector is in its near future.

Here is what I have done so far:
Replaced both O2 sensors/ verified harness to O2s was in perfect working order
Cleaned mass air flow sensor
Replaced both knock sensors and wiring harness
Swapped out the ECU with a spare

Reasons:
O2 sensors
Rear O2 hasn’t been plugged in for over 8yrs with no running issues
I replaced both with new plugs
I still have no voltage reading from rear O2

Mass air flow cleaned just because

Knock sensors
I saw coolant dripping from bell house and found the cross over coolant pipe was leaking which corroded the kick sensors and corroded the wiring harness

When I found the knock sensors under water I thought this had to be the issue but still zero change.

As far as fault codes go the only codes I have got since day one of this truck are shift solenoid codes because I am running a R150 5 speed trans with an automatic ecu. This has never seemed to cause an issue. When this problem started I did get a “bank 1 running too lean” code but I haven’t been able to get it to come back on.

Back Story:
About a year and a half ago the oil pan was damaged from a rock and I lost oil pressure which cause me to spin a crank and rod bearing. I rolled new bearings in just to get by while I built a new long block. During last summer I rewired the truck bumper to bumper minus the engine harness. I don’t know if I did something to cause this issue from my wire job or if something happened while sitting in my garage all summer in Arizona heat. I’ve re traced all my wiring and the only thing I touched that has to do with the engine would be the aftermarket ignition switch. I’ve tried different ignition switches and different relays to eliminate that being an issue.

Ive had multiple Toyota mechanics who specialize in the 3.4 and other excellent mechanics try to help me with the issue and none have been able to figure it out. I’ve been told the rear O2 not having voltage on this particular ecu is an issue but I haven’t been able to find the source of the problem. I’ve been told to trying buying a new MAF sensor so I have one on order.

Im at the point of buying all new sensors, engine harness, ecu and or building a new harness from scratch. I feel like something I did during my wiring on the chassis has something to do with my issue or it just randomly happened sitting all last year. Part of my daily job is automotive wiring so I’m confident in my wiring abilities but no one is perfect.

Anyone that has any advice on diagnosing my issue please please help! Thank you in advance
61854
 

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Sounds fuel/air mix related as if its starving for fuel near WOT. Things to check would be your TPS, fuel pressure, fuel pressure regulator, fuel filter. I don't think you have a compression issue since the issue doesn't appear to be isolated to a specific cylinder. Might also check the intake for leaks to make sure your MAF is measuring the intake flow correctly. Check your MAF readings to make sure it is reading flow correctly and the element isn't damaged. Readings from both sensor and ECU should be confirmed if you suspect wiring problems.
 

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Discussion Starter #5
Sounds fuel/air mix related as if its starving for fuel near WOT. Things to check would be your TPS, fuel pressure, fuel pressure regulator, fuel filter. I don't think you have a compression issue since the issue doesn't appear to be isolated to a specific cylinder. Might also check the intake for leaks to make sure your MAF is measuring the intake flow correctly. Check your MAF readings to make sure it is reading flow correctly and the element isn't damaged. Readings from both sensor and ECU should be confirmed if you suspect wiring problems.
MAF readings on a OB2 scanner say everything is correct but I know that doesn’t always mean it’s good. I’m gonna put a new OEM MAF in just to check that off. But yes to me it feels like a fuel/air issue. I have a AEM wide band gauge in the truck and I get solid readings until it does it’s thing then it’s all over the place. I have a in line fuel pressure gauge mounted on my fuel cell so I was thinking about temporary extending it so I can monitor it in the cab while driving. I think replacing the other sensors you mentioned aren’t a bad idea weather they are bad or not. I live in lake Havasu AZ and there is open desert in all directions. My goal is to make this thing 100 percent so I can do hundreds of dirt miles in a weekend without being stranded due to engine failure
 
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