Cut out under load

I bought a 1997 Toyota Tacoma 2.7 and it idles perfectly fine but under more then a quarter throttle it immediately dies or cuts down to about 10 RPM and fires out the intake until it dies. Runs perfect with just a tiny amount of pedal though.

I have changed maf x3, it had a blue streak I replaced with blue streak, the maf was wired with those heat shrink crimp connects, I took them off and just twisted and taped the wires together as a temporary fix just to eliminate a possible continuity issue.

I have replaced TPS x3, idle air control valve aswell.

Sensor wise I took everything off and went sensor by sensor


Runs maf only

Runs tps only

Doesn’t run only o2 sensors

Without o2 and tps only will run but stutters on start up



Maf plugged in when running with only tps idled up, when unplugged it killed it


The truck will start and run the exact same with maf unplugged as maf plugged in, but as soon as I unplugged while running it dies. or if I take maf off of intake while running it makes no difference, so it’s definitely not working.


It gets really strange when I had the maf unplugged with the truck running and I tested for ground continuity on each and when I got to the one that would originally be the 2nd pin with a white/red it idled up and then when I took it off it died, which is exactly what happens when the maf is installed and plugged in to the truck.


I cleaned every single ground.

It doesn’t have a catalytic converter

I replaced the fuel pump

All vacuum lines are good

It’s plug on coil style, no distributor.

The ignition has been replaced with some BS one, maybe that’s what causing it? Not energizing the maf circuit or something? Idk.

The motor was supposedly rebuilt less then 10k miles ago and the engine bag is freaking clean, no wack wires or anything, this truck used to perfect just the last couple owners messed it up.

before you say “the problem is your Chinesium maf go get you a toyoter one!” I’m going to and I think if I can activate it with touching my volt meter to it we got more issues.

I had to buy it, it was 2k and I drove it on the trailer.

my 4Runner isn’t squatted! The trucks just heavy with the trailer.

 

I would smoke it as my first step.

 

First, is the engine spitting oil through the intake? Looking at the air filter, it’s soaked in black oil.

Second, twisting or cramping vital electrical components creates resistance. They need to be solder properly.

Third, looking at all the red jinky quick splice connectors it has at the steering column, there’s probably more issue to it than you think. It’s probably a Frankenstein setup with the harness from a different year and an engine/parts that is not compatible with the harness or ecu.

Last, I would question the solid axle swap if the entirety of the truck look like that. Also, we know the 4R isn’t squatted, the better term is overloaded…

 

I don’t know if you reply direct or just to the thread (I don’t know how Tacoma world works) and no that oil is because I was really tired and accidentally left the oil pressure sensor out thinking it was the knock sensor in my brain, so I started it and I just shot all the oil out. I’m not worried about the SAS I know it needs work, truck has a broken leaf and is missing shock bushings, that’s all a later problem, I think the splice connectors in the steering column is just because someone replaced that ignition, (they did do a shite job) and I would tend to agree with you the issue is. But the truck runs absolutely perfect and will idle for hours with zero other strange issues, and it seems no matter what I change the problem remains the same. Could it be ECU? Idk anymore, maybe the cam is a tooth off? I just need someone that has specific knowledge. Unfortunately I am in the middle of an entire body harness/engine swap on my VW’s and I can’t pull the truck in the garage.

 

Since she is new to you... start with a compression test, all of the parts replacment "fixes" are a waste of time/money if the motor is not mechanically sound. Do you have a scan tool?

 

I do have a scan tool. it had a maf and throttle position sensor code, that’s why I replaced them. I get the reasoning and I will eventually but I don’t see why I would rn? I know there is a maf connection issue, and it has power and idles great under minimal throttle. I think it’s an ecu issue communication with the maf, I checked timing today to make sure it was good, and the head is squeaky clean.

 

Ok, great that you have a scan tool. With your scan tool pluged in you are going to want to look at the MAF airflow in g/sec, if it isnt reading in metric, change the setting. At idle you will want 1 g/sec of liter displacemnet of motor, so you will want 2.7 ish g/sec give or take 10%. If your scan tool can graph this so much the better, you will want a liner increase in g/sec as you slowly raise the RPM's, This is where a graphing capability will rule, scan tools dont react fast enough to changes and watching the just the numbers might not show something.

Check to see if it goes into closed loop mode.

Check to see what the PCM reports as the engine coolant temp.

Check your fuel trims 0 +- 10% is "normal" anything more than a 10% deviation from zero indicates a problem. A negative fuel trim is the PCM pulling fuel away from the norm where a + is adding fuel. This is done by changing the millisec injector open time.

I am sure there is something i am forgetting, it is late and I am tired.

 

Alright this is exactly what I was looking for, I’ll check that tommrow, I didn’t see this today so I just swapped the coil packs because I put a timing light on the coil wires just to make sure I was getting spark when it was dieing out, and 1/3 were only sparking when then engine was dieing, so I swapped the coils and plug wires and it “fixed” it but actually ran exactly the same so I think it was just some feedback thing, I swapped it back to how it was.

 

The mystery deepens I figured I would pull the glove box just to see if the ECU was plugged in and mounted right and bank E5 pin 8 is jumped and then running all the way over under the carpet into a separate harness https://people.well.com/user/mosk/images/Early_Tacoma_ECUs_v2.pdf that link is the diagram in case anyone is interested, I’m not sure if the truck came auto, it was a pre runner I think so it was non 4WD I’m gonna look into it once I swap the throttle body back

 

This is what I have access to for wiring diagrams and I cant see where than pin is... problem is is I am on vaction and do not have access to my factory stuff, maybe someone else can upload a factory diagram. What does the VIN say as to how she was equipted as built?

 

I have to look the vin up, I just swapped the throttle body it came with back on and now it just starts and dies, I think that seal is leaking heavy, I’m gonna go get some gasket material a vin lookup and come back
4TAPM62N1VZ269055

edit: I think the upper intake to lower intake might not have a gasket, the medal looks completely touching I’m pulling the intake tommrow


Edit to the edit: definitely not a pre runner because Toyota didn’t release the pre runner until 1998, it has a button for a locking rear dif, which obviously doesn’t work because it’s a axel Found On Reserved Dump. But it does have the button for it and the clutch start cancel, the vin report says it was the deluxe model (DLX=base model) but it also says it was 4WD which it can’t be both so I’m just gonna go with base model and they chose the locking rear dif option.


Edit #3 glamisman my scanner can not pull MAF data unfortunately, but I did rent a fuel pressure and compression tester. That will be sometime this weekend, tommrow I’m going to try to get that intake apart and cleaned as I have the gaskets coming in Friday (2.7 makes it a more likely 4wd) And the grill looks 4WD so that’s what I’m going with.

 

It seems like a smoke test would go a long way to eliminate some of the leaks.

 

Alright I went through, fixed the throttle body and fixed all the leaks I think, I’m gonna go get a smoker but I’m at the truck right now, I’m not sure if this video will ever load but, if the maf is half way plugged in the truck idles down to where it should be and it can fucking Rip, like I mean runs perfect, but as soon as it’s unplugged fully on start up it runs the same as fully plugged in, and if you fully unplug it while it’s running it dies, but half way plugged in it’s fixed.

 

Sure sounds like a connector issue. Maybe a wrecking yard for that harness, take the time and solder the wires if you go that route.

 

Glamisman, I agree with you, untill I started taking off wire by wire and the ONLY wire that makes any difference is they grey with red stripe going to the fourth pin with the mag facing away from you

 

I have a spare maf laying around, I start the truck with the maf connected to the truck, it idles high cuts out under load ect, I unplug it truck shuts off, if I plug it back in I have about 3 seconds of truck running perfect and idling low, then it goes back to idling high and cutting out, so I have the truck running, maf in truck plugged in, I unplug it from the one in the truck and plug it into the spare one before the truck dies in the open air and it’s the exact same results, the truck is reading that the MAF is there through that one wire but not actually reading anything at all.

just found this