1995/6 Era SC400 1UZ-FE - MAF Sensor

[LT_Chambers]

Hi all,

I have been having a strange hesitation issue in my Supra with a 1UZ from a 95/6 SC400.

I had just replaced the plugs, I had NGK Iridiums in it before. I just put BOSCH Plats in and the yesterday it seemed to have solved it, but today the hesitation has came back same as before. Going up hill in very light throttle I can feel the engine hesitate, and on occasion on level ground in second or third with very light throttle the car begins to "buck". As soon as I push the throttle down more the "bucking" goes away and the hesitation seems to dissipate slightly but is still noticeable.

So today I stopped after driving for about one hour, kept the engine running and un-plugged the MAF, and the engine bearly changed if at all. It didnt stall or sputter, nothing, only the CEL turned on. So I drove it around for about 15 mins, it pulled good and didn't seem like it wanted to "buck" or hesitate. I shut it down with the MAF unplugged, and started it back up and it still ran just fine, it was holding idle and still had the CEL. So when the engine was running I plugged in the MAF, I heard the rpm rise very slightly. The CEL turned off, so I drove it around for another 15 mins, and it seemed to be ok. It didn't hesitate or "buck". I have tested the MAF via the Lexus Repair Manual and it checked out but I was getting odd readings on my meter so its unreliable. So I'm slightly confused, shouldn't the engine not be able to hold a idle if the MAF is unplugged? Also, is there any way to tell if my ECU should be using the Karmin Vortex (old MAF) or the Hot Wire (new MAF)? The engine did not come with a MAF so I'm unsure what it should be using. Any help or suggestions are welcome.

So, cliff notes:

- 1995/6 SC400 1UZ-FE
- Slight hesitation on occasion and "bucking" on occasion both at light throttle
- BOSCH Plat plugs
- When running + unplugging MAF = no stall, CEL, and runs pertty good and starts back up and holds idle entire time
- When running + re connecting MAF = no stall, CEL off, and runs pertty good.
- Need to determine what MAF i should be using (old vs new)
- New Coils, NGK plug wires, Igniters have good ground, engine is grounded to the body.

Thanks for reading!


Most recent photo:

 

[BigKriss]

Slightly off topic here and really chucking a cat amongst the pidgins but has anyone ever used a product named "Mapecu" from NZ. ?
Does away with the maf totally and in effect converts the system to map sensor.
I bought one brand new many years ago but have never used it ...

Back on topic...

 

[LT_Chambers]

I'm going to be installing a MAP ECU 2 in a friend’s 1JZ-GTE Supra here soon, and I just recently sent scans of the 1996 SC400 engine wiring diagrams to MAP ECU and they put together information to wire it up. I still haven’t decided if I want to go with the MAP ECU 2 or the new ECU 3, from what I have read the ECU 2 is plenty powerful enough but the ECU 3 lets the user define more parameters.

Right, back on topic.

 

[taka21]

looks like you have the early karman vortex meter from the picture, the setup is different, the 96 has an actual maf.
and the way the stock ecu is designed its got quite a few failsafes built in, one of wich is the fact that the car runs just fine without the maf. it will however run a bit richer and as you stated turn on the cel

 

[LT_Chambers]

Yup, I know I have the earlier MAF, I know the two sensors have a different signal but I'm wondering if the newer ECU could receive a signal from the older MAF and still function with no CEL on. I'm leaning more towards I have a faulty MAF or the pins on the plug are not getting adequate connections. Yesterday I cleaned the pins with a Emory board and it ran and pulled good for a while then I got some hesitation again, then it cleared up. That is what is making me think the connection is faulty, but it also confuses me because I never get a CEL, and I have never pulled any codes other than a speed sensor.

 

[taka21]

Yup, I know I have the earlier MAF, I know the two sensors have a different signal but I'm wondering if the newer ECU could receive a signal from the older MAF and still function with no CEL on. I'm leaning more towards I have a faulty MAF or the pins on the plug are not getting adequate connections. Yesterday I cleaned the pins with a Emory board and it ran and pulled good for a while then I got some hesitation again, then it cleared up. That is what is making me think the connection is faulty, but it also confuses me because I never get a CEL, and I have never pulled any codes other than a speed sensor.

hmm what ecu are you running