CRESSIDA 1UZ SWAP: ECU ISSUES AGAIN

The 1UZFE EGR Delete Kit is available for sale here.
so WHERE to begin....

1988 cressida , 1uzfe out of a 1995 ls400. over the last year , since i have got the engine swap done, i have gone thru three computers all with the same problem , loss of m-rel output. it always seems to end the same way. no throttle response then loss of the m-relay output. luckally i made it back to the shop , and after letting the engine cool down and trying to restart, no throttle then no check engine light.

the codes i have always been the same all trans codes ( MANUAL SWAPPED) , egr code( EGR DELETED) rear 02 sensors (DELETED)

THE code that did show up which i am thinking fried my ecu was a p0120 for the throttle position sensor . I got a used ebay throttle body due the the one on the car having a broken ear on the tps. i used the tps that came with it and it seemed to be ok this morning , but after driving at idle for a long time (FURNERAL PROCESION) IT OVERHEATED due to my electric fan not working( THIS IS A NEW PROBLEM THAT JUST STARTED LAST TIME IT WAS AT IDLE FOR LONG PERIODS ). this is when my throttle sucked!

but i did get it back to the shop, and thats when the ecu fried.

so my question to the community is, can a bad tps take out the ecu?

this ecu is the 4th gen revisement # 50224 so it should have good software, and the guy i bought the ecu from (LScowboyLS ) via facebook> said he replaced all the capacitors. SO what the hell!!! i wish i could fix this damn problem , Has anyone experienced such issues with a 1uz swap
 
I had a extra computer ( California emissions >>) but it worked . the engine runs , it idles real low and doesnt have the best take off, but computer is running , so it does look like something is killing the m relay output on my computers. has anyone had this issue where voltage out from the ecu drops so much that it wont turn on external relays?
 
The The P0120 will be logged when the TPS input to ECU goes above or below the reference voltage.

  • Stable 5v power is supplied by the ECU to TPS via the VC terminal
  • E2 should be constant ground
  • IDL1 should be grounded when the throttle is closed
  • VTA is your variable input when the throttle is operated
VTA reference range should vary between (approx) 0.5v closed to 4.5v fully open. If the voltage goes above or below these values, the ECU will determine a fault is present and throw the P0120 code. This can occur if the sensor is unplugged or shorted (to either power or ground).

P0120.png

Having a signal out of range wont fry an ECU, but short circuit in the VC line could, because VC5 also powers the processor inside your ECU. The processor is also responsible for turning on the check engine light and the M-REL output.

I would check VC for a short circuit.

Also, is the sensor you fitted from the ebay throttle body the same part number as the original? Even though they look the same, wiring pins and output voltages can be different between models.
 
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thank you for the response , but i think i figured it out.
After thinking about it i remembered that when i was first done and driving the car it was like it was in fail safe mode. The issue was that the maf didn't have a power source i forgot to repin the II1 connector #5.
So i repined the #5 power wire for the maf , and guess where i tied the switched power source for it??

from the M-rel out put wire. So after looking at some diagrams , i realized the factory lexus gets its power from the maf thru the +b circuit out of the main relay. So when i get my ecu back from having the capacitors replaced , im going to test this theory
 
Yep, the current draw from the MAF would be too much for the M-REL. Its only designed to power a low current solenoid in the relay. I would recommend you check your wiring diagrams though... I have several here and they all show VC powering the MAF. Would suck if you fried a MAF.

Diagram 1.pngDiagram 2.jpgDiagram 3.png
 
Yep, the current draw from the MAF would be too much for the M-REL. Its only designed to power a low current solenoid in the relay. I would recommend you check your wiring diagrams though... I have several here and they all show VC powering the MAF. Would suck if you fried a MAF.

View attachment 14211View attachment 14212View attachment 14213
according to my diagrams the mass air flow gets its switched power thru the +b circuit coming off of the main relay , so i was going to tap into that wire for power . what do u think
 
My bad - was thinking early model. If those are the correct diagrams for your engine then it looks like 12v
 


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