coug66

Solved see bottom post!!!!!



Here are my symptoms. I turn onto a main road from a stop sign. I gas the car quickly to feel it accelerate. It dies and stumbles, lights come on and my car throws codes the P0100. Car goes into limp mode requiring two turns of the key to start and no signal from the MAF on torque obdII software.
I then open the fuse box and it is a EFI 2 fuse. I also just two weeks ago blew a EFI 2 fuse.

I swapped Mass air sensor and later after driving it 10 miles. I stop the car going up a hill on a one lane road. I let the truck and trailer go down then I accelerate and the car blows another fuse.

p0100 codes no air flow being measured?

what can be triggering the fuse blowing when I accelerate?

Can loose wires grounding on an O2 sensor cause this?

My air cleaner was really dirty but I still blew a fuse later after cleaning it.

I strangely had a couple of codes pop up after putting spacers in my downstream 02 sensors.

p0174 and p0171 I think?

Too lean was the read outs. I reset ECU and they (171 and 174) have not come back. This is an intermittent problem that happens when I suddenly accelerate from a stop or going very slowly?

Thanks for your help.

weldthedif

Take an ohm-meter to each injector, look for a short.

coug66

Tomorrow I will try taking an ohm meter to the injectors.

same condition car drives great maf sending accurate and consistent signals then I go very slowly to go up hill on gravel. I gas it to get up the hill and pop out goes the fuse and into limp mode it goes.

I thought it might have been a bad maf and since I have three of them I installed a different maf with same outcome.

so its ohm metering the injectors tomorrow.

coug66

its actually the fuse above the left arrow. 7.5 EFI #2 which directly affects the MAF function.

I have a suspicion that I frayed the wires when installing the spacer on the secondary downstream O2 sensor and going uphill and accelerating causes something in it to short which blows the fuse?

I havnt changed anything else recently and I swapped the MAF sensors with the same result. Up hill acceleration when I turn into my steep driveway causes the fuse to burn out

I accelerated n a flat road and no fuse issue. it seems on steep hill that a wire might be shorting during acceleration up hill?

I will remove the spacer and clean up and insulate any exposed wires on the o2 sensor.

I believe my cats failed prematurely due to installing cheap and defective coils and an engine that probably burns oil.

I was trying to solve the p430 and p420 code with spacers. THe drivers side was very tight and I might have pulled the wires causing a short?

coug66

This report may be early so I will let you know once I drive the car for a while. I went to put my car on a block and as I drove it up on the side with the O2 sensor in question the fuse blew on me.
going up and accelerating tripped the fuse.

I the removed the spacer and spread the wires apart and covered the area in silicone sealant.

The initial results are the o2 sensor readings are OK. I am going to wait for the silicone to cure and then test it on a road ride.

I will keep you updated once I have this tested.

coug66

Thank you for the information. As always you give the information clearly to understand and the supporting manuals.

I cant find a short in the system so far. What if I put a 30 amp fuse and let it short out?
I am Ok risking a new ECM since they are only a $100 on Ebay.

the wiring is so close I could just put a jumper wire and remove the old wire.

I will spend more time watching the wire and seeing if I can find the short.

I will also test drive the car for a while and see if I still get blown fuses.

Yamae

Are you sure on this?
Toyota would use a smaller fuse if the MAF were the only load.

rkw77080

In this particular topic of discussion, the symptoms included “EFI No.2” fuse being blown under acceleration and DTC P0100 being triggered. My observations and comments in this posting are therefore strictly related to DTC P0100. To this end, the only electrical load on “EFI No.2” is the MAF as depicted below.



I’m not an attorney by profession and my writings will not likely to survive scrutiny of an “are you sure” fact-check. Accordingly, I have removed my comments on this posting to avoid confusions.

coug66

I think my problem is solved!!!


it was the O2 sensor that had exposed wires and they were causing shorts that caused the fuse to blow.

The way I was able to determine this was early on I fought the MAF failing and the car going into limp mode. I took forever to find the blown fuse.

The fuse blew right after I installed the spacers. I thought I had fixed my cat issue and then my car bam at a stop light went into limp mode.

trying to fix it I took the O2 spacers out and it fixed the short but it took me weeks to find the fuse to get me out of limp mode.

I used rkw07780 schematics and his help and that's where I had this fuse and maf diagram from. when I went to trace the problem back to the fuse my issue went away.

Fast forward and my reinstallation of the spacers and I exposed the wires to the heat shields and the wires were shorting out EFI 2 fuse.

I found another ECM schematic and the downstream O2 sensors connect to the EFI 2 fuse through the white wire.

I am just really happy to have the issue resolved.


I should give another shout out to RKW77080 becasue he has helped me on several issues and cumatively it has enabled me to solve this.

I had no issues today and went to every situation that I had the fuse blow before all of them had no issues.

At the end it was easy to cause just go up hill and gas it. The car flexed and the fuse blew.

Yamae

So it was the heater line of the O2 sensor that caused the open fuse EFI 2.

coug66

I believe so, look on the engine management control wiring schematic and see the white wire connect from the down stream o2 to the fuse.

the best proof I have was the fuse blew three or 4 times going up steep hills and accelerating. I tried to recreate the situation and couldn't yesterday.

Yamae

Thanks for the wiring diagram. I now understand that the “EFI No.2 fuse" line powers 3 of VSV related solenoids/valves, 4 of O2 sensors and a MAF. Sorry that I didn't have any wiring diagrams for UCF30/31 and I was not able to inform you what should be checked. The only thing I was able to say was that usually Toyota seldom places only one load under one fuse to avoid placing too many fuses. If done so, there would be hundreds of them needed in a car. But Toyota does many experiments to design to optimize the fuse allocation. A 7.5A fuse for only a MAF was very strange to me.

It has been always a time consuming job to find out the exact short-circuiting point. As a RF engineer myself, I often use a TDR (Time Domain Reflectometry) to find it. It helps me to find the exact length from the measuring point but sometimes it is inside of the body and not easy to access.

Yamae

Thanks for teaching me, rkw77080. I know you are a nice guy who help others a lot and I admire you. Unfortunately the schematic above is not showing all the loads under the fuse EFI No.2. It is natural that you think the MAF is the only load as long as you see it.

I happened to know some about Toyota's way and I couldn't believe what you wrote. Sorry for the interruption by me but to help coug66 to troubleshoot quicker, I dare did so. Don't take me bad, please.

My intention is to keep our UCF series longer on the road helping each other. Since I know some of engineers related the car, and I always try to post what I know. Since you know things very well and may be we can do more in the future.