Efi fuse short, power loss

Basic info: 2009 6 cyl. Auto Access cab Tacoma TRD Sport, bone stock 90k miles

Story time; I was driving home on the highway last night. I had just filled the tank with gas. It was raining pretty good and water was pooling on the road. After about 20 miles of this I noticed I was getting some hesitation and power loss on acceleration. I would be at medium throttle and power would go in and out every second or two in a rythmic pattern. I waited until today to take it for a drive and the same thing was happening. Except this time I made it less than a mile and it stalled and wouldn't start. The air filter was a little damp, not wet, and clean.

Now for the current problem. It blew the efi no. 1 fuse. I replaced it, turned the key to on, I could hear the pump prime up. Go to crank it and it blows the fuse. I put another fuse in, this time I took out the fuel pump relay. It didn't blow the fuse. I need to try this again to confirm but had to go to work. So, any ideas? I'm good with electrical tracing and testing and obviously something is shorted. I need a manual for the circuitry to see what all is down stream of that relay to start testing. Anyone have one?

Update: Bad fuel pump. More details below.

 

Maybe the MAF is fried because of the water that got through the intake.

 

Update: It's no longer blowing the efi fuse. Which kind of sucks because I got a bunch of fuses and was just going to unplug stuff until it didn't blow. I'm still having the stuttering with acceleration and it finally threw a CEL. P0171, P0174, Lean bank 1 and bank 2. Its bad enough I don't want to drive it. I'm going to grab some electrical contact cleaner from work today and clean the MAF. If that doesn't work I'm going to wait for my buddy with a Tacoma to let me try his MAF. I really don't want to throw parts at it. Does it make sense that something got wet and shorted to blow the fuse then dried out and is no longer shorted? Also, Is there a big difference between the Toyota MAF and the Denso with the same part number? DENSO Part # 1976030 {#2220422010}

 

Cleaned the MAF, no change. It's still not blowing the fuse but a little hesitant to start and you can't even Rev it up in park with it stuttering and hesitating.

 

20 miles is a bit much for bad gas w/o really showing symptoms early, but it's the most obvious. You didn't indicate you'd soaked the engine running thru a flood.
Reco. drain the tank/siphon if you can and replace the fuel. IF the fuel is really that bad it'd be hard to tell how any of the fuel system electronics would react. EFI fuse may blow if it sensed plugging of the injector(s).
Also lean bank1/bank2 might indicate this too. If it was only a single bank it'd be different but it sounds like both front air fuel ratio/o2 sensors are bitching like crazy so both sides (separate left/right exhaust manifold sensors) of the engine are reacting the same.
Sure no one put some sh!t in your gas when you weren't looking. Hopefully no diesel mistake but that's hard with pump nozzle setups.
I'd say you may have a bad coil or 2 but I think they're a long shot for your symptoms.
Fuel change-out first imho.

 

This is what the service manual says are the trouble spots for the P0171/P0174 codes:

• Air induction system
• Injector blockage
• Mass Air Flow (MAF) meter
• Engine Coolant Temperature (ECT) sensor
• Fuel pressure
• Gas leakage from exhaust system
• Open or short in A/F sensor (bank 1, 2 sensor 1) circuit
• A/F sensor (bank 1, 2 sensor 1)
• A/F sensor heater (bank 1, 2 sensor 1)
• A/F sensor heater relay
• A/F sensor heater and A/F sensor heater relay circuits
• PCV valve and hose
• PCV hose connections
• ECM

I would look at things that are common to both banks such as the air intake, MAF ...

 

Try disconnecting the MAF and see if it runs better. If so you may be on to something.

 

I tried that, it dies immediately. Which from what I've seen is what it's suppose to do. Thanks

 

I can't be positive someone didn't put something in my tank but it's highly unlikely. The engine did get wet as well as the intake. I'm going to dig into this weekend. Thanks for all the help I'm going to try everything I can.

 

It isn't going to run without a MAF connected.

 

No misfire codes - either random/multiple or cylinder specific? Even though it's noticeably stumbling / missing?

I'd still pull your coil packs to check for moisture in the spark plug tubes - blow them out with air or compressed air to be sure. Misfires can cause lean codes, since the primary O2 sensors are reading the oxygen in the unburnt fuel / air mix - therefore reading lean.

If all OK there, check fuel pressure. A failing fuel pump will cause both of your symptoms - both the fuse blowing, and low fuel pressure. It may not be related to driving though the monsoon at all.

 

I wasn't sure if yota was like my ferd as if it ran better disconnected it was the maf. Good info to know as I'm not up on Toyota just ferd and chebbys

 

Today I took it for a drive and I'm still getting the hesitation and it didn't make it but 1/4 mile and blew the fuse again. This time I happen to feel the fuel pump resistor and it was hot, real hot. I looked up the specs and its suppose to have a resistance of .71 to .76 mine is .5X (meter only goes to tenths). Trying to source a new one, its 50 bucks from the dealership and will take a few days from the warehouse. Anyone have any experience with that problem. Could that be my problem?

 

I would guess a partial short to ground Down stream of that resistor. There isn't much difference between 0.71 and 0.5X Ohms.

 

Agreed, especially if it was still hot when the resistance was measured. I'm going with first guess of fuel pump, 2nd guess of short / ground in the wiring to the fuel pump.

 

Update: It was the fuel pump, it runs great now. One thing I noticed when I was going through everything that I want to point out in case anyone else has a similar issue. Pin 5 (output to pump) of the fuel pump relay while running is supposed to have 10v at idle then up to 13.4 with gradual increase when adding throttle. Mine was 6v, not gradual increase just jumped to 13.4 at WOT. I measured this on two Tacomas. The resistance of my pump motor was .06 well below spec and the reason it was over current and blowing the fuse. Not having a fuel pressure tester this was the best way I could try to diagnose it.

I also want to add I took the bed off to do the pump. I had just filled it up and didnt feel like draining it for balancing a full tank on a jack. It was very easy to remove the bed. Undo the taillight harness, power outlet, and back up camera. that harness is secured to the bed underneath along the bumper, unclip that. Take the six T55 torx bolts out. The filler neck will just slip right out of the opening just take the cap off. Its fairly light and was able to lift it off with just two people. Then you have wide open access to the pump. You could do it in about 2 hours if you tried, I was testing everything along the way and taking my time not to mess it up.

Thanks everyone for the help!

 

Landphil for the win