Horribly degraded performance

I'm running a 2008 Toyota Tacoma prerunner with almost 330k miles on it. Has been an outstanding truck up until the last 10 to 15k miles with performance issues.

It's a lot worse than it use to be. It use to just kinda bog and buck when you try accelerate from a stand still or at speeds under 65 mph. A buddy of mine assumed it was a fuel pressure issue. I test fuel pressure the incorrect way by deadheading the gauge on the fuel line. I got a reading of 60+. I assumed that wasnt the issue and really started to go down the line.

I've replaced the MAF and that helped a considerable amount up until about 6 or so hours after the replacement then it started to run like crap again. I researched and researched and came about the throttle body being dirty. It was pretty caked. Probably a dime's width of carbon build up. I cleaned it, reset the ECU due to it revving really high as expected, and did it again and I swear it running worse than it ever has before.

The only codes I've ever got were lean codes on bank one and as I was about to clear that code my engine rumbled and the check engine light came on after that and said it was bank 2. Keep in mind this happed after the MAF replacement and before the throttle body cleaning. My brother-in-law, who is an instructor for automotive mechanics at a college, suggested it was a clogged cat. (He hasn't been much help in this situation believe it or not) I put a vaccum tester on the truck and it reads normal vaccum.

I'm at a stand still. I'm getting horrible hesitation in acceleration from a stop, a pulsing drop in rpm cruising between 45 to 60 mph, fuel economy hasn't changed all that much considering it has sucked since the day I got the truck. No abnormal smell from the exhaust. The last thing I can think of is when you suddenly give it gas cruising along at whatever speed it will misfire but wont throw a code.

Sorry for the long post but I've been battling this for well over a month. Any advice would be eternally appreciated.

 

I would look to see what your short term and long term Fuel Trims are at currently.

Just because you have fuel pressure doesn't mean it's getting to the cylinder.

 

Based on what I've read here, I would wonder about the condition of the fuel injectors.

 

Considering what you two just said, would fuel trim issues come from bad/dirty injectors?

 

Fuel pump 2nd speed failure. It's failing under load. You need to test pressure while driving.

Pump's dont have check engine codes. They can only cause lean codes.

 

Do you have any recommendations on a tester that can be used on a Tacoma while driving?

 

At 330k miles don't bother testing fuel pump, just replace. They are fairly cheap and easy to fix.

 

I’m not questioning you. ( I think you are an actual Toyota Tech, Right?)
But I didn’t know the fuel pump had different speeds.

I have heard of a case where the filter/screen was clogged. (In the tank)
In the case, it would run fine under light load.
But couldn’t keep the flow up under higher engine demand.

Either way, I think you are on the right track with the fuel pump.

 

2005+ tacomas and 2007+ tundras run the FP power through a resistor at low speeds, and straight power at high speeds. The pumps like the low speed and often idle fine, but cut out on power once the demand for full flow is asked.

The resistor is located by the drivers headlight.

 

Lol. And now I know how the FP Resistor works.
Thanks man. This place (TW) is addicting.
You can learn something new every day here about our trucks.

 

I appreciate the input. I'm just gonna say screw it and throw a new pump on it. I've been trying to avoid it but there seems to be no denying. Plus it's like $150-$300 for it

 

Hopefully the tank is low on fuel.

I haaaaaaaaaate doing pumps on full tanks.

Good luck! Hope we are correct haha.

 

I can be a tight wad but not when it comes to that truck. Its probably the most expensive part I've ever bought for it alone lol. I think I'll just end up pulling off the bed so I'm not having to work laying on my back as much as I possibly can.

Hopefully that's the "easier" way. I've helped drop tanks and they were a pain.

 

You haven't said anything about the plugs, have you checked them?? Before throwing a fuel pump at it I'd check all the basics first.

 

I replaced plugs at the 305k mark if I remember correctly. I was probably 50k over due at the time.

 

Look at this:



You see where the ECU controls the Fuel Pump Relay which Inserts the Resistor or Bypasses the Fuel Pump Resistor as demanded by the ECU. With the resistor the pump runs slow, without the resistor it runs fast.

 

Thanks for the actual explanation.
Makes it even better with visual reference.

 

I'm just curious what the ECU reads to determine the FP speed...throttle position? rpm?...all of the above?
Cheers, Jeff

 

The only explanation I have is on the schematic posted here: https://www.customtacos.com/tech.ol...6toyewd/06toypdf/ewd/2006/tacoma/h/em01d3.pdf

∗ Fuel pump control system: The engine control module supplies current to TERMINAL FPR, and controls the operation speed of the fuel pump with the FUEL PUMP relay.

Contrary to what many think the fuel pump relay is not what energizes the fuel pump. That is done by the ECU through the EFI Relay and then the C/OPN Relay which provides power to the Fuel Pump Relay. The fuel pump relay is either in high speed position or low speed position, there is no off position. The ECU then switches the ground to cycle the Fuel Pump Relay between high speed and slow speed operation as determined by the ECU.

 

Thank you, sir.
We've come along way since the mechanical, diaphragm controlled FP that was on my '74 Corona SR5.
jeff