Fuel Pump? Or...?

[denvermaxd]

2000 4Runner SR5 3.4 5-speed, 189,000 miles

Today as I was driving home from work, I merged onto the highway and was cruising along at about 55 mph when all of a sudden my truck lost power.

The engine did not die outright, all electronics kept working. I just suddenly felt the truck lose momentum and RPMs started dropping. I depressed the clutch and started pumping the gas a bit, but there was very little if any response (at highway speed in traffic I couldn't really hear the engine, but the RPMs didn't really respond to my throttle actions). RPMs kind of swung slowly up and down like the truck was trying to respond, but never really got above 2000 RPMs no matter what I did on the gas.

Glided onto an off-ramp, pulled to the side and came to a complete stop. At that point the engine died outright, dash lights all lit up.

Sat for a minute pondering my situation. Cranked it back up (maybe 30 seconds after the engine died). Truck started, didn't sputter but felt sluggish when I revved it. I let it idle for a minute or two, then took surface streets home. It never repeated the power loss, but a few times I seemed to feel hesitation or "weakness" in the throttle response.

I have a Scangauge II in the truck, and it shows no codes thrown.

A little history:

• Truck got a new OEM fuel filter about 2 years ago.
• I have noticed hesitation/weakness several times in the past, but it was so subtle (felt like a gust of headwind could have caused it) I convinced myself I was paranoid
• This summer I drove a road trip 400 miles each way, and at the very beginning I felt a definite "shudder" under normal cruising speed of 35 mph, twice. Spent most of the drive afraid the truck would die, but it soldiered through the entire adventure.
• Last weekend coming home from the mountains the truck definitely had 2 "hiccups" where it totally lost power for a second or two. It felt like bad gas.

I'm inclined toward suspecting the fuel pump is going bad, but don't really want to start throwing parts at it without some idea I'm targeting the right problem.

Any way to check the fuel pump beyond the "pressure at the rail" test? Clearly, there's intermittent pressure, as I drove 20 miles after it died.

 

[4Reak Show]

I've been a technician for an independent shop for 10 yrs and have not seen a fuel pump go bad on a Japanese car. That being said, obviously it's not unheard of, just highly uncommon in my experience.

Based on what you're saying I'd stab at a bad mass air flow sensor. Vital input for engine performance and that's a much more common failure.

Many write ups of cleaning and such around here. Those can be expensive to replace however.

Good luck

 

[denvermaxd]

I've been a technician for an independent shop for 10 yrs and have not seen a fuel pump go bad on a Japanese car. That being said, obviously it's not unheard of, just highly uncommon in my experience.

Based on what you're saying I'd stab at a bad mass air flow sensor. Vital input for engine performance and that's a much more common failure.

Many write ups of cleaning and such around here. Those can be expensive to replace however.

Good luck

I cleaned the MAF a year or two ago. I do have a K&N filter, which I'm now seeing has lots of negative opinions floating around.

Would a visual inspection reveal anything?

I have some MAF cleaner still, maybe I'll clean it tomorrow morning and put in a stock Toyota filter.

 

[denvermaxd]

It's weird that the engine could completely die like that and throw no codes, especially if it happened because of a sensor?

 

[JayRolla]

I've been a technician for an independent shop for 10 yrs and have not seen a fuel pump go bad on a Japanese car. That being said, obviously it's not unheard of, just highly uncommon in my experience.

Based on what you're saying I'd stab at a bad mass air flow sensor. Vital input for engine performance and that's a much more common failure.

Many write ups of cleaning and such around here. Those can be expensive to replace however.

Good luck

That's because denso is bad ass!! That being said I've had them fail in my DSM (Mitsubishi) and in my 4runner. I've had three failures in my time. Each instance I could hit the fuel tank with a hammer and rod near pump and it would bring there pump alive enough to start it drive home. It's a good test.

 

[miken6570]

I think you have a bad connection or corroded line from the top of the fuel tank to the fuel pump. You have to drop the tank to get access to the corroded line.

 

[denvermaxd]

I think you have a bad connection or corroded line from the top of the fuel tank to the fuel pump. You have to drop the tank to get access to the corroded line.

Well, I hope that's not it, but we'll know eventually!

I pulled the MAF yesterday, and it was really dirty, so I cleaned it thoroughly with MAF cleaner. Also pulled out the K&N filter (which was filthy) and replaced with a standard non-oil filter.

I'll drive it and see if the symptoms continue. If they do, I'll remember your idea and circle back to it.

 

[denvermaxd]

UPDATE: Slight power loss again today

So a couple weeks ago when I updated this thread, I had cleaned the MAF and replaced the K&N filter with a Fram filter. This was all done during the process of installing a 2nd generation TRD Supercharger.

Truck has been running well after Supercharger install, but obviously feels and sounds pretty different from how it felt pre-Supercharger.

Today driving home from a friend's house I felt the same "weakness" I have experienced before. The engine didn't die, but for about 2 seconds there was an obvious power loss—I feel forward momentum fail, engine sounds weak. It literally is over so quickly that by the time I glance at my tachometer or Scangauge II, the episode is over and nothing shows any record of it ever occurring.

If it wasn't for the singular experience that prompted this thread—full power loss to the point where the engine died—I would almost be convinced it's in my head.

Today it happened while cruising around 50 mph, 3200 RPM. I had just accelerated to pass someone, and was rolling along at a consistent speed and power when I felt the "lurch". It feels very much fuel related, but who knows?

Any tips or tricks I might use to try to isolate and resolve the problem?

 

[RPS99SHO]

I didn't see anything in this thread about spark plugs and wires. I was having the same symptoms in mine at 194k. Replaced them all and have not felt it since. A few miles short of 200k now.

 

[denvermaxd]

I didn't see anything in this thread about spark plugs and wires. I was having the same symptoms in mine at 194k. Replaced them all and have not felt it since. A few miles short of 200k now.

The plugs are brand new Denso IK22s, and the problem preceded them and continues with them, so I doubt it's the plugs.

I replaced 2 out of 3 ignition coils when I bought the truck 4 years ago, and got a new wireset from Toyota at that time, too. Could be the 1 coil pack I didn't replace, I suppose.

Still surprised this doesn't fire a code.