Abrupt loss of power

Hello everyone! Yes, I'm a noob. My technical experience is in motorcycles, but mostly off-road! My '04 Toyota PreRunner 3.4l V-6 has an issue that is eating my lunch. Any help would be greatly appreciated!! Here goes.... while driving under normal conditions, engine loses power abruptly, tach drops suddenly, then returns just as quickly. The problem does not happen until engine is sufficiently at operating temp., usually after 20 mins. of driving. Intervals of power loss start increasing quickly, but the engine will Never die out, but will not rev up unless the accelerator is pushed to the floor, and then, it takes about 3 secs. to come to life again. When it does wake up, it will pull as far as I want it to, but, the power seems sluggish at this point. The only way I can get this problem to go away sufficiently, is to get down to 35 - 40mph, stomp the throttle enough to engage the passing gear and hold for 3 - 5 secs. The problem disappears until speeds drop to 45 - 50mph range, but it is still pretty random. The problem rarely shows up at highway speeds. NEVER AT ANY TIME, DOES THE ENGINE CHECK LIGHT EVER LIGHTS UP!! NO CODES WHATSOEVER!!!I was reluctant about it being a fuel filter issue, so I didn't change it. I know a genuine Toyota Technician, so I contacted him. He hooked up his 15yr. old scanner, and he felt the Mass Air Flow sensor was the culprit according to its parameters. So, he installed the new OEM MAF sensor, cleared computer memory, and sent me on my way. After 15- 20 mins of driving, it shows up again.... no change. I finally decide to change the fuel filter, and the engine response is significantly improved. I take it for drive, about 30 mins long, and No issues. I start thinking to myself, what a fricking dummy I was, waiting so long to change that filter....what a bozo I've been... I could just kick myself!! However, I'm still not convinced it was gone, so Sunday morning, I take it on a cruise through the country. There was no traffic, no start - stop, just steady driving....still no issues. Get in it later that afternoon, drive into the city for about a 1/2 hr, and can You guess WHO shows UP?! That's right, my stalling issue!!! I decide to take it a private mechanic that owns his own shop. I've known him for years, and we have mutual respect for each others knowledge in our respective fields. He checks for any codes, checked all parameters (all test fine, with the exception of a O2/ fuel/air sensor just before exhaust enters the catalytic converter), but NOT EVEN THIS WILL MAKE IT THROW A CODE!!! I fixing turn the safety off my 12guage, and have a chat with my truck!!!!! My thinking is, the fuel filter may have been somewhat restricted, which was making the fuel pump work harder. This is turn caused it overheat, and thermally failed. But everyone I speak to say, that when a fuel pump fails, it stops...period. It is never intermittent. Sorry for such a long post, being a newbie and all, but anyone who has had a similar issue with this engine issue, please help me before I have to repair the holes in the block from the slugs of my 12ga.!! Thank you for reading! Keeneaux

 

I know this is way off but include checking the ground strap from the engine or any ground point for the electrical. I have a hunch-

 

Thanks Ridgerunner, but I actually have checked the groundstrap, and it was a solid connection. But please don't give up on any other suggestions. I'll entertain just about any thought on resolving this issue. Thanks for the input!

 

Plugged catalytic converter? I have heard stories of the insides moving back and forth like a check valve.

 

OP, did your old fuel filter have a bunch of crap in it? I think you may have the culprit, sounds like you have some crap in your fuel tank that's plugging the filter up. I'm only basing this on you saying it ran great for few days when you changed the filter and is now acting up again. It's reasonable to think the new filter would take a little time to get clogged. Was there a bunch of crap in the old one when you replaced it?

 

but it runs well when you have the accelerator floored? Sounds like a bad o2 sensor to me then. Anytime you are in open loop (warm-up or wide open throttle) the truck is running well. Anytime it is inbetween and relying on fuel maps, the o2 sensor is misreading and your computer is giving the wrong fuel mixture.

did you test / replace the o2 sensor yet?

 

I didn't find anything in the fuel filter to speak of, not even any signs of water. I had a mechanic gave my truck, a look over and the only O2 sensor he found giving readings, that may have been out of spec, was the sensor just before the catalytic converter, but also, he said that it should throw a code. It doesn't. A plugged catalytic converter has crossed my mind. Both Fletch aka, and 98tacoma27, may be on to something. I will check the "glowing technique", good idea by the way. This may be what is causing the sensor ,just before the catalytic converter, to give my mechanic the questionable readings. I will let you know my findings on the C/C. Vegetopia, it only will respond to a full throttle to get moving again. And it does idle fine.Believe me, it is not running normal at that time either. It is rather sluggish and will usually get back to normal afterwards. But, I guess I'm asking you, why won't it throw a code, if it is an o2 sensor? No, I didn't test it myself, but I'm pretty sure my mechanic did, since he's the one who found the sensor before the C/C to be giving questionable readings. Which again, has me questioning the C/C. My auto mechanic skills have not kept up with the current vehicles, simply because....I own a Toyota. These vehicles never give me issues. which is why I own one. Back to my skills, I have no clue how to test an O2 sensor. I'm guessing a volt meter? If so, how would I go about it? Parameters? Electronics have never been my forte'. My knowledge is still stuck in the older motorcycle days, and even that is based mostly in my simple little 2-stroke engines. And those don't have ANY o2 sensors....LOL! I know enough to know, that I'm out of my league.LOL Again, a BIG THANKS!! to everyone for the input, and I'll post my findings asap!

 

TPS?

 

i would grab a new o2 sensor from autozone and try it out. The one before the cat is the one that would be giving you your problems, so if it is not testing within spec, then I again say it might be your culprit.

if you swap it out and it works, you're golden. If not, then you can return it, just try and keep it a bit clean

I can't tell you why the faulty o2 sensor (if that's what it is) isn't throwing a code. Maybe it's just close enough to out of spec that the ecu isn't picking up on it? No idea.

g/l



TPS (throttle position sensor), like crazy suggested, might also be a good one to try.

 

Sounds like a sluggish O2 sensor.

Do you have access to an O-Scope? Or graphing scanner?

 

I do not have access to a O-scope or graphic scanner. As for TPS, well, on the 3.4L v-6, Toyota does not offer it separate from the throttle body, and throttle body sells for a cool $1034.00! Yes it does have screws holding it to the throttle body, and it even has a part # stamped on the actual TPS sensor, but the part# is not available!!! I will try the O2 sensor you suggested. Thank you again for the input!

 

OP, I don't mean to scare you but something to maybe keep in the back of your mind. If you're finding sensors giving faulty readings and its not throwing code, your ECU might have some issues. I had this problem with an old car and once I replaced the computer, then I found everything else that was wrong with the car. It's a slippery slope. I'm hoping it's not the case with your truck but like I said, something to keep in the back of your mind if you find a handful of faulty sensors and no error codes.

 

do a search for that part number on the net. I bet someone will have it.

OR go to a pick a part. OR I'm sure you have friends with the same truck? Just ask to swap it out real quick.

 

Just to cover all the bases, have you checked the spark plug wires, boots, distributor/coil packs for arcing? It will show up as grayish white discoloration. Detonation and knocking will set codes, but a miss may not.
A fuel related problem can be diagnosed with a pressure gauge on the manifold. Run it to the cab and drive it.
Throttle position sensor is attached to your right foot as you drive. Disconnect it, attach an ohm meter and look for a steady change in resistance over the pedal's range of motion.

Happy hunting.

 

not probable but here is another option. check all the vacuum hoses. a buddy of mine rebuilt an old toyota motor and couldnt find where all the lines went so just plugged them with bolts (dumb i know) but he had a similar issue at idle where it would almost stall out then rev way up then back down to almost stalling

 

Well, I think I may have found the source of my problem. The morning I replied to DocBrown about the O-scope, I found out a relative had passed away, and her wake was held that night. I drove my truck that night, and sure as hell, it started losing power while enroute on the highway. I made it to the funeral home, and realized I'd needed to get fuel on the way home.I stopped at a no name gas station and I noticed there were no stickers on the pump regarding ethanol, so I inquired to the store mgr. about it. She informed me they were still buying NON-ethanol fuel, and also informed me they owned another station that was just down the road from my home. I put 5 gal. worth and went on my way. From this point on, the power loss issue has DISAPPEARED completely. I never changed the O2 sensor, and never found if the catalytic converter was glowing. My intentions of driving the truck the distance( about 30mins from my house), was to get the cat glowing good and hot, but it NEVER had an issue on the way home, and I didn't think much of it. I figured it would show up again, but it hasn't. So, either there was trash(water) in my fuel, and I've completely lost my mind to keep me from recognizing the visible signs in my fuel filter, which is highly doubtful, Or my truck absolutely hates being filled with fuel that contains ethanol. So, I'm sticking with the "new" fuel station, and I'll post my analysis of my observations in a week. Again, and I can't stress this enough, THANKS!! to everyone for their input!!!

 

That seems bizarre! Ethanol should only HELP a vehicle run better, bot hinder it. Ethanol has an effective octane rating of like 130 ( I don't know exactly...) but it's higher than race gas. Should help prevent detonation and give you overall increased performance.

Anyways keep us informed!

 

Yeah, I guess you're right. When I think about ethanol, I am coming from the forced induction world where it's a godsend for controlling detonation at high boost.