Pulsing Lack of Power when warmed up.

[BFG Previa]

Glad to have found this forum folks. Have a '91 AWD LE Previa with 384,000 km's (Canadian, eh!). Bought it off the original owner (Dentist) who took it to Toyota religiously, for everything, until I bought it in 2007. Bought it with 285,000 km's so I'm celebrating 100,000 km's of ownership with a mystery on my hands.

I've also maintained her religiously through a 25yr experienced Master Toyota Technician who loves Previas. But alas, I've moved and had to leave my mechanic behind (sigh). Now I'm on my own trying to troubleshoot this issue.

THE ISSUE: Once warm, and a load (usually going up a hill), the van will begin to pulse. The van jerks with power, as if someone is clamping the fuel line (Rock your head back and forth and you'll get what I'm talking about). When cold, or after it has sat for awhile I can put the pedal to the floor and she'll give me all she's got...shifting into OD at around 110km/hr and then going strong in OD. After it warms up, symptoms start and beauty turns into beast. Although this has only occurred while going up a hill, the other night (during the video attached below) I put the van in neutral and with the gas pedal somewhat depressed it produced the same pulsing symptoms (you can hear this near the end of the video)

WHAT I'VE REPLACED ALREADY:
- Plugs (2012)
- Wires (2012)
- Cap (2012)
- Rotor (2012)
- Cat Conv. (2011)
- Toyota Muffler (2008)
- Valve Cover (2012)
- Dist. O-ring (2012)
- TPS wiring harness and possibly TPS by original owner (My mechanic said he noticed this when I first bought it).
- Fuel Filter (2010)
- Other mechanical things but I don't think brakes and stabilizer bars would really explain the symptoms.
- I did put larger tires on 215/75/15 BFG AT's about a year ago. I hope these didn't mess


I checked for codes tonight. Straight blinking, no codes, on either CEL or OD lights.

Oil level is fine.
Tranny fluid is clear red with no sign of burning or shavings.
Good airflow coming out the tailpipe.

Included is a link to a video I took while driving. You have to listen very carefully and you can hear the engine sound closer to the end of the video best: http://www.youtube.com/watch?v=bNxAZ...ature=youtu.be



Thanks for your opinions in advance!

[BFG Previa]

Turned out to be a faulty Fuel Filter...had replaced it only a couple years ago but I suppose something messed it up somehow.

I've been driving it for about a week now and took it for a long weekend road trip and it didn't miss a beat once.

I was hoping it was something simple...especially because I was getting nothing from anybody on the forums!!!

Well, I suppose for $30 it's a good place to start when similar symptoms arise again.

Cheers!

[timsrv]

LOL, When you 1st posted I watched your video and thought fuel filter..........but you had already done that. Since I didn't have much to offer I didn't respond. Unless you have contamination in your system these filters should last for over 60k miles or 100k kilometers. Perhaps you got a bad batch of gas??? Since it's happened once I'd keep an extra filter around as it's likely to happen again. I sure hope that's all it was. Tim

[BFG Previa]

Bad news. My wife just called me on the cell as she is away with the kids on vacation up in the mountains or British Columbia. The van started acting up as it was before. Could it actually be another fuel filter? Again, this pulsing lack of power is happening on hills (under load) and usually when it's warm (especially hot today!).

There have been others on here that have had similar symptoms but the diagnosis has been MAF's, TPS, distributor and even starters (maybe not all those from this forum). I'm hoping my wife can limp it to our mechanic about 3 hrs away and go from there. Maybe there's crud in the fuel tank or a fuel pump issue?

Anyways, I know I didn't get much response on this last time, but I thought I'd throw it out there again.

Cheers!

[timsrv]

Since it's already plugged up twice in the last two years I would check this 1st. Fuel & air demand is the highest when the engine is working hard. If the problem only occurs in these conditions, then I'd be looking for restrictions in both of these areas. Things that can cause these issues are: plugged fuel filter, failing fuel pump, pinched fuel line, restricted intake air (filter or debris in air box), or plugged up cat converter. Another thing to check would be ignition coil (although I haven't heard of these failing on a Previa yet), pick-up coil (in the distributor), or igniter. There are other things that can potentially cause this problem, but these are the big ones.

Fuel & air issues usually won't throw codes, but electronic issues often will. Check the ECU for codes as this might give you some valuable clues. Good luck. Tim

[BFG Previa]

Thanks Tim!

She made it to her next stop after letting it sit for a few minutes and said it didn't miss a beat for the rest of the three hour journey. At least she wasn't stranded somewhere!

I'll be sure to look into the areas you recommended. As far as the original post goes, the van never threw any codes whatsoever.

Hmmmm...you know what...I did replace the fuel filler neck in December and they sent the wrong part and it was too short so I bought some fuel line (NOT CHEAP!!!) to use as an extension from the tank to the filler neck...could that cause either some kind of vacuum or pressure leak if one of the clamps has come loose or something?

[timsrv]

The fuel system should be sealed, but I don't think a leak there would create that problem.

[czechadians]

Thanks Tim!

She made it to her next stop after letting it sit for a few minutes and said it didn't miss a beat for the rest of the three hour journey. At least she wasn't stranded somewhere!

I'll be sure to look into the areas you recommended. As far as the original post goes, the van never threw any codes whatsoever.

Hmmmm...you know what...I did replace the fuel filler neck in December and they sent the wrong part and it was too short so I bought some fuel line (NOT CHEAP!!!) to use as an extension from the tank to the filler neck...could that cause either some kind of vacuum or pressure leak if one of the clamps has come loose or something?

Hi BFG,

I think we're having the same problem with our 95 Previa (265,000km), and so hope that maybe we can help each other figure out what's wrong. Although I should confess I'm not too mechanical ;)

In my case I am getting a CEL with a code of P0171 (System Too Lean (Bank 1)). I replaced my front oxygen sensor last October, and then at my mechanics suggestion did it again a couple weeks ago, but that didn't help solve the problem. I replaced the fuel filter a couple months ago but that didn't help either. I have an OBDII scan tool and so read live data as I drive. My long term fuel trim value is always at least +7% and can go as high as 24%, which I think is too high, but would love to receive confirmation of that. I know that I need to consider the sum of short term and long term fuel trims, but in my case, it's not unusual to have the sum of these two values above 25% which is too high for Previas, according to the research I've done.

Anyway, this hesitation problem last Fall and it has gotten worse. For us, it's most noticeable on hill climbs when the transmission upshifts into the next higher gear.

From reading http://www.edmunds.com/toyota/previa...liability.html, it sounds like the Throttle Position Sensor (TPS) and TPS Wiring Harness are common issues and so was going to start checking this out when I came across your thread. I guess you don't think these are at fault on your Previa?

Oh yeah, I almost forgot to mention that we also replaced our fuel filler neck in December 2011 and the part wasn't quite the right shape and so our mechanic bent it a bit and made it fit in. And since we were having problems before this, our hesitation issue is not related to this.

Cheers!

[BFG Previa]

Thanks czechadians!

According to my mechanic, our TPS was replaced a long time ago. He checked it when I started going to him and noticed that the wires had been extended by Toyota. I suppose it wouldn't hurt to re-check it though.???

I'm glad (in a self pity kind of way) that someone else is experiencing the same thing...it may increase the chances of pinpointing the issue.

What I found interesting was that it ran like a top for over a month after replacing the fuel filter! It acted up once for my wife on a 3-week road trip, and hasn't missed a beat since. I just want something to actually break so we can know what we're up against!

Good luck and I'll post anything which moves us in a positive direction on this.

Cheers!