Firefyter-Emt

OK, on the way back North from deep southwest VA my 4Runner started doing this. To my best diagnostics, I have ruled it down to the fuel pump. Here it goes, (keep im mind, I was towing a 2000 lb camper with 32's and 4:56's) I found that after towing for an hour or so my truck would statr to sputter and buck but only if brought over say 3500 rpm at wide open throttle (WOT) If I lugged the truck in a lower gear at WOT it would be ok. If I pulled over and let it sit for a couple minutes it would be fine for about 20 miles or so (I am thinking it would start to heat up at that point) I also found that with a full tank of gas or about 3/4 it would then run for about 80-100 miles just fine. Elevation did not change it, I had it at close to 2000' and at 500' above sea leval doing the same thing. Now my cat is a year old, as well as the filter. The fact that if I fill it up it goes away for a long time vs a cool down leads me to think that the pump is getting hot when it has to work hard (IE WOT and less gas in the tank.) But once full, the gas cools it more and it don't have to push as hard. I was able to travel 400+ miles keeping the tank about 1/2 to 3/4 (yea, that was fun) I have bought a pump and it is going in anyway (Heck, it has 145k on it) But I thought I would just throw this out there for any ideas...

PS, Can I get at the fuel pump from under the seat??
:wtf: :pat: Dare I say I think my Jeep is more reliable??

Oh, did I mention that I have a rough idle again?? Gonna bring the 4Runner back to the guy who did the heads a third time now.. Damn, I need head work more often the firggin' oil changes!!

AgRunner06

Man that sucks. I can't believe you are having head problems AGAIN.

Anyways, I know that my truck was different but this is what happened when my fuel pump went out in my 1995 Dodge Ram. Once it got down to about a 1/4 of a tank and ran at 70 mph it would miss really bad and buck like you said. When this happened I would have to pull over and sit for 5 or 10 minutes. Then it would be fine for 15 or 20 minutes and do the same thing again. It's funny how much that sounds like your symptoms. And yes, the fuel pump was in the tank on the Dodge.

The fuel pump may also be contributing to your rough idle. So you may want to replace the fuel pump first.

I'd say the fuel pump is probably your problem. I'd go ahead and do it (since you have one anyways) then take your truck back to the shop for the head work.

You may be pushing it a little to say that the heep is more reliable than the 4runner.

Good Luck

asudan96Runner

I just got done doing the fuel pump in mine. (Yeah, I'm still dirty and all)

I did it because my old stock pump wasn't up to snuff.

Changing the pump is a PITA. I don't have a transmission jack, so lowering the tank sucked.

There is no way to do this without removing the tank - and there is an evap hose that runs from the top of the tank to the fill-up spout that is a major PITA to remove . (you can only drop the tank 4-5" until you must remove this.)

Once you get that hose removed everything is cake. I'd do this with nearly an empty tank. Gas is heavy.

Dan

AgRunner06

I don't know about the 3rd gens, but the 2nd gens have a drain plug for the gas. I hope you didn't go through all that trouble with the gas still in the tank if you didn't have to.

Firefyter-Emt

So what you are saying is that these is not an access cover under the seat?? Damn.. I thought I remember there being one there..

I don't think the pump is causing the idle though.. I runs rough when cold and gets a little better once it warms up.. Just like all the other times..

So in the last 1700 miles I have replaced the alternator (did I mention that it craped out on my down in PA for the EC4RJ.. leaving me out the best damn day of wheeling of the weekend!!) And now the fuel pump seems to be crapping out. Well hey, at least I had a full day to myself to wash my K&N filter while everyone else was wheeling! Farkin truck!! how much more crap can possiably break on it at once.. I know it has 145k on it... But Damn.. Do I have to replace every freaking wearable item in the last 10k miles!!

apc

Lee,

How are your spark plugs? Clean and gapped properly? I recall my Runner had the same symptoms as you describe, but without the 1/2 full, 3/4 full tank scenario. It turned out to be the gapping of the plugs. After 3 years without a tune up, the plug gap eventually increases.

Good luck.

Jay

I suspect you have debris in your fuel tank (rust / floaties). When the tank is low on fuel, the fuel is more saturated with this debris. It would be collecting on the fuel pump filter sock/screen. When you shut the car off the debris will float around, but when the pump is running, it is gradually being sucked against the sock.

Firefyter-Emt

Jay.. I like that theroy.. I will look when doing this job and see what the tank looks like. As for the plugs.. Brand new Toyota plugs (less that 10k ago like just about every other part on the truck it seems) If it is the filter and crud, I will be changing the pump ayways.. it does have 145k on it..