Well, new to this site, hopefully I can draw on the vast resources of the many experienced individuals here. This is long so bear with me. I have a 90 v6 3.0 4runner with 100k on it. I peformed a double head gaket job along with the perifereals (timing belt, etc.) Vehicle ran excellent for the first few months then slowly but surely an interminent problem started surfacing. Now its all the time.

Here are the symptoms. It will not rev beyond 3 to 4k rpm. As the throttle body is opened, a threshold point is reached where the engine suddenly starts cutting out and continues to the point WOT. when at wide open throttle, the engine sputters and misfires barely sustaining 1200 rpm. I am extremely sure this is a fuel issue. Here is why, when I introduce raw fuel or carb cleaner through the pvc inlet tube by the throttle body, rpm shoots up and through the roof and sustains if continued.

I have checked, replaced and done the following;
1. Fuel filter replaced twice.
2. TPS replaced with new part and set.
3. Fuel pressure regulator replaced with new.
4. Fuel pump and tank filter replaced with new.
5. Fuel tank drained, inside checked including tube into baffle.
6. Air box swapped out for second unit.
7. ECU swapped out for second unit.
8. Exhaust uncorked before cat.
9. Temp sender for ECU ohm checked at unit and at ECU plug.
10. Checked ohm, voltage readings for airbox, tps, temp sender, fuel injectors (no.10,no.20), all these things checked at the ECU plug also.
11. Checked spark on all cylinders even though fuel issue, checked ok.
12. Flow tested new pump, was excellent.
13. Pump energizes when airbox flap is opened.
14. Infector cleaner added n ran through three times.

Now, as you can see to this point i've checked a lot. I have 1990 factory manuals at my disposal. I have not been able to check the knock sensor as I do not know how to do so and how to jump it out so that the ECU thinks it is ok. I did replace the knock sensor wire as i was warned to do so by the dealer do to heat degragation of the wire. Like I said, if you manually add fuel, you instantly get the engine to come to life, it is as if the injectors are not fire-ing or they are being cut out. I love my 4Runner but I am feeling like it should be crushed by my dozer at this point. Any help or input would be very much appreciated. Thanks n great forum.
RII.

 

have you checked the distribitor cap for cracks or water also maybe the coil or ignighter timing could be off on the cams. if all else fails i can hook you up with a dozer

 

I doubt it's that because adding fuel wouldn't increase the rpms because it isn't firing correctly. My guess is it's the AFM. These have been known to go out. If it isn't sending the correct signal to the ECU, the injectors won't fire when they are supposed to for the time they are supposed to. Try swapping in a used one and see if that fixes it.

I originally thought fuel pressure regulator but you already did that.

Good Luck and Welcome to the site

:bounce2:

 

Thanks agrunner, do you mean by AFM the airbox, i tried swapping that too and did all the checks on it that the factory manual said, checked ok

 

That vehicle had a MAFS?

 

says that he swaped the air box out isnt the afm on the box?

 

Yep, you guys are right. My bad.

Duh!!! Why didn't I think of this earlier. Check your timing. I'd be willing to bet your problem lies there. It seems like the only logical thing left that you haven't checked.

 

How about the valve adjustments? Maybe a valve or two is not opening/closing properly.

Also, what about a clogged injector? If an injector is electrically ok, but clogged, wouldn't it still read ok through a multimeter? Maybe they should be pulled and cleaned.

 

First check your codes....then clear any that might be present and rectify whatever may be up....

if that doesnt rectify the problem I bet you have timing belt issue OR there is a fualt btwn the VAFM and the ECU when the ignition is energized however this will throw a code...

I doubt a valve having the wrong lash is the culprit.... On exhaust valves, the lash tends to decrease with wear as indicated by my #6 exhaust valve, 0.003" lash when spec is .013" to 0.009". This leads to fine performance until the valve burns out from not closeing.... I've never heard of a valve's lash increasing from use though, but IF that were the case, this could casue your problem

Could definately be a clogged injector or the fuel feed line from the in tank fuel pump. Ever test your operating fuel pressure?

 

I had one of these with the O2 sensor failing that did this.....Toyota Japan did not want to replace the O2 sensor becasue it bench tested just as your has ...after the replaced it the problem went away.....If I read correct the "idle" is smooth up to 3-4K then cut out and sputter to WOT but what happens when you come back down to "idle" does it smooth back out? and just to make sure I have to ask...the CEL is not coming on during any of this?

 

Fuel pressure was checked, was excellent, flow is excellent. My friendly retard mechanic cut the line in half to check it n installed a plastic tee which I later used to check flow n pressure before replacing with a brass union. As for the timing, I believe I already checked it and it was good ( I'll do again). Did all the checks of the feed from the Airbox to the ECU. Did these checks at the ECU and was to manual specs.(voltage n ohms). I fail to see why the timing would affect it in this manner being that when I introduce fuel it picks right up, am I missing something Can the knock sensor cause this problem?, and if so how do I jump it out? I have not pulled the injectors or rail yet to check for obstructions, this will be next if all else fails to be wrong. Thanks for the input guys, it is really nice to get more input. By the way, two mecks couldn't fix it and i refuse to go to my local stealership, they're not very bright <----<<< 4Runner.

 

Ya dragon, thats right. it smooths back out when it drops back down and yup the voltage checked ok when read at the plug. If the O2 sensor was failing, wouldn't it just go to a fail safe mode and operate fairly normal Could it be that the O2 sensor is fractured?!?! and shows it's ugly head at rpm? Oh, I have a dumb question, what is the CEL??? Thanks

 

CEL = Check Engine Light

 

Iron,

Could the air meter be what is jacking you up....I know you tried a differernt one but the problem is only coming in when the vane on the meter has to open wide to let the air through......I do not like that one as when you put more "fuel" in the problem seems to clear, which points it to a fuel problem...you have checked all the fuel parts up front and the filter, I also see a flow test on the pump was that at the return line to the tank at the tank, if the return line to the tank clogged up it could cause this problem yet flow from tank to eng could check good depending on where the test point was....now for another really good one....could the fuel supply and return line be crossed.....I have done that on more than one eng and a couple of time they would run sometimes they wont even start....I do not want to go with a clogged inj as you do have the smooth idle but the inj could have a flow or spray pattern problem that would only show up at higher rpms....ME i would check the sig from the air meter at the ecu while opening the vane by hand to rule it out, then check the fule line from begining to end looking for a pinch or crack that could restrict the flow of fuel. Then check the fuel return line at the tank for good flow while at idle and while the problem is coming in at or near the wot area. This is a strange one as you have a nice run at idle and you can get a "nice" run at wot by adding fuel. The big ticket fuel items have been changed yet the problem remains....after the above all that is really left is the inj system itself......and the knock sensor.....but I do not see how that one could be casuing this problem.....

AgR,

I do not know if helps you but I have the FPR.....in Japan......it is the same one but shipping could take a week or even longer....

Dragon

 

In attempt to keep it simple.....
The dealer removed my fuel tank for service. When I got it back, it had zero power above 3k rpm. It would barely run at all. Obviously they didn't test drive it!!
The problem was a hose that got kinked when they put the fuel tank back on. Whatever it was only took them an hour to fix.
Good luck!!

 

Iron, any update on the problem?????