Hello Everyone,

I am brand new to posting on forums so please excuse my ignorance when it comes to selecting the correct forum. I have a very odd problem happening to my 1988 Toyota 4runner SR5 22re. At temperatures around freezing or below, the truck misses and hesitates at WOT on the Highway usually in 4th or 5th gear (around 60-70 mph). When this happens the power is substantially cut i guess for obvious reasons. The truck has around 294,000 miles on the body. I just recently rebuilt the engine myself around 7,000 miles ago and it has great compression and burns no oil. Here are a list of parts that I replaced during the rebuild:
New TPS Sensor (OE Genuine Toyota)
New Oxygen Sensor (Denso)
New Fuel Filter
New Fuel Pump with sock (Denso)
New Fuel sending unit (old one was too rusty for me)
New plugs, wires, rotor, and cap (Denso, NGK, generic, generic)
New ECU temp sensor (Genuine Toyota)
and other parts that are not directly related to the fuel system such as transmission ect.

The odd thing about the problem is it normally happens early in the morning when I am headed to work and it is cold outside. When I leave for work in the afternoon and the temperature is a little warmer the truck runs like a champ. No hesitation/power loss at WOT. Timing is set right on 5 degree BTDC with the diagnostic port jumped and my fuel pressure is excellent. I made sure my TPS is within spec according to the FSM. Also, I might add that when it is hesitating at WOT and I gently let off the gas I can feel it buck a second or two and then it smooths out. I checked my VAFM and everything is within spec as well

I am by no means a mechanic or expert and I humbly ask for help. My only theory that I have is that it may have something to do with the VAFM temp sensor, or the VAFM door "movement". Would that sensor adjust fuel mixture due to temperature or no? Like I mentioned above, this ONLY happens when it is at freezing or below. The truck starts hot and cold perfectly and it idles like a champ. Any advice that you guys may give will be greatly appreciated. Thank you for your time and efforts and I am like you, just wanting my runner to run like a well oiled machine.

 

Welcome!

This thread is in the wrong section (it should be in the 1986-1995 Trucks/4Runners sub-forum), but a moderator will have to move it. No big deal.

How warm is the engine when you are at Wide Open Throttle and the problem happens? Is it up to operating temperature yet?

 

Does the vane in the air meter stick when it's colder out?

Yes the intake air temperature is an important part of the air fuel ratio calculations.

 

Thank you old87yota for the reply. One day I'll get it right haha. The engine is at full operating temperature when it happens, and it only happens at colder temperatures. I meant to add that the valves are adjusted correctly. I just am stumped on what it could be

 

Co 94 PU: It doesn't seem to be sticking when I tested it by hand the other day when it was cold. I guess i am just not sure what the "mechanical" resistance should be on the flapper door. In other words I am not sure how stiff the door needs to be when opening. It seems to be smooth and returns quickly when pressure is released from my hand.

 

Has anyone else experienced anything like this before?

 

Good morning Yotatech,

I hope everyone is staying warm, especially after this polar blast that has hit us. I am still at a loss here. I am still having an issue with 4 runner. This morning on my way to work the temperature was around 19 degrees. The truck started right up and I was on my way, but when I hit about 3rd gear it started missing like crazy and I couldn't get over 35 mph. It felt like I was dragging something. I went ahead and changed the VAFM since my readings were indeed out of spec. I am really confused because the missing problem ONLY happens when the temperature is under freezing. When the temperature is above freezing the truck runs like a top with plenty of power. i for the life of me can not figure this out. It is really frustrating and embarrassing, especially only going 35 in a 45 during rush hour traffic. Any help would be GREATLY appreciated.

 

bump.

 

Alright everyone who is more mechanically skilled then I am (which is probably about everyone haha) The 4runner is still missing at the upper end of 3rd gear and up. I went home last night and checked the distributor's cap which checked out good. I checked the resistance to the pickup coil inside the distributor: good at 150 ohms. I checked the wires: good. I checked the air gap in the distributor which measured 10 thousands: good. I then moved to the ignition coil. This is where I am puzzled. The secondary reading is within spec but for the life of me I cannot get a reading on the primary. Now correct me if I am wrong but the truck wouldn't run if there was a short in the primary, correct? I might have been doing it wrong. I am going to check on my lunch break this afternoon. Any help would be greatly appreciated.

 

Well the verdict is in. The fuel filter was full of rust and junk. It measured 38 psi at idle but the pressure went down as the throttled moved. I guess the moral of the story is, check EVERYTHING first then post for advice hahaha. I am going to clean the lines out, replace the filter, and tank. The fuel pump is brand new and was replaced a month or so ago. Fortunately the fuel pump was not damaged. Thank you everyone for your help and suggestions.

 

Thanks for posting what you found!

Depending on how badly the tank is rusted, it is possible to clean out and reuse, maybe with the help of tumbling the tank with something inside to knock the rust loose, and coating the inside of the tank with a fuel tank sealer.

Post back up to let us know if the cleaned up fuel system fixed the original Wide-Open-Throttle problem.

 

Thank you old 87yota, I think I am actually going to just replace the tank because it seems REALLY BAD rusted. I am sure it will fix the problem. The problem was happening more and more and eventually I couldn't get it above 60mph even on flat ground.

 

Is the problem still solved, or did the problem come back?