Topic: Odd miss fire at WOT in freezing temps

[chris4runner88]

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 it is really cold, the truck misses in 3rd gear. 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 the temperature is either freezing or below. 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. 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.

[gnob]

I would be looking at weak ignition components. Or possibly wiring/relays to fuel pump.

[chris4runner88 [OP]]

Thank you Gnob, I will try that. I just can't figure it out. This morning I was pulling out of my subdivision headed to work and it started hesitating and missing in 3rd gear and I couldn't get it above 35mph for a few minutes. It was like I was dragging something. I was really embarrassed, especially since it is the morning rush hour.

[chris4runner88 [OP]]

Another observation is that when I rev the engine in neutral it revs up fine, but when I put load on the engine it misses. Also, it does this both when warming up and when it is at full operating temperature and only when the outdoor temperature is at freezing and below

[chris4runner88 [OP]]

Alright another observation. Drove the truck into work today and it was still cold (below freezing) I noticed that power was ok if the throttle was 1/2 or less, but as soon as I opened it up past 1/2 throttle it started bogging and missing. It didn't matter if the engine was cold or at operating temperature. I hope this helps.

[chris4runner88 [OP]]

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.

[Lewis Hein]

Hey Chris,

Visual inspection of wires can miss breaks in the insulation. Here's what I would do:

When the misfire is present, pull and replace wires in sequence, noting if the misfire gets worse or not. Either you will find a wire that makes no difference plugged or unplugged, or the misfire will be random. In the first case, swap two wires completely, and see if the misfire follows the suspect wire or stays at one cylinder. If it stays at one cylinder, double-check the distributor cap, spark plugs, and fuel injector for that cylinder. If it follows the wire, problem solved

If the misfire is not present in one particular cylinder, then look for general issues in the fuel or ignition systems. The best way I have found to troubleshoot an ignition coil is to replace it with a known (often expensive) good one.

Best of luck! Keep us apprised of how it goes.

[chris4runner88 [OP]]

Thank you Lewis for your reply, I will definitely do the wire trick. It just puzzles me that it happens near the upper end of 3rd gear and up. Another question I have is, do coils show signs of failure or do they just fail all at once? 

[chris4runner88 [OP]]

Live Oak: The battery is around a year and a half.

[chris4runner88 [OP]]

That is true, I can check the battery. It truly is odd. I am meeting a guy to exchange the boots on my intake to see if that might help. I couldn't detect a vacuum leak but I they are old, plus its free sooooo.

[Lewis Hein]

Theoretically, I think that an ignition coil could maybe produce a weak spark or an intermittent misfire on it's way to quitting. More often it seems like they just die suddenly. At least, when mine went that's how it went: One minute the truck was running, the next it was dead as a doornail.

Another possibility that occurs to me is a plugged cat. I once saw an engine that would run smoothly at idle but fell flat on it's face at high RPM or when torque was asked of it. Although that should be independent of temperature...

[Snowtoy]

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.

You should be able to get a reading on the Primary.


Does the missfire/no power over at WOT only happen when the engine is cold in cold weather, or will it run fine until the air temp drops below freezing?

How long do you let the truck warm up when temps are sub freezing?

[chris4runner88 [OP]]

Thank you Lewis and Snowtoy for your comments. Well I know it is not the ignition coil now. I replaced it with a good spare that I had. Lewis it does makes since that the CAT could be clogged but the only problem is that it does not have a CAT anymore. I did find a small vacuum leak that I repaired on the cold start injector which I thought would surely fix it but it didn't  The misfire is much less but the truck still does not have the power to keep up on a flat highway. Also, when I ever so slightly let off the pedal from WOT, it stumbles very briefly then smooths out. Weird I must say.

[chris4runner88 [OP]]

One thing I do notice is that the 4runner will not go over 3000 rpm under load without missing slightly. It is like it hits a brick wall and will not go over 3000 rpms. Even if I am on a slight downhill, I will floor it but the Rpm's only make it to roughly 3,200.

[chris4runner88 [OP]]

Well Guy's I believe I was looking in the wrong area. It is definitely fuel related. I have a friend looking at it and I will keep you posted.
 

[chris4runner88 [OP]]

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.