user6137

On 12-03-2006 member 91ToySR5 posted:
"i had this problem with my 91 pickup when i first got it. usually after going up a grade in 5th gear on the highway - i'd let off the gas slightly as the road leveled out and i'd get that hesitation - the tach needle drops approx 500rpm and if u look real quick the CEL flashes real quick. after i set timing to approx 12 deg's it never happend again. after i replaced my motor a year later and had stock timing i get it once in awhile again. i'm sure if i turn back timing to 12 deg's it won't happen. from talking to a toyota parts manager, he had mentioned they had some problems with the inards of the distributor where they'd start to pull apart. try changing ur timing and see if it goes away."

This describes the problem that I have been having. Either the motor was misfiring or cutting out, hard to tell, but the cel would flash very briefly (by briefly I mean a fraction of a second). Initially, I had the timing set to 10 deg's, and the truck would jerk all the time going down the highway, but when I set it to 12 degrees the jerking/misfiring almost went away: only once in a great while would the truck jerk going down the highway. When the timing was at 10 deg's, sometimes the truck would throw code 25, sometimes code 26, and sometimes code 25/26, but setting the timing to 12 deg's made the cel go away for the most part.

Here's a list of what I have done:

1.) Made sure that the grounds were good inside the engine bay. Ignition coil bracket, fenders, rear of engine, and firewall.

2.) Replaced the distributor (remanufactured one from autozone). The original distributor had the timing jumping all over the place.

3.) Replaced the O2 sensor.

4.) Replaced the fuel pressure regulator. When I put vacuum on the original, the gauge went to 0 pretty quick.

5.) Adjusted the AFM (air flow meter), and the air-bypass screw next to the AFM using the VF1 signal as a guide aiming for 2.5V (while cruising).

6.) Repaired the wires going into the connector for the TPS. Right where those wires go into the connector they were nearly broken. On a couple of them only a few strands remained.

7.) With the cover of the AFM removed, I sprayed Deoxit D5 onto the trace where the wiper slides, and worked the AFM back and forth about 50 times.

I took the truck out for a long drive today. Normally, the truck would jerk several times, but today it only misfired once while coasting down from 75 mph on an exit ramp. So, I turned the air-bypass screw out 1 turn to lean it out a little, and after driving the snot out of it on roads that would normally cause it to misfire: no more misfires.

Hope this helps somebody else fighting the same problem. If it isn't fixed then I'll post back.
1995 4runner 3.0

superex87

2 issues that a lot of old Toyota's suffer that you may all so be dealing with.

1. The air intake hoses like to crack and leak un-metered air into the intake. This causes the engine to run lean and miss/ stumble. On my 3.0 4runner it would occasionally have a random miss at idle and would hesitate and jerk going down the road,.
2. The timing pulley / damper is made of 2 separate pieces of metal with a thin piece of rubber between the two. The rubber with age will begin to deteriorate allowing the outer portion (with the timing mark on it) to spin. This creates the allusion that you are setting the timing correctly but in reality it is way off. To inspect your timing pulley, pull it off of the engine. Hold it up and look through the hole and note where to wood ruff key slot is, the timing notch on the outer pulley should perfectly line up with the wood ruff key slot. If they are misaligned you need to buy a new pulley to correctly set your timing.

user6137

Still getting the misfire every once in a while. Not nearly as bad after doing the recent work, though. A couple of days ago, I smelled gasoline. So, I jumpered the B+ and FP terminals in the diagnostic port to turn on the fuel pump. Turns out one of the injectors just started leaking. It is leaking through where the electrical plug connects to it (had to remove the electrical plug to see the leak). I guess I'm glad that it started leaking, because it turns out that somewhere back in the ownership history someone put in mismatched injectors, which I never noticed before now. The injector that is leaking is for a completely different vehicle with a smaller engine (2.0L). Hopefully, after I replace the injectors that'll take care of the misfire/jerking. I'm thinking about using the yellow Bosch type 3 injectors (supposed to spray a mist, whereas the stock ones spray a straight stream). Will see how it goes.

I think Jesus is helping me to fix this truck (I did say a prayer). If that injector hadn't started leaking, I never would have in a million years thought to look for mismatched injectors.

I'll take a look at the intake tube for cracks, too. Thanks

user6137

1.) Installed the new Bosch injectors. Readjusted the AFM since the new injectors flow a little more fuel. Still misfired.

2.) Cleaned grounds under the dash. Still misfired, but those grounds needed cleaning anyway.

3.) Replaced EGR vacuum modulator valve, and verified that EGR system was functioning properly. Still misfired.

4.) Replaced the igniter with one I bought used off of ebay. Misfire improved a little.

5.) When I bought this truck, it was used. So, the first thing I did was a tuneup with aftermarket parts, which included a new distributor cap, rotor, and spark plug wires. Glad I put the originals on a shelf and didn't throw them away. Reinstalled the factory DENSO distributor cap, DENSO rotor, and Toyota spark plug wires. Been driving the truck for a pretty good while now through cold weather and now hot summer, and no more misfires. I wanted to make sure I got plenty of drive time before I posted in here again.

The way the truck would misfire before was violent enough that it seemed more like a spark plug was being fired at the wrong time. Sort of like crossfire inside the distributor cap. Since I replaced the spark plug wires, distributor cap, and rotor at the same time, I don't know which of those fixed it, but one of those or a combination is what seems to have done it. If I had to take a guess which parts actually fixed it, I would guess the original DENSO distributor cap and DENSO distributor rotor are what did it. BTW, I've used various aftermarket brands of distributor caps, rotors, and spark plug wires through the years and had the misfires/crossfires on those aftermarket parts. My guess is that these aftermarket parts have some flaw (maybe insulation not thick enough or something???) So, if I had to troubleshoot all of this again, I would start with replacing the distributor cap and rotor with original DENSO brand parts first(part numbers below).

These are the part numbers for my 1995 3.0L 4runner:
Genuine Toyota spark plug wire set part number: 90919-21579
Genuine Toyota distributor cap part number: 19101-65040 (has DENSO stamped on the cap)
Genuine Toyota distributor rotor part number: 19102-70160 (has DENSO stamped on the rotor)

If it misfires again (and I hope it doesn't), then I'll post back in here to let you guys know, but the truck has been running really well with no more misfires for a pretty good while now. So, it looks like Jesus was helping me fix this truck after all!!!

user6137

It's 2021, and no more misfires. I think it's safe to say the misfire is fixed. Truck runs like a dream. Smooth. No error codes. Passes emissions testing almost like it isn't running at all. It actually emissions with cleaner numbers than my 3-cylinder Geo Metro. However, now my fuel pulsation damper is leaking gas. I wish I had replaced that thing when I had everything taken apart. I was trying to save some money. Now, I have to take everything back apart again. My advice to anyone who reads this is: if you have to go as deep as I did into the engine, then go ahead and replace your fuel pulsation damper even if it don't leak.