TexJJ

So this problem is about to drive me insane. I love my '91 4Runner 3.0, but this "random" jerk has really undermined my sense of reliability with this vehicle. I hope someone out there has some more ideas.

A quick recap of the symptoms.

While driving, the vehicle will jerk, JUST ONCE, then continue running like nothing happened. The jerk feels like the engine just shuts off for an instant then the momentum of the vehicle push starts it up again. (This has always happened while driving at some speed with a 5 sp manual, so it feels like the ignition dies and then gets a bump start from the vehicle's drive line inertia.)

The JERK is very quick. Sometimes you are not sure what has occurred. In attempts to trouble shoot I have installed a digital voltmeter (attached to the cigarette lighter), a true oil guage and a vacuum guage. Here are my findings.

Jerk occurs at:
Ambient Temperature anywhere between 30 deg F and 105 deg F.
Engine Temperature in Normal Operating Range (use a new clutch fan assembly, no electric fan)
Humidty between 0% and Rain (100%?)
Voltage never drops below 12.0 with crusing coltage in the 13's
At the moment of Jerk, Tach drops to near zero! This would be an impossability as there is no (minimal) drive line slippage and at 65mph if the engine speen really dropped to say 500rpm in 5th gear I'd look up the rear tires or at least severly slow down!
Have not noticed the Vacuum Guage changing but hard to look at everything when the jerk occurs.
NO CHECK ENGINE LIGHT EVER

What have I done to date:
Replaced the
Ditributor Cap, Spark Plugs, Wires
Replaced Coil/Igniter pack with NEW Toyota parts
Removed Electric Flex A Lite Fan and replaced with NEW TOYOTA mechanical fan unit
Replaced main EFI relay
Replaced Distributor (actually twice!, first rebuild was a dud and would not start, the second however has worked got me excited that I found the problem and then jerked on my this weekend!)

The ONLY OTHER THING I HAVE NOTED, is that when the engine is cold and I am in 2nd gear say running about 15-25mph gently accelerating (Dad taught me never race the engine when warming up!) I feel a slight surge/retard/surge/retard. It is very hard to describe and very faint. It may just be a tire wobble that levels out at other speeds, but I don't note it when I push in the clutch and coast at that speed. There is no discernable changes to the vacuum and tach. Maybe I am just going crazy.

So here is what I am proposing:
1. Dad says let's change out the distributor again. Third time is the charm. I doubt it is it, but it would explain the tach as my understanding is the tach signal follows from the distributor pick up coils, to the igniter up to the tach with no other interplay.
2. I say change out the MAF (I know it is a vane type, guess and AFM or whatever they call it.)
3. Take 10 gallons of gas to it!

Outside of 1 & 2 all I can think of that is left is the ECU ($$$) and the wiring harness ($$), neither of which I am too anxious to attempt to replace.

Any ideas? Any trouble shooting suggestions?? I wish it were OBII as then I'd just run a scanner on it.

Thanks guys.

Corey

iTrader: (1)

It sounds like a classic case of a clogged fuel injector.
My rig when I first got it would surge and jerk on the freeway if I let off on the go pedal a little.

To the tune of almost $500 my dealer pulled all of them, sent them down the road to a shop that ultrasound cleans them, the dealer reinstalled them, and a new PCV tube for something.
This was way back in '99.

There are also shops that can clean them while on the rig.
They hook up a machine to the fuel rail and run a solution while idling the engine.
Runs around $100 or better to do that.

TexJJ

Interesting, but wouldn't a clogged injector be much more of a steady JERK, or is this just an idea on the retard/surge phenomena? I think my dad maybe on point when he says we probably have a compound problem.

But at this point, what's another $100 for an injector cleaning?

JJ "At some point the new FJ payment will be cheaper" Noyola

Corey

iTrader: (1)

Mine mainly only did it on the freeway when letting off the gas to slow down for traffic.
Bucked like a bronco.

04 Rocko Taco

Had this same argument with myself many times on many cars and trucks, at some point a new payment has got to cheaper than the repair bills. Hang in there. Keep us posted!! This one has me very curious!!

getitdone

We do that at my shop. What it intails is running the car directly on techron fuel injector cleaner. It is the same stuff that is an additive to your tank. If you can't afford getting the service done, the next best thing is adding the chemical to a nearly empty gas tank. The more you put in the more concentrated and closer it will be to the actual service.

Getting it done with a machine is definatly much better though.

TexJJ

Thanks for the support guys! It is very frustrating, but a great way for my dad and I to talk about something!

Unfortunately mine doesn't really buck, but again, I don't mind the injector cleaning. I've mentally given the project till about November with a budget of 4 months of car payments. I really like the 2nd gen, but driving the new taco's is NICE and the FJ is just sweet. I just wish they would get one in with the options I want. If I am going to spend $$$ I want the 6sp and ATRAC. Damn Corey, I am envious of both your rigs!!!

JJ

Corey

iTrader: (1)

If you get an FJ, do not order the A Trak.
It has been proven already all you need is the switch ($60) or get a cheaper switch and hook up the wires.

The 6 sp already had the E locker standard, so you could order a base 6 sp FJ, add A Trak yourself, and be good to go.

I ordered the extra packages as I needed a few things not included.

TexJJ

Wow! I did not know that. Good info on the A-Trac. Well the only ones I've seen here in Austin (and they go quick) have been base 4wd. I kinda want the bloody instrument cluster. I miss that from my 1st generation. I know I know, a dumb reason to not buy a car, but if I am going to make payments on a vehicle...