Ok, I have 89 toyota pickup 22RE. When I accelerate she "bucks". Sort of hesitates then stops. Sometimes she does it, sometimes she's ok. I've spent a lot of money trying to get her fixed. No mechanic, to include my brother, 2 master techs, the top mech in NC who's been doing it for 30 years can't figure it out. So far, I've replaced:

1. Rotor button
2. Distributor cap
3. O2 sensor
4. plugs and wires
5. fuel filter
6. timing chain

The first time she bucked was after I took her through some mudd/water. Then she dried out and ran fine. Then when I washed her off underneath and engine, she did it again, dried out and then ran fine. Now, she just does it sporadically. I also did switch gas stations, but not sure if that matters. She idials fine, she runs fine when RPMs are increased (sitting still), but when she is under load (accelerating) she bucks/hesitates. No idea....?????????

 

This most likely is not the solution, but I don't see that you have inspected it.

Sometimes the intake can crack deep within the belows and can be hard to see. When the engine flexes these cracks can open and allow more air into the system than the ECM can "see". Causes sporadic bucks, stalls and can stop.

Just an idea.

It's strange that their seems to be some relation to water exposure though.

 

May be the TPS. Fan will blow water all over it and if the seal is leaking, it will get damp and really screw up you ride. Could also be the Mass Air Sensor or MAF which is also electrical and sensitive to water intrusion. I would pull the tps off the throttle body and put it in an oven at 150 degrees to cook off any water for about an hour. Let it cool overnight. May have to cut the rubber top off MAF and lightly run a warm hair dryer over the circuit board. Can reseal the MAF with silicone caulk. That is where I would start.

My $0.02

 

If it hesitates/bucks only when under severe load, wouldn't this be related to air or fuel issues? Either not getting enough air down its throat (e.g. crack in intake like Elvota suggests) or the fuel pressure not remaining high enough? Does it throw any codes or CEL light lit?

 

Why do people always consider their vehicles a 'she'?
I know mine's a man because everytime I have to work on him, I have to buy more tools.

Anyways... any trouble codes?
Otherwise, it looks like you're down to the ignitor, coil, distributor pick-up, throttle position sensor, engine coolant temperature sender, AFM, ECU or wiring harness.
Yep, I mentioned just about everything you didn't.
In the order I would do them-
1) replace the coil- don't know how many miles you've got on it, so maybe it's due anyways. That fixed my wife's truck this morning. Besides, they're not all that expensive and if it doesn't fix it, you know you have a good spare for when you do need it.
2) TPS- follow the instructions here- http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml - and replace if necessary. They are succeptible to water....
3) ignitor- check and replace, find someone who will let you swap for a bit, maybe a friend with a truck like yours or maybe you can get a wrecking yard to allow you to test it out first, if you leave a deposit they might let you try it out...
4) Engine coolant temperature sender- test and replace if bad.
5) check the distributor pick-up and replace if necessary

 

 

Read on "fuel pressure up" vacuum switching valve....

http://www.autoshop101.com/

The FPU VSV is located on the top and towards the back of the valve cover. It has an electrical connector and two vacuum hoses running to the fuel pressure regulator. It is activated at high speeds or heavy loads to supply atmospheric air (through the vent cap on it....creating a small, controlled vacuum leak) to the fuel pressure regulator/fuel rail keeping the FP at maximum and above manifold pressure.

In other words, it sounds like the motor is choking out under load.

 

HaHa...lol...I have that same problem...my truck keeps eating my tools!!

 

this might be something you want to take a look at also:

https://www.yotatech.com/forums/f116...ration-139265/

 

On mine, the bucking under load means the spark gap is too wide.

 

I would agree with most here that it would be electrical related, Ignition stuff. Like abecadarian said I would start by changing the coil, plugs and wires. Also try revving it up at night and see if you can see an arc. I had a coil that was cracked before and you could watch it arc to the bracket at night. I would definatly start with the coil.
Also bucking under load would usually point to spark related I have found. When the pressure goes up in the cylinder due to load, the spark has a hard time jumping so if the spark is weak you will get a miss under this condition.

 

My money is on the VAFM.

 

I bet TPS or AFM.

 

I had a semler prolbem with my 86 4runner try unpluging the EGR vacume and plug that line then drive it i dont know why it stoped but it worked on mine

 

just a thought, I've been reading alot of stories abou this and it occurs to me that my brother had the same problem with a jeep he had. He did everything you did and nothing worked. Same story about mechanics....eventually he had to have his ECU replaced. Once he did that no more probelms

 

Does is seem to be loading up or anything. I know since my 22rte swap I have had quite the wiring trouble. Injector connectors, tps connector, and temp sensor connector. Replacing them 1 at a time problems are starting to fade away. Also TPS. I had to replace it and Majority of throttle related sputters and misfires are resolved but I can't seem to get it set 100%

 

Thanks. Will check it out for sure.

 

Thanks. Will check it out for sure.

 

Thanks. Checked that to no avail.

 

No codes, no lights. We firgured that since it doesn't do it while idialing or high reving it in neutral, it's probably nothing with the fuel system, though I did change the filter.