Full Throttle Hesitation

My 1999 Tacoma 4x4 has 195,000 miles on it. I changed the timing belt the first time at 90,000 miles. The water pump started leaking a little bit two years ago. In the past 6 months the leak got worse. I started noticing that when you got into the throttle the truck started (bucking), like the timing was not advanceing for the amount of fuel going in. Took it to a local dealer and a Tec. test drove it with me. He plugged his computer in while we drove and it showed all six cylinders were misfiring. His thoughts were that anti-freeze and dirt had gotton on the crankshaft sensor and was causing the issue. I bought all my parts and changed everything. Timing belt, water pump, idlers, plugs, wires, etc. When I unplugged the crank shaft sensor, anti-freeze poured out. I blew out the connector and took out the sensor which had black gum on the face of it. Great, problem found. Put all back togather and it ran like a new truck. Two weeks later the problem returned , at any speed when you get down on the throttle I get a hesitation or a bucking type feel. I have no anti-freeze leaks. Just wondering if the anti-freeze in the electrical connection could have made the crank shaft sensor go bad? Or could another sensor be causing my issue? Wanting to use my truck this coming weekend and would like it to be fixed. Anyone had any dealings with this or any ideas? Thanks for any help.

 

Ever figure this one out? I picked up a 1996 2.7 tacoma that bucks as well when accelerating. i have changed plugs and wire and cleaned the maf. not sure where to go next. was thinking of cleaning the throttle body.

 

Tip in and light throttle, ok? Half throttle, ok? Is there an rpm where this bucking starts? I'm thinking egr system, possibly. EGR solenoid?

 

get a cheap obd 2 setup and report back your fuel trims

 

It doesn't seem to be at certain rpms but I'll check. It's a stick shift and seems to happen in all gears. I don't drive it everyday so it's harder to diagnose. I have an obd reader. Giving no codes but I'll check the fuel trims.

One thing I do know is that my cast manifold is cracked all the way through and a lot of exhaust escapes in the engine bay. I have a 2001+ mini header to replace it but haven't gotten around to it yet.

Also, doesn't happen as much or at all when engine is cold. Once it heats up it happens a lot more often.

 

Drove around a bit and the short term fuel trim seemed to hover mainly at 0 going a max of +/-10% in either direction. I did seem to notice (i think) that when I felt the bucking the STFT would pop down to -5% or so then back to 0. Long Term fuel trim is at +7%

I don't know why, but I really feel like this problem is related to the exhaust manifold being basically cracked in two. I mean this has to mess with the front o2 sensor. I am prepping and painting the new mini header and down pipe and collecting gaskets. Hopefully I'll have it installed soon so that I can either solve the problem or cross it off as a culprit.

Finally, it seems pretty evident that the truck bucks more once the temperature is warm. Not sure what this means.

 

yeah sorry for not replying earlier. your cracked exhaust manifold is causing a big issue. the exhaust isn't reading the equivalent airflow being reported by the MAF sensor cause air is escaping and not being read by the O2 sensors.

then if you have LTFTs hovering above 0, you probably have a very small intake leak. but look for it after driving around with the new exhaust manifold. the positive LTFT may go back to 0 after the manifold is replaced.

and it's normal to be within -+5 to 10% of 0. though you do want to be as close to 0 as possible.

 

No need to apologize. I appreciated the help. I'll be sure to update after I get the new header on.

 

Out with the old. Got the old one out without too much trouble. Got the new headers and down pipe ready to go. I have all new felpro gaskets but I have a question: should I use additional copper rtv to make the seal or stick with just the gaskets? Aslo, check out the wire ties that were being used to hold the oxygen sensor down put on by the PO. That couldn't have been helping anything.

 

what paint did you use?

 

I used the Rustoleum Automotive high Heat 2000* paint and primer. Paint color was flat aluminum. We'll see how it holds up. I'm going to ghetto bake it by starting the truck up, idling for a few minutes, then letting it cool off a few times. No way my wife would let me put it in the oven haha.

 

no barbecue?

 

good point. Can't believe I didn't think of that. Should be able to fit in gas grill no problem. And that has a built in temperature gauge. Thanks!

 

The exhaust gasket is mls right ?
No need for rtv if you know for reasonable certainty the face is flat.
Back in the day manufactures did not use a gasket between the head and manifold.
I never have either.
Make sure the flange is flat and a bead of copper hi temp rev around each port install, and torque all hardware.
Never a leak , no fighting with a wayward gasket trying to get bolts in and keep gasket in place.
I use the same practice with headers.

 

well the thread is very old but its obvious the OP solution is he needs to do the timing belt again
first changed at 90k and now it has 195k plus leaking water pump

as to the guy resurecting the thread, you guys already solved that one as a header issue plus he doesn't have the same engine as the OP

 

very old? he revived a 1 week old thread....

 

I was just looking for some closure on the OPs topic and kind of stumbled into thread jacking a bit. Sorry for that, but information is information and at least it's getting documented for someone else to search. I'm re-installing the headers today if it ever stops raining (Maryland area, aka new Seattle). If my jerking and hesitation problem still exists I'll consider starting a new thread.

 

I am older, and use search methods about every time I have a question I have, that I can't find readily .
Often times it will bring me to this site, if it is a toyota question.

Frankly, I wouldbfeelbabsence of accomplishment , if a thread had response , even 5 years after the last post.
Reason is , we were able to help some one out , that had asked for help, and was willing to learn.
Rare today, most take it to their " GUY ".
Be but hurt today.
When you are 60,if you make it , think about how you had the chance to be a teacher, without a 6 figure debt, a state certified certificate, and a genuine love and passion for the hobby , of working on your own junk, no matter what it is.

 

did anyone mention that you couild just have a clogged cat and/or muffler?