Old guy with an old truck

A new truck

 

When in doubt try new plug wires our trucks eat them especially in hot climates. Every three or four years my truck runs bad and its fuel pump or wires. Three pumps four sets of wires all in twenty years DELETE...YOU DID WIRES

 

Problem: 1st discovered going up a short grade with heavy acceleration and wind drag (kayaks on top) Air Conditioning on full. Wide open throttle until 4000 rpm, engine stumbles and quits accelerating. Releasing the accelerator for 5 seconds, the engine returns to normal operation. It does this in all gears.


Vehicle: Stock 1998 ToyotaTacoma SR5 3.4L V-6 5 speed manual. Slightly smaller tires to make getting in and out easier.


Parts changed: Fuel Pump

Fuel filter

Fuel pressure regulator

Spark plugs

Spark plug wires

Ignition coils

Ignition control module

Air filter

Cleaned MAF

Replaced MAF

Replaced TPS

Cleaned throttle body

Catalytic convertor

Checked muffler back pressure

Replaced gas cap

Replaced upstream O2 sensor


Notes: Truck starts easy, runs strong to 4000 rpm, about 17 mpg. Not a daily driver, 2000 miles in a year. 305,000 miles now, new short block @ 200,000 miles,18 years ago Timing belt replaced 4,000 ago. Checked fuel pressure 40 lbs.


Currently stuck on replacing upstream O2 sensor. Sensor came out easy, wiring connector is bolted on top of transmission in a place too small for my hands. Pulled console, I can see the back of it now just can’t reach it. Next step pull crossmember and lower back of transmission, unless some one has a better ideal

 

Read this. It’s a ways down the page. But you’ll find a step by step process of what @turbodb did

https://adventuretaco.com/chasing-the-p0171-engine-light/

 

Can you rev the engine past 4k in neutral or do you get the same stumble?

 

Good luck with this! I was going to suggest checking the TPS but it seems you have already marked that off the list.

However the cutout at 4k RPM in every gear seems very suspect and usually always sounds like a TPS issue.

Any chance the new one was DOA?

 

I get the same stumble in neutral as any gear. It is like I am taking fuel from a small reservoir that can run the engine for two seconds. After 3500 it starts depleting it faster than it can be replenished. It will hit 4500 and then drop off with audible misfires. Holding the accelerator it continues to deplete droping rpm to 3000. Releasing the accelerator for a few seconds will return the engine to normal operation.

I put a jumper cable from the negative battery terminal to the intake manifold to insure a good ground, no improvement. Visual inspection of the brown ground wire showed no defects. Measurement the an ohmeter showed only test lead resistance.

Replacement of the upstream O2 sensor made no difference. Shrtft1 = 5.5 - 12.5%
Longft1 - 3.1%
The exahaust flanges seem to have a gap between the manifold and the catalytic. I measure about .030 at the bottom of the flange, but can not press .005 into the pipe area. Moving a hand around the area with the motor running does not show leakage. There is no gasket but no measureable leakage. My truck has always had " a toyota tick" but i assumed that to be an exhaust problem. The exhaust valve clearance has been checked many times.

 

I don't see the crank position sensor on your list. Have you replaced the original? The symptoms you have described are almost identical to what I was seeing. Could not get past ~4200. It was not fuel but I could see where it might be mistaken. It was similar to bumping up against the rev limiter. A Denso replacement isn't too expensive at Rock Auto. And it is a fairly easy swap out.

I may have missed it, but does your diagnostic tool give you readout list for error codes or pending codes?

 

Replacement Crankshaft Position Sensor ordered from RockAuto. It should arrive by end of the week.

Yes, my Autel Maxicheck does have seperate catagories for pending codes and current fault codes. Both are empty. It just passed California smog testing.

 

Hey Digiratus,
is there a button on this forum for handing out Gold Stars, because if there is, you deserve Two of them!

Your suggestion was spot on. The Crankshaft Position Sensor cleared the problem immediatly. Several had told me I sould be having starting problems, codes, etc. I had none of that. I was starting to think I was too picky, do I really need to go over 4k rpm?

Rather than dwell over all the needlessly replaced parts, I can take stock in the maintenance that my last the rest of my lifetime, and enjoy a great running truck in the mean time. Things I have been putting off (like kayaking) can now be enjoyed for the rest of this summer and next.

My thanks to all the members that offered suggestions, I followed up on each of them, you can see all the logical hunches I tried before arriving here, they are all good. Different perspectives and experiences make for solutions that may take AI years to approach.

Thanks to All

 

Happy ending!!

 

Appreciate the End Result post!!!!!!

 

Great example of the saying: "All of us are smarter than any of us." A "textbook" example of the power of TacomaWorld.

 

This may suffice:

 

This is the essence of TW. Good to hear the truck is back to where it should be.

 

Upgraded spark plug lines

Upgraded spark plugs

Upgraded battery cables

Cleaned MAF sensor

New air filter

Cleaned throttle body

Fuel pressure test