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Discussion Starter #1
Hello All...

I am experiencing a performance problem with my '99 5VZ-FE 3.4L V6, Automatic Transmission, 4WD Taco with about 235k miles. I'm hoping to get some guidance/suggestions on rectifying my problem. I am currently at a loss. I'll summarize here, but below is the link to a thread I started in another Tacoma forum.

(It seems I cannot post a URL, so please PM me for the link, if you feel you may be able to help)


Symptoms:

Difficult starting. I have to go through about three cycles, before it will start, and then it stumble-starts

Very low power until it warms up, especially at low RPM's.

Acceleration improves after full warm up and as RPM's increase, but still not normal. When cold and accelerating from stopped, VERY Sluggish. Dangerously so, if entering traffic. Power during acceleration seems follows a "step pattern". Not smooth.

Mileage has fallen to about 10 MPG, City. Seems to be stable at that level.

Idles rough after warmup, stumbling (I've been shifting to "Neutral" at stop-lights, to avoid stalling)

OBD-II Readings:

Previously had code P0136 (O2 Sensor, Bank #1, Sensor #2)

Prior to code P0136 and performance issues, was getting flashing CEL and codes P0300 (random misfire) and codes P0302 and P0305 (misfire cyl's 2 & 5), above 70 MPH, but only above 70 MPH with no noticeable missing or performance issues.

No codes currently being thrown, but Long Term Fuel Trim is running around -4

Catalyst Test is "Incomplete". Other tests are Green (see screenshot from Torque, below)
Goes from Open Loop to Closed Loop at what appears to be normal operating temperature.

Action Taken To-date:


Swapped coil-pack feeding Cyl's 2 & 5 to another cylinder pair (no change. Misfire remained on Cyl's 2 & 5)

Renewed downstream O2 sensor with new (Denso part number 234-4162)

Renewed Upstream O2 sensor with new (Denso part number 234-4162)

Changed spark plugs. (Correct Denso dual electrode; wires renewed with OEM, about four years, 50,000 miles ago) Old plugs looked good. No oil fouling or anything like that.


Checked for vacuum leaks, using carburetor cleaner. Test was negative for vacuum leaks

Cleaned old and then replaced with new, MAF Sensor.

Removed and cleaned throttle-body and idle air port.



Obviously, I have a blue-tooth enabled OBD-II tool and Torque Pro. Therefore, I can perform any tests/capture any readings possible with those tools. Please offer guidance and/or offer suggestions for the information necessary to resolve my problem.

Please ask any clarifying questions and/or offer input.

My truck was running well before all of this, and I need it back again.

Grateful for any input/advice. If you can direct me to a resource that may be able to help, I'd appreciate that too.

Thanks!
 

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The misfire sounds like you have/had a wiring issue with the coil. Check for loose connections. Air intake sounds good, but fuel might be an issue. I'd recommend replacing the fuel filter if it hasn't been replaced recently. That then rounds up most of the air/fuel/spark related tests/maintenance. You might try a compression test, but I don't think you have any issues there.

When you shift to N at stop lights, do you then rev up the engine to keep it from stalling, or is shifting out of gear enough to get the idle up? When you rev the engine to 4-5k in N or P, does it sputter as the RPMs raise and does it continue to sputter once it reaches the higher RPM level. You might want to check the TPS and see if it has some bad spots or giving bad readings.
 

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Discussion Starter #4
Solved ( I hope)

Thanks for the input.

I took my truck to the shop, and they discovered that the timing was indeed off. The belt has moved by a lug or two. This explains why no codes are being thrown.

I changed the timing belt and water pump about a year ago, but did not change the tensioner, though I DID change it during the previous belt change about 5 years ago. I can only guess that the tensioner is bad. Not sure there are any other reasons the belt could move.

I've ordered a new belt and tensioner and will change those ASAP.
 

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Thanks for the input.

I took my truck to the shop, and they discovered that the timing was indeed off. The belt has moved by a lug or two. This explains why no codes are being thrown.

I changed the timing belt and water pump about a year ago, but did not change the tensioner, though I DID change it during the previous belt change about 5 years ago. I can only guess that the tensioner is bad. Not sure there are any other reasons the belt could move.

I've ordered a new belt and tensioner and will change those ASAP.
You said ignition wire were replaced 4 years, 50,000 miles ago, plenty mileage. Maybe spark is jumping to ground, probraly replace them, do the easier chit first.
 
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