I have noticed the past few days that my truck appears to "jolt" to various degrees. These jolts feel a lot like the transmission shifting and usually come in pairs. I have noticed them at all speeds but the problem is most reliably reproduced while doing 45 or so uphill (overdrive on or off makes no difference). The transmission feels smooth when accelerating even when giving it full pedal, I have not noticed any noise either. My rpm remain constant, no engine light and transmission fluid temp is normal. I also drained a bit of fluid from the aux cooler and it appeared in good condition and I did not notice any debris in it. I changed my plugs and wires about 8k miles ago and just changed my coil pack today, I did not notice any change with the new pack but I am hoping the truck will cold start better. (the truck has 108k miles on it). Any ideas?

 

Clean MAF sensor and change Fuel Filter if you haven't changed it recently.

RPMs should change if it was transmission shifting or slipping.

What you describe is a loss of some power when engine is under load, this often doesn't show on RPM but you feel it.

 

Alright I'll try cleaning the sensor in the morning and see about the fuel filter. I can put the truck under more load, for example rapid acceleration to highway speed and not notice this jerk. Thanks

 

You would notice issues at higher MPH if it was fuel filter issue, but at under $15 the fuel filter should be changed every 5 years or so.

If cleaning MAF sensor didn't help, then try unplugging the Throttle Position Sensor(TPS) and driving truck, it will be sluggish(and CEL will come on) because computer only has MAF sensor air flow to tell it you want to accelerate, which is slower to respond.

But if there is no "jolting" then TPS could be the problem.
It can be tested with a Volt Meter and sewing pin
TPS has 3 wires
Upper wire will have 5volts, from computer
Center wire will have variable volts, .6 to 4.9volts, sent back to computer so it "knows" what driver wants to do
Lower wire is a Ground

Remove the throttle linkage cover so you can move the throttle open and closed manually.
With key on engine off, pierce Center wire with the sewing pin
Set Volt meter to DC Volts, 20vDC if available
Put meter's black probe on a good Ground, Battery "-" is a good ground
Touch Red probe to the sewing pin
With throttle closed you should get .69 to .99volts
Slowly open the throttle manually and voltage should start to rise, there should NOT be any jumping around of this voltage.
Continue opening the throttle, at Wide Open Throttle you should see above 4.5volts.
Now slowly close throttle, again watching for jumping or dropping voltage not matching throttle position.

The computer relies on this variable voltage to "know" what driver wants to do.
Say you are accelerating and TPS voltage is at 3volts, then suddenly drops to 1 volt, then back to 3volts.
Computer thinks YOU took your foot off the gas pedal, even if you didn't, so engine would stumble(jolt) during that voltage drop.

TPS is a mechanical part, a Variable Resistor, like a light dimmer or Volume control, while they don't often get "bad spots" they can.

 

Cleaning the sensor did not help and the TPS read withing those specs. When unpluged the problem got about ten times worse with no check engine. I tried leaving it pluged in and unplugging the mass airflow but the trans. was shifting very hard, though the check engine light came on when I first unplugged the MAF it went off with it unplugged as well.

Another note, whereas I can reproduce it best at 45 mph I have felt it at higher speeds and was able to make it do it at arounf 60 last night.

 

Yes, trans shifting goes into "limp mode" with MAF unplugged, won't hurt anything, just hard shift points

Is it possible to go by an auto parts store and have them check all the codes in history, many do this for free?
WRITE them down, don't buy anything based on a code number.

 

I just went by and had them clear all the ones I had thrown testing it today. Now Im just trying to drive it around enough for the drive cycle test or whatever to complete and have them recheck. (All the codes from before where for the TPS, and MAF sensor, there was also a misfire on cylinder 6 which I believe is from my cheap spark plug tester)

 

Also I have a bit of a rough idle, and it appears that I will have to wait for the engine to cool down then run it and or wait for my gas level to drop before the code scanner will read again.

 

[Deleted]