jerk/buck

[P_A_B]

Hey!
Its been a while since I posted lol. But I got a problem. I sear he'd but didn't seem to find solutions so here we go.
Ford Taurus 99 3.0 dohc. 122000 miles.
No engine light.
When driving at 65 mph only while accelerating there is a jerk/buck almost like it tries to go faster but it gets stopped violently. I Checked spark plugs,wires,etc. The plugs were twice the gap so I just replaced them with wires and coil pack since they were original. Still have the problem...and now I am testing several things. Tps seems OK. Voltage does not jump but it doesn't go higher than 4 volts even if its rated for almost five. I checked on a cheap scan tool voltage for o2 sensors. Both upstreem seem to be normal. Down stream seem low and a bit jumpier than I would expect. And I am hoping its not the cat.
Any ideas? Input?
Thanks

[P_A_B]

https://youtu.be/-x9YJmVTk_M
This seems quite similar to my problem

[shorod]

What does your tachometer do when the jerking/bucking starts? If the tach jumps around rather wildly, I'd suspect the camshaft position sensor. Is there any abnormal noise under the hood at idle? After the car has been doing this does the exhaust smell rich? Did changing the spark plugs and wires make any difference (better or worse)?

-Rod

[P_A_B]

Tachometer jumps a bit, but I thought it was due to speed jumping a bit. Idle noise seems to be normal and I do smell a bit of richness when the jerking happens. Changing plugs did help with overall performance but did not alter the issue at all.

[P_A_B]

I I literally cannot go faster than 67-68 mph

[shorod]

I took a look at the ignition system wiring diagram for your 1999 DOHC and per the diagram, the Crankshaft Position (CKP) sensor is what provides engine speed and spark information to the PCM rather than the Camshaft Position (CMP) sensor. My experience with CKP sensors on Fords is that when they go intermittent or fail it will cause the engine to stall and/or not want to start. The CMP sensor is more related to the fuel injectors and wouldn't explain a rich condition when the bucking occurs.

What are the chances you have access to a scan tool or smart phone device that will allow you to monitor various engine parameters real time? It would be useful to monitor the Mass Air Flow reading, TPS reading, CMP, CKP, fuel pressure, and B1 and B2 Sensor 1 O2 sensors and see how they all react when the bucking/jerking occurs.

-Rod

[Crvett69]

could also be something in the transmission acting up and shifting out of OD or converter locking and unlocking

[P_A_B]

First off, thanks for the response. I do have a cheap scan tool that may be able to record most if not all sensors you mentioned. I will try doing that today or tomorrow.
Regarding transmission, it may be that but I thought it usually gives that tkpe of problem at around 40-45. I know it does need a transmission fluid change.
Thanks again

[P_A_B]

update.
sadly my crp 123 is pretty much the biggest waste of money ever made. It says it records data, but it actually does not. So...all that to say I cannot post live data. I may try to get someone to drive while I record with my phone in the near future if issue is not resolved.

[P_A_B]

update on issue. I noticed while getting the car to jerk at about 67 mph, the rpms are always at exactly 3800 rpm. I cannot get the rpms any higher no matter how much I try. RPM does not jump around, it actually stays very close to 3700. Same with speed at around 67 mph. I forget what I said earlier and apoligize for any possible misguided informatioin. If I try to get RPMs higher than 3700 when at lower speeds by getting Wide open throttle the car will act like I put it in neutral. thanks again for the help

[shorod]

With that info it's feeling more and more like a CPS issue.....

-Rod

[P_A_B]

cps being crankshaft position sensor?

[shorod]

CPS = Camshaft Position Sensor, also sometimes called CMP sensor.

CKP sensor = CranKshaft Position sensor.

-Rod

[P_A_B]

Hey there! Sorry for the very long delay, but some things came up and haven't been able to work on the car.
After you mentioned the cam sensor I decided to do something I don't like to do...which was replace it before testing it since it was cheap...and it still has the issue. Honestly at this point unless I can find tools to borrow, I am not sure how I can proceed with diagnostics. Any ideas? I know it has o er 100 k miles....and may not be worth fixing...but until I know the issue I can't make a decision.
Thanks for all the imput

[shorod]

My next suspicion would be the Mass Air Flow (MAF) sensor, but they can be rather pricey and another part that you would not want to swap out without more diagnostics. If you have an Android smart phone it might be in your best interest to purchase one of the $10 OBD-II Bluetooth dongles, download the Torque Lite application, and use that to help with diagnostics.

-Rod