Misfire mystery

So I've been chasing the same issue for a few months now. When I press the accelerator I'm feeling some hesitation/bucking which makes the thing lurch and drive really poorly (mostly observed during light driving around 1800-2200 rpm, accelerates better when I floor it). Nothing noticeable when coasting.

I've gotten "running lean" and "misfire on cyls 1 & 4" codes, so I figured maybe the coil pack which controls both of those cylinders was shot. What I've done so far:

- All new coils, plugs, boots, and wires
- New fuel filter
- Cleaned mass airflow sensor

And sure enough after all that, thing still drives exactly the the same and feels like its misfiring when accelerating. No codes yet since the recent coilpack replacement. Been putting high octane in it every other fill-up for a few months now to see if that would clean up my fuel injectors but that hasn't seemed to make any difference.

It's an '00 V6 4x4 manual w/ 190k miles.

Any suggestions?

 

Injectors would logically be next, followed by a compression test.

 

So codes are P0301 and P0304?

 

There are some other directions to investigate……

 

Start with a compression test… if the motor is not mechanically sound all of the other things done are a waste of time and money. If the compression is even in all 4 then check fuel pressure. Then check the fuel pressure regulator for fuel leakage at the vacuum port.

 

I had a misfire issue on 1 & 4 also. Ended up being the plug wire for the #4 wasn't pushed down all the way. When I pushed it in, I would hear a pop like it had seated which was very deciving, but if I pushed it harder it would pop again to really seat. after finding that, my misfire went away.

 

That's a fair point to check compression before spending more on it, but I think OP has a v6, so if the compression is even in all 6

 

I've been chasing #5 for a bit, it's cold here now so tearing apart the top end in sub-40s wouldn't be fun.

I've swapped coils, replaced plugs/wires, and even spent $300 on injectors from reputable source. even replaced the FP regulator

I may have to test fuel pump/pressure in the spring (can't remember but #5 may be first or last in the line for fuel rail)

 

Didn’t see TPS mentioned.

 

Thanks everyone for the responses & suggestions! The codes I've seen are P0171, P0301, and P0304.

Sounds like I ought to run a compression test... Seems to be getting worse.

 

95% sure I got to the bottom of it (fingers crossed). It seems i've been chasing two separate but concurrent issues:

1. A sporadic jerking while driving. Thing was bucking like a bronco. Good sir, this is no rodeo nor is this a Ford. I started playing around with the accelerator position and how much gas I was giving it -- always seemed to occur with very very minimal engagement of the gas pedal & while driving lightly (1800-2000 RPM). If I floored it, it did alright but sometimes would feel like it wasn't getting the power I expected. Seemed to be getting worse every time I drove it.

2. Misfiring & running lean. To address the P0171, P0301, and P0304 codes I started by replacing the O2 sensor, plugs and wires. Running lean came back again, so I cleaned my MAF. It liked that for a moment, but the CEL came back on again (and it was still bucking). So I decided to replace all three coils. I didn't get a CEL (nor any pending codes) since I replaced the coils (100+ miles ago). But still running horribly.

After making this post and much deliberation I decided to surrender it to a shop today. Demonstrated the issue to the tech and he went to town on it. Said they went down a laundry list of possibilities because of how difficult it was to isolate/capture the symptom. They pulled the crankshaft position sensor and found it to be pretty fowled so they threw a new one in there. But still no improvement. Turns out, it was the Throttle Positioning Sensor. Thing runs like a dream. And sure enough, a quick google search of "faulty TPS symptoms" comes back with:

• An unexplainable bucking and jerking in the vehicle.
• Sudden idle surges.
• Sudden engine stalling without any apparent reason.
• Hesitation while accelerating.
• Sudden surges in speed while driving on the highway.
• Intermittent flashing of check engine light for no apparent reason.

Hah... that sure sums it up. Now I'm out way too much money. but alas, we don't like new trucks.

Hope this can help anyone who runs into a similar issue. Cheers!

 

Nice! And it makes sense since most of the time people drive on X% of throttle and eventually the TPS wears down in that range.

 

Awesome update/info
Thanks