Sorry, but I need help again

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2002 Ford Ranger Edge 3.0 67k

Hey guys,

I know I'm beating a dead horse about my truck, but I am about to lose my mind with this. I did a compression test this past Sunday and cylinders 1,2,3,4,5,6 were 165,164,160,160,165,170 respectively. My compression seemed good.

I thought I had fixed the rough idle by replacing the coil pack, but no. Also, tonight on my way home from work at 60-65mph on the interstate I feel what feels like a misfire. It's not bad enough to be scary, but it's noticeable. I pulled off my exit to a stop sign and magically there's no rough idle. Engine was purring. After pulling off, I get to around 50 mph and I feel the "misfire" again. The next 18 miles until I arrived home would produce the "misfire" between 40-50 mph. The symptoms don't exactly match what I have researched as possible culprits.

Bad/faulty fuel injector(s)- wouldn't this produce a more constant misfire and rough idle? Fuel economy seems decent for the age of the truck. First full tank of highway miles produced 335ish miles on a 16.5 gallon tank.

O2 sensor(s)- no rotten egg smell that I have read about associated with this and again fuel economy doesn't seem affected.

Engine has no EGR valve.

No check engine light or codes....

Replaced parts- coil pack, plugs, plug wires, serpentine belt/tensioner/idler pulley(needed changing), cam sensor and synchronizer, and fuel filter.

I'm out of ideas guys.
 
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Originally Posted by KrisZ
Did you check for vacuum leaks?


Yes and I did not find any. Doesn't mean I missed a leak, but I did not find one after multiple checks with carb cleaner.
 
Originally Posted by Marco620
Bad gas?


Considered this. I have filled up multiple times from local "prominent" gas stations and have the exact same issues across 87,89 and 93 octane.
 
Originally Posted by A_Spruce
Is there a relation of misfire to speed, rpm, or engine load?



Rpms do not jump/bounce or change at all with the "misfire" or the rough idle. Under load going up a hill for example, there is no misfire feeling. Seems most noticeable on level ground at cruising speeds of anywhere from 40-65mph. The rough idle is intermittent between stops seeing as I don't feel it every time I come to a stop.
 
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I feel like I am chasing a ghost seeing as I can't find anything in my troubleshooting, yet have an issue. I am a maintenance technician by trade and my livelihood is based off of precise troubleshooting and fixes on equipment that is running 24/7.
 
Originally Posted by Dylan1303
Hows your ltft? That might tell a story


Ltft?


Edit: long term fuel trim. Gotta love google. I have no clue honestly. How would I go about checking this?
 
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Before I make myself out to sound like an idiot, I'm a maintenance tech on industrial electronics and mechanical. Saying that my livelihood is based on precision yet I'm being bested by a rough idle on a truck lol I'm only so versed in automotive stuff.
 
Something is telling me a dirty MAF sensor, but I have nothing to back that theory up. Did you check the intake snorkel for air leaks between the MAF and intake manifold?
 
With a scan gauge or plug in obd thing. +10 to -10 is acceptable. If your ltft are say -30 that means its pulling 30% fuel over stock map. So that would say leaky injector you know stuff like that. If it was like +30 you would have a large vacuum leak or something since its adding %30 fuel.
Originally Posted by NavyVet88
Originally Posted by Dylan1303
Hows your ltft? That might tell a story


Ltft?


Edit: long term fuel trim. Gotta love google. I have no clue honestly. How would I go about checking this?
 
NEW MAF sensor. I threw one in a friends car and it fixed the rough idle. A gamble and threw some money at it and that was it.
 
Originally Posted by Dylan1303
With a scan gauge or plug in obd thing. +10 to -10 is acceptable. If your ltft are say -30 that means its pulling 30% fuel over stock map. So that would say leaky injector you know stuff like that. If it was like +30 you would have a large vacuum leak or something since its adding %30 fuel.
Originally Posted by NavyVet88
Originally Posted by Dylan1303
Hows your ltft? That might tell a story


Ltft?


Edit: long term fuel trim. Gotta love google. I have no clue honestly. How would I go about checking this?



Or Forscan and appropriate cable/ELM327.

Did you check/change the PCV elbow?

Agree motorcraft coil pack (and plugs) only.

I will repeat, this engine isn't a very smooth idle when things are all correct, i'm assuming since you note changes that something is in fact wrong, but it is odd that it hasn't set a code, the two I have experience with are quick to set codes.
 
I would also inspect the fuel pump -- sounds very much like an issue I experienced on a vehicle with a failing pump.
 
I have a similar problem with my Ranger. It is intermittent, sometimes feels like it is running on 4 cylinders. I also experience jerking if lugging the engine. I will be doing plugs and wires, plus cleaning the throttle body, where I think the issue lies.
 
OP, I have the same Truck, same Engine.

I never had the symptoms your having but did have a rough idle at Stop Lights.
Changing the Throttle Position Sensor @ 132,000 miles fixed the problem / $34.00 and easy to replace

PCV Valve: Had a leaking (vacuum) hose @ 99,000 miles / bad design
Really wasn't causing any noticeable problem, but I didn't want any vacuum leaks.
The replacement was totally redesigned and a lot better.

Fuel Filter ?

Good luck.
 
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