SOHC 4.0 Rough under load, help diagnose - Ranger-Forums - The Ultimate Ford Ranger Resource


4.0L OHV & SOHC V6 Tech General discussion of 4.0L OHV and SOHC V6 Ford Ranger engines.

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Old 02-09-2016
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SOHC 4.0 Rough under load, help diagnose

Everything was going good a few weeks ago. Drove 30 miles away in no hurry. Topped off the tank on the way back bc gas was cheap. Started running rough immediately afterwards. Temp started dropping to the bottom of normal and bumping around there. Poured in a can of seafoam with fingers crossed. Nothing. Couldn't drive more that 2k rpm. Revved fine in neutral. I'd rev it and dump the clutch and get a little speed then lose power. Called my mechanic while limping down the highway. He was stumped and hesitantly mentioned water in gas. I got to an Advance and added some Heet. Immediately ran better. Got home but the temps never came back up. Ran that tank out and filled up with 89 just to help things along.

2 weeks later I made another decently long trip. Started running bad again just before I got home. CEL started flashing -- misfire. No codes were stored and I can't get it to blink again while plugged in to scanner. This time it hasn't run right again. Won't rev past 2k without bogging down, and sometimes cutting off. I can go about 10 mph in 4th gear but no power or torque. So here's where I started:

1. NGK plugs and wires
2. Swapped out used coil
3. Replaced fuel filter
4. Replaced CKP sensor
5. Swapped out used CMP sensor
6. Cleaned IAC with MAF cleaner
7. Cleaned MAF with MAF cleaner
8. Compression Test (162-178psi)
9. No milk in oil. Coolant bright green and
9. Faint smell of coolant in cab at startup. Heater core?

This did nothing. There is a faint repetitive noise in the top underneath the intake. Maybe valves? So I've taken off the intake. Pulled the drive valve cover and checked the timing guides. I replaced them about 2 years ago and they still look good. Here's where I'm at now:

10. Replaced thermostat (old one checked out good in boiling water)
11. Replaced temp sensor and sender (in the unlikely event that its just reading cold).
12. Checked resistance on injectors. All between 14-14.5 ohm.
13. Cleaned injectors (a la
)

Before I stitch everything back up, I'm wondering what I can do to hopefully prevent having to take intake back off.

14. How does one check valves on the SOHC? Just want to make sure they are not bent or broken. Can't find this in Haynes or web. Will I be able to visually inspect them without much fuss?
15. Knock sensor?
16. What else?

Things I plan to do after getting it back together
17. Check for vacuum leak with brake cleaner
18. Test fuel pressure. I know the schrader is at the fuel pump. Can this be done without removing bed/dropping tank (I prefer the former)? Can't find anything in Haynes or web.
18. Came from the factory without EGR, so no DPFE.
19. O2 sensors? Could these cause severe rough run?
20. Cat's? How does one test them?
21. The lingering question in my mind is could water in the gas have caused this?
22. Tried O'reilly's radiator pressure tester, but it leaked at the seal. I'll try my mechanics snap-on if nothing else works.
23. What else?
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Old 02-10-2016
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1994 Ranger had 4.0l OHV, 1990-2000 Rangers, 2001 and up got the 4.0l SOHC so a bit confused on that part??
What year Ranger?


First hook up a vacuum gauge and check engine vacuum and if exhaust is blocked

Good read here on testing engine vacuum: Technical Articles: Engine testing with a Vacuum Gauge - at Greg's Engine & Machine

This will also test if valves are good, high vacuum

The blip test will tell you if exhaust is clear

An engine is an air pump, self propelled if fuel and spark are added, but it is still just an air pump.
Doesn't matter how much electronics they add to an engine, it is still pulling air in and pushing it out.
A $25 vacuum gauge can help diagnose most engine problems.

Compression test says valves are OK, numbers are high for OHV but inline with SOHC

Partially clogged exhaust will give symptoms you describe, so blip test it
Also, when system is cool bang on Cats and muffler, listen for rattling inside, a bad sign

Last edited by RonD; 02-10-2016 at 11:12 AM.
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Old 02-12-2016
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Quote:
Originally Posted by RonD View Post
1994 Ranger had 4.0l OHV, 1990-2000 Rangers, 2001 and up got the 4.0l SOHC so a bit confused on that part??
What year Ranger?


First hook up a vacuum gauge and check engine vacuum and if exhaust is blocked
2003 4.0 SOHC.

Put it all back together today. Found a bad pcv elbow up front passenger side of intake. Thought that would fix the problem but it didn't. Sprayed brake parts cleaner over the intake and didn't get any stutter. Still idles fine but chokes down around 2200rpm.

I'll check the vacuum asap. But how does one check the fuel pressure on the '01+? Everything I've read says the schrader on the back of the passenger rail is not for testing. Haynes says its in the tank? I'm guessing its electronic? Can it still be tested?
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Old 02-12-2016
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Nice upgrade from your profile, 2003, I still have my '94

Schrader valve will be on passenger side toward the rear of engine, blue cap usually.

Video here: www.youtube.com/watch?v=F7mYC9JwMLg

End of the fuel rail is the Pulse Damper, and no it is not to test pressure, it also has a vacuum hose attached.
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Old 02-12-2016
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Quote:
Originally Posted by RonD View Post
Nice upgrade from your profile, 2003, I still have my '94

Schrader valve will be on passenger side toward the rear of engine, blue cap usually.

Video here: www.youtube.com/watch?v=F7mYC9JwMLg

End of the fuel rail is the Pulse Damper, and no it is not to test pressure, it also has a vacuum hose attached.
Yeah, I wanted electric windows and locks and a simpler 4wd system. I also added an Ex mirror with auto lights and several other mods.

I saw that video before posting but it doesn't make much sense. I had the intake off and found the blue cap schrader on the rear of the passenger rail. Didn't see anything else anywhere that could be the pressure testing schrader. Book and several online places say the pressure tester is in the tank. But that doesn't make much sense either. How would one test without taking the pump outů

Can you or anyone be more specific as to where it is? On the side of the rail? Nowhere near the rail?
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Old 02-13-2016
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It is listed in 2003 Ranger 4.0l parts at Ford.

This is the pressure relief valve part number: 9H321
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