There are so many threads that mention such familiar symptoms, so I'm writing this down as a "solved" issue to give data points that the search robots and fellow FTE'ers can hopefully find if they need it. Maybe my methodology can help somebody, including my future self when I forget in a couple years

Also, I'd like to shout out to the extensive knowledge and willing participation of sages like Subford and Conanski, among others too many to list. Your advice literally saved me money and made me a better mechanic in the meantime.

1995 F-150, 4.9, SWB, 2WD, E40D A/T. O/A 305,000 miles it started doing the famous EGR bucking. I found lots of recipes for restrictor plates and drank the kool-aid for a while. I pulled the PCM and soldered the new capacitors because I found unmistakable, tell-tale evidence of the original's failure. I got pretty good at soldering on very small surfaces, so I'm glad to have that experience at very little cost (under $5 for the caps). I lived with it until around 319k as slightly improved.

At 319k, I got codes 327 and 332, and figured I'd wait until I got to GA to fix it. I was still stationed in Hawaii then, and in the middle of an overseas move couldn't get enough of my tools in one place to get anything done.

I got sick of the CEL yelling at me in bright yellow every day last week now that I'm here in GA with 80% of my tools unpacked and decided to tear into it. First stop, I listed to Subford's advice and tested every vacuum line under the hood with a vacuum pump (free to rent at AutoZone once returned). I ended up replacing literally everything for about $25, including the hard hoses that you can also find in the "Help" section of your favorite parts store.

With new vacuum lines, I had a definite improvement in idle quality but the codes persisted. Driveability being slightly improved and only $25 in, I kept going. My vacuum can held 20" of vacuum for as long as I wanted- this is where many old trucks fail, so NEVER skip this step- you must know if your can is leaking! There are a lot of ways to make a new one if you need to- just FTE for it. Oh, and now it had a lovely hesitation off-idle. Never stalled, just acted like it tripped over itself before accelerating.

I wanted to start throwing parts at it now. The EVP Sensor, EGR Solenoid, EGR valve, PCM...I started shopping...then kept diagnosing...

This weekend, I hooked up a vacuum gauge to the EGR solenoid on the supply side, and taped the gauge to my windshield so I could watch it while driving. My new tubing was supplying a steady 20", so I moved it to the output on the solenoid, and in fact just hooked it to end of the hose that plugs into the EGR. This is where I had to take a drive, also with my multimeter taped next to the vacuum gage with the EVP sensor (EGR Valve Position sensor- an acronym within an acronym, 'RAH!!!), just to make sure they were both doing their jobs.

The EVP sensor manipulates the reference voltage from 0-5 volts as the EGR valve opens, telling the PCM that the EGR did move when instructed. the EGR solenoid should supply 8" to the EGR valve under partial acceleration under normal driving conditions. The supplied vacuum to the EGR should drop to 0" when you go 1) wide-open throttle; or 2) idle. You should see the voltage and the vacuum move at the same time. Oh, and keep the truck on the road or you will have solved a problem by creating a bigger problem! Distracted driving need not involve smart phones.

Anyways, mine tested fine. The needle jumped right to 8" vacuum when it was supposed to, and the reference voltage was moving but the reading was jumping around a little. I thought this was because my $20 multimeter just wasn't fast enough (this is true- but this critical assumption is part of the problem).

Time to start throwing parts at it now that I've physically watched everything do what it's supposed to and still throwing codes!

First up, the $1.49 Throttle Body (TB) gasket. Yeah, there's a TSB out on this, and for good reason. CHECK YOUR TB GASKET and just replace it if you don't know when you last did it. Mine was sucked up into the contours of the TB. I don't even understand how air got around it to idle correctly- ever. Idle quality improved further and part-throttle cruising is noticeably smoother and more powerful. The garbage that comes out of a 300k TB...

Codes persist...

IAC valve. This was my theory for the stumbling off-idle problem, not really a stab at the code 327 and 332. That was $45 that I don't know that I needed to spend, but the throttle transitions are clearly better now, but it still has momentary hesitation when hot sometimes...still! I kept the old one in case my new one fails. It's a NAPA/Echlin, so should be good for some time.

MAP sensor. Yes, I paid $40 for a new one, because I lost patience and remembered last time, around 200k, when my OEM MAP went out. It caused mayhem and the engine could only limp around. That was a lucky guess with parts-throwing on the first shot, but the memory of that good fix back in '07 made it my go-to part to change out. It did seem to help part-throttle power, but did not cure the codes or off-idle stumble.

EVP Senor- bought it on Amazon for $19. Even though I tested mine and it seemed within spec, I'm in parts-throwing mode now. IT WORKED- no more codes! CEL was out and driveability is PERFECT. It actually reminded me of why I love this damn truck on the test drive.

I also took the Throttle Position Sensor off and cleaned it. Mine had mud inside it (long story, involves a salvage title). Cleaned with Liquid Wrench Lubricating oil, dried off the excess, installation is the opposite of removal. NO MORE HESITATION.

Both problems are now solved.

Always question your diagnostic tools just like you question the parts you are testing. A wise professor once told me: "YOU DON'T KNOW WHAT YOU ARE MEASURING". There are three values that you get when you test:

1) What you WANT to measure
2) What you measured
3) What you THINK you measured

...and they are never the same. You can get close if you're careful. I didn't get close enough with my EVP sensor measurement. Checking two points, open and close, seems logical, but gave me a false data point that kept me from fixing this problem for many months and I could almost cry over the fuel I wasted by just dealing with it.

Anyways, that's my EGR saga. Hopefully it helps somebody. My truck has 324,000 miles and is back to it's 21 MPG form again. I could have fixed it with a $19 EVP sensor, and cleaning the TPS. I don't regret rebuilding the vacuum lines for about $25, but I did probably spend almost $100 on parts I didn't really need.

I actually bought a new PCM at one point, held it in my hands, and took it home. I thought about it, then took it back and got a refund. Good thing- it would have done absolutely nothing to fix either problem. Your case might warrant replacement of the PCM, but make that probably the very last part you throw at it since it's the most expensive.

Cheers,
John

 

Good write up! My 4.9 has a slight hesitation at initial throttle increase from idle, so I will pursue this as a possible fix. I have no CEL's coming on though. ????

Anyway, thanks for the write up!

 

Nice write up and success story. Proper diagnosis of the root cause will save you a lot of money.

I have never seen any reference to an EPS sensor in any Ford manuals. I have seen and used the term EGR Valve Position (EVP) sensor for the sensor on top of the EGR valve.

 

You could probably get past that issue for about $10:

Throttle Body gasket, $1.49.
IAC Valve gasket, $4.49 (for some reason it's 3x as expensive, even though it's smaller!)
Can of throttle body/carb cleaner, $3
Roll of paper towels and used toothbrush, $1

Remove the two rubber hoses from the top of the TB, the throttle morse cable, the wiring harness on both the TPS and the IAC, and the 4x 13mm bolts that hold the TB on the upper intake. You'll probably have to scrape that old gasket- it's an aluminum mating surface so be very careful!

Clean everything thoroughly. Take your time and scrub the years of crusty carbon out of there. When you get the TPS off, use a Liquid Wrench Lubricating Oil or maybe WD-40, just wipe off the excess, making sure to blast the throttle bores with the carb/TB cleaner. I like to use a little chassis grease around the boots for all electrical connectors, to make it easier to work with.

Here's a really helpful YouTube video describing it:

I would bet money that just cleaning your parts up and a couple new gaskets should have you running perfect again.

 

Great feedback- updated accordingly.

In any case- "EPS sensor" is redundant...like "PIN number". Good catch!