97 expedition 5.4 stumble at 1300 - 1500 rpm

[James Meyers]

Engine stumbles when slowly accelerating. When I reach 1300 rpm egr valve lifts off its seat. Continues stumble thru until I reach 1500 rpm. Egr drops back on it seat and it smooths out. New egr. (Old one had a leaking diaphragm). New backpressure transducer. No codes are thrown. Ecm is signaling vac relay to allow 3 in vac to egr at 1300 to 1500 range then drops off. Just annoying. It idles, starts & runs great other than this. O2 sensors check out fine on scanner. Coolant temp 190. Doesn't do it in open loop.
This is my first post. Take it easy on me guys. I'm new at this!

 

[MikeA]

Take a look at your
MAF (mass air flow ) sensor, might need cleaning or replaced.

But first make sure there is no air leak between the MAF and the throttle body, if there is a leak, this will cause problems, there should be zero leaks in area just mentioned.

MAF sometimes , gets over looked as a possible problem, because it will not always throw a code out, but will cause hesitations and make the motor feel like its dumping power.

To clean MAF , spray it with CRC brake cleaner.

I dont remember the specs on testing MAF, shouldn't be hard to find on internet, or someone here knows .

 

[James Meyers]

Thanks Mike for the fast response. I will definitely try the MAF cleaning and get back to you. Have checked for vac leaks but not the air intake. Will add that to the list. Thanks again for your time.....

 

[Mr67Stang]

watching...

 

[James Meyers]

Hello again! Just did a thorough inspection of air intake ducting for leaks and connection status. It's in good health. Did test to confirm status of the MAF sensor.. The voltage and ground test are good. Voltage at operating temperature at idle is
. 954. At 1500 and 2500 voltage is in spec. and moves smoothly through rpm range. I hope you have some more good suggestions on further testing as I'm at a brick wall.

I'm not sure why ECM is sending a signal to the vac regulator solenoid at 1300 rpm then drops it at 1500. Something is talking to the ECM feeding it bad info.
I've been swearing at it. ( hasn't helped)

Any and all suggestions would be appreciated!

 

[MikeA]

inside the throttle body there are two small ports from the EGR valve. these ports may be clogged up with carbon, open your throttle up and if its all black inside, remove throttle body and clean, specially the 2 small port holes to the egr.

Have you tested the egr vac solenoid?
Has your check engine light come on, if so what codes show up?

 

[James Meyers]

More info. For thought...
Tested vac solenoid ohms. Looks good. Did vac test with tee in vac line while driving. My testing source said I should see 5 in vac under acceleration. Only have 3 in. vac. Not sure if it's a faulty solenoid or my Guage. Hate to sling more parts at it if I can narrow it down to one thing.

Still TESTING in TEXAS......

 

[James Meyers]

Sorry I missed your post Mike.
I have removed the throttle body for inspection earlier when I found the faulty egr. Port is clear. Did a thorough cleaning of the throttle body at that time. I have done a lot of testing and checking before I ever posted on this forum. I am running out of ideas.
I know people on here are alot more knowledgeable than me. I really appreciate the fact there are people like yourself that share your time and knowledge with a guy like myself.
Forgot to mention that no codes displayed

 

[MikeA]

Ok, just seen your post

Did you test the egr itself?, had to reread original post, you replaced egr already

 

[MikeA]

Found this link, lets see if it helps us

http://easyautodiagnostics.com/ford/4.6L-5.4L/how-to-test-the-egr-system-1

 

[MikeA]

Test TPS (throttle position sensor)

I can not think of anything else to check, leaves me pointing to pcm/ecm may be the problem, if not bad connection someplace.


Tossing this one out there, try clearing pcm, or if you are lucky like I am and have a junkyard near, to get a used one cheap for testing

 

[James Meyers]

Thank you Mike.
My 97 is the same as your 98.

That is the link I've used to diagnose my system.
Went through each step carefully on each device. Even double checked the backpressure transducer. Everything tests OK. That's what has me stumped. I keep going back to the ECM signal to the vacuum solenoid at 1300 rpm. Why am I getting a signal?
Wondering if ECM is faulty. Been told they don't go bad very often. Usually something is telling it to do whatever.

 

[MikeA]

Try clearing pcm , get a cheap used one from junkyard for testing, can not think what else could be problem.

I am pointing at pcm or loose wiring.

 

[James Meyers]

Latest update!

Checked TPS as per one of your last post. Found a gap in signal going to the PCM. I'm hoping this cures my problem. Gap in throttle movement is near WOT. Stumble is lower in rpm range but still could be the culprit.
Will keep you posted. Just ordered one from Rock Auto. Be here end of week.
Thank you again for your time Mike. YOUR THE MAN!

 

[MikeA]

I hope that fixes it for you!

 

[1997SCEBFEX]

I've replaced the TPSs twice in almost 20 years (purchased May '97). it does get memory especially that rpm range for a lot of roads I drive.
hopefully it's your huckleberry.
Let us know.

 

[James Meyers]

I am glad to announce that with the help from the guys on this forum that I have solved my problem. Received a new TPS today. After instalation and test driving confirm that was the culprit. I can't explain it but my fuel trim numbers are closer to being neutral than before. Idles and runs better throughout rpm range.

Not only did I solve this problem, I got an education regarding the engine control system.

Thank You for your time........

 

[MikeA]

Glad your all fixed .

Thanks for coming back to post problem solved