Results 1 to 11 of 11

Thread: Occasional engine "bucking"

  1. #1
    Join Date
    Jul 2018
    Location
    Northern Kentucky
    Posts
    26

    Occasional engine "bucking"

    1989 SC V6 3.8L, 54K actual.

    Over the past month or so, I'm having what I've read in other thread described as engine "bucking".
    Doesn't happen often but when it does, I have to pull over to the side of the road.
    Otherwise, "bucking" occurs. Like an on/off, felt thru the drive shaft.
    Engine runs but car is not drive-able.
    I'll let it idle for a few minutes (1 to 5), watching the tach surge from 600~800.
    As soon as the surge smooths out, all is well and I drive away.

    I thought it might be my fuel pump but the more I read here, seems like it could be a cam position sensor problem.

    Read on one post here from TbirdSCFan that seemed to describe my issue.
    He recommended unplugging the sensor, then starting the engine (which may take longer than normal) and see if the problem persists.

    Could use some help troubleshooting this.
    I didn't know that shutting off the engine, unplugging the sensor, then re-starting would isolate the issue.
    Can I unplug the cam sensor while it's surging without damaging the EEC or other components? Assuming this can be done keeping all fingers attached / away from belts.
    I'm willing to shut the car off and unplug the sensor if needed, just trying to prevent getting stranded or needing a tow.

    Any other thoughts on this would be appreciated.
    Video's below to help describe.

    On the highway, I could feel the "Bucking" coming. Let off on gas, pulled over and shot this video of how it surges at idle. If I would have attempted to drive away, bucking would have occurred.

    Last edited by CR125Honda; 02-19-2020 at 11:06 PM.

  2. #2
    Join Date
    Jul 2018
    Location
    Northern Kentucky
    Posts
    26

    Video #2

    Only allowed one video per post.

    Three seconds into this video, surge goes away.


  3. #3
    Join Date
    Jul 2018
    Location
    Northern Kentucky
    Posts
    26

    Video #3

    Running fine..


  4. #4
    Join Date
    Jul 2018
    Location
    Northern Kentucky
    Posts
    26
    Just to add..
    I did both Key on Engine off (KOEO) and Key On Engine Running (KOER) scans today.

    First one engine cold. KOEO
    Codes 21 and 24 came up.
    Read up one them and I think they are normal for cold scan.

    Warm scan. KOER
    Codes 77 and 74.
    Determines those are probably normal too.

    Did the "goofy?" procedure - steering wheel right/left, brake pedal,accelerator pedal. KOER
    rescan - no codes
    Last edited by CR125Honda; 02-19-2020 at 08:46 PM.

  5. #5
    Join Date
    Jul 2005
    Posts
    466
    Good evening


    When I experience the infamous "bucking" the first four components to suspect and check for are the following:


    MAF sensor could be on it way out. Try cleaning the sensor. Use an approve cleaner to prevent damage. Check for operation voltage range.

    https://youtu.be/JulcFtjirqs

    DIS could be on it way out. Remove DIS and inspect for compromised heat sink compound. Check bolts for evidence of corrosion (one of the four DIS bolts serves a ground}.

    Cam sensor could be on it way out. Check clearance between the cam sensor connector and the supercharger belt. Swap with a known good unit.


    Harmonic balancer could be on it way out. With the car in idle and park check the harmonic balancer pulley a visual wobble. Shut down car and check for missing harmonic balancer and pulley bolts.

  6. #6
    Join Date
    May 2002
    Location
    Dallas, TX
    Posts
    5,746
    Quote Originally Posted by sam jones View Post
    Good evening

    Cam sensor could be on it way out. Check clearance between the cam sensor connector and the supercharger belt. Swap with a known good unit.
    Also, to confirm if its the cam sensor, simply unplug it. It takes a few tries to get it to start, but if the bucking problem goes away, replace the cam sensor.

  7. #7
    Join Date
    Jul 2018
    Location
    Northern Kentucky
    Posts
    26
    Quote Originally Posted by sam jones View Post
    Good evening


    When I experience the infamous "bucking" the first four components to suspect and check for are the following:


    MAF sensor could be on it way out. Try cleaning the sensor. Use an approve cleaner to prevent damage. Check for operation voltage range.

    https://youtu.be/JulcFtjirqs

    DIS could be on it way out. Remove DIS and inspect for compromised heat sink compound. Check bolts for evidence of corrosion (one of the four DIS bolts serves a ground}.

    Cam sensor could be on it way out. Check clearance between the cam sensor connector and the supercharger belt. Swap with a known good unit.


    Harmonic balancer could be on it way out. With the car in idle and park check the harmonic balancer pulley a visual wobble. Shut down car and check for missing harmonic balancer and pulley bolts.
    Thanks for all the suggestions.

    I'll pull the MAF and clean it. I do have Valvoline MAF spray.
    Just a quick visual on the DIS give me a little concern. Will pull, clean and apply new compound.(been reading up on that can of worms - dielectric grease, silicone, thermal paste, etc. - wow)
    Here's a pic of the clearance. Only known good unit for me would be to buy a new one.
    Looking at the harmonic balancer while it's running "looks" fine to me. I see no wobbling,etc..

    Quote Originally Posted by TbirdSCFan View Post
    Also, to confirm if its the cam sensor, simply unplug it. It takes a few tries to get it to start, but if the bucking problem goes away, replace the cam sensor.
    And thank you.
    Will try the things above and see where that gets me.
    If/when it bucks again, I'll shut the engine off then unplug the cam sensor and try to re-start.

    Appreciate your help to all

    belt to harness clearance
    Name:  IMG_9564a.jpg
Views: 96
Size:  38.0 KB

    old compound around DIS
    Name:  IMG_9566a.jpg
Views: 99
Size:  68.3 KB

  8. #8
    Join Date
    Jul 2018
    Location
    Northern Kentucky
    Posts
    26
    Update...

    Replaced the Cam sensor. Think that did the trick!

    After a 30 minute drive the other day, and subsequent 20 minute rest, the car would not start. Was trying but would not fully start.
    I unplugged the cam sensor.
    2ea. 10 second cranks, no start.
    3rd start attempt, it started. Ran good above idle. It never died but idle rpm was very low and somewhat rough.
    Got on the highway and drove home. Ran fine on highway.
    Replaced the cam sensor yesterday.
    Have driven it a few times since without issue!

    BTW - couldn't find motorcraft locally. O'reilly's had the brand "Standard", $33.
    As I read in another thread, I could see where the Ford number had been scratched off the new part.

    Thanks again for everyone's help..
    Ken

    ***************

    Forgot to mention..
    Before I took that drive above, I pulled the DIS.
    The old compound was still pliable.
    No need to reinvent the wheel so I cleaned the dirt off around the edges.
    Then worked the existing compound with my finger To make a smooth, consistent layer covering both surfaces.
    Torqued the screws (21in/lbs) back in place.
    Turns out, this wasn’t the issue for me.
    Name:  C8AF1093-ACE3-49E3-9097-41D1B9B1241E.jpeg
Views: 79
Size:  3.20 MB
    Last edited by CR125Honda; 02-24-2020 at 09:16 AM.

  9. #9
    Join Date
    May 2002
    Location
    Dallas, TX
    Posts
    5,746
    Great! Cam sensors are fairly consistent with that problem.. And here's a heads up, just because its a new one, it might still act up.
    I've had 1 give me problems, I've unplugged/replugged and it runs fine for a long time. Something to keep an eye on is if the tach starts to consistently drop out and come back, or not.. try swapping it out.

  10. #10
    Join Date
    Jul 2018
    Location
    Northern Kentucky
    Posts
    26
    Quote Originally Posted by TbirdSCFan View Post
    Great! Cam sensors are fairly consistent with that problem.. And here's a heads up, just because its a new one, it might still act up.
    I've had 1 give me problems, I've unplugged/replugged and it runs fine for a long time. Something to keep an eye on is if the tach starts to consistently drop out and come back, or not.. try swapping it out.
    Thanks Tbird,
    Another drive today without issue.
    Sure hoping that was it!
    Will do on the noticing the tach if/when it acts up again. Understand how they're directly related.
    The worst my tach did do with the old sensor is shown in the first video above.
    Just a slight on/off hunting motion at idle and when slightly rev'd.
    KC

  11. #11
    Join Date
    Sep 2003
    Location
    Poughkeespie NY
    Posts
    1,150

    PM box

    Quote Originally Posted by sam jones View Post
    Good evening


    When I experience the infamous "bucking" the first four components to suspect and check for are the following:


    MAF sensor could be on it way out. Try cleaning the sensor. Use an approve cleaner to prevent damage. Check for operation voltage range.

    https://youtu.be/JulcFtjirqs

    DIS could be on it way out. Remove DIS and inspect for compromised heat sink compound. Check bolts for evidence of corrosion (one of the four DIS bolts serves a ground}.

    Cam sensor could be on it way out. Check clearance between the cam sensor connector and the supercharger belt. Swap with a known good unit.


    Harmonic balancer could be on it way out. With the car in idle and park check the harmonic balancer pulley a visual wobble. Shut down car and check for missing harmonic balancer and pulley bolts.
    Sorry to interrupt thread but Sam your PM box is full. Tried sending a reply to our discussion but will not go through until inbox is emptied.

    Randall
    '90 35th Anniversary 5spd 53k
    '95 SC 5spd 65k

Similar Threads

  1. Head work quote: $950.
    By Dahoopd in forum Technical Forum
    Replies: 15
    Last Post: 07-13-2004, 09:41 PM
  2. Hmmm...Occasional check engine and chech gauges light..
    By SLP007 in forum Technical Forum
    Replies: 1
    Last Post: 06-16-2004, 01:13 PM
  3. Quote from a commedian
    By cary Jackson in forum Non Technical Forum
    Replies: 4
    Last Post: 10-05-2003, 01:22 AM
  4. ?How to "quote"?
    By lazybird4pt6 in forum Super Coupe Club of Ontario
    Replies: 13
    Last Post: 08-15-2003, 12:25 PM
  5. INSURANCE QUOTES ---> which to take?
    By Bill McNeil in forum Super Coupe Club of Ontario
    Replies: 11
    Last Post: 03-05-2003, 12:25 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •