Occasional engine "bucking"

CR125Honda

Registered User
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.

 
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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
 
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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.
 
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.
 
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..

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
IMG_9564a.jpg

old compound around DIS
IMG_9566a.jpg
 
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.
C8AF1093-ACE3-49E3-9097-41D1B9B1241E.jpeg
 
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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. :cool:
 
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. :cool:

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
 
PM box

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
 
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