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carlislesc
04-01-2009, 05:58 AM
Strange Problem Here. Every other day at slow or highway speeds, the car starts bucking. I get it to stop bucking by turning off the ignition and restarting. This stops the bucking everytime until the next trip. Sometimes the car is difficult to start after it was bucking, but it does start. At times after the restart the RPM guage does not kick in right away. But it does kick in shortly thereafter.

Which of the following would be the one to look at first? Dis pack; MAF or cam sensor, vacuum line, fuel pump or fuel line, fuel filter, Something else??

Let me know how you resolved the issue

QuickMustang
04-01-2009, 06:51 AM
Cam sensor...It sends the signal to your tach...

S_Mazza
04-01-2009, 10:53 AM
It could be the ignition module (the gray one on the passenger side). It's probably not the coil pack.

Do you have a check engine light? If so, read the codes. Be aware that a failing DIS module sometimes gives codes that seem to implicate the coil pack too (but it's often the DIS instead).

It sounds, however, like the cam sensor is a likely place to start.

boltz
04-01-2009, 12:23 PM
It is your cam sensor trust me on this one. Been there done that on both my S/C's. It's an intermittent fault with the sensor.

the-big-e
04-01-2009, 01:08 PM
My vote is for the DIS module.....

But it could be the cam sensor, as well....

Evan_90SC
04-01-2009, 03:10 PM
I had the EXACT same problem with my car... It was the cam sensor.

mikedenton49
04-01-2009, 05:20 PM
Cam Sensor.

Same exact thing.

89SCBoosted
04-02-2009, 12:05 AM
dirty hot wire in maf needs cleaning i would guess, happened to me 3 weeks ago, the oil from my k&n screws it up regularily. i still had my tach operating properly and had a failing cam sensor pickup before.

jimmy303
04-02-2009, 01:10 AM
Had a similar problem with my '90 SC, over the past few days. I would get a mid-range bucking, (at which time this was happening, the tach would jump all over the place) and it would seem to be more severe at cold start-ups than any other time. Downright scary, since it seemed to show itself at the worst times (such as, during a maneuver where I needed the expected power which was not there, or while it was raining, when the sudden return of power was unexpected:eek:).
But, a good (drinking) buddy of mine - who is a very trusted service mgr. @ the local Ford dealership, said it sounded like her coil pack was dying or losing supply voltage or trigger signals. His first suggestion was to check the supply harness to the coil pack, and jiggle it around to see if that helped. If the problem persisted, his next suggestion was to replace the pack. So, I unplugged and plugged the harness into the coil pack several times, and she has been behaving herself since. May be a fluke, or an intermittent connection problem solved by moving the plug at the coil-pack and getting a more solid connection. We'll see tomorrow morning, when she has had some time to rest and cool off overnight.

jimmy303
04-02-2009, 01:13 AM
But, the way you say your tach was acting, I may look at the cam sensor, since that is quite responsible for your RPM monitoring...

S_Mazza
04-02-2009, 10:15 AM
Just so you guys know, a failing DIS module (not the coil pack, but the small gray module) can also take out your tach signal. Had it happen twice.

thunderkid84
04-02-2009, 11:21 AM
Had a similar problem with my '90 SC, over the past few days. I would get a mid-range bucking, (at which time this was happening, the tach would jump all over the place) and it would seem to be more severe at cold start-ups than any other time. Downright scary, since it seemed to show itself at the worst times (such as, during a maneuver where I needed the expected power which was not there, or while it was raining, when the sudden return of power was unexpected:eek:).

ya know, i've been having the same problem with mine. also on cold start ups it is hard to start and has trouble keeping an idle. but once warmed up vacuum is perfect and no more hard starting.

i'll try the little trick you did. but im leaning towards bad DIS/cam sensor.

TbirdSCFan
04-02-2009, 12:36 PM
Not DIS... not wires... not even MAF... and certainly not the blinker fluid.

Cam sensor :cool:

TbirdSCFan
04-02-2009, 12:42 PM
But, the way you say your tach was acting, I may look at the cam sensor, since that is quite responsible for your RPM monitoring... Actually the DIS/ICM is responsible for the tach signal to the guage and the EEC. The only thing the cam sensor is used for it to identify where cylinder #1 TDC is during the 2 crankshaft rotations for the DIS/ICM. 1 pulse every 2 revolutions. It can wreak havoc with ignition timing if it sends a spurious or fluttering signal. Thats why it may be better to unplug it and run without it until you can replace it.

thunderkid84
04-02-2009, 01:53 PM
Not DIS... not wires... not even MAF... and certainly not the blinker fluid.

Cam sensor :cool:

already swapped wires and cleaned the MAF.

Havent checked my blinker fluid tho......:confused:

:D:D

S_Mazza
04-02-2009, 03:16 PM
Actually the DIS/ICM is responsible for the tach signal to the guage and the EEC.

Yeah, that's why I keep mentioning it, even when people tell me "No." :rolleyes:

carlislesc
04-11-2009, 03:21 AM
I replaced the cam sensor last week with no problems since then. Looks like an oil residue was on the underside of the bad sensor. I replaced it with a used one that still had a small orange circle in the middle of it on the underside. Not a 15 minute job for me, but not too bad. Once you find it and disconnect several electrical connections to make it easier to work, you can actually get your hand in there (somewhat). Watch that you do not break the tabs that hold the electrical connection to the sensor and as always do not drop the screws during removal!!

Pick up a case of Yuengling Larger to throw in the back of the SC with those obsolete parts after you leave the Ford Nationals show in Carlisle, PA this June. You'll need one or two after some of your future repair work.

toronto_1990sc
06-25-2009, 03:45 PM
sounds like I have a similar problem...can you tell me exactly how you replaced the cam sensor?

thanks.