Hello everyone. I have a 89 sc and every now and then the car will start bucking and the tachometer moves up and down. Most times it will only do it for a little while but as of lately I've been having to throw the car in neutral, shut it off, then turn it back on to stop the bucking while driving. I've did some searching and found that it nas something most like to do with my cam sensor, crank sensor, or my dis. Please help.
please help!!! why is my car buckin?
- Thread starter turshin
- Start date
Well its like this. Some days it doesn't do it and other days its bad on hot days or cool nights. Which leads me to believe that whatever is causing the problem hasn't completely clonked out yet but its on its way. I'm almost to the point of replacing all components of the ignition system. But I don't wana spend any money I don't have to.
BirdofPrey97
Registered User
X2. Why? Because of years of experiance with the SCs. Not 1 or 2 but 100 to 200 of them.
TbirdSCFan
Registered User
Like some of us, Ed has SC collection syndrome.
Maybe with 100 or 200 you guys haven't had enough drive time to have the cam sensor fail.The issue is 99% cam sensor. The diagnostic test is to first pull codes to see if a CID code is set (which it probably won't be, but theres a chance). The next step is to disconnect the cam sensor and see if the problem goes away.
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90sc35thann
Registered User
I thought the cam sensor instructed the computer on when to throw fuel and once the car was started it didn;t instruct the computer on anything else. Which is why there is a one in three chance of the car starting without a cam sensor. Crankshaft sensors on the other hand can cause the ignition to intermittently cut in and out. I agree with the other two posts above that it sounds like a DIS issue. Only time will tell until it gets swapped out.
TbirdSCFan
Registered User
OK. Let me put it more directly.. I'm not just guessing about the cause of the problem or passing on hear-say about how something might do whatever. I've been through all 3 of the related failures more than once. Its the cam sensor.
S_Mazza
Registered User
OK. Let me put it more directly.. I'm not just guessing about the cause of the problem or passing on hear-say about how something might do whatever. I've been through all 3 of the related failures more than once. Its the cam sensor.
... unless it's the DIS.
Seriously, I think either one could cause this. But my car had very similar symptoms and it was only the DIS. Still, since disconnecting the cam sensor is a free test, I would check that first.
With engine off, disconnect it and make sure the wires are out of the way of the belts. Then start (it may take a few extra tries) and drive. See if it changes.
S_Mazza
Registered User
If your mechanic is the type of mechanic that listens to you, you might want to give him some direction as to what components have been suggested here.
suprchargeit
Banned
I agree that "most likely" your problem is your cam sensor... BUT! I think most anyone on here can say or agree that without actually driving the car ourselves, diagnosing this kind of problem over the net by a slightly incorrect description can lead to replacing more than what is actually wrong. I mean we are talking about SC's right!
So here is a ballpark check list to go through that could cause "similar" issues starting with the easiest. In the process, you may find something that could be replaced later to have piece of mind
I am going to assume you have a multimeter or can get one. And that you know how to use one.
- Voltage check- check the alternator charge voltage- should be *no less* than 13.0v
- Check coil voltage (while running)- red wire with green stripe- no less than 11.9v *I think*
- Check fuel pump voltage- pink wire with black stripe- either test @ the harness connector under the car ( near the front of the gas tank strap on the passenger side) or lift up the rear seat cushion and probe the wire before it goes through the floor. no less than 11.9v
- Check grounds (while running) - make sure you have a good ground connection the the engine. check continuity from the ground battery terminal to the engine block and especially the accessory brackets on the front of the engine. the closer to 0.00 it reads the better the ground connection!
- Fuel pressure- key on engine off- should be right around 40 psi- key on engine running- 30-35 psi
- Check the harmonic balancer- while running look at the balancer and see if it is wobbling. these are notorious for breaking, right where the steel sleeve stops (for the front seal). When they do break the outer section rotates on the crankshaft causing the ignition timing to be thrown off. while there I would check the torque on the main balancer bolt just so you know it is tight!
- check the connectors at the ignition (DIS) module these are more often broken then not due to incorrect removal. make sure it is making a good connection with the terminals inside the ignition module. make sure all of the wires going to the connectors for the ignition module are in and clipped in all the way. I have seen a couple of times where a wire had just worked its way out of the plug to the point of no connection.
- check for die-electric grease under the ignition modules heat sink. if none then apply some.
- make sure ALL of your engine harness connections are good!
If all of that checks fine then I would go ahead and replace the cam sensor. Because you have an issue with your tachometer needle when it starts "bucking" I will also say that it is a 90% chance that the cam sensor is your issue!
If it still acts up after changing it then the you will need to change the ignition module.
A couple of the things I suggested above, would be considered unnecessary but if you are having an intermittent issue like this then why not make sure most everything else is good, so you dont have to worry what will be going bad next! After all remember, you are driving a SC!
I hope that this helps in some way for you.
Good luck!
! So here is a ballpark check list to go through that could cause "similar" issues starting with the easiest. In the process, you may find something that could be replaced later to have piece of mind
I am going to assume you have a multimeter or can get one. And that you know how to use one.
- Voltage check- check the alternator charge voltage- should be *no less* than 13.0v
- Check coil voltage (while running)- red wire with green stripe- no less than 11.9v *I think*
- Check fuel pump voltage- pink wire with black stripe- either test @ the harness connector under the car ( near the front of the gas tank strap on the passenger side) or lift up the rear seat cushion and probe the wire before it goes through the floor. no less than 11.9v
- Check grounds (while running) - make sure you have a good ground connection the the engine. check continuity from the ground battery terminal to the engine block and especially the accessory brackets on the front of the engine. the closer to 0.00 it reads the better the ground connection!
- Fuel pressure- key on engine off- should be right around 40 psi- key on engine running- 30-35 psi
- Check the harmonic balancer- while running look at the balancer and see if it is wobbling. these are notorious for breaking, right where the steel sleeve stops (for the front seal). When they do break the outer section rotates on the crankshaft causing the ignition timing to be thrown off. while there I would check the torque on the main balancer bolt just so you know it is tight
! - check the connectors at the ignition (DIS) module these are more often broken then not due to incorrect removal. make sure it is making a good connection with the terminals inside the ignition module. make sure all of the wires going to the connectors for the ignition module are in and clipped in all the way. I have seen a couple of times where a wire had just worked its way out of the plug to the point of no connection.
- check for die-electric grease under the ignition modules heat sink. if none then apply some.
- make sure ALL of your engine harness connections are good!
If all of that checks fine then I would go ahead and replace the cam sensor. Because you have an issue with your tachometer needle when it starts "bucking" I will also say that it is a 90% chance that the cam sensor is your issue!
If it still acts up after changing it then the you will need to change the ignition module.
A couple of the things I suggested above, would be considered unnecessary
but if you are having an intermittent issue like this then why not make sure most everything else is good, so you dont have to worry what will be going bad next! After all remember, you are driving a SC!I hope that this helps in some way for you.
Good luck!
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suprchargeit
Banned
suprchargeit
Banned
If you are going to bring it to a shop then before getting into any description of your problem, ask them if they have a oscilloscope! that is what will be needed to test the cam sensor and ignition module signals. If they dont have one then I suggest going somewhere else, otherwise they would be doing the exact same thing you would be doing on your own!
TbirdSCFan
Registered User
They will be cluele$$.
Ford was clueless when trying to fix the same issue on mine back in 1995. However, 3 trips to the shop, 1 DIS, 1 EEC, and 1 cam sensor later they figured it out.
I gave them $750 for their efforts.
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S_Mazza
Registered User
They will be cluele$$.
Ford was clueless when trying to fix the same issue on mine back in 1995. However, 3 trips to the shop, 1 DIS, 1 EEC, and 1 cam sensor later they figured it out.
I gave them $750 for their efforts.
They changed the EEC? Oh, boy. That's the classic "I have no idea what I am doing" move. I think I can count the number of legitimately failed EECs I have seen on one hand.
TinManSC92
Registered User
Uh huh! Dont get me going on part changers. I mean car mechanics. Its almost an oxy moron. Ha!
They never seem to tire of the guessing game either. $$$$$
They never seem to tire of the guessing game either. $$$$$