Quick acceleration= misfire or jerk

Chicago SC

Registered User
My '91 SC just started to misfire or run rough when i get on the gas. If I drive it normal, it runs perfect. But once I really get on the gas, it will start to drive erratic. From 50 MPH or so, I can accelerate almost to the floor with no or little miss. But from a dead stop or when slowing down from a turn, it misses qiute bad when I punch it. The quicker I hit the gas the worse the shake. If i accelerate to WOT gradually, its okay or misses slightly at higher RPMs if anything. However, I can rev it to near redline in park or neutral without any misfire at all. Also it sometimes has a rough time finding idle when started up. this happens about 10% of the time, but it never completely dies. Could a clogged cat or muffler do this? how about a loose or frayed wire in DIS area? I'm stumped........... please help....
Thanks
--Chicago SC--
 
This is a bit hard without actually beign able to drive it. I'm a bit new to the SC world, so won't comment on whether this is typical of the ECU or anything else. But, in the old engine world, I'd say that it's bad plugs or wires. When were the plugs changed last? I understand that the plugs are difficult to change, so you should wait to hear from other veterans if this is a typical SC problem. Sorry I couldn't help more.

Regards,
John
 
90% of the time it can be caused by bad spark plugs and wires. When was the last time you changed yours?
 
Ignition is the first thing I would guess too, plugs and wires. Of course, in our ignition, the DIS and coil pack could also be at fault, but there are simpler problems to eliminate first.

Now, because you mention it happens more during quick accel, I think fuel is also a real possibility. The first logical thing to check here is the fuel filter. Its easy to change, cheap, and probably needs to be done anyway. Under the passenger side floor, below the door. The fuel pressure regulator might also cause misfire, but thats a long shot. It could also be the fuel itself, did this just start after a refill?

You might also take it to somewhere like Autozone and check for stored codes.
 
Original plugs????

I just bought the car a month ago, but have only driven every day for about two weeks( I bought it with bad ABS and had to fix). I havent changed the plugs and wires yet because I've been working long days. Normally I change them on all my new cars right away; so that came to mind right when it started to misfire. When I checked the wires for cracks or burns they looked fine, but there was something I did notice. The wires were Motorcraft so I figured that whoever did them last time either bought them from Ford, or had them switched at Ford. But then I noticed that each wire had 1990 or 1991 printed on it.. my SC is a '91 ... If you bought Motorcraft wires right now; would they have a year printed on them like this, or does this mean that they are the original wires that came on the car new...........?????????
 
lol I guess you've determined the reason for your misfire!

God I hope the rest of that car wasn't maintained that way :eek: :eek:

Welcome to the club BTW; nice to see another SC in the Chicagoland area :)
 
Holy *****!! Thats Crazy!!! It has 132k! I bet the plugs are original too then! If that year printed on them means they are that old, someone must have not been able to do them thereselves or couldnt afford to have it done. I know changing them sucks, but that is no excuse for this.....BTW the rest of the car was maintained well. I drove it out on route 53 and 294 (digital chaos should know these roads) and after that it started to misfire. Probably because I fouled a plug; or have sparks jumping between wires. I was running it kind of fast on the tollway for a good 15 minutes above 90 MPH.. I need to change those tomorrow night for sure!!!! I'm sure it will help but I'll let ya know if it takes care of everything..... lets hope so..

Chicago SC
 
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Yes I know them.. I am pretty far from there but I was near those roads when recently going to the auto show :)

If those plugs are original, they should look interesting. Post pictures if you can get them, include the date stamping on the wires. Its possible the original wires were simply reused. I've a Wranlger TJ which has gone as long as 100k on OEM plugs/wires, lol.

I would also definately change the fuel filter. If that car was exposed to a lot of city traffic, it probably could benefit from this.

Another thing while you have the top apart, I would look at your motor mounts. The stock units were hydralic, liquid filled, and had a bad habbit of failing around 50k. Even if yours were replaced w/ OEM, they may be bad again. This condition can cause a number of other problems inc a cracked oil pan, so it is serious. You can find significant information about this through a search.

Goodluck, and let us know what you find!
 
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I bought my 89 SC in 2000 and it had stock wires (with cylinder numbers on them) and maybe even plugs as they were correct Motorcrafts. The car had 92,000 miles and ran great . The car ran great so I bought new Motorcraft wires and plugs. You would be hard pressed to get better performance from the Motorcraft plugs or wires.
 
Considering all of the Ford engineers screw ups on the car, you got to hand it to them on the plugs and wires. When I replaced mine they were AT LEAST 4 years old (The plugs) and the wires seemed to be OEM from 1990. 13 years+ on wires is a darn good set. Hope my Magnecors last that long....
 
Autolites are supposed to be the next best thing to the motorcraft AWSF34PP plugs. Auto Zone is going to start carrying them so keep checking, prices should be right around those of the Bosch Platinum +2's.

As for wires, I went with a set of Borg Warner wires on one of my SC's and Carol wires on my other SC. Both run fine. Wires were about $40.00 as compared to the $119.99 I was quoted from Ford.

By the way, I paid $11.95/ea. for the motorcraft plugs in my 92 SC but I am going to change them out this summer. Its been two years and it misses a tad every once in a great while but only when the engine is cold, maybe its not the plugs but I think they clean when they hit higher temps.
 
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