SC Bucking Under Boost

BlackSC

Registered User
Ok, here's the deal - this is a new to me car with only 70k miles on it. I love the car but the problems are cropping up very early. This is a 93 SC with the M5R2. Lately whenever I try to push more than about 3 or 4 pounds of boost through the sc it bucks like a belt is slipping badly or something. I was wondering if anyone else had had similar problems or any ideas.

Maybe whatever's causing the boost problem also caused the other problem I just had - the front cat just completely melted and broke down on the inside, which in turn slagged the next converter as well. Related maybe? Thanks in advance for comments.
 
More than likely your bucking condition is related to your plugs and wires. I got mine about 7-8 months ago and the same thing was happening. I ended up replacing the plugs, wires, DIS module and belts for good measure. The plugs are generally good for about 60k. Just sounds like you need a tune up. Mine ran great after those adjustments. Now I just need O2 sensors! General rule of thumb for the supercoupe is to fix the small stuff first. These cars are very sensitive to any problem, no matter how small. Short story, when my car was under warranty, it had a similar 'bucking' problem. The dealership ended up putting new heads on it, but the problem was a bad spark plug wire. I'm not complaining, because I have newer heads on the car, but it was just a plug wire. Check the small stuff first.

And watch out for the #4 plug. It's a bit@# to get to without removing the upper IC tube.

Also, use the search function on this forum, it may answer a lot of questions for you. It has me. We all have the same troubles with these cars.
 
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Makes sense....

Yeah, that sounds reasonable. I have searched and seen other posts about this problem but none of them mentioned problems with the cats - but if plugs aren't firing, I suppose that it's running too rich anyway. Thanks for the suggestion, the new ones will be on the car as soon as I've got time.
 
I had exactly your problem in August. Everyone said plugs but I wasn't sure it could be that easy because my plugs only had 8K miles. Sure enough, it was plugs. I got lucky and only replaced the left 3 to cure the problem - kept the right 3 in place. Now I have 3 new Autolites on the left and 3 slightly older Motorcrafts (with 8K more miles) on the right.

It would run great up to 3-4 lbs boost then buck like hell.

Change the plugs.

Jon
 
sounds like plugs to me as well. but they may not need to be replaced (you should anyways...) but what was happening to my friends car is that under boost, the plug would work itself loose some how, and cause it to buck. so he got new plugs and wires. same thing happened. so he really wrenched them in and put some anti seize on them and no problems since.
 
thanks guys...

Car is runing perfectly again!

Thanks for the tip - replaced the plugs, didn't fix it. Then replaced the wires, and she runs beautifully! What a xmas present! Now she just needs tranny work. Thanks again for helping out an inexperienced sc'er!
 
Bucking

Mine does the same thing, but only when it's hot....i think. Mine gets up to about 8 or 9 then bucks like hell, right away i step off the gas 'cause i don't want anything (else) to break. it's wierd because if i'm at a high RPM, then it bucks at a high boost, but if i'm at like 1,200 RPM in third and i step on it, it'll buck at like 6 psi boost.
I've read so many of these forums to find the problem and every one has said something about the plugs and wires - i just spent $20 on supercharger fluid....i know, what a jack-*** i am. here's what's confusing me though - if it is the wires/plugs, why would it only do it under high boost and not while driving regularly?
And lastly, i'm almost definitely going to get new wires, which ones should i get? i was planning on buying the "Carol" wires from autozone because they're $40.00 and my dad works for that company so i could get some of that money back, but now i'm not sure after reading these threads....someone help, i'm 17 years old and since i just bought the car that i really want - a '93 SC - i'm trying to get into bein a "grease-monkey" because i care about this car and i want it to look/run well. thanks
 
It will probably buck (miss) at different boosts depending on the load on the engine. If you are driving slowly in 3rd around the neighborhood it will miss easier because you are putting quite a load on the engine (lugging) stepping on it in 3rd at slow speed. At higher rpms the engine isn't loaded so hard so it will take more to miss.

The miss under load (and boost) is due to the boost actually preventing the spark from crossing the gap due to high pressure in the cylinder. It can happen if the gap is too wide or the plug is faulty. Under no boost a weak plug will still fire okay.

I would stick with the stock Motorcraft wires from Ford or maybe Autolite wires. There may be equal or better wires but Motorcrafts seem to always work great.

Good luck.

Jon
 
DONE!!!

Well, i got sick of the bucking so i decided to do something about it. I took out a few of the plugs to see if they might be the problem, there didn't seem to be anything wrong....but they weren't platinum plug. It saddens me that somebody would do that to an SC. When i put the plugs back in it ran even worse than before, so i ordered Autolite Double platinum plugs (part # APP 2544). I put those in, put the old wires back on and it ran worse. I drove it to AutoZone and bought a set of wires, i got Carol brand wires because my dad works for the company, i can get a good deal, they were only $30 and they had a warranty. I put on the new wires and it ran beautifully, the wires were the problem.
Looking at the engine from the top I thought i would never get to the plugs to take the out and put new ones in, but i lifed up the car and i got all of the from underneath, except for the one near the AC - i got that from the top. A lot easier than I thought. The hardest part was snakin the wires under the fuel line, those retards at Ford couldn't have found an easier place to put them?
 
bucking/cutting out

my car was doing this too...wasnt' sure why. also didn't think it was wires or plugs...i unplugged my battery for 30 minutes to reset my computer...runs BEAUTIFULLY!!! no idea why. anyone else want to try this and see if it fixes it? i can boost fine and play around all i want again. i love it. steve.
 
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