Misfiring

[chrism3784]

My SHO's was running great with all the work I've done to it. Last night I drove up to Orlando, about 175 miles, no problem, hauled ass. I even got into a race with a VW and won, we got up to 130 and I really started pulling away from him. I park at hotel to pick someone else. I sleep 4 hours.

Start car up, drive, and notice the car misfires horribly during normal driving. Especially when accelerating heavily under low rpms. Like when I have it in a higher gear and accelerate. It misfires. It did this when I first bought the car and changed wires, and spark plugs and drove fine since then.

When I drove back home on Turnpike I cruised 77 mph and drove fine, anytime I go to accelerate, misfire, the car bucks. As long as I cruised at steady speeds, felt no problem.

Any idea the cause. I changed the DIS with my spare and does same thing so I don't think its that. The wires and spark plugs have been changed about 12,000 miles ago. Think it could be the coil? I'm going to junkyard tomorrow in search of one. Or could be spark plugs went bad again?

 

[sholover719]

just a thought on this, my dad had the same problem with his 1990 cougar s/c, it turns out a few of the wires either touched the exhaust manifold or got someplace really hot and they melted and frayed. idk if this helps any but i guess its worth a look.

 

[shonuffmine]

Pull a cpl of wires n see if the plug wells are full of oil or water!Is the CEL coming on? Also check for any loose ground wires

 

[sdpatt]

A misfire without any electrical EEC codes is usually the plugs or plug wires. Low quality plug wires can cause this even with the low mileage on your "new" set. Non standard plugs or plug gaps can also aggravate the problem.

 

[SHOtimer]

^^^^what he said. What brand plugs and wires do you have in there? Are the plug wells dry?

Doug

 

[tps761]

i had the same problem with my mustang. bought a pair of accel coil packs. worked great for 3 days then started misfiring horribly every time i tried to accelerate. so i went to a junk yard and pulled some stockers off another car. maybe worth trying to same thing

 

[frosho]

bought a pair of accel coil packs.

There's your problem.

I gotta find Mels' quote about Accel ignition products....

I'd rather make a paper airplane out of my money and toss it off a bridge into the water than waste it on any Accel ignition product - at least I'd be able to enjoy watching it do what I'd intended it to...

 

[tps761]

hahahahaah thats halarious and so true!!!!:laugh_ti:

 

[bigblock]

check your maf. i had that same problem. it was a combo of wires and maf. just get some maf cleaner at a local auto parts store and see if that doesn't work.

 

[chrism3784]

I changed out maf from one from a working sable, doesn't seem to change anything. I changed the spark plugs to NGK iridium, changed coil, changed dis, it seems a lot better, but still misses. If at 1,200 rpm in gear and heavy accel, it drives really really rough and make loud clatter under the hood. When rpm goes up, it goes away, still jerking once in a while. after like 3000 drives like normal sho, fast. But once in a grear while will miss.

 

[llamaking122]

maybe a cam sensor? i've heard ngks arent that good use autolite. but thats if i remember correctly

 

[chrism3784]

They cost 50 cents more then autolights. They looked good and durable. I drove at 7000 rpm steady for a bit and it drove just fine.

 

[shotime1994]

Why would you drive steady at 7k for a bit what gear where you in?

 

[K-Dawg]

Driving at 7000 rpm is much better than accelerating at 1200 rpm. Don't do that unless you like motor swaps.

Try running the cylinder balance test. You've either got a spark or fuel injector problem. My guess is a plug isn't firing. Does it backfire?

 

[oneqwicksho]

I had a set of NGK's foul out in 2000 miles threw in autolights and runs like a champ now. Did you see if your timing has slipped or crank cancer

 

[chrism3784]

How do I know if timing slipped? What is crank cancer.

Darn, a little late with the NGK plugs, it drives fine with them it seems. I dont feel like taking it all apart again. Dont even think I could find the reciept if I tried. Are they really that bad?

Anyways I got new fuel injectors coming.

Link

 

[Rythymaxe]

Thanks to all for the advice on this thread

My 91 started missing and backfiring when I put serious throttle to it. I read this thread and decided to start with wires, which is what my friend and mechanic determined what would fix it. I went with a good set of Standards, the set on the car were Motorcraft with a 2002 stamp. While they were putting the wires on, I asked for a MAF cleaning also. He said the MAF was dirty, but he's seen dirtier. After the new wires and the cleaning, the car runs like it's supposed to and is fun once again. I couldn't be happier and want to thank all of you that made my decision easier with your advice about the wires. I was unsure about the wires as I had just put some new plugs and a different DIS on it, but the proof is in the way it runs again. I don't have any miss, the Tach stays at 950, and in first and reverse, I don't have any trouble idling without throttle. Again, thanks for all your wisdom that saved me money and headaches. :thankyou: