95 fluctuating engine

[mkc414]

95 3.8 with about 90k miles. I am driving along and the engine started fluctuating while accelerating and also while idling (fluctuating as in running bumpy and going weak-strong, weaker acceleration as a result); check engine light turns on. I find a burnt spot on the 6th cylinder wire and replace the wires. Check engine light goes away and I havent had problems idling since, but still it runs unsteadily while accelerating and at all speeds above 5-10. RPMs are steady, car starts fine. I tuned it up about 4 months ago.

I am not sure if this is a problem with the spark plugs/cylinders/engine, or the fuel system. What do you guys think this sounds like? The mechanics around here are all crooks.

Mike

[brentmcq]

Probably time for a tune-up (plugs+all wires), injector flush, fuel filter change, throttle body cleaning. Something either in the electrical or fuel delivery is causing a hang up.

[351wStang]

If its only running rough at higher speeds it could be any number of things...but are you sure its under the hood? It could be suspension. How are your tires? When was the last time you had it aligned? Does it vibrate when braking? If it is mechanical then i would check to make sure you are getting good fire. Then start worrying about fuel. O, is this happening under wide open throttle or normal acceleration? Try some lucas or techron before you start spending the big bucks.

[mkc414]

Thanks for the suggestions. What is "good fire"?

I am pretty certain its a prob under the hood, cause the engine has a bumpy idle and it's the impression i get from the way the gas pedal feels. My shocks (changed about 4 months ago) have been through a move but i dont think they are it. Brakes/align/tires are fine. I have found that after the car warms up the idle runs smoother on the next start.

Little more- engine has a put-put-put sound to it at low speed acceleration, which it didnt use to have.

Problem seemed to have developed over time with slightly bumpier idle after starting in the morning, beginning prob about 2-3 weeks ago. Lower performance on high end than half a year ago, used to glide from 60 to 80 easily, even easier from 40-60.

Most recent tank of gas seemed to be going down about twice as fast as normal.

[351wStang]

Does the car smoke? Also check the coolant for any discoloration. If you are looseing gas that fast and its not leaking onto the ground then it is either getting past your rings and down into the crankcase, or you have a head gasket leak and its getting into your coolant. Check your oil, if its real thin and smells like gas then you have gas in your oil. As far as the rough idle, have you checked the timing? Does it ever try to spark knock under a load? It may just be loading up giving it that put-put sound. Pull a spark plug off of your dist. cap and lay it near the prong it came off of, then turn the motor over a few times. If you can see a spark then you should be getting plenty of fire. Unless it is just a real weak spark, then I would suggest changing plugs, wires, rotor button, and dist. cap. See if that helps you any.

[mkc414]

Thanks 351

I changed the gas filter (improved the power and made it run smoother in general) and looked at the pcv valve (not much suction on either end). Checked all the spark plugs and found one with a reddish coloration and crack in it. That was the problem.

For newbies trying to do tune-ups I advise against that T-shaped "Spark plug wrench" with a bunch of flexible things, couldnt get anywhere with it. With a flexilbe socket wrench it was a breeze. Check engine light came on after replacing the 6th plug (the one that came on in the diagnstic) but the car runs fine.

The Ford place I took it last was mighty crooked. They charged me $60 for 6 spark plugs. These were the crappy kind with just one prong that would prob be like $2-3 normally.

[duplox]

Unless you're running some biiig HP numbers, mainly forced induction, you don't need and wont benefit from anything more than a single prong stock plug. Think about it.. you have the same energy going to the spark plug, the same distance between the electrodes.. whats the difference if there is one or two of them or four of them? I run stock plugs in my turbocharged 351c, they do just fine and save me a bunch of money when they need to be replaced.

[mkc414]

I had heard that fancier plugs improve fuel efficiency, I could be mistaken.

[351wStang]

They can, but the only reason some plugs have more than 1 prong is because electricity takes the path of least resistance. Such as Bosch platinums. Which suck by the way. Very overrated.

[motor_head_429]

Check your vacuum hoses, always a possibility.

[duplox]

Agreed, but if there you're close enough to the brink of a misfire that the minute difference in resistance between the two prongs would make a difference, you need more spark power! Just my opinion, I personally will never spend more than 3 bucks for a spark plug.

[xyfalconsrock]

Definately try the flush of injecters, my dad had a similar prob with our falcon.After the flush it runs nice but higher temp 4 som reason.