I changed the plugs on my truck, along with an oil change. After the oil change, My '94 5.8L still idled along at around 600 RPM's...
So i did a plug change, and now the truck idles strangely. It sits at like 950, then drops to 800 or so, then back up, then down, and all the while, the truck is makin strange, humming noises. And, the check engine light is on. Help!

 

1994f150XLT,

Do you have a way to get the code from the truck.

I hate to do searched on similar things, and suggest stuff, as you could wind up replacing stuff that is not needed.

I can take a few guess, or rather I should say SWAGs, as I would only have conjecture and BS to back it up what the SWAGs are.

If you could post the code number, myself or another member can try to shed a little light on the problem.

Just an offer...

 

What is a code number?? is that something to do with the computer? cause if it is, I'm lost on that one...Maybe Neil could swing by and look? he lives in windsor...Maybe...I dunno..Help!

 

Actually now that I look at your profile ( name indicated the same thing..duh ) Isn't this a turn the key on and off, and you get a blinking light for what is wrong ?

Dumb @ss me, "oh scan the pcm for a DTC...hummm maybe a ODB II port would be useful in doing that, and oh BTW they were not standard until 1996 ( did I get that correct for the year ? ).

If you have access to a service manual, the sequence should be in there for getting the flashig light ( which ever it is, I cannot recall myself ) and this would point to a "code" ( not a DTC per say ) that indicated where the problem is at. Very similar in function as a DTC, but there were a heck of a lot less of them back then.

Not to imply that you are not cappiable or the likes, could there have been a chance that you accidently hit the plug on the edge of the spark plug hole, and dinged the gap to nadda ? That was one of my SWAGs, nothing to say why, just a thought, again backed by conjecture as the supporting data

Finding out the exact way of getting the trouble code out of the truck, would still be the first place to go, to see what is up. The mis-fire could be something else, and maybe a VAC line got accidently knocked loose during plug chance ( yet more conjecture and BS ), and this is causing the CEL ???

 

SSCULLY,

You forgt the plug wires. 94 didn't say he changed the wires. He might have snapped a wire while pulling the boot off the plug. But like you say without the code it is a futile search.


94,

Why were you changing the plugs? Did you change the wires?

JMC

 

Another good one, thanks for the catch.
Now 3 things 1994f150XLT can play hunt and peck on without the code, then again it maybe #4, #5, or #9 for all we know at this point.

Do you happen to know the key on-off sequence to get the flashing light ? Got me things like that get purged when I don;t need it anymore
Then again, without the service manual to tel what it means, I guess it really doesn't matter.
1994f150XLT, maybe a troll through the per 97 forum might shed some light on these topics...?

 

Ya...I didn't change the wires...I don't have the money to right now. Went for a drive with my Dad out to our barn today, and it's still on. My dad said to check the plugs, and make sure the wires are all on, and to check and make sure i didnt bend a plug goin in...Like you guys said...I haven't checked it yet, as it's 12:30 am, but i will check it out first thing in the morning, and let you know what i find. I do know this...After starting, the engine light stays off for like 5 minutes, then comes on, and stays on continuously.
I don't know!

 

JMC posted the resistance value per foot in another post, if you want to take the plug wires off and check them, to make sure they are good.

Take a look at his back posts adn it will provide these.

If you could get your hands on a service manual for your year truck, it would make your life so much easier, now and in the future. Just something I found out years back, rather then playing hunt and peck.