Ok, here's the deal, changed out the trucks spark plugs like 2 years ago. Truck only gets like 13-15 mpg combined. I think about last september, after you drive the truck for a while, and shut it off, when you start it again, it feels like it only runs on a couple of cylinders, then a couple more pick up, until the engine smooths out and runs like normal. My question is, when we changed the spark plugs 2 years ago, we put in Autolite plugs, their part nuber is AP765 i believe. I've been reading some threads that make it sound like i should have put in the double platinums? Should i go and get some motorcraft dp's? Does anyone know the autolite part number i'm supposed to be using for my spark plugs? Also if someone could tell me what the difference between the platinum and the double platinum plug is, and why a DP is needed on a DIS?

 

there is a good amount of info on this subject in:sticky tech info about double platinum plugs. it is covers alot.

 

Hey thanks, lot of good info there!

 

no problem. just payin' ya back for the excellent directions you gave me when i 1st signed on in 2/04.

 

I doubt it's the plugs. The Autolite single platinums are a pretty good plug, they just won't last as long as the double platinums.

The hard start after shut-off sounds more like a fuel-related problem ...I know a leaky fuel pressure regulator can cause similar symptoms.

 

well, i was wondering, cause i pulled the electrical connector on my IAC and it started acting like it does somtimes when i start it up when its hot, so that kinda leads me to believe i should clean it off. or possibly replace it. I think i'm gonna get some double platinums just for the practice of doing things right.

 

peter, when did you last change the wires? they should be changed every couple of years, at least pull and clean the contacts at the DIS. I run single plats and have no problem, change 1 a year (approx 30000 plus miles). You didnt say how many miles on truck, could be other ares causing poor milage. You do hav a 4x4 and they are notorious for poorere milage, xfer case, etc to have to drive even when in 2wd. Your truck also weighs a little more than the 2wd types so you will have a deficit there. I posted on another thread, check the accuracy of the odometer and speedo (I think its pg 4 on fuel milage thread). I found my odo off 3/100 miles traveled, you could have maybe worse if running alt size tires etc. air filters, oil weight, tire pressures alignment all cause milage probs. Look at the reply I mentioned already.

Hank

 

yeah,i have a 94 4x4 4.0l ext cab. I dont expect 20 mpg, i have 3.27 rear end, which i know sucks for town driving, which i do alot of, but even 100 miles on the highway and 100 in town i still get like 13 or so. Truck has 114k on it, i'm using p235/75 R 15's for tires, all matching, inflated to reccomended air pressure. It seems like its running rich. There have been a few times where i stop at a stop sign, and quickly push the gas to 1/4 throttle, and i hear a backfire. Its not a huge one, but its like, bumb, and then the engine picks up. Then when I drive it for a while and it does the thing where it does not want to start, I hold the gas down at about 1/4-1/2 throttle, and i hear it backfireing, alot louder than before though. So this must mean that its getting fuel right? Its almost like there is no spark in some of the cylinders, and they are getting doused with gas, then when the plug finally fires, boom. I have new wires, which makes me wonder if the single platinum plugs arent wearing out or somthing, i dont know????

 

peter best thing actually would be go to an independent shop that has a computer and get the system checked. Your plugs should be fine. There is a possibility that the computer is going out causing some milage and engine problems. I replaced mine sometime back after getting poor milage and having a computer scan of the system, I dont mean a code reader scan either. You could possibly have a bad injector now that I think a little, will work intermittently, also should show on a computer scan. Problem with the scan is they usually run about $75, but I got mine done when it was slow at the shop for 1/2 price. Paid off in the long run. On the tires you say recommended, which recommendation the owners manual or the sidewall (cold) pressure.

 

I got it from the piece of paper they filled out for me at sams club when they changed my tires. I think they did some calculations or somthing to figure it out. its 35psi front and 30psi rear. I looked at the sidewalls and it said that the max inflation is like 50psi or somthing.

 

have you tried putting something like Marvel Mystery Oil in the fuel?

 

yeah, i used that a couple of times. I dont remember it doing anything too marvelous though.