1997 developed intermittent miss

[missinglinc]

My 97 Thunderbird 4.6 was running great for well over a year, but has recently started missing periodically. I have changed the coils and fuel filter, it seemed to be better for a day or so, then back to the odd miss. I took out the MAF and gave it a good cleaning, was surprised at how much detritus had accumulated since I last cleaned it, again, seemed to run better for a short time, then back to the periodic misfire. I have put my code reader on, but it has no DTCs stored.
Last fall I installed a new intake manifold due to a coolant leak and had no trouble following that. It seems to run ok when the ambient temperature is cooler, like in the morning on the way to work it usually runs ok, but in the heat of the afternoon it starts to misfire again. I've had the car for about 3 years now, it didn't run when I got it, I replaced the PCM, plugs, wires, coils, fuel pump, and probably a few other things that I can't remember now.

I've read some other member's posts about replacing a canister purge valve, or some bad vacuum lines connected to the purge valve, but not sure what the symptoms of these issues are. I'm moving in a couple of weeks and would like to get this resolved before if I can, any help/advice/suggestions are greatly appreciated. I have also noticed that it will seem like there is more "drag" when I'm coasting at a steady speed.

Thanks

Randy

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[mcm51]

First off you said that there's no codes, this is assuming that you have not had the battery un-plugged recently, pcm will not give a code until it's through a "drive cycle" which on my '95 4.6 is about 20-50 miles of normal driving.......
IT does sound like you are describing a faulty mass-air sensor, you say that you cleaned it out, BUT, how old is it ? consider swapping it out with a brand-new piece of crap from rock auto, that new cheap piece of crap will work better than a 30 y/o motorcraft that's been cleaned six times, and cost on cheapest mass-air from rock is'nt that much, And if your planning on keeping this Bird for a while, I'd consider swapping out the a.i.t. sensor that's screwed/twisted into the air filter box.........My o.e.m mass-air went out when the car was about 20 years old BUT was doing as you described, like a complete dead miss always at cruise..........
On the purge valve, on mine the vac line rotted out right where it connects to the purge valve AND all I ever got from that was a low idle nothing more......

 

[biddle]

Try running Top Tier gas and also add Royal Purple Max clean to it.

I've seen recent tests about gasoline and the difference between some of the cheap gas versus top tier gas is alarming, especially with recent pressures on oil supply.

The cheapest place you can get top tier fuel is Costco.

 

[missinglinc]

Battery has not been disconnected recently, it has been driven plenty of miles so I would expect if there were any DTCs there should be a code, I drive it hard typically, full throttle acceleration at least a couple times per trip. I will try replacing the MAF and IAT sensors, looked them up today on Rock Auto, reasonably priced, pretty sure the originals are still in service. I have no plans to sell this car anytime soon, it's generally very reliable, comfortable, and it makes a great bookend with my 89 Super Coupe, first and last years of the MN-12, both are oxford white, and both are fun to drive, the 97 has about 130k miles, while the 89 has about 70k miles.

I buy all of my gasoline at Costco for all of my vehicles, it's only minutes from my house and is usually considerably cheaper than any other local stations. the only exceptions are when I am away on vacation, then I stick to well known brands.

Thanks for the help and suggestions.

Randy

 

[mcm51]

Hey Randy before ya buy an a.i.t. sensor, you might want to pop yours out first and see if it's a screw-in type or the push-in and turn type, might save ya some time there........
Ya did'nt say how old was that maf that's in the car now ?.......
Ya I'll go along with that on first mn-12 and last ownership, I've had this '95 since new, stopped being hard on it 10 years ago, mines in Black w/opal grey leather, I've tryed to keep mileage down forever but I still hit 150k a couple months ago.....

IMO, a bad maf "should" have set off a dtc, it did on mine, BUT, though the years, I've seen dtc's set days or even a week after the pcm picked something up, in other words, I don't bet my life on a "check engine" light, to me it's just a very good indicator "most" of the time, I'm sure you know BUT I'll write this for others, only half of the stuff out under the hood is being "watched", other things are not, thats why my first couple questions to someone having any issue is "how long has the battery been plugged in", "how long have you drove it since" and "is the check eng. light on", that alone will cut half of the probabilites of the ongoing issue......

I was at my local Ford dealer when I first checked out that first SC, I was driving 5.0 fox mustangs at the time, but did'nt that thing sticker for $30-32 grand back then ??

 

[missinglinc]

I'm pretty sure the MAF is original and I would have expected it to set a dtc in the pcm too. However, when I was experiencing a condition of poor running previously after a highway trip, and higher than normal idle speeds, there was also no dtc set. I believe it was mcm51 that suggested cleaning the MAF at that time, which completely resolved the issue.
As for the 89 Super Coupe, I didn't buy it new, but I might have the original window sticker around somewhere. My mother bought it in 2013 or 14 from the original owner's family, it had about 58k miles on it then, and she gave it to me in the spring of 2025 when at age 92 she found it too difficult to push in the clutch pedal.
My 'bookends'

 

[mcm51]

Don't remember suggesting to clean maf but ya said it worked before, do you run any kind of fancy air filter, any kind that would dirty up that maf before it's time ?
On the v8, besides the possible maf issue, has your mpg changed any recently like a loss of 3 or 4 mpg on the highway and maybe feeling like the timing is retarded a tad, I just went thru those symtoms with mine and it turned out to be connection issue at that plug under hood, pass. side, real close to firewall, this plug connects the wire harness to the pcm and to the rest of the inside, it's one of those bolt-type plug in's, I believe it was a 10mm, when I unplugged mine after 31 years, it was kinda nasty, the oem di-electric had turned into some brown looking stuff, long story short, blasted plug out with maf cleaner, all new permatex di-electric and once I drove about 40 miles(pcm to get really dialed in) she is running like she did many years ago, mileage is back in the high 20's highway......FYI
That's a great pic of the bookends minus the garage seen, you need to get those two out in a green grass area in the woods and set up a nice pic for a framed 8x10............I did notice that SC has cornering lamps, to my knowledge not all SC's had them, but I could be wrong...............

 

[missinglinc]

Don't remember suggesting to clean maf but ya said it worked before, do you run any kind of fancy air filter, any kind that would dirty up that maf before it's time ?
On the v8, besides the possible maf issue, has your mpg changed any recently like a loss of 3 or 4 mpg on the highway and maybe feeling like the timing is retarded a tad, I just went thru those symtoms with mine and it turned out to be connection issue at that plug under hood, pass. side, real close to firewall, this plug connects the wire harness to the pcm and to the rest of the inside, it's one of those bolt-type plug in's, I believe it was a 10mm, when I unplugged mine after 31 years, it was kinda nasty, the oem di-electric had turned into some brown looking stuff, long story short, blasted plug out with maf cleaner, all new permatex di-electric and once I drove about 40 miles(pcm to get really dialed in) she is running like she did many years ago, mileage is back in the high 20's highway......FYI
That's a great pic of the bookends minus the garage seen, you need to get those two out in a green grass area in the woods and set up a nice pic for a framed 8x10............I did notice that SC has cornering lamps, to my knowledge not all SC's had them, but I could be wrong...............

I haven't noticed any big drop in fuel economy, but I only drive it about 10 to 12 miles a day typically, to work and back. Still running the factory airbox, and I just came in from checking the filter and which type of IAT it has. I will check out the harness plug when I get time, probably won't be until after I move now, still debating on ordering the other parts as well due to the impending move.
I appreciate the compliments on the bookends, the 89 is pretty well equipped, but has no sunroof, no keyless entry, and strangely no leather wrapped steering wheel. It does have leather seats with side bolsters, power windows, locks, tilt steering, a/c, both front seats are power, power trunk, premium sound, and auto headlamps, that may be the reason for the cornering lights, part of the option package. I don't miss the sunroof/moonroof, but keyless entry is a nice feature to have and the 97 has a leather wrapped steering wheel, although it is pretty well worn at this point, I find it far better than the plastic one in the 89.