The Unofficial "Ask a Stupid Question" Thread

[theterminator93]

The 94/95 4.6 PCMs are somewhat notorious for hanging injectors open and dumping fuel, but I don't know that the 3.8 PCMs have a bad rap for that. Regardless, these are ~30 years old now... so nothing can be ruled out until it's swapped out for something that's known to be in good, working order.

 

[XR7-4.6]

The PCMs are physically different hardware from the 4.6 cars too, 3.8s still used EEC IV obd 1 PCMs in 94-95

 

[White Lincoln]

I dug through my records and found I had replaced my PCM back in 2018. Bought it on eBay from AutoZone. I am glad I found my receipt on eBay cause I never documented that I replaced the PCM, just that I suspected it was part of my issue.

 

[White Lincoln]

The PCMs are physically different hardware from the 4.6 cars too, 3.8s still used EEC IV obd 1 PCMs in 94-95

Yes and why you have to be sure to get the exact numbers off your PCM if you go to buy a new one. I think the require the VIN number as well.

 

[XR7-4.6]

Yes and why you have to be sure to get the exact numbers off your PCM if you go to buy a new one. I think the require the VIN number as well.

Hardware is what truly matters, VIN is meaningless, catch code will have some slight software variations(stuff like shift scheduling) but really in our world all that really matters is V8 or V6 and year ranges, which for a V6 boils down to 96-97(because EEC V), 94-95(because 4R70w), 91-93(because MAF) and 89-90 (because MAP(minus SCs))

 

[1997ThunderbirdLXV6]

what a PITA to replace.

The PCM? It's just behind the glovebox/kick panel. I mean it's tedious maybe, but far easier to swap that any single O2 sensor.

 

[XR7-4.6]

The PCM? It's just behind the glovebox/kick panel. I mean it's tedious maybe, but far easier to swap that any single O2 sensor.

I’ll dispute that. The plastic bracket that holds the PCM in is EXTREMELY tedious to get out and it’s almost an inevitability your hands will be all scraped up afterwards. Oxygen sensors on the other hand while tightish are right there and if you have a cheap o2 socket for them takes minimal effort to get out, even on rusty cars those never give me problems.

 

[1997ThunderbirdLXV6]

I’ll dispute that.

Ok...
But while working on the sensors, you're surrounded by dirt, rust, and grease. Taking out the PCM, you're surrounded by luxury cloth, leather, and in my case, soft faux suede and genuine wood accents. You're just in a different state of mind swapping a PCM! Ha!

On a serious note, once you take out that one little screw at the bottom of the white plastic PCM bracket, it slides right out.

 

[theterminator93]

I guess it depends how big a guy you are, and/or how big your hands are. I've never had a problem getting at the PCM. On the factory exhaust, I'll take PCM swaps over O2S swaps any day.

 

[MadMikeyL]

If you just want to test to see if the PCM is the problem, you can leave the original in place, just unbolt the connector and lay the test PCM on the floor. That way if it turns out not to be the cause, you haven’t wasted the effort pulling it in and out of the bracket.

 

[1997ThunderbirdLXV6]

If you just want to test to see if the PCM is the problem, you can leave the original in place, just unbolt the connector and lay the test PCM on the floor.

Omg...this^^^! Why didn't I think of that?!

 

[White Lincoln]

The PCM? It's just behind the glovebox/kick panel. I mean it's tedious maybe, but far easier to swap that any single O2 sensor.

WHAT???? Okay, okay... I'll give you that an O2 you have to jack the car up, crawl under, hope the O2 is not rusted on, etc... but the PCM is in this weird place up the side wall next to the glove box and the seat is in the way and if your not limber, it won't be easy. I did mine some 4 years ago and the process still haunts me.

I’ll dispute that. The plastic bracket that holds the PCM in is EXTREMELY tedious to get out and it’s almost an inevitability your hands will be all scraped up afterwards. Oxygen sensors on the other hand while tightish are right there and if you have a cheap o2 socket for them takes minimal effort to get out, even on rusty cars those never give me problems.

My hero.

If you just want to test to see if the PCM is the problem, you can leave the original in place, just unbolt the connector and lay the test PCM on the floor. That way if it turns out not to be the cause, you haven’t wasted the effort pulling it in and out of the bracket.

See! I told you all the smart people left TCCOA to come over here.

 

[Grog6]

I've never bought an o2 socket, I use an open end wrench to pop it loose,then unplug and use the wires to unscrew it.
hookig up a solenoid light is much fucking easier than either.

 

[Rodeo Joe]

Omg...this^^^! Why didn't I think of that?!

I did!!

Joe

 

[Stanley]

Anyone know if AJE is discontinuing their tubular front subframe offering? It's no longer listed on their website, though SCP still has it.

I'd rather not have to buy it now, but if it's vanishing from production then I probably should.

 

[White Lincoln]

I've never bought an o2 socket, I use an open end wrench to pop it loose,then unplug and use the wires to unscrew it.
hookig up a solenoid light is much fucking easier than either.

22mm open end wrench is all you need. Unhook the connector, break the o2 loose and start spinning!

Put the wrench at an angle to get the wrench to grip the o2 bolt.

 

[White Lincoln]

Anyone know if AJE is discontinuing their tubular front subframe offering? It's no longer listed on their website, though SCP still has it.

I'd rather not have to buy it now, but if it's vanishing from production then I probably should.

If you have intent to use something in the future, buy it now cause it may no longer be offered and sure as shit, the price will keep going up.

 

[rampagingsloth]

New stupid question, is the Volts gauge supposed to have the needle in the middle, or just to the right of the middle of the range, when idling? I've noticed lately that my car idles low, like 600rpm at a stoplight and the Volts gauge needle is just to the left of NORM. As soon as I hit the gas the needle is back to centered or just right of center. I ask because my battery is losing charge (it is old, it probably could need replacing) to the point that a couple times I've had to boost it to start the car.

A related question, what rpm should this car ('95 4.6 V8) be idling at? Sometimes, when cold, it idles at around 750rpm and the Volts gauge shows the needle at the normal(?) position of just right of center. But after some minutes of driving it's back down to around 600rpm at idle and the Volts needle is just left of NORM. With the lights on everything dims (lights, dash lights) at idle until I give just the slightest bit of gas, then it's back up to normal again. This is with and without A/C on. If I put it in park it idles at 750rpm and the charging is normal.

So, it's that expected? Is there something wrong with my alternator or maybe what the computer thinks it should be idling at? Would a weak battery cause the charging system to react differently compared to a new, fully-charged battery?

 

[1997ThunderbirdLXV6]

Your idle rpm while in Drive seem normal-ish to me. I don't have the voltage gauge, and I never really paid much attention to the voltage readout on my obd2 app. I don't observe any dimming lights, etc.

One scenario I do occasionally observe is this: I'm in Drive, standing at a red light, and then the cooling fan comes on. For a second or so, idle can drop below 600 rpm, which feels a bit odd; then everything goes back to normal. Seems like the cooling fan adds significant alternator load which the PCM has to adjust for.

I think your problem is more on the electrical side and not with the idle rpm.  Think being the operative term here.


Side note: my parents had a VW Passat in the 90s. That car had an unusual feature to limit load on the electrical system. The power windows did not operate simultaneously. If you hit the windows down buttons, the windows would open in sequence, one after the other.

 

[theterminator93]

Cold idle will be higher than idle at temp. Idle at temp is ~560 RPM in drive, and 800 in park/neutral.

FWIW at drive idle the voltage always seems to dip a few points on my cars, especially with high current loads (headlights, fans, or on the Mark the air ride compressor and/or AIR pump). If the battery is weak it wouldn't supplement the alternator when alternator output doesn't meet the load and you'd get a bigger voltage drop.

 

[Grog6]

Alternator output is 130A@2500 rpm; what it is below that, is a guess. A bad diode bridge will make it run down sitting. low output is the brushes/regulator.
Victory lane makes a kit with all the parts. I clean the copper rings the brushes ride on with 800 emory cloth.

 

[KevinVarnes]

This is what I do for an informal load test on alternators. Check the voltage at the battery with a multimeter at idle with no accessories on and see what it is reading. Ideally you should see around 13.0V-14.0V. I then load it up (rear defrost, brights, blower fan on, etc.) and check voltage again. The alternator should be able to keep up and maintain voltage. Depending on the results of that test (low voltage) I then test for voltage right on the alternator output stud and compare. I would not consider dimming lights to be normal. Is this a new thing or has it always acted like that? Does it have an underdrive pulley on the alt by any chance?

I do notice the RPM dip at idle that Martin mentions mostly in the winter idling at a stoplight and the compressor kicks on for the defrost. The lights would dim for a split second until the idle came back up. It used to really annoy me, but I don't drive the car as much anymore so out of sight out of mind. My gauge cluster doesn't have a voltmeter and no other MN12 I've ever owned has had one so I cannot comment on that gauge reading.

How old is the battery in the car? Lifespan of batteries seem to be all over the place these days. I normally assume 7-8 years for an OEM battery and 5-6 for an aftermarket, but I've seen OEM batteries fail in 3 years or less too. You can have it load tested at a parts store (one of the few parts store electrical tests that I actually trust) for free to see how the battery is doing. I don't trust their alternator or starter tests and I resort to my test above for alternators. Half the time they don't know how to connect the alternator and probably don't run the test properly so they just tell you it is bad. I really don't trust their starter tests at all. I've had too many bad starters pass their no load test just fine.

I wouldn't think that low voltage at idle in drive would be enough to allow the battery to discharge that much, but it all depends on what your driving cycles normally look like. If you are in traffic a lot where you are at idle in drive then maybe.

 

[rampagingsloth]

Alternator output is 130A@2500 rpm; what it is below that, is a guess. A bad diode bridge will make it run down sitting. low output is the brushes/regulator.
Victory lane makes a kit with all the parts. I clean the copper rings the brushes ride on with 800 emory cloth.

Victory Lane? Googling gives me a lot of Victory Lap kits. Are stock '95 Thunderbird alternators 130 amps? I thought they were less. I was thinking of getting a higher output one to handle the various stereo add-ons I have/want.

 

[rampagingsloth]

This is what I do for an informal load test on alternators. Check the voltage at the battery with a multimeter at idle with no accessories on and see what it is reading. Ideally you should see around 13.0V-14.0V. I then load it up (rear defrost, brights, blower fan on, etc.) and check voltage again. The alternator should be able to keep up and maintain voltage. Depending on the results of that test (low voltage) I then test for voltage right on the alternator output stud and compare. I would not consider dimming lights to be normal. Is this a new thing or has it always acted like that? Does it have an underdrive pulley on the alt by any chance?

I think it's acted like this (dimming lights) for some time. The battery is some years old now, an Optima though now I'm reconsidering that type of battery if I need a replacement. The pulleys are stock, I believe, though the alternator is an aftermarket replacement. I will try to get the battery load tested soon.

 

[KevinVarnes]

Might not be a bad thing to check grounds too. I've never seen the need for an AGM battery in any of my cars until they won't let me buy conventional anymore. I have an aftermarket (rebuilt) alternator in the '97. They seem to work or they don't. Unless it is on a new car where they try to regulate alternator output based on system load I haven't had too many problems with parts store alternators.

 

[Jae 'Bird]

are the rear speakers in the 97 cougar objectively better than those in my 90 tbird? A pretty complete 97 cougar just popped up at the junk yard and I would only consider braving the cold and going to check it out if there was a good chance the rear speakers were better than mine. Further question, are there any other known, easy upgrades for parts from a 97 cougar to my bird? and before anyone just says to buy new speakers to upgrade my current ones, I know I would need to spend way more than the 10 dollars a speaker it would be at the junk yard in order to get new ones that are good

 

[XR7-4.6]

are the rear speakers in the 97 cougar objectively better than those in my 90 tbird? A pretty complete 97 cougar just popped up at the junk yard and I would only consider braving the cold and going to check it out if there was a good chance the rear speakers were better than mine. Further question, are there any other known, easy upgrades for parts from a 97 cougar to my bird? and before anyone just says to buy new speakers to upgrade my current ones, I know I would need to spend way more than the 10 dollars a speaker it would be at the junk yard in order to get new ones that are good

The entire powertrain lol

Speakers depend on the level of sound system the car has rather than the year, base “stereo” speakers are the same 89-97, Premium Sound speakers are the same 89-97 and JBL speakers and sub are the same 89-94 so if your car has the base stereo and the 97 does too it’s not an upgrade, if you have the base stereo and it has premium it’s a slight upgrade… but yeah, just get aftermarket speakers. The cheapest set of Pioneers are way way better than anything these cars came with.

 

[Jae 'Bird]

The entire powertrain lol

I guess yeah, it would be pretty cool to do a v8 swap, considering my year never came with a v8

 

[KevinVarnes]

The newer front spindles allow you to install Cobra brakes on your car, but that would require a few other changes including 17" wheels. The '97 speakers are 7 years newer than yours. Other than that as XR7-4.6 stated, no real upgrade.

 

[XR7-4.6]

The newer front spindles allow you to install Cobra brakes on your car, but that would require a few other changes including 17" wheels. The '97 speakers are 7 years newer than yours. Other than that as XR7-4.6 stated, no real upgrade.

He could do twin piston V6/GT PBRs with those spindles with the stock wheels however, still a good upgrade