Don't know what this plug is

[collinselectric5]

Hi guys, I just got an 86 mustang gt. My first since my first mustang which was an 86 GT. I have a lot of things to button up but I'm gonna replace the coolant temp sensor, my gauge isn't working. There's a 2nd plug coming out of the same wire loom that I have no idea what it is. Need ur expertise, thanks

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[homer302]

That plugs in to the harness that heads behind my alternator and disappears after that. Maybe yours has a 1 wire conversion or some other alternator mod? Also, your car does not use 5W20. That's a cap off something else but it's not a 5.0 cap. And lastly, that sensor by your hand there is the temp sensor for the ECU. It has nothing to do with the temperature gauge and won't affect it's operation in any manner.

[Ourobos]

No, his ECT sensor you mention is plugged in right BELOW his hand on the heater pipe.. That is the canister purge solenoid plug, part of smog, and depending on what state you are in, likely not required. Won't affect drivability regardless

[collinselectric5]

I thought was the coolant temp sensor under my hand, so where is the sensor & what oil do u guys use?

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[Ourobos]

The sensor will be on all the the smog piping running off of the smog pump and charcoal canister. If you lack those, just let the plug hang or tuck it away. If a stock 302, I like 10w30

[homer302]

I thought was the coolant temp sensor under my hand, so where is the sensor & what oil do u guys use?

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Nope. That's just for the ECU. The one for the gauge is on the other side screwed in the intake manifold. It is brass colored and the single-wire connector just pushes on, it's not a wiring harness clip. There is no coolant temp sensor in any smog plumbing. Not sure where that came from.

[collinselectric5]

Maybe this motor isn't the stock 302, I found another harness connector where u said the temp sensor should be. No single wire connectors. And advanced auto parts gave me a temp sensor with a harness clip.

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[homer302]

I can see the end of the temp sending connector in your picture. It is directly under the "ES" in suppression on that one plug wire. The 16 year old kid gave you the wrong part? Shocker. Haha.

[homer302]

And the other 2 wire sensor in that last picture is the ACT (Air Charge Temperature) sensor for the ECU. Probably could stand to be replaced as well after all these years. And it appears the answer to your original question is that goes to the "cansiter purge solenoid" as noted above by the other poster and is part of the emissions system. It doesn't help to remove it but if it's already gone, there's probably no harm aside from your car likely stinks like fuel or exhaust.

[collinselectric5]

What the heck... that kid was a little prick too lol... so before I take this back could this be the air charge sensor? Thanks a lot for the help u guys, I really do appreciate. Hopefully u won't mind me having questions, i had a 96 cobra before this and I'm having to learn new things. My project for today is to change the 02s, they ran a 91 & 41 code I believe? But this car bucks really bad, hopefully that fixes it & the temp sensor

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[homer302]

Nope. That in your hand is the temp sender for the ECU and goes on the passenger side under your hand in that first shot. that does tell the computer what temperature the coolant is but doesn't have anything to do with the gauge. The ACT sensor is in the last shot on the driver's side and the temp sensor for the gauge is the single wire one about 2 inches in front of the ACT.

[Ourobos]

^ It's called an ECT sensor, engine coolant temperate FYI

[homer302]

Bucking is a really hard issue to diagnose. The weirdest one I had was a failing (not FAILED) fuel pump that caused it. It met all the requirements for pressure during testing but something was going on with it while running. I thought it was going to break a motor mount at times and after months of diagnosing a new fuel pump fixed it. USUALLY (but not always as in my case) bucking is timing/ignition related. I am pretty sure you can unplug the O2 sensors totally and the car won't buck and jerk. Plugs, wires, cap, distributor, TFI are the top causes of bucking.

[collinselectric5]

Thanks! I guess I'm the prick lol... he gave me the part I asked for haha

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[collinselectric5]

I unplugged the upstream o2's earlier today and it still was bucking the same as when they were plugged in. I still have speed density if that matters

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[homer302]

Ha! Well, you know what they say. Be careful what you ask for.....you just might get it! Yeah, that's what I thought about the O2 sensors. They really help MPG and help the ECU fine tune the fuel but they really don't affect the way a car RUNS for the most part. They aren't going to cause a heavy misfire etc.
Nothing wrong with speed density either. The 707HP Hellcat is speed density. The early 5.0 engines made more power than later MAF cars but the engine can be controlled more with MAF which helps meet emissions and mileage requirements. Ford didn't rate the HP higher when they went to MAF and eventually they actually lowered it.

[collinselectric5]

So even with the O2 sensor codes the problem could be something completely different?

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[homer302]

Correct. See post #13. It's like having a bad water pump. It needs to be fixed but it won't make the car run bad as long as you keep water in it. A clogged fuel filter won't cause an anti-freeze puddle under the car etc. You have to narrow down what you are working on and focus on it.

[collinselectric5]

So can I rule out o2s since I unplugged them and it ran the same?

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[collinselectric5]

I'm gonna go out on a limb here and say that this spark plug and screw are not supposed to be there 😂

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[erratic50]

My car would buck like hell right before it burned off the distributor to coil wire. Has done it multiple times.

Throw on a new coil wire, cap, and rotor. Double check base timing. 10 degrees BTDC is stock. Most 5.0L ho's like 13.5-15

[Haystack]

Only times ive had both o2 codes, my fuel pump was going out. Explains the surge/bucking as well.

You can jumper off the test port to make the fuel pump run continuously. Get a cheap harbor freight fuel pressure tester and hook it right to the filter. Then let the fuel pump run non stopped for a minute or so and see what it does. The pressure should be at least 60 psi.

Don't buy a cheap parts store pump, i have pulled two out of the box and tested them and they were weaker then the bad fuel pump i was replacing. Another one ran okay for about 20 miles then died.

[Ourobos]

Your plug and screw are blocking off the smog where it was removed.. So unless you complete remove it and plug the thermactor holes on the back of the heads, you're best leaving that there..

41 and 91 are lean codes, probably starving for fuel. Check fuel pressure, possibly replace filter. Should have about 35-40 psi running with vacuum to the regulator plugged. Should also hold that pressure for several minutes when turned off..

Seen four cases of the little hose from pump to pickup being rotted in just the past few months also.

[collinselectric5]

I'll check on those later today, but maybe this will give a little insight. Last night I changed plugs, coolant temp sensor and one of the o2's sensor harness wires were broke, I crimp them back together the best I could but I'm pretty sure they're connected, they were broke close to the base of the harness. I test drove it and it was running real good, this morning too but then started to hesitate a little bit. I'm not sure what I did to make it run good for that short period of time

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[collinselectric5]

I went to check my fuel pressure but this cheap harbor freight tester was leaking and spraying gas lol... I checked my timing and it was set at 14°... I was thinking, if something was bad with my fuel system it would be all the time correct? My car will idle fine on a cold start for a minute or 2 then will have poor idle. And I think it was running good after I was working on it over the weekend because my battery was disconnected the whole time and the computer reset itself, does that make sense that it is the o2's? By the way the o2's are rusted out so I can't imagine they're working properly. Thanks guys, I'm trying not to get frustrated with the car but it's hard

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