Stumped on a possible vacuum leak? - MustangForums.com


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Old 02-26-2017, 03:04 PM   #1
Bigfootb168
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Default Stumped on a possible vacuum leak?

Alright, this car has me stumped the most I've been in my entire life.

Recently bought my car a couple weeks ago,a 1986 Mustang LX w/ 5.0 HO, ran outstanding. Completely original drivetrain, had zero problems. Drove it around for the last couple weeks, and it was suggested to me to run some seafoam through it just for preventative maintainence. So I thought, oh what the heck.I pulled the supply line going to the vacuum T on the firewall, ever-so-slowly adding the seafoam to the vacuum supply line, ensuring to rev to prevent stalling. Finished pouring into the line, plugged the line back in, got in the car for a drive.

After I pulled out of my drive, it hesitated for a second upon acceleration, but was smooth after the hiccup. I just figured it was still the seafoam left in the lines. I've driven it for two days, quite aggressively, and it still does the same thing. I literally did nothing but pull the vacuum line, pour in seafoam, and re-attached and clamped the line.

So my next thought, ok well I don't know how I did it, but I'm going to check for a vacuum leak. Got out my bottle of ether, in which I've found numerous other vacuum leaks in other vehicles. Nothing. I even sprayed into the intake just to see if it would affect my idle. Nothing. This car literally will not even react to ether. No move in RPM or anything, unless you spray a ton in and kill it.

I pulled the codes for the car, KOEO I came out with 82, and 82. KOER I came out with 21, 41, 91, 33, and 13. I'm still not sure if I'm doing the proper procedure for running the codes because the car died, and then displayed its codes. So I don't know if the o2 sensors are clogged from the seafoam or what. I replaced spark plugs thinking it fouled them out, but nothing changed.

I apologize for the extremely long post, but I'm at a loss. I don't even know what to do next. All because of a can of Seafoam. Thanks in advance for your input!
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Old 03-01-2017, 07:58 AM   #2
88 orangepeel notch
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Welcome to the forum.

Ahhhh the Seafoam treatment....lol. Some guys swear by the stuff, and I've personally used it with great results on our snowmobiles. But I've never done the vacuum line, Internal engine cleaning treatment.

As for your codes, 41 and maybe 91 are for your O2'S. I'd verify the wiring first, making sure they're connected and that the wires/harness are in good shape. I don't know how many miles are on your car, but a new set of O2'S might not be a bad idea. I believe there's a way to verify if they're bad with just a multimeter. Google will help you with that so test old ones before buying new ones.

33 is an EGR . Verify if that's working correctly.

21 is saying your coolant temp is out of a specified range. Usually just a bad sensor when you get this. Verify with testing before replacing.

Good luck and maybe just use the Seafoam in the tank next time lol.

Good luck
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Old 03-02-2017, 02:11 PM   #3
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I've spent some time dwelling on it for the past few days, and I'm willing to make abbey my O2 sensors bit the dust. I'm also willing to bet that the Seafoam maybe were the last straw for them, because

I'm sure the plumes of smoke passing through them during the treatment wasn't good for them. I also had noticed the exhaust had become extremely rich just a couple days before I did the treatment, like to the point I thought it was a leak around the H pipe area. Also, I had noticed upon downshifting when coming to a stop I would hear a "ping" sound coming from the pre-H pipe area (or so it sounded far up the system)...

Long story short, the 2-step-like hesitation when stabbing the throttle, the rich smell, and the possible backfire lead me to believe it's the o2 sensors. Planning on running a multimeter test, then going from there. Thanks for the reply!
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Old 03-03-2017, 06:26 AM   #4
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Glad to help.

Post back with what you find....
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Old 03-04-2017, 02:39 PM   #5
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Ran some tests on my o2 sensors. Multimeter checked out as they were good. Unplugged them and reset the computer to see if the engine still ran the same with an open loop, and to no surprise, still hesitated and dipped on initial acceleration. So now I'm between a bad MAP sensor, or maybe a clogged fuel filter. It has no issues starting, or revving if I ease into the throttle, but if I rev it by stabbing the throttle quickly, no matter the RPMs, it still seems like it's loading up or something. I'm so confused.

I figured had it been the fuel filter, it would've had some issues starting or idling, or would've had issues supplying fuel at higher RPMs. It doesn't matter if I stab it at idle, or if I stab it at 3k, still does the same thing.. The idle seems to be ok. Could be better, could be worse. Doesn't stall all too often, but does on occasion.

So I'm at a loss. I guess I'm just gonna pick up a fuel filter anyways, because it couldn't hurt anything at this point.. If that doesn't work, then I guess I'll go with a MAP sensor.
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Old 03-05-2017, 07:28 PM   #6
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Just a final update, after all is said and done, it was most certainly my MAP sensor. Changed the fuel filter last night, which made the car idle smooth for the first time since I've owned it, however it still had a hiccup. Went to the parts store, bought a MAP sensor, took about 30 seconds to swap out, fired it up and took it for a drive and ran even smoother than before. When I swapped out the old sensor, some Seafoam dripped from the vacuum port, which gave me a reassuring sense that's what it was anyways.

Long story short, for the love of God, do NOT run Seafoam through your vacuum supply line. It just plumb isn't worth the headache!
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Old 03-06-2017, 07:16 AM   #7
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Lol, glad to hear she's running better.

Funny about the Seafoam, some guys swear by it and the miracles it can do. I'd just say don't ever use it on a perfectly good running motor lol.

Lesson learned...
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