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The car runs great when cold, but once it heats up it tries to cut off and loses power

Tiny
MICHAEL MASSARO
  • MEMBER
  • 1996 FORD MUSTANG
  • 3.8L
  • V6
  • RWD
  • MANUAL
  • 150,000 MILES
The car runs great when cold, but once it heats up it tries to cut off and loses power. The car has headers with straight dual exhaust, and what appears to be one small catalytic converter on each pipe just behind each O2 sensor. I was wondering if they are catalytic converters, could they be causing this problem? I had diagnostics run on it and received eight codes, all representing air/fuel mixture.
P1443-cntrl system control valve malfunction
P0156-02s ckt malfunction 2/2
P0401-EGR flow insufficient
P0420-catalyst efficiency below threshold bank 1
P1131-insufficient switching 02s 1/1 sensor/lean
P1151-HO2s 2/1 insufficient switching lean mean
P1071-system to lean bank 1
P1074-system to lean bank 2
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Tuesday, September 13th, 2016 AT 7:14 AM

13 Replies

Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
From the codes you could have a plugged catalytic converter. A back pressure test at a exhaust shop when it is happening can tell you if there plugged. Also with the p0171 and p0174 you could have a vacuum leak somewhere.
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Tuesday, September 13th, 2016 AT 8:10 AM
Tiny
MICHAEL MASSARO
  • MEMBER
  • 7 POSTS
The problem is when it is happening, it is extremely hard to get from point A to point B. This car was not designed with enough floor space to drive heel/brake toe/gas with a size 11 boot. Lol. I appreciate your advice SATURNTECH9.
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Tuesday, September 13th, 2016 AT 8:40 AM
Tiny
HMAC300
  • MECHANIC
  • 48,600 POSTS
Just to add on this check your fuel pressure as a lot of them throw the 171/4 code when fuel is not suffiecent.
https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator
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Tuesday, September 13th, 2016 AT 9:23 AM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
You try unhooking the exhaust before the catalytic converter and see if that helps.
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Tuesday, September 13th, 2016 AT 4:13 PM
Tiny
MICHAEL MASSARO
  • MEMBER
  • 7 POSTS
Okay, I changed the spark plugs and replaced bad vacuum hoses. The car started, but now the car wont idle at all with MAF sensor plugged in, but unplugged it idles at 1500 RPM. I drove it about 10 miles and I had to drive it home with three feet keeping RPM way up. It fouled out the new plugs. Cleaned new plugs back up, cleaned MAF sensor, cleaned cold air induction filter, cleaned the throttle body, and it still won't idle with the MAF sensor plugged in, but unplugged it idles at 1500 RPM. Normal idle was previously about 950 RPM. Could the MAF sensor be the root of all the problems?
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Saturday, September 17th, 2016 AT 9:54 AM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
So did you replace the plugs because they were fouled out with fuel?I have seen bad mass airflow sensor make the engine run so rich that the exhaust was burning your eyes. Did you ever check to see if the cat was plugged?Running excessive fuel thru the exhaust will damage the cat.
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Saturday, September 17th, 2016 AT 2:50 PM
Tiny
MICHAEL MASSARO
  • MEMBER
  • 7 POSTS
I did not check the cat because it had plenty of power with the MAF disconnected and new plugs until I ran it for 10-12 miles and it began to sputter and lose power. When I cleaned the new plugs they were burnt white on the tips. The car will not idle with MAF connected.
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Sunday, September 18th, 2016 AT 7:47 AM
Tiny
MICHAEL MASSARO
  • MEMBER
  • 7 POSTS
It has headers with straight welded duals. The only way I can disconnect the exhaust is to cut the pipe, which I'm holding as a last resort.
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Sunday, September 18th, 2016 AT 7:51 AM
Tiny
CJ MEDEVAC
  • MECHANIC
  • 11,004 POSTS
Different feller (Manly-er than the other two! LoL!)

Might be a good idea to seek out a really cool muffler guy (or other welder kinda guy) Find the best place to do the choppin' whereas it will be EZ to weld back for him. These kinda consultations sometimes build good relations and work might get done less expensive.

With the tone of your plea, I'm really sensing that you really should be in a Jeep?

The Medic
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Sunday, September 18th, 2016 AT 8:35 AM
Tiny
SATURNTECH9
  • MECHANIC
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If you have have plenty of power with the mass air flow sensor unhooked then I wouldn't suspect the cat. Also a back pressure gauge can be hooked up to the exhaust to measure for excessive back pressure. There would be no need to cut the pipe. Have you checked there are no damage to the intake boot where the mass air flow sensor is?Also are there any codes?You would have to stop unplugging the mass air flow sensor and clear the codes and run it with the mass air sensor plugged in to see if any codes reset?
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Sunday, September 18th, 2016 AT 9:00 AM
Tiny
MICHAEL MASSARO
  • MEMBER
  • 7 POSTS
The boot appears to have a good seal, and no cracking or dry rot. Can I clear the codes by disconnecting the battery or do I need a diagnostics machine to clear them?
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Sunday, September 18th, 2016 AT 9:42 AM
Tiny
MICHAEL MASSARO
  • MEMBER
  • 7 POSTS
Just noticed white smoke coming from the drivers side exhaust pipe.
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Sunday, September 18th, 2016 AT 10:21 AM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
The best way to clear codes is with a code reader unhooking the battery doesn't always clear the light and codes from memory. Is that coolant coming out the tail pipe?
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Sunday, September 18th, 2016 AT 10:10 PM

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