OBD1 code 51

Tiny
KEN15401
  • MEMBER
  • 1993 CHRYSLER NEW YORKER
  • 3.3L
  • V6
  • 2WD
  • AUTOMATIC
  • 158,000 MILES
It pulled code 51 after I reset codes via the battery disconnect method wouldn't run on the first few startups it acted like the TPS was bad. Then every start after that was fine, then rough idle when cold, no vacuum leaks, new fuel filter, cleaned throttle body and cleaned idle air control motor it was carbon all over it. Code 51 for Chrysler just says air/fuel at limit don't know what it could be or what that meant it also has small exhaust leak at muffler.
Thursday, April 28th, 2022 AT 5:54 PM

4 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,052 POSTS
Hi,

The code is related to the air/fuel mixture. However, to be more specific, it indicates a lean fuel mixture based on oxygen sensor signals. (See pic 1 below)

A lean mixture is usually the result of either an engine vacuum leak or a low fuel pressure issue. Here is what I suggest.

First, confirm there are no engine vacuum leaks. Here is a link that explains how it's done:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

If nothing is found, confirm the fuel pressure is within the manufacturer's specifications. Note the test port is at the front center of the fuel rail. See pic 2. Pic 3 provides the pressure specifications.

Here is a link that explains how to test pressure:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Let me know what you find or if you have questions. Please remember, the fuel system will be under pressure, so cover the port with a rag and have the engine cool when connecting the pressure gauge. Also, protect your eyes.

Take care,

Joe

See pics below.
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Thursday, April 28th, 2022 AT 9:02 PM
Tiny
KEN15401
  • MEMBER
  • 3 POSTS
Ran vacuum test and fuel pressure test replace O2 sensor right after the manifold because the vacuum test and fuel pressure test came back within specs. It seems to clear that problem I was having. Also, while I was back there, I also changed the three spark plugs and believe me it looked like nobody touched them for quite a while.
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Saturday, April 30th, 2022 AT 6:07 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,052 POSTS
Hi,

That's good to hear. I'm glad you got it running properly.

Please feel free to come back anytime in the future if you have questions. You're always welcome here.

Take care,

Joe
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Saturday, April 30th, 2022 AT 7:30 PM
Tiny
KEN15401
  • MEMBER
  • 3 POSTS
Will do. I'm more of a I'll fix it guy, as for diagnosing the problem that's another story. Thanks for the help and advice you gave really helped me out.
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Saturday, April 30th, 2022 AT 10:12 PM

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