Obd1 code troubleshooting

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Jul 16, 2025 | 10:55 AM

BluWhale1957

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Obd1 code troubleshooting

I have two codes that appear at medium to heavy load. They are 172 and 181 and i usually get spark knock while im under medium to heavy load. i run 93 octane so im fairly certain its not octane rating. im mechanical stupid so assume i don’t know much. thanks!

Jul 16, 2025 | 11:18 AM

wwhite

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What engine?

Those codes could be from the following:
- exhaust leak
- vacuum leak

What condition is your exhaust? Does it have full exhaust?

Jul 16, 2025 | 11:31 AM

rla2005

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From: Kentucky

Add low fuel pressure into a cause of those codes and pinging symptom.

Jul 16, 2025 | 12:26 PM

BluWhale1957

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It’s got a 5.0 just had the muffler removed and new pipes added in its place. but it was doing this before that and is still doing it after.

Jul 16, 2025 | 12:27 PM

BluWhale1957

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Quote:

Originally Posted by rla2005

Add low fuel pressure into a cause of those codes and pinging symptom.

so maybe a fuel regulator?

Jul 16, 2025 | 12:41 PM

aquanaut20

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From: BC Canada

Measure the flow and running fuel pressure.. Dont be guessing..

Jul 16, 2025 | 12:41 PM

rla2005

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From: Kentucky

Could be regulator, pump or a clogged filter. Process of elimination by testing.

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Jul 16, 2025 | 01:22 PM

wwhite

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Quote:

Originally Posted by BluWhale1957

also idle is close to 1000 in park. just remembered that also

* points again to possible vacuum leak
Unplug IAC, does the idle change?

Jul 16, 2025 | 01:53 PM

#10

BluWhale1957

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Quote:

Originally Posted by wwhite

* points again to possible vacuum leak
Unplug IAC, does the idle change?

dies immediately after i crank it

Jul 16, 2025 | 02:00 PM

#11

wwhite

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Quote:

Originally Posted by BluWhale1957

dies immediately after i crank it

then the IAC is working, and probably not a vacuum leak.

Jul 17, 2025 | 04:52 AM

#12

manicmechanic007

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From: Near Salt Lake City

Agree, check the fuel pressure and do a volume test
But
The upper intake gasket used to crack and come out on those early EFI 5.0's
Sometimes you can see the cracked gasket sticking out back behind the distributor
I'd sprat down the intake gaskets with some carb foam or brakleen and double check it for a vacuum leak