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Truck will not pass smog.


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skydogdonn
New User

May 5, 2011, 4:29 PM

Post #1 of 8 (2544 views)
Truck will not pass smog. Sign In

 idle HC 642 (max 100) CO 4.99 (max 1.10) 2500 rpms HC 35 (max 180) CO .05 (max 1.1)
1993 Chevrolet C1500 Suburban Base 8Cyl5.7L - Engine
OBD1 code is 35 -idle air control sensor circuit fault..which jives with all info I have.. where do I begin? any takers?


zmame
Veteran / Moderator
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May 5, 2011, 4:40 PM

Post #2 of 8 (2534 views)
Re: Truck will not pass smog. Sign In

Sounds like could be high fuel pressure maybe fuel regulator inop. I don't have the specs for that perticular vechical for fuel pressure. Possible missfire at idle. That would be my guess.

keep in mind I know very little on TBI engines not sure how they regulate fuel pressure..


(This post was edited by zmame on May 5, 2011, 4:41 PM)


Mr.scotty
Enthusiast
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May 5, 2011, 5:33 PM

Post #3 of 8 (2523 views)
Re: Truck will not pass smog. Sign In

Pressure should be around 10-14 i read.
Fuel regulators run off of vacuum.
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Your only as good as your tools!

(This post was edited by Mr.scotty on May 5, 2011, 5:55 PM)


zmame
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May 5, 2011, 5:41 PM

Post #4 of 8 (2519 views)
Re: Truck will not pass smog. Sign In

Are you sure i thought TBI engine run lower pressures. I though it was only actually 13psi at the injector(s) it's self. I belive the fuel regulator is in the TB it's self (not %100 sure). Line pressure might be 68, but I think it's only 13psi at the actual injector if I remember trade school.. but that was a while ago.


Not sure how you go about testing it hopfully somone here will have some insight on that.


Mr.scotty
Enthusiast
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May 5, 2011, 5:56 PM

Post #5 of 8 (2517 views)
Re: Truck will not pass smog. Sign In

Sorry, For some reason i looked up a 98..Unsure
For this year i read 10-14psi.
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Your only as good as your tools!


Hammer Time
Ultimate Carjunky / Moderator
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May 5, 2011, 6:01 PM

Post #6 of 8 (2510 views)
Re: Truck will not pass smog. Sign In

[quote[Sorry, For some reason i looked up a 98..
For this year i read 10-14psi.



SURE, just dig your hole deeper....

The 98 spec is 55 to 66PSI



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Mr.scotty
Enthusiast
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May 5, 2011, 6:01 PM

Post #7 of 8 (2507 views)
Re: Truck will not pass smog. Sign In

This is what i found:
  1. Turn engine OFF to relieve system pressure.
    • Disconnect negative battery terminal to avoid possible fuel discharge if an accidental attempt is made to start the engine.
    • Loosen fuel filler cap to relieve tank vapor pressure.
    • The constant bleed feature relieves fuel pump system pressure when the engine is turned "OFF".
  1. Uncouple fuel supply flexible hose in engine compartment. Install fuel pressure gauge between steel line and flexible hose.
  2. Tighten gauge in line to insure no leaks occur during testing.
  3. Connect negative battery terminal and START engine and observe fuel pressure reading. It should be 62-90 kPa (9-13 psi). If not, refer to DIAGNOSTIC CHARTS/FUEL SYSTEM PRESSURE TEST (CHART A-6).
  4. Turn engine OFF to relieve system pressure.
    • Disconnect negative battery terminal to avoid possible fuel discharge if an accidental attempt is made to start the engine.
    • Loosen fuel filler cap to relieve tank vapor pressure.
  1. Remove fuel pressure gauge.
  2. Install new O-ring on fuel feed line. Reinstall fuel line.
  3. Connect negative battery terminal and START engine and check for fuel leaks.
  4. Install air cleaner assembly.

--------------------------------------------------------

Your only as good as your tools!


Mr.scotty
Enthusiast
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May 6, 2011, 2:47 PM

Post #8 of 8 (2479 views)
Re: Truck will not pass smog. Sign In

I said to Zmame that I looked up a 98 spec by mistake.
I posted 10-14psi for the 93 5.7 the guy has posted.

Should have made that a little more clear, sorry.
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Your only as good as your tools!






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