92 chevy 350 5.7L runs a little too lean for CA smog

50

Asked by Jan 23, 2016 at 06:15 PM about the 1992 Chevrolet C/K 1500 WT Standard Cab LB 4WD

Question type: Maintenance & Repair

so trying to get my truck smogged.  232K
on motor.  edlebrock headers and
edlebrock intake both California legal.  also
have a magnaflow exhaust with one cat.  
failed smog with a high NOX reading at
both 25mph and 15mph.  replaced
Catalytic converter, EGR, and O2 censor.  
my CO's on the test are reading 0.00 wich
is means my NOX reading is gonna be
higher and that my fuel mixture is lean.  
tried the smog test 4 different times after
each new part.  the new cat fixed my
25mph but not the 15mph.  and the egr
next made it fail the opposite.  I then tried
the new O2 and cleaned the throttle body
and now I'm failing both.  they want to run
a diagnostic test for 160$.  are there any
other options I have besides getting the
test done? I

25 Answers

37,935

Go to Auto Zone and have the codes read. Write them down and post them here.

2 out of 2 people think this is helpful.
Best Answer
9,055

If there is codes. DIY. The '92 TBI is a OBD1 system. Instead of blindly changing items and hoping for the best you need some diagnostics. Instead of relying on them you could pay a little more and get your own wide band O2 and go from there. Decent ones start around 200. EFI 101 your truck comes from the factory with basic fuel and spark tables (on your "chip" (EEPROM) for the ECM to use and run the engine. Once you added the headers and intake allowing your engine to breath better you strayed to far from the norm for your ECM and leaned the motor out. The O2 sensor on your truck is more like a trim, it can offset a small change from the factory fuel table but not a large one (It is also a narrow band O2 and cannot tell you what the air/fuel is only whether it's rich or lean). Other factors can add to the lean condition also. If you don't have time to play pay the fee but stay and see what your truck is doing. If you have time I suggest getting a ALDL cable (50 to 100) and free software to read the codes and live values from your truck plus the wide band O2 to see the air/fuel and find your problem. I'm glad I don't have to deal with emissions. If you need to pass asap and fix later and are sure it's lean restrict the air cleaner or exhaust but use caution you might go to rich.

56,625

I'd suspect a vacuum leak with a lean air/fuel mixture or the carburetor is jetted too lean. How's it run? Check the spark plugs. If the electrodes (tips) are white it's running too lean. Since your truck is OBD I the auto parts store probably won't be able to scan the computer. You'll have to jump the A & B terminals on the ALDL connector to flash out any codes with the check engine or service engine soon light. HTH. -Jim

56,625

The ALDL connector:

56,625

You'll want the two terminals in the upper right corner. You'll get a reference code 12 to let you know you have successfully entered diagnostic mode. HTH. -Jim

50

vacuum lines from the purge to the tbi? the vacuum line to the egr doesn't seem to leak, egr diaphragm opens up just fine. i mean i assume it's too lean if my NOX is high and the CO's are low. is there just one o2 censor? just did the plugs cap rotar and wires under 1000 miles ago along with filters and oil. could a bad pcv valve cause it? and my o2 censor is before the y pipe and only reads off one header

50

No carb, fuel injection. truck runs smooth especially with the nex parts. except for the top end of any gear it sounds like its wide open but has a deep flutter to it. not sure if its lack of fuel or a valve floating

1 out of 1 people think this is helpful.
50

timing light says it's at factory 0 degrees

1 out of 1 people think this is helpful.
9,055

To check for vac leaks use an unlit torch while your truck is running and hold it near each vac line blowing a reasonable amount of propane.. If you have a vac leak it will suck in some propane and rev up slightly.

1 out of 1 people think this is helpful.
37,935

Use spray can of carburetor cleaner then

2 out of 2 people think this is helpful.
9,055

Most stores have newer cheaper scan tools that only read the codes on OBD1 and concentrate more on the OBD2 vehicles. A GM dealer or any decent domestic mechanics shop should be able to connect to a OBD1 ECM and read the live values from all of your sensors. I use a ALDL to USB cable and TunerPro to read my vehicles live data (except for the half bread OBD1.5 crap on my 94 95 w cars.

50

how many vacuum lines I got, just 5 right?

1 out of 1 people think this is helpful.
9,055

There should be a diagram on the rad support by the hood latch. I'm 4.5 hours from my truck right know but sounds right. Evap Canister, EGR, MAP, brake booster and PCV?

1 out of 1 people think this is helpful.
50

so what if I have no vac leaks? my only option is to hook a scanner up?

1 out of 1 people think this is helpful.
9,055

It makes a world of difference seeing what your sensor are reading in trying to diagnose a problem. I used to guess and check for issues too, but never again. Laptop and the cord and good to go. Takes awhile to get some of the software going but worth it.

1 out of 1 people think this is helpful.
50

yeah I'm sure it's very effective but how much am I looking at spending? Also thought about chipping the truck but not sure if it'll be worth it without rebuilding the pistons valves and maybe a cam. 232k is quite a bit for a 350 that hasn't been rebuilt

9,055

Here you go. Oh it's now Android compatible. I will need to check that out. This is who I got mine from. Free software on disc. http://www.ebay.com/itm/GM-OBD1-Scanner-Cable-Software-USB-to-12-pin-ALDL-direct-GM-OBDI-/121525227654?hash=item1c4b77d086:m:mpDR99tAgFQxv-15YmvDatw&item=121525227654&vxp=mtr

9,055

The air fuel ratio is what costs the money. I borrow that from a friend when I need one.

9,055

232k that's getting up there. I would suggest a crate motor or pull a lower mile good motor rebuilt it and swap them.

1 out of 1 people think this is helpful.
50

yeah I got a good oil leak where the tranny bolts up to the motor. crank seal maybe? thanks for the links and help, greatly appreciated!

9,055

No prob. Good luck.

37,935

I agree, 235K its getting tired, That is when my motor gave out.

1 out of 1 people think this is helpful.
50

found my problem... the egr and cat may have been bad my timing was about 15 degrees advanced at idle. turns out the guy smogging my truck was lying to me so I would spend repairs through him. needless to say i got my test money back, the truck passed with a really good NOX and I processed a complaint through California BAR

1 out of 1 people think this is helpful.
37,935

That is totally unreal!! Ho, I'd be steaming mad! Put the screws to him!

9,055

People these days, anything to make a quick buck. Glad you got it fixed. Are you still planning on keeping the truck for awhile. They are good trucks except for the transmissions. Just FYI. That cable will read 95% of GM OBD1 vehicles from 1995 and older. If you have any friends you could help them out to. I checked out the app for android, they want 20 bucks, I will most likely get it. I just hope it works with my cable. If you are still interested in the ALDL I could report back here on whether or not the ALDLDroid app is worth it.

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