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Premium Member
1989 XLT 5.0 - Auto Trans, Manual Hubs
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178 Posts
Discussion Starter · #1 ·
Hey Team,

So I took the 89' 5.0L in to get it smog tested (I have a temp reg at the moment) and she failed. Here is the report:

172583


If you look at the HC readings, its says I'm quite a bit over. The max is 73 and I'm at 108. I'm reading for things to check like vacuum leaks, plugs/wires (changed last week), catalytic converter, timing, etc. Just wondering if anyone has run in to this and what the likely culprits are for these broncos and where to start.

Thanks all...

Mike
 

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1,316 Posts
O2 sensor.

I have the Probst book on EEC-IV systems and it says the O2 sensor is the primary cause of emissions test failures. They get lazy with increasing age too.

The computer will run open loop till the sensor is hot (30-60 seconds if it doesn’t have a heating element) so make sure emissions aren’t tested with a cold O2 sensor.

It could be many other things too - leaking FPR to lazy fuel injectors to lousy spark plugs. But a functioning O2 sensor should be able to adapt to those conditions within reason.
 

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29,153 Posts
Yo Mike,
Try a Self Test for Diagnostic Trouble Codes by my pal, BroncoJoe19 @ Code Reader.....
Or ask local mom and dad parts stores if they will test it for you.

See my Vacuum leak test in post #9 incl @jowens126 HVAC Control Panel info & @Mikey350 tests @ Help with dtc codes and idle
One tip is When vacuum leaks are indicated, search out and correct the condition. Excess air leaking into the system will upset the fuel mixture and cause conditions such as rough idle, missing on acceleration, or burned valves. If the leak exists in an accessory unit, such as the power brake, the unit will not function correctly. Or Air Conditioning when in MAX mode may switch to Defrost.

"High HC;
  • Inoperative/missing catalytic converter
  • O2 sensor malfunction
  • Internal engine problem
  • Vacuum leaks (hoses, vacuum operated devices, intake manifold, carburetor)
  • Ignition system malfunction (plugs, plug wires, points, dwell, etc.)
  • Improper fuel injector operation
  • Incorrect ignition timing and/or idle speed
  • Incorrect carburetor air/fuel mixture
  • Defective EGR valve or air injection system failure"
by Common Reasons for Failure | EnviroTest


 

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Premium Member
1989 XLT 5.0 - Auto Trans, Manual Hubs
Joined
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178 Posts
Discussion Starter · #4 ·
Thanks miesk5, appreciate the write up and I'll definitely go through the list. The truck is in the shop getting 3 leaks fixed (valve covers, main seal, and oil pan). I asked them to double check the plugs while its out and the fuel injection system. Once I get it back, down the list I'll go. May need a catalytic converter as well. I hear some rattling down there in that area too. Thanks again!

Mike
 
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