Won't pass smog test 454tbi

[junkyard]

Hi,
I have a 91 K3500 dually 4wd ext cab. 454 throttle body injection auto trans.
In California so needs smog test.
.
The truck passed 7 weeks ago fine.
.
Problems are:
1) No vacuum at left front of TBI (erg source)
2) Rich at idle
3) Idle speed to high (1100 rpm)
.
the truck runs and drives fine.
I changed the coolant temp sensor today no improvement.
.
Any help?
.

02 sensor?
Iac ?
Tps?
.
????????
.
Thanks
Ken

[OrangeAnimal]

Need to know what the readings were. If you have that info that would be helpful.

Also you might not have any vac at the port for the EGR on the Throttle body at idle but once you raise it above idle speed you should get some. Best to hook a gauge to it. Then go drive it while monitoring the gauge to see if there is vacuum there. Also you can try cleaning it to get some of the gunk out of there to insure it's not clogged.

If it failed for high HC (unburned fuel) then you need to check out the plugs wires etc. Also don't forget the fuel filter and you may want to check the fuel pressure while you are at it. Clogged vacuum lines and throttle body also can cause problems.

You can test the TPS with a volt meter. Connect the negative lead to ground then test each wire with the key on engine off. There are three wires there I can't ever remember the colors of each wire but test each one and you will have one with 5v, one with no voltage(ground) and then one that "should" have around .5 volts with the throttle closed slowly open the throttle and the voltage should climb to close to 5v. If your reading it more than .5v with the throttle closed then you may have a problem. Let me know if it's more and I can go in depth on what to do.

The IAC is a source of trouble for some people but if your idle is steady and the truck doesn't try to die when you turn on the A/C or abruptly close the throttle then you should be good. You can and I do recommend checking the connector going to it those plastic tabs that hold the connector to the IAC are important so if they're broken you may want to replace the connector. Next remove the IAC for the TB. Get a flashlight handy and take a peek in the IAC bore if it's got a lot of crud built up in there then use can use a little carb cleaner and a soft toothbrush to clean it up. DO NOT use anything abrasive in there or worse a screwdriver.

The oxygen sensor is another thing that is easy to check with a voltmeter. Negative lead to ground and the positive to the one wire on the sensor. The voltage should fluctuate between .250v to about .800v on the meter. You will have to have the engine warmed up good to test it. However new sensors can be had for a decent price and may just be worth changing out. If you test it and the voltage doesn't fluctuate then you could have a couple of issues. I really just recommend replacing it unless you already have recently.

If it failed for high NOx then it's related to a few things but these three are the most common EGR Valve, Catalytic Converter, and Ignition Timing. Check your EGR Valve itself it's simple. Unplug the line going from the valve to the solenoid at the solenoid, reach inside of the EGR you should be able to "operate" it by hand, lift the diaphragm and once you have it up as far as it will go then put your finger over the end of the vacuum line. release the diaphragm the valve shouldn't return completely to the closed position. If it does the diaphragm may be busted. If that's the case don't remove it yet. Test to make sure the ports in the intake are clear. Start the engine go try and lift the diaphragm on the EGR again. If you do this and everything else is working then the truck should just stall out. If it doesn't then the ports in the intake need to be cleaned. Lastly there is the EGR Solenoid this one is tricky and you really either need a gauge or an assistant you trust. If your wife's mad at you then I don't suggest getting her to help. LOL. This involves someone in the truck to power brake it just to the point the tires would start to spin while you put your finger over that port that comes off the solenoid to the EGR valve. Block the front wheels and try not to stand directly in front of the truck unless you always wondered what it was like to get run over by a couple tons of steel.

Which brings me to the last thing. Has any changes been made to the truck since it passed the test last time??

I hope some of this has helped you in your quest.

[junkyard]

Thank you for that info.
.
The reading that it failed was at idle speed only, at the 2500 rpm it passed fine.
Idle reading for CO% was 1.37 max allowed is 1.20
.
All other readings both high rpm and idle were good.
.
I will be gone tuesday but will check as you instructed when I get back,
.
Thanks again.
Ken

[LynnJr]

Dirty or restricted air filters
Excessively dirty or contaminated oil
Saturated charcoal canister
Non-Functioning PCV valve system
These are straight from the Roseville California smog test website.
If they don't fix it a new Cat will get it to pass.
Lynn

[junkyard]

Originally Posted by LynnJr

Dirty or restricted air filters
Excessively dirty or contaminated oil
Saturated charcoal canister
Non-Functioning PCV valve system
These are straight from the Roseville California smog test website.
If they don't fix it a new Cat will get it to pass.
Lynn

Hi and thanks for the input.
air filter is new.
oil has about 3k on it but is clear (see thrugh it)
I'll have to check on the canister
pcv works properly
.
new cat might catch the %co number but won't address the high idle or no vacuum to erg valve.
.
will keep informed
Thanks
Ken

[LynnJr]

Ken
My truck is also a high idle truck at its smog test sessions and while they tell me all the time about it they have never failed it for that.If they did I would pop out the litle plug on the right hand side of the TBI and lower the idle.
The only other way I am aware of is swapping out chips until you get a lower idle.

[OrangeAnimal]

The idle issue may be able to be fixed. There is a step by step process to remedy it.

IAC reset/min idle speed- This sets the throttle plate on the throttle body to a specific rpm. I recommend about 500 rpm for most engines. Procedures- Go to sheet 7 of the pinout diagrams. At the top is the ALDL connector. You need to put a jumper between pins A and B of the connector. These are pins A9(wht/blk) and A12 (blk/wht) on the ECM. This puts the ECM into aldl mode. Turn the key on (not start) and the IAC should drive completely closed. You will normally hear a buzzing from the IAC. If you have the winaldl up and running on your laptop, you should see the IAC went from 145 to 0. Now unplug the IAC connector. turn the key off. Remove jumper. Start motor. If the idle is too low you may have to keep it running. On the front drivers side of the throttle body is the adjustment screw. It may be behind a silver plug. If so just use a nail or punch to poke it and remove it. Then use a #20 torx bit to adjust the idle speed to at least 100 rpm less then your warm idle speed. if 600 then set to 500 rpm. You are looking for the lowest consistant idle your motor will do. When set, turn off motor and reconnect the IAC.

Disregard the colors of the wires listed above, They are for 3rd Gen F Body. Also Here is a link to show the pins on the OBD-1 port you need to jump.

http://www.obd-codes.com/faq/read-gm...codes-free.php

[junkyard]

Thanks guys,
Been down since wed. still not functional.
I will update as soon as I see again.
Ken

[Zane M]

I'm no help on why it isn't passing now, but do have a question:
If it passes 7 weeks ago, why is this an issue now. Couldn't it be registered with the "certificate"(or whatever is used in CA) from that test?

[junkyard]

Originally Posted by Zane M

I'm no help on why it isn't passing now, but do have a question:
If it passes 7 weeks ago, why is this an issue now. Couldn't it be registered with the "certificate"(or whatever is used in CA) from that test?

-
-
That was for yearly registration renewal. Now it needs one foe title transfer to new owner.

[Zane M]

Originally Posted by junkyard

-
-
That was for yearly registration renewal. Now it needs one foe title transfer to new owner.

Understood.
Hopefully you get it sorted out soon.

[4x4toy]

The undersides of the TBI units get carbon build up, best to remove and clean the vacuum ports from bottom side while throttle body is removed. Dont forget to clean the throttle blades and the IAC passage. Carburetor cleaner should break up the carbon/gunk.

[Rod_Lei]

^Yeah I would take the throttle body off and clean all the passages on the bottom with some carburetor cleaner. Use a flashlight to shine through the front vacuum port and clean until you can see the light clearly shining through the vacuum passages. They really gunk up, you'll need patience and a small metal utensil to pick away.
Good Luck man.

[Russell]

The vaccum port on the back of the intake is ported vaccum, aka there will be none present with the throttle blades closed. Crack the throttle open and you'll get suction on that port.

Do not adjust the idle screw on your throttle body if it wasn't idling high before, you'll just be compounding your troubles by adding a whole new variable to the mix. High idle can be cause by a number of things including incorrect timing, failed IAC or even vaccum leaks. You need to be 100% sure something else isn't causing the high idle condition before you make a change in that setting.

I am going to go on a limb and guess you most likely are suffering from an EGR problem. Do yourself a favour and test the EGR system properly. Follow the following troubleshooting guide to test it out...

Troubleshooting:

The most common EGR system failure on our trucks is the valve itself; the diaphragm fails so the EGR valve will not open. You can eliminate this possibility right off the bat by testing the valve with a vacuum tester (Mityvac.) Shut the engine off and connect the tester directly to the EGR valve. Pull vacuum (around 15 inches is plenty) and be sure it holds for a minimum of 20 seconds. If it does not build or hold vacuum, the valve could be held open by a chunk of carbon, which you could attempt to clean out – but most likely, the valve is bad and needs to be replaced.

If the valve passes the hold test - with vacuum still showing as holding on the tester, have a helper start the engine while you watch the gauge. The vacuum should bleed off immediately.

Determine whether the EGR passages in the intake are clogged by carefully depressing the EGR diaphragm with your fingers. Take care to not burn your fingers or get them caught in the openings under the EGR. When you press the diaphragm, the engine should stumble noticeably, and possibly stall. If there is little or no response, the passages in the intake are likely clogged with carbon. Effective cleaning of these passages requires removal of the intake manifold.

Check the vacuum source to the EGR solenoid. Connect a vacuum tester (Mityvac) to the line leading from the TBI unit to the front (single port) side of the solenoid. There should be full vacuum at idle, around 20 inches/Hg on a stock engine. If not, remove the line from the TBI and connect the tester directly to the TBI to verify vacuum. If none, the port itself may be clogged.

Reconnect the line from the TBI to the solenoid and move the tester to the line exiting the rear of the solenoid. At idle there should be NO vacuum reading (be sure you purged your gauge if necessary so that it reads zero before connecting.) Snapping the throttle should show some activity on the gauge as the solenoid briefly commands the EGR open.

With the meter set on ohms, you can test the EGR solenoid coil across the two pins in the socket; any reading less than 20 ohms indicates a bad solenoid winding.

With the meter set on DC voltage, or using a test light, check the EGR solenoid harness terminal A (pink/black) to ground. Key on, meter should read 12V or the test light should light up. Do not pierce the wire to test, simply unplug it and touch the test lead to the connector pin.

Another possible failure that is difficult to test for is a weak spring inside the valve allowing it to open too easily. If you have exhausted all other efforts you may consider replacing the valve.

If the EGR tests out as good, then you need to look for vaccum leaks next. Pay special attention to the throttle shaft bushings at the base of the throttle body. They are known to wear and begin leaking over time. Make sure all your vaccum lines are good, check the PCV system and make sure the brake booster is good as well.

If your EGR is good and you cannot find any issue with vaccum leaks then I would be checking my timing is set correctly. Then checking the IAC pindle for smooth operation and clean passages. Finally I might consider adjusting the idle screw a bit. This should be done with a data logging tool which will allow you set it via the IAC counts (~20 at idle).

Notice that none of the above involves buying and throwing random sensors at your injection system. You need to take the time to troubleshoot it and positively identify the problem. This isn't always easy but is always very rewarding when you turn that key and it runs just like new again! Unfortunately these old TBI ECMs are not very good at providing help by telling you what it sees wrong like the newer injection systems do haha!

[junkyard]

Thanks for all the information everyone.
As soon as my health issues clearup I will get back on this
and check all your suggestions.
Thanks again.
Ken