Failed Utah Emissions

dcarnut1 · #1 (**permalink**) 08-15-2006, 10:01 PM

I have a 75 F250 390 that has failed the IM test twice. I have changed Plugs, Plug wires, cap and rotor, checked the coil, timing, carb, and cant find anything wrong. The truck passes CO2, O2, CO, and NO, it only fails on the HC test which leads to an electrical problem (according to mechanic freind). Does anyone have any ideas? Im running a stock dist., pertronix ignition, stock coil, the timing is at 14 deg. BTC with no vacum. any help would be appreciated.

76supercab2 · #2 (**permalink**) 08-15-2006, 10:07 PM

High HC is unburned fuel. Anything that can cause that should be checked out. Look for a miss, carb leaking/needing rebuilt, stuck choke, try changing the oil, check compression (burned valves or worn rings).

rusty70f100 · #3 (**permalink**) 08-15-2006, 10:10 PM

Sounds like you might have it set too rich at idle.

Here's what I would do, assuming you have a Holley / Autolite carb:
Turn the idle mixture adjustment screw all the way in on one side. The motor should stumble. If it doesn't, you have a bad power valve that needs to be replaced.

Now, turn it back out to where the engine smooths out and NO FURTHER! Now, go repeat on the other side.

Could also be that the stock coil is getting weak. How much plug gap are you giving it?

dcarnut1 · #4 (**permalink**) 08-15-2006, 10:15 PM

Rusty
Im running an edelbrock 600 cfm carb. Tunning Is the same as you describe for the holley. I Have a spare coil and have swapped with no change in the reading.

Scouder · #5 (**permalink**) 08-15-2006, 10:45 PM

Move up here to Evanston. We don't have emissions testing. Or state income tax. Or the Utaliban.

Just kidding. Sounds like you are rich. If the carb hasn't been jetted properly for your altitude it'll fail.

-Scouder

dcarnut1 · #6 (**permalink**) 08-15-2006, 11:18 PM

Scouder,
Amen brother, taxes, emissions, and beer laws, why am I still here?
I am going to tear into the carb tommorrow. Any Ideas what size jet and needles to use? Most driving is in the SL valley, 4200 feet, weekends are spent in the mountains at around 10000 feet. My carb is an edelbrock model 1406, 600cfm electric choke.

Mike G · #7 (**permalink**) 08-16-2006, 10:32 AM

Quote:

Originally Posted by Scouder

... Utaliban.

-Scouder

You're killing me....

I would step down a jet size and then lower your float level a touch as well. There is also a product you can get at the auto stores which supposedly reduces emissions. I haven't tried it, but you can bet I eye-balled it few times. Believe me brother, there is nothing more frustrating than not passing the emission tests. They are tight here as well, fortunately, if your vehicle is older than a 1981, you can still use an independent shop. I hooked onto a local racer who does emissions on the side, needless to say, I always manage to pass on the old cruisers.

--Mike

krewat · #8 (**permalink**) 08-16-2006, 11:50 AM

The one thing I can think of is this:

Since your F250 probably never came with a catalytic converter, is it possible the inspectors are not aware of that and are using an F150 (or passenger car) specification to test you?

A catalytic converter will certainly lower your HC's.

Since you pass on all the others, sounds like you're running pretty perfectly.

Did you have air injection and now it's gone? (not that that really changes much).

76supercab2 · #9 (**permalink**) 08-16-2006, 12:19 PM

Actually, in '75, 48 state F-150s didn't have cats either.

But good suggestion, is the IM station using the correct thresholds for your year truck? Do you have the numbers your truck blew?

dcarnut1 · #10 (**permalink**) 08-16-2006, 06:13 PM

I have changed jets and re adjusted carb on the lean side, it hasent made a noticable difference. I will have it tested on thurs. and see if anything changed.

Just for the heck of it, I did a compression test and found that #3 is 18 lbs lower than the rest. Im not blowing any blue smoke, so it must be a valve. I have noticed a puff of white smoke when it first fires in the morning.

Do you think this could be causing the High HC count?
Any ideas or tricks, just to get it to pass until I can pull the heads?

Mike G · #11 (**permalink**) 08-16-2006, 06:15 PM

One more note... I would always do a fresh oil change and go straight to the emission shop.

--Mike

dcarnut1 · #12 (**permalink**) 08-16-2006, 06:26 PM

A freind of mine owns the IM station, I Know that he is running the right test.

The truck Blew the following:
Part 15mph 25mph Max Pass/fail
CO2 (%) 12.0 12.0 na Pass
O2 (%) 1.2 1.5 na Pass
HC (ppm) 503 664 486/466 Fail
CO (%) 3.70 3.28 3.93/3.83 Pass
NO (ppm) 371 380 3405/3205 Pass

krewat · #13 (**permalink**) 08-16-2006, 06:38 PM

Wow, right on the line with the CO...

CO is the result of inefficient combustion.

Still sounds rich. You sure the choke is opening? (just checking).

Hypoid · #14 (**permalink**) 08-17-2006, 01:48 AM

Quote:

Originally Posted by dcarnut1

Im running a stock dist., pertronix ignition, stock coil, the timing is at 14 deg. BTC with no vacum.

No vacuum advance at all? I'm thinking you could start the burn much sooner.

Is this a treadmill test? Wouldn't the 15 & 25 mph reference points simulate cruising just above idle with little or no load? If I have the concept right the vacuum should be pulling gawdawful amounts of advance just to get the burn started sooner.

IIRC the NO is affected by cylinder temperature. It's probable you could lean out some, but I have to wonder what your operating temp is, what thermostat? Did you get the beast warmed up before testing?

Quote:

Originally Posted by Mike G

I hooked onto a local racer who does emissions on the side, needless to say, I always manage to pass on the old cruisers.

Geeeeeez Mike, you make him sound dubious. We're lucky to have guys who made the change when the state dumped the old system. They know what they're looking at when you get there, they sniff the air and tell you if you are wasting your time, and what you should be looking into before you try. Those are the guys you want to see next year; tip well! LOL
And yes, "I've been hosed by Envirotest!"

Evil corporate empire...

Mike G · #15 (**permalink**) 08-17-2006, 10:32 AM

Quote:

Originally Posted by Hypoid

They know what they're looking at when you get there, they sniff the air and tell you if you are wasting your time, and what you should be looking into before you try. Those are the guys you want to see next year; tip well! LOL [/size]

That's exactly the service I get. After the "consultation", he even looks over my shoulder as I make the adjustments, run it around the block hard and then hook up the machine.... After having wasted $$ here and there, it's terrific to have a place that you can turn to and receive a learning experience as well.

--Mike