Bullnose Enthusiasts Forum

Failed emissions test

Classic

List

Threaded

28 messages Options

delco1946

Failed emissions test

This post was updated on .

My mechanics sniffer is broken so he can’t help diagnose this. All I know is that my truck failed emissions with 12% co (limit is 3). Even my mechanic said this is sky high. My truck has been sitting in a shop for ten months but before that had just had the carb rebuilt, new cat, new vacuum lines, new egr, runs reasonably well etc.

High co seems to mean it’s running rich.

I don’t see any mention in the manual of sensors - does an 81 have an oxygen sensor? Another common failure from generic lists also seems to be an engine temp sensor but I don’t know if my truck is that “smart”. Also sounds like I should check my thermactor system, which I thought worked but I can’t recall if I ever really tested it.

Where to start?

Christopher in Portland Or. 1981 F250 Ranger XLT 4x4 trailer special 351M, and auto C6

Rusty_S85

Re: Failed emissions test

High Co = running rich. On a carb setup could be high float level, incorrect jet size, stuck choke, high fuel pressure.
High Hc = unburned fuel in exhaust
High NOx = running lean or faulty egr system

Question is when it failed on the Co was it the idle portion of the sniffer test or the low speed/high speed test?

If it failed the idle portion but passed the low speed/high speed test then you need to look at your idle circuit on the carb. If it passed the idle portion but failed either the low speed or high speed test then you need to look at the primary fuel circuit. If it failed on both the idle and the low speed/high speed test then you need to check the choke, float level, fuel pressure.

an O2 sensor would be on electronic systems with computers. California did have them earlier than the federal mandate for the other states I cant remember the exact year but I know federally you wouldnt see feed back carbs/electronic sensors and EFI till around 1984/85. Based off your tag with you being in Oregon your truck unless it was built for california sale should be a federal emission truck and for a 1981 it wouldnt have a computer it wouldnt have a O2 sensor and it would just be a basic traditional carbed truck with DSII ignition system.

"Old Blue" - '56 Fairlane Town Sedan - 292-4V, Ford-O-Matic transmission, 3.22:1
'63 Belair 2dr sdn - 283-4V, Powerglide transmission, 4.56:1
'78 Cougar XR7 - 351-2V, FMX transmission, 2.75:1 9inch
"Bruno" - '82 F150 Flareside - 302-2V, C6 transmission, 2.75:1 9inch, 31x10.50-15 BFG KO2

Gary Lewis

Re: Failed emissions test

Administrator

I agree with Rusty. But will add that a clogged air filter will also raise the CO levels, but it would have to be really clogged to be up that much.

So I'm going to guess it is the choke as it might have stuck shut or not have been properly adjusted after the rebuild. (I don't change the choke's settings in a rebuild if it was working correctly.)

As for a computer, it should have one if it has the California emissions system. The pages below are from the 1981 EVTM (Documentation/Electrical/EVTM/1981 EVTM) and show that the CA-spec 302 and 351, which was an M in '81, had a computer. I don't know where it was on an '81, but in '82 they were under the driver's seat. And there is an O2 sensor, engine temp sensor, MAP sensor, etc. Any of those can cause problems.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

85lebaront2

Re: Failed emissions test

Administrator

Gary, I agree that 1981 CA spec 351M would have a feedback carb, now the question comes which one? A relatively standard 2150 or a 7200 VV? 2150 could have a bad power valve, 7200, good luck, those need a bunch of specialized tools to set up properly.

Check that the EVAP system is working correctly and the canister isn't saturated, PCV in good order. Sometimes doing an oil and filter change can bring it back into spec. All this makes me glad I don't have to deal with this.

Bill AKA "LOBO" Profile

"Getting old is inevitable, growing up is optional" Darth Vader 1986 F350 460 converted to MAF/SEFI, E4OD 12X3 1/2 rear brakes, traction loc 3:55 gear, 160 amp 3G alternator Wife's 2011 Flex Limited Daily Driver 2009 Flex Limited with factory tow package Project car 1986 Chrysler LeBaron convertible 2.2L Turbo II, modified A413

Gary Lewis

Re: Failed emissions test

Administrator

Hadn't thought about what carb it might have. Yep, if it has a VV then there could be a problem. And you are right, a bad power valve would certainly cause the CO to go through the roof.

Gary, AKA "Gary fellow": Profile

delco1946

Re: Failed emissions test

Thanks all! Rusty - we never even went past the idle test

. This was at idle, and it was early in the morning and my truck sat in line for a bit so there’s always a chance it wasn’t super warmed up, but that seems like a stretch

.

When you say a problem with the idle circuit, are you just saying the idle screws? Sorry it’s been so long - there’s a screw that controls air/ fuel mixture too right? It’s idling at good rpms so I don’t think I’d want to change that Willy nilly….

This is indeed Oregon and my truck was built in Ca but was sold from Seattle so it was never a CA truck. I’ve never once seen anything computerized on this truck so that would makes sense that I don’t have O2.

I should add it’s a motorcraft 2150. The oil, filter, and PCV shouldn’t be old/ bad but I should change all that I guess since it was sitting for so long. It was certainly dusty/ filthy after that time.

Christopher in Portland Or. 1981 F250 Ranger XLT 4x4 trailer special 351M, and auto C6

delco1946

Re: Failed emissions test

Also, if memory serves I paid a shop to rebuild the carb - they did a bad job ( would barely run after) so I rebuilt it myself. I replaced the accelerator pump but I don’t think I ever changed the power valve which looks to be under the carb sorta. Unless they replaced it, it’s likely old.

Christopher in Portland Or. 1981 F250 Ranger XLT 4x4 trailer special 351M, and auto C6

Gary Lewis

Re: Failed emissions test

Administrator

Yes, the power valve is probably at the front/bottom of the carb and the cover is held on with 4 screws.

On some of the carbs the cover has a fitting that is for vacuum and that goes to manifold vacuum. Not all 2150's have that, but one of mine did. And that vacuum hose is important as w/o it the PV won't work.

Gary, AKA "Gary fellow": Profile

Rusty_S85

Re: Failed emissions test

In reply to this post by delco1946

delco1946 wrote

Thanks all! Rusty - we never even went past the idle test . This was at idle, and it was early in the morning and my truck sat in line for a bit so there’s always a chance it wasn’t super warmed up, but that seems like a stretch .

When you say a problem with the idle circuit, are you just saying the idle screws? Sorry it’s been so long - there’s a screw that controls air/ fuel mixture too right? It’s idling at good rpms so I don’t think I’d want to change that Willy nilly….

This is indeed Oregon and my truck was built in Ca but was sold from Seattle so it was never a CA truck. I’ve never once seen anything computerized on this truck so that would makes sense that I don’t have O2.

I should add it’s a motorcraft 2150. The oil, filter, and PCV shouldn’t be old/ bad but I should change all that I guess since it was sitting for so long. It was certainly dusty/ filthy after that time.

In that case then it will be something that effects both circuits. Could be clogged airfilter which doesnt seem likely as to be that clogged it would cause a issue with driveability you would notice. Could be a stuck choke, could be a improperly set float where it is just flooding the carb out with fuel, could be excessive fuel pressure over powering the needle and seat flooding the carb out. Could even be trash in the fuel bowl that is sticking the float even.

delco1946

Re: Failed emissions test

I am trying to test the thermactor system and after reading lots and lots of material I still can’t make heads or tails of when air is supposed to be injected into my exhaust manifold. At idle, is air supposed to be going into the EM? Or not?

It appears that I have an early CT style system with no vacuum at idle going to the “do hicky” on top of the belt driven pump.

Christopher in Portland Or. 1981 F250 Ranger XLT 4x4 trailer special 351M, and auto C6

Gary Lewis

Re: Failed emissions test

Administrator

We don't have the shop manual section on the thermactor systems on the website, but I can probably fix that tomorrow. I have the '81 and '85 factory shop manuals and will cut the sections out, assuming they differ, and put them on the site.

However we do have the 1982 Engine Emission Diagnosis manual on the site and there is a section on thermactor systems here: https://www.garysgaragemahal.com/thermactor-systems1.html

Gary, AKA "Gary fellow": Profile

delco1946

Re: Failed emissions test

This post was updated on .

Thanks Gary! It looks like my version is an older style which only helps with confusion. In my reading in sounds like that also means when vacuum is/isn’t applied also flips compared to later systems

.

Anywho, my current setup is resulting in a vacuum line going to the bypass valve, which is also part of the egr circuit per my hoods diagram ( with a couple delay valves in line). It’s not explicitly labeled ported vacuum, but since it’s part of the egr circuit, that makes sense in my mind (?) as vacuum to the egr would cause exhaust to circulate - not desirable during idle.

Assuming this is correct thinking, with no vacuum/ low vacuum, my thermactor system should be pushing air into my EM, and dumping air during high vacuum ( like decelerating) to prevent combustion to far down the exhaust headers. Tomorrow I will disconnect my hose to verify that air is indeed being pumped. If functioning correctly that would indeed seem to suggest the power valve as I feel like most everything else has been addressed.

Christopher in Portland Or. 1981 F250 Ranger XLT 4x4 trailer special 351M, and auto C6

85lebaront2

Re: Failed emissions test

Administrator

In reply to this post by delco1946

Christopher, just because the truck was sold in Oregon, does not guarantee it is not a CA spec or 50 state truck. Many years ago, I believe in 1980 or 81, my late mother-in-law and her brother were visiting us here in VA, on the way back to Washington state, they went back through Texas (her brother's home state) and bought her a new Chevy Citation, specifically to avoid a CA spec car. I had called a good friend at the local Chevy dealership and found that except for high altitude areas, all West coast cars were CA spec, definitely Oregon so they couldn't be bought and carried into CA to avoid the CA emission packages. Check your emission label.

Bill AKA "LOBO" Profile

Gary Lewis

Re: Failed emissions test

Administrator

In reply to this post by delco1946

Christopher - We now have the 1980 factory shop manual section on thermactor systems on the site. And I've also included the sections from the 1982 and 1986 Engine Emission Diagnosis manuals on the page. They are at Documentation/Emissions/Thermactor Systems. (Yes, the '82 and '86 info is still on the pages in the respective Engine Emissions Diagnosis books, but it seemed appropriate to include it on the Thermactor page as well.)

Sorry that I don't have the 1981 info. In '80 the thermactor chapter was in the Engine book of the FSM. But in '81 it says to refer to the Engine Emissions Diagnosis book, and I don't have the '81 version of that. So 80, 82, and 86 were the best I can do. Hope that helps.

Gary, AKA "Gary fellow": Profile

Gary Lewis

Re: Failed emissions test

Administrator

Also, I discovered in the 1980 document that there's the statement below on Page 5. So I did a bit of research and found SSD-4 & 5 in a 97-page chapter called "Light Duty and Heavy Duty Truck Engine Diagnosis and Service". I scanned it in and then extracted SSD-4 & 5 and inserted them at the end of the 1980 Thermactor FSM document.

So if you click on the blue box around SSD-4 or SSD-5 (in the document, not here as that's a picture) you'll be taken to the respective page. For reference SSD-4 is "Thermactor System - Non-Catalytic" and SSD-5 is "Thermactor System - Catalytic". And they have testing and repair procedures.

Gary, AKA "Gary fellow": Profile

delco1946

Re: Failed emissions test

Thank you Gary! I’ll look through all of it!

Christopher in Portland Or. 1981 F250 Ranger XLT 4x4 trailer special 351M, and auto C6

Gary Lewis

Re: Failed emissions test

Administrator

Welcome. Hope it helps.

Gary, AKA "Gary fellow": Profile

delco1946

Re: Failed emissions test

This post was updated on .

Took the carb off. the power valve looks new, clean and dry. So I left it in place as it looks to function. Even pulled on the plunger slightly to make sure it could move freely.

The accelerator pump also appears to move freely, no gasket tears etc. however I don’t think it’s adjusted properly- shouldn’t the pump shaft be allowed to “push” thru it’s full range Toward the radiator when off the gas? Currently the button is always resting against the lever that’s attached to the gas pedal, so the pump is only pumping for half its range or so. I thought I read somewhere that the lever should just barely be touching the button/ shaft?

Everything else in the carb looks good too. The float and needle move freely and don’t appear to be stuck.

Christopher in Portland Or. 1981 F250 Ranger XLT 4x4 trailer special 351M, and auto C6

delco1946

Re: Failed emissions test

I’ll check my thermactor system once I assemble the carb, but I’m wondering if all that’s needed is to turn the mixture screws clockwise slightly to lean it out.

Christopher in Portland Or. 1981 F250 Ranger XLT 4x4 trailer special 351M, and auto C6

Gary Lewis

Re: Failed emissions test

Administrator

We have the factory shop manual section for the 2150 on the page at Documentation/Fuel Systems/Carburetors, Chokes, & EFI/Motorcraft 2150. However, in looking at that document for information on adjusting the accelerator pump I found this: "Adjustment procedures and service instructions for this carburetor are contained in the Engine/Emissions Diagnosis Manual." But looking there I don't see anything about the accelerator pump.

So I don't know what to tell you about that. Perhaps Bill will?

As for the idle mix, yes you can screw the adjustment screws in and that will lean the mix. Perhaps that will be enough?

Gary, AKA "Gary fellow": Profile