Hi,

I've got a 1977 F-100 302 5.0L V8 in California that recently failed it's smog check. It's got about 180,000 miles on it, manual transmission, beautiful truck but got tagged as a gross polluter. Here's the results from the emission test.

Test @ 828 RPM - %CO2=11.3 - %02=4.0 - HC (PPM)=1125 - CO%=0.69

Test @ 2351 RPM - %CO2=13.5 - %02=1.5 - HC (PPM)=263 - CO%=0.60

It failed on the hydrocarbons section where the allowable amount is 250 (PPM) max for the first test and 200 (PPM) for the second.

I'm looking for likely causes for this particular read out. I checked the timing and found that it was retarded at 4 degrees BTDC. I've since adjusted it to about 8 degrees BTDC. Any advice about timing would be appreciated.

I tested compression on all cylinders and this is what I found-

Cylinder #1 dry 126psi, wet 130psi

Cylinder #2 dry 130psi, wet 130psi

Cylinder #3 dry 131psi, wet 132psi

Cylinder #4 dry 119psi, wet 120psi

Cylinder #5 dry 132psi, wet 135psi

Cylinder #6 dry 131psi, wet 132psi

Cylinder #7 dry 134psi, wet 135psi

Cylinder #8 dry 125psi, wet 125psi

I know that all around this compression is fairly low, particulary in cylinder #4. I'm wondering if an engine with this compression reading would have trouble passing smog. Is the low compression a reason for high hydrocarbons coming out the tailpipe? Or is the cause for the high hydrocarbons likely something else. The truck runs alright, lacks some power but that's to be expected for an old fellah. I'm hoping I can pass smog without an engine rebuild. Any info about compression is appreciated.

Finally I plan on replacing the carburetor which numerous mechanics have said is shot. Still, the plugs all look to be wearing normally, maybe a touch lean from the looks of them but nothing serious. How likely is this to correct the problem?

Also, could a bad catalytic convertor be a cause for the high hydrocarbon output? Any way to test of the catalytic convertor is good?

I really want to keep this truck running well and keep it legally on the road. Any and all help/insight is great appreciated. Thanks in advance.

Pad

 

I'm back with an update.

I replaced the carburetor with a remanufacutred one, replaced every vacuum hose I could find, replaced the PCV valve, replaced all the necessary gaskets, replaced fuel filter and added an extra in-line fuel filter (to keep new carb clean). Then I tuned the carburetor using the lean drop method so that vacuum pressure was pulling at about 19 psi. I also set the timing to the manufacturer's recommended 6 degree BTDC.

The truck seemed to idle and ride real nice, so I took it in for a second attempt at passing smog.

Again, it failed with the same problem, very high hydrocarbons at idle. Here's the new smog results.

Test @ 867 RPM - %CO2=12.3 - %02=2.4 - HC (PPM)=1131 - CO%=1.12

Test @ 2338 RPM - %CO2=13 - %02=2.2 - HC (PPM)=195 - CO%=0.22

This time it did squeak by the HC limit at high rpms (200 PPM) but the idle HC is still at gross polluter levels.

The tech thought it was probably two problems, getting the mix dialed in and finding and solving a likely vacuum leak somewhere.

I would love help figuring this thing out. Once I do, I'll be sure to post the solution in case someone else is having similar trouble. Thanks again.

 

buy a 76?

Sorry I couldn't be more helpful, we don't test for that kinda stuff here.

 

Those compression numbers are fine and have nothing to do with your failure. #4 is a little lower than the others but still close to 10% of the others.

You need to go through the entire emissions setup and make sure that (1) it's actually there and (2) it's functioning properly. This most likely means:

(1) EGR valve and spacer plate, including any vacuum hardware that runs it, such as a PVS.
(2) Catalytic converter.
(3) Smog pump and diverter valve.

These often get scrapped by previous owners. You won't get your truck to pass without its original emissions equipment from a tune-up alone.

 

^ Smog pump, check valve and diverter valve. The check valve threads onto a metal pipe that bolts to the backside of each head. Over time, rust causes the valve to become adhered to the pipe.

Unknowing peeps put a wrench on the valve, turn it, the pipe corkscrews, splits open. Not pleasant!
------------------------------------------------------------------------------------------------
The factory installed EGR/Carb spacer plates were made from aluminum. Hot exhaust gasses caused them to melt internally. They also tended to carbon up.

The Ford replacement spacer plates were cast iron.

Coupla days ago, someone was looking for one of these 1977/79 F100/150 302 EGR/Carb spacer plates. Obsolete, no longer available from FoMoCo, but...

If this turns out to be the problemo: D7PZ-9A589-B (Motorcraft CM-2642).

WESLEY OBSOLETE PARTS in Liberty KY has 354 (!!) = 606-787-5293.

Fellow I found the spacer plate for contacted me, said WESLEY is selling them on ebay for a "blowout price" of about 17 bucks. Last MSRP was $55.47, dealer net cost was $30.51.
Did'ja know (probably not) that there are more vehicles in LA, San Berdoo & Riverside Counties than there are in 46 of the 50 states COMBINED?!

Air pollution (smog) has been a major problemo here in the LA LA Land basin since the 1950's. Basin surrounded on 3 sides by mountain ranges, sea breezes wafting off the Pacific Ocean blow the smog eastward.

If you lived here, you probably would know that CA smog tests all 1976 and newer vehicles.

ALL the emission parts have to be present and in good working order. If the vehicle cannot pass a smog test, it cannot be registered.

There is no waiver if the parts are obsolete. It's fix it...or park it!

 

Thanks for all the tips everyone.

Fmc400 - I really appreciate hearing that the compression numbers aren't the issue. I wasn't sure about that, since compression was fairly low all around, I wasn't sure how it might effect emissions. It's great to know that's not the problem since it eliminates major rebuild costs.

Actually, the EGR valve is shot and I plan on replacing it but I figure that wouldn't cause high HC at idle since the EGR valve doesn't function at low speed anyway.

As far as catalytic converter, I was told that a bad CAT would post high numbers everywhere, both at idle and at high rpms and both with HC and CO. That's not the case with my reading. Could a new CAT correct HC numbers as bad as I've got?

I'll definitely investigate the smog pump situation.

Thanks for all the information everyone. I'll keep posting as I make progress on this.

P.S. As a side note, this is a single family truck, had it since new so there aren't any previous owner modifications or tinkering to deal with. The only things that might be funky or non-stock are things done by various certified mechanics over the years.

 

I've got some new findings. I'm trying to figure out how to upload some pictures.

 

Alright. I investigated possible vacuum leaks by spraying throttle body cleaner around possible leak areas with the engine idling. I saw no change in rpms. I tried the same test method again with an unlit propane torch, still I couldn't find a vacuum leak that would cause rpm change. Then out of curiousity, I sprayed throttle body cleaner and then propane straight down into the carburetor with engine running. Strangely, I still didn't get any change in rpm. What's up with that? Makes me distrust the whole test.

While poking around for vacuum leaks I did find two lines that connect to the exhaust manifold on the passenger side of the engine and then lead up and connect into the back of the carburetor. Both of these lines were broken off or compromised where they connected with the exhaust. Here's a picture of both the lines right next to each other and me pointing to where the insulated line should connect into the exhaust.



The mechanic at the parts shop said both of these lines run into the carb to control the choke mechanism. That with them broken the choke might not function perfectly but worst case scenario would be a high idle. Anyhow, he said it wouldn't account for my high HC on the emmissions test. Anyone else have any thoughts on this? Could it be the culprit?

Next up, for anyone as clueless as I am, I figured I'd post a pic showing where the smog pump is located. That's me pointing to it, just below the alternator.



I followed the hose up from the smog pump and it led to this canister that I'm pointing at, before branching off into two other hoses that each bring air to either side of the engine exhaust. What is this canister? What does it do?



Same question for this vacuum diaphragm. Name? Function?



I want to understand these smog pump components and how to check them to make sure they're functioning properly. Any tips are appreciated.

So to summarize -

1) Why didn't the rpms change when flammables were put straight down the carb while idling?
2) Could the two broken lines from the exhaust to the carb be causing my high HC at idle problem
3) What are the components shown relating to the smog pump and how do I check the smog pump system (canister thing, diaphragm, and valves) for proper function.

Thanks a bunch. I'll keep posting as the saga continues.

 

This test must be run with the engine leaned out such that it's barely running. Otherwise, the jump in idle speed will be hard to notice.

The lines in question are for the choke mechanism. Refer to this writeup for more information on what the choke does, and what those lines are for: https://www.ford-trucks.com/forums/8...ml#post6939116

Your mechanic is correct; if these lines are broken, the choke may never open and the fast idle may never kick off. If the choke is stuck on permanently, HC count will be higher across the board because the engine will run rich. However, you would notice this while driving (the engine will run very poorly if the choke stays on past the point the engine reaches operating temperature). This is very easy to check; pull off the air cleaner and see if the choke opens in the few minutes it takes the engine to reach operating temperature.

Your first picture shows the smog pump. Its job is to literally pump air into the outgoing exhaust to help complete the combustion process before the exhaust goes out the tailpipe. The item in the second picture is the diverter valve. When it senses an increase in manifold vacuum (as would be seen when letting off the gas to decelerate), it cuts off the output of the smog pump to keep the engine from backfiring. The item in the third picture looks like a vacuum delay valve. I haven't seen one used here before, but it does exactly what it's name says.

The smog pump is easy to check just by removing the belt and turning it by hand; you should feel air come out of the outlet. Make sure the diverter valve with the vacuum delay valve in front can hold vacuum. With no vacuum applied, air should be able to pass through the diverter valve. With vacuum applied, no air should pass through the diverter valve. I do not recall if air should continue to be blocked as vacuum is held (or does the diverter valve slowly let go again) - someone else will need to refresh my memory. Sorry.

As far as ignition timing goes (your first post), set it to whatever is shown on the emissions sticker (valve cover, or under the hood). It's also important that you set your idle mixture with a vacuum gauge.

 

Cannister = Evaporative Emission (Evap/Em) System. Has nothing to do with T/E (Thermactor Emission-smog pump). Evap/Em: Unleaded fuel, non vented fuel cap.

Evap/Em charcoal cannister located on right inner frame rail below the alternator. Round fuel vapor valve located adjacent to fuel sending on fuel tank.

Line routes from nipple on valve along right frame rail to valve on cannister. Corrogated paper hose routes from valve on cannister to elbow on side of air cleaner.

If dual fuel tanks, one valve in each tank, lines routes from valves to valve on cannister.

Pic 4: D6DZ-9G328-A .. T/E Idle Vacuum Valve Assy.

Where in CA is the truck located? If in LA LA Land, I could swing by, take a look-see. I know all the CA emissions parts and where they're supposed be hooked up.

 

Your HC numbers are very high. I just checked my last smog check for my truck and the HC measured at 19 for idle and 14 for the 25 mph check. That is for a 1977 f150 with a 351m non catalyst as it has a gvw of 6050. You said you replaced your carb with a rebuilt one... but you didn't say which one it is. An aftermarket carb might take a lot of tuning to get it diale in to your engine. Your catalytic converter might be burned out, but I'm not sure that it could lower the HC levels that much any way. Have you tried turning in the mixture screws to try and lean out the idle mixture? I think you also need to check your air pump to make sure that it is actually working. I'm not sure what else could cause

 

Before the most recent smog attempt, I set ignition timing to the manufacturer's recommendations as labeled on the engine (6 degrees BTDC). Didn't make any difference for smog numbers.

77blue - The carburetor I put on there is the same one I took off, the original stock motorcraft two barrel carburetor. I took it to a specialty shop in Pittburg, CA, called RecarbCo and they rebuilt it. I did the best I could tuning it myself with a vacuum gauge.

As for the smog pump system, fmc400, thanks for all your tips. They were super helpful for understanding and checking the system. The smog pump is blowing air strongly and the diverter cuts the flow when vacuum is applied and opens the flow when vacuum pressure drops, just like it should. So the smog pump system seems to be working fine.

I wasn't sure how to check the 'check valves' that attach the smog pump lines into the exhaust but I'm thinking my problem is not with the smog pump system.

I also checked to see if the choke functioned even with the lines broken and it does. The choke opens fine once the engine warms up.

So after a good amount of investigating and fiddling I still don't know what the problem is. There's still the catalytic converter to consider but is that likely to be the problem with the smog data I've posted? Could a CAT correct HCs as high as mine?

I think I'm about ready to take it to a shop. I still welcome any information or ideas in the meantime.

Bill, thanks for the offer to come by and check it out but I'm up in Northern California, a bit of a drive away, even by LA standards.

 

One way I used to sneak past is unplug the PVC so it sucks more air, BUt that was in Vegas where they dont do a full visual inspection and have no idea of how much the smog laws have changed now.

Did you change your plugs...wires and even the coil...

Turn in your low idol screws so its leaner and bring the idol to just under the limits of the inspection rules, Some will let pass with a 1500RPM idol speed...So glad I dont have to do that crap anymore.

Then readjust back to your settings later...

 

A couple of things that you might want to check on your carb would be the jet size My carb has #57 jets in it. That is what my original carb also had. Maybe someone put much larger jets in at some time in the past.Also look at the idle passages where the mixture screws are, if someone tightened them down too hard it could have damaged the passages allowing too much fuel to flow at idle. Other than a blown power valve I don't know what else could cause such a rich idle mixture.

 

Jet sized based on altitude. A truck that was sold new in CO will have different jets (5,000-10,000' or 10,000-15,000') than one sold new in the Central Valley (0-5,000').

Carb ID tag number will determine which jets the carb was equipped with originally.