My 79 Bronco failed emissions today. Yeah, emissions. The Nitrogen Oxide level was to high. Theytold me to take some timing out of it. I know it is running rich and I will fix that, but can anyone help me with the timing? How do it do it and how will I know when I've made a difference? Thanks in advance.

 

Oxides of nitrogen are (almost) always a symptom of excessively lean mixture, not too rich. It's possible your ignition timing had a minor affect on NOx emissions, but it's much more likely the cause is your carburetor tuning.

Give the specific results of the test (i.e., measured levels of CO, HC, NOx, CO2, and the pass/fail limits for each one).

What was the test method? Was it a 2-speed idle or dyno treadmill test? If it was a dyno test, was it IM-240 or a different test protocol?

Also give some information about your engine/drivetrain. What engine do you have (351M or 400), and is it totally stock, or modified? If modified, how? Manual or automatic transmission?

Are all of the OEM emissions control systems intact and functioning?

 

I havent got under the hood yet to find out about all the emissions stuff is in tack. Here are my numbers. It is a dyno test with the tailpipe sniffer.

HC -- ppm 139 allowable 281 @25mph
CO -- % 2.25 allowable 2.26 @25mph
rpm -- 1664 allowable 2500
CO+CO2 % 12.3 allowable 6.0 min
all these passed

HC -- ppm 120 allowable 286 @15mph
CO % 1.27 allowable 1.64 @15mph
NO -- ppm 2789 allowable 2125 @15mph failed
rpm -- 1769 allowable 0-2500
CO+CO2 % 0.1 allowable 6.0

It is a 351M with a holley 600 4bbl. It has roller rockers with a roller cam and headers. I do not know if the egr is there. I am at work and left home without a clue as to fix it. The guy at the station said to lean up the carb and to take a little timing out of it. I know the truck runs rich, the previous owner told me, but that was fine, barely, but I have read that if the egr is not installed then you have to lean the carb and adjust timing. Hope this gives you enough info.

 

2Fords, Bubba is the expert here, but here's my 2 cents:
The NO2 is caused by very high combustion temperatures, probably because of a missing or non-functioning EGR valve. As Bubba suggested, it sounds like the mixture's too lean. If your initial timing is high (12-14*), you can indeed drop it down to about 6*. This will cool the combustion temps, and drop the NO.

You can also enrichen the carb mixture a little. Bigger main jets does it in the Motorcrafts; I believe the Holleys have metering rods....???

Another 'trick' is to add several bottles of alcohol to a low fuel tank. Since the alcohol burns cooler than gasoline, it will reduce the NO until the alcohol is gone. (I only mention this for information, I don't necessarily recommend it..... )

 

my question is how did it pass visual inspaction with 4bbl and headers

 

they dont care about that. these are run by used car lots, and independents why have shacks set up in parking lots. as long as the computer tells them its ok, then its fine. A waste of $25 for a 25 year old vehicle. I am in Atlanta, GA they dont do visual inspections

 

Where do you get alcohol? Is it just rubbing alcohol, or a different type?

 

Many (most?) states don't have visual inspections. When I got my '79 the PO had removed the cats years before and it always passed smog. Actually the inspectors never even lifted the hood, I could've had a blown 460 for all they knew. They directed me onto the dyno, handed me the tach to plug into into the cigar lighter, stuffed the probes in the tailpipes and off we went.

 

It's the other way around actually, the mixture is leaned out by the EGR, cuz it's diluted by exhaust gases when EGR opens.

You can plug it back in for the test, then unplug it after passing. As easy as that. It will run RICHER with the EGR disconnected, not leaner- which is probably why you flunked if it is disconnected. One test ride will show that. I've been messing with EGR's for over 20 years now.

Now, another way to pass emissions is, run the gas tank to empty. Put in 1/2 gallon of rubbing alcohol, then put about 2-3 gallons of gas in, that drive it in for the test. Alcohol burns much cleaner, and it should pass. You could also just buy about 3-4 bottles of so called "octane booster", it's mostly alcohol anyway. OR, try a gallon of lacquer thinner, it's toulene content may help you pass emissions.

It will be VERY hard if not impossible to pass emissions with a Holley 4-barrel performance carb, they are just jetted way too rich. The big 3 automakers had to go in injection and computer controls to get new cars to pass emissions, it ain't easy.

wow, emissions suck. But I'd enjoy the challenge of cheating the sniffers ! I strongly advise anyone running EGR's and cat converters to get a textbook or shop manual discussing emission controls. Don't just go to net message boards, cuz by experience reading threads here, very few actually understand what and why emission controls are put on cars.

bottom line, they ain't on there to enhance performance ! Only to meet federal and state emissions laws...they detract from performance !

 

Here's an interesting sidenote- my dad bought a new car in 1981, it was adjusted so lean to meet fed emissions standards, that after a few break in miles it started bucking and having driveablility problems. He had to take it back to the dealer, and have it richened up, it had a primitive computer controlled EGR, carb, cannister purge. (1981 Subaru wagon). The dealer tech told him straight out, the cars ALL have to be richened up to run right, as they are leaned way back to pass emissions, so the feds will allow them to be imported.

So basically, the new car dealers' themselves are circumventing the emissions laws, with down the road "tune ups" on new vehicles, to improve driveability.

 

That may have been true in 1981 but it's not now and it hasn't been for many years. Emissions systems have changed significantly since 1981 and with today's computer controlled OBD systems you simply can't have a dealer "richen it up" to make it run better then lean it out to pass an emissions test.

 

I disagree, the dealers do it all the time, they install new chips and reburn them to new specs. They have the burner to do it, dealer only op, unless you have the laptop setup and adapters to do it. I worked for a Cadillac-Olds dealership, that also sold Toyota-Acura-Honda-Volvo-Mercedes-Hyundai.

What do you think the performance chips for the newer GM Firebirds, Camaros, and Ford Mustangs do ?? They richen the fuel curve and bump the timing up.

You should really research things first before you give a knee-jerk answer. I've been doing this for over 20 years, and have a Degree in Automotive Technology, and had my own garage business for 7 years. I worked in the automotive field directly for over 10 years.

The only thing you have to do to richen up a new car injection, is bump the fuel pressure up on the regulator. Our local garage here can do it no problem. You can also just unplug the fuel pressure regulator valve if so equipped, that is vacuum actuated to bump fuel pressure up at LOW vacuum levels, at WOT. Just unplugging it makes the system think you're always at WOT, and it goes full rich.

Again, I'm talking from experience. 1981 cars had O2 sensors, EGR's, TPS, MAP sensors, cat converters, canister purge. And so do 2004 cars. SO THEY'RE BASICALLY THE SAME, with exception of computer controlled injection rather than carb- and no distributor- instead a coil pack. Hope you don't mind me setting you straight, but you've been misinformed. No hard feelings.

 

Dealers who intentionally flout emissions laws pay huge fines and run the risk of losing their franchise rights. I've been working with dealerships since 1982, including working in a Ford service department for 2 years. Nowadays a dealer who diagnoses a warranty drivability problem has to hook it up to a computer in the shop and run a diagnostic test just to get paid for doing the diagnosis.

In 1981 OBD was just a theory, today it's reality. Today's new vehicles basically have "flight recorders" on board which record virtually every function of the engine/powertrain as you drive down the road. Yes it is possible to enhance the performance of computer controlled vehicles, in fact the very nature of the ECM/PCM makes it easier in some cases to do so. Like you said, all it takes is a new or reprogrammed chip and you've got 25 more HP even if it is mostly at the top end.

I can tell you that in the 2 years (86 & 87) I worked in the Ford dealership we never did a "down the road tune up" on a new vehicle to enhance the drivability and any changes we made which would affect the emissions output were documented and checked to verify that the vehicle would pass the sniffer test before they left the shop. BTW this was also in CA which is notorious for having the strictest emissions laws in the country.

 

I see your angle going from your experience, but the local independents are all re-calibrating new cars based on engine wear, here's why:

One of the major inputs to the engine computer is engine vacuum. As an engine gets older, it has less vacuum. The computer reads this as a demand for more fuel and timing, and will gradually increase the base settings as the engine wears. It eventually leads to driveability problems.

I spent 7 years going to college to study this working on my degree. Other mechanics I know still go a few times a year to update. They often change the prom to one that compensates for a worn engine, once it gets around 60,000 or more on it, for optimal mileage and performance. There's no idle mixture screw or jets to change, or distributor to turn. So how else can they do it ??

My '91 Saturn commuter had a bad computer, the dealership said they would sell me one, and burn the new chip at the dealership. Only the dealer had the ability to burn that new chip, I could buy the computer anywhere. But the new chip also had "updates". The parts manager said he recommends the new chip with a new computer, not your old one, cuz the new programs for fuel/spark management have changed that much. That's basically what it's doing, running your car on a computer program, adjusting spark and fuel at all times based on inputs.

So I know for a fact, the dealers do it also. Your experience is a bit dated, now they also have the ability to reprogram for driveability problems. If they don't, the local garages who are up on it just get the business instead.

It's all in the prom. FWIW, I've been driving a DOHC Pontiac GTP, with V-6, injection, and four cams. I've had the EGR unplugged for the last 10,000 miles, and it runs MUCH better. The car has 110,000 miles on it now, and runs like new. (mostly because I always ran Amsoil synthetic oil in the engine and trans)

Of course, NO DEALER will remove emission controls for a customer for fear of a fine- but they all know it makes the car run better if they disconnect them, and many mechanics tell their customers to disconnect them, on the side...sort of with a hand over their mouth....you know the deal.

I've already had a local large muffler/brake outfit tell me they'd remove the converter from another truck I had, if I just signed a release, that was this year 2003. So it's not as strict as you think it is.

thanks for discussing the matter in a civil manner

 

cantedvalveford, if you are at a dealership that is programming its own pcm,s beyond factory programs, you are not only violating manufacturers rules, but you are in severe violation of fed. EPA laws. manufacturers reprograms have to be certified before release, and performance chip upgrades are certified. any other programming is for offroad use only and your employer, if caught, could get fines enough to close him down....