Another emissions (smog) question

[Mazatrol]

I've heard that timing being off can cause emissions problems. I've also heard that being too far advanced is usually the problem. The question is....could too far retarded throw things off as far as emissions? I should be at 8* BTDC and am at 4*. Some background....85 S-10 truck. 2.8 V-6. 156K miles. The engine runs great and idles smooth. Clean oil, new oil filter, new air filter, new cat last year, uses no oil between changes. This truck has the veri-jet carb and engine running temp is 195*. Failing bad in HC and CO. Seems to indicate a rich condition? After failing last year I was able to get a low mileage pass. This requires at least $100 in repairs (the new cat) and less that 5K miles use per year. Now...after failing again (HC&CO) I've changed plugs to one range hotter and checked the timing. Any ideas on this timing thing? Is 4* retarded (from specs) enough to cause me these problems? Thanks for any help or comments.

 

[Jimbo]

It would be worse with the timing advanced to spec. What about the O2 sensor? Mom's Dodge has a crude electric jet carb and with a bad sensor it was a "gross polluter". A new O2 sensor and all was well, as long as the timing is retarded also.

 

[Mazatrol]

Thanks Jimbo.....actually, this old truck doesn't have an 02 sensor. Not sure what year they started putting them on these trucks. You've confirmed what I thought I had heard....that too advanced was bad, and retarded was OK. Maybe I should just leave it where it is. Appreciate the reply..

 

[m2200b]

Try recarbco.com for some other diagnotics for your HC and CO high .

 

[zstalker]

what are the exact numbers for the HC and CO%? if the CO is really high, and the HC is somewhat high, that can actually mean it's a lean conditiuon, producing a lean misfire...so don't assume it's running too rich because of the high HC's ~Erik~

 

[vizvo]

Hey zstalker, you have it slightly wrong. High CO is always a rich indicator. CO is even a better rich indicator than HC. This engine is running rich. Lean misfire will have low CO and high O2 and high HC. This vehicle is not a case of lean misfire. Mazatrol, this is most likely a carb problem. However, out of spec retarded timing will increase HC because the mixture doesn't have enough time to fully burn before it is expelled. If this is the case, it will also overheat your catalytic converter, and possibly destroy it. Realistically speaking, it is very possible that you will need a carb rebuild. The Rochester VariJet uses a metering rod to control the enrichment. Under low vacuum conditions (like WOT), the metering rod retracts from the main jet passage and enriches the mixture. Anything that gives you low manifold vacuum will cause a rich condition. Also any damage, decay, or leak in the piston diaphragm which controls the metering rod will cause a rich condition. Also the spring which calibrates the metering rod can go out of spec. And it is always possible that a previous owner could have modified the metering rod spring to make it run richer for more power. Put a vacuum gauge on your manifold and verify that you have normal vacuum, about 18 to 20 inches at idle. Check all your vacuum hoses which connect to the carb. On a 20 year old car, it might be smart to go ahead and replace all the vacuum hoses anyway. Anything which causes abnormal manifold vacuum will affect carb enrichement. Even a leaking brake booster could cause problems. You may want to find a good emissions guy who really knows carbs. It is a dying art. You need someone to put your vehicle on the emissions machine and check your carb. Sometimes speed shops can give you the names of good local carb guys who do rebuilds and troubleshoot.

 

[Mazatrol]

Thanks guys. Very helpful thoughts. After reading the replies here and studying this site http://www.aircare.ca/index.php?repinfo-ere-causes.php it appears that I do indeed have a rich condition, although zstalker makes a good point also. The exact numbers? I'll use the high speed test (25mph) as both high and low tests are about the same percentage off. HC standard is 223...my number is 248. CO standard is 2.79...my number is 3.62 These #s are before the new hotter range plugs. BTW, the old plugs did show some signs of rich mixture, although not what I'd expext from a failing test. I tend to agree that the carb is most likely the problem. I'll probably go for my free (2nd) test and see what happens. If I fail again (likely) then do my reqiured $100 worth of parts (carb) and go for my low mileage waiver again. I just use this thing to run into town for fence posts or whatever. Geesh.....I've got like 900 miles on it this year. I just happen to live in a county connected to Dallas county. Thanks agaion for the help fellas.....I appreciate it.

 

[Gary Allan]

Don't they have an exemption for vehicles under so many miles per year In PA, if you're under 5000 miles ..you don't even pay or get subjected to the test. They hook up the machine (assuming it's OBDI - if not -they don't) just to record it with the DMV and slap on a $5 EXMEPT sticker

 

[Mazatrol]

Gary, here in Texas the only total exemption from smog check is for cars 25 years and older. Anything under 25 yrs. has to be smogged. If the car has less than 5K miles since the last check it can apply for a low mileage waiver....provided at least $100 has been spent (on parts) trying to pass smog. I'm not sure what the law is on cars over the 500 mile limit. There's some literature they hand out dealing with this. The Texdot site probably has it as well. Oh....and the older cars....they have to run on a dyno with a sniffer in the tailpipe. It's 40 bucks whether you pass or not. For an older retired guy like me that just needs a truck for chores it's quite a hassle. To get the waiver I have to make the white knuckled drive into the heart of Dallas (Irving actually). They test it again there and slap a sticker on it.

 

[Quest]

Mazatrol- Just to remind you that "hotter" plugs doesn't necessarily equates to "hotter" running engine/"hotter" burn. The main purpose of a spark plug heat range (and each application requires it's own specific range) is to keep the plugs "hot" enough to be able to maintain it's self-cleaning ability at all operating speeds and loads w/o fouling up, and yet "cold" enough not to cause pre-ignition (or pinging if you want). Unless your combustion chamber has been custom-modified or similar, usually I personally would start from the factory recommended heat range and then go from there (usually +- 1 to 2 max.)

 

[Mazatrol]

Thanks Quest, yes I was aware of the pinging issue with hotter plugs. I was just looking for some "shots in the dark" before I did my free re-test. I just went up one click on heat range, and went ahead and set my timing to specks. ....and, just to update....did my re-test and the numbers hardly changed. This is looking like a carb thing for sure. I guess I'll have to spend the required money on this old truck, and get my low mileage waiver. Once again....I appreciate all the input from you folks.

 

[tom slick]

put 1 gallon of denatured alcohol in the gas and I'll bet you pass.

 

[m2200b]

20 year old hoses on this carb is where I'd start. After about 15 years in hot climate like CA or Texas you always have at least one leak. Once you try and pull the first one or two off you'll see their condition. At least its an S10 - some of the toyotas and mazda last years of carbs are like spagetti. I usually do the fuel lines at the same time because having one of those leak fuel is far more dangerous than just failing smog.

 

[Mazatrol]

I totally agree about the hoses....or anything else rubber. I've replaced maybe half the hoses over the years. I'm currently restoring (my hobby) a car that turned 32 years old in April. It spent about 15 years stored in a barn. I've replaced pretty much every piece of rubber on the whole car. Speaking of the foriegn trucks....I'd like to find a used small Toyota or similar. The problem I'm having is finding a regular cab. What I need is space to haul stuff. Kinda why I was trying to keep the S-10......single cab with an 8 ft. bed.