L-88 and emissions test

**Ol' Geezer** · September 17, 2000, 05:04 PM

Re: L-88 and emissions test

Geezer here. I had the devil's own time passing the Illinois EPA test with my '70 350/370. Ended up retarding the spark, disconnecting the vacuum advance, and loading the fuel tank with alcohol to provide oxygenates that burn out cleaner. Worked for me -- don't know about any other route.

**Chuck G.** · September 17, 2000, 05:04 PM

Re: L-88 and emissions test

I'm amazed and somewhat shocked to hear that in Arizona, you have to pass an emissions test with a 31 year old antique car, L-88 or not. I thought we had it bad here in Maryland. With historic/vintage/antique tags, we're exempt from emissions tests. Chuck

**Jon S.** · September 17, 2000, 05:04 PM

Re: L-88 and emissions test

Yep. The cutoff here is 1966, so I missed it by a couple of years. Judging by that yucky brown cloud that hangs over the valley this time of year, I can't say I blame them.

**Jack H.** · September 17, 2000, 05:04 PM

Re: L-88 and emissions test

Question: with a factory concours L88 in the middle of desert Arizona, why do you want the car to pass emissions? Unless you're going to drive non-stop on public highway, odds are REAL good this sucka is going to overheat on you as Zora intended (off road application target, with no radiator shroud, Etc.). Does Arizona require emissions test for vehicles without street license that act in show only capacity?

**Bill Clupper** · September 17, 2000, 05:04 PM

Re: L-88 and emissions test

Jon, I think your real problem is that the L-88 didn't pass emissions in '67. It was sold for "off road use only" to bypass the manditory testing. That's why manditory radio/heater delete, to maintain the off-road status. You may have to do some serious work, like opening up the valve lash to shorten the effective cam duration, or trying the "hole in the butterfly" approach to get the carb to pass more air with less fuel signal at idle. You need to consult a serious carburetor specialist, or try to see if the state has a special exemption for "off road" cars.

**George Daina** · September 17, 2000, 05:04 PM

Some tricks in passing emmissions....

New oil, air & oil filter, new plugs, cap, rotor, plug wires. Before entering the testing area, drive the car about 30-40 miles to get at a solid operating temp. Disconnect the PVC valves from the valve covers. My 188K Blazer flunked our test miserably, even with all new parts described above. I disconnected the hoses from the valve covers....Bingo....buried the test, trouble is it created a vacuum leak, but who cares, for 15 minutes it didn't matter, it passed.

**Joe L.** · September 17, 2000, 05:04 PM

Re: L-88 and emissions test

John-----

My frame of reference with respect to emissions testing is, of course, California. So, I don't know if everything that I mention will be applicable in Arizona. I suspect that it will, though, since I also expect that Arizona modeled its system, at least in part, on the California system.

In California, the emissions standards are set according to model year range of the vehicle, NOT the specific vehicle model and drivetrain combination. These standards are NOT designed to be reflective of the emission standards to which the vehicle was originally certified, but a range which, considering wear and tear and vehicle age, a "well maintained" vehicle should be able to pass. As a matter of fact, at least until 1973, vehicles were not certified to ANY standard with respect to tail pipe emissions. In any event, and providing that the Arizona standards are set in the same manner, you should be able to pass the test. In California, the standards for older vehicles were so lenient that almost any reasonably maintained and tuned car could pass. I say "were" since pre-74 cars now enjoy an exemption from the biennial emissions check requirement. It is STILL illegal to modify or tamper with emissions controls, but no inspections are required.

In your particular case, and considering the manner in which your car fails the test(HC at idle), I strongly suspect that your problem is idle mixture adjustment. A VERY SMALL CHANGE in idle mixture setting can have a DRAMATIC effect on idle HC. But, you have to do it very carefully since if you lean it out too much, your CO will increase and be over-limit.

Your car should have an emissions label mounted near the master cylinder. For your particular car, that label should be GM #3959136 and coded "CN". This label has emissions-oriented idle mixture adjustment instructions for both the L-71 (435 hp) and the L-88 (430 hp). If you adjust the mixture by VERY CAREFULLY following these instructions which describe the "lean roll" idle adjustment procedure, you may be able to solve your problem. Also, note the asterisk(*) which applies to AUTOMATIC TRANS equipped L-88s and make sure that you follow that instruction, too.

If this fails, I'd take the car to a shop with an emissions analyzer that can monitor the HC and CO emissions WHILE the carb idle adjustment is being performed. Then, they should be able to get it right.

**Duke W.** · September 17, 2000, 05:05 PM

Re: L-88 and emissions test

Uh.. correct me if I'm wrong, but an L-88 with an automatic(?). Was this an available configuration. Beyond this, if CO was in spec then the idle mixture is probably okay. High HC with low CO at idle is usually an indication of misfire. If it is an L-88 then the exhaust gas dilution from all the overlap results in a mixture with poor ignitability, and an occasional misfire would not be felt but show up as a high HC reading. I'd leave the carb alone, but thoroughly check the high voltage ignition circuit. Put in new plugs, maybe one heat range hotter than production, check the high voltage wires for proper resistance, and the cap and rotor for cleanliness. Doesn't AZ have some sort of exemption for historic cars with the historic plates? Even here in CA everything prior to '73 is exempt and '74 and up will be exempt on their thirtieth birthday. If AZ expects you to get your car tested I'd be talking to my state assembly rep and read him the riot act.

Duke

**Duke W.** · September 17, 2000, 05:05 PM

Oops, forgot...

... to mention one other scenario. Since your CO was low relative to the standard, you may actually have a case of lean misfire, in which case richening the mixture would probably be the cure. Once you are sure your ignition is in proper order, it might be best to find a decent shop with an exhaust gas analyser, and have them set up the proper mixture to get both the CO and HC in spec. Also, you should set the idle as high as allowable. This may be based on the manufacturer's recommended speed, or it may be an absolute number programmed into the emission test computer. A decent emissions tech, preferably one who used to do tests, at a commercial shop should be able to set your car up.

Duke

**Joe L.** · September 17, 2000, 05:05 PM

Re: L-88 and emissions test

Duke----

In 1969 L-88s WERE available with the Turbo Hydramatic automatic transmission. I don't know how many were actually produced, but I have seen at least a couple of documented cars. As a matter of fact, I understand that one of the two ZL-1s produced is equipped with the THM. This the rather "reclusive" of the two extant, supposedly original ZL-1s and is owned by LA Times publisher Otis Chandler and resides at the Vintage Museum of Transportation and Wildlife in Oxnard, CA.

The fact that emissions adjustment instructions for BOTH manual and auto 430 hp engines was shown on the "CN" emissions label indicates that GM, at least, intended to produce them.

**Jon S.** · September 17, 2000, 05:05 PM

Re: L-88 and emissions test

Well, you bring up a good point. Unfortunately I've never been much of a trailer guy, so I need to DRIVE the car to shows/events/whatever (or change my ways). I'm not really looking to use it to go the grocery store daily (unless I need something really quickly), but I'm also not counting on the good graces of the Az. State Patrol as I tool down the road to the car show.

The environment aspect is something that I've had to get used to down here. I moved here from Chicago, and the car season there pretty much ended from October to April. Down here it ends (or at least slows) from June through September, so the winter weather is perfect for driving those overheating, overpowered, non-air conditioned cars!

**Jon S.** · September 17, 2000, 05:05 PM

Re: L-88 and emissions test

That's what I was afraid of, and I didn't really think of it from the 'off road use only' perspective. Thanks for the suggestions, however. I'm going to collect all of these, see how much I can do practically, and give it another go. If I can't pass, I guess I'll just have to pick up a trailer for a couple of years - until the window passes. I'm also going to check with the state to see if there are exemptions.

**Rob Brainard** · September 17, 2000, 05:05 PM

Emissions...

High HC at idle can be caused by the following: 1. Lean mixture [idle mixture adjusting screws too lean, vaccuum leak, bad valve guide] which can cause a misfire resulting in high HC readings [unburned fuel] 2. Ignition timing too far advanced again causing a misfire. If the car runs OK and you have no diveability problems, then start checking the setup of the engine. Dwell, ignition timing, operation of the vaccuum advance. Before making any carb adjustments, check for vaccuum leaks everywhere -- anything that has a vaccuum hose should be suspect. If no leaks are found, then adjust the carb. I think you will find too much timing at idle or a vaccuum leak, which effectively goes away above idle.

**Duke W.** · September 17, 2000, 05:05 PM

Re: L-88 automatic

Yeah...I looked in the Corvette Black Book, and it lists an engine suffix LV for the HD 427 automatic. Surprise! Surprise!

Duke

L-88 and emissions test

L-88 and emissions test

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Debug Information