QuestionQUESTION: Greetings: I have restored a 1974( half year model, CA) TR6 and recently moved near Lake Tahoe on the NEV side. It requires a SMOG test to register it. It has failed twice, idle mode. Can I put catalytic converter's in line? If so, what type? Thanks, Lon
ANSWER: Hi Lon,
You can install a CAT in the exhaust however, you should first try to correct what is wrong. What were the test results and what were the limits. (the rejection sheet will quote both)
let me know,
Howard
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QUESTION: Thanks for the response. I had the carbs rebuilt twice, The engine has maybe 2k mile on it since it was rebuilt. The following SMOG test results: HC limit < 700 passed at 290 (2500 rpm) failed at idle (775 RPM) with a reading of 2692 (10 TIMES LIMIT) - CO% limit < 3.50 - failed at 9.24 and 10.27 ( same rpm's as presious) CO2 17.90/17.30, o2% 0.3/2.5 (SAME rpm'S AS PREVIOUS) Thanks again Lon
ANSWER: HC and CO are your main tools to locate a problem.
HC is mainly electrical or mechanical and CO is Carb mixture.
With a very failed HC at idle you need to run some tests on the engine itself. First do a compression test (dry and wet test) 4 or 5 complete revolutions with the throttle wide open and wires off of one side of the coil. Then squirt 4 or 5 squirts of engine oil in each plug hole as you test each again. You should not see more than 10 to 15% higher reading on the "Wet" test.
Compression should be 130PSI or higher. Anything as low as 100 or lower will not fire at idle. If you have a low cylinder check valve clearance for a tight valve. If you find a tight valve adjust them and do the dry compression test again. If it is still low. You will not correct the problem with a CAT you need a valve job. If you had a larger than 15% difference between the wet and dry test you have a ring problem.
The only way CO could have been the cause is if the CO was very low and was causing a lean misfire so you can forget CO and CO 2 until you correct the engine.
An ignition misfire can give you high HC if it were at either all RPMs or just at high RPM. Ignition rarely fails at idle and get ok at higher RPM.
let me know the results of the tests.
Howard
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QUESTION: Greetings again: I did a compression test today - my compression gear - said remove all plugs then test - I would presume you would call this dry? I thought I had some engine oil - but didn't so didn't get the "wet" done
#1 120, #2 118, #3 105, #4 110, #5 118, #6 120. Adding oil to do wet and the +15% predicted gets me to the 130 range, excluding # 3 & 4. The engine is blowing no smoke - so, nor do the plugs show any evidence. I will check #3&4 valve clearances. I presume your recommended 130psi is at the "wet" side?
Thanks Lon
AnswerIf you held the throttle open during the dry tests, the 105 and probably the 110 cylinders are dropping off running at idle. When you get down close to 100PSI a cylinder will not even attempt to fire, thus it still has an intake stroke of raw fuel which is HC and that is thrown out into the exhaust on the exhaust stroke. If you don't find any tight valves on 3 and 4 there is another test that is for sure 100%.
This test needs to be done with compressed air and a fitting that adapts the air hose to a fitting that takes the place of the spark plug. The fitting is not expensive but may need to be purchased from a tool company like Snap-on or one of the other pro tool trucks that visit shops.
You put #3 piston at TDC of the compression stroke and put the car in 4th gear and the hand brake on firm. Then connect the air pressure to the fitting. Open the throttle and listen at the intake of the front carb with the aircleaner off. Even the slightest intake valve leak can be heard. Now go to the tail pipe and listen closely to the tail pipe. Again even the slightest leak can be heard. Do the same test for #4 cylinder and listen in the back carb and tail pipe.
Unrelated, but this test is also a 100% test for a blown head gasket by filling the radiator and applying air pressure and watch for a raise in coolant level. Even a small head gasket leak that don't even cause overheating will show up in this test.
The "wet" compression test is a test for compression rings but not effective for the oil rings.
Let me know what you find.
Howard
