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Thread: Finding TDC to time for smog.
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dhood
Hauling
Posts: 134
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posted September 25, 2012 09:52 PM |
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Finding TDC to time for smog.
Starting with an aside... Checked past posts and maybe time to revisit this.
Truck has been running just fine but failed smog this year for CO at idle. Funny that the exhaust seems to be running very hot. A couple of years ago had the presilencer replaced with a glass pack they said would work for a rotary. So I'm thinking maybe it wasn't and it has collapsed but the exhaust at tail pipe is very fast flowing, and for some reason the cooling air pipe is just as hot and flowing as the exhaust. ?? This is a red flag, factory manual says to replace the reactor. I took it out but didn't see any cracks or holes. Its really just a big iron oven with a heavy sheet metal jacket around it. The tip of the flow diverter (insert) for the rear rotor looked a little melted some and cracked, but that shouldn't affect smog. It seems that this should help emissions but its not so I'm looking at timing the engine.
My engine is a who knows what, front cover ? and pulley itself has 6 notches on it. When the engine was replaced, the guy *said* he put in a resealed cosmo 13B; it looks like an early 13B. Not sure how to determine which engine I really have.
At the garage, stepwise, mark the pulley when you see an apex seal pass the T and L plug holes in the rear rotor, then the half way mark between them is TDC. This is assuming the two plug holes are symmetrical to the housing. So TDC measures about 5 degrees before the first notch on the pulley.
Next,line up pulley TDC with cover pin and line up the dist notches for TDC and install dist with timing slot halfway. If for some reason the pulley can be installed on the EC 180 off, or dist gear was installed 180 off, then dist could be installed backwards. Would this be noticable as severely retarded timing? And this would also be the problem with the heater buildup in the reactor as unburnt fuel combusts in the exhaust?
So I thought the different engines, and as equipped with different dists or other stuff would required different timing settings. The REPU for 77 is supposed to be 5 ATDC, but it seems to run smoother, as setup this way, retarded around 15 ATDC. I always got better performance in advancing the timing, but can hardly get it to idle at factory spec.
Any enlightenment truly appreciated.
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repumax
Redlining
Posts: 427
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posted September 26, 2012 09:49 AM |
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Remove the flywheel inspection cover by the intake manifold. Rotate the engine until you see the flat cutaway portion of the flywheel. Line the flat side of the flywheel parallel to the engine and that is tdc.
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jm1fd
Revvin Up
Posts: 83
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posted September 27, 2012 05:00 AM |
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Retarding the timing is an emission control strategy that Mazda employed under certain conditions to richen up the mixture and thus increase the temperature of the thermal reactor. The "computer" would use the retard relay to cause leading to fire at the same time as trailing. I'm thinking your timing being retarded is correlated with your hotter exhaust.
Can you bring the timing to where it ought to be (or close) at idle then fiddle with the idle mixture to get CO in line? Seems like the shop manual says to set the idle mixture screw on the carburetor based on CO readings from the tailpipe....
Disclaimer: I hate carburetors and my truck has no emissions equipment on it. I'm just going off what I've read in the manual.
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dhood
Hauling
Posts: 134
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posted September 27, 2012 07:01 PM |
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Thanks for all the suggestions. I thought the problem was timing, It is not idling well and if I get it to idle then the exhaust catches on fire. I thought either bad timing, exhaust backpressure, or carb problem, too rich.
Inspected the flywheel and found the pulley to be in agreement so am confident now the timing is set correctly. It would be nice if the flat edge was flush with the engine plate so an accurate measure could be taken, but happy just to know that the timing is not reversed. I did reverse the timing and it wouldn’t even start.
The ECU does retard the timing on the leading plugs but not sure how it does that. When I installed my only mod, an electronic dizzy, the retard relay was disconnected. The ECU would have to be getting the crankshaft position data from somewhere to do that, but it just looks like it was a simple cut over to the trailing magnetic pickup until water temp is up. Have to study that some more. Even so, the engine formerly ran real smooth right off when stone cold, then would run rougher after warmup. Now the exhaust is literally on fire after warmup, the grimy dirt above the presilencer ignited yesterday and I had to get an extinguisher.
Call me a noobie if you want, really old age I think. After removing the exhaust from stem to stern found that my *new* old muffler has two tailpipes. When did that happen? The cooling pipe now terminates behind the spare tire next to the muffler, hard to see. So backpressure is not the problem. Tested the TR and found it is leaking cooling air into the exhaust side. This is at least one of the problems. Since cooling air is on during idle, HCS don’t even have a chance to combust in the TR. If anyone has a good TR for sale, let me know. Please tape up the exhaust inlets and the cooling outlet holes and blow air (like shop vac exhaust) into the cooling inlet. If air comes out of the exhaust outlet it is bad.
Last could be the carb. One more rebuild and I’m going to submit it to the Guinness Book of Records. If anyone has an unmolested 77 California Carb for sale please PM me. My kingdom for a new one. I would be happy to trade for something else I have. If you list what you need I’ll look for it.
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jm1fd
Revvin Up
Posts: 83
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posted September 28, 2012 07:09 AM |
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quote:
it just looks like it was a simple cut over to the trailing magnetic pickup until water temp is up.
Yup...trailing signal goes to both coils in "retard mode". Although as I recall there are other situations besides cold start that make it toggle over to "retard mode".
All that wiring was in general disarray on my truck from the previous owner, and at some point there was a small fire under the dash in the portion of the harness leading down to the "computer". This past winter I pulled the whole harness and got rid of all the unused emissions bits. I'm glad I don't have to keep emissions stuff working.
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