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fixing the LT1 Optispark nightmare
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Tue Aug 17, 2010 1:04 am    Post subject: Reply with quote

well, i finall managed to burn a full tank of fuel. i put a little over 350 miles on it and so far, so good. strangely though, i havent put the EGR valve on it yet and it still hasnt set a code Confused . its OBDII and should have turned on the CEL the second trip. i did notice that its a bit down on power. not much but since its my car, i can feel a difference. im wondering if its the EGR. just thinking out loud but im curious if maybe the PCM isnt giving it full advance because its running into spark knock without the EGR. dunno, it runs really well (hard NOT to run 100 mph down the highway Twisted Evil ) it just doesnt have the bottom end torque that i remember. when i get time ill hook up the scanner and watch the timing to see what its doing. may even need to tweak the distributor a bit. all in all, im very pleased with the results Cool .
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af2 wrote:
It seems we can look at our magical Balls and come up with a fix?

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squeeezer
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1991 Chevrolet Camaro

PostPosted: Tue Aug 17, 2010 9:24 pm    Post subject: Reply with quote

how fast does it fire up???

instantly???

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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Tue Aug 17, 2010 9:53 pm    Post subject: Reply with quote

yes. instantly.
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af2 wrote:
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Thu Aug 19, 2010 1:17 am    Post subject: Reply with quote

ok, thinking about the timing thing on the way home. what do you guys think the chances are that the Opti has a built in advance for base timing ? in all honesty, i dont know exactly how accurate the rotor is phased with the distributor because i dont have a timing mark. i just watched the top of the piston with a camera and got as close to TDC as possible. im thinking i need to get a degree wheel on there and make a timing pointer. of course, this may all be pointless because i dont really know if the computer will take over and make mechanical timing adjustments irrelevant or not. it DOES see the cam and crank sensors so i may not be able to affect the timing without getting it WAY out. Confused ....... looks like i have some testing to do.
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Big Dave
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PostPosted: Thu Aug 19, 2010 12:38 pm    Post subject: Reply with quote

I would think that there must be an initial timing set up by where the distributor plugs in. After that the computer retards what ever the springs and weights are adding if it runs into detonation. I do not think it advances the timing out side of a fixed map like that found in your fuel air map. I figure about 12 degrees initial and play with the timing map with a computer and software if you have an adjustable ECU.

I feel the ECU is bound by those two parameters( the spark map and the knock sensor). But you could play with springs and weights just like a regular old distributor if you do not have an adjustable ECU.

Big Dave
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Wed Sep 22, 2010 1:49 am    Post subject: Reply with quote

time for an update. i have put about 2500 miles on it and its still running great. i still havent put the EGR valve on it , it hasnt set any codes, and it actually passed an OBDII emissions test saturday Shocked . im thinking it has to be retarded timing. it feels like the timing is slow and makes sense why it would still pass emissions. dropping the timing is how (when i did emission repairs) i would get some vehicles to pass that were just a bit over on NOX. all the electrical part of the EGR system is hooked up, it just doesnt have the valve. best i can tell is that the PCM only opens the EGR when its needed. with slow timing i guess it doesnt need it . i know the PCM is monitoring because about two weeks before the ignition crapped out i accidentally knocked off the vacuum hose to the EGR valve and it only took two "trips" to set a P0401 EGR flow insufficient. i was going to try to turn the distributor but its already as far as it will go to advance it. hopefully ill get time this weekend to play with it.
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Knarley Darley
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PostPosted: Wed Sep 22, 2010 2:09 am    Post subject: Reply with quote

Can you advance the plug wires one hole in the cap which would be 42 degrees, and then have enough room to retard back to close to where you were with a net gain in timing advance?
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Wed Sep 22, 2010 2:29 am    Post subject: Reply with quote

no because the cap is made where 1,3,5,7 are on the left side and 2,4,6,8 are on the right. however, i do think i have room if i move the distributor one tooth and crank it the other way. i wont really know until i try. problem is, theres no real way to verify timing. i dont know if it would work the same by making a timing pointer for zero. theres no way to take control away from the computer to set base timing. i think the main problem is that the PCM still sees the sensors in the opti and on the crank as they are factory. without some sort of base timing in the dist housing its not advancing timing to where it thinks it is. i wonder if it were over advanced if the PCM would have better luck controlling the timing. at least that way it would have max advance. think it could retard it enough without setting codes ?
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af2
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1933 Willys Coupe

PostPosted: Wed Sep 22, 2010 2:16 pm    Post subject: Reply with quote

If you move the distributor you will loose rotor phasing. The system is like a crank trigger from my limited understanding.
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SMOKEmUP
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1979 Chevrolet Camaro

PostPosted: Wed Sep 22, 2010 3:04 pm    Post subject: Reply with quote

What about putting a scanner on it to see what the timing the PCM thinks it is and matching it to a timing light (after you put a TDC mark on the balancer).
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10sec.et
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Joined: 29 Mar 2006
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1969 Oldsmobile Cutlass

PostPosted: Wed Sep 22, 2010 4:53 pm    Post subject: Reply with quote

af2 wrote:
If you move the distributor you will loose rotor phasing. The system is like a crank trigger from my limited understanding.


thats how i figured it would work originally but after driving it and no EGR issues im thinking it has to be timing. it feels slow on timing, the only thing changed was the distributor and now the PCM is perfectly happy without the EGR. only other things i can think of to lower cylinder temps without EGR is extra fuel (mileage is as good if not better) or coolant temp (coolant is exact same as it always has been). by process of elimination i keep coming back to slow timing.


SMOKEmUP wrote:
What about putting a scanner on it to see what the timing the PCM thinks it is and matching it to a timing light (after you put a TDC mark on the balancer).


i tried reading the timing with a scanner yesterday but its not in the data pids. i dont have a Tech 2 so i dont know if that will show timing or not. even then it would just show what the PCM is adjusting based on the CMP and CKP sensors. i think that is part of the problem. the actual rotor phasing is now independent of the CMP sensor where, inside the opti, they were phased together.

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