Vette started running rough.
I took opti out, cleaned it up, resealed it and reinstalled it.
The engine started, idled rough at 600 rpm. It would not rev above idle.
I checked ignition timing. It was 10 degrees AFTER top center.

I got a new Cardone opti. I installed it.
Engine fires right up. Idles at 1800 rpm. Runs good though.
Timing is 38 degrees BTC at 1800rpm. Won't come below 1800.

I don't touch anything. I put old opti back in. Idles at 600rpm. Timing is 10 Degrees AFTER top center.
I have tried to install it wrong, but I can't. Only goes in one way.
Anyone have any thoughts on why 2 different opti's do this?

I have spent hours checking fuel related things.

 

Perhaps you have an underlying vacuum leak causing the new Cardone unit to appear to be the culprit?

That's all I can muster ATM.

 

Any idea where?
What should it be? Where is proper place to check vacuum?
Any intake side port?
At 1800? at 600?
I have gone over hoses... replaced a few.
I pulled and plugged some of them.

 

Well, common ones on the LT1 engine are the PCV valve, which goes in the drivers side of the intake manifold. Sometimes I see people put a PCV valve in the passengers side cover, which you should NOT do. If your PCV valve is missing or the hose leaking that would cause a real high idle.

Another one is the brake booster vacuum. I'd check that.

Depending if you had or have a vented distributor will dictate if you have vacuum lines for the distributor, I'd check them.

I only figure a vacuum leak because you said the old distributor would never rev past 600 and the new one worked good but the idle was just too high.

@ 1800 RPM's I'd imagine you could hear it hissing. A $5 stethoscope modified with a rubber hose rather than the rod works great for a pin point. Also, carb cleaner works but is risky for people not familiar with areas not to spray, but at that high of an idle you might not even notice a change with carb cleaner. Best to listen for the tell tale hiss of a vacuum leak.

 

I took apart new Cardone opti and compared the two.
They sit different on cam.
The flat on the shaft spline is in a different spot. I have the booster vac line plugged.

 

Interesting... Can we get a look at the backsides?

 

Just curious...

This is a photo of an engine I built and I took a photo of it while it was @ TDC and #1.



Hope it helps.

 

Your pic is exactly like the new cardone opti I have.
If I touch the throttle the timing goes to 45 BTC. (that would be 22degrees of rotor)
Heck at that angle the opti would be firing the #2 cylinder??
The pin in the cap for #1 is left of center.
I will put up pics of the difference of the spline cutout difference.
Thanks for pic. Makes me know I am not totally out to lunch on my thinking here.

 

 

The Chinese messed up rot row.

Sound like the original problem was fuel what did you check in those hours? Are your injector fuses good? Did it jump timing?
Yes plugged cats could be it.

 

Static pressure is 45
Checked at 5000 rpm-good
Injectors all move fuel pressure from 45 to 35 in about 1 sec.
I am thinking if it jumped chain timing my rotor would not be pointing at #1 pin on cap?
I think the problem was I had catalytic converters plug my mufflers with honeycomb stuff. I spent 2 weeks doing exhaust.

I just took the timing disk out of new opti.
I dremel tooled the alignment slot a little.
I reassembled the opti with the disk turned counterclockwise a little.
I just fired her up.
Idle is down to 900 RPM. I did not assemble pulley yet to get good timing numbers.
I will do this till tunerpro and my timing light are the same.
Tunerpro was saying 26BTC at 1800 rpm when light was saying 40.

Check done: 950RPM 20BTC

 

Keep the old opti.

 

It is rather odd... Did you buy the opti local? Perhaps exchange it out?

Seems like the new one installed in the proper position, and FYI the nub on the hub isn't used as a marking index for #1 on the distributor. That's for the alignment of your hub and balancer.

I'm still thinking if it runs good with the new one, but it just idles high, then maybe there is something else going on in addition to the distributor. Then again the shaft on the back looks a bit longer on the old one, cant tell the condition of the bearing on the old one from a photo. I'd figure out what is causing that idle to spike.

 

They are not balancer and only fit on the hub one way.

 

Do any of you with a known good scanner on an LT1 know what the computer timing says at 1200 rpm?

My tunerpro 4 says 30.
Does this sound right?

 

It really depends on what kind of "load" the MAP sensor is reading. I tried telling some other knuckle-head about this correlation in timing but I think it went over their heads.

Here is a random LT1 Ignition/MAP map;



I still think you issue is vacuum related but more information would help. Information like when you noticed there problem, how long it was going on, and other such details go a long way.

Good luck!

 

I understand the pressure readings of load to throttle to RPM to desired timing. Thanks for the graph.
I guess asking for timing was not the best question.

Few weeks ago... vette starting running bad at idle. It would get a little better as it was driven and warmed up.
I started checking fuel related things first.
I noticed oil leaking down front of engine... so I tore into the front so I could check the opti spark and reseal the front of engine.
I put new w/p seal and opti seal in. I also replaced the ignition coil.
I checked backlash of timing chain. Less then 3 degrees.
The opti didn't look the best. Bearing was rough.
I cleaned it up, resealed it and reinstalled it.
I was after another problem, so I went with same opti for now.
I reinstalled everything on front of engine.
When I fired her up, I had to hold throttle to get her to start.(first time I had to do that)
I did get her to run and idle, but within 3 minutes of idle...the exhaust manifolds turned orange from heat.
She would not come above 650 RPM.
That is when I found the timing was 10 degrees after center. I also found honeycomb material from the cats embedded in my mufflers.
I spent 2 weeks doing exhaust. Broken bolts removed, and honeycomb removed.
I also ordered a Cardone opti.
I got exhaust done. I put in new Bosch O2 sensors.
You have seen the story from that point.
Something happened when I tore the opti apart, replaced coil, and reinstalled everything. I replaced the wiring end on Idle air control as the plastic was broken. But that was after the manifolds turned orange.
I am really lost. I don't see how I could have made an opti sit different on cam??
I can't believe it was like that before?

I got tunerpro4 and my timing light to agree within 1 degree by moving opti wheel.
Engine still idles about 1200rpm according to my inductive tach. 1775rpm according to tunerpro Tunerpro desired idle is 725 at startup.
I have been doing this with short runs(less then 20 seconds) with no water pump on.
Block is full of coolant. Hour wait till next run.
I will put water pump on and fill and purge coolant.
I am now going after a high idle issue as you suggest.

I am still thinking the rotor is aligned wrong.
According to your graph the desired timing is between 6 and 44 BTC.
Halfway between that is 25.
So, If I put #1 cylinder on 25BTC the center of big rotor tab should line up with the pin on the cap?
That will allow the ECU the room to move the 19 degrees each way??
I saw my timing go to 45 with my light.
After looking at the rotor and cap pins... I don't know how it made it.

 

In my experience there is only one reason your manifolds would turn cherry red/orange.
The exhaust valve is open before the air/fuel combustion process has completed. This is allowing combustion gas that is actually on fire to pass into the manifolds. Maybe I'm totally wrong, but that is where I would focus my efforts. Sounds to me like your timing chain has skipped a tooth.

 

The backlash from moving crank to the waterpump drive moving is only 3 degrees. Just like a brand new one.
When I installed the new opti... the manifolds did not get red hot.
I think you are correct about the fuel burning in exhaust.
I am thinking it was the ignition firing 10 degrees after top center.
My rotor alignment with new opti is just like the one SELLC posted.
Perhaps I should drop oil pan and get new chain and gears too.
New oil pump and drive also.

 

10 Degrees ATDC wont cherry red the manifolds, but 3 degrees of slop in the timing chain does not seem like much ...

All I can tell you is that I cant even imagine a set of circumstances where something besides the valves opening at the wrong time would cause the manifolds to turn red. Even if I had an acetylene torch with a rosebud tip in each hand, I couldn't turn the entire manifold red/orange. If you plug the exhaust then I would expect even less heat to be transferred to the manifolds because there will be less combustion in the first place ....

I would hate to steer you in the wrong direction but in my opinion if you figure out why that happened or happens then you will solve your problem. I would forget about all the other symptoms. Let us all know what you find out.