Originally thew ICM went bad. Now the motor will run but like the timing isnt correct. The O2 sensor voltage bounces from 50-800mv rapidly. When I unplug the knock sensor they are stable. I have replaced everything from the ECM to the spark plugs with no help. While cold it is easier to feather up in RPM but once it reaches operating temp it retards the timing when I hit the accelerator. timing at idle is from 18-21 degrees cold or warm. I have next to no hair left. Can anyone provide any help?

 

more info would be nice. have you had the opti off? what year model is the car? is it throwing any codes?

 

Wow your right. . 1993 Z28 Opti spark has been replaced and it has been off but everything is keyed so I don't think it could be backwards can it? It threw a 41 originally. Opti spark ground out or something.

 

The 02 sensor is performing as it should. It should constantly cycle between what you posted. Sometimes even slightly higher, like 900 mv.

Here's how it works: The ECM/PCM constantly tries to maintain 14.7:1 air fuel ratio in Closed Loop. It can't and wasn't designed to be able to maintain that ratio at a constant 02 voltage reading.

So the 02 to constantly cycles from low voltage to high and each time the voltage crosses .450 the count number changes. As the voltage cycles, the injector pulse width (on time) and sometimes the ignition timing can change in the system's attempt to maintain 14.7:1 A/F ratio. In my experience, the faster it cycles the better.

Many times when the timing retards it's a result of knock being sensed. Check your knock count to see if that's what causing it. Also, in many instances a knock detection can result from FALSE knock with valve train noise being one of the primary causes.

Hope this helps.

Jake

West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine! Graduation Day Parade 20 May 2010!!!

 

There is a major tick on the passenger side of the engine. I believe it is coming from an exhaust manifold leak. I have a small scanner that tells me the "knock retard" and seems to stay on 0 degrees. When I unplugged the knock sensor which is also on the passenger side of the block below the manifold, It read 3 degrees of Retard. So would you reccomend tracking the tick down and fixing it still?

 

In my case, an exhaust leak up-stream of the 02 sensor caused the 02 to send incorrect info to the ECM. I had a very tiny hole in #5 header tube, about 4 inches from the cylinder head exhaust port, which effected my idle.

Finding the leak took a while since it was so small, but once I did and welded it shut, all returned to normal.

Yes, you need to fix that leak. The leak could be effecting your engine like it did mine.

Jake

West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine! Graduation Day Parade 20 May 2010!!!

 

sounds like your rocker arms need to be adjusted on that side , and u could possible just have a malfunctioning knock sensor too. fix the tic first then see how it acts, if u fix the exhaust leak and still have a tic adjust the valves u may have a collapsed lifter

 

How can you tell if a lifter is collapsed. I had the the Valve covers off and didn't see anything out of the ordinary.

 

Its actually very easy to assemble the Opti incorrectly, with the splines in the incorrect register. Many say it can't be done, but I'd bet 10% of the people who install the unvented Opti manage to assemble it incorrectly. But - did it ever run correctly after the Opti was installed? If it ran OK, then only developed a problem when you got DTC 41, its indexed correctly.

When you unplug the knock sensor, the ECM intentionally retards the spark a variable amount, to protect the engine. That's normal.

Any unusual noise, like a "tick" should be tracked down. Its a sign that something is wrong.

Minor clarification - the ECM does not swing the A/F ratio back and forth from rich to lean because is can't maintain a constant voltage. It dithers the A/F ratio because that's what the cat needs to operate - run lean, it stores O2, run rich it uses the O2 to reduce CO and HC's.

 

The spline is keyed one way with a flat spot on the spline. In to the opti and through the timing cover. How could it be off? This would make complete sense if that's the case. I just didn't understand how it could be. I replaced the opti before finding the ICM was bad so no it hasn't run correctly.

 

If you want to argue about it, go right ahead - but I'm telling you that is can be assembled incorrectly, and that we have helped literally dozens of people realize that it was possible, and that they actually did manage to install it incorrectly. A "search" would turn up threads where people SWORE they installed it correctly, only to find out when they rechecked that they got the splines indexed incorrectly. How do they do it - I don't have the slightest idea - maybe they pull it on with the bolts, forcing the splines to mesh incorrectly. By I can assure you.... it happens all the time.

I'm out of this one.

 

One suggestion. Put a cylinder and top dead. Then remove the cap from the distributor and see if the rotor is pointing in the direction where that cylinders contact would be with the cap in place. For example the number 1 cylinder contact is just left of the 6 O'Clock position. #2 is at about the 5 oclock position.

 

I knew it could be indexed wrong so I made SURE I indexed it right......to bad my friend who installed the spline INTO THE OPTI did not know it. He managed to cram the spline in the opti wrong . Needless to say that took me a little bit of time to figure out. It was on a 94 Camaro I rebuilt for a guy. Fired right up when I figured it out. I KNEW I was right on too......so I thought!

 

I didn't mean to seem like I was arguing. Thank you very much for your help. I guess I have checked that before but not very closely. I will look again and try to look into that leaky manifold. I am not looking forward to taking that water pump off again.