Thanks for your input Chris, I appreciate it.

The O2 sensors were new in 2015 and have less than 2000 miles on them, including what I've put on the car. I have no idea what brand they are and if there are good brands and bad brands. I'll do some reading about the O2 sensors and if there are any tests that can be performed to verify they're good.

I was reading about testing the knock sensors and think I'll try that test next. I also got a quick release tool for the fuel lines and I should get a new gas filter soon and I'll change that as soon as I get the car up in the air.

I'll also read about testing the EGR valve as you mentioned. Before I try to take it off for a visual inspection it's worth trying any possible test while mounted.

 

When I started this thread it was my intention to carry it through to some conclusion so folks who might have a similar problem in the future could see what I did in its entirety, I'm not there yet.

I may have mentioned that my neighbor was a GM dealership mechanic during the 90s and is now a mobile mechanic for the state of NJ. He has helped me at various points this summer with the vette when I needed a second hand, or information, he also read the ECM with his Snap-On reader and charged my A/C when I discovered it was low.

I've been looking for an opportunity to get him to take it out for a test drive to provide his professional opinion about the symptoms I've been noting since I got the car. I've been assuming it's an EFI problem, at least partly, based on the fact that the PO replaced almost all the components in the ignition system in 2015, about 1000 miles before I bought the car. I listed those components in the first post of this thread. I finally caught him at the right time last Sunday and we went out with him driving. It didn't take him long to opine that it's an ignition problem, not an EFI problem. Given that, and the things I've done to trouble shoot the EFI, I'm going to focus on the ignition for a while. The problem is pretty minor, it only misses (assuming my neighbor is correct about it being a miss) at light throttle settings. He suggests looking for a wire that might be grounding enough to affect the engine at light throttle.

I just got one of those cheap Ebay endoscopes. I'll try using that to do a visual inspection of the plug and coil wires and see if I can visualize the optispark. I have no idea if I'll be able to see anything but if I do I'll try to take pictures to post.

Onward and sideways.

 

Not sure anyone is checking out this thread anymore but I want to keep posting to it till I get to a resolution to my drivability issue.

Last week I spent some time working on the Vette. I wanted to have a look at the ignition components as best as I could. I used the endoscope I bought off Ebay. I particularly wanted to get a look at the optispark to see its external condition. The PO said he installed it new in 2015 so with less than 2000 miles since then it shouldn't be covered in schmutz and if it is that might indicate a problem. I also had a look at the plug wires coming out of the optispark. Everything looked good though I can see that I need to pull the intake and reseal that. The images below were captured when I was looking around.

Being a dedicated masochist I decided to pull and check all the plugs. I wanted to be sure they were in good condition and the insulators were not cracked. It was a PITA but, surprisingly, the passenger side, which I thought would be easier, was more difficult. On the driver's side I pulled the ASR off it's mount and removed the AIR hoses to make it easier to access the plugs. In terms of my personal measure of difficulty CPM (curses per minute) it wasn't as bad as some of the jobs I've done on my old shovels. I found the PO had installed AC Delco plugs, 14 (on the insulator) 208 4m (on the hex flats), I found them all gapped to about 65 thousandths, the owner's manual specifies 50 thousandths. I'm guessing whoever installed them didn't bother to check the gaps. They looked new no problems with any of them. I re-gapped them and put them back in.

Here are some pics from the endoscope.


Thought I'd found a wear though spot on the coil wire. Turns out it was just a dirt spot.


Coil wire plug at optispark.


You can see the oil running down the front of the block but none on the optispark. In every view I got of the optispark it was this clean.

 

There is. I appreciate the posts.

 

Yesterday I decided to do a parasitic drain test on my car. Twice in the last week, while I've been working on the car, I've discovered the battery voltage reading in the single digits. I always leave the car with the hood down and the doors closed so I didn't think the drain was due to me leaving something open.

I followed the procedure found all over the internet for performing the test. When I made the final connection of the meter with the negative terminal the left headlight door motor cycled for about 4 of 5 seconds and during that time the meter read, if I remember correctly, between 3 and 4 amps. Once that finished I closed the hood and the reading dropped to 30 mA and stayed there for as long as I left the meter connected.

I wanted to check the grounds under the battery box so I pulled the battery and box and disconnected them all, cleaned up the mating surfaces and put it all back together. Today I'll put the battery back in, once I see if it's held its charge without being connected, and see if it made a difference.

There is one mystery. Below is an image of Figure 39 from Book 2 of the FSM. It shows G106 as being on the left rear of the engine but I'm not finding it there. I'm going to have another look today using the endoscope but I'm wondering if my manual is wrong for my car. My FSM is a CD copy of the 1992 manual. I ordered the manual for 1993 and this is what they sent. Did the location of G106 change between 1992 and 1993?


In this image G106 looks to be on the exhaust manifold, I'm not seeing it there. Where is it? Or is it behind the manifold?

 

In my post above I forgot to mention that I had the battery load tested at Autozone before I did the parasitic drain testing and it tested good and I fully charged it before performing the tests.

When I turn the key on, before starting the engine I've been checking the voltage reading on the dash gauge. I've tested the battery with my digital VM and gotten 12,8 or higher but the dash voltage reading shows 12.5 or even 12.2 so I'm going to have to assume the built in voltage reading isn't accurate. Having said that, and even though I've done multiple parasitic drain tests and always see 30 mA or less, I'm going to install a battery cut off switch just to be safe.

 

my copy of the service manual also shows that. But if i remember right mine is bolted to the back of the block. mine is so far from stock it would be hard to compare though

 

I finally printed out that page to try to get a better look at it. Once on paper it appears that the ground, as you say, on the block. Thanks for your input.

 

Hello again rusty76,

It is not uncommon for the oil pressure switches to leak oil. When you are driving the hot oil can flow pretty much anywhere it wants. If not the oil pressure sender then it might be the rear china wall gasket starting to leak. I had a buddy with a small block Corvette with silicone on the rear China wall and when he picked at it, the seal virtually fell out because it had not adhered to the surface of the aluminum. Less than perfect cleanliness can make real trouble with gaskets adhering properly, on my buddies Corvette we literally pulled the whole rear china wall gasket out while standing on the side of the car. Not good.

When I looked at the first set of pictures I thought you had a standard valve cover drip we see often on older cars. Since you are not using the factory valve covers a lot of us here in the CF would check that very closely. Replacement valve covers are always suspect when you have a oil leak.

G106 is a Ground location on the engine block, it notes where the ground cables are attached to the block.

Take a small mirror and see if you can identify the leak from around the OIL PRESSURE SENSOR as that is the most popular place for leaks.

Testing a knock sensor is fairly easy on the L98. On your LT1 it might be different. The L98 knock sensor test is simple. With the Engine idling take a metal object and rap it against the block (To make a Knock noise) and the idle should drop for a second or two. A Bad knock sensor can make your car run poorly but few check them out as per the manual. My C4 was not performing well and when I did the rap on the block nothing happened, I had a bad knock sensor. A new sensor and the car ran MUCH better and would chirp the tires again.

We are still here waiting to see what happens with your Corvette!

Best regards,
Chris

 

Well Chris, you told me something I didn't know, my valve covers are NOT stock. I just picked up a set of Felpro rubber gaskets yesterday. I can see evidence that both covers are leaking down the side of the block. I also see that the intake manifold is leaking at both front and back. I can also see, from underneath, that something at the front of the engine is leaking a lot, maybe the pan, I couldn't get to the front pan bolts when I was under there. Those issues I'll tackle after I put the car away for the year. The pan gaskets I'll try to do in the next couple weeks, I'll see how bad it is getting them off.

I've used my endoscope to look at the area of the block where I THINK G106 should be. I see some kind of sensor, maybe the low oil level sensor but I'm not sure. I'm hoping when I jack the car up I'll be able to see/access it from below. I tried getting my mirror down there without success. If I take the AIR lines off I'll have better access. When I had those lines (rubber) off to do the plugs I lubed the ends so it's easier to get them off and on now.

Thanks for your comments Chris. As I've said before I intend to keep updating this thread until I can post that I found the problem and this is what it was. There are too many threads in which a problem is laid out but we never get to see the resolution. At this point I just hope I live that long.

 

I'm still seeing an issue with the battery being drained. Today I installed a negative terminal disconnect and then hooked up my digital VM to detect parasitic drain. As the 2 or 3 times before, it reads 0.03 with the digital voltmeter on the 10 Amp scale. Can someone please confirm, am I reading that correctly as 30 milliamps?

I didn't put the battery on the charger. I just read it a few minutes ago and it was 12.56. Just after I installed the disconnect it was reading 12.52. I'll read it again in the morning and see where it is. I mentioned before that I had the battery load tested at Autozone and it read good. Not sure what's going on.

I've also noticed that everytime I connect the battery, the left headlight motor cycles for several seconds during which I'll see between 3 and 5 amps being drawn then it settles down. Sometimes it takes longer than other times before it gets down to 0.03 but it always ends up there.

 

Between 25 and 30 mA is normal for parasitic loss of the electronics staying awake. The cycling of the headlight motor is concerning as I have never seen or heard of a Corvette doing that.

There are devices mounted on the front of the engine that can cause leaks. When you have the Opti ignition then you might have problems with leaks on the front of the engine as they find their way to the OPTI unit. I am sorry I can't help you regarding the Opti as I know very little about them. After reading and hearing about them I am not a "fan"of the Opti ignition system

I hope I did not offend you regarding your valve covers! Whenever the valve covers are replaced the seal is never as good as the factory original. You have to really clean those surfaces well before applying the gasket. I use alcohol prep pads and wipe everything down before applying new gaskets.

The picture showing the G 106 location showed 4 wires secured at this point. Follow the ground cables from the battery. The hole will have a bolt in it securing the ground wires. It appears to be a bit higher and to the rear of the oil filter location. I can take a look at my 1988 out back if needed.

After charging a battery you will see the voltage drop slowly back to the normal open circuit voltage. I would not worry about the .02 volt difference. It should hold between 12.4 and 12.6 if it is brand new. De-Stratifying a battery is a very important thing to do to get the maximum life out of the battery.

IF your valve covers are leaking the oil gets down on the metal which is hot and it flows from there. If you are stopping a lot or parking nose down the oil will get all over the front of the engine. You might not have an oil leak up front, it is likely from the valve covers even on the front of the engine. Just be really careful cleaning the engine. You do not want to hurt the Opti in any way. I am at a loss on how to clean the front of an engine with Opti installed. It is possible to have a oil sending unit leak oil at the very back of the engine but that frequently ends up on the catalytic and burning off instead of the front of the engine. Everything points to the valve covers as the primary source of the oil leaks. When you have the valve covers off take them and check them for flatness so that they seal better. Frequently aftermarket covers don't have as good a sealing surface as the factory valve covers do. They are more prone to warping and leaking than the factory valve covers. If your are not perfectly flat replace them to save any more problems.

We are still here trying to help you resolve the issue that you are dealing with and will be till we are done!

Best regards,
Chris

 

Thanks for your input Chris. I've been reading about other folks in the C4 tech section that have problems with fuel or spark - not at all surprising given that way the systems were designed back in the C4 days and the age of the cars.

One of the reasons I'm hot to trot on the main ground is because of the amount of oil I have on the sides and bottom of the engine, it's just too obvious a potential cause to ignore.

You did NOT offend me with the remark about the valve covers, quite the opposite, I'm grateful you informed me because I didn't realize they are aftermarket. It's so dumb to put aftermarket parts on a car because of how they look. Now I'll have to start looking around for a stock set, hope they're not ridiculously expensive. I'll also have to make sure I know what they look like.

I guess you noted I performed a visual inspection of the optispark and water pump with an endoscope, they both looked good. There IS oil leaking down the front of the block but it doesn't appear to be ON the optispark, at least not yet.

The first order of business is to stop the valve cover leaks. During the winter the intake manifold is coming off for a look and reseal. I haven't decided when, where or how I'll clean the lower block. I hate the thought of doing it in my driveway and I don't like the idea of having it done unless I can be very sure of the person/shop doing it. The wrong procedure can cause more damage than good. I'll follow your suggestions regarding the covers, assuming I don't just buy new stock ones.

I appreciate you looking in on this thread from time to time. I never know when I'm going to do something on the car. It depends on what I have going for a particular day and how I feel. Being retired I can react to how a feel when determining what I'm going to do. This afternoon I'm going to make a set of ramps out of scrap 2x4s to lift my front end enough to get my floor jack under the car to lift on the front cross member. I REALLY didn't like lifting from the sides, it's precarious to say the least. Getting the front end up is prerequisite to doing the valve pan gaskets (don't like working on my knees) and maybe I can reach that ground from below, we'll see.

 

This afternoon I jacked up the front end to see if I could find the main engine ground. I found it, right above the driver side cat. I could see it really well and I could get a socket on it and I broke it loose . . . but . . . it turns out the grounds are mounted to a bolt with extended threads and a nut so it wasn't the ground nut that broke loose, it was the bolt. There's no way to get a wrench on the bolt head unless I take the cat off. It'll have to wait till winter when I get it up on jack stands. The area where the ground rings are attached are dry but appear to have some rust. I definitely need to clean that up and maybe find a way to relocate it to make it easier to access in the future.

 

So . . . a new development in the ongoing quest to resolve my driveability issue. The other day I had Shifty Red out and decided to turn off the ASR to see if that might impact my issue. I tried it on and off several times for short periods but wasn't sure I could see a difference.

Then I decided, since it was cool outside, to go without the A/C and put the windows down for a while just to see how I liked cruising in the wind. I realized I wasn't feeling the miss. Hmmmmm. I wasn't sure if the wind buffeting might be masking the feel of the miss so I closed the windows and punched up the high flow setting button on the climate control. I recalled that setting provided vent air without running the A/C compressor. I didn't seem to feel the miss.

Today I took it out and tried it again; with A/C, miss; without A/C, no miss. I pulled out the owner's manual to check again to be sure I remembered correctly that that setting didn't engage the A/C compressor, it didn't - but - I noted something I hadn't read before:

"When the air conditioner is on, you may sometimes notice slight changes in your vehicle's engine speed and power. This is normal, because the Automatic Electronic Climate Control system is designed to cycle the compressor on and off to keep the desired cooling and to help your vehicle's fuel economy."

Again, hmmmmmm. Could it be that simple? Every time I turned the Climate Control on I felt the 'miss', every time I turned it off the 'miss' went away. I have a 2003 Chevy Malibu and with the A/C on I don't notice anything that feels even remotely like what I feel when driving with the A/C on in shifty red.

I'm hopeful that this is the issue . . . there is no issue . . . or maybe I'm the issue. Or maybe it is the issue but the fact that I can feel the A/C compressor constantly cycling indicates I have a problem. All I know is for the first time since I got the car I feel hopeful that I might have a clue about what's causing the 'miss'.

As always any comments are welcome, even from those that want to make fun of me for considering a normal function might end up being my 'miss'.

 

From the 1st read of your logs (via graphing in MS Excel) the only thing to comment about is the spark knock retard. When you put the engine under any load you get way too much knock retard.

That has nothing to do with your miss feel and you may have just figured that out is seems. The AC switching on and off is probably all that is. Good find.




But address the knock sensors or the actual knock. That can be caused from carboned up and gunked up piston tops. Real knock is not good and your engine computer PCM is saving the motor by taking out 8 deg spark advance.

Right now I don't see your motor making full factory power at wide open throttle. It will never pull hard until that knock is addressed.




The LT1 is very prone to spark miss for numerous reasons but you don't have that going on. The logs looked great actually (in all areas), EXCEPT the knock retard. That is your one problem that needs to be looked at.




Hope this helps. Good thread. It took so much restraint on my part to not post reply right after your 1st post....but needed to wait to see if you found the fix.




Karl Ellwein

www.ellweinEngines.com

 

Thank you Karl for your response. I think someone else also mentioned the knock sensor data in my logs. I've been thinking about that in terms of what I should do about it. I was reading a thread here that suggested the knock sensors rarely go bad, what is your take on that?

Come winter, assuming I have the 'give a dam' during those short, cold days, I'm going to get into the top of the engine; resealing the intake, I'll do a compression test before I tear into it and a leak down if I get a tester. I'll stick my endoscope down the plug holes and see what the tops of the pistons look like. Worst case, I'd pull the heads but I hope it doesn't come to that. When I did a smoke test a month or 2 ago the only place I noted smoke escaping was around the throttle shaft and there was very little there. Not sure how concerned I should be about that.

 

I agree that the knock sensors rarely go bad. Always believe knock until it can be proven that it is false knock. With a stock tune I don't believe that it would be "false" knock. Real knock.
The slight leak at the throttle shaft is worth fixing but not a high priority.

Investigate that knock under higher load. I don't have any suggestions other than cleaning out the piston combustion chambers.

Karl

 

Thanks Karl. My approach in the short time I've owned the car (since May of this year) has been to put miles on it while checking the basics I can check without tearing the engine down. I DO NOT drive it hard, and I won't until I KNOW there are no issues and I don't know that yet. Early on I did hear some detonation if I applied enough throttle in a high enough gear but I avoid audible detonation like the plague.

The PO didn't drive it much (a thousand miles in 4 years) and likely only short local drives. I'm trying to simply drive it. On Thursday I'm heading out across I-80 for a trip across PA (from NJ) for a second thousand mile trip this summer. I'm assuming running tanks of gas through it and doing some steady state driving like interstates is the best thing I can do for the engine. I've not seen any evidence that there is anything major wrong with the engine. When I pulled the plugs (installed new in 2015, 2000 miles or less) they looked good. I've been thinking about putting some kind of fuel system cleaner in it for the trip but I've never really bought into their effectiveness. Given that you're an engine builder what is your opinion of fuel additives?

 

I'm no engine builder (well, a couple backyard engines) but I have seen reports and used a few. Techron (Walmart even carries it) seems to work.
Use it in three consecutive tanks.