1991 OCC L03 Engine Pinging

On a funny side note, the 307 in our '90 CC doesn't ping at all and runs great!

If you change your knock sensor, put the hose of a cheap vacuum cleaner with a rag over the end into the radiator filler neck. Keep it running during the change out, you won't lose a drop out of the knock sensor hole.

I yanked the computer, all numbers appear relevant to the car and what it is.
I would like to invent some sort of EGR valve that is capable of calibration. I have had a rough idea for one that would be comprised of countersprings mounted underneath the diaphragm.
If I can't compensate for the mixture or timing since that is out of my hands, I can compensate by allowing the EGR valve to open more.

I replaced the TPS, intake air temp sensor, knock sensor and O2 sensor.  Firework smell is gone but the ping/knocking is still there.  I had my wife put it in gear and hold the brake and sure enough at 1500 RPM it does it even not climbing or under load.  Like I said sounds almost diesel like and I think it is coming from the back of the engine.  I never used to hear it like that before, can't be good.  I haven't driven it much since.  I added a second shudder fix but have only driven it around the block once, so nothing to report on that.  Sometimes it seems like the more new stuff I put on it the rougher it runs.

Still pinging but smells better. I finally was able to jumper the cycle switch and low and behold the old compressor still runs. Just got air though. It also got a little better MPG.

Try unplugging the computer and plugging it back in. I once had a Oxygen sensor code on mine, it went away after I did that. Stands to reason maybe other terminals in the connector could be affected after the passage of time.

I don't have any codes, just knocking especially when shifting and passing through 1200 to 1800 rpms up or down. My wife was convinced I was crazy, but now she even hears it. It shifts fine and has power, just knocks. Will loose bolts on a flex plate or torque converter make knocking noises? Since it is associated with a certain RPM/shift range I'm just curious.

Yes, it can. Cracked flex plates make noise too but generally they are going to be louder than that.

You ever get anywhere with your quest?

It got much quieter with the new EGR solenoid but now I get intermittent EGR codes on the highway. I haven't needed to use it over last week though.

I had another idea, one that I explored briefly, in that I am still using the factory plug heat range. The stochiometric ratio is lower with E10 than with whole gas. The new engine may have slightly higher compression ratio than the previous one. These two variations from stock may result in a leaner condition than what the engine can adjust for. The next step down in the plug heat range may negate some of this as it appears in my case that the combustion temps remain mostly on the higher side.

The tailpipe is full of black soot which would indicate that the car runs rich most of the time, which makes no sense that the ping would be there at all, unless the fuel mixture is being exaggerated at both ends.

Okay, so I reached out to a chip tuner, and this is what he said.

The 9.3(compression ratio) is actually a little too high for the tiny stock cam gm used in those motors and 9.5 is borderline for iron heads and 87 octane regardless of camshaft. Your options are retard that timing and lose power or run higher octane fuel. With a chip(tune) I would just be reducing that timing just the same.

To which I replied:

Although that answers my question, it makes me wonder how others in the forums claim to be able to run 87 in their L03's.

Still the mystery remains as to why it pings with 93 octane. I was hoping it was something to do with the fuel tables being too lean to account for the ethanol.

My 68 chrysler with a 10:1 CR ran fine on 93 but then again it had a 160 degree thermostat vs. The L03's 195.

His reply:

60’s motors ran a lot more cam than smog engines after 1971 which is why compression ratios plummeted. Also if (an) engine is remanufactured they could have machined a little extra off the block and heads any you may be closer to 9.8. Wouldn’t be the first engine that compression ratio was higher than it should be. I always try to run a couple points lower compression to allow for such error.

Not that I am doubting anybody here, or his expertise, but something here just isn't adding up.

I can't say for certain on the Chevies, but I have run a true 9 to 1 on iron heads with small cams in my turbo Chrysler V8 small blocks. I could run 14 psi boost on 91 octane non ethanol fuel in the last one and it ran fine at 4-5psi on 87 octane with ethanol, but I would but a global fudge on the fuel map to allow for the ethanol. The critical thing that is often missing from the picture is that even though the factory heads may have full quench pads and small chambers, they often have fairly large runners and most people aren't careful in getting good quench in them. The difference between .065 and .040 quench height is often worth a whole point of compression in iron heads with full pads, especially if they are set at zero deck. Flat pistons with D shaped pockets and only two valve cuts usually run very well in that kind of setup to keep detonation down.

The other big thing in factory setups from a while ago can be intake manifold design and/or small vacuum leaks that cause lean cylinders. The single plane throttle body manifolds were pretty bad for cylinder balance. We had an 89 S10 blazer with a 4.3 TB and single plane and balance was horrible.

Good cylinder balance for airflow and fuel, plus having really close to the same compression in every cylinder goes a long ways to kill pinging.

On an existing vehicle like in this case it is harder to do much, but if other cars of the same make, model and engine don't all have the issue it is very possible something is not right. Reading the plugs may be a good place to start, but need to do it right away after the pinging issue is seen without driving under other conditions before reading them.

booster wrote:

I can't say for certain on the Chevies,  but I have run a true 9 to 1 on iron heads with small cams in my turbo Chrysler V8 small blocks.  I could run 14 psi boost on 91 octane non ethanol fuel in the last one and it ran fine at 4-5psi on 87 octane with ethanol, but I would but a global fudge on the fuel map to allow for the ethanol.  The critical thing that is often missing from the picture is that even though the factory heads may have full quench pads and small chambers, they often have fairly large runners and most people aren't careful in getting good quench in them.  The difference between .065 and .040 quench height is often worth a whole point of compression in iron heads with full pads, especially if they are set at zero deck.  Flat pistons with D shaped pockets and only two valve cuts usually run very well in that kind of setup to keep detonation down.

The other big thing in factory setups from a while ago can be intake manifold design and/or small vacuum leaks that cause lean cylinders.  The single plane throttle body manifolds were pretty bad for cylinder balance.  We had an 89 S10 blazer with a 4.3 TB and single plane and balance was horrible.

Good cylinder balance for airflow and fuel, plus having really close to the same compression in every cylinder goes a long ways to kill pinging.

On an existing vehicle like in this case it is harder to do much, but if other cars of the same make, model and engine don't all have the issue it is very possible something is not right.  Reading the plugs may be a good place to start, but need to do it right away after the pinging issue is seen without driving under other conditions before reading them.

The LO3 cam is 178/194 @ .050, .350"/.385", 109* lobe separation installed at 112* intake centerline. It has been said that the L03 has the saddest, flattest camshaft in history. Don't know what kind of cam you were running in that LA block but regardless, I don't think my problem is the cam. Might be exacerbated by it but not the root cause.

I don't think the L03 uses a single plane intake, but short of doing a 4/7 swap, I don't think there's a whole lot I can change there either.

I am curious about this spark plug thing. It pings after it warms up, which tells me that its a mixture issue at heart. I've already replaced the spark control module which is in charge of the advance with no change in operation. I would only have to run the car for about 30 mins to read the plugs.

As far as what is left to replace, I am still running the original MAP sensor and fuel injectors. Definitely things that can affect mixture. I should shut up and order the MAP first.

FINALLY

I replaced the Map sensor. The ping went away.
now i can sleep.

Ok so the ping came back. Not as bad, not as often but still very much there. I got some advice from one of the guys that handled TSB's for olds back in the day that the delco 45 were too hot, and one of the fixes was to swap the plugs with delco 43's gapped at .045". Well I just did that, and it pings more. So don't do that, if you were thinking of it.
I love this car, its been on the road so long it defies the laws of physics.
On the upside during this process, I did find that my EGR valve adjustment screw wasn't staked in correctly and I could unscrew it by hand.
The guy also told me there may have been revisions to the PROMs as TSB corrective actions over the years but of course he doesn't have them all memorized.

had a pinging in my 87 Pontiac Safari with a 307 and used a higher octane fuel, premium instead of regular unleaded and it helped a lot with the pinging.

goldwolfnhn wrote:

had a pinging in my 87 Pontiac Safari with a 307 and used a higher octane fuel, premium instead of regular unleaded and it helped a lot with the pinging.

Mine pings on premium.

well one thing you could try as I'm planning on doing it with my Pontiac eventually is a full fuel system cleaning, the type where you have a pressurized canister misting a cleaner in through the air stream combined with a cleaner in the fuel.

as with my Pontiac it started pinging out of the blue after it had sat all winter with regular unleaded in the system, so it could just be some fouling from the ethanol. but also I had the carb rebuilt that spring, and all the fall no problems but then it sat all winter and next spring it started pinging, I switched to premium and the pinging was reduced drastically but still there under heavy loads.

smparr wrote:

On a funny side note, the 307 in our '90 CC doesn't ping at all and runs great!

Good news. As a last effort, I did the final two things within my power. First, I soldered the connection where I had spliced in the oxygen sensor wire, which was previously crimped and heat shrinked. Second, I disconnected the battery so the computer could relearn the new setup. On the drive to work and back, I couldn't get the car to ping, not even once. It ran better than it has in almost 7 years. It even idles better, with such a smoothness it doesn't even feel like it has an engine.
I hope it stays that way for a while. That would be nice.
I'm not sure which corrective action made the difference, but maybe the new plugs are helping. I know I said don't do it, but maybe it may help your situation. Just remember to clear out the computer afterward.