Spark Plug / Timing ?'s

[gedmeyer]

I was getting a little pinging on my '81, so I decreased the timing advance from the stock 6 degrees to somewhere around 4-5 degrees BTDC. I was curious as to how much advance is ideal for my vehicle. Also, would switching spark plugs enable me to run more advance?

I have limited "feel" when it comes to timing the factors that control what I set my timing at. After I decreased the advance, I felt like the car was a little less "peppy", if that makes any sense (but the pinging went away I believe). Do spark plugs affect timing at all?

Currently, I have a 383, stock heads (CR ~9.5:1), 270H Comp Cam, stock intake, carb, distributor, and ECM. I did richen up the carb at WOT by switching secondary rods/hanger. Hooker sidepipes will be on probably next weekend.

Thanks everyone. Your insight is greatly appreciated.
-gedmeyer

 

[74bigblock]

As I recently learned... you have to experiment with what the best timing for your motor will be. You are correct that if you retard the timing slightly, you will have a little less power. You may want to check the gaps on your spark plugs... if they are off, you might find that it will cause pinging and rough idle. Other than that, you should be all set.

I'm currently running the 454 at 16deg BTDC (stock is 10 Deg BTDC) and she is running great.

 

[wishuwerehere82]

If you're pinging at 6 degrees, you probably got a bad tank of gas. It shouldn't be pinging at that low of an advance. try putting some octane booster in it until you can get a fresh tankfull.

 

[gedmeyer]

This was just after a refill, so a majority of the tank was 92 octane. When I am installing my headers this week, I will pull the spark plugs and take a look at them. Maybe they need a replacement, although 3000 miles shouldn't wear them out.

What other factors could cause pinging? It only occured when I "got on her" and there was some load placed on the engine. Of course, the tank of gas before this was from last summer (with stabilizer in it). How about weak spark? The other thing is that the advance set was just the base timing. I have the '81 ECM actually controlling my timing. I wonder what/if any other factors are screwing around with it. I will have to take a look at that section of the manual tomorrow.

Am I correct in that I would like to use as much advance as I can get away with, without pinging, etc?

-Tim

 

[wishuwerehere82]

I have torn my whole intake apart and replaced all of my sensors because of one tank of bad gas. I didn't need to. All I needed was good gas. But when the SES light comes on and the Vette dies at 55 MPH, you have to assume something is really wrong. Nope! Just bad gas.

 

[gedmeyer]

Well, I kinda lied about my timing before. I just realized that I was reading the marks wrong on the timing tab. Somehow, the timing on the car was ~14degretes BTDC before I adjusted this year (when I was getting pinging). So now knowing what the marks really mean:
At 6BTDC (factory setting), the cars rpms drop down to 500ish and sounds like it is struggling at idle. So I moved it to 8BTDC, and sounded better.

The problem that throws the monkey wrench at all of this is that I am now getting some skipping under load. I'm not sure whether this is a timing issue or plug/wire issue. I will pull the plugs tomorrow to see (it's too damn hot after running it). In anycase, I moved the timing to 10degrees BTDC and the problem seemed slightly better, but still there.

Should I still assume that it is a non-timing related issue? It seems to me that the car should run OK at 8-10BTDC w/out problem (albeit, not at optimum power). When the side pipes come next week, I'm going to reroute my wires and shorten them (see Plug Wire Loom Thread in General Topics), but this is still annoying.

I did pull the #1 spark plug earlier and the tip looked a light brownish color, no build up.

I guess I have more variables in my problem than equations...
-gedmeyer

 

[74bigblock]

gedmeyer...

A couple of things:

If you have vacuum advance, you should check the initial timing with the vac adv hose pulled off the distributor and plug it with a screw or golf tee (I used the end of my air cleaner bolt).

Once you have the vac. adv. plugged set your timing to the recommended degree.

Then plug the adv. line back in and adjust your idle up or down to get it where it needs to be.

This will take you back to the stock setting. If she isn't running well after this... then you can repeat the steps advancing the timing or retarding the timing.... just remember to set the timing with the vac adv off and plugged, then set the idle with the vac adv on.

If you can't track down the miss then... check your plugs and wires. Make sure your plugs are gapped correctly, and your wires touch nothing metal (steering box, frame rail, valve covers).

Let us know if this helps.

Dave

 

[wishuwerehere82]

Gedmeyer,

If the plugs and plug wires are OK, then you better check the cap and rotor for cracks and burn marks. Brand new spark plugs can be bad from the factory, especially if you buy the from discount auto parts stores. Can you do a compression test while you change the spark plugs?
Skipping at load will be either plugs/wires, cap/rotor or Valves/lfters.

 

[gedmeyer]

I have the '81 ECM controlling my spark...so no vacuum advance.

Both the plugs and wires have about 3000 miles on them. The rotor and cap are more like 6000 miles. The engine was rebuilt 3000 miles ago (with valve job). I do not have a pressure gage for the compression test.

I did adjust the valve lash last week, but I had a few days after that when it ran OK. I thought i was pretty thorough on the valve lash adjustment. Tighten the nut until their is resistance against rotation on the pushrods... Then tightened just slightly more than 1/2 turn. Considering the factory manual specs out 1 full turn after zero lash, I highly doubt that I over tightened the nuts, causing valves to stay open.

I will play gumshoe tomorrow. The guy who built my engine is inspecting the car tomorrow, so I'm sure he'll have a suggestion or too.

-gedmeyer

 

[jdp6000]

If you have an ECM the advance is electronic. There should be a wire to the driverside of the distributor that MUST be disconnected before adjusting the timing. This wire is not on the distributor but about a foot away. I believe it is brown and has a connector inline.

Jim

 

[gedmeyer]

If you have an ECM the advance is electronic. There should be a wire to the driverside of the distributor that MUST be disconnected before adjusting the timing. This wire is not on the distributor but about a foot away. I believe it is brown and has a connector inline.

Jim

Yup, I disconnected that so that I could set the base timing.

 

[jdp6000]

Sounds like its something else. Now the fun starts. I'm interested in your situation because mine is similar. I get ping...I call it valve chatter...under load and a miss.

I have not been able to figure it out. I have replaced everything,MAP, TPS, CTS, IAC's,02, distributor cap, coil, rotor, everything in the distributor, EGR, EGR solenoid, ballanced TBI's, plugs, wires, vac hoses, and PCV valve. Nothing has helped.

Next is Fuel injectors and fuel pump.

Jim

 

[gedmeyer]

Well, I just pulled all off my spark plugs. The electrodes were a light chocolate color. The one thing I did notice was that the gaps were on the order of .020 to .035. If i'm not mistaken, they are supposed to be .045", correct? While I have the plugs out, I am going to go ahead and change them. The wires look pretty good. Kinda ticks me off that I have to go through all of this now and then will have to take it all apart again in a week when I put hte side pipes on. Unfortunately, I cannot sacrifice a weeekend of driving to leave it all apart!

-gedmeyer

 

[gedmeyer]

Well, the new spark plugs are in and the car is running fine. I removed all of the plugs/wires and distributor cap, cleaned, and put back together. I'm not sure if the solution was in the new plugs, the new plug gap, or better routing of the wires. In any case, it works.

I also put the timing at 6debrees BTDC. I figure that, since the ECM was built to have the base timing at 6, I might as well put it there. Regardless of what I set the base at, the computer puts the idle at the same amount of advance.

-tim

 

[wishuwerehere82]

Success!

 

[74bigblock]

Sweet! At least you know what to do if she starts acting up again!

Have a good cruising weekend.... take some pix before and after your side pipes!!! You will LOVE them!

 

[gedmeyer]

Sweet! At least you know what to do if she starts acting up again!

Have a good cruising weekend.... take some pix before and after your side pipes!!! You will LOVE them!

Yeah, I will take pictures during the install. Unfortunately, my pipes and inserts are both scheduled to be shipped on Monday, so I may have to wait another week to let the rip. We'll see, considering I should be studying for finals next week, not installing side pipes!

I think I may remove the old pipes, manifolds, starter, clutch shaft, on Sunday to get a head start though (it's supposed to rain early next week).

 

[wishuwerehere82]

Get your finals finished and out of the way first. That way your mind will be clear to start the project and you can go play to your hearts content afterward.
Just my .02.

 

[jdp6000]

Could it be that simple? The plugs and wires are the only thing I didn't do personally. What did you gap the plugs at?

Jim

 

[gedmeyer]

I used AC delco R45TS gapped at .045". Generally when there is a problem on a car, remember KISS. Keep It Simple, Stupid. Randomly replacing parts gets expsive quick and doesn't usually fix the problem. I would definitely check your plugs and make sure your wires are routed good. Sometimes it doesn't take much.