258 Pinging

[donnyeagle]

I have been trying to get rid of some bad pinging in my 258. I has been pingng since I bought it 3 months ago. Here is  what I had done so far.
ECM Test bypass, rebuilt carb, replaced egr valve, replaced cap and rotor with ford truck parts, replaced wires, replaced plugs with 2 step cooler plugs, pulling steady 19 on a vacuum gauge at idle, tightened intake/exhaust manifold bolts, tried many timing settings.
Then I found a post on a jeep sight about attaching the vacuum advance to manifold vacuum not ported (like many seem to  recommend after the ECM Test bypass) and so far this has fixed the pinging and the engine is running much cooler. Wow. Now I am going to try to lean out the carb to get better gas mileage. Getting 15 mpg around town in hilly PA.

I post again with results.

Here's the post
http://www.jeepforum.com/forum/f12/vac-advance-ported-vs-manifold-confusion-1160739/

[Pa sx/4]

Have you ajusted the timing? Have you tried other gas? My wifes car pings on sheetz gas.

[thereverendbill]

my wife's car did the same thing until i ran some lucas fuel injector cleaner through it and had her start putting midgrade gas in it

i agree with Pa sx/4 try another station, check your timing, and maybe try running a few tanks of midgrade 

[donnyeagle]

I am running Exxon 89, I have tried Sunoco and Gulf, I also ran seafoam thru the carb and let it sit overnight, I ran three tanks of Techron. Non of that had any effect. I was amazed that just switching to manifold vacuum would lower the engine operating temp (just like the link above said). When it was hooked up to ported sometimes temp would go up to 225 degrees. Now it never goes above 200. Of course that helps a alot with pinging.

I'll keep you posted. Time will tell. Haven't had it out on a long hot trip yet.

[eaglefreek]

Sounds like your timing is way advanced. Have you checked it with a timing light?

[Draekon]

I have done a lot of reading on the manifold vs ported vacuum debate for distributors, and while it seems like a convincing argument that you should switch to manifold vacuum, our distributors are NOT tuned to be run on manifold vacuum.  The problem is that the vacuum advance will advance the timing by around 24 degrees at full vacuum (idling).  Add this to the base timing, and you are running around 32 degrees at idle, which is way too much.

What true ported vacuum does (not venturi vacuum, but ported) is eliminate vacuum at closed throttle, but once the throttle starts to open up, vacuum shoots up, and started to behave like manifold vacuum.
Here is a diagram from the TSM that shows how manifold, ported, and adjusted vacuum behaves:


If you want to run manifold vacuum on your car, the best way would probably be to switch to an HEI dizzy, limit it to about 10-12 degrees vacuum advance and increase the amount of centrifugal advance to an amount about what we have with our stock dizzies.

[donnyeagle]

It does seem like man vac would add to much advance at idle. So then why is the standard setup on a computer run 258 man vac. Does the computer limit the advance at idle similar to ported vac.

[Draekon]

It does seem like man vac would add to much advance at idle. So then why is the standard setup on a computer run 258 man vac. Does the computer limit the advance at idle similar to ported vac.

I haven't really looked into how the later model eagles deal with the ignition.  The later models might have less initial timing or less vacuum advance built into those distributors.  It could also be that the computer leans out the carb enough at idle that having that much advance would be okay, since it would take longer for the flame front to propogate.

[donnyeagle]

Now that I have made all of these repairs it might be interesting to hook up the computer and see how it runs and check the gas mileage. That stepper motor in the carb sounds like when it was conceived it was a good idea.

[ammachine390]

Now that I have made all of these repairs it might be interesting to hook up the computer and see how it runs and check the gas mileage. That stepper motor in the carb sounds like when it was conceived it was a good idea.

The whole CEC system is all actually a pretty great idea. As far as feedback carb systems go, it was pretty far advanced, being that it also controlled ignition timing as well as fuel mixture, and even had a knock sensor to prevent pinging but allow as much as advance as possible. I don't think GM feedback systems incorporated the timing control, except on 81s. Ford did, but the CEC system was all made by Ford too. The only thing inferior about the CEC system was its lack of computer memory and a check engine light.

[priya]

Now that I have made all of these repairs it might be interesting to hook up the computer and see how it runs and check the gas mileage. That stepper motor in the carb sounds like when it was conceived it was a good idea.

The whole CEC system is all actually a pretty great idea. As far as feedback carb systems go, it was pretty far advanced, being that it also controlled ignition timing as well as fuel mixture, and even had a knock sensor to prevent pinging but allow as much as advance as possible. I don't think GM feedback systems incorporated the timing control, except on 81s. Ford did, but the CEC system was all made by Ford too. The only thing inferior about the CEC system was its lack of computer memory and a check engine light.

One of the Eagle instrument clusters I have has a check engine light.

[ammachine390]

All of the instrument clusters from Eagles, Spirits, Concords, and 78 Gremlins have a check engine light on the dash, but they never actually made them functional (they do not have a bulb) except on 81 Concords, 81 Spirits, and 81 Eagles with California emission controls. Also, you cannon just hook a bulb into the dash, as the computer does not have any pins for a check engine light.

[carnuck]

I killed the ping with NGK BKR6EK plugs (same as modern VWs and Audis use with US gas) Dual ground and cool heat range.

[BenM]

It does seem like man vac would add to much advance at idle. So then why is the standard setup on a computer run 258 man vac. Does the computer limit the advance at idle similar to ported vac.

The computer can retard the timing.

It has an idle setting that it uses several of the vacuum sensors to determine when to use, you can sometimes get it to "cycle" if you unplug the vacuum advance. The computer will retard the timing too much and if it thinks the engine is just about to stall it will quickly cut itself out of the loop, advance the sol-vac, and set the stepper motor to full rich in an attempt to fix the problem. It can get into a cycle of stalling and coming back that will drive you crazy until you notice the vacuum hose is in the wrong place.