My 260 wasn't in as fantastic a shape as I thought!

[King_V]

Ok, so as mentioned in these threads: http://gbodyforum.com/viewtopic.php?f=3&t=46741#.Ukivbj9JHIg and http://gbodyforum.com/viewtopic.php?f=10&t=47725#.UkivQD9JHIg, my car pings despite the 7.5:1 compression that the 260 V8 has. By the way, the diagrams at Autozone that one of those threads links to - well, my car is fig 25 - the more complicated one. Of course.

Previously, it seemed like it got a little less sensitive, and would ping a little less than before. However, in the past few days, it's gotten REALLY touchy - even the lightest throttle may cause some pinging once fully warmed up, and heavier throttle will rattle unsettlingly.

Well, finally got the time to start playing around with it, and discovered a few things:
- Minor oil leak around the valve cover in the #8 cylider area... of COURSE the hardest to reach area...
- Some blow by - if I get the engine at 2000 RPM or so, I can see vapor coming from the crankcase tube (that goes from the driver's valve cover to the air cleaner assembly)
- My timing is only at 18 deg BTDC,
- At idle, vacuum is only around 16 or 17 mm Hg

Found most of this while trying to track down the reason for the pinging. Well, the timing isn't too advanced, as it's actually 2 degrees retarded from spec, and vacuum is being supplied to the EGR valve... though I don't know how MUCH should be supplied at any given time. It obviously varies given the amount of throttle opening, and doesn't get any when the throttle is at idle.

When things finally warmed up, I figured I'd see if the EGR valve was actually working... could've sworn I'd checked that before and it did. Now, however, using a vacuum pump . . . nothing. The EGR valve will not hold any vacuum at all.

Ok, so I guess there's my problem. I suppose it was intact when I was barely using the car, then regular use caused it to finally give up the ghost.

But HOLY CRAP . . really? These things are over $50 new???

 

[DoubleV]

Aftermarket EGR valves are known for their not so great quality. You'd be better off with an old used one from a boneyard, providing of course it's the right one. Another option is you could recurve the distributor, lower the vacuum advance and just get rid of the EGR valve altogether. Personally, I would just get a new/used factory EGR valve.

 

[Fox80]

Aftermarket EGR valves are known for their not so great quality. You'd be better off with an old used one from a boneyard, providing of course it's the right one. Another option is you could recurve the distributor, lower the vacuum advance and just get rid of the EGR valve altogether. Personally, I would just get a new/used factory EGR valve.

Spot on advice, however I chose to eliminate the EGR valve on my car and re-tune the motor around it.

 

[King_V]

I'll probably see if I can get a GM unit without it costing me a fortune.... barring that, RockAuto has one from Standard that runs about $35 - and two other brands whose names I don't recognize for cheaper than that. It'd be nice to find one that does the job as reliably as the OEM unit, but is physically smaller.


Another thing I sort of realized before going under the hood, but got to see in action now, is that my cold-idle control doesn't work right.

If I understand it correctly - on cold startup, the choke plate closes (then opens partially with vacuum), and car is on high-idle.

Tap the gas immediately, and the idle steps down slightly. As the car warms up, tapping the gas will bring it down to normal warm idle.

The choke plate gradually opens up independent of the throttle, though I'm not 100% sure on that.


What my car is doing, however, is the normal first start up and high idle, but if I tap the gas, I see some sort of bar or lever on the passenger side of the carb "fall forward", and the idle drops to the normal warm-idle level. Which will likely get the car to sputter and stall if the engine's still really cold.

It seems like this lever/bar/whatever on the passenger side of the car is supposed to only move forward partially when the engine is still cold. I can't quite figure out what controls that, and only know that it's independent of the choke itself. Are there TWO temperature springs, one for the choke, and one for the cold-idle speed? Any sort of clear diagram that shows what manipulates what?

 

[axisg]

Another thing I sort of realized before going under the hood, but got to see in action now, is that my cold-idle control doesn't work right.

If I understand it correctly - on cold startup, the choke plate closes (then opens partially with vacuum), and car is on high-idle.

Tap the gas immediately, and the idle steps down slightly. As the car warms up, tapping the gas will bring it down to normal warm idle.

The choke plate gradually opens up independent of the throttle, though I'm not 100% sure on that.


What my car is doing, however, is the normal first start up and high idle, but if I tap the gas, I see some sort of bar or lever on the passenger side of the carb "fall forward", and the idle drops to the normal warm-idle level. Which will likely get the car to sputter and stall if the engine's still really cold.

It seems like this lever/bar/whatever on the passenger side of the car is supposed to only move forward partially when the engine is still cold. I can't quite figure out what controls that, and only know that it's independent of the choke itself. Are there TWO temperature springs, one for the choke, and one for the cold-idle speed? Any sort of clear diagram that shows what manipulates what?

Sorry no diagram. Sounds like your choke system is operating as intended but with a weak or misadjusted choke spring ( there is only one ).

When the engine is cold and you depress the pedal the choke spring will close the choke and pull that "bar" into the upright position engaging a small "fast idle" cam on the PS of the carb behind the choke which is where you are seeing the bar rise.
With the key in the "on " position the electric choke is heated. And once the car is started and vacuum created the vacuum pull off will open the choke flap slightly ( so as not to flood the engine )

As the choke coil is heated, the spring pressure reduces. The heated choke sping will open the choke accordingly. The reduced pressure from the heated spring in addition to the weight of the "bar" will allow the fast-idle cam to disengage once the pedal is touched and the engine "should" return to curb idle.

You can adjust the spring tension of the choke by backing off the 3 screws in the choke housing and turning the plastic spring housing. Sounds like you may need more pressure to keep the choke engaged longer.

 

[King_V]

Ok, thanks!

I think I saw the spring housing (it was fairly large, and I remember 3 screws) - I'll probably give that a go. Hope the spring itself isn't broken - though I suppose that's a possibility.

 

[King_V]

Aftermarket EGR valves are known for their not so great quality. You'd be better off with an old used one from a boneyard, providing of course it's the right one. Another option is you could recurve the distributor, lower the vacuum advance and just get rid of the EGR valve altogether. Personally, I would just get a new/used factory EGR valve.

Quick question - are the aftermarket ones correctly functional, but simply failure prone, or is the problem that they don't regulate the exhaust gas re-entry in the way that the system was designed to expect?

If they're simply failure-prone, I really only need it to work (correctly) for about a year or so... so an aftermarket might do the trick....

Just curious...

 

[olds307 and 403]

I got a cheap replacement, lasted a couple of years so far, no EGR codes.