SharkSkin

Doc, that usually works great -- but you forgot the advice about having a Halon Spritzer nearby while you do it.

Solid Snake

The connections are correct as far as I can tell, if the EGR is depicted in the diagram looking down on it from the engine bay, with the more clockwise connector going to the thermo valve and the more counterclockwise one going to the pressure regulator on the right bank.

I just did this with propane gas and found nothing.

At this point I'm willing to do whatever works, and right now the EGR kills the engine dead at idle.

I did some more tests tonight and found the following:

1. There is no leak in the brake booster.
2. The engine responded well to a very slight enrichment of the fuel mixture.
3. Throttle response improves with late timing (moving the distributor CCW?)
4. With the distributor fully CCW, manifold pressure is a steady 21 in/hg. Does this rule out a vacuum leak?
5. When I connect the thermo valve back to the EGR valve, the engine takes a dump.

I believe the low manifold vacuum is simply a symptom of the super-low idle. How much vacuum can an engine be expected to develop at 450 RPM?

If I'm not mistaken, the EGR valve opens if, and only if, it has vacuum on both ports, correct? If so, this would mean the pressure converter is sending vacuum when it shouldn't be.

Lizard928

you will need a timing light to set the timing to what it should be.

if you manage to get 21 in HG vacuum then I would say there are no leaks

docmirror

Well, you have found leaks, but you didn't find it with the propane. If you started at 5" Hg, and now you have 21", what does that say?

Dennis Wilson

Timing should be at 31 degrees BTDC at 3K rpm with the vacuum advance line detached.

Dennis

SharkSkin

Nothing wrong with defeating the EGR to troubleshoot an idle problem. I just thought that you should know that a working EGR is integral to the way the rest of the system is tuned, and there are good reasons to keep it besides the fact it's an inspection item. To see if it's leaking at idle, just disconnect the vac hoses from it and let the engine idle for a while. If the EGR pipe heats up faster than the surrounding intake parts, you've got a leaky EGR.

The fact that pulling the thermo-valve for the EGR made it run better indicates that something is wrong with the vac connections -- something reversed or plugged to the wrong TB port.

Dennis, timing is 31° @ 3K, not 2K. It should advance another 1°-5° at 5K:

Dennis Wilson

Dave,

My bad. I knew that. Guess that's what happens when you get old and the eyesight starts going. Why didn't they publish a bigger tech booklet for us old f@rts.

Dennis

hupp

My understanding of the EGR system is that it has no performance effects and only emissions reduction effects. Here are my thoughts and I stress that I could be wrong:

In general, the function of the EGR is to reduce combustion temps, which results in lower NOx emissions. This done by essentially "diluting" the higher O2 intake charge with a lower O2 stream under certain driving conditions. This results in lower heat of reaction and lower heat/BTU's = lower NOx.

My EGR is gone, timing is to spec. and I have no performance or pinging issues at any throttle position.

Solid Snake

Well, it says that the timing is fully retarded. Is it normal for the engine to idle fastest with the timing this way? If I move it back towards the center, vacuum drops.

If I pull the vacuum advance, wouldn't the timing be the same at all RPM rather than just 3K?

I am sure the EGR is not leaking at idle. When it was hooked up, I burned myself on it and with the vacuum line disconnected, it's no hotter than the intake runners. However, when I reconnect the thermo valve, the engine falls on its face.

There is a constant vacuum through the thermo valve where the EGR is supposed to go, is this correct? That would mean that the vacuum on the pressure converter is erratic.

Dennis Wilson

Changing the timing should change the vacuum. The distributor has centrifugal as well as vacuum advance. Trying to time your car based upon vacuum is not very exact as optimum vacuum changes based upon altitude.

Until you time the ignition and reroute the EGR vacuum lines according to the chart something isn't going to work correctly.

Dennis

Lizard928

idle is always fastest with the most ign advance, not retard.

Solid Snake

So when I turned the distributor all the way counterclockwise, was I advancing the timing or retarding it?

I thought retarded timing causes high vacuum.

Lizard928

advancing causes higher vacuum, and a higher idle.

I am not familiar with single dizzy 928s to know which way is advance or retard.

Solid Snake

It seems to also cause a much snappier throttle response. With the distributor the other way, the revs take off as if I were in 5th gear.

SharkSkin

I figured it was a typo... just wanted to set the record straight. Large tech book scans like the above are on my site -- look in the top row of links. I found the printing to be a bit small as well...
Obviously results will vary. Reducing combustion temps via EGR is also used to maintain high ignition advance under circumstances where the engine would ping otherwise. I'm running a couple degrees advanced from spec. Not so far that I can't use 87 octane in a pinch, but enough that my butt-o-meter is pleased with the extra kick. My Thermal valve failed closed at one point, and I would get part-throttle pinging under certain conditions(esp. when very hot) until I fixed it... apparently the timing spec is a bit conservative and the problem will not always manifest unless you're one to tweak the specs a bit here and there. YMMV.

The timing will vary with RPM even with the vac hose disconnected & plugged, as there is a mechanical advance inside the distributor.

I think CCW is advance -- might want to pop the cap & bump the starter to confirm.

Sounds like you have either a bad thermo-valve or it's connected backwards(it matters) or to the wrong port if there is always vacuum, even when cold. It's hard to say, since you may have the throttle plate open further than it ought to be due to chasing this problem. Below is a better vac diagram, which clearly shows the thermal valve connected to port vacuum(only sees vac at part-throttle). If you had cranked in the idle screw a few turns this port might see vac all the time.