79 runs like crap after top end rebuild
#32
I think that having the lines reversed will make the EGR misbehave, yes. Are the other connections correct?
It doesn't take much of a spritz, in fact a small amount is better than a flood. To test, pull a vac line, and spritz in the port to see what it sounds like. Then, go around all the fittings on the intake one at a time. I think you'll find some more leaks.
I don't think you're going to extend the life of the motor much by defeating the EGR. Most particles coming out of the combustion chambers will tend to go straight out the exhaust rather than make the sharp turn into the EGR valve. The resulting pinging would reduce the motor's life to a greater degree, I'd think. Or, as I said, you would have to retard the timing and lose power, or get the distributor modded.
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.
#34
Shameful Thread Killer
Rennlist Member
Rennlist Member
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?
#36
Rennlist Member
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:
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:
#37
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
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
#38
Burning Brakes
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.
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.
#39
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?
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.
#40
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
Until you time the ignition and reroute the EGR vacuum lines according to the chart something isn't going to work correctly.
Dennis
#44
advancing causes higher vacuum, and a higher idle.
I am not familiar with single dizzy 928s to know which way is advance or retard.
I am not familiar with single dizzy 928s to know which way is advance or retard.
#45
Rennlist Member
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.
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.
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.
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.
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.