Just got back from Phoenix last night and find many, many messages on
the net that I haven't even had time to read yet. I see that there
are a few about not having any good news about travelling with a GMC.
Just wanted to tell everyone that I drove about 1400 miles and did
not have a single problem with the GMC. Even though it was about
115+ in the shade in Phoenix my overheating problems have been solved
(I'll post more on that later).
I did find out some interesting things about the timing that I really
had not realized all these years. I had reset the timing at 14 deg.
BTDC prior to leaving (I have the Caspro knock eleminator) and found
that I did not have much power on the hills going from Santa Fe to
Albuquerque so I had my wife drive while I set the timing by rotating
the distributor while going up a hill. I did it so that it just
started to ping and then I adjusted the EKE so that the pinging would
stop after just a couple of pings.
The GMC ran great from Santa Fe to Flagstaff (ranging from about 7200
to 5000 feet elevation) and my gas mileage was close to 10 mpg even
when towing the CJ-7 Jeep up the hills. I travelled the interstates
at 65 to 75 MPH and the motor ran extremely well.
However, when I started down toward Phoenix at lower elevations I
found that I would ping constantly when accelerating from a stop
light at about 25 to 35 mph or when I went up hills. I had to adjust
the distributor back down to about 14 deg BTDC to stop the pinging.
Prior to doing this I marked the base of the distributor and checked
the timing to see what I had set it to when moving the distributor
while driving by Santa Fe and found that it was about 30 deg BTDC at
idle with the vacuum advance plugged off.
When I started back up to higher elevations north east of Phoenix at
about the 4500 foot level I had to advance the timing back to the
mark that I had placed on the base.
Now I am wondering about this large amount of advance. I think that
my mechanical advance is working properly and I also know that there
is not much vacuum advance at high elevations.
Has anyone else had any experience at high altitudes like this?
There was a huge increase in power when I advanced it at elevations,
but it wouldn't stop pinging at lower elevations. I suspect that the
maintenance manual was written for lower elevations.
I am considering designing a mechanical advance so that I can rotate
the distributor by turning a knob or a lever at the dash while
driving. My son has drawn up a schematic for a knock sensor light
that he will build for me soon. If that works OK then I'll see what
I can rig up to change the distributor advance while driving without
opening the motor box cover. Hopefully more on this in the near
future.
Emery Stora
77 Kingsley
Santa Fe, NM
the net that I haven't even had time to read yet. I see that there
are a few about not having any good news about travelling with a GMC.
Just wanted to tell everyone that I drove about 1400 miles and did
not have a single problem with the GMC. Even though it was about
115+ in the shade in Phoenix my overheating problems have been solved
(I'll post more on that later).
I did find out some interesting things about the timing that I really
had not realized all these years. I had reset the timing at 14 deg.
BTDC prior to leaving (I have the Caspro knock eleminator) and found
that I did not have much power on the hills going from Santa Fe to
Albuquerque so I had my wife drive while I set the timing by rotating
the distributor while going up a hill. I did it so that it just
started to ping and then I adjusted the EKE so that the pinging would
stop after just a couple of pings.
The GMC ran great from Santa Fe to Flagstaff (ranging from about 7200
to 5000 feet elevation) and my gas mileage was close to 10 mpg even
when towing the CJ-7 Jeep up the hills. I travelled the interstates
at 65 to 75 MPH and the motor ran extremely well.
However, when I started down toward Phoenix at lower elevations I
found that I would ping constantly when accelerating from a stop
light at about 25 to 35 mph or when I went up hills. I had to adjust
the distributor back down to about 14 deg BTDC to stop the pinging.
Prior to doing this I marked the base of the distributor and checked
the timing to see what I had set it to when moving the distributor
while driving by Santa Fe and found that it was about 30 deg BTDC at
idle with the vacuum advance plugged off.
When I started back up to higher elevations north east of Phoenix at
about the 4500 foot level I had to advance the timing back to the
mark that I had placed on the base.
Now I am wondering about this large amount of advance. I think that
my mechanical advance is working properly and I also know that there
is not much vacuum advance at high elevations.
Has anyone else had any experience at high altitudes like this?
There was a huge increase in power when I advanced it at elevations,
but it wouldn't stop pinging at lower elevations. I suspect that the
maintenance manual was written for lower elevations.
I am considering designing a mechanical advance so that I can rotate
the distributor by turning a knob or a lever at the dash while
driving. My son has drawn up a schematic for a knock sensor light
that he will build for me soon. If that works OK then I'll see what
I can rig up to change the distributor advance while driving without
opening the motor box cover. Hopefully more on this in the near
future.
Emery Stora
77 Kingsley
Santa Fe, NM
