86 blazer 305 timing vacuum advance problem
Ken Condron
knock problem with the vacuum advance hooked up. With the vacuum
advance unhooked I can set the timing to about 2 degrees btdc (spec is
4) and most pinging goes away (only minimal left under heavy
acceleration) The problem comes when I hook up the vacuum advance.
There is a lot of vacuum at idle and the timing goes way off the scale
at idle. (maybe like 20-30 degrees btdc) The engine will idle fine but
I get heavy spark knock at any slight acceleration (even while sitting
still). I've been running with the advance unhooked and it seems to be
ok, but am I getting the best fuel mileage/performance this way? If
anyone knows a good way to troubleshoot this advance could you please
let me know. Does the change at idle with the advance hooked up seem
normal? Should I have such heave vacuum at the vacuum advance hose
while idling? Thanks in advance.
Ken
Ken Condron
Greasemonkey
source. What carb are you using, and did it get removed for some reason
recently? You have definatly isolated your problem quite a bit, now lets
just figure out what hose is misplaced.
Grease
"Ken Condron" <cond...@knology.net> wrote in message
news:3BE4AFE2...@knology.net...
Dean Dardwin
Grease knows his stuff. Here's a hint. Ported vacuum is always available
ABOVE the throttle blades, manifold vacuum BELOW them. A ported source
will always show no vacuum at idle, a manifold source will have a strong
vacuum at idle.
Dean
Greasemonkey
there is a T right above the choke diaphragm on the passenger side front
top. One side goes to the choke diaphragm, the other goes to the flapper in
the air cleaner or to the smog equip depending on the vehicle. This is full
port, and will make that problem, the dist should be connected to the nipple
on the bottom of the carb. Check it by starting the engine and feel for
vacuum, this will find your best source.
Grease
"Ken Condron" <cond...@knology.net> wrote in message
news:3BE4AFE2...@knology.net...
Ken Condron
and everything is hooked up according to the vacuum chart under the hood. The
engine is completely stock with a M4ME quadrajet carb. Here's the routing for
the line that goes to the vacuum advance.
Names of the items in the chain are right off the vacuum chart.
Line goes from the Top/Front of Carb and into a T fitting - one to the
Distributor Delay Valve, and one goes to another T and into the Decel Valve and
the AIR pump (which has been removed by the previous owner) AIR pump line is
simply plugged (could this cause a problem?) then after the Delay valve the line
goes to a T which goes to the vacuum advance port and to the EFE/Dist TVS (On
top of water inlet/thermostat housing).
The vacuum seems to be coming from the port in the carb. If I unhook the hose
right at the carb that starts all this chain, I get a pretty strong vacuum
there....seems to be the same vacuum I feel at the vacuum advance hose.
Hopefully this all makes sense. I'm pulling my hair out.
Thanks again
Ken
Ken Condron
carb has an electric choke.
Dean Dardwin
You're so close it hurts! Get out your vacuum gauge. Hook it up to a vacuum port. If it has vacuum at idle, move on to another port. Then, when you find one that DOES NOT have vacuum at idle, blip the throttle. You should see the gauge jump to 15-20 in. then go right back to zero. When you find one that does it that, hook your distributor vacuum hose up to it and go for a ride! It should be good.
At this point you have the right (ported) vacuum source. Hook it into the EFE/TVS and then route the other EFE/TVS line to the vacuum advance unit and go have a beer!.
Grease might be able to help with the other hose routing. I don't have a Q-jet to look at. Dean
Dean Dardwin
To be really honest, I could guess but unless I saw the truck, that's all I could do, guess. That's the frustrating part of trying to help someone remotely. If I was there we'd have it going faster than than you could open a couple of beers!
Let us know how it goes!
Dean
Ken Condron wrote:
Thanks a bunch Dean...It's dark now so I'll have to give that a shot another day. I'm still curious. Why would the stock arrangement not work out (Now that I have verified it with the vacuum routing chart under the hood?) I have also verified that this is the stock carb. Could this have something to do with the fact that the AIR pump was removed?Thanks for your help
Ken
rjb
There was ported vacuum at the T-fitting in the front top part of the carb.
I looked and looked and found nothing that would work or the reason why that
the port had vacuum when it should not.
I even ask the mechanics here at GM what I should do and there answer was to
for get the Underhood sticker and reroute the hoses to ported vacuum and all
should be fine.
I did and removed all smog devices on the vehicle and now the thing purrs
like a kitten and actually increased the mileage by 2 mpg.
I did try and get the things to work out, but there was no answer to this.
Just like my alternator has a serpentine belt and the water pump has a
regular V-belt again no answer either on this one!
Ken Condron
Also, Should all the things in the chain with the vacuum advance be moved to the
new source also? (I explained all the routing in another post to the same
original message) Or should I just hook a ported source to the vacuum advance
only?
Thanks
Ken
rjb
Also if you need to have the vehicle smogged I would not recommmend that you
remove all the smog devices.
I don't have to have my Suburban smogged, but I'm sure sooner or later I'll
have to put all the smog devices back on.
I did save all hoses and all parts that were removed though, can get very
expensive to replace later if I had too. Plus everything worked minus the
unported vacumn advance.
I quess the guys on the assembl line at GM were sleeping when they installed
the line to the vacumn advance.news:3BE73194...@knology.net...
Chris Blastin
correctly. The vac-line to the distributor should have no vacuum at all at
idle, and increase as engine speed increases. The line you have it
currently hooked up to is probably decreasing as engine speed increases, so
the timing is retarded as you increase speed. As the previous post suggest,
find the right vacuum line. It's usually on the left-front-bottom of a
rochester carb when facing towards the front of the engine.
chris
"Ken Condron" <cond...@knology.net> wrote in message
news:3BE60355...@knology.net...
Come on over. The Florida Gulf Coast is great this time of year. Still in
the 80's!
Thanks again, I'll let you know what I find out.
Ken Condron wrote:
Thanks again
Ken
Greasemonkey wrote:
Grease
Ken
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