DevX83z

Hey all, new member here, long time lurker. Got myself an 1983 z28 w/ the L69 HO setup, T5. Solid, almost no rust body, but the prior owners did a number in the engine bay. They pulled the air pump and air pipes, removed AC compressor, disconnected vacuum lines to the air cleaner (dual snorkel style), no heat riser to said air cleaner, broken/frayed/disconnected wires, heater core disconnected (found puddle of coolant in passenger side footwell) etc. I'm in the process of repairing the items one at a time, mechanical before cosmetic. Before I get too deep into it, I wanted to ask a question I did not find an answer to.. which is simply, HOW is it supposed to run?

At a cold start I need to crank a few times, pump pedal, repeat once or twice and it fires up (assuming fuel bowl leak but that's for later diagnosing when I do a carb rebuild). When it fires up the choke is on (plate mostly closed, choke light on). It idles rough, around 600, sometimes drops and stalls. I was under the impression that at cold start (and choke on) we should be in high idle mode? That's my biggest question. When I tap the accel after that, choke drops out, light goes out, and the idle stop solenoid kicks in. Which right now is too high due to my meddling, and running around 1000-1200 rpm. I know how to adjust that. It however does not drop out at that point, which I read might be worth testing the TPS. (Also on the list of tests and possible fixes). Solenoid was not even connected when I got the car, probably because it never kicked down...

So I guess if someone could post a quick and dirty of how the engine should operate at a normal, cold start, in terms of idle rpm and diff solenoid engagements, assuming everything else is normal (vacuum, timing, fuel filter not plugged, etc..). Once I know what I should be looking for, I'll know better what order to test things in, without blindly throwing parts at it.

Thanks!

sofakingdom

iTrader: (1)

Normal cold start:

Pump the gas a couple of times. Add another pump for every 10° below 60°F more or less. Turn key. Car should start, maybe run slightly rough for a few seconds, smooth out, and idle. Idle speed should be 900 - 1100 or so depending on temp.

It's best to wait briefly before trying to drive if it's below 40° or so out; maybe 10 seconds at 40°, 20 seconds at 30°, and so on. Shouldn't ever take more than 2 minutes anywhere in the continental US before it's completely ready to go.

Choke should warm up and come off within just a few minutes.

Fast idle solenoid should pop out any time the RPMs are above about 1350 or 1400 RPM, and should retract below that. It should hold the idle up to just about that speed, maybe 1200 or so. Normal idle should be around 650 RPM.

Sorry to hear the car had got "improved" so much before you got it. I've never figured out why the first thing some people feel obligated to do to a NICE car, is trash the parts that make it NICE (like AC). I just don't understand idiots.

DevX83z

I agree about the 'improvements' as well. It was also 'nice' to see cut-off heater hoses hiding under the air cleaner... just more for me to fix the right way, and learn a thing or two as I go.

Regardless, thanks for the info. That sounds about like what I was thinking. The higher idle during warm up is controlled by the fast idle cam which is connected in with the choke/choke pull-off? So on a cold start when it's sitting way too low I should be checking that the choke is actually engaging/energized and that the pull-off is in correct operation (along with the various linkages there, and the idle cam not being broken)?

GM B-body

7:40am 50*F California morning stock cold engine start 4BBL E4ME QuadraJet

1. Get in the car and insert key into ignition switch
2. Choke plate will be open from previous driving. Pump pedal half ways one to three times (three times usually in colder temps). With the first pump the choke plate should snap closed and with every pump of the pedal the accelerator pump should squirt a stream of fuel into both primary carburetor barrels.
3. Turn ignition key to the run position, idiot lights should come on and carburetor mixture control solenoid should be clicking. (On some 80 to 81 cars the Mixture Control Solenoid may not click)
4. Turn the key further to start the engine. Engine should start within two seconds of cranking, release the key the moment engine starts.
5. When engine starts idiot lights should be off, carburetor choke pull off should fully retract into its vacuum diaphragm housing pulling the choke plate slightly open and lock out the upper secondary barrel butterflies. During this moment the engine fast idle should start off around the 1,000 rpm range and choke plate should start to open slowly as it warms up
6. After a few minutes the choke plate might be almost fully open and engine idle might of kicked up to 2,000 rpm. This is when a light depressing of the accelerator pedal should disable the choke and rpm's should fall back to normal idle speed.
7. There might be times where after lightly depressing the throttle the choke might not fully disable and the engine rpm only decreases to around 1,000 rpm's. This is because the thermostatic choke has not fully warmed up, allow the the engine to warm up about 1 more minute and afterwards try depressing the accelerator pedal again to disengage the choke.
8. After the carburetor has gone thru it's warm up stage, DRIVE!!

Hope this helps. Any further questions?

NoEmissions84TA

iTrader: (1)

Great explanation GM B-body. Don't be afraid to post more like this.