Weird, at a loss. Need to learn how to test electrical circuits.....

[Lou Merrell]

Ok, 1996 K1500 5.7 vortec, 180k.
Have spark, 56-58 psi koeo, leaks down to 30 psl in about a minute and continues to zero slowly. Lowest cylinder pressure 70-90 (3) psi due to sticky valves or other chamber issue, rest of cylinders 120-170 (been that way since I purchased) . Battery at 12.6v static.
No start! Running good one day ( can't even tell there's a valve train issue), wouldn't start next day. Not even with ether down throttle body.
Upon inspection of cap and rotor I noticed about 10 plus degrees of rotational play in distributor so I'll be purchasing one. Advise on which dizzy?
Given these conditions, what direction should I start my diagnosis as I have no codes being set?
Thanks!

 

[Frank Enstein]

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Also when the new dist. goes in make sure you follow the correct procedure. There IS such a thing as "off a tooth" with a Vortec.

Check the timing chain play as well.

Rotate the engine with the distributor off clockwise until the notch in the harmonic damper lines up with the tab on the timing cover.

Put masking tape on the distributor body so you can mark EXACTLY where the rotor is pointing.

Rotate the engine counterclockwise while watching for the rotor to move. Using a ratchet on the alternator pulley nut makes this easier.

When the rotor JUST moves check the timing marks to see how far it went.

Less that 5 degrees it's fine. More than 10 and the timing chain and gears are shot. In between? You decide.

If you remove the timing cover you are supposed to replace the cover.

Check crank position sensor.

Give it a small shot of starting fluid to see if it kicks. If it does it's getting spark.

 

[stutaeng]

Ok, 1996 K1500 5.7 vortec, 180k.
Have spark, 56-58 psi koeo, leaks down to 30 psl in about a minute and continues to zero slowly. Lowest cylinder pressure 70-90 (3) psi due to sticky valves or other chamber issue, rest of cylinders 120-170 (been that way since I purchased) . Battery at 12.6v static.
No start! Running good one day ( can't even tell there's a valve train issue), wouldn't start next day. Not even with ether down throttle body.
Upon inspection of cap and rotor I noticed about 10 plus degrees of rotational play in distributor so I'll be purchasing one. Advise on which dizzy?
Given these conditions, what direction should I start my diagnosis as I have no codes being set?
Thanks!

What is the history with the truck? Did you just buy it? Was it running well before?

First issue is the fuel pressure not holding. Likely a fuel pressure regulator leaking inside the intake and/or leaky injectors. That needs to be fixed.

Not sure what to say about the low compression. 70 psi I doubt is enough to get the engine started. I thought 90 psi was minium spec? If engine is worn out and mechanically in poor shape, is it even worth trying to fix the other issues? I don't know. You say it ran fine one day?


If you have spark, I don't see any issues with electronics circuits. Just make sure your distributor is set correctly.

 

[Lou Merrell]

What is the history with the truck? Did you just buy it? Was it running well before?

First issue is the fuel pressure not holding. Likely a fuel pressure regulator leaking inside the intake and/or leaky injectors. That needs to be fixed.

Not sure what to say about the low compression. 70 psi I doubt is enough to get the engine started. I thought 90 psi was minium spec? If engine is worn out and mechanically in poor shape, is it even worth trying to fix the other issues? I don't know. You say it ran fine one day?


If you have spark, I don't see any issues with electronics circuits. Just make sure your distributor is set correctly.

Distributor will be first, along with upgraded injection unit. I suspect a worn gear anyway. While checking the fuel pressure I did hear a gurgling sound when the key was turned off but I didn't smell any fuel.

 

[Lou Merrell]

What is the history with the truck? Did you just buy it? Was it running well before?

Not sure what to say about the low compression. 70 psi I doubt is enough to get the engine started. I thought 90 psi was minium spec? If engine is worn out and mechanically in poor shape, is it even worth trying to fix the other issues? I don't know. You say it ran fine one day?

Truck has always started right when I initiate the starter when cold. Warm, it takes a couple seconds.
I've had the truck for a little over two years. It replaced my 90. I've known about the valve open issues for a while now. I believe my short block is good. Upper engine issues though.
I have my list somewhere. I'll post it when I find it.

 

[Schurkey]

GM spec used to be 100 psi cranking compression minimum. I've seen cylinders run at 80 psi cranking compression. Saw one 400 Ford that had a cylinder at 50 psi, wouldn't run at idle but ran with more throttle opening. I'm not saying these engines ran RIGHT. They were slow and lazy, but they ran.

Get a fresh distributor in there. Wouldn't hurt to look down the hole to verify the gear on the end of the cam that the distributor meshes with. Fix the fuel-pressure leakage. Could be an injector, could be the regulator, could be the check-valve in the fuel pump. Could be all three. Clean the plugs-or replace them--they're probably fouled. Verify cap, rotor, plug wires.

Expect the bad cylinder(s) to get worse. They rarely heal. That engine is just about done.

 

[Lou Merrell]

GM spec used to be 100 psi cranking compression minimum. I've seen cylinders run at 80 psi cranking compression. Saw one 400 Ford that had a cylinder at 50 psi, wouldn't run at idle but ran with more throttle opening. I'm not saying these engines ran RIGHT. They were slow and lazy, but they ran.

Get a fresh distributor in there. Wouldn't hurt to look down the hole to verify the gear on the end of the cam that the distributor meshes with. Fix the fuel-pressure leakage. Could be an injector, could be the regulator, could be the check-valve in the fuel pump. Could be all three. Clean the plugs-or replace them--they're probably fouled. Verify cap, rotor, plug wires.

Expect the bad cylinder(s) to get worse. They rarely heal. That engine is just about done.

Thanks.
As far as I can tell, I have no leakage into the crankcase. All the loss of compression in all 3 low cylinders is either exhaust or intake.
I think I put my test results in the Haynes manual that I use for storing notes and receipts but I'm at work right now so I'll look when I get home.
I'll tell you, with all the issues the engine has it fired up and ran real good. Except for now.......
I was hoping to get through winter before I got into it but guess I'm getting into it....

 

[Carlaisle]

Before you replace any parts it would be prudent to figure out why it quit starting. From what you have shared here, the first thing I would do is check for spark. It sounds like you don't have any. After you get it running you can work on the other issues as time permits.

 

[Lou Merrell]

Before you replace any parts it would be prudent to figure out why it quit starting. From what you have shared here, the first thing I would do is check for spark. It sounds like you don't have any. After you get it running you can work on the other issues as time permits.

That's the way I work. I don't throw parts at something.....anymore. I am getting a new distributor though, or at least the gear. I'll know more when I get it out.
The first thing I did was check fuel pressure- good. Then I checked for spark- present in #1. Then I grabbed the ether- engine kicked but didn't fire. Then I said to myself, 'self, your taking the car to work tonight'. Then it got too cold to work outside and here I am with a dizzy that has too much rotation. I'll know more this weekend. We have a heatwave of over 30 degrees coming tomorrow.

 

[Lou Merrell]

Here is the trucks compression/leakdown numbers:

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