Low low vacuum at idle

[josehf34]

I had similar symptoms. My issue turned out to be a bad connection at the Ballast Resistor. Using a multimeter, check voltages at all the wires pertaining to the ignition system. You could have a poor connection somewhere. Is the motor grounded?

The motor has a new ground wire directly to battery, also the ignition system doesn't has ballast resistor, is directly wired to alternator output

Have someone sit with it idling in gear and try pulling the wires again one at a time and see if that makes a difference.

I'm going to try with car idling in gear and see what happens

 

[josehf34]

I just performed a compression test and here're the results

Cyl # -- Dry -- Wet
#1 -- 85 -- 115
#2 -- 85 -- 125
#3 -- 80 -- 120
#4 -- 80 -- 125
#5 -- 85 -- 125
#6 -- 95 -- 135
#7 -- 80 -- 125
#8 -- 95 -- 130

Also, removed the timing cover to inspect if maybe the camshaft was badly install and the unique weird think I found was that the timing chain looks like some tensioner is broken, I think is very strange because this comp cams chain has less of 400 miles on it

like the one in this video:


Is that normal?

 

[josehf34]

I replaced the timing chain and advanced the camshaft 4 degrees, now the car starts and idles A LOT better and the vacuum signal increased 2"

But the engine still shakes a bit and I can hear some lifter noise. I know the hydraulic lifters are not adjustable but, is there something more that can be adjusted in the valve train? how is adjusted the lifter preload?

 

[mr. fix it]

All you can do is replace the lifters. I have seen a beefy camshaft cause issues for old lifters. as a matter of good practices, any time you replace a camshaft the lifters need to be replaced as well since them lap in with each other.
Do you know if that was done when you replaced the camshaft?

 

[mr. fix it]

depending on how precise you want to be as well is a total valve train review.
The big boys will check angles and distance travel with the push rods and rocker arms to valve stem heights to get the perfect stroke and angle

With most of us trying to gain a few horsepower it doesn't usually matter but a perfectionist will spend the extra bucks to make sure everything is perfect.

Some of the bolt on upgrades can actually performance down grades...
here is a link to enlightenment ... Engine Tech: Understanding Valvetrain Geometry and Getting It Right! - EngineLabs

 

[josehf34]

All you can do is replace the lifters. I have seen a beefy camshaft cause issues for old lifters. as a matter of good practices, any time you replace a camshaft the lifters need to be replaced as well since them lap in with each other.
Do you know if that was done when you replaced the camshaft?

I replaced the lifters with the new kit from comp cams but I'm not sure why they are being so noisy

 

[mr. fix it]

I replaced the lifters with the new kit from comp cams but I'm not sure why they are being so noisy

Could be breaking in or you are using a heavier weight oil than what the manufacturer is specifying.

I have personally seen people using too heavy oil viscosity which can starve the top end of oil supply
Heck if 10w30 is good, then 20w50 is even better right???

 

[josehf34]

Could be breaking in or you are using a heavier weight oil than what the manufacturer is specifying.

I have personally seen people using too heavy oil viscosity which can starve the top end of oil supply
Heck if 10w30 is good, then 20w50 is even better right???

I'm using 15W40 diesel engine oil with comp cams additive and planning to switch to 10W30 or ven 5W30

I'm not sure if the lifters are really breaking in, when I did the cam break in I let the engine run at 2500 RPM a half hour and then other 15 minutes at 1800 RPM

 

[mr. fix it]

It's been so ling since I had to break a cam in I don't know what the current best practice is for that.

What does the FSM call for for oil?
10w30 or higher?

 

[jrm]

If your compression # are that low on a fresh rebuild I think there is a bore or ring problem. By putting oil in the cyl and getting a 40psi increase thats not right.
I would do a leakdown test on the cylinders and listen for air coming out of the crankcase or where ever.

 

[josehf34]

If your compression # are that low on a fresh rebuild I think there is a bore or ring problem. By putting oil in the cyl and getting a 40psi increase thats not right.
I would do a leakdown test on the cylinders and listen for air coming out of the crankcase or where ever.

But can be normal to have a bore or ring problem on all cylinders? If my memory is right the numbers of this engine months before the camshaft swap were between 110 - 120 PSI on dry test and something between 130 and 140 PSI with wet test

Can be possible to have the rocker shaft too much adjusted that maybe the valves are always a bit opened?

I just ordered the leak down tester, maybe is time to go further with this problem and find a real solution

 

[1966newport]

sounds like too much cam for stock pistons

 

[josehf34]

sounds like too much cam for stock pistons

How can a cam be "too much" for pistons? I've never read something like that

So according to that, the unique way to solve it is changing pistons or maybe increasing compression ratio can help?

 

[superfragl]

How can a cam be "too much" for pistons? I've never read something like that

So according to that, the unique way to solve it is changing pistons or maybe increasing compression ratio can help?

That means the cam is possibly bleeding cylinder pressure due to it`s design.

Do a leak down test first to see if you have a problem with rings or valve train. Those pressure numbers are waaay too low. On my newly built engine (not even broken in) I had 145 on all cylinders, cold engine, no oil in bores and cam is more aggressive than yours.

 

[mr. fix it]

So let's review for a moment.

Did you disconnect all vacuum accessories such as the brake booster and PCV system?

 

[rexus31]

Are you sure you have the correct length pushrods? It almost sounds like the valves are hanging open a touch.

 

[superfragl]

I was wondering how did you check for vacuum leaks? Just spraying started fluid around intake might not be enough. I used cigar method.

So let's review for a moment.

Did you disconnect all vacuum accessories such as the brake booster and PCV system?

Why would you disconnect PCV?

 

[jrm]

[QUOTE: 2828"]But can be normal to have a bore or ring problem on all cylinders? If my memory is right the numbers of this engine months before the camshaft swap were between 110 - 120 PSI on dry test and something between 130 and 140 PSI with wet test

Can be possible to have the rocker shaft too much adjusted that maybe the valves are always a bit opened?

I just ordered the leak down tester, maybe is time to go further with this problem and find a real solution[/QUOTE]
Could be a lot of things, ring gaps al

 

[jrm]

I guess it could be valves but by putting oil in the cyl which covered the top of the piston, rings, bore walls your compression went up a lot, that should mean the problem is in the bore, rings. Doesnt happen often but it could have been machined wrong.
leakdown check will tell u where its leaking from.
goodluck w it.

 

[josehf34]

So let's review for a moment.

Did you disconnect all vacuum accessories such as the brake booster and PCV system?

No i didn't, why do I need to do that for a compression test?

Are you sure you have the correct length pushrods? It almost sounds like the valves are hanging open a touch.

Are the engine stock pushrods so i think they have the correct length

I agree about the possibilty of having valves open just a bit, can the rocker shaft produce that if it's bolts Are too tighten up?

I was wondering how did you check for vacuum leaks? Just spraying started fluid around intake might not be enough. I used cigar method.



Why would you disconnect PCV?

Yes, sprayed carb cleaner around carb and intake, I have read about the cigar method but i've never tríed it, don't the cigar smoke will escape through the carburetor?