Freshly Rebuilt 455 engine with new camshaft .
Symptoms: Lean pop off idle. ( Not sure if related)


Cylinders #2 and #3 have different temperature readings at cylinder head using heat infrared test gun.


1-370, 3-220, 5-380,7-390
2-185,4-365,6-390,8-385


I double checked the following:


Firing order- Good

Timing- Correct
Plugs and Ignition Wires- Good

Compression test - Good
Vacuum Leaks- None


What am I missing?

 

So a rich mixture would cause lower cylinder temperatures and a lean mixture would cause higher cylinder temperatures.

I have never tried to measure the temperature of a cylinder head.

 

Manifolds or headers?

 

Did you take a reading at the headers?

 

Headers.

 

Readings at headers are:
1-215,3-208,5-235,7-207
2-136,4-276,6-430,8-430

 

What intake are you running? Carb?

 

Stock intake with pelnum divider milled. Rochester Quadrajet

 

My guess would be you have a vacuum leak on cyl's 6 and 8 to start with.

 

Cylinders #2 and #3 have different temperature readings at cylinder head using heat infrared test gun.


1-370, 3-220, 5-380,7-390
2-185,4-365,6-390,8-385

 

FWIW I'm thinking you have no combustion or intermittent combustion in 2 and 3 despite having new plugs, wires etc. That might be the cause of low heat readings. Even with no combustion or intermittent combustion some heat will transfer through the block possibly accounting for the low readings

Its not unknown for new plugs to be bad. When I rebuilt my 455 it idled poorly. Took me a while to check the same things you did and finally pulled the plugs. One plug was grossly fouled. replaced it with another new plug. End of problems.
Jerry

 

I changed the plugs twice
What can be the cause of intermittent or no
combustion ?

 

Distributor bad? points or hei?

 

If you are getting good spark in all cylinders I'm at a loss to explain why the low temps in 2 and 3. Maybe something mechanical? Cutlass EFI had good advice with regard to checking for vacuum leak on #6 and #8

Have you asked your engine rebuilder these same questions? What do they say?
Jerry

 

Distributor was checked and I tried a known good one- same issue.
We assembled engine - did not talked to any engine builders yet

 

Water in the combustion chamber would decrease the temperature.

 

sometimes when the valves and seats are ground it requires adjustable rockers because the valves won't seat, this could also cause a pop. a vacuum gauge may verify this problem, good luck

 

He said compression good, and I assume he meant he checked all of them, and it shouldn't be good I would think, with a valve leak with it off the seat.

 

Vacuum readings steady at 15 Inches

 

I agree with Cutlassefi because I had the same problem as you. I tried everything I could think of to find out why. I did find the problem after swapping in a Torker intake. The stock intake manifolds are bad for cracking on the bottom side, mine had 3 hair line cracks. Also don't take readings of the head because the water flow will confuse you. Always take readings of the exhaust manifolds or beater yet the header pipes.

Ray

 

Problem was the intake gaskets. Fixed- Vacuum now steady at 17-18 inches

 

That's great!!!