2 weak cylinders?

4-cyl cut out test is not very good test to pin point a week injector.. There was an injector guru Far_Call posting on this site and here what he said about 4-cyl test:
"Unfortunately the 4cyl Cutout test in ET is masked by the second injector so trimming this way can be tough. the best way is a 5 cylinder or a manual cutout but u have to be careful that the engine temp stays the same and the air compressor doesn't gut in"

I ran few test after that and here what I got...
4 cyl cutout test result:
#1 8827 3.11
#2 7701 3.16
#3 6627 3.24
#4 3887 3.13
#5 1796 3.08
#6 6758 2.98
4-cyl cut out test shows #3 is the weakest...

Then I ran 5cyl twice..
Test #1 results: Test #2 results:
#1 8827 4.32 #1 8827 4.30
#2 7701 4.24 #2 7701 4.17
#3 6627 4.05 #3 6627 4.03
#4 3887 3.98 #4 3887 3.93
#5 1796 4.10 #5 1796 4.05
#6 6758 4.11 #6 6758 4.12
Now it clearly seen that #1 cylinder is the weakest one.
A weak #1 in 5cyl cutout test makes #3 to look weak in a 4 cyl cutout test....
We tried to change trims on the injectors and trimmed the #1 all the way up....
#1 9839 4.30
#2 7707 4.20
#3 6627 4.17
#4 3886 4.19
#5 1796 4.19
#6 6730 4.19
Still #1 is the weakest but runs pretty smooth and I decided to leave it alone at that point...

 

Nope... The cylinders with the higher numbers are the weaker cylinders. Too bad that Far_Call does not show up here as often as he did before... Nobody understands injectors better than him.

 

The higher number means more fuel needed to keep the RPM at the same number...

 

I am not sure we are on same page with you, lol....Run the 5cyl test.... And the ones with the higher #s will be weaker cylinders... It can be a bad injector, incorrect trim # or low compression causing that...

 

There's some confusion here and this is the reason cat stopped supporting the 5 cylinder automatic tests years ago.

For a basic 1 cylinder test, the baseline is the total fuel for all 6 firing. When each one is cut-out, fuel needs to be added to the other 5 to push the dead cylinder and the engine should become less efficient, in that case, the higher numbers mean stronger cylinders. If no fuel is added, the cylinder was dead to begin with.

A 4 cylinder test is basically the same thing, but it cuts out 3 cylinders first so your basically diagnosing a 3 cylinder engine twice. This places more load on the 3 firing cylinders and could help in certain cases identify a problem. Same rules though, cut out 1 cylinder at a time on 3 firing cylinders. Higher #'s are stronger cylinders.

The 5 cylinder cutout can be really useful, but this is where things flip flop. It's only running on 1 cylinder, so an injector that is not flowing as much or has a poor spray pattern would need a longer pulse to keep it running. This test is where the the higher #'s mean weak cylinders.