Confused on cylinder balance issues?

[softy91]

When I got the new version of HPT I was overjoyed with all the new bells and whistles. It is a great package!

For some time I had been chasing a lowspeed missfire and couldn't isolate it. I thought that one of my new expensive Iridium plugs was already gone, but I never read a missfire? Also I am not getting missfires anyplace above light TPS 5% or >.

The first thing that I did with the new software was to run the cyclinder balance test. Results were : 98-100-102-104-106-104-100-100. How can I have a 98 and a high of 106? Also with no missfires read the logical thing would be a weak injector. (I am Guessing) I also changed to 9MM MSD wires just for grins.(No help)

Is there any way to compensate the weak injector to see if it really is the problem? It seems that I saw something about skewing injector width on individual injectors.

Should I try moving injectors around to see if this changes my readings?

Help! This has me going in circles.

[Dirk_Diggler]

Move the injectors around and see what happens. I think the cylinder balance test checks to see how strong the cylinders are by dropping one injector at a time and then monitoring how hard it is to keep the rpm at its target idle. THen some algorithm calculates the numbers that you finally see

[ozorowsky]

where did you guys find that test?

[luv2spd]

It under VCM control and then click on special.

[QUASAR]

Move the injectors around and see what happens. I think the cylinder balance test checks to see how strong the cylinders are by dropping one injector at a time and then monitoring how hard it is to keep the rpm at its target idle. THen some algorithm calculates the numbers that you finally see

But what does shutting down a cylinder, have anything to do with how strong that particular cylinder is? It's not like a compression test, or is it? Or maybe it is an idle tuning aid?

[QUASAR]

Thought about it some more, and have a theory. Maybe it is just a guage of how much a given cylinder "contributes" to the entire engine. It is called a "balance" test. One cylinder is shut down, and then a measure is taken (what kind of measure I dont know) of what it takes to maintain the idle RPM. When it is difficult for the engine to maintain its idle when a cylinder is shut down, it could mean that that cylinder is a larger "contributor" to overall engine operation.

What does that mean? I dont know We cannot adjust fueling cylinder by cylinder like on some aftermarket management systems, so i'm not sure if anything can be done with the results of this test.

The HPT guys put this in for a reason, so I'm wondering how we use it now.

[luv2spd]

Thought about it some more, and have a theory. Maybe it is just a guage of how much a given cylinder "contributes" to the entire engine. It is called a "balance" test. One cylinder is shut down, and then a measure is taken (what kind of measure I dont know) of what it takes to maintain the idle RPM. When it is difficult for the engine to maintain its idle when a cylinder is shut down, it could mean that that cylinder is a larger "contributor" to overall engine operation.

What does that mean? I dont know We cannot adjust fueling cylinder by cylinder like on some aftermarket management systems, so i'm not sure if anything can be done with the results of this test.

The HPT guys put this in for a reason, so I'm wondering how we use it now.

That makes sense. Any of the HP guys want to add?

[Screamn03]

I feel there are many things that can all add up to an even running engine. Cylinder compression I think has a big part to do with it, if you did a compression test on all cylinders I don't think you would find them all exactlly the same-they should be close though. I think this impacts it the most. I never thought of the injector idea but it does make some sense and it could lead to a weak cylinder just like an ignition problem could. Now it comes down to what is a reasonable range for the numbers. I'm thinking somewhere in the 5-10% range myself, although less is more.

I did my motor the other night with the IAC counts maxed at 127 and got 95,94,95,95,96,95,95,95 but the motor in this car is fresh with about 15K on it, it has a small cam, the motor was idling at about 1200rpm (off the cam), the rotating assembly on this motor was balanced when it was apart, and I always run Chevron 91 through the motor with a bottle of techron every 6K. So I guess mine is just a freak. I did do the test at idle and my numbers were in the 90s with a varience of 4 or 5 high to low.

I think for you guys with bigger cams that chunk are going to have problems with getting near perfect numbers because it's going to freak the test out with its 'random' idle.

Now if you run the test and see one cylinder that stands out from the rest then you have a problem.
Example:Say you had 92,93,81,92,95,94,91,93 . I would be looking at cylinder number three for problems.

Use the tool now, save the results, then run the test again in a month or after a big race. Compare results and keep a log. As soon as you start to spot variences then you'll know something is up. I believe this is how the tool to work.



-Mike-

[Chris@HPTuners]

The test is a simple one, you maintain a constant idle sped by controlling the IAC motor steps, we sample that RPM as use it as the refernce RPM.

Then each injector is disabled for 2 seconds and the RPM sampled during that period and the result is presented as a % of the reference RPM. The theory is that if you disable an injector, and the RPM doesn;t drop much then that cylinder is weaker, and another cylinder that results in a larger drop is stronger.

It's not highly accurate but is a basic indicator of an issue somewhere if you see large variances.

Chris...

[softy91]

Thanks Guys!

This does give me some ideas to chase.

The first thing I am going to do is get out an old fashioned compression guage.
This is an LS6 with stock cam (short), so I would expect around 150psi.

I'll keep you posted. 8)

[DanaliHD]

i can't figure it out. mine says "not ready-stop scanner"

[DanaliHD]

got it. cylinder 1 seemed to be the lowest every time i tested it. 91-95ish. all others were 95-99

[Dellz06]

Ok,

So lower percent means better then?

If I disable injector 1 and the percent stays at 100%, that means it wasn't contributing to the rpm and might be bad.

If I disable injector 2 and the percent drops to 85%, that means it was contributing alot to the rpm and is probably good.

Right/Wrong?

John.

[chrisj6]

I would think higher is better, mine are all 97-100%.

Chris

[S2H]

if you are only off by a variance of 98-106 then you are not off...
if you saw 100 on one and 70 in another...then you have an issue...but they all hover around 100..so all is good.

the small difference could just be your car seeing the difference between springs that all wear slightly differntly as time goes on

do a real compression test with a compresion test fitting and see what you get....that will be a true indicator...then if your PSI is off..then you have an issue..LOL