Power Balance Test Question

[louiegz]

Well, I have an interested buyer for my Q. He took my Q to the local dealer to have the car inspected. All in all they found the car to be fine but they say that the #6 injector has to be replaced. These are the results of the Power Balance Test.

PWR BALANCE DIAG RESULT

OK

REFERANCE DATA

No.1 100rpmNo.2 99rpmNo.3 111rpmNo.4 101rpmNo.5 112rpmNo.6 62rpmNo.7 113rpmNo.8 102rpm

BASE DATA

CMPS-RPM(POS) 864rpm

COOLAN TEMP/S 179 F

My question is what does this test mean and what are they refering to with the rpm after the number? Thats not engine revs, right? How do the other injectors look like?

[96Qowner]

The power balance test shuts off one cylinder at a time, so your #6 is weak - only drops 62 rpm, where the others drop 100 rpm or more.

Not necessarily an injector, but probably. You'll know for sure by ohming it.

Here were my readings after an intake cleaning:

#1 -49rpm#2 -54rpm#3 -48rpm#4 -23rpm#5 -70rpm#6 -55rpm#7 -57rpm#8 -49rpm

CMPS-RPM 1063Temp 84*C

zerothread?id=180323

Not sure what the serious difference in rpm drops between vehicles means. Q45tech is the expert on Consult.

[captainluigi]

96Q, what was the dealer chrg. for that service? for louiegz, if this is not a thread jack, what was your intake cleaning procedure?

[96Qowner]

Tsk, cap'n, you coulda read the thread.

The test was $92 at the Nissan dealer and I did the BG system flush - don't recall how much that was - something over $100 - well worth it, though.

[captainluigi]

well g-whizz louiegz, we key billys are a little slow from to much sun & rum however i re-read the thread & i still didn,t see that info. i'll have these bi-focals adjusted asap.

[96Qowner]

LOL, I ain' louie, either. Check my posts in that thread.

[captainluigi]

lol myself. my error. please accept my sincere apology and a promise of it will never happening again.

[maxnix]

And all interested should read Q45tech's posts on power balance tests and how to do them correctly and interpet the data.

[louiegz]

Well I did a search and I still don't know what these numbers mean. Anyone has something helpful?

[Q45tech]

With 8 cylinders one assumes each provides 12.5% of the power to create the rpm so, with 1000 rpm each provides 125 rpm's worth.

The power balance test shuts off fuel and ignition sequentially to each cylinder while disengages the automatic idle rpm maintenance circuits.

Don't expect perfect numbers in an older engine just look for deviations from average and dead cylinders.

When ever you have minor deviations, a can of BG44k usually reduces them. On cylinders that are half the average or worse, extra work may be required.

[louiegz]

So that's how they figure that the #6 injector is bad by the number being lower than the others. OK, that makes sence. Thank you Dennis. That was helpful.

[96Qowner]

Also, your system is in better health than mine is/was, since your numbers average over 100 rpm drop from the overall 864 rpm = 11.6%. Mine averaged about 50 rpm drop from 1063 = 4.7%, far less than half the ideal of a 12.5% drop.

[maxnix]

I believe Q45tech comments in his previous posts discuss rpm to test at.

1250 comes to mind, but idle or near idle reveals less.

[96Qowner]

I believe Q45tech comments in his previous posts discuss rpm to test at. 1250 comes to mind, but idle or near idle reveals less.

Interesting. I did some searching for those posts and found these threads:

zerothread?id=225290

zerothread?id=189504

zerothread?id=155725

From the last thread:

The Consult works by locking the ignition advance and injector fuel time along with the IAC duty cycle so nothing changes as the injectors and spark are sequentially shut off except the rpm.

Since each cylinder provides 12.5% of the total torque [over 2 rpms] and supposedly creates the same drag [negative IMEP and friction] as it is shut off...........all that remains it the locked test rpm [BASE RPM REPORTED]which is a function of IAC bypass setting and TB cleanliness.

So, Consult doesn't actually set a base rpm. A low base rpm indicates something afoul with the intake path? Not clear if the test is less valid at lower rpm.

[maxnix]

Not clear if the test is less valid at lower rpm.

I know he has discussed testing at above idle, but can't remember in which post. May be in my archives.

Seems logical that even though the IAC is fixed by the Consult, at higher rpm it wouldn't operate any way.

[96Qowner]

Found this:

Low rpm power determination is problematic because there is no LOAD on the engine during the power balance test other than the drag of TC.

All one can say is the range of typical rpm drops is around 75-87 rpm with a Consult I.

The other problem is injector flow may not be equal at such low [2.4 millisecond open duration].

zerothread?id=72832

The test should ideally be done at 1100 - 1300 rpm. He also cautions not to read too much into the power balance test. It's primarily used to check cylinders against each other - to spot weak ones, like Louie's 62 rpm #6.

[Q451990]

Louiegz,

As far as attacking the isuse, I would ohm the injector first. If that's normal, there's a really good chance that a pressurized rail flush would make a big difference in that number. The reduced contribution to that cylinder is probably just a dirty injector, not a defective one.

I'm amazed by two things here:

1) The prospective buyer actually had a pre-inspection, and did it at a dealership. Hopefully he'll buy your car and become a member here!

2) The dealership actually felt that the RPM vairation was enough to be a cause for concern. My local deaership thinks any contribution is fine... probably because the Consult says "OK" at the bottom of the screen. They only care about negative numbers or zeros...

Heath

[Q45tech]

Well as we all know few dealerships have automotive engineers as technicans or service managers. Heck few Nissan Field employees are graduate mechanical engineers with specialites in engines.

What scares me is the new Consult III+ which is designed to take any thought from the diagnosis process .........so simple a real caveman can do it.

I do a loaded [ AC on and in gear foot on brake, headlights and every electric load on] powerbalance as a double check.

For some reason sometimes back to back powerbalances vary and can improve.