High calculated fuel rate

[davig]

So I've been trying to take a look at my injectors health and in doing so I checked my calculated fuel rate at 15mm3. From what I gathered that is supposed to be more like 8mm3 is this correct? And if so what could be the cause of the high flow rate? Here are my balance rates with fuelrcalc.

Fuelrcalc. 15mm3
Cyl1 1.7
Cyl2 0.5
Cyl3 -0.4
Cyl4 -0.7
Cyl5 -1.2
Cyl6 0.8
Cyl7 -1.3
Cyl8 0.4

08 lmm

 

[Chevy1925]

engine up to temp? how many miles on injectors? stock tuning?

 

[davig]

Engine was up to temp I am guessing stock injectors at 175k efi live tunning

 

[Chevy1925]

you need to be on stock tuning to check balance rates correctly. areas can be modified on tunes that will effect balance rates

 

[davig]

I don't have original stock tunning. Can I put it to the "stock" tune on my tunes?

 

[Chevy1925]

I don't have original stock tunning. Can I put it to the "stock" tune on my tunes?

couldnt tell you as i didnt tune it. only the original tuner could tell you.

 

[davig]

Ok what do you think about the calculated fuel rate? Should I be looking at the main injection rate instead?

 

[Chevy1925]

Ok what do you think about the calculated fuel rate? Should I be looking at the main injection rate instead?

yes, for sure. if they do not match, go off main injection rate

 

[roder]

I recently purchased an LBZ with 171K miles. I have some concerns about the injector's health, so I just performed the diagnositics and researched this yesterday. I found this post to be the most useful. From what I've read, it seems at sea level the expected FUELRCALC should be 8mm3 in Park for the LMM.

I also have a DSP5 + EFI Live. I performed my test on #1, which should be the stock tune. My FUELRCALC was 6.37mm3 on average and 15mm3 seems high to me. Here are my results:

 

[davig]

So I did have factory tune so once I loaded these are my new numbers.

Main injection 11mm3
Calculated came out to about 13mm3
Cyl1. 1.4
Cyl2. 0.3
Cyl3. -0.1
Cyl4. -0.8
Cyl5. 0.2
Cyl6. 0.4
Cyl7. -1.8
Cyl8. 0.3

Do these numbers look better?

 

[roder]

I don't have enough experience to give you an a definitive answer, but in this post (although I think some of the author's math is wonky) they talk about high CFR:

Even the high CFR itself, at 11 mm³, is often a sign of something going wrong – it’s common on engines with compression differences of this size, and may be mistaken for a bad injector.

 

[davig]

What's cfr

 

[davig]

Calculated fuel rate?

 

[roder]

Calculated fuel rate?

Correct

 

[2004LB7]

I would not be worried about high (or low) calculated fuel rate unless you had other symptoms. If the engine runs good, gets decent milage, isn't blowing excessive smoke, etc then don't fret it. Same for balance and main rate.

Unless you actually have a problem, then looking at those numbers is not going to do much other then make you think you have a problem.

I would not think 11 mm3 main rate with otherwise good balance is not that big of a deal. Lots of variables can change the rate from baseline. Lower engine or transmission temperature. Torque converter type and age, elevation, dirty air filter, dirty or out of calibration MAF and MAP sensors. Cylinder compression is a big contributor. And maybe even the viscosity and age of the oil can change it a little. Or things like additional resistance on the accessory belt, A/C on, failed bearings in an idler or alternator. Low battery charge can put additional load on alternator that raises the main rate. Little things add up. Unless you actually have an issue then stressing over a small increase in main, or even calculated rate is going to do nothing but make you loose more hair

 

[Chevy1925]

sounds like tips/injectors are plugging up a little. wont hurt to do an injector clean/service on them

 

[2004LB7]

So I did have factory tune so once I loaded these are my new numbers.

Main injection 11mm3
Calculated came out to about 13mm3
Cyl1. 1.4
Cyl2. 0.3
Cyl3. -0.1
Cyl4. -0.8
Cyl5. 0.2
Cyl6. 0.4
Cyl7. -1.8
Cyl8. 0.3

Do these numbers look better?

Main looks fine depending on what I mentioned above.

I think calculated rate is the average of the balance + main rate or something close to that

 

[08lmm72mm]

I've read a low calculated fuel rate could mean injectors are worn out and returning alot of fuel but I'm no expert. Judging from the numbers you posted on yours I'd say they are in good shape.

 

[2004LB7]

I've read a low calculated fuel rate could mean injectors are worn out and returning alot of fuel but I'm no expert. Judging from the numbers you posted on yours I'd say they are in good shape.

Not returning a lot of fuel but leaking it into the cylinder. The ECM detects higher power in one or more cylinders and pulls back fuel to try and compensate. If you get too many leaking or applying too much fuel from worn out nozzles then the ECM pulls fuel from all of the injectors and you end up with a lower calculated / main rate

 

[kidturbo]

Used to think Bal rate was the gospel. But as stated above, if not stock, it's more just a decent guide to possible issues.
I run an emulator tool on crank/cam lines with injector solenoids wired up on LMM in bench setup. My bal rates read +- 0.1 and there is no engine attached. It's all about crank cam coloration and fuzzy math..