Injector Swapping Process?

[kmyfm20s]

I have read a lot of post on the forums that mention swapping fuel injectors to help with EGT and GAMI spreads.  I have not seen an overview of the process from ground zero.  As I have read some of the threads it seems as simple as swapping the high EGT injector with the low EGT injector. As I read more it seems like there are contributing factors to EGT discrepencies such as induction leaks, probe placement, spark plugs and fine wire spark plug cables.

I asking this because my plane is going in for its annual and would like idea of what questions to ask before having them swap injectors or if I need to at all. I have a 82 J with a EDM 700, FT 101 fuel flow indicator and GAMI injectors. My FT101 appears to be almost .5 GPH off indicating a higher fuel burn but I have a few result of flights I can share.

 

Flight #1

5500 MSL, 24" MP, 2400 RPM, 9.4 GPH LOP. #1 1421 356, #2 1407 321, #3 1360 308, #4 1425 333

 

Flght #2

7500 MSL, WOT 22.5"MP 2500 RPM, 9.5 GPH LOP, #1 1417 352, #2 1408 326, #3 1348 290, #4 1447 343

 

The best I can tell so far my GAMI spread is between .2-.5, I'm still playing with it but my feeling is .3, but is that possible wth almost 90 degree difference in EGT's. The order in which the cylinders peak is #2,#3,#1,#4

 

After I get the EGT's figured out I'm going after the CHT's

 

Any advice is appreciated.

[N601RX]

The absolute temperatures you posted above are not the ones you want to use when balancing the injectors.  You need to know how for each one is away from peak and balance them so they all peak at the same fuel flow.  Be sure they are all completely clean before starting to move them around.  Hoppe's 9 gun cleaner is the best thing I have found for cleaning.

[kmyfm20s]

The absolute temperatures you posted above are not the ones you want to use when balancing the injectors.  You need to know how for each one is away from peak and balance them so they all peak at the same fuel flow.  Be sure they are all completely clean before starting to move them around.  Hoppe's 9 gun cleaner is the best thing I have found for cleaning.

Luckily I took video to refer back to. I am still learning the LOP operation of the EDM 700. The read out goes in this order cylinder #2 leanest, -11 degrees, #3 -13 degrees,#1 -27 degrees, #4 Richest. After reading the manual is appears the difference between the leanest and richest is 51 degrees. Assuming they are clean would I just swap #2 with #4? or is 51 difference OK? I am having a little bit of trouble with the GAMI spread since the fuel flow is not integradted with the EDM 700. The FT101 is a little jumpy at the rate of leaning per the EDM manual.

[bnicolette]

The GAMI Spread is calculated by determining at what total engine fuel flow each cylinder reaches peak exhaust gas temperature (EGT) and subtracting the lowest flow from the highest flow. Most engines are considered to have good fuel/air ratio balance if the GAMI Spread is less than 0.5 gph.

 

  Fuel flow when the first cylinder peaks 

- Fuel flow when the last cylinder peaks

_________________________________________

= GAMI spread

[kmyfm20s]

The GAMI Spread is calculated by determining at what total engine fuel flow each cylinder reaches peak exhaust gas temperature (EGT) and subtracting the lowest flow from the highest flow. Most engines are considered to have good fuel/air ratio balance if the GAMI Spread is less than 0.5 gph.

 

  Fuel flow when the first cylinder peaks 

- Fuel flow when the last cylinder peaks

_________________________________________

= GAMI spread

 

Thank you, I did calculate it that manner but my Engine monitor and fuel flow indicator are seperate so it is not as precise as the integrated ones.  I am .5 max but pretty confident I am in the .2-.3 area. So it sounds like I am good with the GAMI spread. Should I be concerenred with the absolute temperature spread of the final EGT's?

[N601RX]

@-11, #2 would be the richest.

[kmyfm20s]

@-11, #2 would be the richest.

I was in the LOP mode not the ROP mode of the EDM 700. From my understanding of the manual in the LOP mode when the first cylinder hits peak EGT the graph invert and the leanest cylinder show first then as each additional cylinders peak it is also indicated on the graph in an inverted manner. So as the #2 hit peak it flashes leaneast then as I cont to lean it indicates the difference in temp of the last cylinders peak EGT as each additional cylinder hits peak. Opposite of the ROP mode which is more familar. For example I think my peak EGT on cylinder #2 was 1488 so subtract -11 from that and you have the peak EGT of #3 1477 subtract -13 for #1 1464 and subtract -27 you get #4 1437. I still learning the EDM 700 but I believe this is correct.

[bradp]

I had swapped fuel injectors last year a couple of times until I was very happy with the gami "spread".  Had dirty stuff in the injectors at this year's annual.   So we took them off and sonicated them in cleaning solvent for a few hours and they got much, much cleaner.  Unfortunately have to go back to square one and re-measure and will re order the fuel injectors tomorrow.   The procedure for figuring out the gami spread is as described above and pretty straight forward.  I really like the video idea, and may try it tomorrow.  I guess I could just download the data, too.

 

Remember that engine RPM is also linked to fuel flow and, indirectly, mixture, so make sure that RPM is at least in keeping with what you plan to cruise at.  Are you getting any engine roughness with 24/2400 configuration?  I've found that my engine seems to really like 25/2500 for LOP operations.  Running the engine too "fast" can halt your attempts at LOP pretty quickly, and pulling the RPMs back too much seems to shorten my nice buffer zone between appropriate LOP and the onset of engine roughness.  

 

Have fun with it... my fuel savings in a single year of flying LOP has already paid for the EDM almost twice over.  :-)

 

Brad

[jetdriven]

Do the GAMI spread above 4000 feet and at WOT.  Get the engine slightly ROP, and write down all 4 EGT values. Lean .2 GPH, allow it to stabilize for 10-20 seconds, write down all 4 EGT values again, repeat until all EGTs are falling.

 

As Brett stated earlier, the difference in FF between the first cylinder to peak and the last is your GAMI spread.

 

Interesting note. Our new A3B6 engine will not run well LOP, and after 4 rounds of injector swapping, including to a whole new set, it still is very poor.  Anyone else had this problem?

[Marauder]

Byron - was anything done with your fuel divider during the overhaul?

[kmyfm20s]

I had swapped fuel injectors last year a couple of times until I was very happy with the gami "spread".  Had dirty stuff in the injectors at this year's annual.   So we took them off and sonicated them in cleaning solvent for a few hours and they got much, much cleaner.  Unfortunately have to go back to square one and re-measure and will re order the fuel injectors tomorrow.   The procedure for figuring out the gami spread is as described above and pretty straight forward.  I really like the video idea, and may try it tomorrow.  I guess I could just download the data, too.

 

Remember that engine RPM is also linked to fuel flow and, indirectly, mixture, so make sure that RPM is at least in keeping with what you plan to cruise at.  Are you getting any engine roughness with 24/2400 configuration?  I've found that my engine seems to really like 25/2500 for LOP operations.  Running the engine too "fast" can halt your attempts at LOP pretty quickly, and pulling the RPMs back too much seems to shorten my nice buffer zone between appropriate LOP and the onset of engine roughness.  

 

Have fun with it... my fuel savings in a single year of flying LOP has already paid for the EDM almost twice over.  :-)

 

Brad

It ran really smooth at 24"/2400, I was at WOT/2500 which I felt was best speed vs economy but I did not write down the data. I think everything is pretty in line with my injectors because I don't experience any ruffness but just a constant loss of power like I'm putting the engine to sleep.

[jetdriven]

Byron - was anything done with your fuel divider during the overhaul?

The new engine included an OH flow divider and a new Precision RSA-5 fuel injection system. I think the flow divider is interfering with the fuel flow. Changing one injector for another one totally changes the entire distribution to the injectors, including the order in which they peak.

[kmyfm20s]

Do the GAMI spread above 4000 feet and at WOT.  Get the engine slightly ROP, and write down all 4 EGT values. Lean .2 GPH, allow it to stabilize for 10-20 seconds, write down all 4 EGT values again, repeat until all EGTs are falling.

 

As Brett stated earlier, the difference in FF between the first cylinder to peak and the last is your GAMI spread.

 

Interesting note. Our new A3B6 engine will not run well LOP, and after 4 rounds of injector swapping, including to a whole new set, it still is very poor.  Anyone else had this problem?

I will go up tomorrow and determine GAMI spread in the ROP mode and do as you suggested. Bummer about the new engines LOP operation.

[larryb]

I have a gami spread of about 0.5 gph. I peak 3,4,2,1 with 3,4 and 1,2 very close together. I swapped injectors and wound up with a 0.8 gph spread. I quickly put them back. I seems smooth enough lop although I would like a tighter spread. Io360 in an 84 j.

[N177MC]

jetdriven - You might try checking fuel flow without the injectors - II know of cases where an injector line had a very small defect that threw the flow off.

 

Just remove all 4 (or 6) injectors, put the open end of the inj. lines in graduated cups then place WOT and full rich, put electric fuel pump on and run for about 30" or whatever works without over filling the recipients.

 

You are looking for variations between cylinders , not absolute qty.

 

Hope this helps .

[danb35]

Should I be concerenred with the absolute temperature spread of the final EGT's?

Since I didn't see an answer to this: no.  Absolute EGT values are all but meaningless, and EGT spread is entirely meaningless.

[N601RX]

I had been told before that the spider affected fuel flow at idle to each individual cylinder, but a higher flows it just opened up and the diameter of the hole in the injector took over.

[Cruiser]

Yes, at cruise speed, the restrictor in the injector controls the flow. These are what GAMI change to balance the flow. 

The injector and the restrictor are supposed to matched for flow but "in spec" can vary enough to be noticed LOP.

It is not necessary to remove the entire injector when swapping them around, you could just disconnect the fuel line and remove the restrictors and swap them. Leave the nozzle in the cylinder. 

[smccray]

Do the GAMI spread above 4000 feet and at WOT.  Get the engine slightly ROP, and write down all 4 EGT values. Lean .2 GPH, allow it to stabilize for 10-20 seconds, write down all 4 EGT values again, repeat until all EGTs are falling.

 

As Brett stated earlier, the difference in FF between the first cylinder to peak and the last is your GAMI spread.

 

Interesting note. Our new A3B6 engine will not run well LOP, and after 4 rounds of injector swapping, including to a whole new set, it still is very poor.  Anyone else had this problem?

 

My A3B6 won't run LOP.  1, 2, and 4 are all pretty close, but #3 is way off.  I haven't done a lot of investigation on it- I need to get it setup to run LOP but I haven't gotten that done yet.

[pinerunner]

No you should not be very concerned about the absolute value of the EGTs. Busch and/or Deakins (I forget  which) had a whole article on it. With the GAMI spread you're reporting it sounds like you're in great shape for LOP if you want and your ROP operations will be better for having them closely matched as well. 

[David Brown]

The GAMI Spread is calculated by determining at what total engine fuel flow each cylinder reaches peak exhaust gas temperature (EGT) and subtracting the lowest flow from the highest flow. Most engines are considered to have good fuel/air ratio balance if the GAMI Spread is less than 0.5 gph.

 

  Fuel flow when the first cylinder peaks 

- Fuel flow when the last cylinder peaks

_________________________________________

= GAMI spread

 

Correct. And if it is a 4 cylinder engine aim for a bit lower if you can get it in my experience.

 

DO NOT go monkeying with your injectors. Chances are they all flow the same anyway. This is the problem. If the injector flows are all the same and the mass airflow is different in each cylinder, you have an imbalance in the F/A ratios among the various cylinders. You can't fix the air flow (except fixing leaks) but you can easily adjust the flows. And this is why GAMI do what they do.

 

Go to here > http://www.gami.com/gamijectors/leantest.php and print this page off, and look at the pictures (click to enlarge) and learn the process.

 

Next step would be sign up for the next APS class.

 

 

 

 

It is not necessary to remove the entire injector when swapping them around, you could just disconnect the fuel line and remove the restrictors and swap them. Leave the nozzle in the cylinder.

Not with GAMIjectors please!  Shouldn't your A&P be doing this?