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EGT's up for no reason

W

wrgway

Member
I have an RV-7 powered by a Superior IO-360 with 185 hp and a Hartzell constant speed prop.. About a month ago I noticed on take off that my egt readings were about 50 to 60 degrees higher than normal. Old reading was @ 1315 degrees F, 2660RPM, WOT, full rich and 460 ft above sea level. New readings 1365 degrees F with all other factors the same. I don't remember exact fuel flow numbers from original data but fuel flows now read 17.2 gph during above condition. It seems to me that fuel flow should be closer to 18.5. Am I screwing up the BSFC calculations? Pulled all injectors and cleaned both nozzle and restrictor in Hoppe's #9 as recommended and saw absolutely no change. The only change made to the engine from stock was to use Air Flow performance to help in balancing fuel flow to cylinders using 2
(2) .0225 and (2) .023 restrictors. This was done @ 2 years ago long before the change in EGT's. Also pulled fuel filters on fuel line into injection system and before electric fuel pump. Found a few small black specs in electric pump and nothing on FI filter. Talked to my field A&I who opined that all these glass panel ships show way too much info just fly the thing it's probably nothing. Dead end there. Help
 
Has your CHT's typically changed as well?

Have your magneto's been touched lately? Checked the timing?

How old are the spark plugs?

When did you check the gaps and reset them to 0.016-0.018" last?

What brand of plug?

Your fuel flow is on the low side of acceptable, but lets look at the above mentioned first.

DB :)
 
CHT's have been about the same all along. Warmest cylinder runs just shy of 400 on TO then cools down to 330 to 350 in cruise.

Magneto's were checked at annual last Oct. Found left mag to be about 2 degrees retarded. Corrected until both mags were dead on 25 degrees.

Plugs are set to .016-.018 cleaned and tested before installation. I have two sets of plugs, one with @ 250 hours on them and the other with @ 100. No change was seen when swapped the plugs out in December but did note plugs removed looked very sooty. plugs are Champion URM40E I believe.

I'm not sure on small changes in fuel pressure as the gauge reading was erratic but they always seemed to stabilize @ 25 psi and they do the same now with the new sensor.

I forgot to mention in original question that the fuel pressure sensor failed and that was replaced at annual. Failure was a sticking problem where AFS engine monitor would show high fuel pressure after turning on electric pump that could be resolved for a time by rapping sensor. Over time it took longer and longer for pressure to read correctly. Once new sensor was installed all went back to normal. In retrospect this problem showed up last year after the annual inspection but for the life of me I can't see anything that was doen that would cause this issue.
 
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wrgway said:
CHT's have been about the same all along. Warmest cylinder runs just shy of 400 on TO then cools down to 330 to 350 in cruise.

Magneto's were checked at annual last Oct. Found left mag to be about 2 degrees retarded. Corrected until both mags were dead on 25 degrees.

Plugs are set to .016-.018 cleaned and tested before installation. I have two sets of plugs, one with @ 250 hours on them and the other with @ 100. No change was seen when swapped the plugs out in December but did note plugs removed looked very sooty. plugs are Champion URM40E I believe.

I'm not sure on small changes in fuel pressure as the gauge reading was erratic but they always seemed to stabilize @ 25 psi and they do the same now with the new sensor.

I forgot to mention in original question that the fuel pressure sensor failed and that was replaced at annual. Failure was a sticking problem where AFS engine monitor would show high fuel pressure after turning on electric pump that could be resolved for a time by rapping sensor. Over time it took longer and longer for pressure to read correctly. Once new sensor was installed all went back to normal. In retrospect this problem showed up last year after the annual inspection but for the life of me I can't see anything that was doen that would cause this issue.
Click to expand...

Absent any supporting evidence there is a problem, it may be something as simple as the equipment measuring EGT morphing a bit.

There was a time when there were no EGT indicators except maybe on one cylinder on some airplanes. Even today, I don't pay any attention to it during take off as it is somewhat meaningless information during that part of the flight. Engine rpm and MP are prime power indicators and get full attention.

Your A/P makes a good point, too much information can drive you nuts. EGT is the squirreliest bit of information on the panel, especially on take off. I pay no attention to it.
 
Hmmmmmm :cool:

I can't say I agree 100% with Davids post above but lets look at a few things here.

I think you should pay some attention to EGT during takeoff. In fact you should be using a "Target EGT" during climb, and that is based on the typical EGT you get at full rich on a near sea level takeoff.

A slight increase in EGT could be a sign, slightly less fuel flow could be also. I do not think everyone will ever see this happen, but let me tell a short story and you can check this out for yourself. By the way, if it were not for an all cylinder monitor, we would have never known, and by now would have been replacing two clyinders at least.

About 350 hours ago we spotted some higher EGT's but more alarming were the rapidly rising CHT's on a couple of cylinders. You may not be experiencing this, but it does not mean you are not having the same problem. So after much checking and looking and blaming all sorts of things like injector flow rates, which were all perfect, we had a close look at the mixture cable and arm linkage.

What we found was the Mixture cable Vans supplied, was not really long enough. It just reached, and when FULL RICH if there was any force applied to the cable the mounting bracket would flex, and the micture was being cracked back a bit. I do not remember the gap on the end stop but you measured it in millimetres not microns :eek:. With the thrust of the engine pulling forward, and the engine rubbers settling, it was pulling the mixture off the full stop despite the cable being pushed fullying in. :mad:

So I had made a new longer cable, and found an alternate length arm, twisted the bracket, and plenty of cursing......problem long gone.

Now you may not be seing this show up in terms of CHT yet unless the fuel redction is enough to create detonation in a cylinder or two, but it may well be happening. Make sure you can wriggle the cable body around a fair bit without the mixture control arm being pulled off the FR stop.

For any given mixture, Retarded timing increases the egt. And the opposite advancing will reduce it. So go check the timing again, but please check the mixture cable.
 
Sound advice

Thanks for the input. I do check the EGT's on T/O and this is where I'm noting the increase EGT"s across the board on all cylinders. I did look at the mixture cable and it does appear to be on the stop when fully open however I did not jiggle the cable and see if it moved. As the plane is just about at the 300 hour mark I wouldn't be surprised if things are not settling a bit. That will be my first look as soon as the plane comes back from the paint shop where it's getting freshened up for the season. I also adjusted the timing and retarded the left mag about 2 degrees to 25 where the right mag was just about the time this started. Run ups afterward were close for a 4 cylinder difference being about 70 to 80 rpm cold and 40 to 50 warm. I didn't realize the timing could make for changes in EGT's so thanks for that info also. I greatly appreciate the help and will let you know what I find. Thanks again!
 
Have you downloaded the engine logs from the EFIS? If you have a newer "S" cpu you should have almost 50 hours of data to look at.

Send me the data logs and I will review them for you, call me if you need some help.

Rob Hickman
Advanced Flight Systems Inc.
 
Retarding the "combustion event" rises the egt for any given mixture.

If you think about the timing of that event you will see the trend.

Mixture controlled " combustion event" timing is what we do in a fixed spark timing engine. The Peak Pressure Pulse is not only varied in magnitude but also it's timing relative to crank position.

So it is important to consider all inputs to validate the output.

So after a couple of hundred hours.....yep check those cables as mentioned above.
 
Gross advance timing can cause high EGT as well

My LASAR equiped new engine came from Lycoming timed at ~90 deg. BTDC instead of 25. It pegged the EGT Unless I pulled the throttle back (closed direction) to a certain setting. Since I got the LASAR timing box and set it correctly I've never had a problem.

Bob Axsom
 
I think it was a common error at Lycoming with LASAR

The first time I followed Unison's timing instructions I came up with exactly the same setting that Lycoming had. I knew that had to be wrong so I went back and did it again very carefully following the instructions and I found that the instructions were very easy to misinterpret. For instance the use the letters TDC to mean a light on the box and not top dead center of the compression stroke of cylinder #1. The scarry thing was I flew it that way out of Chino across Corona, down the back side if some fairly rugged mountains to my designated test area. I coordinated with everyone on the problem and initially Van's rep. told me that if Lycoming tested it and said it was good you can assume it is OK.

Bob Axsom
 
Data download

Hi Rob,
yes I did download the data before plane left for the paint shop. I'll send it along ASAP and thanks.
Don
 
Pull the EFT probes and check them. Just a guess but I suspect they are at end of life and can give bad temps. I had 2 do this within the same week once upon a time.
 
How would you inspect them? I've installed a couple of sets and replaced a few over the years that stopped working but didn't really notice any change in physical appearance when I pulled them. Is there something specific to look for or are we talking about a resistance or some other electrical measurement that would indicate a faulty part?
Thanks for the input.
Don
 
Thanks for the helping hand here. i finally got the RV back from paint shop. Pulled the cowl and checked mixture cable..no problems. Pulled top plugs and checked timing..holy **** the left mag was @ 2 degrees off. Weird that's about where it was last time before I retimed mags. Retimes again but checked timing after I tightened retaining bolts on the mag…bingo timing was retarded again @ 2 degrees. Retimed a third time placing mag so when tightened it would be at 25 degrees, buttoned up engine and cowl and went flying, problem solved, EGT's back to normal.
I really appreciate the help and I also appreciate this site and all the great information I see being shared every day.
Thanks again,
Don Riggs
 
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