Potential Fuel pump issue

[N350ka]

Hey there everyone! 

I’m having a weird issue with my bravo. I’m having EGT fluctuations that happen in all cylinders at the same time. They first cool down 20-50 degrees then back up 60-70 and back to where they were when I leaned the engine out. This is in level cruse flight without any adjustments to the prop, mixture or throttle. 

 

My suspicion is the engine driven fuel pump. The only other correlated indication I’ve noticed is the fuel PSI gauge which will flicker from it’s normal cruise level of  40psi to 36 or so for just a second. Shortly thereafter the EGTs start their rollercoaster. 

 

Common sense tells us the engine is getting less gas during the rise and falls because of the rise and falls of the EGT and the correlated fuel PSI indication makes me believe the engine driven fuel pump is on its way out. I’ve attached a video of one of the more tame fluctuations I’ve managed to catch on video. 

 

Side note: I’ve had a mechanic check this out and I was told “I’ve never heard of an engine driven pump going out before” they didn’t find anything else relevant. 

 

Any help at all

 is greatly greatly appreciated! 

[FoxMike]

There was an AD note against the fuel pump years ago.  Pump could leak so every so many hours it had to be inspected for signs of fuel stain.  The problem you describe could be a fuel servo that is wearing out or a mixture cable that is worn out.  The end of mixture control that attaches to the fuel servo has a ball which when worn out can cause slight jamming that is overcome by engine vibration.  Sounds like a problem that needs to be solved.

[kortopates]

Video links wouldn't work for me, but I wouldn't expect to get anything useful from them. What would be really helpful though is to download your engine monitor data, preferably with a 1 sec data recording rate or sampling rate, and see what the data shows. More specifically, what is leading what. For example, is the FF changes alone triggering the events that EGT follows or could it be MAP, or even RPM fluctuations, that has accompanying FF fluctuations that are followed by EGT fluctuations. You may also need to fly the Savvy Test profile to provide the diagnostic data to enable separating mixture from ignition issues as well. http://content.savvyanalysis.com/static/pdf/SavvyAnalysisFlightTestProfiles.pdf  You're probably not going to get much diagnostic value out of a video. But your mechanic is right that its unlikely to be your fuel pump. See where the data takes you.

Edited May 21, 2018 by kortopates

[N350ka]

Thanks for the advice guys! This may or may not be related but over the last few months hot starts have become almost literally impossible. I happened to stop at my mechanics airport this morning so I’m going to see what they can find.

[LANCECASPER]

If it is spark related, new Fine wire spark plugs and a new ignition harness may help with hot starts.

[Rick Junkin]

On 5/20/2018 at 6:29 PM, N350ka said:

Hey there everyone! 

I’m having a weird issue with my bravo. I’m having EGT fluctuations that happen in all cylinders at the same time. They first cool down 20-50 degrees then back up 60-70 and back to where they were when I leaned the engine out. This is in level cruse flight without any adjustments to the prop, mixture or throttle

Where in the flight is this happening? Initial cruise? After an hour of cruise? Lean of peak or rich of peak? Are you doing anything different from before this started happening? 

Your fuel flow fluctuations sound similar to something I was seeing with my airplane right after level-off and going to lean of peak for cruise, when I was first learning to operate LOP. I would get an intermittent drop in fuel pressure and momentary change in EGTs. I thought I had a fuel pump problem, too. But I was going to LOP too quickly after climb, and was percolating the fuel due to the engine temperatures from the climb and the reduced fuel flow. Leaving the mixture full rich for about 5 minutes after leveling off to allow everything to cool before the BMP (big mixture pull, if you aren't a Mike Busch devotee) to LOP cured my problem. Shoutout to @Awful_Charlie for the recommendation on technique.

I hope that's helpful!

Video link didn't work for me either.

Cheers,
Rick

[carusoam]

50KA,

For more views of the video... consider posting the video in YouTube, and then copy the link here...

About half of your audience is reading on an iPad...  Steve Jobs didn’t want us to view your video...

Best regards,

-a-

[Awful_Charlie]

Rick shouted

I've had the odd fuel pressure indication fluctuation, but normally only after levelling off in the climb - I don't get a misfire with it in flight however. It did get slightly worse as the engine got well past TBO though, to the point that taxiing with a hot engine, in high temperatures and with low fuel tank levels at low RPM that the electric pump needed the odd blip to maintain even running.

From the symptoms, I also had a suspicion that the engine fuel pump might have been struggling, but then went for a factory rebuild at nearly 2200 hours (all being well, get the aircraft back tomorrow!), but even then, a change will not be conclusive on the pump.

My theory (which is of course subject to many opinions) is that in the climb, you are pulling 20+ GPH through the fuel pump which gives quite a considerable cooling, The airflow is relatively low, so the back of the engine, accessory housing (where the fuel pump is bolted to) is relatively hot. At top of climb, when you then reduce power, the heat is still gradually dissipating, and if you pull the fuel flow back promptly, then the fuel cooling is substantially reduced (for me, to about half the climb burn). Hot engine (fuel pump), less fuel cooling and the fuel vaporizes on the suction side of the pump, and there is not enough time/cool bits to condense it again before it gets to the injector, hence to odd blip in pressure.

SOP for me is at TOC (as the trim is winding in) to close the cowl flaps (to reduce the shock cooling, which may or may not be an OWT - your engine, you choose!) and then wait for the cooling rate on the JPI to reduce to less than 10dF/minute. This takes a minute or three during which time the back of the engine is getting a higher airflow, and the heat in the fuel pump (and the bits that feed heat to it) has reduced, aided with continuing with the high fuel flow. When the cooling rate has slowed, I then go to change the power & lean, and this work ok for me.

Some things to consider:
In the FLs, the air out of the injector assembly can easily exceed 60dC and this is heating up the fuel that passes through it  - some components of avgas can start boiling at as little as 40dC.
The engine pump is normally higher than the fuel level, so it is sucking fuel making vaporization more likely, compared with the electric pump, which will normally be below the level of fuel, hence it normally has positive pressure on its inlet.

[N350ka]

hey everyone, 

sorry fir the issue with the video. Here is a re-upload of it! 

this is one of the more mild times it happened however it comes unannounced and its hard to catch. I had to sit there with my phone ready for this for about 7 minutes to catch this one! 

Edited May 22, 2018 by N350ka

[N350ka]

On 5/20/2018 at 8:27 PM, FoxMike said:

There was an AD note against the fuel pump years ago.  Pump could leak so every so many hours it had to be inspected for signs of fuel stain.  The problem you describe could be a fuel servo that is wearing out or a mixture cable that is worn out.  The end of mixture control that attaches to the fuel servo has a ball which when worn out can cause slight jamming that is overcome by engine vibration.  Sounds like a problem that needs to be solved.

I had my mechanic take a look and they think y'all are correct about the fuel servo, 

 

2 hours ago, Awful_Charlie said:

Rick shouted

I've had the odd fuel pressure indication fluctuation, but normally only after levelling off in the climb - I don't get a misfire with it in flight however. It did get slightly worse as the engine got well past TBO though, to the point that taxiing with a hot engine, in high temperatures and with low fuel tank levels at low RPM that the electric pump needed the odd blip to maintain even running.

From the symptoms, I also had a suspicion that the engine fuel pump might have been struggling, but then went for a factory rebuild at nearly 2200 hours (all being well, get the aircraft back tomorrow!), but even then, a change will not be conclusive on the pump.

My theory (which is of course subject to many opinions) is that in the climb, you are pulling 20+ GPH through the fuel pump which gives quite a considerable cooling, The airflow is relatively low, so the back of the engine, accessory housing (where the fuel pump is bolted to) is relatively hot. At top of climb, when you then reduce power, the heat is still gradually dissipating, and if you pull the fuel flow back promptly, then the fuel cooling is substantially reduced (for me, to about half the climb burn). Hot engine (fuel pump), less fuel cooling and the fuel vaporizes on the suction side of the pump, and there is not enough time/cool bits to condense it again before it gets to the injector, hence to odd blip in pressure.

SOP for me is at TOC (as the trim is winding in) to close the cowl flaps (to reduce the shock cooling, which may or may not be an OWT - your engine, you choose!) and then wait for the cooling rate on the JPI to reduce to less than 10dF/minute. This takes a minute or three during which time the back of the engine is getting a higher airflow, and the heat in the fuel pump (and the bits that feed heat to it) has reduced, aided with continuing with the high fuel flow. When the cooling rate has slowed, I then go to change the power & lean, and this work ok for me.

Some things to consider:
In the FLs, the air out of the injector assembly can easily exceed 60dC and this is heating up the fuel that passes through it  - some components of avgas can start boiling at as little as 40dC.
The engine pump is normally higher than the fuel level, so it is sucking fuel making vaporization more likely, compared with the electric pump, which will normally be below the level of fuel, hence it normally has positive pressure on its inlet.

Most of the time when I experience this its in level cruse flight after having been trimmed out for awhile. However I believe what youre describing is something I hav e experienced before, they are prone to these types of issues 

 

11 hours ago, Junkman said:

Where in the flight is this happening? Initial cruise? After an hour of cruise? Lean of peak or rich of peak? Are you doing anything different from before this started happening? 

Your fuel flow fluctuations sound similar to something I was seeing with my airplane right after level-off and going to lean of peak for cruise, when I was first learning to operate LOP. I would get an intermittent drop in fuel pressure and momentary change in EGTs. I thought I had a fuel pump problem, too. But I was going to LOP too quickly after climb, and was percolating the fuel due to the engine temperatures from the climb and the reduced fuel flow. Leaving the mixture full rich for about 5 minutes after leveling off to allow everything to cool before the BMP (big mixture pull, if you aren't a Mike Busch devotee) to LOP cured my problem. Shoutout to @Awful_Charlie for the recommendation on technique.

I hope that's helpful!

Video link didn't work for me either.

Cheers,
Rick

Level cruise flight is the only time I notice it, it seems to be well into the cruise never right after leaning.  I run 20 degrees rich of peak typically. ( I try to keep the TIT's below 1600 and the CHTs below 400 at all times!) I noticed this in the last few long cross country flights ive been doing. Nothing in my procedures or techniques have changed recently.

 

21 hours ago, LANCECASPER said:

If it is spark related, new Fine wire spark plugs and a new ignition harness may help with hot starts.

I wish I knew what to do about those! the last few months hot starts have literally become impossible. ive tried everything under the sun to get it going but it never works. I have fine wire plugs less than a year old, not sure about the ignition harness though. 

 

sorry for the late reply everyone and the video! I have a few more trips this week and it goes in for annual at the end of the month so that should identify some for these gremlins. 

[carusoam]

Thanks for reposting the video 50KA...

 

generic ideas regarding pumps and fuel pressure....

The fuel pump generates flow of the fuel...

Pressure is generated by a restriction to the flow, downstream...

So...

For pressure to drop, it could be the pump misbehaving... not providing the same flow... or a flow restrictor to not restrict as much...

A few diaphragms may be asking to be replaced?  A pressure regulator for the fuel divider?

Other things to look for are indications that FF is changing or EGTs are changing in sympathy with the change of FP...

Also Check for fuel leaks at each pump drain or system drain if they have one...

Fuel screens can get clogged, but they usually don’t unclog...

 

Who would be a good resource for the Bravo Fuel system OH?  There might be a website with ideas of how to decide if OH is a good idea...

 

PP logic only, not familiar with the Bravo fuel system...

Best regards,

-a-

[LANCECASPER]

2 hours ago, N350ka said:

I wish I knew what to do about those! the last few months hot starts have literally become impossible. ive tried everything under the sun to get it going but it never works. I have fine wire plugs less than a year old, not sure about the ignition harness though. 

I have an M20M and recently bought a Champion Slick Start to install which is supposed to help a lot with hot starts. I just need to get it on there as summer is here in TX.

 

[Danb]

Make sure the timing is spot on.

[N350ka]

1 hour ago, LANCECASPER said:

I have an M20M and recently bought a Champion Slick Start to install which is supposed to help a lot with hot starts. I just need to get it on there as summer is here in TX.

 

Are those known to help significantly? Trust me I’ve read that thread many times whilst sitting in the plane trying to fire it up almost killing both batteries. 

[N350ka]

3 hours ago, carusoam said:

Thanks for reposting the video 50KA...

 

generic ideas regarding pumps and fuel pressure....

The fuel pump generates flow of the fuel...

Pressure is generated by a restriction to the flow, downstream...

So...

For pressure to drop, it could be the pump misbehaving... not providing the same flow... or a flow restrictor to not restrict as much...

A few diaphragms may be asking to be replaced?  A pressure regulator for the fuel divider?

Other things to look for are indications that FF is changing or EGTs are changing in sympathy with the change of FP...

Also Check for fuel leaks at each pump drain or system drain if they have one...

Fuel screens can get clogged, but they usually don’t unclog...

 

Who would be a good resource for the Bravo Fuel system OH?  There might be a website with ideas of how to decide if OH is a good idea...

 

PP logic only, not familiar with the Bravo fuel system...

Best regards,

-a-

When I first had the issue I stopped immediately and had some mechanics look at it. They suspected a fuel leak and checked everything they could without being too invasive on the fuel system. (Pressure checked the lines, checked the tanks for contaminants, dropped the belly and checked the screen and gascolator) couldn’t find a thing and they basically told me “good luck” I’m going to make a point of having the fuel system thoroughly checked at annual (annual is at the end of the month) 

[kortopates]

On 5/22/2018 at 7:21 AM, N350ka said:

hey everyone, 

sorry fir the issue with the video. Here is a re-upload of it! 

This is one of the more mild times it happened however it comes unannounced and its hard to catch. I had to sit there with my phone ready for this for about 7 minutes to catch this one! ....

That sure looks like a common case of vapor lock that should be easily suppressed with turning on the aux fuel pump per your POH to stabilize fuel pressure. As soon as it stabilizes, you may turn off the aux pump but that would be the first step too see if indeed its vapor lock. 

The higher you go in altitude the more susceptible the fuel system is to vapor lock and the more volatile the symptoms are. Some of the more modern POH's including the Acclaim call for the (aux) boost pump to be tuned on in climb above 12K and in cruise at or above 18K'. But warns us it can happen anytime lower and to use the boost pump whenever it happens.

The M20M POH, for whatever reasons is very lacking in details but does address this in a note in the Normal procedures for Cruise that the boost pump may need to be turned on for this and also in the emergency procedures under vapor suppression to use the boost pump to clear and cool the fuel system.

Let us know it that clears it up, since most likely that's all this is. Its actually quite common in our turbo charged aircraft.