O-360 RayJay Turbo Issue

[MarkM20C]

Hello Guys, I have a 1965 M20C with a Rajay Turbo. Turbo installed in 1966, not that that means anything.  My issue that has cropped up is when dialing in boost, EGT's for both rear cylinders increase quite a bit above fronts. I can run 24/2400 all day long low and normally aspirated.  I would even lean a bit to get EGT's around 1300-1350, with all EGT's being within 50 degrees F of each other.  But if I try to run 24/2400 up high, even full rich, both rear cylinder EGT's climb over 1450, and I have to back off boost to get them to come down.  Front cylinders close to 150-200 degrees cooler.  I don't see any air leaks in intakes tubes. Reference line from air box to fuel pump is good, no leaks.  I do think my fuel pressure at altitude under boost used to be higher, so I am wondering if that's the issue.  I remember my fuel pressure gauge would go red at altitude under boost, previous owner said his mechanic said that was normal due to something with the fuel gauge.  I now understand why, the fuel gauge is not referenced to boost pressure, just atmospheric pressure, so reading is off at altitude under boost.  Just looking for Ideas at this point, I am an A&P, but have haven't been working on planes or flying for 24 years, just getting back into it.  My fuel pump was repaired 4 years ago (around 200 hours ago), not sure what issue was at that time.  I called the shop that repaired the pump and spoke to the tech, he seemed to think diaphragm in pump was probably bad, so pump not compensating for boost pressure properly.  Any ideas?  Kind of a bummer to have turbo but not be able to take advantage of it.  Flew it to 9000 feet yesterday and fuel pressure did go up as I climbed, gauge was reading just under 8 psi at 9000 feet, 24/2400.  Seems like that should be enough, is around 6.5 psi when low and N/A.

Thanks, Mark

Edited March 6, 2020 by MarkM20C
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[N201MKTurbo]

That looks like a timing or fouling issue, have you cycled your mags when this happens? Have you checked your timing?

[carusoam]

Mark,

Got any JPI or engine monitor to go with that?

Are your EGTs matching the CHTs?

Are you familiar with posting JPI data if you have it..?

 

We have a Rajay guy around here if you think the turbo is related to the issue...

Best regards,

-a-

[MarkM20C]

Timing is good, both at 25 BTDC.  Mag drop both 75ish RPM's.  I do have an engine monitor that records on USB stick, not sure how to post it.  CHT's are all good, I don't let rear cylinder EGT's run hot long enough for CHT's to increase.  Just completed annual and all plugs looked good, but since problem is only at altitude under boost, plugs could clean up on decent when boost removed. I think the turbo is working fine, no problem in boosting, but for some reason rear cylinders are leaner then fronts, only under boost.  Possibly carburetor issue?  I'm not sure what modifications are done to carburetor when rayjay installed.  

Mark

[carusoam]

Mark...

Find the Savvy website...this is the place to go to post the JPI data...

you will have to agree to share the data...

Then post the link here...

This allows all of us to see your data and make recommendations that apply...

otherwise, you get so many recommendations that are plausible... generating a bit of excess work for you...

The JPI website has a fare amount of details for getting your data onto the USB stick, then onto a PC...

Its a few steps... all worthwhile...

Why the turbo would be able to change the fuel distribution in the carburetor is interesting... one part pressure, one part air speed, one part fuel droplets....

It would be great to see what you have...
 

There are only a few people with a RayJay on their O360s... you may want to adjust your title to try and attract their attention...

 

It sounds like fuel and air distribution before, through, and after the carb may be an issue... that IO360s just don’t have...

PP thoughts only...

Best regards,

-a-

[MarkM20C]

Thanks guy, I'll see if i can get some engine data posted. Any ideas on a good title to attract other O360 RayJay people?

Mark.

[carusoam]

Put the word O360 in the title...   

There is an edit button that only you as the OP will be able to see...

Best regards,

-a-

[Oldguy]

Would @tomgo2 have any thoughts on this issue?

He might have some info on Ray Jay turbos...

[Prior owner]

I would really like to know what limits Rajay put out for EGT’s with that STC. Are you really that close to the max EGT limit at 1450 F?

[N201MKTurbo]

You should really have a TIT gauge. The EGTs aren’t as important. If your TIT gets too high it will melt your turbine wheel.

[Chessieretriever]

I used to fly a M20C with a Rajay and my guess is that the line from your manifold to your carburetor bowl so that your carburetor (fuel level in the bowl) references the pressure in the intake tract (above atmospheric) may be leaking a little allowing the bowl pressure to lower than what it needs. The same thing would happen if your carburetor is leaking (air now for this pressurization event) at the seam where the unit comes apart (there is a gasket there that may be compromised). The Rajay is a blow-through system which needs the top of the fuel level in the bowl inside the carb to be at a pressure that is higher than atmospheric when your turbo is operating (with a manifold higher than the then current atmospheric one); it appears that you may be stratifying your mixture. Ironically I remember that my little C would actually fly LOP when the turbo was working but not down low without it; I always attributed that to having warm air from the compressor discharge which helped with the atomization. Why you have a front and back difference could be a could be something else (like ignition) that is unable to work as designed with a mixture that weak and therefore hard to fire. Worth the look. Good luck with it.

[MarkM20C]

Chessieretriever that makes the most sense to me.  I know the fuel in the float bowl needs to be referenced to boost pressure and I was wondering how that happens.  I didn't see an external line though, I will have to take a closer look at the carburetor and the installation instructions.  I was just figuring the float bowl vent was somehow internal and was referenced that way.  Or maybe there is a gasket compromised?

Thanks! Gives me more to check.

Mark

[carusoam]

Thanks John,

@tomgo2 is our RayJay turbo guy (note for my memory improvement)

He can be pretty helpful with some install details.

+1 for having a TIT instrument... EGTs average a lower number than the combined flows into the Turbo... the TIT will be significantly higher than any single EGT.  Knowing your TIT limit will keep you from melting the blade tips off... an expensive maintenance snafu...

+1 for having a good engine monitor... with an O360 knowing the carb temp would be extra sweet icing(?) on the cake...

PP thoughts only, not a mechanic...

Best regards,

-a-

[tomgo2]

@carusoam, thanks for touching base with me.

@MarkM20C - The fuel pressure gauge should also be reading properly at the higher altitudes. There is a boost reference line from the airbox assembly to the fuel pressure gauge.  It's not a clear picture but I highlighted in yellow for you. Also keep in mind that the fuel pumps are unique to RAJAY.  Most shops don't know what that is.  RAJAY offers fuel pump overhauls working in conjunction with Tempest.  

We also find many times the carburetor is replaced with a non-RAJAY version.  This too is unique for RAJAY.  If you don't know was done last, you may want to check that out.  The carburetor is supposed to be sealed using bushings and gaskets.

 

[MarkM20C]

Mine doesn't have the automotive style fuel pump, it has the gear driven pump RG15980-P, which is correct and referenced to air box for boost compensation. I have an electronic fuel pressure gauge, which isn't referenced to boost pressure, which is why it doesn't read properly under boost at altitude.  The thing is, 3 months ago I didn't have this problem, and no components have been replaced, so something has happened. I'm leaning towards a carburetor issue at this point. 

Mark

[MarkM20C]

Just an update. I had the carburetor overhauled by Marvel Schebler and now all is well. Flew yesterday to 9500, ran it at 25/2500 and had to lean to get get proper mixture.  Was getting just under 150 knots at 25/2500 approx. 12.5 gal/hr. I wouldn't normally run it that hard but nice to see I can. Before carb overhaul it just didn't have enough fuel to keep the EGT's where I want them and I would have to pull back manifold pressure. Eventually I'll take it high enough to really test it out. I have a brand new oxygen system I haven't used yet! 

[carusoam]

Sounds like slow and steady progress towards having the fastest M20C on and off the planet!

Great pirep Mark!

Make sure Your O2 system is up to snuff... back-up, and O2 measuring finger tool as well...

Best regards,

-a-

 

[M20F]

I would try 20 degrees instead of 25. 

[cliffy]

On 6/3/2021 at 4:08 PM, MarkM20C said:

Just an update. I had the carburetor overhauled by Marvel Schebler and now all is well. Flew yesterday to 9500, ran it at 25/2500 and had to lean to get get proper mixture.  Was getting just under 150 knots at 25/2500 approx. 12.5 gal/hr. I wouldn't normally run it that hard but nice to see I can. Before carb overhaul it just didn't have enough fuel to keep the EGT's where I want them and I would have to pull back manifold pressure. Eventually I'll take it high enough to really test it out. I have a brand new oxygen system I haven't used yet! 

Just as a reference for you I'm getting 136-140 kts TAS at 9500 (depends on DA) with my NA M20D  at 9.5 GPH and max MP and

2500 RPM    I'm done climbing realistically at about 12-13,000' for all practical purposes in the summer. It would be nice to go to the mid teens in the summer for cruise. 

Its nice to find a fix for a problem