2.5 260 EGT when backing off the throttle

[Markus]

Finally got my 2.5 260 to run good. A set of rebuilt injectors did it.

EGT at WOT is a tad below 1200 at WOT (7300 - 7800 rpm depending on prop), but when I back off the throttle after a WOT run, I see EGT way above 1300 at 5000-6000 rpm. Is that normal?

The absolute temperatures may not be reliable due to gauge calibration issues, but is it normal for the EGT to increase?

[stvhelm]

the Brucato PCU takes care of that problem.

[Markus]

So it is not unique to my engine then?

[Russ]

What is the source of his problem, and how will the PCU correct this? Thanks - Russ.

[Superdave]

From the reviews and reading I think most guys want to shoot fuel into the engine after a WFO run ti cool the cyls. I'm sure the PCU can be programmed to do this. Not sure how the carb guys do it.
Dave

[Rickracer]

OMC even had a vacuum diaphragm - solenoid set up to do it automatically on some of the V-8s. :cool:

[Markus]

I do it with the "choke" too since I have an analog ECU. But is it normal and do I need to press the choke?

[espen]

On the PCU I think you can get away with using very rich mixtures at the load,vacum point/rpm you go to when the trottle are shut after a WOT period at high rpm ,lets say you manage to get a low pressure shutting the trottle ,in this aria you will never drive the boat therefor will the setting not effect the mixture other than on cost down, same could be done on the Merc unit if
someone had the software to do it .
It could also be that you are measuring the flames at this point because the low cyl filling could need more advance on the timing to be burned to give hp... I tryed that on a car ,had lot of advance on the low pressure /high rpm points and there was almost no break on the engine on cost down...strange feeling and the rpm would go much slower down for a smooth gear shift
Espen

[Markus]

Yep. It could sure be flames.

[capnzee]

Try backing off the throttle and selecting an rpm range just below 5000 rpm or a tad above 6000 rpm (hot range) and watch your EGT. I have a "hot' range when backing out of the throttle so I simply stay on one sided or the other of the hot range. I never thought of squirting the enrichment valve, but I certainly will try that next spring! CapnZee

[sosmerc]

On my Analog-equipped 2.5 I also noticed the egt climbing higher as I slowly "backed down" from a full throttle pass. It's a bit un-nerving thinking you are "frying" things at that point. Sometimes I would quickly push the rpm's back up and as soon as I saw the EGT starting to come down I would quickly drop back to 4000. But I also know that my 1987 220 Laser ECU calibration was pretty lean between 5-5700 and I made a point of not spending much time there. It's my understanding that the PCU does some additional enrichment if you back out quickly from wide open...if so, that's a neat feature. I believe it also does a little extra enrichment on the way up also if it detects rapid throttle movement. Still waiting with eager eyes for the PCU Part #2 evaluation. I guess Santa is waiting until Christmas!

[Markus]

Seems like I am not alone, then.

Will investigate the issue further next season.

[stvhelm]

The pcu is equipped with a decelleration compensation feature. what it does is , It allows you to adjust how much richer you want the fuel mixture when you start to get off the throttle. It will keep the EGT down when you slow down where as the merc box will go lean when you pull off the throttle. I had the same problem with my merc box and sometimes I found my self cutting the throttle to quick to get the egt down and getting out of shape. The pcu lets me slow down much safer from high speed runs.

[capnzee]

I understand the PCU costs around 1000 bucks, there must be a less expensive way to go! For that money, I'll control the EGT manually. Capnzee

[Markus]

Well, the least expensive way is to push the choke button like I do. (With an analog ECU) Somewhat more expensive is this ECU, but you are supposed to send cash stuck between color magazine pages.

http://www.x-dsl.hu/genboard/

It is based on the Megasquirt ECU project. Someone in Hungary is building finished ECUs.

[Russ]

I see what your saying, this decel comp feature must be a seperate routine from the basic fuel map in the PCU's system.

capnzee - a less expensive method to possibly ward off the effects in leaning tendency would be to change the ECU vacume pickup orifice size. Going to a smaller sized orifice changes the response time for a change in vacume "load" to register upon that map sensor inside the ECU. In other words as throttle is cut back, the change in vacume tracks to the rpm drop more slowly, hanging behind the RPM's rate of decay, which keeps the fuel delivery in an area of the fuel curve that the RPM isn't actually at. This is actually more effective with sharper cut backs in throttle position.

[capnzee]

Markus, I checked the website out that you mentioned in your last thread and have decided I would have to be a "freakin guru" to figure that one out. Until something simpler comes along, I will hit the choke button when I come off WOT as you are doing. I think it is important for the V-6 boys that donot have an EGT gage to know of this phenomena. It could be the source of problems that would never be thought of! GREAT THREAD! Capnzee

[ultrafast]

You Merc guys are something. A few days ago you were rattlin on about how stupid it was for us OMC guys to wash down a motor after a hard run. Could it be you' just now gettin those Welfare motors to run?

[chris_lacey]

I was about to say the same thing. The other day everyone was bashing Bmac for having to washdown his OMC, now we find out the Merc EFI guys are doin' it too.

[Rickracer]

....as pointed out by Instigator, is that the Merc lower unit can ratchet when you let off the gas, OMCs will not, thereby dragging the rotating assembly along via the prop at boat speed. I love the information exchange on this site, we all have stuff to learn from each others experiences. :cool:

[espen]

wow rickracer ... I did not know that...makes me think of the SAABs of the 60s with 3cyl two stroke engine :-) it had free wheeling...when you let of the trottle it would not break on the engine, they kept that feature when swapped to 4 strokes for a while to. Remeber I seized the cart engine when letting of the trottle at the end of the straigt... I started to chocke the engine with my hand over the carb and the engine would stay alive :-)

[capnzee]

In the old days they called it "free wheeling" and it came out just before "overdrive" . A few years back, I seized a 2 cycle motorcycle equipped with oil injection simply by coasting down a long hill, letting the engine do the braking for me. The dealer said it was "pilot error" and I should know better than to "brake" the motorcycle with the engine, and the throttle closed. I didn't know how else to brake using the engine.
In addition to my "stable" of boats, I have an experimental airplane with a 2 cycle, oil injected engine. When I installed the engine, I learned that the oil injector output was connected directly to the throttle. As the throttle was " opened up", so was the oil injector control so that somewhere along the way, the oil injector produced a 50:1 ratio. At idle, the oil injector was producing a 100:1 ratio. I remembered my motorcycle experience, that I discribed in the paragraph above and thought that this is no way to go in an airplane. Fortunately, the engine manufacture left room for adjustment and I set the linkage so that it would provide me with 50:1 gas/oil ratio, even at idle.( I can afford to change the plugs if they gather a little carbon, but they haven't!) To make sure the oil injector pump was working properly, I then added oil to the gas at a ratio of 50:1 for the first few tanks until I was completely satisfied tha the oil injection was working properly. This may not be a bad idea when setting up a new outboard engine. I also like the idea of adjusting the oil injector out put so that the engine is getting at least 50:1, even at idle. Can this be done on the V-6 engines? Until the oil injection engines have proven more dependable, I will continue to remove the pumps and mix my own gas/oil at a comfortable 42:1.

I apologize to all for the length and for straying from the original thread, but it seems like oil is a subject a lot of guys are asking for and I kon't mind "splitting threads" if we can learn something along the way. If there is a way of adjusting the oil injection pump on a V-6 I would really like to know how it is done. Capnzee