Another FDC bypass question

[ldmack3]

I know how to do this, and I understand it gives more power. But from what I have read it changes the full throttle stop for different fuels. More throttle for gas, less for diesel. So it really only gives more power at full throttle from what I have read. Then also I may need to turn down the fuel if the EGT is too high.

So FDC bypass for more fuel but then turn down the fuel to keep the temps down. Why not just use throttle control and downshift if necessary? Seems kind of senseless if I am interpreting it all correctly.

This is my first deuce (limited knowledge and experience) and I have yet to give it full throttle as I'm not a believer is dumping in more fuel than can be burned in a 50 year old engine. So far when I need to pull a hill, and there is only one so far, I just downshift to keep the RPMs up so as not to bog it down and yet keep them at 2,000 or below. Running 395s.

What am I missing/not understanding?

Thanks for everyone's patience.

 

[DaneGer21]

I bypassed for two reasons, more consistent fuel delivery, and to stop the possibility of a fuel leak into the oil.

It’s not so much it gives more fuel, but sets the delivery at a solid set point. Which with most engines will be set “high” hence you need to turn down the fuel. My egt climbed fast before I made adjustments. I HAD to keep my foot out of the pedal! Or else I had high boost and high egt’s

Confusing at first…

 

[Floridianson]

When looking at the FDC wedge plate you will see the taper or how it looks like a wedge. When FDC is working and engine running it goes to the setting for what fuel you are running and stays there or higher on the ramp decreasing fuel but as said going to working specs. Then we bypass and the servo does not move but the arm rides low on the wedge or more forward which is allowing more fuel. So in most cases we have to reduce the main fuel by way of the twin nuts. No doing so even if you try and just use your right foot the fuel might be turned up to much even for foot control. Bypassed and pyro I mark the a twin nut inner nut flat with a black marker and you can increase or decrease and be able to tell how may flats you are adjusting the main fuel to get your EGT's where you want them. If you read other threads you will see when the FDC is bypassed the smoke cam and droop screw if your IP has one long longer work a long with the wedge so we can no longer used the adjustments on them to control the lower rpm end fuel / boost.

 

[ldmack3]

ok. Just finished and am going to a test drive for temp and for speedo check.

Will advise.

 

[Floridianson]

The close to correct fuel adjustment will be a truck size puff of black unburnt fuel till the turbo spools and you up and running then clearing as you reach higher speeds /RPM. Incorrect fuel setting a mile long black soot cloud will kill all mosquitoes in the area and most likely piss off the tree huggers.

 

[ldmack3]

Ran great. Slightly hotter - got up to 450-500 but not a big hill. I was able to pull it in 4th high all the way. I will check on a longer/steeper one close by, but the wife had had enough. Forgot ear protection.

2nd gear a little easier to get into. Maybe because I'm learning, maybe because its warmer.

Speed is very close. No need to work that one (whew!)

Still going for the toe in check as a little wandering at 50 and up.

 

[DaneGer21]

Ran great. Slightly hotter - got up to 450-500 but not a big hill. I was able to pull it in 4th high all the way. I will check on a longer/steeper one close by, but the wife had had enough. Forgot ear protection.

2nd gear a little easier to get into. Maybe because I'm learning, maybe because its warmer.

Speed is very close. No need to work that one (whew!)

Still going for the toe in check as a little wandering at 50 and up.

450-500? That’s LOW, max temps in my opinion are up around 1000*. Now I wouldn’t want that all the time, but I tend to cruise up around 750-900*, and idles around 275-290 when up to temp.

 

[KN6KXR]

450-500? That’s LOW, max temps in my opinion are up around 1000*. Now I wouldn’t want that all the time, but I tend to cruise up around 750-900*, and idles around 275-290 when up to temp.

450 to 500 is just fine. If you're using Centigrade. That would be 842 to 932 F. Of course it will be the only metric aspect of your truck.....

 

[Floridianson]

Ran great. Slightly hotter - got up to 450-500 but not a big hill. I was able to pull it in 4th high all the way. I will check on a longer/steeper one close by, but the wife had had enough. Forgot ear protection.

2nd gear a little easier to get into. Maybe because I'm learning, maybe because its warmer.

Speed is very close. No need to work that one (whew!)

Still going for the toe in check as a little wandering at 50 and up.

Well glad your happy but. Ok the hill test is ok but you did not say what RPM you were at when took on the hill and what RPM you climbed the hill. AS we know a true dyno is the way to set EGT's but we have to do the best we can. If you do the hill test a couple of time I would make sure everything is the same when you hit the hill as speed RPM and gear. O and have fun always. 1200 EGT getting close. I know my Duramax is not the same or as old plus precious as our multi but I have taken the duramax to 1650* for a short time for fun or passing and the truck has been running great for years. Saw a post where someone said pistons will melt at 1200. Not going to happen. You want safe 1000 little more heat 1100* for a while and keep rpm way up.

 

[ldmack3]

At the bottom it’s coming out of a 20 mph school zone so not much time to build up speed. I can lean on the throttle and take the hill in 4th high about 40-45 mph and under 2000 rpm. I try to stay 2000 rpm or less always. Tomorrow I’ll watch the tach more and the EGT. Cruising on level ground 2000 rpm is 50 mph and 300 to 350 EGT.

 

[ToddJK]

At the bottom it’s coming out of a 20 mph school zone so not much time to build up speed. I can lean on the throttle and take the hill in 4th high about 40-45 mph and under 2000 rpm. I try to stay 2000 rpm or less always. Tomorrow I’ll watch the tach more and the EGT. Cruising on level ground 2000 rpm is 50 mph and 300 to 350 EGT.

Sounds like your settings are at a safe level. Just keep an eye on the egt's when driving at a steady pace and while hauling a load or climbing up hill. Otherwise it sounds like you're doing a good job at keeping your truck in a good operating condition for the long haul.

 

[Gypsyman]

Is your EGT probe pre or post turbo? Those sound like post turbo numbers.

 

[ldmack3]

Is your EGT probe pre or post turbo? Those sound like post turbo numbers.

Post

 

[DaneGer21]

Post

That makes sense now

Gotta picture?

 

[INFChief]

I know how to do this, and I understand it gives more power. But from what I have read it changes the full throttle stop for different fuels. More throttle for gas, less for diesel. So it really only gives more power at full throttle from what I have read. Then also I may need to turn down the fuel if the EGT is too high.

So FDC bypass for more fuel but then turn down the fuel to keep the temps down. Why not just use throttle control and downshift if necessary? Seems kind of senseless if I am interpreting it all correctly.

This is my first deuce (limited knowledge and experience) and I have yet to give it full throttle as I'm not a believer is dumping in more fuel than can be burned in a 50 year old engine. So far when I need to pull a hill, and there is only one so far, I just downshift to keep the RPMs up so as not to bog it down and yet keep them at 2,000 or below. Running 395s.

What am I missing/not understanding?

Thanks for everyone's patience.

Where is the FDC located? Do you have pictures? In the Army FDC was an artillery term.

 

[cattlerepairman]

From years of reading this forum, I have concluded that
- max pre-turbo EGT should be below 1200; this is also meant to mean "sustained", not just a "blip"
- the LDT is happy and will run forever at 2,200 rpm

As far as my LDS is concerned, "what's a hill?" He, he, he

 

[ldmack3]

From reading about the temp differences between pre and post I've seen some statements of 200–300-degree difference and 400 to 500 differences. I think the hottest mine has gotten is 450 - 500, which I think is still safe.
Not sure why a previous owner installed it post and I will look moving it as well as adding a boost indicator in the future. I do have some concern about the probe coming apart and trashing the turbo.

 

[Gypsyman]

After 30+ years of working the heavy truck and high performance business I've never seen a probe fail. Go pre-turbo and get some accurate readings. Your engine will thank you. =)

 

[ldmack3]

After 30+ years of working the heavy truck and high performance business I've never seen a probe fail. Go pre-turbo and get some accurate readings. Your engine will thank you. =)

Thanks. That's the info I'm looking for.

 

[ldmack3]

Just looked up the egt installed to review the install instructions. I understand why they installed post, but agree it's not as accurate as pre. But since it's designed for post I will likely need to change it.