3 bar map with NO programming???

[RyanA]

Just wanted to see what the consequences of doing this would be. I ran into a guy locally that has a GM 3 bar map sensor on his 6.5 turbo diesel suburban. He has had it like this for quite some time and has not had any problems out of it. He has no programming and the truck spikes to over 15 psi and he said about the lowest boost he sees when on the accelerator is 12 psi. I understand why the boost is higher (because the PCM thinks the boost is lower than what it truly is due to the scaling of the 2 MAPs being diferent) but I am concerned about fuelling. He told me he's had it like this for a while and has had no problems at all.

Any opinions/input on this? Is this a possible low buck mod for some people? He's running a #9 calibration resistor and a 3 bar map. It's in a 1998 Suburban.

[xtrempickup]

you should be more concerned about the temps considering the truck has no intercooler or after cooled and basically anything more can due some seriously damage as the air coming from the turbo is HOT rather than cool like on 6.6Ls with an intercooler. you should have more fuel, but a performance computer to better control it would be smarter than just a 3bar map

[DA BIG ONE]

IAT's w/o IC most probably get so high fuel is cut.

[RyanA]

Actually, he is probably pulling fuel, too. This really concerns me as he uses this as his daily transportation. I just don't see how it has worked for so long without any catastrophic engine damage.

My reasoning behind his boosting/fueling is this:

Since the MAP is a 2 bar, not a 3 bar, it's basically reading 33% lower boost wise at all times. So, when in boost, if the PCM sees 8 psi, it's fueling for 8 psi but the truck is really making 11 or 12 psi. So, 11 to 12 psi with 8 psi fueling in my thinking would mean he does not have enough fuel. I told him the other day he really needs to get a pyrometer on his truck to see what his EGT's are. He has a VDO boost gauge and that's it; it goes to 15 psi and he said it will peg it. So, in a nutshell, lots of boost, high IAT's, low amounts of fuel should equal catastrophy in a short period, right?? Why hasn't this been the fact?

[Robyn]

Actually over fueling is the road to high EGT.
Having an abundance of air will not in and of itself cause high temps.
The boost pressure being high can and will cause high air temps especially when the air is dry and warm to start with.

A diesel simply burns what is injected into the hot compressed air.
A gas rig with too much boost and a lean fuel charge will see very high temps or a missfire depending.
Not so the diesel.
Actually with more air and less fuel he could be seeing lower temps in fact.

The only real way to know for sure is a set of gauges.

My dually is chipped and the wastegate is set to allow about 12 psi on a hard pull. The temp never exceeds 900 Post turbo and this is on a hard pull with a heavy load and my boot right down into it hard.

Boost goes hand in hand with fuel. The more boost the more fuel it can handle to the point at which the engine cant produce any more power due to other restrictions such as the inability to get rid of waste heat.

A 6.5 in a truck is limited to about 300 shaft horsepower before the cooling system cant deal with it any longer.

A boat application can handle far more simply because the cooling of the engine and the air charge can be dealt with via a limitless supply of cold water from the pond.

Having too much fuel and not enough air, resulting in copious amounts of black smoke out the stack will generate far more heat than will simply too much boost.

Boost simply for the sake of boost is a moot point.
Boost when applied with the correct amount of fuel will make power, boost when applied with a much lower amount of fuel (Stock setting) will burn clean but produce little more power than the stock settings of 7 PSI

Ya gotta feed the pony if ya want him to work harder.
The harder he works the more he sweats. :D

My DaHoooley has a late design power chip and is using the stock 95 model turbo.
The chip will allow the DS4 IP to fuel all it can deliver. 91 cu mm (balls to the wall)
Once the IP is delivering everything it can the secret is to pack in enough air to keep the burn clean with no black smoke.
A large exhaust system will allow the engine to flow all that it can and as such will allow excess heat to be released.
The stock wategate casting is sort of like the little pig with a cork in his butt. It really stops up the flow and this is a source of agravation and limits things some.
Unfortunately the design constraints of the body demanded that the down pipe drop out the bottom.

I would not be too worried about the temps with stock fueling even with a more boost.

It would be nice to know though.

best

Robyn

[DmaxMaverick]

You might as well save the money and effort of changing the MAP. Just wire the wastegate shut and ignore the SES (or put a piece of tape over it). At 15 PSI, it's gonna grenade after a while. Much depends on how you drive it, but it will if you are seeing anything over 10-12 PSI for any extended periods. Watching EGT's is good, but remember, EGT's are reactionary. By the time you see it on the gage, the temp cylinder temp has already been there for a while. If you tow or haul any appreciable weight, it will melt down much sooner. Same with drag racing (even between traffic lights). There's really no point getting the boost up that high electronically. That's about all a stock system will do, and the turbo will be operating well outside of its efficiency window (a lot of fuel and heat for not much more power). Your 3 BAR mod is going to keep the PCM from opening the wastegate, in any case, so why bother with spending the money and effort. Black smoke may be cool, but it comes at a price.

I suggest you start collecting parts for your rebuild. And, don't get too far from alternate transportation.

[RyanA]

After doing more research (elsewhere on the net) I have found out that people either put a 10k ohm resistor inline with the signal wire on the MAP OR they acutally put a 3 bar map on to do the same thing. 10k resistor is a cheap boost fooler that requires cutting. 3 bar map ends up doing the same thing but for about $60 and with no cutting.

Link: http://www.pirate4x4.com/forum/showthread.php?referrerid=57133&t=393142

So, this appears to be a fairly common (maybe not on this site since almost no one seemed to have any idea what I was talking about....) way to bump your boost on a budget. Not necessarily the right way but it appears that it will work for people before they buy a chip ONLY if they have appropriate gauges installed.

For those of you ASSuming that I was the one I was talking about in this post, you are DEAD WRONG. My truck has stock map. 2.5" crossover, 3" dp, 3.5" mandrel exhuast, LS1 K&N (yes, the LS1 filter is an exact size replacement for the rectangle filters in our trucks...), Kennedy chip, EGT and boost gauges. Also, my truck is a 95; the one I am talking about is a 98.