6.4 boost/mileage question

08Monster · Dec 8, 2014

I have an 08 Spartan tuned 6.4 on the 310EL tune. I towed with it this weekend, a V-nose fish house that weighs about 3k. Why did my truck have a hell of a time pulling it? 37s and a 4.5 lift. 3.73 gears. Boost was at 30+ all the time, 8mpg. Why? 70mph mostly flat.

strokin08 · Dec 8, 2014

I run spartan tuning and I tow and dd the 210 almost all the time and tow a 11k enclosed trailer and never have had a problem. When tc is locked and pulling hills its pulls like a train. Now I have had people with me and when starting from a stop people thinks its sluggish but I'm only pushing throttle a total of an inch so its seems slow but ain't giving it no power. Thats my only case with it. Never have run 310 tune so cant help you to much with it. I have towed light with 300 with no issues.

stroker221 · Dec 8, 2014

35's would really help Yu out

stroker221 · Dec 8, 2014

Try a smaller tune

09strokerpwr · Dec 8, 2014

I have pulled my 22' v nose enclosed trailer with mine i have 33's and 3.55's if i stay under 70 boost stays low but as soon as it get twards 70 jumps to 20ish. That is in the 275. Truck has no shortage of power tho

footlong70 · Dec 9, 2014

08Monster said:
I have an 08 Spartan tuned 6.4 on the 310EL tune. I towed with it this weekend, a V-nose fish house that weighs about 3k. Why did my truck have a hell of a time pulling it? 37s and a 4.5 lift. 3.73 gears. Boost was at 30+ all the time, 8mpg. Why? 70mph mostly flat.

It has nothing to do with the tires/gearing, something else is wrong. 3k weight trailer is pretty well a joke for the 6.4 on a 310 tune even with the tires. That kinda boost constantly without pulling hills or extreme wind is usually related to a VGT issue. Whats back pressure reading throughout? Is it changing consistently in relation to the boost? Almost sounds like a bad/unplugged BP sensor or froze off BP sensor tube. The bp sensor is the primary sensor used for controlling the VGT position. Been there many times making 30-45psi boost on flat ground, completely empty just because of a froze off sensor. Also just for giggles, what gear were you pulling in? 4th or 5th constantly? Was the converter locked?

08Monster · Dec 9, 2014

Converter locked.

08Monster · Dec 9, 2014

5th, locked. Cruise set at 70. Figured this should tow a house, so a little fish house shouldn't be a problem. Haha how do I check for that stuff? This truck has been problematic with high boost before. Should it be able to hit 60psi on the stock chargers, stock fuel? Towing the house I could hammer it down and hit 58psi

sootie · Dec 10, 2014

*** no it shouldnt hit 60 psi on stock chargers.

what are your ebp and boost readings with key on engine off?

have you replaced your map sensor or ebp sensor and tube recently?

AllGo'N'Show · Dec 10, 2014

^^ +1 pronto! 60psi wowzers!

08Monster · Dec 10, 2014

No, I haven't replaced any of that. I was pretty sure it should hit that much. Haha I always thought something was weird, this truck has waaaaay more power than my buddies on the same 310 tune. He's never seen over 45 on boost either, I hit 50+ all the time. I'll check at lunch about the key on readings.

sootie · Dec 10, 2014

a stock turbo/fuel truck shouldnt see over 52psi even on a race tune.

just because it is boosting that high does not mean it makes any more power. i actually gate my truck down to keep the turbo in its map and that nets more power imo

ckrueg · Dec 10, 2014

At 60psi boost i bet the BP is over 80. That could damage the valve train and it would be robbing power with all that restriction in the exhaust.

johnp115 · Dec 10, 2014

Like said somewhere else on this forum.....

Just using this as an analogy... It holds alot of truth with 6.4's and how much air the heads can flow, just don't take the numbers too seriously because I'm not sure at what point the boost becomes wasted....

so here...

If the heads can only flow a maximum of 50PSI from the turbo chargers.. and say you make "55PSI" That 5 extra PSI is not doing anything but back tracking up the system. Its a pretty logical point.

My truck is gated at 48PSI.. runs 12.7 in the 1/4 stock fuel stock turbos.

So i would get some readings on your BP asap like said cause you could be putting some unwanted strain on your motor.

footlong70 · Dec 10, 2014

Yes its a VGT control issue. More than likely a back pressure sensor causing it. First use your Dashdaq? and put exhaust back pressure parameter up on the screen so your can monitor it. If its not changing in correlation with boost pressure then the narrow tube off the egr catalyst pipe to the sensor is plugged/froze off or the back pressure sensor is ***ed. 2nd, if its reading properly, you need to pop the hood and move the VGT arm/linkage back and forth checking for smooth easy operation. If it doesn't cycle back and forth easily by hand with the truck off it is stuck.
Whats happening is your vgt isn't opening up properly and your over speeding the hell out of it making stupid amounts of boost. The high pressure charger won't last long before it explodes/breaks a shaft/eats the bearings and seals, if its not already damaged. Also your actual back pressure is going to be pushing 80 or even 90+ PSI which is extremely hazardous for your valves and pistons. If you've been driving like this for a while and have been flooring it, then I put money on you having valve/piston contact. Definitely shouldn't be driving the truck like this. Especially flooring it.
I climbed a steep grade hill once, empty, with stock chargers/fuel but a froze off back pressure tube,then it down shifted, and I hit 62PSI boost. EBP was stuck at 18 PSI. I came off it very quick hoping no damage was done. Limped it onward. Anyways I guarantee its a similar issue and it needs to be fixed ASAP if you wanna keep your truck driving.
Whats the outside temps been like there when it does it? EGR is deleted?

08Monster · Dec 11, 2014

Around 10°, yes EGR is deleted. I'll check those things when I get off work today. So just monitor them both and make sure my EBP is moving according to my boost? Accounting for the 16.x psi it always shows, air pressure in the atmosphere I assume

08Monster · Dec 11, 2014

If I unplug the VGT would that temporarily solve that problem? Also, what size single would that be a comparison. I want a single but want to test lag first. Thanks!

footlong70 · Dec 11, 2014

Yeah so the ebp tube only tend to freeze off with the egr coolers deleted. It takes away the extra heat and wind blocking around the tube and sensor. Does it always make excessive boost or ok in the summer? Mine typically only did it when it hit -10c on the highway, in town it seems to stay warm enough under the hood that it wouldn't freeze even at -20c. But if it still does it when its warm its probably a bad ebp sensor/plugged tube.
When you check it, during most normal driving they should be within a few psi of eachother. When you get heavy on the throttle the ebp should be significantly higher than the boost. I'm not sure about the barometric pressure for spartan, whether its already subtracted from the ebp or not. Someone with a spartan could probably chime in and confirm that. If it shows pressure with the engine off then yes its probably just atmo pressure, however it can also be trapped pressure behind an ice plug. Like I said someone can confirm it. For now you just subtract that pressure with the truck off from whatever values it shows while you test it.
Unplugging the vgt is suppose to open the vanes all the way so yes it would prevent over speeding and over pressuring. However it will be very laggy and smokey.

Dzchey21 · Dec 11, 2014

unplugging isnt really a good compareson since the housing goes way bigger that any non vgt will but i would say around the 66mm range.

Your getting good advice here boost should not be that high, It could be that tune tho alot of race tunes are more agressive with the VGT to control smoke esp spartan tuning. I would try and lower tune as well and see what that does.

You will also see higher back pressure than boost thats just a nessessary evil of the stock turbos, you can monitor VGT duty cycle as well, if its holding 90% then something is making it stay there.

Also if the back pressure sensor is reading incorrectly in this case it will be reading low amounts of back pressure. Not high, if the sensor reads high you will have a lag issue. thats what a freezing tube will do because the moisture expands and applies false pressure to the sensor.