For those who aren't familiar my truck is a 96 GMC Yukon with an '02 24 Valve, it is backed by a 6 speed Allison transmission. The tires are 285/75/17 and I have regeared so that at cruising speed (70 MPH) I am right at 1960 RPM. I am currently getting about 10 MPG and I am trying to figure out why. I run a Quadzilla on standard tune, level 4 and I have a bit of a lead foot but most of my driving is freeway miles. I also run a FASS 150 and a 5" straight exhaust with 4" down pipe.

 

Now then...at cruising speed I am approximately 20% throttle and my EGT's are in the low to mid 800's. My load ranges between 30 and 36% based on the slope of the road. The boost at cruise is 11psi and I never really paid attention to the IAT's until recently but they stick in the mid 130's; because of space constraints I use an air to water intercooler and I noticed a drip from the filler cap recently so there's a chance the fluid is low. I recently adjusted the valve lash and I have plans to clean the IAT sensor and MAP sensor in the next week but from what I understand about the sensors if they were dirty they would read low not high. I am admittedly not an expert in the field, in fact this is the first diesel truck I've ever owned or even driven.

 

So the question is: Where can I start looking for inefficiencies or out of service conditions that are burning extra fuel? I would really like to take the old girl to the coast in the spring but at 10mpg I'd need a second on the house. Any help is appreciated.

The funny part is looking at the racing tires. Smooth wheels, no spokes or holes. Then racing slicks are smooth and no tread design per se. From that standpoint are the absolutely most efficient tire and wheel setup.

7 hours ago, Marcus2000monster said:

@pepsi71ocean I cant make up my mind on what injectors to get. Im thinking about a setr of genuine Bosch RV275s flow matched adnd popped to my specs. What would you have a set of RVs set at? 

Being that they are so close to stock fuel flow I would say 310-315bar. What do you think @Mopar1973Man?

It seems to me that the gain in raising pop pressure is proportional to the side of the fuel injected. the larger the injector the more you can raise the pop pressure.

Rv275s will not be popped or flow match it will ruin the Bosch warranty. You can only pop and flow match custom build injectors like what DAP sells. 

 

Bosch stock and RV275 are as is. No pop or flow match.

On 1/7/2019 at 3:24 PM, Dieselfuture said:

 your kidding

Also make sure your check back side of compressor housing for Boost leaks with soap water,  I ended up selling mine with light coat off rtv

What's the easiest way to get that stupid ring back in there. I think rtv is a great idea but the last time I had it apart it took nearly an hour just to get the ring back in. Finally had to ask my wife for help...that wasn't embarrassing.

I used chanel lock pliers, but took a few tries, keep your hands clear when that thing flies out of . If yours are bent to where pliers keep sliding off, you can heat just the ends and bend them tabs a little or tack weld few beads, something to grab on.

36 minutes ago, Scottfunk said:

What's the easiest way to get that stupid ring back in there. I think rtv is a great idea but the last time I had it apart it took nearly an hour just to get the ring back in. Finally had to ask my wife for help...that wasn't embarrassing.

 

The silencer ring?

Oh to funny... ask wife for ring back and tell her that her new ring will be silencer ring. Probably not recommend...

 

I used ice pick to get my ring out on turbo.  Couldn't tell a difference, so I put it back in.

I know this doesn't exactly fit here but...

 

On my 1996 Dodge Ram I pulled the Mopar Performance PCM and pit a stock PCM back on I'm now at 19 MPG on the little truck. What I'm pointing out is the wrong tune can pull MPG down by overadvancing timing. Where the stock PCM is more retarded and now doing better than my Cummins. Price of gas is lower, I can now run 87 octane again. Bonus both ways.

19 hours ago, pepsi71ocean said:

 

The silencer ring?

No the back end of the housing. I like your idea of some rtv there but getting that snap ring back in there sucks.

ignore my last post. I screwed up and was looking at the wrong truck data. 96 was only 14.6 and the 02 was 18.6. 

So I'm still working through this. My egt's are still higher than I'd like and I've done everything I can think of. This weekend I replaced the intake plate gasket and RTV'd the hell out of it, as well as the compressor cover on my hx35. While I was putting the fuel system back together I got to thinking about the fuel inlet. Since I was doing a conversion I had the opportunity to build the whole fuel system from scratch. I replaced the banjo fitting going into the injection pump with a 3/8" elbow. The reason I'm mentioning this is I'm wondering if I'm producing more fuel at any given throttle than the hx35 can keep up with. Any chance a 35/40 hybrid would help keep up with the fuel  I'm supplying to the engine? 

20 minutes ago, Scottfunk said:

I replaced the intake plate gasket and RTV'd the hell out of it

 

Bad idea. No RTV or sealant should be used on that gasket. 

 

20 minutes ago, Scottfunk said:

I replaced the banjo fitting going into the injection pump with a 3/8" elbow.

 

 

Should be all 1/2" fuel lines from the fuel tank to the VP44.

 

20 minutes ago, Scottfunk said:

Any chance a 35/40 hybrid would help keep up with the fuel  I'm supplying to the engine? 

 

HX35/40 Hybrid is basically same as HE351 turbo on the 3rd Gens. The only different my exhaust housing is 12cm² vs 9cm² .

Edited January 28, 20196 yr by Mopar1973Man

24 minutes ago, Mopar1973Man said:

Should be all 1/2" fuel lines from the fuel tank to the VP44

If I recall this banjo had a 5/16" line going into it. Those two puny little holes don't hold a candle to a 3/8" swept elbow. In any event I'm getting too much fuel. What would you suggest? My turbo is not the he351 so would I be gaining by doing the 35/40 hybrid or would it be better to pick up a 351? I'm planning on going VGT at some point this year so I don't want to sink too much into it but would like to increase my efficiency some in the meantime.

I disagree with Mike, I'm running 3/8" from my fass95 to the vp44 and I have no issues with fuel supply.

 

My next question is Joe is your drive train? Anything dragging? How's the VB and transmission?

The only reason for 1/2" lines is pressure stability. 3/8" lines work OK for stockish trucks. When you start to see wild pressure swings its time to go up in size. I just opted for large lines in the beginning and just not worry about it. 

25 minutes ago, pepsi71ocean said:

I disagree with Mike, I'm running 3/8" from my fass95 to the vp44 and I have no issues with fuel supply.

 

My next question is Joe is your drive train? Anything dragging? How's the VB and transmission?

I agree. I don't know exactly what size the holes in the banjo are but I still have the fitting at home...I'll check it when I get home from work. I definitely don't remember them being any bigger that 1/8" so basically it doesn't matter if you run a fire hose up to this fitting, if that's the point of restriction you'll never flow any more than that banjo allows.

 

I don't believe I have excessive drag...other than the 35" mudders I put on last week, hehe. Everything in the trans is brand new and all the clutch clearances were exactly middle of the specs so I don't think that's the problem. I put the truck on jack stands and the rear wheels spin freely, as do the fronts. Stopped, and in gear, if you let your foot of the brake the truck feels like it gets moving on its own without excessive resistance. I really think this is an internal thing. I'm going to make a new boost test boot (I blew the last one up) and I'll check for leaks again. I'm new to this whole positive pressure intake situation and it's kind of blowing my mind.

Clue. More boost you see going down the road means typically your burning more fuel. I've got to ask what is your engine load and boost pressure like at highway speeds?

 

Boost you should be below 5 PSI for 65 MPH. Engine load should be around 20% or lower if possible. 

 

Injectors what are you running? What was the pop pressure at? How many miles on the injectors?

30 minutes ago, Mopar1973Man said:

The only reason for 1/2" lines is pressure stability. 3/8" lines work OK for stockish trucks. When you start to see wild pressure swings its time to go up in size. I just opted for large lines in the beginning and just not worry about it.

 

I hear you, but ever since I moved to 1/2" from tank to fass, and changed my spring to a spring out of a fass150 I've never had an issue, even with my 100's smarty and boost elbow pushing 35+ lbs of boost she barely moves the needle. 

25 minutes ago, Scottfunk said:

I agree. I don't know exactly what size the holes in the banjo are but I still have the fitting at home...I'll check it when I get home from work. I definitely don't remember them being any bigger that 1/8" so basically it doesn't matter if you run a fire hose up to this fitting, if that's the point of restriction you'll never flow any more than that banjo allows.

 

I don't believe I have excessive drag...other than the 35" mudders I put on last week, hehe. Everything in the trans is brand new and all the clutch clearances were exactly middle of the specs so I don't think that's the problem. I put the truck on jack stands and the rear wheels spin freely, as do the fronts. Stopped, and in gear, if you let your foot of the brake the truck feels like it gets moving on its own without excessive resistance. I really think this is an internal thing. I'm going to make a new boost test boot (I blew the last one up) and I'll check for leaks again. I'm new to this whole positive pressure intake situation and it's kind of blowing my mind.

 

 

This begs me the question of what rear do you have on this truck?  35's are fairly big, and no matter what if you have a 3.55 rear your gonna be  struggling with the load. 

29 minutes ago, Scottfunk said:

I agree. I don't know exactly what size the holes in the banjo are but I still have the fitting at home...I'll check it when I get home from work. I definitely don't remember them being any bigger that 1/8" so basically it doesn't matter if you run a fire hose up to this fitting, if that's the point of restriction you'll never flow any more than that banjo allows.

The idea is to get rid of the banjo fittings all together.  You are right, those banjo bolts are restrictive.  I've replaced my banjo bolts with larger fittings altogether.

1 hour ago, pepsi71ocean said:

This begs me the question of what rear do you have on this truck?  35's are fairly big, and no matter what if you have a 3.55 rear your gonna be  struggling with the load. 

I have regeared the pumpkins to 4.10. With the smaller tires I was right at 1860RPM at 70MPH and now with the 35's I'm closer to 1730 at 70. I'll probably step back down a size when I have to buy new rubber. 

 

2 hours ago, Mopar1973Man said:

Clue. More boost you see going down the road means typically your burning more fuel. I've got to ask what is your engine load and boost pressure like at highway speeds?

 

Boost you should be below 5 PSI for 65 MPH. Engine load should be around 20% or lower if possible. 

 

Injectors what are you running? What was the pop pressure at? How many miles on the injectors?

I'm between 7-9 PSI cruising at 70MPH depending on the grade of the road. Engine load jumps between 24 and 33. The injectors were just built earlier this month and are 50 horse injectors popped at 315.

 

Before I changed the tires I was having problems with high egt's. I was up around 840* at 70MPH. I chased down quite a few boost leaks and was able to get it down in the low 600's. There were still a couple minor leaks I knew about. After I changed to the bigger tires I was back up around 850* but after sealing up the compressor housing, intake plate, and grid heater housing I am back in the mid 600's. I will check the load numbers on the way home tonight.

 

What is the best way to dial back the timing a little for winterized fuel? Just bump it down a couple degrees across the equalizer or in the individual timing settings? I have not played around in the Quad custom tunes much but everytime I do it seems like I make it worse.