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.

8 hours ago, Scottfunk said:

Is this realistic? It's not that I can't afford to pay for pop testing but I can't afford to have my truck down and I can't afford to drop the injectors and have a guy tell me I can pick them up thursday and then listen to some excuse about how they won't be able to get to them until next month.

 

I don't know about Idaho, but I did 2 day shipping on my Injectors from NJ to DAP in UT and had them back in the same week, and that included getting them re popped, flow tested, and having them ship them back.

I went through the same gambit. I had 4 injector shops tell me everything from 5 day to 2 weeks to get my injectors done, since no one stocked shims and springs etc. So I was concerned about that. But DAP had that stuff in stock and I believe that it was done in the same day and finished.
 

Mike may even have an injector tester set up or know of a place up that way?

Edited December 21, 20186 yr by pepsi71ocean

8 hours ago, pepsi71ocean said:

Mike may even have an injector tester set up or know of a place up that way?

 

I wish. I would be pop testing my own injectors.  Head gasket and this PCM project have wiped me out.

 

The best place I know of is in Lewiston, Idaho they do pop testing for free. Then if you next to actual pop to set then its $9 an injector.

Edited December 21, 20186 yr by Mopar1973Man

Master Tech in Boise will pop them right in front of you for free. Mine were all sorts of bad...low pop pressure, bleed off, you name it. They are rebuilding them right now for $65 a piece, genuine Bosch parts and matched, not a bad price just bad timing. I will report back how it affects my situation.

1 hour ago, Scottfunk said:

Master Tech in Boise will pop them right in front of you for free. Mine were all sorts of bad...low pop pressure, bleed off, you name it. They are rebuilding them right now for $65 a piece, genuine Bosch parts and matched, not a bad price just bad timing. I will report back how it affects my situation.

 

@Marcus2000monster you might want to follow this. 

Apparently they also have a one hour turnaround time when there's a shop hand available. Brand new genuine Bosch nozzles matched to 305 Bar =/- 5 Bar, "These are technically 50HP nozzles," he tells me. And I got a free T-shirt! Great experience all around.

3 minutes ago, Scottfunk said:

Brand new genuine Bosch nozzles matched to 305 Bar =/- 5 Bar

 

Why do all the shops always pop them low?

 

Right out of the FSM.

 

Then within the next little bit of mileage, the pop pressure will fall a bit more after everything settles. It sure does shorten the injectors lifespan before the pressure falls off again. 

 

30 minutes ago, Scottfunk said:

Brand new genuine Bosch nozzles matched to 305 Bar =/- 5 Bar, "These are technically 50HP nozzles," he tells me

Why didn't you asked him to pop at 315 or so, we all know they'll settle 

Simply put the bottom limit of injectors are 293 bar according to Dodge FSM manual. If they are popped 305 +/- 5 bar which makes the lowest injector 300 bar and just another 7 bar lower you'll be out of specifications again. Why do they do this? 

Any reason not to send my oem injecotrsnin and have 90 hp vco nozzles installed and popped to 320?

You might be right, I do remember hearing something about 315, maybe it was 315 =/- 5. I was so distracted by shiny new nozzles I was having a hard time concentrating.

19 minutes ago, Marcus2000monster said:

Any reason not to send my oem injecotrsnin and have 90 hp vco nozzles installed and popped to 320?

 

You could. Nothing wrong with that...

 

15 minutes ago, Scottfunk said:

You might be right, I do remember hearing something about 315, maybe it was 315 =/- 5. I was so distracted by shiny new nozzles I was having a hard time concentrating.

 

 

 

Might want to check. Hate to see you install and have to pull them back out again. 

My concern with popping 50hp Injectors so high is the fact that you may have issues with that small of an injector? That maybe why?

I’m thinking I’m going to send in my oem sticks and have either 75 or 90 hp nozzles installed and popped at 320 bar. Pop pressure sound good? Should I do 75 or 90? Obviously smoke and lag is reduced with higher pop pressures but are 90s going to create egt issues? I will eventually have tuning but not for a while. @pepsi71ocean @Mopar1973Man

4 minutes ago, Marcus2000monster said:

but are 90s going to create egt issues?

 

Should reduce the EGT's some. 

5 minutes ago, Mopar1973Man said:

 

Should reduce the EGT's some. 

I’m seeing about 650 right now cruising flat. 

5 minutes ago, Marcus2000monster said:

I’m seeing about 650 right now cruising flat. 

 

Minus 50*F off that for correct EGT's as shown by my ISSPro. The Quad is +50*F higher.

Edited December 22, 20186 yr by Mopar1973Man

7 minutes ago, Mopar1973Man said:

 

Minus 50*F off that for correct EGT's as shown by my ISSPro. The Quad is +50*F higher.

I’d like my egts to be below 550 is that possible with 90s popped high?

Remember, that's injectors and a tuner. Take notice to timing. 

oops!!

Edited December 22, 20186 yr by dripley

5 hours ago, Marcus2000monster said:

I’m thinking I’m going to send in my oem sticks and have either 75 or 90 hp nozzles installed and popped at 320 bar. Pop pressure sound good? Should I do 75 or 90? Obviously smoke and lag is reduced with higher pop pressures but are 90s going to create egt issues? I will eventually have tuning but not for a while. @pepsi71ocean @Mopar1973Man

I'd be really interested in seeing how your truck performs. I  believe that you should be fine with that set up. 90's on a HX should be ok, unless your towing heavy.

If you do move forward I would love to see the results, because we do need more data then we have which is literally myself and two other guys.