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.

1 hour ago, pepsi71ocean said:

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.

Im going to try it. Might not be right away though. 

OK @Mopar1973Man I need help. My #6 injector won't go back together. It feels like its in all the way, the keeper feels right when you bolt it down, but the tube won't seat in the side of the injector. There is evidence on the tube and the nozzle that the tube is riding low in the seat but I can't find anything wrong. I used a flathead screwdriver to make sure the old copper washer isn't stuck down there and it's not. Of course it's number 6 so I can't look down the injector bore. Check out the pictures...

Use a mirror and a small flat blade screwdriver bent an L shape to hook the copper shims. There has to be something in the base of the hole if the injector isn't seating completely.

18 hours ago, Scottfunk said:

OK @Mopar1973Man I need help. My #6 injector won't go back together. It feels like its in all the way, the keeper feels right when you bolt it down, but the tube won't seat in the side of the injector. There is evidence on the tube and the nozzle that the tube is riding low in the seat but I can't find anything wrong. I used a flathead screwdriver to make sure the old copper washer isn't stuck down there and it's not. Of course it's number 6 so I can't look down the injector bore. Check out the pictures...

 

I use my smart phone and turn on the light and take a video, and move the phone over the hole, and look at it.

 

Sometimes my injectors don't sit all the way down at first, and I lube up the Injector O rings and use the valve cover bolt to give it a love tap and she will seat. Its best to torque the crossover lines first before tigtining the lock bar on the injector top. But always rememebr to loosen the blue colored lock bars that hold the injector lines first, high pressure leaks are a ***** to diagnose, its best to avoid them in general.

 

Does anyone know how many bar the injectors drop when they settle in? 

21 minutes ago, Marcus2000monster said:

Does anyone know how many bar the injectors drop when they settle in? 

Roughly 5 to 10 bar drop. 

 

1 bar is 14.5 PSI.

 

 

Edited December 23, 20186 yr by Mopar1973Man

10 hours ago, Marcus2000monster said:

Does anyone know how many bar the injectors drop when they settle in? 

 

The consensus among the guys who did a few repops on their injectors for the raised injector testing saw an average of 10 bar over the first 5,000 miles or so. So while some hard starting or stalling may exist, the issues will lessen. Even for me at 320 bar the first few times the truck stalled was hard, but after a week of driving the issues went away.

 

Although, i still suspect I have transmission issues, so i can't say that is why I had stalling issues since the truck doesn't stall in manual 1 or reverse.

 

Not much to 24V injector. 

 

The little washer looking thing is a shim next to the body. The spring is a fairly heavy coil and rides directly on top of the shim. In all the injectors I've messed with the shim will wear over time with the pulse of the fuel pressure popping off. Between the nozzle and pintle wearing and the spring shim wearing this is where the slack is gained and the pop pressure falls. As the VCO nozzle wears the nozzle typically becomes pissy and leaky at low pop pressure like idle this why some report a strange misfire at idle with a warm engine.

Edited December 24, 20186 yr by Mopar1973Man

On 12/22/2018 at 7:17 AM, Mopar1973Man said:

 

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

 

Is there a 50° difference when cold/off as well?

 

On 12/22/2018 at 7:17 AM, Mopar1973Man said:

 

 

I drove the truck this morning and this photo came to mind, so I got on I-84 and set the cruise at 65. It puts me at ~1850 rpms. Coolant was 190°, IAT was 40°.

 

I'm currently running my single event 12V Tow tune, which has 14° of timing at this rpm/load. Load was around 18% and 30-36 mm3. 

 

EGT's floated right at 600° ±25° and after 8 miles my economy was 22-23, but not enough miles to see how it holds nor enough to be fully warmed up and have temps settle to their "normal" range. (Warmed up I'll see 500-550° under the same conditions). 

 

The truck was also cold, oil temp didn't get to operating temp until 4-5 miles onto the interstate so I was burning some extra fuel there, especially when you think about the 8 qts of 75w-90 in rear diff with minimal load to warm them up. It usually takes me 40+ miles of winter driving to see the cruise load/EGT's drop to "normal" once everything is warmed up. 

 

 

So when I consider the truck wasn't fully warmed up, I'm around 1K lbs heavier, and have more parasitic drag I'd have to say they run pretty similar temps/load/economy.... but the intriguing part is the timing difference which does nothing more than highlight the differences in VP vs CR injection. 

 

So on a VP you have to really increase the timing at lower loads since that's when the VP starts building pressure, whereas on a CR the timing is when the injector opens... big difference there!

 

When I am running a tune with a pilot and getting similar mpg's the EGT's are always higher, which comes from having a pilot and not being able, nor needing, to run the main with that much timing. The retarded timing means more heat out the exhaust, but the mpg's mean I still getting peak efficiency out of it. If I get much above 8° of timing with a pilot event I start to haze and lose efficiency. 

 

Just some morning commute thoughts and such 

 

 

 

 

 

2 minutes ago, AH64ID said:

Is there a 50° difference when cold/off as well?

 

From bottom up is the same +50*F off. This is why I'm got the defuel limit of EGT set to 1350*F because it actually fully engaged at 1,300*F and comes on at about 1,200*F. 

That screen capture was back during the summer time. Now with winter time I'm running slightly retard timing right at 19.5 to 20* at 2K.

4 hours ago, Mopar1973Man said:

That screen capture was back during the summer time. Now with winter time I'm running slightly retard timing right at 19.5 to 20* at 2K.

 

I'm toying with running the single event tune for some towing to see how it does. If that's the case once it warms back up I'll redo my numbers. 

 

 

Can a fuel return t leak cuase symptoms that would indicate low popping injectors? 

no,  Low popping injectors can only be due to the build of the injector.

1 hour ago, Me78569 said:

no,  Low popping injectors can only be due to the build of the injector.

Or how much use is on them??

1 hour ago, Me78569 said:

no,  Low popping injectors can only be due to the build of the injector.

 

12 minutes ago, dripley said:

Or how much use is on them??

So i have an intermittent miss/lope at idle hot or cold that im trying to figure if its injector or associated with the fuel leak at the back of the head that i have. 

16 minutes ago, Marcus2000monster said:

 

So i have an intermittent miss/lope at idle hot or cold that im trying to figure if its injector or associated with the fuel leak at the back of the head that i have. 

I dont believe a leaky return line can cause a miss. Loss of prime and extended starts yes. 

1 hour ago, Marcus2000monster said:

 

So i have an intermittent miss/lope at idle hot or cold that im trying to figure if its injector or associated with the fuel leak at the back of the head that i have. 

Bad injector spray pattern will cause the miss or lope.

32 minutes ago, Mopar1973Man said:

Bad injector spray pattern will cause the miss or lope.

Dam I’m not impressed that these injectors have issues with only 10k on them. I can’t decide what I should do. Funds are tight and cheapest option is repop my stock injectors for 175$ and ideally a set of brand new 75hp vco for 350$. 

35 minutes ago, Marcus2000monster said:

Dam I’m not impressed that these injectors have issues with only 10k on them. I can’t decide what I should do. Funds are tight and cheapest option is repop my stock injectors for 175$ and ideally a set of brand new 75hp vco for 350$. 

Have you spoken to DAP about the problem? If you want a decent kick in power and are a ways away from a tuner, get you some new RV275's. You will not be sorry. They are very good injectors and should give you a good life. Not sure what NEW 75hp injectors you are seeing on DAP's site. I have a set of their 50's, with aftermarket bodies, with 100k on them that are just now showing some weakness. The RV's are great on a stock truck or with a mild tuner.

4 minutes ago, dripley said:

Have you spoken to DAP about the problem? If you want a decent kick in power and are a ways away from a tuner, get you some new RV275's. You will not be sorry. They are very good injectors and should give you a good life. Not sure what NEW 75hp injectors you are seeing on DAP's site. I have a set of their 50's, with aftermarket bodies, with 100k on them that are just now showing some weakness. The RV's are great on a stock truck or with a mild tuner.

No I plan to speak with hem tomorrow. I would like to get a Adrenaline eventually when they come out with they’re monitor. I’m also contemplating 90s with higher pop as they can be a smokeless stock without lag if popped right. I could handle the egts until a tuner shows up I think.