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.

Someone correct me if I am wrong here, but to expect 90hp injectors to burn clean with no lag on a stock truck is a lot to ask. My 50's with the comp are smokey and laggy if I just stick my foot in it, If I take a short roll into the throttle and let the boost build a bit before I stick my foot in it I can limit the smoke and the lag but you have to use your foot for a governor on both.  I get  pretty good results for me with that method.

58 minutes ago, dripley said:

Someone correct me if I am wrong here, but to expect 90hp injectors to burn clean with no lag on a stock truck is a lot to ask. My 50's with the comp are smokey and laggy if I just stick my foot in it, If I take a short roll into the throttle and let the boost build a bit before I stick my foot in it I can limit the smoke and the lag but you have to use your foot for a governor on both.  I get  pretty good results for me with that method.

 

Ironic you mention this. This is with my Smarty on SW5, TM4-T4-D3.

 

 

Edited December 27, 20186 yr by pepsi71ocean

7 hours ago, pepsi71ocean said:

 

Ironic you mention this. This is with my Smarty on SW5, TM4-T4-D3.

 

 

Thanks for the video. 

@pepsi71ocean What have you been getting for fuel economy?

Nice to see your face @pepsi71ocean ... Now I've also seen the rust bucket that you working with. 

 

As for injectors yes pop pressure makes a big difference in how the engine performs in cold start and smoke. Like mine are low in the pop pressure I roll off an initial bluish cloud and then the haze of bluish vapor continues. Smells of raw fuel. 

At throttle, the injectors are OK the line pressure is high enough to produce a good burn but not optimal. 

Edited December 27, 20186 yr by Mopar1973Man

What's the best way to find a leak in the intake? I can't build boost sitting in my driveway and I can't put my head under the hood while I'm driving...Rebuilt injectors helped some, and I'm hoping once the seats get worn in it will get a little better, but it's not good enough yet. I saw 1380* today getting on the freeway (aggressively yes, but still). My intake exists of sections of 3" aluminum tube joined with silicon rubber 90* connectors (rated to 90 psi). Also, maybe I should have looked into this earlier but a previous air filter I used, which was installed directly on the turbo inlet, had a little metal button on the tip of it that held the filter together (see pic, my description doesn't do justice). It's not totally obvious from the picture but this little button has an outside rim that makes the button EXACTLY the same size as the turbo inlet. So...one day I was driving down the road and hear this weird grinding sound. I pulled over to the side of the road, opened the hood, and listened for the sound but of course it went away. I got back on the road again and the sound came back so I headed home immediately. Upon removing the air filter I found the button in the turbo inlet and it had worn off the turbo wheel around the outside of the inlet hole. Considerably. Could this possibly be the source of my problem? I immediately replaced the filter and the power felt like it came back but honestly the filter could have been THAT bad. They get real dirty riding right behind the alternator. I bought a TIG welder and I'm practicing up so that hopefully some day soon I can build the whole intake system out of stainless including a cold air that's routed away from the filth of the engine. Anyways, worn turbo wheel affect fuel consumption and EGT's yes or no?

I would part a photo so we can look at the turbo compressor. 

 

As for checking for leaks you can build a boost boot. It is basically a  4" PVC pipe cap with an air nozzle on it that you can pressurize. I use the regular on the compressor to turn the pressure up. If there is a leak you'll hear it by 20/25psi it so.

4 minutes ago, Scottfunk said:

What's the best way to find a leak in the intake? I can't build boost sitting in my driveway and I can't put my head under the hood while I'm driving...Rebuilt injectors helped some, and I'm hoping once the seats get worn in it will get a little better, but it's not good enough yet. I saw 1380* today getting on the freeway (aggressively yes, but still). My intake exists of sections of 3" aluminum tube joined with silicon rubber 90* connectors (rated to 90 psi). Also, maybe I should have looked into this earlier but a previous air filter I used, which was installed directly on the turbo inlet, had a little metal button on the tip of it that held the filter together (see pic, my description doesn't do justice). It's not totally obvious from the picture but this little button has an outside rim that makes the button EXACTLY the same size as the turbo inlet. So...one day I was driving down the road and hear this weird grinding sound. I pulled over to the side of the road, opened the hood, and listened for the sound but of course it went away. I got back on the road again and the sound came back so I headed home immediately. Upon removing the air filter I found the button in the turbo inlet and it had worn off the turbo wheel around the outside of the inlet hole. Considerably. Could this possibly be the source of my problem? I immediately replaced the filter and the power felt like it came back but honestly the filter could have been THAT bad. They get real dirty riding right behind the alternator. I bought a TIG welder and I'm practicing up so that hopefully some day soon I can build the whole intake system out of stainless including a cold air that's routed away from the filth of the engine. Anyways, worn turbo wheel affect fuel consumption and EGT's yes or no?

You need to build a boost cap that mounts on the turbo and squirt all piping with soapy water. Any leaks will bubble up immediately. 

Just now, pepsi71ocean said:

I would part a photo so we can look at the turbo compressor. 

 

As for checking for leaks you can build a boost boot. It is basically a  4" PVC pipe cap with an air nozzle on it that you can pressurize. I use the regular on the compressor to turn the pressure up. If there is a leak you'll hear it by 20/25psi it so.

Dang we were typing at the same time! 

Can low popping injectors also make the engine clatter/knock more? Obviously these trucks are loud as is but I’m sure mine just got way louder as far as timing/fuel knock. 

Typically timing advancement is what makes the knock. Retarding makes it quiet typically.  

All the talk about boost got me thinking...when WAS the last time I heard the wastegate open? Since I couldn't remember I made a pass through downtown Boise on my way home last night and did a couple 5-35 MPH full throttle blasts and sure enough no wastegate. I threw together a test boot and slapped it on and sure enough leaks everywhere. Must just be settling in from normal heat cycles. Anyways I tightened down all the clamps on the intake and it sounds much better, EGT's are down a bit but I still hear a bit of a wheezing sound from under the hood so I guess the search is not yet over. Don't tell my wife I could have saved $400 on new injectors if I would've thought to test for boost leaks BEFORE getting the injectors rebuilt. Shoot they needed it anyhow...

6 minutes ago, Mopar1973Man said:

Typically timing advancement is what makes the knock. Retarding makes it quiet typically.  

Wowed that it would start knocking louder. I run the mpg cooler full time and that should retard  the timing right? What else would cause that timing knock?

Low pop pressure means advanced timing. Then being you don't have a tuner the ECM cranks up another +4 degrees advancement.

 

Yes MPG fooler prevents that +4 jump in timing. Then lower pop pressure means early injection event.

 

This why when you raise pop pressure above 310 bar you now start regarding timing and possible make it difficult starting because retarding.

On 12/27/2018 at 6:40 AM, Marcus2000monster said:

Thanks for the video. 

@pepsi71ocean What have you been getting for fuel economy?

Sorry I'm just seeing this.

 

My mpg didn't change, however it's been getting worse over time. I suspect this is due to hanging brakes, a worn unit bearing, and several fuel leaks I've discovered under the Dodge.

 

Just so Mike can appreciate some Jersey rust, this is the war I've been waging.

 

So for me I can't say it went up, but I can go based on how the truck was running before I downed her for this massive job. The performance, stupidly fast low end spool, lack of smoke, and even my transmission shifting patterns were all different. She was a totally different truck once she settled down. The first 15 starts were goofy, but she's always started, and I'm really excited to see how she runs once it's back together.

 

 

This puppy was seized in there.

 

 

This one the passenger brake was constantly sticking and I was seeing 450f with a temp gun, there wasn't any grease left in her when I took her out.

 

On 12/29/2018 at 9:14 AM, Marcus2000monster said:

Can low popping injectors also make the engine clatter/knock more? Obviously these trucks are loud as is but I’m sure mine just got way louder as far as timing/fuel knock. 

 

Mine is very quiet now compared to before I got them popped. I can't give you a scientific answer, but warm at temp she's quite quiet.

 

Even cold you can see in my video how quiet it idles. I have too look and see but I may have a video with some idling with the lower pop pressure injectors in it.

OK I've had my injectors rebuilt and matched and chased down multiple boost leaks. My load/egt numbers are still pretty high and I haven't seen a marked improvement in fuel economy. I observed a couple weeks ago when I started on this quest that my compressor wheel had sustained some damage. I think SOME damage may have been a serious understatement. Judging by the pictures, would this be a possible source for my problem? I noticed recently that even under FULL acceleration I couldn't get 30psi. Assuming that at least most of my leaks are gone, should this be my next focus?

 

That being said what would be the best way to fix this? I can get a replacement wheel on Amazon for $40, a whole new hx40 with t3/t4 adapter on eBay for $220, or an hx40 wheel/housing combo for abot $180. I know there would be some adaptations with the second two and maybe some turbo lag which I could probably adjust for slightly with the Quadzilla. I'm happy with the power I have now but do plan on using her for a towing rig in the future and it feels like the bigger turbo should help with EGT's, but if that's not going to be significant then I'll stick to stock. Keep in mind I have a Cummins/Allison combo in a '96 GMC so adaptation is the name of my game. Thoughts?

Yea your compressor is toast. I wouldn’t buy a cheap eBay turbo they won’t last. Maybe consider a 351cw  swap.

Edited January 2, 20196 yr by Marcus2000monster

On second thought I think I'll just replace the wheel for now and upgrade to a VGT in the future. Think that'll make me happier for top end and spool up. Thanks

12 minutes ago, Scottfunk said:

On second thought I think I'll just replace the wheel for now and upgrade to a VGT in the future. Think that'll make me happier for top end and spool up. Thanks

 

This is a good plan as well. personally i would do a HX40/35 turbo rebuild.  When you had those injectors rebuild what pop pressure did you set them to?

This is who built mine, http://www.northamericanturbo.com

They probably have parts for whatever you need. 

I have a 35/40 something else hybrid, but if you're not using exhaust brake that bolts to turbo with 5 bolts then I would just get sx362 I believe is what I was recommended, close to what I have now but with 4" exhaust outlet, mine is only 3". 

2 hours ago, pepsi71ocean said:

 

This is a good plan as well. personally i would do a HX40/35 turbo rebuild.  When you had those injectors rebuild what pop pressure did you set them to?

I believe it was 315. They said they should settle into the middle of the range once the seats wear in.

 

1 hour ago, Dieselfuture said:

This is who built mine, http://www.northamericanturbo.com

They probably have parts for whatever you need. 

I have a 35/40 something else hybrid, but if you're not using exhaust brake that bolts to turbo with 5 bolts then I would just get sx362 I believe is what I was recommended, close to what I have now but with 4" exhaust outlet, mine is only 3". 

I don't have an exhaust brake yet, but I would like one. A 4" outlet would be nice too! Maybe a 35/40 with a billet wheel? hmmm...

6 hours ago, Scottfunk said:

On second thought I think I'll just replace the wheel for now and upgrade to a VGT in the future. Think that'll make me happier for top end and spool up. Thanks

 

You need to find out what/why it is ingesting foreign objects. Is your air filter being eaten alive? You may have intercooler/engine damage.