Engine/Transmission (1994 - 1998) Crappy Mileage is p***ing me off

[cluckmaster]

OK. Haven't had a chance to check my timing yet, but w/ the new overflow valve, I got 13. 5 (uncorrected for 35" tires and 17" wheels) mpg on my last tank. I guess my plan is (after my transmission goes in Mon) check timing, reclean prefilter screen, then switch out the injectors. Not sure what else to do. This is not cool.

 

[bmoeller]

EDMed injectors get (such as the DDP3s or 4s)

The DDP injectors AREN'T EDMed injectors. Extrude honed, unless they switched since I bought mine.



Have you checked the fuel pressure? Overflow valve condition?

 

[cluckmaster]

The DDP injectors AREN'T EDMed injectors. Extrude honed, unless they switched since I bought mine.



Have you checked the fuel pressure? Overflow valve condition?

Brand new overflow valve from TST. Working on getting a fuel gauge. I thought they were EDMed and THEN extrude honed to clean up the edges, but you're probably right. -Josh

 

[bmoeller]

Could be wrong, but my understanding is that the EDM injectors start with blank tips only. That is why they cost more.

 

[Cooker]

Could be wrong, but my understanding is that the EDM injectors start with blank tips only. That is why they cost more.

The majority of EDM injectors being sold do not start with blank tips.



I agree, DDP injectors are not EDM.

 

[cluckmaster]

The majority of EDM injectors being sold do not start with blank tips.



I agree, DDP injectors are not EDM.

From the site:



"What is the difference between Hone, EDM, and AFM?

Electro Discharge Machining is a process where an electrically charged wire burns a hole through metal. Bosch uses EDM to create nozzles, but on a very advanced machine that controls the angle and speed of the wire insertion. The angle of insertion is very important to keep correct or the spay angle will be changed, resulting in possible engine damage. When Bosch changes the speed of insertion they can achieve a cone shaped hole that will improve atomization. EDM’s used in the aftermarket are usually decommissioned medical instruments that do not have the ability to control either angle or speed precisely enough to create a quality product. Electro Discharge Machining that is done by Bosch is followed by Abrasive Flow Machining, to clean up any imperfections, remove burn residual and balance injector flow. Aftermarket EDMing does not use AFM to balance flow, or clean up any imperfections. DDP Injectors use Hone Technology. We start with an EDM’d nozzle with the correct spray angle, and finish Hone them to remove imperfections, polish the inside of the nozzle, and radius the inside of the holes where the fuel flows. This leads to better atomization, which provides less smoke and heat, and more power and mileage. Adding volume without helping atomization only adds heat and smoke, which means less useable power. "

 

[JGK]

Just read this thread for the first time. I'm going to go with the suggestion that it's your home-brew porting job. The other mods you've done may add to the problem.



I have a throw away head (hairline crack) and I spent probably a dozen hours or more working over the ports one or 2 at a time and testing them on a flow bench. It was amazing the results I got. Most importantly, it was extremely difficult to get consistent results. In some cases, I improved flow at low valve lift and had it drop of considerabley at high lift. In other cases, just the opposite. And as the flow rate changed, so did the results. The point is, you just can't realistically go in and remove a bunch of metal and expect great performance or mileage unless you're extraordinarily lucky.



Everything else you've checked and double checked, it appears. This is the one thing you can't check. I may be wrong, but from my little bit of experience with porting, that's where I'd say your loss is from, at least a fair amount of it.



FWIW,

-Jay

 

[Cooker]

The majority of EDM injectors being sold do not start with blank tips.



I agree, DDP injectors are not EDM.

A little clarification.



It is no secret that Bosch, or any OEM injector producer, uses EDM to create the holes. When referring to aftermarket injectors the terminology takes on a little different scope. The injectors are commonly classified as whatever process the aftermarket vendor applies to them.



In the aftermarket, most aftermarket EDM injectors do not start with blank tips. They start with stock tips and make them larger with an additional EDM process.



DDP starts with stock tips and their modfications involve honing them. They are then referred to as extrude honed injectors.

 

[Vaughn MacKenzie]

I have a throw away head (hairline crack) and I spent probably a dozen hours or more working over the ports one or 2 at a time and testing them on a flow bench. It was amazing the results I got. Most importantly, it was extremely difficult to get consistent results. In some cases, I improved flow at low valve lift and had it drop of considerabley at high lift. In other cases, just the opposite. And as the flow rate changed, so did the results. The point is, you just can't realistically go in and remove a bunch of metal and expect great performance or mileage unless you're extraordinarily lucky.

Interesting observation Jay. I did my own head on the '96 and it's the first time I've ever done it. The engine has never been quite as smooth as it was before so based on what you're saying that could be the cause. And maybe that's what's contributing to the mysterious miss I chased for a long time which started about 1000 miles later.



Before you even posted this I'd already made the decision to leave the head alone on the '98 and improve breathing via a cam upgrade. Your post helps justify my decision. The only thing I may do is open up the area just behind the valve seat and smooth the ports a bit without affecting the contour, and knock down the big blob in the intake near #1.

 

[cluckmaster]

Just read this thread for the first time. I'm going to go with the suggestion that it's your home-brew porting job. The other mods you've done may add to the problem.



I have a throw away head (hairline crack) and I spent probably a dozen hours or more working over the ports one or 2 at a time and testing them on a flow bench. It was amazing the results I got. Most importantly, it was extremely difficult to get consistent results. In some cases, I improved flow at low valve lift and had it drop of considerabley at high lift. In other cases, just the opposite. And as the flow rate changed, so did the results. The point is, you just can't realistically go in and remove a bunch of metal and expect great performance or mileage unless you're extraordinarily lucky.



Everything else you've checked and double checked, it appears. This is the one thing you can't check. I may be wrong, but from my little bit of experience with porting, that's where I'd say your loss is from, at least a fair amount of it.



FWIW,

-Jay

Ugghhh... . that's not what I want to hear Took a LONG time to get those things just right. BUT, I didn't have a flow bench like you, and you still had trouble, so I'm probably in worse shape. I did talk to a couple of folks about it before hand and they thought it would not do any harm, at least, and would probably help, but maybe I should have left it alone.



How exactly would it cause poor power/mileage if one of the ports flows a little different than another? Thanks. -Josh

 

[JGK]

The relation between bad flow and poor mileage is beyond my limited knowledge, so I can only offer a general theory. Usually, porting is done to improve performance. But performance comes from improved efficiency in getting the most engery out of a given quantity and mix of fuel and air, and getting the mix in and out of the cylinders. If you mess up the flow characteristics, you likely reduce the efficiency, and therefore it would seem to follow that you end up getting less useable power out of the fuel you're burning. Hence, it takes more fuel to get the rig down the road because it isn't being efficiently used (burned).



The intake and exaust ports on these heads are really not at all refined. They are pretty rough. But for their designed use, they work OK.



Actually there are a few things you can do that help that doesn't require a flow bench or hundreds of hours of experience. The hump partially blocking the number 1 intake can be removed. Common sense says that's GOT to help. The exhaust ports where the head mates to the manifold can be matched to the gaskets. Not opened up as big as the gaskets, just evened up and smoothed out, along with equivalent work on the manifold. The same can be done where the manifold flows into the turbo.



But back to the head porting. One thing I did find is that I could improve the intake port flow reasonably consistently. It wasn't a huge increase, but some, and I did 2 or 3 that were fairly well matched. On the other hand, keep in mind the air charge is being forced in at 35 lbs and up under load. So the flow improvements may not have a huge affect. But the exhaust side was tough. And messing things up there may mean you're not getting everything out on the exhuast stroke and so you're messing up the incoming charge and subsequent burn. So, performance and mileage suffers.



In any case, yes, this is not what you wanted to hear. And I may be totall wrong. Your problems may be something else.



I just re-read your original post and I noticed you said the mileage was about 16/17 after the mods, which is about what I get on summer diesel, though I have a different cam (PDR) and the head is still stock. But then you said you've noticed its dropped, so something else could be going on. If it changed over time that would point to something other than the head work. So don't give up hope yet. My mileage drops a bit on winter diesel - I've been getting 14/15 this winter, which is normal. Also, as bmoeller suggested, check your fuel pressure - it could be a clogged fuel filter or a wead overflow valve. So there are a few other things you can check.



-Jay

 

[cluckmaster]

UPDATE- Finally got around to checking the timing- it's dead on at 17. 5*, just where we set it. I have removed the prefilter screen and cleaned it again, and like I said, the filter and overflow valve are new. This weekend, I pulled my #8 plate and replaced it w/ a #100 plate full forward w/ the acf full foward. Might as well get some power w/ my crappy mileage. Haha. I'm going to check this tank and I'll post up w/ latest results. -Josh

 

[Cooker]

A full forward AFC will not help mileage.



I did not reread this thread but low fuel pressure will hurt mileage as will air leaks into the fuel system.

 

[RDelissen]

and if you haven't changed the gearing after going from 30" tires to 35" tires, how do you expect the truck to keep the mileage in the 20 mpg range, even with all the engine work?