In another thread I read something about new DS4-5521 pumps having horribly less fuel mileage than a rebuilt one? What are the reasons for it? Mine was replaced June of last year and it is not getting anywhere near the mileage others are claiming. I have not been driving heavy footed and I have 3.73's with 245/75/16s. I know I am due for injectors since I am at 102K miles. Will that help too?

I just filled up at $2.69 a gallon http://www.dieselplace.com/forum/images/smilies/censored.gifhttp://www.dieselplace.com/forum/images/smilies/Throwup.gifwhich is what brings some of these questions on.

Here are some pics of my pump incase pump gurus need to see which one I am running.

Thanks in advance!

Minw was replaced last year, and I didn't notice the fuel milieage change. Seems that whatever I do to the truck doesn't change fual mileage except for one thing the will increase it- slowing down. I have the same truck as you, and get 14-15 solo, and 9-11 towing my Blazer (15-16K total) or my travel trailer (12K or so). I also have a heavy right foot, and drive 70-80 MPH depending on location/conditions. I really want to lift the truck 4", and put on the brand new set of 35" H2 tires and wheels I have in the garage to lower the RPM's some.

Yeah, 14-15 but I keep it below 70 (by GPS)

Here is when my pump was done:

CLAIM HISTORY
Repair Order Date : 01/06/2003 Repair Order Number : 050096 Odometer Reading : 83650 miles
Serviced By : WINKEL PONTIAC-GMC TRUCK
PO BOX 7380
RENO, NV 89510-7380
(775) 329-0831 Selling Source : 16 - PONTIAC
Site Code : 23404
Business Associate Code : 116693
Cycle Date Cycle Nbr Case Type Labor Operation Part Auth Code Person Code Line Total Comments
01/31/2003 348 01 # T5550 - 1994-2002 REPLACE DIESEL INJECTION PUMP 12523753 - GASKET KI B N/A $ 527.43 N

iirc, the timing was retarded on some pumps TDG looked at due to customer complaint and the solution was to bump the time advanced.

I don't think the problem is in the pump but more on the install. Timing being one problem and two, I think the dealers may be reflashing some computers without the owners knowing. Just guessing so read the writing below.

Just by looking at those numbers, I'd ballpark that pump to being an '01, and therefore, not 'NEW'. I've not heard complaints of 'horribly' less mileage, just low power, hard/no start and premature CTIME problems. But no doubt the low power complaints probably also had lowered fuel economy.

My observations are rough finish on the FSOL face, shims under the poppet valve spring out of spec, and optic sensor improperly calibrated.

Can you also post a pic of the actual nameplate? Or just verify the Serial #?
Looks like 10142978, thats where I get the '01 ballpark from.

Something else I noticed, your truck is a '94.....did they put the right pump in it?
I've seen some 94s with the 5521s in them that were supposed to have 5068s. They definitely had low power/poor fuel economy. I've also seen a 5068 where a 5521 should be...black smoke, hard start, PLENTY of power and poor fuel economy ;)

That number is correct. That is the sticker on the round thing sticking out the top. If there is some other place I need to look please tell me.

TDG thanks tons for the information. Now I want to learn more. I have read your killer DS4 post but I don't know a damn thing other than what I have read about on here. Does anyone know where I can find an exploded view of the parts inside?

Also, back to my original question... will new injectors help my mileage? What about getting the pump retimed and the optical bump? They are no-joke talking about $3 to $3.50 diesel here in the coming months. I think it's time to get the old 1983 Kawasaki Copcycle out and get it running.

Thanks again all!

If injectors are questionable, either by performance or mileage..and yours are with 102k miles, then you should replace them.

Fuel conditioner with lubricity additive and Cetane improver will help also.

Optic bump is 50/50 whether it will help fuel economy, go a little and it could help, go too far and it probably won't.

Verify TDC Offset and reset if necessary, preferrably in the -1.5 ~ 1.9 area should help.

Okay, the original owner gave me ALL the repair order slips and maintenance history (don't ya just love anal people). On June 16, 1995 the truck got this:

A 94C57 DIESEL PUMP CAMPAIGN

V9333 94-C-57 POOR THROTTLE REPONSE - DIAG CK, INSTALL KIT, PROM & EXCHANGE PUMP - C/K TRK, L65 OR L56 TURBO

10 W94 8.70

Then there is a parts list:

1 12553873
1 16217520 EPROM

Then shows oil and filter and extra labor. Then:

1 25160561 FILTER AS
1 25099849 FITLER AS

FC: SK00
PART #: 12553873

Could this be when I got a new prom and the 5521?? Truck starts fine.

Ok, injectors are already on my to do list. I will have to try to find a scanner. I may just bite the bullet and ebay a tech 1. http://www.dieselplace.com/forum/images/smilies/frown.gif

That could be an updated prom for a 5068 still, I don't know if GM was authorized to replace PROMs with anything other than updated versions of the same ones under warranty.

GM PN for 5521 is 12561307, I don't recognize that PN offhand, nor do I know what it is for a 5068 pump, but I can find out.

I really appreciate it. It's kinda a downer to see people with L65's in dually's with 4:10s getting better mileage than I do. I always run lubricity additive with cetane boost and I see an improvement but daaaym. The other reason I want to get this ironed out is I eventually want to get a chip. If I have to buy a prom (OBD1) I would *really* like to get the right forking prom for the injection pump I am running.

Thanks for the help guys!

The 4068 was in the HD F engine only, far as I know.

Something else I noticed, your truck is a '94.....did they put the right pump in it?
I've seen some 94s with the 5521s in them that were supposed to have 5068s. They definitely had low power/poor fuel economy. I've also seen a 5068 where a 5521 should be...black smoke, hard start, PLENTY of power and poor fuel economy ;)
Tex,

How would a simple guy know what pump is supposed to be in his '94? What determines the correct pump? Is it the prom?

Tim

I am doing some research now. Here is an interesting thing I found:

<table bordercolordark="#666666" bordercolorlight="#CCCCCC" background="whttxtr2.jpg" border="1" cellpadding="2" cellspacing="3" width="100%"> <tbody><tr><td width="175">1994 <!--mstheme--></td> <td width="200"><!--mstheme-->DS4-5068<!--mstheme--></td> <td width="200"><!--mstheme-->DS4-S5068<!--mstheme--></td> <td width="150"><!--mstheme-->10225929<!--mstheme--></td> </tr> <tr> <td width="175"><!--mstheme-->1994 - 1998<!--mstheme--></td> <td width="200"><!--mstheme-->DS4-5067<!--mstheme--></td> <td width="200"><!--mstheme-->DS4-S5288<!--mstheme--></td> <td width="150"><!--mstheme-->12558156<!--mstheme--></td> </tr> <tr> <td width="175"><!--mstheme-->1994 - 1998<!--mstheme--></td> <td width="200"><!--mstheme-->DS4-S5288<!--mstheme--></td> <td width="200"><!--mstheme-->DS4-S5459<!--mstheme--></td> <td width="150"><!--mstheme-->12561405<!--mstheme--></td> </tr> </tbody> </table> <!--mstheme--> All pumps are rebuilt to latest factory specifications and upgrades. Please note the latest upgrade from DS4-S5288 to DS4-S5459. This change is for a new style drive washer and an upgrade to the latest model encoder sensor. This upgraded pump will fit all regular duty 1994 - 1998 model 6.5L GM trucks. The DS4- S5068 pump was for 1994 Heavy Duty trucks only.

Actually, 5521 is the latest, updated stepper motor. 5288 came out back in '95 or '96.

If you have a 94 truck with a egr it's a light duty. No egr it's heavy duty DS4-5068 pump.

Some maybe different but I don't care to discuss it.