Horrible Mileage...STILL...after alot of work/troubleshooting

[Doakster]

I can not believe i'm still getting low 30 mileage after all the things I've looked at over the last few months. Here is what i've done or looking at.

-Was getting 43mpg when i first got the car.
-Mileage dropped to 33ish
-Completely replaced all front end parts, bearing, brakes, (brakes are not dragging and bearings are good)
-Completely replaced all rear brake parts and bearings, they are not dragging either.
-Had small turbo boot leaks, which i fixed, no boot leaks anymore.
-Checked compression, all cylinders were within spec.
-Checked IP timing, all was within spec.
-Just installed rebuilt stock injectors by Giles, with new Bosch nozzles.
-Installed 2.25in exhaust from turbo back
-Pulled trans due to replacing clutch, tore down trans for rebuild and put in taller 3.94 Ring and Pinion in place of my 4.25 AVX trans, installed peloquin LSD.
-Checked my speedo against a GPS, only off by 2-3mph when above 45-50mph, mainly due to my larger tire size.

Got the car up and running today and did a mileage run for about 110 miles. My mileage was the worst i have ever gotten, 31.5 mpg

I'm going to check internal pump pressure tomorrow with a gauge and adjust to the recommended, i'll have to dig up that thread to get the RPMs vs Pressures, or if someone knows them please post them up.

The only other things i can think are the problem are the IP going out or the turbo going out, (don't have gauges yet to check boost pressures, that will be something in the future). I'm leaning toward the IP being the issue.

I have seriously had enough with this issue, i would love some other suggestions.

[burnt_servo]

do a 4 wheel whel aligiment  ,  pay attention to how the rear wheels are setup .
check the air pressure in your tires , and find the max pressure rating on the tire , and fill the tires to that , and take note of your millage .

measure your injection timing dynamicly .

i noticed a decent improvment in millage just from going to 0w-40 oil from 15w40 .

[Doakster]

do a 4 wheel whel aligiment  ,  pay attention to how the rear wheels are setup .
check the air pressure in your tires , and find the max pressure rating on the tire , and fill the tires to that , and take note of your millage .

measure your injection timing dynamicly .

i noticed a decent improvment in millage just from going to 0w-40 oil from 15w40 .

Alignment was done when i did all the front end work, the alignment still feels good, before and after the alignment i was getting 43mpg.

I'll check my tire pressure but i think they are near the max pressures.

I already run 15w40 oil.

Can you explain what you mean by checking the timing "dynamicly", how is this different than a normal timing check?

[Doakster]

On the oil, i re-read the previous post and saw you switched to 0W-40.

I think you'll probably agree that a 10plus mpg drop can't be solely the result of running 15w-40 oil. I have always run that oil and got 43 mpg with that oil before my mileage dropped big time.

[Doakster]

It takes some fairly expensive tools to check the dynamic timing advance, namely a diesel pulse adapter and timing light with advance and tachometer functions.

I think it's a really good idea to check the internal pressure which is one of the most significant factors that affect the dynamic advance.

Hopefully i'll be checking it tomorrow, is there anything else to check on the pump besides internal pressure and timing?

[Doakster]

Checked the internal IP pressure tonight.

At 500 pump rpm, I was only at about 25psi. Made an adjustment up to between 40-45psi at 500psi. I couldn't get it exact because i was using a cheap gauge that didn't have a pressure dampener and bounced a bit, but i think i am at about 43/44 psi now.

Checked 750 and 1000 rpms, the 750 looked good at around 60psi and at 1000rpm i was just over 70, so a little shy of the suggested 75psi at 1000 rpms.

I did a mileage run, only did about 40 or so miles, so it really isn't all that accurate as it's not a broad range, but i think i got about 35ish, but about 1/3 of those miles were before the adjustment, so hopefully I'll still see an increase. If it get's back up in the 40's i'll be pretty happy. I'll be able to do a 100plus mile run this weekend.

Any other thoughts?

[Doakster]

What car is it?  What engine?

Sorry about that, i should have stated it earlier.

91 Jetta, 5spd, 1.6 ECO, stock pump (besides the recent adjustment), freshly rebuilt stock injectors with new bosch nozzles from Giles, 2.25in exhaust turbo back, stock turbo.

[Doakster]

Forgot to mention earlier, i've replaced the air and fuel filter, to rule that out.

[Vincent Waldon]

Your internal pressure was almost half of what it should be... I'd run a least a tank thru for accurate mileage measurements before adjusting anything else.

[Doakster]

Your internal pressure was almost half of what it should be... I'd run a least a tank thru for accurate mileage measurements before adjusting anything else.

Your right, i knew is wasn't going to be an accurate reading when i ran it this evening, I just wanted to post some general numbers up tonight for reference. I will run a tank through it hopefully this weekend.

Would that low of a pump pressure really have a 10mpg decrease? I can't speak from experience since this is the first time for me making the changes.

[Rabbit TD]

I didn't read the whole way through your thread but have you eliminated air getting in the pump from the fuel lines sucking in air.  I just recently put a new clear fuel line on my TD and was amazed at the amount of air going in the pump from a line to the filter that I re-routed when I had to relocate the fuel filter.  My mileage was good though but it was getting harder to start.  A good clear line does help diagnose things though

[Doakster]

I didn't read the whole way through your thread but have you eliminated air getting in the pump from the fuel lines sucking in air.  I just recently put a new clear fuel line on my TD and was amazed at the amount of air going in the pump from a line to the filter that I re-routed when I had to relocate the fuel filter.  My mileage was good though but it was getting harder to start.  A good clear line does help diagnose things though

I do have clear lines on the supply and return lines to the pump and don't have any visible air, so i think i am good to go there.

Maybe there is hope for me after all. If i get that 10mpg back i would be tickled pink. We shall see.

[SolarSteve]

How did you increase your pump pressure?

[Vincent Waldon]

How did you increase your pump pressure?

Here's the thread ye seek:

http://www.vwdieselparts.com/forum/viewtopic.php?t=5936

[Doakster]

How did you increase your pump pressure?

The picture below is from the thread for a tool that can be made to go in place of the"out" bolt of the pump. Some NA pumps or ECO pumps will have this extra spacer on them. I called Giles (Performance Diesel Injection) and he sent me a spare for $5.00. I drilled and tapped it for a grease line (can be found at any harware/auto place), and installed a 0-200psi gauge on the grease line. This was put in place of the "out" bolt on the pump for the test. I bought a laser tachometer off ebay for $25 bucks so i could check RPMs at the pump pulley (my ECO doesn't have a tachometer). The entire set up probably cost me 40 bucks. Then you run up the rpms to check the following.

-IP Pressure @ 500 RPM should be 3 Bar (43.5 psi)
-IP Pressure @ 750 RPM should be 4.1 Bar (59.4 psi)
-IP Pressure @ 1000 RPM should be 5.2 Bar (75.4 psi)
-IP Pressure @ 2000 RPM should be 10.4 Bar (150 psi)

You can also check with engine rpm if you have a tach in the car and won't have to get a laser tach, engine rpm is twice the pump speed. The ones i listed above are for pump rpms.

If the pressure is low you then all you have to do is adjust it at the plunger assembly which is described in pages 1 & 2 of the thread posted. But the thread goes into more detail, it's a good read but takes awhile.