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Old April 18th, 2018, 09:18   #16
Join Date: Apr 2015
Location: east texas

read the tandem pump thread carefully going to try to check output and pressure. may need to order parts for the 1500 rpm test, i dont think i have a banjo bolt in my fuel pressure test kit
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Old April 18th, 2018, 13:39   #17
Join Date: Apr 2015
Location: east texas

ok, so update on fuel pressure and output tests:

did the lift pump test with it hooked to 12V, it's output was low...about 2.3 lit per min. checked it twice was w/in a hundred ml or so at most 2.4l/min

psi on that same deal was 10 so that part was ok or w/in range but flow was low.

then i did the return leak test and it was way more than the 0 to 25 cc specified. got about 75 ml/ min times two different one minute tests.

then i tried to do the fuel pressure test off the port and failed. my kit has a banjo bolt with fuel fitting for the guage that is 12 x 1.5 and i had a spare oil line so i hooked it up on the fititng and capped off the oil line effectively using it as washer and that was a no go. fuel would run out of the end when i took the cap off but had no pressure, guage would not move.
thought maybe it needed to be on the end of the oil line set up so i adapted it to fit on there and still nothing, could get fuel out when i pressed the relief valve of the gauge in a slow stream but no reading.
not sure if this is because it just has zero pressure or if i am reading it wrong.
it did fail the return test by having high output. lift pump in tank also has lower than spec flow. 2.3 in stead of > than 3 lpm.

any tips on reading the pressure at the port? i have the O Reilly fuel pressure kit and it has the banjo bolt with fitting for the guage on the other end, the 12 x 1/5 thread side threaded right in, hooked the guage up to the fitting. nothing.

thinking about swapping tandem pumps with my other bew even though i hate to screw with the working one but i also dont want to order one of those if i am not sure it is bad.
is the return test enough to verify it bad? i tried blipping the throttle but gauge didnt move which seemed strange when i had it hooked to the test port... think something is screwy there but possibly with my tool, seems like it would read some psi there since it is supposed to be 51 at 1500.
any opinions/tips on what is going wrong there/ how to do it better.. welcome. still trying to sort this.

changed the maf with my good one by the way, no change, my good one ran like a scalded cat with the sick cars maf so def not that, it looked good on vagcom anyway but now i am positive ...

Last edited by speedy223; April 18th, 2018 at 13:43.
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Old April 18th, 2018, 14:26   #18
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Join Date: Sep 2004
Location: Chicago
Fuel Economy: 35-38 avg.

Nice diagnosing.

Sounds like the only real test is to swap lift pumps and see if that cures it.

A new lift pump can be had for $125 (https://www.metalmanparts.com/produc...&categoryId=-1). I'm not affiliated with the vendor, just a satisfied past customer.

Good luck and keep us posted on your progress.
2014 GLK250 BT // 65xxx miles // 37 MPG - current
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Old April 18th, 2018, 17:43   #19
Join Date: Apr 2015
Location: east texas

well... sounds like both possibly doesnt it? i mean the lift pump is underperforming but i believe that the pump leaking too much means it is bypassing in the tandem or have i read that right? possibly the lift pump led to tandem pump failing?

update number one: i read a deal where it says that depending on the BRAND of tandem you have 75ml/min return or so with lift pump running is normal. so i have to check that tomorrow. that was not mentioned to my knowledge in the PD tandem pump write up but i found it in another thread where the guy said he replaced it and fixed a problem he was having but the return flow was still 75 ml/min. think it was a bosch one. i guess the LUK if i remember right would be the 25 ml/min one.

update number two: in regards to not being able to read pressure at fuel pressure test port see below will post tomorrow when i am sure but here is my guess:

i think i have been looking at a diagram with only one place to read fuel pressure and i have a pump with both the return regulator port and the fuel pressure port. bet i have been reading off the wrong one and just used a fitting from my multi kit that fit that and assumed it was 12 x 1.5. . makes sense why there is some fuel but no psi. and also why i was not able to use the bolt from the oil line like the one guy used. i thought i misread what he used when mine wouldnt thread and it was 12x1.25 or something.
feel kind of dumb about that...just hit me in my chair while i was looking at the diagram i was using and then a picture of a pump with 2 ports. i will check in the morning but i may have bought a pump anyway if i lost the spring that goes in that or deformed it. lol. you live you learn. will update it tomorrow.

Last edited by speedy223; April 18th, 2018 at 20:39.
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Old Yesterday, 21:46   #20
Join Date: Apr 2015
Location: east texas

i checked it a the correct test port. still no decent reading. not sure why. took the pump off, it is a bosch, took it apart and cleaned it and reassembled it. seemed fine but hard to say. makes good vacuum. thinking about buying a used one and trying it but wish i could prove it was failing.
again has one worn lobe 2nd to last from end closest to tandem pump. lifter is good.
maf has been swapped with working one.
going to pull the exhaust loose tomorrow see if that helps.
still wont rev past 3800 in neutral sometimes only 3500 or so.
no power past 3k. not limp mode. boosts around 15 psi according to guage.
lift pump has lower output around 2.5 l/min max, psi 10.
tandem pump returns around 75-80 ml/min. with pump wired on engine off. is a bosch, that seems to be what someone else posted theirs did,
tried reading pressure off correct port 2nd time around, get bouncing 10 at idle, nothing when you rev up, weird,
removed cleaned pump, has good vacuum after rebuild as before, no change.
also going to see if i can move the torsion value off 0 to see if it is timed right as per advice previous in this thread
open to ideas.

can one cam lobe cause this? seems weird.... still seems like fueling. doesnt seem like it could make it not rev past 3500 when it is working and the lifter is good

also thinking about swapping lift pump with my other one to see if it could do this...hate to mess with the tandem pump on the working one...

Last edited by speedy223; Yesterday at 22:02.
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Old Yesterday, 23:26   #21
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Join Date: Dec 2014
Location: PNW

I know that it isn't common on these engines, but, any chance this could be due to intake clogging? Symptoms sure are dead-on similar.
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