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Old October 18th, 2018, 23:46   #1
golfere
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Default PD Hiccup / Hesitation under light pedal

trying to fix a 2004 BEW that has new turbo & fuel filter -

Basically when i drive from around 1500-2000rpm and accelerate lightly the car jolts and hiccups (cuts out for a second for it to catch itself, turbo stops working until the rpm is higher or pedal is pressed more)

I can replicate the problem sometimes if i just let the rpm drop back to below 2k rpm and accelerate lightly


What else do you think it could be? Lift pump? Retune?
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Old October 19th, 2018, 08:33   #2
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The turbo is controlled by vacuum so make sure there are no vacuum leaks. The N75 valve is an electrically actuated valve that the engine computer uses to control how much vacuum is being sent to the turbo, so check all the small hoses related to that system to make sure there are no leaks, kinks, or collapsed hoses.

Is the turbo a new Borg-Warner KP39 from a reputable vendor? Or did you use something else. There are a few viable choices, but also some junk from China available.
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Old October 19th, 2018, 08:49   #3
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Unplug the MAF and see if it still does it.
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Old October 20th, 2018, 11:29   #4
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Yes, could be MAF.

A VCDS read while on WOT, would be better to find the problem.
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Old October 20th, 2018, 23:42   #5
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I unplugged the MAF and the car ran terrible; had to plug it back

turbo is an upgraded garrett gt1749v i believe - i will try to get it logged using VCDS and post back here

Thanks!
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Old October 21st, 2018, 06:08   #6
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I had a problem similar to this. Light throttle and usually only on one particular place in the road. I checked everything, lift pump, MAF, etc, a slight torsion adjustment finally solved the problem.
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Old October 22nd, 2018, 11:24   #7
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Quote:
Originally Posted by Tdijarhead View Post
I had a problem similar to this. Light throttle and usually only on one particular place in the road. I checked everything, lift pump, MAF, etc, a slight torsion adjustment finally solved the problem.

I feel like you and i are constantly talking about torsion haha; I guess i need to adjust and record whats going on! Im right at -1.0 / -1.5


Yes it only does it sometimes! I tried recording a log on my way home and it never hiccuped once
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Old October 22nd, 2018, 12:08   #8
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Check also if you have oil on the fuel filter. Since it's a PD ...
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Old October 22nd, 2018, 18:10   #9
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Quote:
Originally Posted by golfere View Post
I feel like you and i are constantly talking about torsion haha; I guess i need to adjust and record whats going on! Im right at -1.0 / -1.5
Yes it only does it sometimes! I tried recording a log on my way home and it never hiccuped once

Youíre right, while torsion is important it isnít the only thing that could cause a slight hiccup.

Did you check the lift pump?

Another forum member had a slight skip and it turned out to be a faulty egr valve.

Unplug the egr and see what happens.
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Old October 22nd, 2018, 20:59   #10
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Good point on the EGR valve, i did an output test with VCDS and it works properly

I can hear the "squish" sound every time i turn ignition so doesnt that mean the lift pump works well?
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Old October 22nd, 2018, 23:20   #11
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http://log.malonetuning.com/chart/24...nCoAAAAA%3D%3D


Managed to log the "hiccups" right around 2k rpm in 3rd gear slowly creeping up a hill

Anything seem crazy? This is with a stage 1.5 tune


Still want to adjust my torsion value as that also could be why my mpg has not gotten past 40mpg right?
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Old October 23rd, 2018, 04:53   #12
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Take the EGR valve out, see that it is completely closed (shine a light around the seat of the valve).

Then, do an Output Test of the EGR valve (KOEO) and see if it cycles properly and closes all the way every time.

Simply unplugging it won't help, as it could still be stuck slightly open when it shouldn't be.
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Old October 23rd, 2018, 05:27   #13
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Also, a boost leak will cause a stumble or "hiccup" when you accelerate. A boost leak will usually be accompanied by a hissing sound when the stumble occurs.

Boost leaks are hard to diagnose because if you rev the engine without putting a load on it you will not hear the telltale hissing sound because the turbo is not coming up on boost.

You can cause the turbo to come up on boost while standing still by maintaining about 1500 RPM's and gently lugging the engine by feathering the clutch while in first. Kinda like starting out from a stop on a steep hill. Only lug the engine for a few seconds at a time so you don't burn up the clutch.
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Old October 24th, 2018, 17:59   #14
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I will remove the egr valve and inspect it, however i remember cleaning it not even a couple months ago and it was in perfect condition once cleaned; Are you saying to do the output test with the EGR removed but connect the cable still?

No hissing is noticed only turbo spooling sound; I doubt its a boost leak but i will check everything as im stumped other than maybe i missed a vacuum line to be replaced or torsion value needing to be set from -1.5 to 1.0??
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Old October 25th, 2018, 04:22   #15
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Quote:
Originally Posted by golfere View Post
I will remove the egr valve and inspect it, however i remember cleaning it not even a couple months ago and it was in perfect condition once cleaned; Are you saying to do the output test with the EGR removed but connect the cable still?

No hissing is noticed only turbo spooling sound; I doubt its a boost leak but i will check everything as im stumped other than maybe i missed a vacuum line to be replaced or torsion value needing to be set from -1.5 to 1.0??
Yes, that is exactly what you do. Clean does not mean it is opening and closing properly.
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