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?

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.

Yes, could be MAF.

A VCDS read while on WOT, would be better to find the problem.

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!

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.

Tdijarhead said:

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.

Click to expand...

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

Check also if you have oil on the fuel filter. Since it's a PD ...

golfere said:

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

Click to expand...

You’re right, while torsion is important it isn’t 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.

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?

http://log.malonetuning.com/chart/2...LZmt8eMO0w7fDu8KYw6nCtw3DoQsBw7TCpCnCoAAAAA==


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?

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.

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.

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??

golfere said:

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??

Click to expand...

Yes, that is exactly what you do. Clean does not mean it is opening and closing properly.

Question about the log, how did you run it? did you run a constant speed? or is this multiple gears and changes. That log really makes it difficult to make out exactly what's going on.

The PD has the sensor at the bottom of the actuator and I wonder if that's affecting things.
MAP sensor or wiring is my first call!Charge pressure is 90% during an underboost! That's just not right! The charge pressure shouldn't be that high, especially when called for boost specified is 2080, actual is 1346 and charge pressure is at 90%.
I only expect this when the requested drops and actual hasn't responded yet, while the graph shows an over-boost for a moment.
Notice in the following graphs of my engine that the charge pressure shoots up when the requested drops off and drops as soon as it requests more. My Charge pressure doesn't get over 65% until I let off the accelerator pedal, then it shoots up...

https://log.malonetuning.com/chart/...wwo/DoGDDrCHDriZ1w4tsw43Cj1MIJ8K3PMOmJ8KPAAAA
https://log.malonetuning.com/chart/...Pw6Bgw6whw64mdcOLbMONwo9TCCfCtzzDpifCjwAAAA==


I call the actuator, or sticking veins second! because of the above and it can be really difficult to tell the two apart.

I call the engine speed sensor or wiring third! the RPM plummets multiple times, once to 815rpm; however, this could be due to shifting. Could be a weird combination of a couple of things.


The fourth thing is a dirty intake causing the charge pressure to be higher than it would if it were clean.

This log was on my way home and i just logged the drive back


The car has a brand new garrett actuator with turbo installed so its not vanes or actuator and the wires look to be good


MAF sensor was upgraded design not even 6 months ago but it runs terrible once unplugged



You are right, the RPM drops suddenly to 700rpm and jolts occasionally past 1.5k rpm



The intake was cleaned and filter changed not long ago and looks decent but i could replace it if needed?



Im leaning towards EGR related issue as i notice when im driving a steady speed and light throttle is applied, you can hear a "gurgling" or a "leaky bubbling sound" "fluttering" until more throttle is applied.




Here is a segment of another log i just did while pulling a load its much more noticeable where it hesitates and boost drops etc

golfere said:

This log was on my way home and i just logged the drive back


The car has a brand new garrett actuator with turbo installed so its not vanes or actuator and the wires look to be good


MAF sensor was upgraded design not even 6 months ago but it runs terrible once unplugged



You are right, the RPM drops suddenly to 700rpm and jolts occasionally past 1.5k rpm



The intake was cleaned and filter changed not long ago and looks decent but i could replace it if needed?



Im leaning towards EGR related issue as i notice when im driving a steady speed and light throttle is applied, you can hear a "gurgling" or a "leaky bubbling sound" "fluttering" until more throttle is applied.




Here is a segment of another log i just did while pulling a load its much more noticeable where it hesitates and boost drops etc

Click to expand...

Probably a good place to start. That map reading though, I don't understand why it is peaking the way it is, so erratic and contrary to expected. The second peak after the drop in rpm is when the request goes back up and the charge pressure should be plummeting, not rising, let alone peaking so high.

And the drop in rpm seems like the sensor signal is dropping out momentarily. Would be consistent with faulty wiring on both aspects, especially it happens at the same time.

Is it possible the map sensor is shorting to the engine speed signal and causing the spike in charge pressure readings that aren't even possible to exist? Basically the engine speed voltage being added to the map signal briefly and not making it to the tach. Map is DC and speed sensor is AC. Map voltage, to ECU, increases with boost increase so it kinda fits

This also sounds like it could be the accelerator pedal. Put a DMM on the contacts(not sure which, the two that change when pressed) in the plug and slowly depress it and release multiple times. If you see any irrational movement you likely have a bad pot in the pedal

Sent from my Armor_2 using Tapatalk

Good news! I removed the connection to my EGR and left it off for the past days; no hesitations anymore but is it okay to drive the car with the EGR disconnected? I searched for a new EGR and it shows its over $200! Ill buy it if needed as ive cleaned this EGR as best as i could 2 times in the past year already! Is it worth the buy?

Im checking if this also solves the burble sound under low throttle and the RPM drop! Will keep you updated!

Could get a tune for that money, maybe the egr minimization or delete and you can plug it back in.

Unplugging the egr is a relatively simple test. I think there is a spring in there that gets a little weak over time. A new egr should solve your problem. Unless of course you want to tune it out. I’d just replace the egr.

Thank you both! Glad i finally fixed the hesitation

the flapping / shuddering noise under light acceleration is still there for whatever reason i dont know...is it worth trying to figure out what it is? its very subtle and sounds like a plastic hollow flap opening and closing very quickly


I also believe the rpm drop is still happening but does this matter?

Either you have EGR problems or there is a boost leak (somewhere it must be). Even I tiny hole can cause the hiccup if its boost leak related. Or your EGR valve is faulty.
You can check it this way. Unplug your EGR and take a drive. If the hiccup goes away your EGR is faulty. BUT!!! While you are driving roll your windows a litlle bit and if you hear more than usual hissing noises (sshhhh) when pressing the gas pedal you have a boost leak somewhere 10000000%.

Give it a try.

Read the thread below.
http://forums.tdiclub.com/showthread.php?t=298735
I remember reading about intake flaps people's are removing. Not sure if you're familiar, or if you have them. But they're inside the intake plenum itself. And the link I just posted definitely read the last post.

Also, I think I mentioned it earlier, but test your accelerator pedal output. It should be smooth and not jump whatsoever. If it does then you have a dead spot in the pot.
This is something that's not so commonly mentioned because it's usually barely noticeable. However, it's more common on gas vehicle's. And if you keep looking everywhere except the pedal you could go round and round not finding it.

Regarding the flapping noise.

The Pd intake has two small additional small actuators one on eithe side of the intake. One under the tandem pump and one under the egr. They are vacuum actuated. You could pull the vacuum hose and test each. Maybe one or both are so bad that the flap inside the intake is just...flapping. Or maybe the plastic mounting tab on the bottom of one of them is broken allowing the same thing to happen.

Medzid22 said:

Either you have EGR problems or there is a boost leak (somewhere it must be). Even I tiny hole can cause the hiccup if its boost leak related. Or your EGR valve is faulty.
You can check it this way. Unplug your EGR and take a drive. If the hiccup goes away your EGR is faulty. BUT!!! While you are driving roll your windows a litlle bit and if you hear more than usual hissing noises (sshhhh) when pressing the gas pedal you have a boost leak somewhere 10000000%.

Give it a try.

Click to expand...

I drove and all i can hear is the turbo whistle but i dont think its a boost leak...

eddieleephd said:

Read the thread below.
http://forums.tdiclub.com/showthread.php?t=298735
I remember reading about intake flaps people's are removing. Not sure if you're familiar, or if you have them. But they're inside the intake plenum itself. And the link I just posted definitely read the last post.

Also, I think I mentioned it earlier, but test your accelerator pedal output. It should be smooth and not jump whatsoever. If it does then you have a dead spot in the pot.
This is something that's not so commonly mentioned because it's usually barely noticeable. However, it's more common on gas vehicle's. And if you keep looking everywhere except the pedal you could go round and round not finding it.

Click to expand...

Im on it to read what you sent; thanks so much for the help and i will check that using VCDS tool! Thanks!

Tdijarhead said:

Regarding the flapping noise.

The Pd intake has two small additional small actuators one on eithe side of the intake. One under the tandem pump and one under the egr. They are vacuum actuated. You could pull the vacuum hose and test each. Maybe one or both are so bad that the flap inside the intake is just...flapping. Or maybe the plastic mounting tab on the bottom of one of them is broken allowing the same thing to happen.

Click to expand...

Should i put my vacuum pump on the actuators themselves? Ill look around to see where they are as this could be a cause also!

Mityvac works wonders.

They are both small black actuators, one is behind and below the tandem pump the other behind and below the egr.

Tdijarhead said:

Mityvac works wonders.

They are both small black actuators, one is behind and below the tandem pump the other behind and below the egr.

Click to expand...

Thanks for chiming in. Do all PD have the internal flaps? As I said earlier I know some do, do they all?