Car shudders on WOT accel at certain RPMS
 

Hi all. I have a Hawk Sti that was recently remapped, it was ok for around 100 miles, but now is experiencing some shuddering (like driving on the rumble strips) at certain RPMs during WOT accel, which appears worse when pulling uphill, and that seems to come from under the car.

I've been advised by the mapper that the issue most likely relates to the prop shaft.

I checked the center bearing and found that the rubber bush appears visually in good condition (not torn or splitting away from the metal housing), but that it's pretty easy to move the shaft far enough that the inner rim of the rubber bush can contact the outer rim.

Is it possible the rubber has softened so that the bush is no longer effective? Has anyone else experience this?

Is this in 5th 6th under 3.5k under wot

it seems to vary but roughly:

4th gear: 3400-->3600 rpm
5th gear: 3300-->3500 rpm
6th gear: 2900-->3300 rpm (sometime very noticeable 2900-->3000)

most noticeable at WOT, slight uphill on a smooth road in 6th, then you can really tell it's not road surface related.

might be worth doing some logging to see if it is map related or something mechanical with the car like the prop.

My mapper said.
It will get worst the higher gear your in!
It's due to the high gearing and the 2.5 engine building boost to low in the rev range.

It puts a lot of strain on the drivetrain trying to accelerate from such low rpm in the higher gears.
Few ways around it.
Modulate your throttle no need to be wot at that rpm, The car will still accelerate as fast as it can at them rpm with half throttle.
Reduce boost,
Change down a gear
Or a larger turbo that has a torque peak above 3.5k

i did some logging and incidentally the FLKC was reading nearly -3 degrees in the 'incident' RPM range, even after an ECU rest, but i seem to have corrected that today by lowering the AFR a tiny bit at the problematic region.

The shudder still occurs. Interesting if it's a limitation of the drivetrain, meaning the soft prop bearing bush might be red herring then?

As you say, it is possible to drive not WOT in such high gears....

Which mapper told you that?

something on this mind you. it's not so uncommon to want to accelerate from from cruise in 6th gear, @ say 2900 rpm, to overtake, and that's when this is really noticeable. In a casual cruise to work, you don't really want to be downshiftting all the time just to overtake, so on that basis I'm keen to understand what could be done to fix it!

What was the IAM reading on your logs?
If you post up the log file we might be able to spot a problem?
Which mapper told you it could be the prop?

Not solved yet, but I managed to get under the car properly today and found 2 witness marks on the prop, one where it looks to have been contacting a large blob of body sealant and one where it was touching against the rear dif front guard plate, images below. I removed the blob of sealant and cut a small notch in the plate. I put some white paint on the body seal area to see if was still touching (it doesn't seem to be), sadly neither action has fixed it, although I was hopeful!


https://cimg1.ibsrv.net/gimg/www.sco...13c700268c.jpg


I logged some fresh data as per the linked files.

1) part of a 5th gear pull with the usual parameters. IAM not logged but showing as 1 in learning view just after. Shudder occurs @ 3200-->3400rpm
https://drive.google.com/open?id=0By...mRFaUN6M0pUc3M

Learning view. https://drive.google.com/open?id=0By...mw5dHBRR3dZNDQ

previously I had -2.8 in the 2400-->3399 & 2.3+ box but I corrected that yesterday as mentioned previously.

2) high resolution 5th gear part pull of manifold absolute (Sea level) and WGDC - shudder occurred @ 3300-->3500rpm rectangle box, graph below:
https://drive.google.com/open?id=0By...VRlc051WXhKdjg

https://cimg0.ibsrv.net/gimg/www.sco...c6a81f3a87.jpg

Thanks for any help!

I would post up the log file in the engine management forum,members such as bludgod have loads of experience and will show a better picture of what's going on,or talk to your mapper.
I can't view the logs(not got the correct software) but the leaning view looks unhealthy,IAM at 1 and pulling a lot of timing,could the vibrations be cause by boost/fuel cut?

I will look at asking around to.

In the meantime I knocked up a chassis ear from a PC mic, laptop and headphones and with it under the car pointed at the prop bearing, still couldn't hear that it was coming from there. Also used the same setup in the engine bay and the engine seems to sound smooth through the shudder. Also found the same setup was pretty good for hearing knock (when passed through an equalizer) so recorded a load of data from around town driving which I'm going to review this evening to see if I can correct the red values in the learning view.

Boost/fuel cut had occurred to me, i'll have a play the limits to see if it has any affect......

Ah so when you say it was remapped 100 miles ago and reading the last post am I right in thinking you're DIY mapping?
Or was it 'pro' mapped and you are now tweaking to sort out the knock?

sports cat fitted and mapped by a specialist. I asked him to use open source not locked so I could tinker. However, the map appears to have some issue in certain areas (before i got anywhere near it!), initially and probably by coincidence in the same rpm and load ranges as the shudder, so I took it back to him and he assured me that it was not the engine causing shudder and pointed me to either Prop or t/m. He suggested replacing the prop to see if it fixed it, but I figured I would at least inspect it first before that. In parallel I fixed the high load 3000-4000rpm issues I was seeing in the FLKC table by adding a little more fuel in that region (timing unchanged).

I just tested with upped boost fuel cut psi values across the board to way above the current figures and no difference, and listened with the mic to the engine again and it does sound steady through the pull, no obvious judder or miss beat etc.

reading some of the forums, some have suggested judder on accel could be caused by too much oil. I changed the oil after the remap and before this started,oil level was on the F hole after the fill. any chance of relation, if so could anyone explain a link?

I had similar issues after fitting a sports cat to my 2.5 STI a few years ago. I think the answer suggesting it's the way the engine builds boost is correct. Was the sports cat you fitted a downpie with an open bellmouth style fitting ??

Not related to your judder problem but the engine speed ranges for FLKC seem to have been calibrated oddly by your mapper. Why go to 12k rpm on an engine that is never going to go much above 6k. By doing that I am pretty sure the FLKC ability is now limited to just a few ranges. Here is my learning view from after I mapped mine, just for comparison.

http://i1189.photobucket.com/albums/...%2036%2004.jpg

cobra sports cat downpipe, it looks like a bellmouth type.

As for the FLKC table ranges, I thought that was odd to, but checked against what I believe to be a stock rom taken from my car pre mapping, and it's the same!

Do you suggest I adjust it to the same ranges as in your picture, I guess that gives more resolution for the ECU's control.

I think open bellmouth downpipes make such a change to the way boost builds that it tends to cause the juddering you have seen. My old 2.5 STI had the exact same symptoms after fitting an open bellmouth downpipe sports cat.

I think it is worth changing the FLKC ranges, makes more sense to me to use ranges that the engine will operate in.

aye, it does seem to be general thinking about the judder.

as for the ranges, I have changed them and now in the process of correcting the timing pulls i'm seeing in new the FLKC table. You're right though it is better with more sensible ranges!

who was your mapper before ?
Seems strange to pay someone to map it if you say you can map.

I don't know anywhere near enough yet for that, so I took it a Subaru specialist to be remapped.

I'm wanting to learn, so that in future I can make mods and understand how to tweek the map to accommodate them, and this seems a reasonable place to start!

Sounds to me that you already know as much as your mapper and have made some worthwhile improvements since it was mapped.

I had the same, been mapping engine's and OBD systems at OEM level for nearly 20yrs but thought I would pay for a remap to see what these guys do. Few months after the map I wasnt happy with how it drove and needed to fit a sports cat due to original having a problem. Remapped it to suit the new cat and improve the driveability issues left by the mapper. Ended up with a car that was great to drive and a much smoother map. I then sold the car :( but that's another story.

Have you tried reducing the boost just to see if it's related to what I previously mentioned?

If you have no way of doing it just connect the actuator directly to the turbo compressor so it only runs actuator boost. Your most likely find the problem will disappear.

I have twin maps on my car and in the higher of the two I get a bit of vibration in 5th and 6th if I use wot below 3k unless I just modulate throttle.

In the lower setting it doesn't happen but there's hardly any acceleration until over 3k

I haven't yet, but it's something i'll look into when I get the time and post back.

Cheers

If it was a mechanical issue with the prop wouldnt it do it on the old map ?
Cant you flash that back to see if the issue disappears ?

I can try that also!

you were right, reflashing back to stock does stop the shudder!

Think it's known as torque groan,
Guess you now have noticed the car wont accelerate hard from low rpm even on oem boost levels in 5th and 6th unless your over 3k.
Adding more boost and torque under 3k is just going to stress the drivetrain.

I've been in a 2.5 with a md321t+ and it doesn't happen but that spools a lot later than the vf43.

now that you mentioned that term I can see that this has been discussed previously, but with no firm solution proposed: https://www.scoobynet.com/general-te...-2-5-stis.html

I'm still thinking the issue might be the prop vibrating & shifting around it's axis with the inside of the bush hitting the outside rim; particularly given the witness marks on the prop and the diff cover plate (previously posted images). I think it's due to the centre bearing bush being too soft.

seems to me like you might be overshooting your boost target a little which the 2.5's will easily do in higher gears once the cats are out of the way. If you look at target boost and manifold pressure you can see it does scoot past what its aiming for:

https://cimg5.ibsrv.net/gimg/www.sco...bdbeb94d00.png



impressive power in 2nd/3rd/4th gears when your on the move but at 5th/6th your just putting the engine under more strain that it needs to be at that point - as has been said above you'll see the same or better acceleration there with less boost/half throttle. You could try reducing WGDC min/max in that area (drop from 50 down to say 45) to see if the situation improves any.

As for the LTV values, you'd have to check the fine correction range (load) as I believe stock switches off at 2.80 load and your just a snip over that in your problem area. If you increase the range and start to see FBKC/FLKC in that area it could also point to something worth investigation (or another reason to reduce the boost slightly).

The Fine correction ranges for RPM and Load i wouldn't be too stressed over. Having the range go from 5400 to 10000 just means that if knock correction is made at 5400rpm then that amount of timing is reduced from the rest of the pull. Whereas with smaller ranges (say 5400-6400) then when you exceed that range you'll be back at full timing unless there is another knock event. So if the car has an issue (say bad tank of fuel/blown MAF causing lean condition/flakey spark plug/ringland popped etc.) at least a small amount of knock in a lower (less dangerous) rpm would help save the higher RPM's from what would now be excessive timing.

thanks for looking and the advice, i'll give it a try with lowering the WGDC by 5 or 6% and see what happens!