Fix DBW response/hesitation - Correctly earth battery

[cpitts]

Well, as the first part of my audio upgrade, I made a quick fix to the first part of a long chain.

I decided to upgrade the earth cable from the battery to the chassis from the crappy OEM cable (better than they used to be back in '02) to a much thicker core (4 AWG).

I didn't expect much, but the nett result not only reduced some of the stereo hiss (as hoping) but it also had the side effect of MASSIVELY improving DBW response and smoothness!

Here's the quick snaps of the day:

Start with 2 x 4AWG gold plated eyes (or 2 x 8AWG that you stretch out to fit 4 AWG). Then bung them on the end of ~30cm of 4 AWG OFC copper line (~$4/m)


then lift the lid off the fuse box behind the battery (it has 2 lift off clips on its engine side) to get better access to the earth mount point (that thin little cable on the strut tower). Also note the thin bump on top of the -ve (black) cable off the battery, that's the OEM earth cable under there.



Next, unbolt the stock earth lead from the strut tower and then (takes a deeeep breath) get a BIG screw driver a scratch off ALL the paint and undercoat from it. You need BARE metal for your earth.



Now, apply di-electric grease to the scraped strut tower painted area (also use it in the cable ends when you make and clamp/solder them). Bolt up your new cable:



and the same at the battery end (remember to clean all existing contact points with petrol/prepsol/metho before applying di-electric grease and bolting your new gold conn to it.



Now you're done! Go for a drive and WOW at the difference. I know I did and the wife commented on how much faster the car was when she jumped in and took the car to the shops.

Well worth the ~$15 and an hr or so of time.

[tangcla]

hmm interesting. I was always under the impression that the earth on cars these days are more than adequate.

Time to see if I got any 4AWG lying around any more

[chriskan]

Thanks for that Craig, cheap upgrade Hopefully it fixes the hesitation at 3-4k rpm which drives me mad.

The OEM cable that was on the strut tower was connected directly to the battery I take it, so it was easy to remove?

[cpitts]

Never trust the factory on these little things. remember it's built to a budget.

W.r.t OEM item. I just gaffa'd it up and left it hanging from it's original (well restrained) mount. It's still in the OEM cable so I can roll-back any time. The dead end cable is well insulated with tape so it can't short/spark or earth to anything. No point cutting up the battery cable. Just tape up the metal end and call it done.

EDIT: Yep, that's the exact hesitation I've got rid of. I get minor turbo lag in S# then I'm linear to redline (just a lot faster now)

[NoOzL47]

afaik the main earth is actually on the gearbox (well thats where mine is, and i have the earth on the strut tower aswel)

[PHAT GT]

all 04-08 libertys have 5 fairly good earthing points in the engine bay

[coyote]

I suspect the difference you are feeling is caused by the fact that disconnecting the battery for long enough to make this change has reset the ECU. The hesitation is learned and you are just unlearning it.

[gtspec]

i have that same hesitation from about 3 to 3,500.. p***es me off too.. makes me speed too hehe

a ECU reset will unlearn it???

[chriskan]

i have that same hesitation from about 3 to 3,500.. p***es me off too.. makes me speed too hehe

a ECU reset will unlearn it???

Yep but it comes back Last time I was at Subaru and i even started hinting at it, the service advisor straight away said "we aren't aware of any problem...". vinny however (another time) said it was partly due to the emissions requirements, and there wasn't much they could do at the moment. However, wouldn't commit to say it disappears with a retune (obviously emissions will be affected).

[cpitts]

I suspect the difference you are feeling is caused by the fact that disconnecting the battery for long enough to make this change has reset the ECU. The hesitation is learned and you are just unlearning it.

I didn't lose any of my time, radio stations, etc so I would be surprised if that was the case. The ECU reset via battery normally takes ~1hr (at least that's common in a WRX) so I'd have WELL and truly lost radio setup. I never disconnected +ve on the battery during the exercise.

[Boxer]

i have that same hesitation from about 3 to 3,500.. p***es me off too.. makes me speed too hehe

a ECU reset will unlearn it???

Yep but it comes back Last time I was at Subaru and i even started hinting at it, the service advisor straight away said "we aren't aware of any problem...". vinny however (another time) said it was partly due to the emissions requirements, and there wasn't much they could do at the moment. However, wouldn't commit to say it disappears with a retune (obviously emissions will be affected).

I used to suffer from it and Subaru always fed me the same line too (until I spoke to the STi service manager who was aware of it and said they were dyno testing it and thought it may be a turbo waste-gate pumbing issue - never heard back)

Anyway, mine has all but disappeared now - dunno why. I got it back a few weeks ago after buying some of the last of the Vpower Racing and it behaved poorly with stutter again. Went away on the next fresh fill of Vpower. I always use Vpower and find it works best for me

[blacknwhite]

Same here, had shocking stuttering between 2500-4000 , would call it almost a pulsing effect ,took it back and spoke to a tech who checked it out and said it was a kink in the waste gate pipe controller causing a spike and then ecu retards it so on and so on causing the stutter.
No probs since then ,about 6 months ago
Whatever they did change certainly fixed it

[chriskan]

I upgraded my cable anyway, since I had some cable lying around and got the terminals for a few bucks. Car is running much better, with no stutter, but let's monitor it and see

I use vpower as well always (well, shell card.. so..)

[cpitts]

I upgraded my cable anyway, since I had some cable lying around and got the terminals for a few bucks. Car is running much better, with no stutter, but let's monitor it and see

For the price, how can you argue with ANY change

The one thing I HAVE noticed having it installed for a week now is that the car is using ~1/2 to 1l/100km more now. Kind of expected this as the ECU map will be getting a cleaner reference of voltage and most likely be dumping more fuel in.

The other interesting thing I noted was that the fuel l/100 graph on the sat nav console moves up & down a LOT more frequently, so the car is clearly jumping around the fuel map a lot more now. Most likely due to seeing more air inbound with the closer monitoring of TPS. (but who really knows)