Assistance sought in diagnosing 'stumbling off boost'

jules · Postby **jules** » Tue Nov 13, 2007 5:36 pm

I noticed it a day or so after getting the car, whilst on the way to work.

I first really noticed it on the run. It was 300kms, so plenty of time to notice. At first I picked it up on bumps, so assumed it may be drive train related due to the beefier drive train in the car. Later during the run I noticed that it actually occurred when using constant part throttle under smooth conditions, so I adjusted the revs to eliminate it. At this point I discounted drive train and thought it may be a fueling hole somewhere in the tune. It seemed to NOT occur when the car was cold, but I wouldn't bet my house on it.

Best bet would be to grab Malibu's leads on Saturday? I'm running Magnacore blues. Borrow them for as long as you like like. They might give Max another 45kw :mrgreen:

, and if Malibu starts choking then we have a culprit.

Jules

ampz · Postby **ampz** » Wed Nov 14, 2007 8:02 am

Hi Uncle,
Are you still running your AFM?

jules · Postby **jules** » Wed Nov 14, 2007 11:02 am

Yes. RX-7

Uncle Arthur · Postby **Uncle Arthur** » Wed Nov 14, 2007 11:06 am

jules wrote:Yes. RX-7

To be correct - RX7 body, MX5 internals.....

And this is a wholly new fault with the car - hasn't happened since I turbo'd it earlier this year.

ampz · Postby **ampz** » Wed Nov 14, 2007 1:08 pm

Try making a mark on the flapper spring (to know where to put it back)
and tightening the spring a couple of notches, I found my spring got a little weaker with time and under cruise, the flapper would be almost wide open pegging it rich.

It happened not quite on boost, just under around 100 kpa.

3 clicks put me back to where the fuelling was pre-turbo for me.

Cheers
Nuno

Sheck · Postby **Sheck** » Thu Nov 15, 2007 5:11 pm

Check your wiring, and re-solder every connection. I had similar problems with my car, and after re-soldering and moving the EManage away from the stock ecu i found it was good for about 2 weeks, but it has resurfaced again, so i'll be checking it out again soon. Also for some reason sometime when i remove the ecu cover it'll fix the problem, then othertimes it'll be crap again.

Sorry i wasnt much help!
Dave

Boags · Postby **Boags** » Thu Nov 15, 2007 9:00 pm

Sheck wrote:Check your wiring, and re-solder every connection. I had similar problems with my car, and after re-soldering and moving the EManage away from the stock ecu i found it was good for about 2 weeks, but it has resurfaced again, so i'll be checking it out again soon. Also for some reason sometime when i remove the ecu cover it'll fix the problem, then othertimes it'll be crap again.

Sorry i wasnt much help!
Dave

That sounds like it might be an earth issue Dave. :?:

I also have a similar stumble... Might be an emanage thing.

ampz · Postby **ampz** » Thu Nov 15, 2007 10:43 pm

Weird, it could be a ground issue.
Are you guys sharing the ecu grounds with the Emanage?

The reason i referred to the AFM is that i scoped mine wilst driving (DVM) and the voltage signal bounced around like crazy showing the flapper moving around quite a bit.

Fatty · Postby **Fatty** » Fri Nov 16, 2007 3:02 pm

the emanage issue you guys are having... could be an earth but it could also be power. where are you guys pulling yr power from? when i tried to use the 12v ecu supply to run my dfa, my car stumbled and ran like sh*t. the ecu power wire just couldn't supply enough current to power both the ecu and dfa. so i wired the dfa up to the 12v wire under the steering column, the big blue one. no more stumbling, that wire has plenty of current.

Uncle Arthur · Postby **Uncle Arthur** » Fri Nov 30, 2007 1:25 pm

I'm thinking I might have found at least a partial solution to the stumbling problem.....

yesterday I found that the wire from the O2 sensor was nearly broken at the connector plug (near the coil packs). I rejoined it, but it is a temporary fix only (the O2 signal wire splices to the O2 clamp to control/alter fuelling according to boost).

The car went fine - for a day.

I'm thinking that my temporary fix might not be good enough, or that the wire itself might not be up to the job.

Does anyone then know if the single wire connector plug is JUST a pulg, or of it includes some internal resistor/sensor?

I'd like to know if I can replace the plug with just a straight length of good wire - from the O2 sensor direct to the O2 clamp? That will remove the dodgy section of wiring entirely.

The Pupat · Postby **The Pupat** » Fri Nov 30, 2007 2:50 pm

Only read this thread. If it's well rich on cruise but fine on WOT, O2 could be the issue. 95% of EFI computers run closed loop on idle and cruise/light throttle maps but switch to open loop under WOT. Also the reason I wonder how an O2 clamp would fix WOT tuning (or is it only there to clean up the AFR whilst transitioning?). Spark problems normally get worse under load since it takes more to get a spark when combustion pressure goes up. Hence sparkplugs can look like the fire fine out of the motor but break down big time when you put them under pressure.

Boags · Postby **Boags** » Fri Nov 30, 2007 3:37 pm

The Pupat wrote:Also the reason I wonder how an O2 clamp would fix WOT tuning (or is it only there to clean up the AFR whilst transitioning?).

Yep, only for transitioning and when in boost under 4000rpm but not at WOT (ie. still in closed loop).

Can't help with your question though Mikey, let me know if it fixes it for you, it's an annoying stumble I'd like to be rid of.

Boags