BlooSooby

Hi, my my01 has just had a new engine built for it. It's an EJ257 short block with C.P. Forged pistons, billet Eagle rods, polished/ported heads, AVO450s turbo, 750cc Deatschwerks injectors and Ecutek remap. It's all but ready for me to pick up but there's a problem with the car surging when cruising on light throttle (full throttle is fine).....so it's staying at the garage until it's sorted.

The problem is worse when the car is stone cold.

From what I can gather this is normally caused by a faulty oxygen sensor or MAF sensor. The builer has replaced these parts, one at a time but it has made no difference to the problem.

Has anyone ever experienced this problem before? The car didn't surge prior to having the new engine. I should have had the car back weeks ago and now it's really starting to take the shine off the whole project

Thanks everyone.

simb 2

iTrader: (3)

This sounds like the problem I had with my 2.5, turned out the injectors were too big, it had 740's, swopped them for 550's and problem was solved.

simb

dazdavies

iTrader: (22)

If that's the case then who ever mapped it is ****e.
I had 740's on a 2.0L with a VF28. No surge and no idle problems.

Later went on to have the same 740 on a 2.5 with gt30R and still no issues.

BlooSooby

Thanks guys, I popped into the see the builder yesterday and he's waiting for the tuner to swing by with his laptop tomorrow to see if he can see what's going on.

He did suggest that the brand new injectors could be to blame but I'm going to be fuming if this is the case as I sourced the injectors from 'FastWRX' in the States. At the start of the build he said a set of injectors would be $850 and suggested that I would need 750cc injectors to give me 250kw atw and leave some headroom.


Due to the silly price of injectors, here in Oz, I decided to get the Deatschwerks injectors from FastWRX online as they are around US$420 inc. p&p.....a big saving. I also got a Walbro 255 l/hr fuel pump and fitted it myself (only $99 for the pump, here in Oz they want $300!!!)

Anyhoo, I find it hard to believe that brand new injectors could be the problem. They are calibrated and bench tested prior to dispatch and are all within 1% of each other for flows. The injectors only do what the ECU tell them to do after all.

Trouble is, the builder thinks that the sun shines out of the tuner's back end and won't deal with anyone else. Catch 22!

What I really don't want to do is try to send the injectors back to the States, the postage will be lost and they might not take them back as the builder has had them for 2 months and has used them.

dynamix

iTrader: (3)

Poor mapping.

BlooSooby

Quick update, tried brand new oxygen sensors - no difference.
Tried Sti 'pink' injectors - no difference. Tried 2 different MAF sensors - No difference. That rules out sensors and injectors.

I'm led to believe that the open loop/closed loop operation of the ECU means that, while cruising at 2000 to 3000 rpm on light throttle, the ECU relies on the sensers to determine the correct fuel/air mixture but when the throttle is planted and the engine is on boost the ECU relies on the mapped information put in by the tuner. My car is fine on boost and only hesitates (surges) on light throttle at 2000 - 3000 rpm (it's almost like a misfire/dirty plugs type of feeling).

I'm baffled why it's still doing it with all the sensors proved ok and i'm wondering if there's an air leak on the induction side but after a quick look all seems fine......

dynamix

iTrader: (3)

I'd say it was the ignition advance in the cruise area too far retarded or the area of the map just outside of cruise so that it is knocking the ignition timing down too far on light throttle application.

Try adding more advance whilst keeping an eye on knock.

Is it hitting lambda at this point according the their wideband?

BlooSooby

Thanks for that, I'll ask the engine builder when I return the car next week so he can pass the info on to the tuner. Now that most other possibilities have been ruled out he might be forced to put the car back on the dyno and get this sorted although I think he believes his map is good.

dazdavies

iTrader: (22)

As Duncan has said it sounds like a mapping issue to me.
If you've no faith in the guy get another mapper to have a look. If he sorts the issue present the builder with a bill for the cost of the proper map.

AndrewC

Have you tried running the car with the front oxy sensor disconnected?

Does your car have AVCS ?

Andrew...