Stumble off idle when cold, flat spot

[Leiden]

Hi,

Just looking for a few suggestions as to what my problem could be, my vehicle is a Altezza RS200 3SGE+T

Basically on cold start the car will stumble with blips of the throttle, once it warm's up things are fine. I've also noticed that when accelerating from about 1000rpm's to about 2500rpm's in higher gears the car will bog.

For instance if I only accelerate with say 50% throttle it seems to have more power than if I accelerate with 100% throttle.

All I can think of is that it must be running lean in open loop. When its cold and the O2 sensor hasn't come online it runs open loop and when accelerating at WOT it runs open loop. This would explain why it doesn't stumble when warm and accelerates better with part throttle than WOT (since the ECU has adjusted the mixture via the O2 sensor)

Just wondering what could possible cause this scenario? On boost it runs perfect, so I'm confused.

[strx7]

what ecu is it running?

[Leiden]

Hey,

Its running the stock SXE10 ECU with a Emanage Ultimate piggyback installed.

Thanks

[strx7]

i've never played with piggy backs so cant offer any advice. could be a coolent temp sensor issue?

[tsoob]

i've never played with piggy backs so cant offer any advice. could be a coolent temp sensor issue?

sound to me like coolant temp sensor is fekd

[Leiden]

Ok guys a bit of an update...

I've started to investigate the FPR being dodgy. It seems like the fuel trims were keeping things happy to a certain point which would explain it running better with part throttle.

On full throttle the bog seems to be as a result of a lean mixture, once boost hits (and the extra fuel is added) the tempo picks up and it seems to be running fine.

I did a little test by adding a global 16.5% more fuel to the entire injector map so whatever duty cycle the stock ECU spits out + 16.5% more. After an ECU reset its running seemingly better, before I had to drive it easy after a reset otherwise it would bog now I can drive it almost normally.

I'm thinking that if the FPR isn't reaching the target 62psi fuel pressure the extra fuel added is compensating for this. Another Altezzaclub member reported having 48psi fuel pressure (meant to be 62) and having to add more fuel to make it run smooth.

Does this sound like a likely scenario? Don't FPR's usually fail to the overfuelling state where they let 100% fuel pressure through?

Any ideas?

[frost]

um how have you got the fpr hooked up?
to my understanding the alteza fuel rail has no return line. and that the fuel pump is on a relay system to control pressure.
are you adding fuel while recording wideband figures?

[matt dunn]

um how have you got the fpr hooked up?
to my understanding the alteza fuel rail has no return line. and that the fuel pump is on a relay system to control pressure.
are you adding fuel while recording wideband figures?

Yeah I thought they were a returnless system that ran a constant pressure too.

Have you run extra lines the length of the car?
or running a reg in the rear with a long vacuum/boost hose to it?

[Leiden]

Its just running the stock intank FPR which should have an output pressure of 62PSI regardless of vacuume/boost

I'm going by feel and watching the ignition timing, before adding the extra fuel it was dropping as low as 7 degrees BTDC, now with the extra fuel its only going as low as 11 degrees BTDC, I can see that its still knocking in a few places as the ignition timing spikes low and the duty cycle spikes higher.

If I can get a gauge onto the fuel rail I'll be able to confirm if its the fuel pressure or not

[strx7]

be extremely careful playing with ignition timing and fuel without a wideband and some form of realtime knock monitoring

[Leiden]

I've just been adding fuel which has seemed to reduce the amount of timing the ECU is pulling which is probably in response to knock because of the lean air fuel mixture.

I do have knock logged but in some cases its hard to determine wether its knock or just signal interference, I get alot of 20-30% spikes and the occasional 100% spike which the latter I think is real knock

[t0ms]

in essence it sounds like you re adjusting the fueling an ignition on your vehicle by "feel" and "ear" using a piggyback to alter what the factory comp is telling it to do???

sounds expensive if it goes wrong.....

have you thought about upgrading the ecu to be able to be a slightly "simplier" set up?

[speedracer07]

I've got a similar issue. I'm running a caldina 3s-gte in my 91 mr2, when cold the car starts fine but gradually leans out the fuel untill it stalls (I have a AEM wideband installed so that's how I know). if I blip the throttle the fuel ratio goes to normal. I also noticed that when accelerating it bogs down and the fuel ratio is lean. But when the car is warm it runs perfectly fine. I'll also check my FPR and see if it changes anything.

Roshan

[Dell'Orto]

in essence it sounds like you re adjusting the fueling an ignition on your vehicle by "feel" and "ear" using a piggyback to alter what the factory comp is telling it to do???

Whats the worst that could happen???
































Oh yeah

[strx7]

that wasn't caused by lean, it was just a rod that couldn't handle the jandle of too much combustion chamber pressure.

[Leiden]

I've always thought that running lean/detonating kills pistons, overboost kills rods, or something like that! In my case I bent a rod trying to force too much pressure into a cylinder.

I added a global 11% extra fuel and its got idle/part throttle cruise back to 14.7:1, no longer stumbles on throttle blips like before.

I've been thinking about removing the pulsation damper as I've heard these can become a problem and cause lean conditions, would make sense because the FPR is intank and thinks the fuel lines/rail is pressurised to 62psi when its actually the pulsation damper being a restriction.

Theres a little screw on the top of it that I had a play around with, as far as I can tell it practically does nothing until it seats against the rubber o-ring, then I think it assists the fuel in pushing the damper upwards to flow onwards into the rail. I've thought about adding a small washer to try and relieve some more pressure, any thoughts on this?

[MAGN1T]

Is it still running stock CR or did you lower it?

Oh and too much detonation breaks pistons, spins worn big end bearings, blows headgaskets and no doubt bends rods too if they can't handle it.

Steve

[Leiden]

Its running 2x factory metal head gaskets stacked ontop of each other to give a compression ratio of 10.5:1 down from 11.5:1 and also 3SGTE rods from a ST246 Caldina.

12PSI is about the limit but I know of one guy making 200rwkw with a bone stock motor with just larger injectors, factory fuel pump and all!

Last set of plugs I pulled out had the sand blasted look so it was detonating at one stage, probably due to the lean fuel because of the lower fuel pressure, thinking its the fuel pulsation damper still...

[MAGN1T]

You might find that advancing the base timing a couple of degrees from stock helps a bit, at the same time removing it as the load goes up.

Steve

[strx7]

Its running 2x factory metal head gaskets stacked ontop of each other to give a compression ratio of 10.5:1 down from 11.5:1 and also 3SGTE rods from a ST246 Caldina.

i'd say st246 rods are probably the same as st215 gtt rods which is what the pic above is. the are the same rod used in the single vvti 3sge engines and cant handle much jandle