Rough idle and bucking under light throttle

[matty88]

Hi all, new to Megasquirt and tuning in general

I have a Stratified PNP MS2 installed in my Mazda BPT powered Ford Laser TX3 (running 98 Octane fuel here in Australia) with a road tune from the previous owner. It will be dyno tuned soon, but I want to have a go at fixing a couple of issues I have:
On cold start the idle sits at bout 2400RPM until warmed up
Bucks under light load in third and fourth gears
Hunting idle

It drives fine under load and on boost (wastrgate pressure, 6psi)
Have an LC2 for wideband and it has Mazda RX7 550cc injectors installed

Many thanks,

Matt

[slow_hemi6]

Post a datalog of the problem.

[matty88]

Took some logs on the way to work. Light/medium traffic

Engine mod list (if that helps)

Mazda BPT rebuilt with Wiseco 8.5:1 forged pistons, Eagle H beam rods, ARP main and head stud bolts, ACL bearings and reconditioned cylinder head
Mazda VJ20/Subaru VF10 hybrid turbo running wastegate boost pressure (6psi)
Custom made stainless steel 2.5” turbo inlet pipe
Exedy Heavy Duty clutch
Front Mount Intercooler- 2” from turbo to 700x180x65mm core, 2.5” to throttle body

[VcrMiata]

My first recommendation is to turn off EAE and then begin tuning VE.

Your tune doesn't look to be stable enough (looking at the VE table) to allow EAE to work correctly and so it will only make things much less stable.
i.e. during start EAE is jumping between 170%->0%->150%->0%->130%->18% - it is playing havoc with your fueling. It may not be the source of your overall issue but it can certainly will make things a lot worse. Your tune is also terribly rich when starting (AFR = 7.6?) - maybe the sensor is not warmed up?.

Turn off EAE, get back to basics and tune your VE table and then then see where you are.

WRT high idle, since you don't have fine control over idle (no PWM control) - you need to determine what is best for fast idle (CLT < 60C) - I think you may have to manually adjust an idle screw somewhere to bring it down. I would say 2200 until warm might be acceptable depending on the temperature ranges you see.

[matty88]

Thanks for that

Rhe car was dead cold so the wideband was warming up, hence the 7.4 reading

With the stock ecu I had a tuner adjust the afm and he said he played around with the idle screw.... will mark it and see if adjusting that makes any difference

Here in Melbourne Australia I can see temperatures from 0* in the winter to 45* in the summer

[matty88]

UPDATE (Long winded but bear with me)


Got the car dyno tuned not long after I posted this. Manual boost controller set to 17psi. (tuner had a problem with tuning the Stratified 3 port boost solenoid. Very sensitive to changes and not enough resolution?) Makes good power (told the tuner to keep it safe). However, we can't get it to idle properly. It'll either match the afr target table and pop and miss, or run smooth and rich (12-10 afr's). Tuner suggested to get the injectors cleaned and flow tested, which I did. They were clean and flowed pretty well. I got the injector place to clean them up and put a rebuild kit for good measure. Made no difference

Cold start, cruise and on boost/ decel are running well.

Fast forward to 2 weeks ago. My alternator was not up to the task of powering a sound system and various accessories, so I upgraded to a 110amp alternator (up from 65amp), with 4 gauge charge wire, with 4ga grounds (battery to chassis, engine to chassis, transmission to chassis). It now runs rich in the whole rev range, from idle to cruise. Haven't seen afr's above 13 on my wideband gauge.

I loaded up TunerStudio to see if the new voltage was affecting the injectors. To no avail. TS is showing under 13v. I haven't checked the voltage going to the ecu yet

I've included my tune file and an idle datalog. Mod list to the car is listed below:

Mazda BPT conversion (1.8L Mazda BP from the AWD Ford KF and KH TX3’s and Mazda BG Familia’s)

Fuel: BP 98 Octane

Stratified Megasquirt II PNP ECU, with GM IAT

Innovate LC2 Wideband with DB gauge (ECU wideband wire and gauge input wire are both running off the LC2’s yellow output Wideband wire)

NGK BKR7E spark plugs

Denso 195500-2020 Mazda RX7 550cc fuel injectors

Turbosmart Kompact recirc bypass valve

Walbro 255lph fuel pump

Rebuilt approx. 30,000km ago with Wiseco 8.5:1 forged pistons, Eagle H beam rods, ARP main and head stud bolts, ACL bearings and reconditioned cylinder head

Mazda VJ20/Subaru VF10 hybrid turbo. Wastegate boost pressure is 6psi

Custom made stainless steel 2.5” turbo inlet pipe

3” downpipe to highflow cat, 2.5” mandrel bent exhaust with hotdog

Exedy Heavy Duty clutch

Front Mount Intercooler- 2” from turbo to 700x180x65mm core, 2.5” to throttle body. 316 stainless with tig welds