I've got a JDM S5 turbo with no acv or airpump. My build is in my signature but here it is again N370 Rtek 1.7, RB REV TII full exhaust, FD Fuel pump, OEM fuel rails and dampener, 550 primaries, 800 secondaries. Fuel injectors were cleaned and flow tested. ACV and air pump are removed. Vacuum spider is mostly not used. None of the emissions solenoids are seeing pressure/vacuum, but they are plugged in to harnesses. I run 91 octane.

I've got my wideband sensor at the end of downpipe just before presilencer. I'm seeing 10.8 afr at idle. Is this normal for emissions deleted turbo?

 

Thats very rich for idle. 12.5 to 13 will probably idle smoother.

 

I've had some other threads about working out timing and idle. Idle is rough, trailing timing is off (though I've been told not to worry so much about that).

Last I drove it (last week) it was driving much better, afr was still 10.8 at idle, then between stops errand running it all the sudden got more rough and for the first time had hot start issues. Pulling the EGI fuse fixes it fine.

I tested the water thermoswitch and it seems to be fine on both resistance and voltage at the ECU. Being summer I could not test at the lowest temp.

I've tested TPS and it has good range and no dead spots on narrow or full. Full range is about .3-.4v off on the low side, but no dead spots.

Last I remember the IAT test good at the ECU, but I have to look at my notes to be sure. I have not tested the AFM/MAF and it is a Cosmo (13B MAF), I suppose that could be causing some of the rich idle? Though I'm just basing that on hunch.

Should I be looking at fuel pressure? I've read conflicting threads about how the dampener on the rail will control pressure. But then I've also read that going FD, Walbro, Supra pump can cause too much pressure.

I may pull my alternator and take it to a shop to be load tested. It's a modified S5 for, IRRC, 130amps. I picked it up off eBay from an alternator shop in CA.

I haven't tested coils but a I have a spare pair that were working fine. I may simply swap and see.

 

its been forever since i had a T2 with a wideband, 10.8 seems really rich though.

WITH the airpump, AFR at idle will be like 16:1 or leaner, but you have to remember the air pump air is injected BEFORE the o2 sensor, so its output of engine + airpump air = 16:1...

seems like it should be in the low to mid 12's but i could be wrong

 

Mine idles around 11.5-12 afr. Rtek 1.8 4/RC 750's.

 

Do you still have the little idle pulse width adjustment on the passenger fender? Try turning that to get a leaner burn at idle.

 

Talk about dashed hopes. I found that the IAT within my MAF/AFM was dead. I tested a spare N350, it tested as good and I put it on. It was like night and day. It idles at 11.7ish afr. Obviously I'll need to source a good N370, but during engine break in I bet the N350 will be fine. Normally I don't boost at all what with it being break in time for the engine. But to test my afr under boost with the N350 I took boost up to 5 psi and afr never rose above 13.

Here's the catch. I drove the car an extended trip and was on the way home.....when I burned up my EGI fuse in mid drive. Tried swapping larger fuses in just to get it home and burned all those up. Ended up towing it home in shame.

I'm not even sure what that is?

 

S5's don't have them so need for you to worry about it.

 

I believe he's referring to the variable resistor, but I'm pretty sure that's an S4 only deal.

It's funny because I've been chasing my own issues very similar to yours and with a combination of finding a couple vacuum leaks and cleaning grounds I'm reading around 16 afr at idle (S5 JDM turbo vert). In the weeks before I was in the low 12s. I wouldn't think the FD pump would make it rich like a walbro, but it may be something to consider. Have you rewired the fuel pump and by passed the stock resister circuit? That would definitely make your idle richer, 9 vs 12+ volts.

 

I have not done the fuel pump work yet. It's on the to-do list.

 

10.8 is really rich. Shoot for mid-12s for idle. Hell, 10.8 is rich even for boost.