Hey guys,

I've come across an interesting problem when trying to tune my car. It seems as if the AFRs start creeping upward, the MAP upward, and the RPM crashes until it stalls. If I pulse the throttle I can avoid the stall and it will even out for a few seconds until it happens again.

The picture shows it happening at idle, but this will happen anywhere on the map, even when holding the throttle at any specific RPM.

I've turned off O2 correction, I have no emissions control, no idle control. Its an S4 T2 in an FB. MS1 V3, SnS, Detoothed CAS.

Any help or advice on where to look would be great!

 

I suspect that is far too lean to idle without random stalls. 13:7:1 might sound like a lot of fuel but I don't think it is. I found with my LC-1 that mine wouldn't idle without being around the 10.5:1 - 11.0:1 range in idle.

But DO NOT tune your idle quality with the wideband meter. The process of how to get your best lean idle is well documented on www.megamanual.com (which is now what www.megasquirt.info) used to be.

Basically, you have a good start, I would richen until it starts to brap, and lift the speed so its at 1k rpm again. And then progressively lean it, as it speeds up drop the rpm screw back. There will be a point where it does not stall, and also where it run smooth.

Basically you are searching for maximum vacuum at minimum rpm with minimum fuel.

With my vehicle I found that tuning to leaner than 13.7:1 under any conditions resulted in misfires when cruising etc. Might be because I run advanced timing but who cares because more fuel + more timing should be better.


Also get a restrictor for your MAP sensor line. Basically what you want to create is a mechanical LOW-PASS filter so that the noise on the signal doens't mess with the fueling. You can create a low pass filter by having a long thin line after an area with a larger volume. For eg a Z14 fuel filter put in the middle of your map sensor vacuum tube will smooth it out considerably.


Good luck getting it sorted!

 

I threw a filter in the vac line that runs to the MS and it seems to work (although I didnt have too much noise to begin with).

Also, the amount of fuel you throw at it is very much dependant on the porting that you have. For close to stock porting on a 13b turbo, I idle at 800 rpm (gotten as low as 500 stably, but the tach doesnt work below 700 so I wanted to keep an eye on it) and right about 12.5-13 AFR best, and in cruise can go as lean as 17 or 18 in some spots without a problem (although I try to stay around 16 below about 80 kPa).

 

Yeah that is a good point. I have a 12A 4port (with what I call I small extend port or streetport) and h4inf has a 13B 4port with a full blown extend port.

We both agree on leanest cruising afr. I'm not sure if he agrees about the idling richer than 11:1.

We both have early motors his is RX4 13B and mine is RX7 12A, so yeah we have agreesive porting instead of 6ports or turbos (yet ).

I know the 6port centre housings ports are tiny compared to my ported tallport housings, so I guess the fuel doesn't attomise so well in our engines.

 

Ok, I didnt know/remember his setup. A full blown extended port will probably be pretty rough and require a lot of fuel and a high idle because of all of the overlap, so some of the fuel could be going straight out the exhaust and vice versa. Plus, the intake port velocity will be very low at idle, so the fuel will not vaporize as much, take longer to get into the combustion chamber, and less air overall will be going into the chamber at idle due to internal EGR, a big lack of charge compaction, and some of it getting pushed back out the intake port depending on closing timing.

 

Ah, forgot to mention its got a mild streetport (RB).

Thanks for the advice! I will try richening it up today and putting a filter in the MAP line. I will post back later today.

 

there is a restrictor pill in the line to your stock map sensor. it works really well and isnt unsightly, it does seem to be directinoal tho.

 

I don't have a stock line or stock map sensor, I guess I could keep an eye out for one at the local JY. I did however pop in a spare fuel filter I had laying around and the MAP signal cleaned up right away.

Also, after adding more fuel - the stalling problem disappeared entirely and I was able to tune quite a good portion of the map. Its running pretty good now in the off-boost portion.

A problem I'm still having though is getting the idle stable, I tried what what Jobro mentioned above as well as what was in the megamanual, but it doesn't want to smoothen out and is always pulsing a bit. I have a feeling that this might be due to my old crusty plugs as I fouled out the new set that I bought.

Thanks for everyone's help!

 

what are you using to set the idle? Just the throttle hard-stop, or do you have a BAC valve in there or anything else?

 

Where are you picking up the map signal on the S4 turbo intake? The ports on the back side of the UIM by the TB is the best one to use for a clean map signal. The one on the side off one of the runners(above the turbo) produces strong pulses.

 

Its just the hard-stop, everything else has been stripped off, BAC as well as all emissions.

The map signal is coming off the small port on the passenger side of the UIM. Its a JDM manifold if that makes any difference? It does look a LOT smoother with the fuel filter in the line though.

 

If possible, take the vac signal from one of the nipples on the plenum, not the runners. The runners will experience a lot more "noise" due to pressure waves within the intake runners from the ports opening and closing. Use this one for actuating a BOV, vac/boost gauge, or something that is not very sensitive to pressure fluctuations.

 

If you like wasting fuel, yes.

Less fuel + less timing + higher MAP makes for better economy, cleaner plugs, less fuel in the oil, etc.

I am only running fixed timing because that was the only distributor I had available at the time. And the fuel economy is horrific.

 

By higher MAP do you mean a more open throttle? or a lower MAP reading?

I have completely changed my opinion about suitable AFR's since getting my injectors cleaned. Due to untuned parts of the MAP i found that the car will in fact cruise at 17:1 at some light loads.

My 10.5:1 - 11:1 idle was rediculous, I think its more around 13:1 now.


I too am having problems with idle consistancy, like FULLY warming up the car tuning the idle, and coming back the next day it seems that it won't idle again. I dunno, I can say that Pulsewidth has the largest effect upon the quality of idle followed by timing

 

Also I think your coolant is too cold. 150 faren is low as, you want about 200F or 90degC

 

Here's an update,

I changed out the spark plugs and after playing with the settings at idle, the best I did was 1100 rpm idle, 18 inch Hg vacuum/38-40kpa, and AFR around 12.3-12.4. Its fairly smooth, I think it still could be a bit better, but its not bad by any means.

The problem I'm having now is that the engine occasionally stalls when coming to a stop, at a stop sign, red light, or sometimes just putting the clutch in while cruising.

What can I do to help this?

 

Well now :p

You can make the VE Bins just above idle rpm richer. And you can also make the VE Bins with weaker vacuum that idle but at idle rpm richer.

This means its richer returning to idle, and also if it does start to stall, being richer should help it come back to life rather than dying.


That said I'm still having the same problems. Mine is hit and miss regarding seemingly random stalls returning to idle.