echoechoecho New Reader
11/9/15 8:21 p.m.

Ok I need some advice/help, I cant wrap my head around whats going on with my challenge car, its a 95 tercel with ITBs. I have a wideband on it and its running pig rich(10.9) at idle and cruise and it leans out(15.4) at WOT. Im using the stock ecu, I have all four runners connected to a vacuum block which the map sensor, FPR, and brake booster run off. the stock narrowband O2 is pegged at .9 volts and does not oscillate as it should, Short term fuel trim is max out at -20%. I wired in a SAFC and to get idle up into the 14s I had to set it at -40%, it ran bad and it spits a code for map malfuntion. I checked the vacuum and its at 66kpa which is low, so I was thinking the fuel pressure is to high at idle. so I put an artifical vacuum of 30kpa on the FPR and with -15% on the SAFC it now idles at 14.3 but still not running right, O2 is still pegged at .9, fuel trims still max at -20%. I dont know what I'm missing

bentwrench HalfDork
11/9/15 9:08 p.m.

A megasquirt?

It has a ITB mode that blends Alpha N with Speed Density to compensate for the lack of map stability at low throttle settings. Depending on the size of the ITB's and the location of the MAP plumbing you may be better off with a full Alpha-N setup.

Paul_VR6 Dork
11/9/15 9:11 p.m.

I have never been able to get an itb swap running on a map sensor with just an afc. The map range and fuel table values are usually way way far off.

SkinnyG Dork
11/9/15 9:28 p.m.

I have GSX-R ITB's on a 4AGE. Everybody said "don't run speed-density," but I figured I could do it. I am stubborn enough, I figured I could make it work. I even had a very solid MAP signal out of the engine.

But.... It never worked just right. If I datalogged and tuned lots of cruise, WOT was too lean. If I datalogged and tuned lots of WOT, idle and low speed was too rich. I could not find happiness.

I kid you not - I tried everything.

I'm telling you now: Don't run speed density.

I gave up, drank the Kool-Aid, was assimilated, and ran straight Alpha-N. I don't even use the MAP sensor on the engine, just for barometric correction. The driveability of the car Was so far improved on Alpha-N, I'm telling you now: give up and run Alpha-N.

Seriously. Alpha-N, dude, seriously.

Stefan (Not Bruce)
Stefan (Not Bruce) MegaDork
11/9/15 9:33 p.m.

Yup, unless you can alter the ECU tables directly, you'll likely need to replace the ECU with one that allows more adjustability.

The MAP signal will be very unstable and very low at idle due to the nature of ITBs and a change in throttle will generate huge swings in the MAP signal. So a factory ECU will likely not be able to adjust to such a large swing in MAP values.

This is why many use the TPS (Alpha-N) instead of the MAP (Speed Density) for judging engine load. Some ECUs allow the blending of Speed Density and Alpha-N tuning so that low RPM and small throttle opening loads can be calculated by the MAP sensor signal and the higher RPM and large openings calculated by the TPS sensor signal.

You can do some things to clean up the MAP signal like adding a restrictor in the line before the MAP sensor and adding a vacuum reservoir to power the brake booster which will reduce load on the rather small amount of vacuum signal.

An adjustable fuel pressure regulator could help get the base fuel pressure closer to what you want, but ITBs generally need more fuel at idle and your A/F goal should be richer than 14:1, like 13:1 at least, if not higher.

You're still going to struggle getting the fuel enrichment correct with the stock ECU.

This site might help:

echoechoecho New Reader
11/9/15 10:42 p.m.

Thanks guys, I was super happy that I got it running a week before the challenge. This thing is the first engine I rebuilt and I learned a lot. Now theres a lot more to learn about tuning. I was always planning on doing megasquirt in the future, guess I have to move up my plans.

Im going to unplug the stock o2 and see how well the ecu handles idle at open loop.

GameboyRMH MegaDork
11/10/15 8:24 a.m.

My mechanic's plan for running blacktop ITBs on my 4AGE is to set it up in Alpha-N mode first and then use that as the basis for a blended mode setup.

alfadriver UltimaDork
11/10/15 8:44 a.m.

If you HAVE to run the stock ECU- use the stock manifold.

The actual gains in using ITB's is heavily, if not completely, reliant on the calibration. Since it's pretty clear that your ITB set up runs poorly, just put the original manifold back on.

If you want some more flow out of it- port it. But keep taking data to see if the learning at part throttle/closed loop applies at full throttle/open loop. On the other hand, it may work in your favor- most WOT calibrations run too rich anyway- so increasing the airflow may make it run at 12:1 at WOT.

If you HAVE to run ITBs, you need a programmable system.

edizzle89 HalfDork
11/10/15 9:44 a.m.

i too also fought tuning issues issues on my AW11 with ITB's on the 4AGE, tried and tried with the MAP signal, ended up using alpha-N

JoeTR6 Reader
11/10/15 10:00 a.m.

I've managed to get ITBs working on a TR6 engine using a Megasquirt with decent results, but it wasn't a cake walk. I got the car initially running and driving using Alpha-N, then switched to the ITB hybrid mode. If you have a clean MAP signal, this will work OK for low throttle openings and load. Tuning the transition to Alpha-N took a lot of logging while slowly upping engine load at several RPM values. That's not easy to do on the street. For anything above 3500 RPM, it's practically running straight Alpha-N anyway.

Getting this to work with a non-tunable stock ECU would be very hard to impossible.

Keith Tanner
Keith Tanner MegaDork
11/10/15 10:08 a.m.

A warning about pure alpha-n (TPS): you will now be at the mercy of weather and altitude changes.

As for making it work with a stock ECU, there is a way. Put a plenum on it.