EFIDynoTuning Forum

Hi All,

I tried to look for answers in the thousands of postings on these forums, but must have missed the relevant information.

I have a 1987 Mustang GT, currently completely stock, with the exception of 1.5" short headers, on which I converted the SD to MAF using a 1990 A9L computer. The engine ran fine after the conversion, but I plan to do a HCI upgrade to the engine. So I got a Quarterhorse onto which I installed Decipha's latest A9L2_240103.bin, GUFX_240206.xdf, and DECIPHA_230417.adx using TunerProRT.

The first thing that happened was the (still stock) engine would hunt a lot while cold idling. I figured the new EEC config was trying to learn the engine. But the cold idle hunting never went away after many miles of driving and stops and restarts. I drove the car around for several miles while recording the readings with TPRT, and maybe some day I'll actually understand all the numbers I recorded.

I noticed that just before coming to a stop, with the clutch disengaged, allowing the engine to idle down, it would hunt again, until I come to a complete stop, where it would sort of smooth out. I know the stock computer would idle down as I came to a complete stop. Then while sitting still and idling (with the A9L2 combination), it would be unsteady, shaking the car with some regular periodicity. Also I noticed that the idle would be around 800-850, where as the stock computer idles around 700-750.

During driving at steady state (on the freeway) I would occasionally experience severe stumbling. It would get worse if I try to give it more throttle while it's doing this. I found that this would clear up if I back off the throttle to idle for a few seconds and resume driving.

I think none these symptoms are correct, though the higher idle is tolerable. What would be causing these, and how do I correct them?

I want to get a baseline configuration that works correctly before I start changing values to accommodate my new engine with all the new hardware.

thanks in advance for any assistance you can provide.

you posted in the wrong section, moved to gufx

sounds like you have something mechanical going on, verify first nothing on the dash turns red while driving and make sure your fuel error is whats expected for stock ~10% then verify your throttle stop is set correctly

Thanks Michael,

I didn't know where the appropriate forum was to post this question.

The only thing showing red on the dashboard with the engine running is DESMAF_PID_N, which shows 1 lbs/min in red. Do I need to deal with that?

I will use your "HIGHLY RECOMMENDED" Option 1 for setting idle rpm in table FN875N.

Currently NUBASE is 800, which explains the higher than stock idle speed. Can I bring it back down to 700, or should I leave it at 800? It's that ever since the first day I had the car, its idle had always been at 700, and seeing it at 800 is just a little unusual. If I bring that down, do I need to add a new entry in FN875N for 700 and a matching AM value?

But I don't think this deals with the random surges I'm experiencing while cruising at steady state. That must be another problem.

yeah thats a major issue it means the engine cant get air to idle, you need to open the throttle stop to giver her more air to idle correctly, thats why your having idling and surging issues

yep you can drop nubase

nope fn875 is already set up and good to go

OK, right after the setting, the idle seems to be smooth, settling at about 800 rpm, as specified by NUBASE (haven't changed it yet). The ISCDTY is at 0.28, so within your recommended

I took it out for a drive, but as soon as I got it up to 20-30 mph, the idle went up to about 1100 rpm, and ISCDTY went to 0.43. As I'm driving, the ISCDTY swings past .7. I took a couple of hard acceleration bursts past 5000 rpm, and the logged ISCDTY shows it reaching close to 0.9.

During most of this time, the FUEL_APT_LAST turned amber and went to -1.

Is the ISC supposed to be this active when not idling? How long will the EEC take to "learn" the engine and adjust idle back down to NUBASE?

Does the A9L2 code disable the canister purge function? I started to smell unusual gas fumes after I started using this code. It's different from raw gas; it is definitely leaking from the carbon canister. I reverted to the stock A9L code, and the smell went away. (And the idle and stumbling problems went away as well after I reset the idle stop screw.)

Stock MAF and injectors?

Idle is the most difficult to dial in, you will spend a lot of time trying settings. (I NEVER had it learn its way 'out of surging'.)

If you have upgraded injectors and MAF, work on getting fuel dialed in first. (maf transfer, injector slopes, inj breakpoint, inj offset vs volts, NOT the tables for startup)
Set throttle stop an additional 1 1/2 turns after the stop screw contacts the throttle plate.

If you adjusted TPS volts, make sure its not too high. This is an old myth that this needed adjustment. If you are really close to the open throttle break point, it can cause high idle after the car warms up. Suggest setting TRLOAD=0, it may help idle transition when coming to a stop.

WIthout a log of the stumble, I don't have a guess as to what it could be.

APT of -1 is closed throttle, are u saying its reading CT while your driving?

yeah iacdc is supposed to increase with throttle and rpm thats dashpot, details on the homepage

there is no learning, sounds like you got something funky going on

a9l2 has same purge control as stock

on a stock vehicle with stock maf and injectors you can load the a9l2 in with 0 issues same as a stock tune.

Keep in mind though any issues you have will be made bigger with the a9l2 since its has very much tighter tolerances than a stock tune.

Thanks Michael, Juice,

All stock parts; injectors, MAF, HCI, TB, ... Perhaps the injectors may be old not squirting as much as they should.

I've heard many talk about setting the TPS voltage, but the mounting on mine is rigid, so I don't see how to do that without carving up its mounting ears.

The APT of -1 was in fact taken during the attempt to set idle. When I goosed it, the APT went to 0.

I have not tried to drive it again after the idle setting that drove it to 1000+ rpm.

Trying to find the spot where the engine stumbled and stuttered is kind of difficult, as it comes and goes after just a second or two.

I will try both again tomorrow with a timer on my watch so I can better close in on the stumble. (It's easier than trying to stop the recording while I'm driving.)

If your tps is 'unmolested', it should be fine. Yes, the holes had to be hogged to make it adjustable.
How does it run without the chip? And with a chip and a stock file?