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5.0L (1979-1995) Mustang Technical discussions on 5.0 Liter Mustangs within. This does not include the 5.0 from the 2011 Mustang GT. That information is in the 2005-1011 section.

89 5.0 COMPUTER UPGRADE

Old 06-13-2019, 07:53 AM
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SSRFUZZY
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Default 89 5.0 COMPUTER UPGRADE

I've got a customer that had his engine built up a bit above stock. custom ground cam (little more aggressive than a stage 1 trickflow), aluminum heads, trickflow intake, 92mm throttle plate, BBK MAF, 2.5" stainless X pipe exhaust, A9L computer, T-5 TRANS. We just got it up and running last night and timed, but it feels like it'll stall when backing down from higher RPM. He's afraid it may kill at a stop light occasionally (and make him look silly). We've adjusted the TPS to where it runs welland responds well to acceleration, but lacks a little when decelerating (like running rich for a few seconds, enough to cause a stall).

Is there a computer upgrade for his application that will eliminate the stall when coming to a stop after cruising.
Chip?
Computer tuner?
Different computer?

I'm and old school carb guy and not that versed with the computer aspects of these ford motors. That's why I had the engine builder here last night with his equipment to bring it around to this point.

Any help would be appreciated.
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Old 06-13-2019, 08:50 AM
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moates quarterhorse is the entry level option for $250. I bought mine for $125 used. After that, you enter the stand-alone world
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Old 06-13-2019, 11:40 AM
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You said it was a 89 with a ecu upgrade,but said it was upgraded to an A9L.What ecu was in it before?? The 89-93 5.0 normally comes with the A9L (5 speed) A9P (aod)
Modifications like you listed can indeed cause idle/stalling issues,but just to make sure,I would run codes on it just to make sure none are present.Why?? If a code (29) is present for the vss,it can cause the engine to stall when coming to a stop,if its a 5 speed.Something called an idle dashpot strategy is triggered by the vss with a 6mph value as its threshold,so an issue with it can cause stalling.So make sure code 29 isnt present.
Code 67 can also cause idle issues because the clutch safety switch & neutral gear switch are also used for idle strategy. If the pedal is down or the shifter is in neutral,a signal is sent to the ecu to tell it so.These two normally cause more of a surging/rolling idle condition vs stalling when slowing to a stop,but code 67 should still be tested for.
The following links explain these sensors/
switches in detail.


http://sbftech.com/index.php/topic,29819.0.html

http://sbftech.com/index.php/topic,29824.0.html
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Old 06-13-2019, 05:05 PM
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Thanks for the replies guys.
A little more back ground info on this build.
The engine came out of an 86 Mustang 5 spd.
I do not know which computer it had when he got it.
The engine builder upgraded it to the A9L from what ever was in the 86, stating the one that was with it was incorrect for that motor/trans combo.
This is all retrofitted into a 70 Mustang coupe Grande with 4 link tubular rear suspension with adjustable coil overs, 8.8 mustang cobra rear axel with 3:50 series gears and Cobra disc brakes, tubular front K member and adjustable struts, Cobra front disc brakes, Full frame connectors, Painless wire harness kits (70 body harness, 86-93 engine harness), New vintage digital gauges, 2.5" stainless exhaust with X pipe w/ O2 sensors (no cats), EGR deleted, dual electric fans on MSD fan controller, NO integrated neutral safety switch (nothing on the clutch or trans to connect it to) so it is wired separately.

We may have to add n EGR sensor and leave it loose just to complete the circuit.
At first we were getting the throttle position senor code, but made adjustments for that which cleared that code. The new BBK MAF was working fine with no codes no matter how we positioned it (trying to hide the big bulky wiring to it).

I still haven't had it out on the road as I'm still running tuning tests and trans tests when I have time. It's the owner that was there last night that's worried it may kill on him coming to a stop (thus making him look like a rookie with a clutch) I'll have to get it down off the stands this weekend and drive it on the road to see if it acts that same under normal road loads and not just while it's in the air.

But it's good to have the upgrade info if it is needed or wanted buy the Owner.
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Old 06-17-2019, 11:36 PM
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If the engine/harness/ecu is out of a 86 model and the ecu was upgraded to an A9L,it likely means a speed density ecu was being used before upgrading to the A9L (which is a mass air ecu) It means the shop done a maf conversion to swap from the SD ecu to the MAF ecu.When a vehicle is converted to a maf system,two wires normally have to be ran to a vss (vehicle speed sensor) If not added,stalling can occur when slowing down to a stop.The vss triggers the idle dashpot strategy when
the vehicle is slowing down and 6mph is the value threshold.Im not sure how you go about remedying this situation??
The 86-88 5.0 iac valve harness came with a diode wired into it.If the iac valve was replaced with a new or remanufactured valve,which has a diode built into the iac valve itself,the harness diode will compete with the iac valve diode and idle issues will occur.
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Old 06-17-2019, 11:46 PM
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so if you unplug the tps, iac, and spout connector. remove the battery cable for a few minutes to erase learned fuel trims, then crank the car and let it warm up for around 5 minutes, what does the engine idle at?

Last edited by TrimDrip; 06-18-2019 at 12:08 AM.
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Old 06-18-2019, 07:52 AM
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Originally Posted by wbrockstar View Post
If the engine/harness/ecu is out of a 86 model and the ecu was upgraded to an A9L,it likely means a speed density ecu was being used before upgrading to the A9L (which is a mass air ecu) It means the shop done a maf conversion to swap from the SD ecu to the MAF ecu.When a vehicle is converted to a maf system,two wires normally have to be ran to a vss (vehicle speed sensor) If not added,stalling can occur when slowing down to a stop.The vss triggers the idle dashpot strategy when
the vehicle is slowing down and 6mph is the value threshold.Im not sure how you go about remedying this situation??
The 86-88 5.0 iac valve harness came with a diode wired into it.If the iac valve was replaced with a new or remanufactured valve,which has a diode built into the iac valve itself,the harness diode will compete with the iac valve diode and idle issues will occur.
The engine builder is the one that upgraded the computer from an 86 to an 89 A9L, and advised which wires were needed and which were not.
The IAC is whatever came on the 92mm Trickflow fuel plate. I will have to check the IAC valve specs (if I can find them on the net) to see if it contains the diode you speak of.
The new MAF is a BBK that the Owner purchased. I'm not sure of the numbers on it but as the engine builder and I were rotating it to get the best performance it remained unchanging no matter the position of the small computer chip connection area.
The engine harness is aftermarket from Painless Performance and has the VSS wires to the speed sensor in the trans.

We have not yet had this on the road. We were tuning it in the shop with the car on stands.

To answer Trimdrips question. This was a completely rebuilt engine and refurbished A9L computer. According to the engine builder this computer for the 89 did not yet have the learning curve adaptation within it. I'm not a big computer controlled person, I prefer old school carburetors, so I rely on the younger engine builders for tuning these newer motors.
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Old 06-18-2019, 07:59 AM
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lol, that is a new one on me

edit: sorry, that was funny. any time change is made to fuel the KAMRF values have to be erased. if you tune the car yourself, or take it to a tuner, this will be done every time a fuel change is made.

what size injectors does it have?

Last edited by TrimDrip; 06-18-2019 at 08:04 AM.
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Old 06-18-2019, 02:25 PM
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Originally Posted by TrimDrip View Post
lol, that is a new one on me

edit: sorry, that was funny. any time change is made to fuel the KAMRF values have to be erased. if you tune the car yourself, or take it to a tuner, this will be done every time a fuel change is made.

what size injectors does it have?

It has 24lb injectors.
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Old 06-18-2019, 02:44 PM
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A9L is programmed from the factory to 19lb injectors. I am not familiar with the bbk meter, but i assume it is a pre-calibrated meter that is trying to trick the computer into fueling correctly.

Idle issues are normally a problem with a pre-cal'd meter and no tuning device.

Do you have the maf transfer data? You may need that when you get the quarterhorse
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