Need some help with my car dying...haven't seen this before

[njmaier]

Well my car is dying and I don't know why. It has done this since I bought it, but it seems to be getting worse. It's a '91 GT...stock motor.

You can watch a video of what it is doing here (YouTube - video) to get a better idea of what it's doing, but I'll try to describe it as best I can.

The car will start up fine and drive normally for a while. Then all of a sudden it will start bucking, missing, and drop RPM. If you watch the video all of the bucking is when I press the gas pedal...it's not me fumbling with the camera. It will stumble around barely running then eventually stop. Once it stops I can try to restart it...sometimes it will start right back up and others it will take a minute before it cranks. Once it starts again it will run fine for a bit, but usually it will act up again and do the same thing.

Anyone one have any ideas as to what's going on?

The car has these mods: BBK cold air, BBK 70mm TB, BBK shorty headers, underdrive pullies,Flows, MSD billet distributor, new Optima battery. The car acted like this before and after these mods.

In chasing down this problem I have replaced the following...none have helped: new fuel pump; new fuel filter, new cap, rotor, wires; new ignition control module; new idle air control; new TPS; cleaned the MAF sensor; new spark plugs gapped correctly; new ignition switch.

I checked the codes and I get:
KOEO 82...can't find a KOEO code but KOER 82 is Air management 1 circuit failure
KOEO 85...canister purge solenoid circuit failure (expected since the emissions stuff is gone)
CM 15...EEC battery powered keep alive memory (KAM) test failed

I think I read them right. It signaled 82 - 85 - 82 - 85...6 or 7 second pause...then 15 - 15 - 15 - 15 (this came out as 15 blinks with no pause between the 1 and 5)

Any help would be appreciated! Thanks!

 

[Gearbanger 101]

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[jrichker]

Code 15 - No Keep Alive Memory power to PCM pin 1 or bad PCM (Memory Test Failure). The voltage to the Keep Alive Memory (KAM) is missing (wiring problem) or the KAM is bad. The KAM holds all of the settings that the computer "learns" as it operates and all the stored error codes that are generated as a result of something malfunctioning while the engine is running. Use a voltmeter to check the voltage to the pin 1 on the computer - you should always have 12 volts. No constant 12 volts = bad wiring. If you do always have the 12 volts, then the KAM is bad and the computer is faulty.

If the computer has to "relearn" all the optimum settings every time it powers up, the initial 5-30 minutes of operation may exhibit surges, poor low speed performance, and rough idle.

Note that some aftermarket chips will cause code 15 to set. Remove the chip, clear the codes and retest.

Before replacing the computer, remove the battery ground cable and the aftermarket chip if there is one. Leave the cable disconnected for 10 minutes. This will clear all the codes. Retest after several days of running. If the 15 code is gone, then don't worry about it. If it is still there, then you get to do some troubleshooting.

See the following website for some help from Tmoss (diagram designer) & Stang&2
Birds (website host) for help on 88-95 wiring Mustang FAQ - Wiring & Engine Info

Diagram courtesy of Tmoss & Stang&2birds

http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

 

[njmaier]

The video should be fixed now. Please let me know if it isn't.

I don't have any aftermarket chips or computers on the car. The battery was disconnected for over a week before I hooked it back up and drove it to film the video. I will reset it again and see if 15 come up again.

Thanks.

 

[Repostyle]

The car has it's own computer (ecm) it's under the kick panel. But I was watching your battery guage and it drops to around 7 volts at idle? I'm thinking the battery is bad or the alternator or both or the batt wire connections. Have you had them tested? It looks more like a voltage problem then a computer problem. I'm leaning more toward the wires/connection due to the fact it restarts pretty strong.

 

[njmaier]

Sorry...I meant aftermarket computers or aftermarket chips.

The battery and battery wires are all new and well connected. I have had the battery tested.

I have done nothing with the alternator. I will have it checked and check the wiring.
I thought the voltage was dropping b/c the RPM was dropping. I always thought the voltage was low b/c of the underdrive pulleys. I did forget to mention that I have UD pulleys.

Thanks.

 

[njmaier]

I had the alternator checked and it is good. All the wiring appears to be as well.

I reset the computer tonight. I then drove it for about 30 minutes, and now the only error code I get is KOEO 85 (expected). It also did not die once during this time.

Ugh...still stumped...

 

[njmaier]

I checked the wiring to the computer. PIN 1 always has a constant 12V so I guess the computer is bad. I ordered a new one...we'll see if that was it.

 

[strtrcr50]

Check your ignition switch...

 

[njmaier]

Check your ignition switch...

Already replaced it...forgot to mention that in the original post.