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Mustang Guys, need some help with my Aunts car
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Posted by: Tang

Ok, my Aunt has an '87 GT Vert, 70k miles, AOD car.

She got it about a month ago. Since she got it, it has had this miss in it below 2000 rpms. In overdrive it causes the car to jerk and jump if it is at low cruise rpms.

Well, found a rats nest on the the intake where the car had been stored. The rat had chewed the wires off the #3 injector. Well got that fixed. Then added new plugs, wires, cap and rotor, and fuel filter.

Today we put a new water pump on it, and changed the O2's because it throwed code 92, figured 70k miles it needed the stock ones changed.

Well, it isnt as bad as it was, but still the miss is there. Now when the car is cold, it seems to run GREAT, but when it switches to "warm mode" or whatever its called, thats when the miss starts. Sometimes it will die when at a stop light holding the brake with it in gear.

My theroy is, its either the TPS, or the idle air thingy on the throttle body, OR, the #3 injector went for so long not working, that it is about half stuck or just not spraying right.

So , you guys think I'm on the right track ? I saved her a bundle today, a guy was going to charge her $90 to just change a water pump

. Good grief, why do people want to rip people off so badly.

Posted by: SVOno5oh

The biggest differnence between open loop and closed loop running when the car is warm is the utilization of the O2 sensors. When the car is cold, it only see the MAP sensor and goes from a fixed air / fuel table. If it were the IAC valve (idle air) then you would have the problem when you start it too. 70K miles its time to do the O2 sensors anyway, and the car is now 16 years old. It's time. The TPS can cause a stumble on acceleration too if it isn't seeing a smooth steady increase in voltage. There are tons of messages at the corral on how to set a TPS. You'll need a multimeter though too.

Honestly $90 for a water pump change is cheap if you have to pay for your own work. It's nice of you to help out though, that's for sure!

Posted by: SVOno5oh

Oh now I see you changed the O2 sensors.... darn. Any new codes?

Also did you route the spark plugs wires so cylinders firing in order aren't in parallel? Are they original wires too? I've had problems with wires shorting out on my GM trucks.... pop the hood at night and look and listen for sparks.

The last possible suspect would be the fuel pressure regulator or maybe even the MAP sensor. That's really about all there is in a speed density 5.0 to check.

Oh wait... when warmed up: coolant temperature sensor could be given crazy readings too and pulling a whole bunch of timing.

Posted by: Tang

The wires she put on it are Accel Super Stocks.

Now the MAP sensor, might try changing it next. It's $44 at Autozone. I didnt have time to check the codes after we got done, had to take her car back to her.

Posted by: VETTKLR

Do you have a fuel pressure gauge to check the pressure when the car is started and then after it runs a little while?

Damn Fuelie Ponies. Hit it with the diagnostic tester again.

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