87 Turbo t engine stumbling

[107WS]

Just got a 87 TT. About twenty minutes away from the sale, engine started missing at light load, I.E. little or no boost and less than aprox 65 MPH, no missing or surging at moderate to heavy load. Scanmaster showed BAT voltage about 11.5 to 21.2 or so. The main battery checked bad and it was replace. Engine runs normal, now scanmaster reads aprox 12,5 to 13.2, even saw 14 once. But Autozone device indicates 13.9 to 14 volt alternator output
What happened?
Thanks
George

 

[TRICKSIXPA]

How much gas is in the tank. Has it been filled recently and these cars take 93 octane. Does the car have any gauges/ scanmaster?

 

[107WS]

How much gas is in the tank. Has it been filled recently and these cars take 93 octane. Does the car have any gauges/ scanmaster?

Car had 1/4 tank of gas. Filled with 93 octane. Car has Scanmaster, that is where battery voltage came from. There are no additional gauges. Car still is running fine. Unsure how a battery change stopped the surging/ missing. BTW after filling the car with 93 octane AND BEFORE replacing the battery, the problems continued until the battery was changed.
Thanks for the reply.

 

[whitehot1]

Congrats on the purchase of the 87 T.

Now to get it running good and making it reliable so you can enjoy it.

Start here. http://www.gnttype.org/maint/basics.html

And post any mods to the car and all the scanmaster readings.

 

[TRICKSIXPA]

Car had 1/4 tank of gas. Filled with 93 octane. Car has Scanmaster, that is where battery voltage came from. There are no additional gauges. Car still is running fine. Unsure how a battery change stopped the surging/ missing. BTW after filling the car with 93 octane AND BEFORE replacing the battery, the problems continued until the battery was changed.
Thanks for the reply.

A lot of things to factor in. Do all the spring cleaning as recommended on GNTTYPE.org. Not getting the proper voltage will do it.
Did you find out if the battery you took out was bad? Looses connections, ECM after battery disconnected was reset, could be getting better voltage to the fuel pump. Did the previous owner do the fuel pump, hotwire kit, and fuel filter recently.

 

[107WS]

Car has green stripe injectors TT chip 20 to 18 degrees 15 to 17 psi all written on the chip. Unsure about the pump or filter, however the car runs fine at WOT. Fuel pressure about 40 PSI at the rail. O2 milivolts above 600 as I recall. Replaced ECM, chip and Mass airflow sensor. car still stumbles/surges at part throttle. O2 millivolts <100 while stumbling, but increases to 600 or greater when throttle is applied.
This problem does not always happen. Drove the car about five hours today at freeway speeds 55 to 85 mph, without a problem. The car started stumbling at freeway speeds and continued to do so for about 1 1/2 hours then I arrived at my destination.
Battery was bad, After battery replaced, alternator charging at 30 amps with air, radio and cooling fan on at idle.

 

[BoyWonder]

Did I count two dead batteries or just one?
The original (dead / bad etc) battery I got.
I almost always replace whatever battery I get with a high quality one - almost like immediately changing the oil when I buy a car.
But according the latest post, the battery again was "bad"
What kind of / brand battery are we talking about?

I sell (industrial) batteries for a living, and there is a vast range of quality in the automotive battery business.
Most people buy on price, and in batteries, that's exactly what you get - a cheap battery poorly made in (insert third world country here)
But if a second battery was discharged beyond it's rated DOD, there seems to be an obvious problem with the float / charging circuit. (i.e Alternator or related)

 

[107WS]

Just one battery was bad. The replacement battery is 700 CCA from Autozone. It was purchased about one week ago and is peforming well. It was not a cheap battery.

 

[BoyWonder]

Ahhh..got it.

It's most likely one of the two demons - either spark or fuel.
I suppose it could be a sensor / ECM type issue but they usallly manifest themselves at other speeds as well.

You mentioned stumbling at highway "cruising speed"
But implied it ran ok on the highway at 55-85 mph.

Was the stumble at one particular speed and / or RPM?
Did you try running the highway without O/D or lockup?
This will not hurt the trans.
Stumble might feel like a torque converter lock / unlock but that is a WAG, without feeling the "stumble"

Or - before I installed the fuel pressure gauge setup to the interior of my cars - I used a little test fuel gauge with line & bracket that I attach to the wiper arm assy for occasional degugging.
Likewise - Ialso have a vacuum gauge inside the car.
Doubting vacuum though, although at perhaps a very low rpm on highway in O/D...
These cars are very sensitive to having good tight vacuum hoses and connections.
It's a common thing, and oft overlooked while chasing what people think are more serious problems.

Once I verified the trans was not the culprit, the fuel and vacuum conditions are proper - I'd then move on to the electrics / spark.
None of these checks cost much, if anything, and it beats replacing things willy nilly or chasing ghosts.

 

[RIFF RAFF]

IT WAS THE BAD BATTERY !! COUNT YOUR BLESSINGS ..

 

[mikestertwo]

Scanmaster showed BAT voltage about 11.5 to 21.2 or so. The main battery checked bad and it was replace. Engine runs normal, now scanmaster reads aprox 12,5 to 13.2, even saw 14 once. But Autozone device indicates 13.9 to 14 volt alternator output
What happened?
Thanks
George

The voltage scanmaster is showing you is ignition voltage not battery/alternator voltage.

 

[107WS]

What should the ignition voltage be? The stumbling occures at light power loading regardless of the speed. It occures from zero MPH until the car makes boost. The car runs fine from about one PSI boost to max boost. This is a part throttle problem. I know little (now, but soon to change) about these cars. The last one I had, about eight years ago was bone stock and I had zero problems with it. The problem is not always present. I drove it about 7 1/2 hours yesterday. The first five or six hours were trouble free, then it started stumbling or missing for the last one to two hours. The missing is not continuous like a bad or loose spark plug lead. Just an interminent issue that stops when the car is under boost. I will see if Autozone can hook up their reader to Snead some light on the issue.

 

[mikestertwo]

What you are seeing on scanmaster for voltage is normal. As far as the stumbling problem check the cam sensor.

 

[Grunk]

Have you checked the coil pack? From each opposite side tower with an ohm meter should have about 11-13K resistance.

 

[107WS]

The coil packs have been replaces, no effect. The cam sensor red LED flashes when the engine is running. Is 1/8 inch adjustment too much to start?

 

[mikestertwo]

You should check the sensor for excessive shaft play. Go through the cam sensor setup proceedure. Without knowing where the cam sensor timing is right now I can't tell you which direction or how much to rotate it to see if it makes a difference. You could try rotating it in either direction a little (1/8 turn should be ok) to see what happens. I designed a timing light that triggers off of the cam sensor so I can set the cam sensor timing while the engine is running.