JonnyThrice

My car's been running great, especially since I fixed all the cooling issues (new rad, water pump, hoses, thermostat)...

Last weekend, I let a buddy take the car to a car show a little ways out of town. Apparently, the car stalled out on the highway and would not start.

After some tinkering, it seems that if we remove/unplug the coolant temp sensor (the one right near the thermostat) the car will start and run like crap, really rich since the coolant temp reading isnt getting to the ECU. We replaced the sensor, but still no go.

This is a strange one. Anyone have any ideas? I was thinking it was the fuel pump, but it seems to be getting a lot of fuel without that sensor.

Car is an 89 Formula, 305 TBI

Go Blue

The running really rich is because the ECM doesn't know the true temp of the engine so it's probably going back to a baseline reading when it is not in closed loop settings (aka all sensors are in their normal operating temperature range) so it's just dumping fuel down the throttle body. Is the issue only happening when the engine is warmed up and at normal temperature? When the car dies, is it just cutting out like you flipped a switch or is it stumbling and dieing? If it's dieing like you just flipped a switch then I would lean towards ignition/electrical. If it's stumbling and dieing, I would look more at the fuel injection system. How's the idle on it hot or cold?

JonnyThrice

Not exactly sure of the details, my friend said it just quit on him and hasn't started since.

I just tried it today again myself. It turns over starts and idles for maybe a second and dies. Doesn't seems to stumble or anything.

I then disconnected the coolant temp sensor and it fired up actually idled and revved very well for about a whole minute, then died again. Wouldn't start again after that.

So it seems to be getting fuel and spark, sometimes

Go Blue

This would be a good question for Tuned Performance as he's great with fuel injection issues on these cars. If it doesn't stumble, then I would think it's more related to the ignition, but that's not always 100% true. I would almost say it's a VATS issue, but I don't see how the coolant temperature sensor/sending unit plays into it.

Tuned Performance

iTrader: (92)

Vats would just stop injector pulse when you first try to start the engine. Sounds like a fuel delivery problem start with checking fuel pressure. Fuel pressure should be between 10-12psi. You could have a bad ignition control module killing spark or injector pulse when it starts to warm up. Like go blue stated the code 15 or lack of cts will make the engine run real rich.

Tibo

iTrader: (15)

I'll lean toward ignition control module. Those issues are well documented. When they begin to go they will usually begin to stumble when warm and after a while they will cut out spark completely. When I daily drove mine I would keep a spare module in the console. One lifetime warranty at O'Rielly and another at Autozone so whatever I was close to would just swap it out.

VATS would not cut out while driving. The VATS is programmed that even if it gets a wrong resistance after start up it will still run.

tealman92

Its your icm in the distributor. I just fixed Shawns Trans am last month with the same issue. His icm was only 200 miles old and it crapped out.

vinny R

ICM for me also. Just got done with the same symptoms almost to the tee!. I have a thread in TPI title Fuel Pressure? as I thought that was the problem.

mmadden55

solution Hei with vac advance and no ecm. Had the same issue on my Astro Van

Tuned Performance

iTrader: (92)

You need a ecm to pulse the injectors. A hei vacuum advance is used with a carburetor this is Throttlebody injection.

JonnyThrice

I took it to a mechanic before I tried anything. They told me spark was OK, but fuel pressure was really low. Seems to be the fuel pump. Yay

tealman92

You will still get spark but once the icm warms up it works erratically.

Tuned Performance

iTrader: (92)

Any idea of how low , Tbi is only 10 to 12 psi