Cat failure stops car from running?

[BartusCompater]

So I replaced the wiring, the connector, and the coolant sensor itself. The problem hasn't been solved. After replacing the sensor I just let the car idle and confirmed what I think to be true, which is that the car is only able to run below a certain temperature, which if exceeded simply causes the car to die. After the car dies and sits for about 5-10 minutes it starts and runs again.

Also, don't know if this could be related to the problem but I thought it was peculiar: When I took the old coolant temp sensor out, no coolant came out after it AT ALL. I was under the impression that there should be coolant above it.

[majicwrench]

I'm gonna really sound like a broken record, but you need to run some tests when the car is dead and not just replace parts.
When car is not starting, is it lacking spark, or fuel??

And yes, there certainly should be coolant at the coolant temp sensor.
Best of luck to you!

[BartusCompater]

The car starts after it has died, it simply won't stay running. It fires up and then instantly dies again if it is around operating temperature. So as I think I've said before but may have not made clear, it still gets fuel and spark. Unless you think that I need to be testing for what causes the car to die... loss of fuel or spark, which I don't know how I could identify given that it stops so suddenly.

[majicwrench]

Stick a fuel pressure gauge on it, "T"d into the line so you can see if you lose fuel pressure. Hook a cheapy timing light up, tape trigger down, and aim at the drivers seat. Now you can see if it loses spark. Pull one injector plug and hook up some sort of noid light or test light between the two terminals, visable from driver's seat, to see if injector quits firing. Do all these BEFORE it starts giving you issues, so you can watch and see how it all works, when it is working correctly. Now get it to die. Now start it, and watch it die. You should be able to get a pretty good clue from the above, and then you can do more specific testing once you know what area is giving you issues.
It is losing something that is why it dies. Your mission, should you choose to accept it, is to find out what.

[BartusCompater]

Simply dodnt have the time to diagnose the thing, so I took it to the mechanic. It turns out that when the cooling fan engages the fuel injectors are losing pulse, hence the car dying when it reaches operating temp. With a replacement battery it stays running (the current one is only putting out 12V). Additionally, the alternator is doing poorly under load. This is all according to the mechanic I took it to.

The car's electrical system has always been questionable (red light with the headlights on). Could the worn out alternator have contributed to the battery situation?

[BartusCompater]

Just ordered one of Mark's high output alternators

[manoa matt]

"Could the worn out alternator have contributed to the battery situation?"

Check the negative battery wire. If the connection at the battery terminal and the connection were the wire attaches to the body is not good, the battery will not be charged by the alternator. (I know this for sure)

Could also be the voltage regulator, a $20 part available at most auto parts stores and simply screws onto the back of the alternator. (This is just a guess)

[TX82FIAT]

I've been following this thread for a while and have really offered no opinion because testing is the only way to find out what is going wrong. However, I have felt all along that you have some type of electrical signal issue. The electrical issues may not be realted and a new battery or alternator may not solve your problems in the long run. I'm not doubting you have an alternator or battery issue. After you have insured you have a strong alternator and battery on the car. Please consider this. You started off talking about the Bosh Mass Air Flow meter. Did you have an opportuntiy to temporarily swap for a properly functioning unit. There are a host of sensors that tell your car how much air and how much fuel it should be sending into the engine running into the CPU. You have altered the air flow meter. The car has a very basic equation for air, fuel, temp, RPM. I would get another AFM and run through the fuel injection diagnostics testing sensors and checking the wires in the engine bay.

I know this type of issue can be frustrating. Also, this started off talking about backpresure via the CAT when the car does start and before it gets to temp for stall. do you have exhaust fumes coming out of the tail pipe. I can't recall at what point you shaved the flap on the AFM.

[divace73]

Some more point to consider....
*Check all Grounding points and ensure they are clean, especially the battery.
*More than likely your Ignition switch may be old and building up resistence which may explain the dull head light.
*The double relay may be faulty (mine use to cause my fuel pump to switch on and off due to a dry joint, easy to fix if this is the case)
*The Tee coolant gauge as suggested previously
*The magnetic pick up in your dizzy could could be playing up (My shaft was use to move up and down which would stop the pickup from picking and and therfor no spark)
I cannot see why the Fan should effect the injectors???, unless when the fan switched on it pulls more current and voltage that the computer needs the operate??

I am hanging to find out what was the actuall problem.

[majicwrench]

Certainly the fan could pull the voltage down enough to shut off the injectors IF the charging system and/or wiring is not up to snuff. The battery, once the car is running, is not likely the problem. Putting in a new battery may have fixed the issue for the moment, just because it was fully charged.
But sounds like the mechanic is on the right track.
Good luck!

[BartusCompater]

So I tossed the new alternator in. It seems to be working great, lights are brighter than ever and I get no charging system light when everything is turned on. Also the car runs with the cooling fan running.

However during my test drive today it died at a stop again. I was able to start it back up after a couple of minutes but every time it tried to come back to an idle it just shut off. So I worked my way home about 2 blocks at a time and got it home by just restarting it.

Tomorrow morning I'll start it up cold and see if it does the same thing, though I have a suspicion that it has to do with the car warming up. That or maybe the AFM that I sanded down? I'm not jumping to any conclusions though. I'll probably just take it back to the mechanic for the sake of my sanity. I'm a little frustrated by this car that I love.

[So Cal Mark]

if you hold the idle higher, will it keep running?

[BartusCompater]

From what I could gather just getting the car home today it seemed to run fine as long as I had the throttle going and/or it was in gear (i.e. around 20000 RPMs). Pushing the clutch in for longer than it takes to shift normally or coming to a stop it would just die. After dying same deal as before- fires up and dies again instantly until waiting for a minute or two. Holding the throttle in as I was cranking seemed to get it running sometimes, but not every time. Also, as I was pulling in to my driveway and coming to a stop it happened to stay running at an idle for a little while, but eventually died. Watched it as it died, didn't notice anything like the fan activating as it died.

This is interesting because even before I replaced the alternator it always seemed to want to die at a stop. Clearly however it was also dying as soon as the cooling fan came on, which it doesn't anymore (or it didn't when I first let the car warm up after putting the alternator in).

I'll update tomorrow morning when I figure out if this is just something that it's doing when it's warm.

[So Cal Mark]

what is the lowest speed you can hold it at and have it keep running? Does it run smoothly at that speed?

[TX82FIAT]

There is some good news in that the new alternator as suspected has improved the electrical system. The car can still run at RPM's > 2000. Is there another Fiat person anywhere close with a Fuel Injected car? I would see if someone will let you do an AFM swap. I think you checked all the connections. The fuel injection troubleshooting can take some time but uncover many problems. Hang in there. Do you smell any gas when it stalls?

Ray