1993 4.3 rough idle then dies.
 

hey guys. Sucks for my second post here to be a cry for help. Got a 93 obd1 4.3 blazer that runs when started cold then when it warms up it dies. Then either won't start again or idles horribly when does. Ie bucks and drops and rises again and dies again if gas isn't hit. Already replaced injector, ignition control module, pcm, ignition switch, injector wiring, fuel filter and fuel pump. 700 in parts and still dead in the water. All replies are appreciated.

Thanks guys, Jack.

This could possibly be caused by a bad throttle position sensor on the TBI unit. OBD1 cars are a little hard to see whats really going on but there should be some type of code stored to help you find out what is going on.

never even thought about the tps...But yeah it doesn't throw a code which is the odd thing. Actually, i take that back, it throws a code 12, which is cause i used the paperclip trick.

Thats really the only other thing i can think of on an early TBi unit. i have had TBi GM trucks since they started using them in 87. The early ones are fairly simple compared to later models. Only so much can really go wrong with them and you have addressed most of the major culprits already so I would take a look at the TPS. not really an expensive part and it couldn't hurt. One other thing could possibly be the ignition module but when they go bad it normally wouldn't run at all. I see you listed that, is there a lot of play in the distributor rotor ? Can you move it around easily? the drive gear could be worn to the point that proper timing isn't able to be set.

Is your motor a TBI or CPI? If it's CPI with the Vortec labeled on top plastic then it is most likely a problem with you EGR valve. What happens is the valve will get stuck open or shut by carbon build up. It's easy too check if the valve is working correctly. With battery disconnected pull your air intake off an it will be right under the intake butterfly. Two 10mm bolts and a wire harness. See if the valves pental is moving freely. Choke/carb cleaner works best. Yours is probably stuck open starts for warm up then when motor gets warm valve shuts, motor dies

would a tps even allow it to start though? And as for the rotor, that wouldn't happen suddenly would it? I should've added that this has been my daily for the last couple years and only started doin this crap last couple weeks lol was on the way to work and it died. Wouldn't start. Then once it cooled off it ran fine for 5secs to 5 min then died once it warms up. Its annoying lol. Couldn't afford the 700 before definitely can't afford to keep throwin money at it lol bout to yank the trans and wheels and just sell it lol

If there's a problem with the TPS, or any other emission control device, being out of range, it will set a DTC. DTC 12 is system normal which means everything that the OBD1 system monitors is within range.

If the problem only ocurrs after it warms up, it could be when the PCM switches to closed loop operation. During open loop, (cold start) the PCM ignores oxygen sensor data. If the oxygen sesnor is "lazy" when the PCM switches to closed loop, there will be driveability issues, and it might not set a DTC. Also during open loop, the ignition module applies base ignition timing to the ignition coil. When the PCM switches to closed loop, it sends a modified ignition pulse through the EST, (Electronic Spark Timing) wire to the ignition control module, which in turn tells the igniton coil when to fire. There is a connector in the EST wire, (red with black tracer) on the passenger side, under the dash, behind the top of the carpet, (just above the passengers feet). Unplug the connector and check, (and adjust if necessary) base ignition timing. White sticker under the hood will tell what it needs to be.

Might be worth checking fuel pressure and leakdown at the service port by the distributor too. The PCM does not monitor fuel pressure, so it can't set a DTC if there's a problem.