1990 SC will start then immediately die

Joe1990SC

Registered User
When I first got my SC it was running rough and had a leaking valve cover gasket on the driver side, I have since replaced both valve cover gasket‘s, I have also replaced all the spark plugs, spark plug wires, also a new ignition coil pack. After that I started it and it ran good cold but as soon as it would start to warm up about 5 minutes,it would run really rough and the engine would shake and it would almost die if I gave it throttle it Would idle up but sputter,After this I replaced the DIS module. That didn’t fix it so I replaced the IAC sensor, the ECT sensor, that didn’t work same result, so I replaced the cam sensor, the MAF sensor, that didn’t work either, so I replaced both O2 sensors. That still didn’t fix it and now it doesn’t even want to stay running When I start it dead cold it will start then instantly die if I push on the throttle it will idle up and sputter a lot as soon as I let go of the Throttle it dies. Oh I also replaced the fuel filter and the fuel pump.


Any and all help is greatly appreciated !

Thank you.
 
Probably a major vacuum leak since you had to take off the blower and ic tubes to get to the valve cover gaskets...its a common issue
 
I resealed them, still having the same problem:confused:

Looking back at your 6/30 message, I noticed you mentioned replacing plugs, wires, and coil.. OK, so you double checked the plug wires and where they were attached to the coil pack, and that it has the 1-5, 2-6, 3-4 pairing, right? Also, the wires snapped onto the plugs themselves? If you attached the wires and your hands didn't ache, you may not have them fully seated.. also, don't trust numbers on the wires, its hard to see on the pass side. I would triple-check it. Grab each one, and pull/tug to be sure its really connected where it should be.
 
Same

I checked and double checked the plug wires are all firmly seated and in the right posistion. I tried to start it again, same result it starts, then as it starts to drop down to idle speed it dies.
 
In that case, I'd confirm the IAC is (a) the correct part, and (b) the connector is fully seated w/clean connections, etc. and (c) no leaks...did the gasket slip when installed, etc.

Seems likely there is a vacuum leak, somewhere, tho.
 
same

I suspected the IAC as well so i replaced it with a brand new one and i had it disconnected from the throttle body and tested it by having someone start the engine and i saw it move. I made sure that when i put it back together the connection was good an that the gasket is in place.
 
It might be the Crank sensor. If it is.. it would gets to some point it would even back fires when you rev it up. like the firing timing is out of whack.
 
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Same

Cant get it to run long enough to do KOER Test and it shows no codes for KOEO test.

I am thinking it is the Crank sensor as well, but it doesn't backfire when i rev it but it does sputter like it is misfiring.
 
Yeah the crank pully does wobble a little bit.

Take a good luck to see if the snout or pulley bolts are loose/missing. See if you can move the pulley by hand with the belt tension relaxed. Also note we've seen stories where the balancer/outer ring shifted on the rubber ring/snout, allowing the embedded trigger to rotate/move away from it's original position, causing a timing issue.

Might want to do a TDC/BTDC timing mark check, but if any doubts about it's health, don't be shy about replacing it, especially if it's original.
 
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Had the same problem with mine

When I got my SC I had the same issue let it run as long as you can before it dies then CAREFULLY feel the temp difference of the cats and the pipe leading out of the cats if the cats are super hot and the pipe isn't they may be clogged preventing the engine from breathing..
 
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