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Discussion Starter #1
The vehicle is a 1996 Buick Riviera, 3.8 supercharged. After running for a half hour or so the engine will sputter, and die, and not restart back. It threw codes only one time, p0300, multiple cylinder misfire I believe. I have changes the fuel filter, fuel pump, and ignition module. All had no impact on my problem. What should I do next???
 

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It is possible a sensor is going bad. If your problem occurs when you car warms up, the crank position sensor may be failing when hot. It may possible that the cam sensor could be failing when the engine is warm as well. If you let the car cool down and it starts right up and runs good for another half hour, I would be looking into a sensor problem.

On another forum, an engineer thought it was important to change out the ignition module and crank sensor after 10 years. The reason is that if it fails, you could be out somewhere with no help.

Best of luck to you.
 

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Discussion Starter #3
I guess I'll swap one out and hopes that fixes it. Is one more likely then the other? Or should I just do the easiest one first?
 

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crank sensor runs the spark, and cam sensor runs the fuel injection, find out whether it's fueling or spark based failure and check the sensor wiring and replace the sensor if necessary
 

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Sorry I haven't gotten back to yall, I been working last couple days so I haven't got to swap out either sensor yet. One thing I did notice is that If when it starts running ruff, that it seems to run fine when I hold the throttle to the floor, it will bounce off rev limiter over and over again. Would that indicate anything to any of yall?? Thanks again for the input guys!
 

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Sorry I haven't gotten back to yall, I been working last couple days so I haven't got to swap out either sensor yet. One thing I did notice is that If when it starts running ruff, that it seems to run fine when I hold the throttle to the floor, it will bounce off rev limiter over and over again. Would that indicate anything to any of yall?? Thanks again for the input guys!
Rev limiter doing that is normal, if it is running a it better when you give it gas, then the MAF sensor could need a cleaning, even if that is not the case, it is good to clean the MAF regularly, get some MAF cleaner and give it a clean, then you should clean it every time to replace the air filter.

Are you using a regular paper air filter, or an oiled one? Just curious.

Original issue still sounds like crank sensor is failing, it is not too hard to test yourself.
 

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Unplug your maf sensor. If the problem goes away, it's your maf sensor. =)

(the ECM defaults to a certain factory setting when it's not receiving info from the maf)
 

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Discussion Starter #10
Well I replaced the crank sensor and it had no effect on my problem. Since the problem started a couple weeks ago it has gotten progressively worse. Now the engine will barely start when cold, and wont run at all unless you hold it at 3/4 throttle or better. To recap I have replaced the fuel filter, fuel pump, ignition module, and crank sensor. I am going to next try what was suggested about unhooking the MAF sensor and see what effect that has on it. After that maybe the CAM Sensor?? keep the ideas coming guys, im in it this deep so id hate to have to take it to someone at this point.
 

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crank sensor runs the spark, and cam sensor runs the fuel injection, find out whether it's fueling or spark based failure and check the sensor wiring and replace the sensor if necessary
I would try to check to see if you have a fueling or spark problem. Make sure that you have a consistant good spark to all cylinders.
What do your sparkplugs look like?
 

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Well I replaced the crank sensor and it had no effect on my problem. Since the problem started a couple weeks ago it has gotten progressively worse. Now the engine will barely start when cold, and wont run at all unless you hold it at 3/4 throttle or better. To recap I have replaced the fuel filter, fuel pump, ignition module, and crank sensor. I am going to next try what was suggested about unhooking the MAF sensor and see what effect that has on it. After that maybe the CAM Sensor?? keep the ideas coming guys, im in it this deep so id hate to have to take it to someone at this point.
If the MAF sensor is ad you could unplug it as suggested, and see if the car will run in PE (power enrichment) mode, note that it will run rough if it does run.

Before replacing all of these parts you have replaced, did you test anything before replacing them?
Like the fuel pump, was pressure low, if so what was it?
Did you check the condition of all plugs to see if any are burning rich, or lean?
Have you verified spark on all cylinders?

Have you tested the fuel pressure regulator to see if it smells of gas, or leaks gas?
If not watch this video, the helpful part starts at 1:50 into it.
Testing for a leaking, ruptured, fuel pressure regulator diaphragm - YouTube

NOTE: I'd not feel like replacing that CKP sensor was a waste, that part is known to fail in older vehicles, so replacing it will keep you from a future breakdown, hopefully you can get this issue figured out.
Do some testing of parts before throwing anything else at the problem, it can get costly when you have to throw parts at something.
Also, on a side note, if you have never replaced your LIM Gasket with an aluminum framed LIM gasket, then that is something I'd look into replacing once you figure this issue out, you do not want coolant getting into your cylinders.
 
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