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1996 Impala P0300 madness

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04 Aug 2019 13:47 - 04 Aug 2019 13:48 #32473 by snuup408
1996 Impala P0300 madness was created by snuup408
Hello, I have a chevy 96 impala ss 87000 miles that I bought in april. When I bought it ran fine except lacking all the power I thought it should have especially climbing hills. 3 weeks in I get a blinkin cel light and a p0300 random misfire. Since I didn't know the history I put new distributor ( common with these cars), The code changed to p0300 and p0303. I put wires and plugs, Code changed to p0300 and P0304. Checked fuel and it was 21psi and didn't change when vacuum pulled to solenoid. Replace solenoid and pump. Now 41 psi. Car seemed to be running rich. Had 3/4 of a tank and just from testing and around the block the tank is near E. I cleaned injectors and found 2 leaky injectors, replaced. Front o2's fluctuate nice on scan tool. Back 02' stay in the 800 range.
Sprayed around engine with carb cleaner multiple times. Sprayed wires for arcing. Check and rechecked firing order. Changed coil and module and checked for spark at cylinder 3 and 4, It does. Vacuum gauge fluctuate rapid between 8 and 12. and pulled upstream o2 and vacuum fluctuates too. Was riding fine on the highway and this just hit all of a sudden. Car has 87000 mile on it. I checked and cleaned egr. When I pressed it at idle car died. Any other direction I can go? Thanks in advance.
Last edit: 04 Aug 2019 13:48 by snuup408.

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04 Aug 2019 14:24 #32477 by Cheryl
Replied by Cheryl on topic 1996 Impala P0300 madness
With the vacuum gauge bouncing I’d be looking for a valve spring or guide issue. Do a compression check yet?? And or leak down test

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04 Aug 2019 16:34 #32481 by snuup408
Replied by snuup408 on topic 1996 Impala P0300 madness
Thats my next move. Thanks. Was hoping i didnt have to do it on a LT1. But hey. Ill post my results. Thanks

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19 Aug 2019 21:44 #32982 by J-D
Replied by J-D on topic 1996 Impala P0300 madness

snuup408 wrote: Thats my next move. Thanks. Was hoping i didnt have to do it on a LT1. But hey. Ill post my results. Thanks


Did you ever figure out what the problem was?

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20 Aug 2019 05:46 #32988 by Vw mike
Replied by Vw mike on topic 1996 Impala P0300 madness
Is this the opti spark that is behind the water pump? Just because new dose not mean good . Also I would do leak down and compression test.

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20 Aug 2019 17:06 #33006 by snuup408
Replied by snuup408 on topic 1996 Impala P0300 madness
Hello. Not yet. Been busy work and traveling. I did get all the plugs out. Looks like all were kind of wet and dark and fouled. They were New plugs but only did test runs around the block for about a total of 5 miles. Yes this is the opti spark behind the water pump. Going to compress test tonight. Thanks for asking. Ill post results

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21 Aug 2019 12:29 - 21 Aug 2019 12:30 #33027 by snuup408
Replied by snuup408 on topic 1996 Impala P0300 madness
Well I got on it this morning but forgot to open the throttle body. I got 118-120psi on all cylinders except cylinder 4. Cylinder 4 was funny. I had a shaky harbor freight tester. Showed 90 ish the first time then came back and tested again. It was 0. came back later it was 60 ish then tested again 0. I was suspect about the shaky tester. But retested other cylinders and it was around 120. Came back to number 4 and it was 0. I still have to put oil in the cylinder and retest plus open the throttle body next time. But it looks like a cylinder 4 problem. That's the cylinder that myscan tool detects a misfire.
Last edit: 21 Aug 2019 12:30 by snuup408.

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