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Virtual Wrench
Virtual Wrench, Chevy Mechanic
Category: Chevy
Satisfied Customers: 14620
Experience:  35 years Master Mechanic
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Chevrolet Impala SS: I have a 1996 impala SS. When I press

Customer Question

I have a 1996 impala SS. When I press on the gas peddle, there is no power behind it. It just doesn't move. RPM's barely move. When it first happened the car slightly sputtered and wouldn't go over 40mph. It got worse and won't move at all. I changed whole distributor, wires, and spark plug. My battery is new. OBD2 codes p0335 and p0336 came up when I ran a diagnostic scan. I replaced the crankshaft position sensor and ensured that it wasn't too long to where it'd be hitting. The car runs idle smoother but not top notch. No longer sputters but just doesn't move. I'm thinking I have to check the PCM but and unsure to where it is and how to check it. I have a multi-meter tool. What do you think? And how do I check the PCM?
Submitted: 2 years ago.
Category: Chevy
Expert:  Virtual Wrench replied 2 years ago.
This doesnt sound like the PCM, it sounds more like a restricted cat converter. When they start breaking up it restricts the amount of exhaust that can get out, and if air cant get out, it cant come in.
Do you know if it has the stock converter still?
Customer: replied 2 years ago.
I was told it had a new one in already.
I forgot to mention that after I had changed the wires and distributor the car ran perfect for about 30 min. The. When I slowed down and tried to pick up speed again is when it started not accelerating
Expert:  Virtual Wrench replied 2 years ago.
Thanks for that info,
The thing about the converter is that when it heats up, the material inside swells up and slows the flow.
What you can do first just to rule it out (or in) is to remove the O2 sensor that goes into the exhaust forward of the converter and it will relieve any back pressure if the cat is plugged. Then take it for a drive and see if it improves.
Can you do that and get back to me. I really feel it is worth it to try because if it were a problem with the PCM it would have set a code.
Customer: replied 2 years ago.
The code that comes up on my OBD2 is p0335 and P0336. I didn't see any of the causes having to do with the Cat converter which I why I never would have guessed. I'm actually not working on the car at this precise moment so I can't try it at this moment. But I will try it and get back to you when I do. Thank you. If I remove the O2 sensor like you said. The car would run just be momentary like before?
Expert:  Virtual Wrench replied 2 years ago.
After you remove it you would notice a big difference in power right away and it would stay that way. It wouldnt run good then bad, off and on. I wouldnt ask you to remove it if i didnt think it was worth a shot bud. It's just that i have seen SO many act like yours is doing that i really think its worth a shot. Also, sometimes if you smack the bottom of the cat when its cold, you can hear pieces rattle around...not always but something to do also.
Take your time and get back when you can..
Customer: replied 2 years ago.
Ok. Will do. Thank you. I'll get back to you when I can.
Expert:  Virtual Wrench replied 2 years ago.
Fair enough. Regardless of the outcome, we WILL get to the bottom of this.
Have a good night my friend!
Customer: replied 2 years ago.
The guy I got the car from said it could also be the fuel filter or pump. He said it could be the engine not getting the right amount of gas pressure to accelerate. I was just wondering your opinion on that.
Expert:  Virtual Wrench replied 2 years ago.
Sorry i missed you last night.
The fuel pressure and filter were the next things i was going to have you check. Go ahead and replace the fuel filter because you have no idea how long its been in there, its just good maintenance anyway.
These fuel pumps are known to have problems so you can do a fuel pressure test by connecting a gauge on the test port on the fuel rail. It has to be real close to 45 psi and no lower than 41. If you dont have a gauge autozone will loan you one for free with a deposit.
It might read ok at idle so rev the engine and check it because they can fool you. Sometimes we have to drive the car with the gauge attached to the windshield to see what the pressure is at when its acting up...pain in the ass but sometimes it has to be done.
Let me know what you find with the O2 and fuel pressure. My PC is acting up so i am trying to fix it so it might take a bit to get back to you.
Customer: replied 2 years ago.
Ok. Thank you.
Expert:  Virtual Wrench replied 2 years ago.
You are welcome.
Customer: replied 2 years ago.
Just tried the O2 sensor. It won't even let me reverse out of my garage. Goes into gear, but when I gas it, it doesn't move.
Customer: replied 2 years ago.
Same as it was before.The fuel filter turns on but I haven't had a chance to check fuel filter. Waiting for the car to cool down now. Same p0335 and p0336 codes coming up. If fuel filter is fine I'll go down to O'reilly's to rent a fuel pump pressure gage.
Customer: replied 2 years ago.
Can you think of any other possibilities?
Expert:  Virtual Wrench replied 2 years ago.
Buy a crank sensor also. Usually when they fail it wont even start but thats what the codes point to. Other than the fuel filter and pump is all i can think of off hand.
Let me know tomorrow. I have to leave.
Customer: replied 2 years ago.
I have a new crankshaft position sensor in already. That's one of the first things I replaced because of the code. But I'll check the pump and things. Then I'll let you know updates tomorrow. Thank you
Expert:  Virtual Wrench replied 2 years ago.
sounds good