SES light on the 96 SS

[JL8Jeff]

I keep getting the P0300 random miss/multiple cylinders on the SS. I just changed the plug wires since it was time for them to go anyway but the SES came back. Any suggestions on what else causes this? The car runs great and you can't even tell anything is wrong when the SES light starts to blink before it comes on. Bill, are you available some time this week after work to do some scanning/observing/tuning? And does anyone know if you can program this code out and still pass inspection?

[NJSPEEDER]

96 would be earlier than the HPTuners software that bill uses will support.
since it is OBD2 bill should be able to scan and view it though, at least give you an idea of where to look.
you replaced the plugs as well as the wires or just the wires? i am not sure how opti spark is set up exactly, but a multi cyl problem could be a sign of a dying coil or loose coil connection.

later
tim

[JL8Jeff]

The plugs looked new when I checked a couple so I just did the wires. From what I've been reading, the P0300 code could be any of a number of little things so it could be a pain in the butt to figure out. I don't want to spend too much money replacing things that might not be bad.

[Squirrel]

puttin it new plugs is cheap security, im sorry, but you may just have dive back in there :P

[foff667]

yeah the best i could do is scan it...but being such an early obd2 car im not sure what things i could scan. As far as tuning out the P0300 code yes it is possible with tunercats or the like but the program itself is ~$400

[JL8Jeff]

I'm thinking it might be more of a lean condition which the computer sees as possibly damaging to the cats. It usually pops up under low speed conditions. So getting a good scan on the engine might provide useful information for troubleshooting. I can't feel or hear any form of a miss so I'm thinking the lean condition or the crank sensor is going bad.

[foff667]

a lean condition probably wouldnt show as a missfire code like p0300...crank sensor maybe but even those failures are few & far between. I would tend to think about changing the $8 in plugs first, but thats me.

[JL8Jeff]

Bill, can your HPtuners scanning record all the parameters to go back and review? I just ran the car in the dark and there's no sign of any spark issues. I really think it has nothing to do with the spark because it runs so good. I was reading that if the exhaust temps are too hot it will trigger the P0300 code beacuse it can damage the cats. But I would still need to find out why it's lean if that is the problem. The P0300 code seems to be the biggest PITA to troubleshoot. It looks like the car has new O2's and some of the injector wiring and EVAP purge stuff has been replaced so somebody was trying to track down the problem and probably gave up.

[foff667]

yes and i can send you the file in excel format once its all said & done...can you meet me at dot sometime this week at 12pm so I can scan you on my lunch?

[JL8Jeff]

Well, I was doing some more troubleshooting and I noticed that the SES light seems to be coming on when the EVAP purge is running. I checked up at the intake by sucking on the purge line and there was almost no resistance and a bunch of tasty bits of charcoal material! A couple of the short purge line rubber hoses were dry rotted and loose so I replaced them. The canister itself must be shot because you can shake it and hear the charcoal bits moving around. I put in my slightly used canister and hooked all the lines back up and tested again at the intake and there's much more resistance so that's a good sign. I think the bad purge line/canister situation was allowing too much unmetered air into the engine causing the lean condition which resulted in the P0300 code. I'll take the car to work tomorrow to see if the code comes back. I'm hoping that's the only issue but I'm worried the purge solenoid at the intake is contaminated from the charcoal bits so I'll probably be replacing that as well.

[JL8Jeff]

Well, I was doing some more troubleshooting and I noticed that the SES light seems to be coming on when the EVAP purge is running. I checked up at the intake by sucking on the purge line and there was almost no resistance and a bunch of tasty bits of charcoal material! A couple of the short purge line rubber hoses were dry rotted and loose so I replaced them. The canister itself must be shot because you can shake it and hear the charcoal bits moving around. I put in my slightly used canister and hooked all the lines back up and tested again at the intake and there's much more resistance so that's a good sign. I think the bad purge line/canister situation was allowing too much unmetered air into the engine causing the lean condition which resulted in the P0300 code. I'll take the car to work tomorrow to see if the code comes back. I'm hoping that's the only issue but I'm worried the purge solenoid at the intake is contaminated from the charcoal bits so I'll probably be replacing that as well.

[JL8Jeff]

Well, after driving around today and doing a good mix of around town and some highway driving, still no SES light coming back on so I think the charcoal canister being shot and the rubber hoses on the purge lines leaking were causing the car to take in too much air and making the car lean out causing the misfire code! Figure that one out. I was pretty sure it had nothing to do with the ignition based on how well the car runs. I can't imagine how tough it's going to be for the 96-99 cars and trucks to pass the newer OBDII inspections in the next couple of years as these vehicle age.

[Ian]

I can't imagine how tough it's going to be for the 96-99 cars and trucks to pass the newer OBDII inspections in the next couple of years as these vehicle age.

shouldnt be too hard. I would expect the earliest OBD II cars (96 and 97) to be the hardest out of all of them. the newer ones are really easy to diagnose. Even the older ones arent hard. once you figure out what the code is you dont have to look much further to find the problem.

I know on the newer cars, if they had your problem with the broken purge lines, they would pop a code for the evap purge system. from there its only about 10 minutes of diagnostic work to find the problem.

[JL8Jeff]

Ha, wishful thinking. My car never gave any form of an EVAP purge code. It gave the random misfire code. That's what I'm talking about. The 93-95 F-body's are a lot easier to deal with. The oldest OBDII cars/trucks are going to have a hard time pinpointing the problems. Do a search on the web for the P0300 random misfire and you'll find some interesting reading on people trying to fix their cars/trucks.

[ar0ck]

My ASR & ABS lights used to come on randomly in the rain.

[jbird99]

i forget what code im getting but it deals with a miss/mulitple cylinders but its cause i need some new sensorssss

[jims69camaro]

this is why i haven't got a newer car yet. seems like you have to go buy a laptop and some software just to be able to diagnose it properly. or take it to the dealership and have them charge you $65/hr...