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95 Firebird 3800 P0300

Model: 95 Firebird 3800 Fault Code: P0300 Posted: 2007-02-26 12:28

I have a 95 Firebird 3800. I constantly have ignition system problems. I've put 4 crank sensors on it in 3 years. About a couple months ago my car was acting like it had a bad crank sensor (AGAIN - after having replaced it only about a year and a half ago for the 3rd time). However, the SES light wasn't coming on. Finally, after about a month of acting up (and me having changed the ignition module with a spare I had and that not fixing the problem) the SES light finally came on and threw the crank sensor code. I replaced the crank sensor (4th time) and the stalling/surging/RPM dropping problem went away. However, immediately after having the crank sensor replaced, there was a misfire. I've had bad wires for a long time (never could seem to get them routed right so that they wouldn't end up touching something hot and arcing). I had a few wires that had some small arc areas and if you moved them a certain way, they'd arc and there'd be a misfire. So I assumed that during the changing of the crank sensor, the wires were bumped into a position causing an arc which was the cause of the miss. A week or two later I replaced wires and plugs and routed them perfectly through the factory wire retainers and some additional wire retainers I bought. I started the car and it had a terrible miss. It wouldn't even stay running unless you kept your foot on the pedal. I assumed I hadn't gotten one of the wires all the way on the plug and went over them again and again and again. They were all on right and secure. I thought maybe I had a bad plug from the box. I looked to see if there were any arcs while it was running but there were none. The next day the SES light came on it and had thrown the P0300 code (random multiple misfire). Now I was stumped, how could I have MULTIPLE bad plugs or wires AT RANDOM? That didn't make any sense. So I stopped looking for a bad plug/wire and looked for something else that could cause it. I noticed that while I was changing the plugs/wires, I had knocked off the vacuum line that goes from the evap up to the front of the intake. I said "wouldn't that be funny if that was the cause of all my problems." I plugged it back in and it immediately ran much much better. However, this line had been broken numerous times and patched w/ vacuum hoses. It still wasn't idling perfect and I assumed that it was that bad vacuum line. So a few days later I bought a new one from the dealer and replaced it. Still ran really rough (but no where near as bad as it had been when it was disconnected). I figured the problem must be another vacuum line. I went over all of them and can't find any cracks or problems anywhere. It ran for another week before throwing the P0300 code again. I printed out some info on the P0300 code and possible causes. First it says vacuum leaks, but I believe I went over that thoroughly. It also says that PCV and EGR valves could cause the problem. Next I replaced the PCV (which was a little sticky) but that didn't fix it. I changed the EGR valve about 50k miles ago, I'm not sure how long they last generally, but don't want to throw $140 at it if that's not the problem. This morning I started it and it ran smooth as could be. Then when I started driving, I noticed the bad random miss again in a few minutes. So it was running perfect when cold, just after being started, but not after driving a little bit. Does ANYONE know what this could be? It's driving me crazy!

Related fault codes
P0300
Comments (19)
Anonymous 2007-02-26 13:47

ignition coils and or module! What brand of crank sensors? You have to be careful that balancer isn't damaged or the reluctor wheel will be all out of whack

Anonymous 2007-02-26 19:59

I use good parts. The last crank sensor (the one I just replaced that was only a year and a half old) was a Borg Warner.

Anonymous 2007-02-27 07:42

ever try a dealer one?

Anonymous 2007-02-28 10:25

Also, for the past couple months, when I first start it, it runs really bad for about 5-10 sec, light it's starving for fuel. When I give it gas it sputters and shoots black smoke. Then starts to run smooth. Could these two problems be related? And when I first start it, it runs for about a minute w/o misfiring, then starts missing.

Anonymous 2007-02-28 11:01

sure

Anonymous 2007-02-28 14:23

Oh, and for about 2 months, when I first start the car and turn on the heater, I can smell antifreeze. I assumed the heater core was on its way out, but could this have something in common w/ the misfire? A head gasket/compression problem? I had the ignition module and coil packs tested today, all good.

Anonymous 2007-02-28 15:21

intake or head gasket both a good possibility

Anonymous 2007-04-21 18:45

Well, I took it into a shop to diagnose it for $70. I gave up on trying to figure it out myself and needed someone who had the equipment to run it on diagnostic and see exactly what was going on. So I told him what the problem was and the possible causes (fuel pressure, intake leak, etc). He said it'd take a few hrs to diagnose it and I'd "know exactly what the cause of the problem was" when he finished. Well, they couldn't figure it out either. I kept calling in to check on it and he said "you have a really strange problem here". He said his lead tech was out sick and it was over his other tech's head. That when his lead tech came back he'd be able to diagnose. So what was supposed to take a few hrs ended up taking a week. Then he finally said it was 3 things: 1. the pcv o ring was crushed, 2. the 1/4 coil pack was weak, 3. the lower intake manifold gasket had an "internal" leak between ports and was sucking in exhaust fumes. He wanted over $800 to fix it. I just needed it diagnosed, I told him I'd fix it myself. He went ahead and changed the pcv oring tho. Then I took it home and changed the coil pack. Still ran almost the same (slightly better). Still threw the 300 code, still stalled at idle sometimes. Idle was really rough. So I put it off for about a month due to bad weather, and finally went out and bought both gasket sets (upper and lower intake manifold). I was gonna do it myself but then I popped the hood and remembered how much of a pain in the a$$ it is to do anything on this engine due to how far back it is. So I decided to take it to a local shop who quoted me $200 to do the job. They completed it today. They verified that part of the lower intake manifold gasket was crushed (and showed me) but that didn't fix the problem. It still runs the same. So now what?

Anonymous 2007-04-21 20:31

Find the best GM Dealership in your city and go to them. Take the vehicle to the Dealership to diagnose & repair. Dealership has better equipment / software & techs to figure out the problem. Ask them to put one of their better techs on it. Write down a list of what has been checked & fixed already ( and dates ) to give to them. P0300 random/multiple misfire code is not enough to figure out what the cause is. And your vehicle symptoms seem somewhat unique ( doesn't seem to be one of those common problems ). Your crankshaft sensor is also going too quickly. ( Jeff may be right about the balancer - your crankshaft out of balance? This could even be the cause? or ? ). Only thing you'll get on here is guessing. PS Forget about going to a repair shop because there are few very good mechanics out there. Most are ok ( and some bad ) and so won't do a good job with the diagnostics and/or repairs.

Anonymous 2007-04-22 21:43

My post here may be helpful to you: http://www.obd-codes.com/forums/viewtopic.php?t=1913

Anonymous 2007-04-23 16:02

Still sounds like an ignition coil and or module problem as well!

Anonymous 2007-04-25 09:15

I just read something this morning about a crankshaft learn procedure being necessary if you've changed the crank sensor. Previously I read that it WASN'T necessary for changing crank sensor (and have never done it in the past when changing the crank sensor on this car). It said that it could cause the 300 code. Now I just had the crank sensor installed by someone who tightened the balancer afterward w/ an impact gun for about 5 min straight. Could that have caused some kind of damage to the crank sensor resulting in the 300 code?

Anonymous 2007-04-26 07:30

yup!

Anonymous 2007-04-26 15:04

@ tonestone57 So Im not sure who you think YOU are, but if I were you, I'd avoid any sweeping statements encapsulating independent shops as "bad" and not doing a "good job with the diagnostics and repairs". We've been through that on this forum already and it's not allowed anymore. Ya know, Too many techs getting pissed off. Like me. Compton already let me have it for slamming dealers, so, give advice, nothing more, and that's it. Leave your ineffectual ramblings where they belong: on your my space page.

Anonymous 2007-04-26 15:37

Well put!

Anonymous 2007-04-27 08:08

Amen!

Anonymous 2007-04-27 16:25

ASE/GM tech here, Master soon! Well put! Honestly, sounds like a relearn/correlation error or damaged balancer! You REALLY need to get someone to do the relearn for you, you'll need either the Tech II or the Snap On MT2500 (big red box as we call it ), others may work but these are fantastic.

Anonymous 2007-05-02 21:17

Ok, I changed the fuel filter, as I figured, no change. I took it to the dealer and told him the whole entire story. Turns out, the dumbass that put the crank sensor on (over 2 months ago), the one I heard tightening it w/ an impact for like 5 min straight and was thinking 's**t that's not good', didn't line up the keyway and forced the balancer on, drilling a new keyway into it w/ the impact as he forced it on. Therefore it was off time. Every single cylinder was firing off time by the same amount every single time. So now I need a new balancer, and the crank to be rekeyed. Total cost I'm estimating to be over $1000 w/ labor from the dealer. They have to tear apart the whole front of the engine to replace the key. I don't know how many hours that calls for, but I'm sure it's over 10. Plus the cost of balancer and labor was already $450. Also, there was a coolant leak after the shop (same shop that did the crank sensor) installed the intake gaskets, so they're fixing that too. I went back to the first shop and showed him the balancer and he agreed to pay the dealer to fix everything (thank god!). He's filing a claim w/ his insurance and having them pay it. Who knows how long this will all take.

Anonymous 2007-05-03 08:30

So I hope you take a lesson from this! The cheaper is very rarely the best option and you would have saved 70 dollars that another shop took form you and obviously they never checked the balancer which is what I said to do very early on! Thank goodness for those dealer techs eh! Some are pretty sharp!