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Anyone care to take a stab at this? Posted By: Michael93Z28 On: 07-21-2008 @ 04:41:43 Reply | Edit Ok this is driving me crazy so any help would be appreciated...lol I have a 93 Z28 LT1 with auto. Trans. Only mods I am aware of is a Hypertech chip and aftermarket exhaust which I think is Flowmaster. I have had the car for about 4 months. It ran good and I ran it pretty hard (Michaelray1969 on youtube or search 93 camaro and find one of the vids. linking the others). I had replaced the plugs & wires, opti cap and rotor a few months ago. Looked to be the original ones. Ok, this time it started with engine almost shutting down at around 4700 to 5000 rpm. Then began doing it around 4200-4500. (Normally would reach 5500-6000 if I would let it). It started developing a slight miss. I have trouble shooted and fixed several things but this problem stays the same. The TB looked a little rough so we had took it off cleaned it. Performed a TB bypass on it and had relocated the air intake (IAT) sensor father away from the TB. Still had slight miss but also idle was higher. When was apart the IAC Valve looked pretty bad but cleaned up so reused it. It was sucking air erratically so we removed it and replaced the IAC with a new one along with new TB gasket. Idle was better but still missed (was seeming to get worse). We put everything back like it was (IAT & the TB bypass), still the same. Looked under the hood at dark and noticed the sides of my coil sparking and would glow light blue when revving the engine. Looked a little more and had a fireworks show going around along some wires. So again, new wires, plugs, and coil. Ran better but miss still remains and is getting worse.Turned to optispark. I remembered 3-4 days before had BIG rain and had seen some pretty high water and seem to recall that the engine had stumbled while going through some. Removed opti cap and seen that it had marks in it? Looked at rotor and noticed it had play in it. Not side to side....but front to back The screws were tight so the wobble wasn't from that. Removed Dist. and discovered was worn out and had SERIOUS play in it..ahhhh..ok. Replaced with new Dist. + Cap + Rotor!! Started up...runs very good... could hit 6000+ rpm if wanted to... But, miss is still the same and worse... sound like dead cyl. almost but when kicked down at 55-60mph to WOT can't hardly tell miss but can also tell not 100%. Went back to drawing board. Had looked at egr before but, checked out ok... Checked fuel injectors you can feel them clicking through a screwdriver (normal I think) all but one.....hmmm. Was very light and intermediate "click"... So, changed fuel injector and cleaned egr and fuel rail and put all back together and..... you guessed it, ran better but still had the same miss. When kicked down from dead stop it misses (shakes) bad and you can hear the miss in the exhaust. Misses at idle with sound in the exhaust. OK, Now here are some other things...1._was ran without air intake elbow for about a week before we got another one, that was around the time we did the TB bypass when miss was very light and it became worse while elbow was off 2._has backfired through the exhaust like only twice throughout this whole time but has a "pop" like dead miss sound in it. 3_sometimes a strong exhaust smell in car almost gaseous but is not gas. My MAP sensor is located on fuel rail and not in the air intake and I have also adjusted the lifters and hasn't made any difference. Seems to use more gas then usual. Has 150,000 miles on it. Light puff of smoke when first started but that's it outside of occasional black smoke which it has done since I got the car. I am going broke due to funds are limited anyway (gas)...lol So any ideas to start next? Timing Chain? Head gasket? Burnt Valve? It is like a vacuum leak but, I have checked everything and tightened on everything, sprayed on everything and can't find one. ANY HELP would be greatly appreciated. Posted By: 94fireturd On: 07-21-2008 @ 17:36:28 Reply | Top | Edit What plugs are you using? Have you replaced the coil lead wire to the opti? Also make sure all the wires are ALL the way on the opti. I think you will hear two clicks. I would also hook up a fuel pressure gauge to the schreader valve located on the drivers side of the fuel rail on the intake manifold. Pull the vacume line off of the fuel pressure regulator (pass side back of intake) and see if you can smell gas. If you smell gas or you see it looks wet with gas then replace the fuel pressure regulator. If you have a laptop computer you can download a program called DATAmaster and plug into the ALDL port under the dash. Make a log and one of us here can take a look and tell you whats going on. GL, Josh. -- 
94 Formula: sold 00 WS6: sold 1993 Z28: CIA, Hooker LT's, Mufflex Y,!EGR!AIR!CATS Posted By: 94fireturd On: 07-21-2008 @ 17:44:55 Reply | Top | Edit Also maybe you could pull each plug and see if one is fouled or generaly looks diferent. this could narrow it down to a specific cyl. Moving your ait could create a fuel rich situation. Also why would you run the car with out the intake? You might also go ahead and pull the intake and reseal it. They are know to leak oil and have the occational intake gasket leak. --
94 Formula: sold 00 WS6: sold 1993 Z28: CIA, Hooker LT's, Mufflex Y,!EGR!AIR!CATS Posted By: Michael93Z28 On: 07-21-2008 @ 18:13:55 Reply | Top | Edit ok, I am running the same kind of plugs I used when it ran perfect(Autolite Plat.)I replaced all wires including coil wire with same wires I used on previous set up.I checked fuel pressure around the time right before changing the injector but and it was all in normal range then but haven't yet since I changed it. Regulator I have suspected but it had checked out but when I had the fuel rail apart there is a tiny screen in it and it looked to have some debris in it but didn't look like it got past the screen.With the laptop I thought it worked on OBD2 does that work on OBD1?When I pulled first plugs looked to be running lean but I figured that was because had been ran without air intake elbow.I am talking about the rubber elbow that the IAT sending unit plugs in to.It was completely ripped off TB when I got the car and they had used duct tape to put it back on.When we started to work on it you could see that the tape wasn't working and we had nothing else to drive (as like right now)and it took me about a 7-10 days to find one. We considered a coldair intake but all the ones I had found said you couldn't use it with Traction Loc and couldn't afford it now anyway...lol We hadn't changed a thing when the miss first occured and everything I found wroung I thought was why and it is still the same.Being that it isn't tripping any trouble codes I am beginning to think it's internal. But I have question, it as gave an occasional egr failure code while running perfect and bad then finally it didn't do it anymore. Someone said with the Hypertech chip and no Cat. converter the O2 sensor would have to been set to run in a loop, if that is so, if that was messing up and the ECM is thinking that it's working properly would it set a O2 code?? BTW I will recheck the FP and Regulator and post back what I find out. Thanks for taking the time to look at this cause we are stranded and I miss my ride..lol Posted By: 94fireturd On: 07-21-2008 @ 19:16:11 Reply | Top | Edit Your car is OBD1 but its a little different than the rest of the fbodys. If you have the cable to hook up to the port underneith the dash that runs to your laptop, then down load datamaster. Its free and will help diagnose your problem and even alow you to tune. You may also want to concider ditching the Hypercrap chip as I hear they dont realy do much but dump fuel. What is traction loc? 93's didnt come with traction control. About the o2 sensor, im not sure on that, but again, I would remove the hypertech. Your o2 sensors are cheap for that car and are located on the exauhst manifolds so they should easily get hot enough to go into closed loop. Even if they are bad they would not cause a missfire like you are describing. If your thinking its mechanical, you might want to look into doing a leak down test on each cylinder. --
94 Formula: sold 00 WS6: sold 1993 Z28: CIA, Hooker LT's, Mufflex Y,!EGR!AIR!CATS Posted By: 94tagt85iroc On: 07-21-2008 @ 19:44:33 Reply | Top | Edit i'm kinda new to fbody but i have had an lt1 for a while and just got a 93 formula first thing i would do is pull the codes by grounding the terminal u can find that on the internet ses light flashes works on the 93 also on the 93 the map and ait sensors make up ur speed density so they must be very caliberated and i would not mess with them or there locations. personal experience with high rpm miss is a coil going bad or spark plug wires mostly that number 7 plug wire likes to be in its grove hope this help -- 1985 iroc impulse blue 355 1994 trans am gt m6 lt4 hot cam cai flowmaster Posted By: Michael93Z28 On: 07-21-2008 @ 22:09:05 Reply | Top | Edit Yeah mine has Traction Control and I had seen someone with a 93 Z28 before post on a forum before about their Trac light flashing on when backing up (mine does the same)as far as the miss, it is throughout all driving ranges and is as soon as you start the car in the morning till your done driving it and gets worse as you drive and it warms up(is light miss at first with some sound in exaust and after about 15mins its a solid miss that you can hear) I am fixing to video it so it can be heard. Posted By: Michael93Z28 On: 07-22-2008 @ 02:03:42 Reply | Top | Edit Also, the map sensor is factory mounted on the fuel rail up close to the TB on the passenger side. I had a guy at the Chevolet garage tell me if you move the IAT from in front of the TB to about half way between TB and air filter that it would get a much more accurate air reading because the air where it's located stock is alot hotter than the normal outside air. Posted By: 94fireturd On: 07-22-2008 @ 17:29:57 Reply | Top | Edit But your car is tuned for the stock location of the air temp sensor. I promiss you dont have traction controle. However your car can sense loss of traction wich is what your seeing. You may not actually have traction loss, but the low traction indicator is flashing most likely b/c of a bad wheel speed sensor. Your MAP sensor is located on the intake manifold itself, not the fuel rail. As is with all LT1's and all other cars equipt with a MAP sensor. Manifold Absolute Pressure sensor (MAP). If you where running your car hard when this started you could have a collapsed lifter or bent pushrod which may also cause your problems to some degree. Also your original post dosnt say that you replaced the Ignition Control Module. This can cause missfire and will get worse as the engine warms up. Usuually the car will begin to die when this goes out and not restart untill it has cooled down. You might even go so far as to pull the timing cover and check to see if the chain has skiped over. This is unlikely but not impossible. --
94 Formula: sold 00 WS6: sold 1993 Z28: CIA, Hooker LT's, Mufflex Y,!EGR!AIR!CATS Posted By: 95ttoplt1 
On:
07-27-2008 @ 14:22:46 Reply | Top | Edit
Any luck? --  Posted By: Michael93Z28 On: 07-27-2008 @ 23:50:11 Reply | Top | Edit got it fixed late lastnight and been driving all day. My exhaust hits sometimes on a speed bump where I live and right before this started it had hit pretty hard and it cracked the exhaust manifold on the pass. side. All the other stuff took out the dropping off over 4000rpm and I replaced the manifold and that took out the miss. It's running like new now. Just have to fix the oil sending unit, it has a short in it. When we were doing trouble shooting with scantool it said oil temp was -36 degrees and my oil gauge runs around 60 to 80 psi. but jumps around like it has a short in it. Don't know if it is having any effect on performance but I am going to replace it. Also I know the MAP sensor is on the manifold I meant to say "by the fuel rail" and I was assuming since you have a low traction light it had something to do with traction controle but I haven't even checked into what it's about, haven't got that far. Anyways Thanks guys for your help and input I appreciate it. Posted By: 94fireturd On: 07-28-2008 @ 13:29:21 Reply | Top | Edit Awsome man, glad its working out!. As for the sending unit, I had problems with mine in the stock location as far as trying to get a new one in ( I couldnt) and I had to buy a one inch nipple, and a "T" so that I could reach the bottom to put a wrench on it. Make sure the wires arent toutching the manifold and getting burnt. Im planning on moving the oil sensor to the top of the engine like the 94-97's. As far as the wheel speed sensors, the usual culprit is located on the very top of the rear differential housing. Just unplug it and soak it down with electrical cleaner and re install. ALSO! if one of your third break lights are out ( lights on the spoiler) it will cause this light to come on. So check those too. --
94 Formula: sold 00 WS6: sold 1993 Z28: CIA, Hooker LT's, Mufflex Y,!EGR!AIR!CATS
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