steiger99

Hey I have posted before and have fixed half the problem. I have a 1995 LT1 camaro with the new 383 stroker (12.5:1) compression. The motor has approx 1200 miles on it with Llyod Elliot stage 2 heads and stage 2 cam. It has an LT4 intake manifold, 58mm throttle body, no cats and Slp loudmouth exhaust (which is really failing miserably to calm her down). 30 lb injectors, 255 walbro, great fuel pressure (adjustable fuel pressure regulator on it), new plugs, wires, MSD opti, new coil, new coil wire, clean MAF screen free from random intake debris. I checked to see if I had spark at the coil itself using a test-light and the spark is very strong and bright blue when it jumped onto the test light. The fuel pressure reamains constant with the Key on engine off position (not running). It also has a brand new TPS sensor. There is no check engine light on.

This is what the car is doing. If it is being started for the first time of the day, it fires right up and holds a beautiful lopey idle just like I want to hear. Idles at 1000 rpms. Now if the car is hot, or ran for more than 5 minutes and I try to start it, it take a good 5-10 turns before it will finally fire and then the throttle response is really sluggish for a few seconds, never really getting crisp or instant throttle response. The car runs a little rough while under 2000 rpms while I am driving but accelerates BEAUTIFULLY until I hit 4000-5000 rpms and then the engine starts to miss really bad and will just keep missing until I let off the throttle. It happens everytime at about the same rpm everytime too. I notice once the car is warmed up and it comes down from anything higher than 3000 rpms, the car barely catches its idle (drops to 400-500 and while it is that low the service engine soon light comes on until the car adjusts up to the 1000 rpm idle or I give it gas to save it from stalling. If I leave it at the 400-500 rpm range for long it will stll completely within 15 seconds. The fuel filter has approx 1200 miles on it as well as the fuel pump. I am getting great power from the battery and alternator has been checked and is perfect also. Basically everything in the car is new or has less than 1200 miles on it.

Note: During the 1200 miles of breaking in the motor there was a time (200miles worth of time or so) when the motor would scream all the way to 6500 rpms without missing at all (but constant at a constant speed you could feel the car miss/hesitate slightly). The missing was a sudden change so something changed for this extreme missing /hesitation at high rpms to occur. You can also feel the car slightly missing if it is held at a constant speed at any rpm, it kind of spits and sputters unless you are accelerating. It accelerates very smooth until 4000-5000 rpms and then misses really bad to the point where the whole car jerks and almost shuts off completely. It will continue to miss until I get off the gas, like I am hitting some kind of rev limiter or something. I was thinking it has to be fuel relate, like fuel cut was happening but I haven't the slightest clue as to what I am talking about with diagnosing these cars correctly. Could it be a bad injector or wouldn't that make the car miss all the time when I was accelerating. I know 99.99% sure its not the opti because that was changed to the new MSD opti and the car runs the EXACT same as it did with the other opti I thought was bad. The car finally hits a real boost of torque at 3500-4000 rpms and its like as soon as I start to feel like the car is a rocket this miss happens and ruins everything. Any help is greatly appreciated. Thanks so much.

P.s. I have a descent intake manifold leak I am fixing this weekend (notorious back part of manifold where permatex was used improperly) The oil is leaking to where a small, half dollar size spot, of oil is on the driveway each morning after driving the car the previous day.

WS Sick

To me, it sounds like that when you first start it of course it is in open loop mode and is ignoring the 02s when it warms up it goes into closed loop and starts monitoring and adjusting accordingly as it reads the 02s.

Now the way I am thinking is that either the O2s are bad, or something is not in line as far as fuel delivery or combustion after its in closed loop.

What kind of tune is in it, does it hold its fuel pressure after you shut it off, or does it drain off pretty quick? Is there any vacuume leaks?

klrz28

I had the same problems i switched over to LTCC and my problems went away. make sure your intake is torqued correctly and check all vac lines.. 383= more power needs more spark. gap your plugs around .050 i got a 383 w/ lt4 heads and intake..

Sweetred95ta

I know it has new plugs, but have you pulled them and looked at them? This might tell you something. Maybe you're sucking oil into one of the cylinders because of the gasket leak.

steiger99

I looked at the plugs and each time I have changed the plugs (3 times in last 1200 miles) where the plug is gapped the spark plugs little ceramic looking cylinder is red on a few cylinders. not just like a little red on a few, but flat out red. On other plugs only half of that little ceramic looking cylinder is red. So my guess is things are getting pretty hot for it to turn a brand new spark plug that red in only a few hundered miles if that. Also the intake manifold leak seems to be getting worse. WOuld that be my vacuum leak? Is there a webpage that has a list of all the places to check for a vacuum leak so I know or have some direction to start. Thanks. P.s. the car is no longer throwing a service engine soon light unless the car dips belowe 500 rpms and then it flashes on until I give it some gas and save it from stalling.

kainZ

sounds to me like it is running a little lean from the intake manifold leak, but I could be wrong. It's no use trying to diagnose it when you have an SES light that you haven't scanned yet.

Tell us what codes it threw, and then we'll bother spending our time trying to figure out what is wrong.

steiger99

it threw code 15 and 22. The SES light is off and the car holds a much better idle. I changed the TPS with a new one and the light went off. however it still misses at high rpms. so now I am going to fix the intake manifold leak and if that isn't the problem I am going to get a new lt4 knock module and then if that doesn't do it I am probably going to find a shop that can get it running and sell the damn thing and start over because this is getting rediculous. I have tried so many sensors, tests that I am completely frustrated and losing interest. I was probabaly running low 13's before the motor and now I would be lucky to see high 11's so the 1.5 seconds (MAX) I would gain should I figure this problem out is not worth all the time and bloody knuckles I have been putting in. What good is a car you can't even drive? Thanks for all your help. Any other suggestions are greatly appreciated.

oneslowz28

mine had a high rpm miss and after weeks of searching i finaly looked back at my data loggs and foud out 1 of my injectors was maxing out at 5200 so i replaceed it and everythings fine

kainZ

DTC 15 Engine Coolant Temperature (ECT) Sensor Circuit (signal voltage high, low temperature indicated)

This probably means your sensor is throwing like -40 degrees or something. That would make the engine dump in way too much fuel, and run like crap. I'd check your ECT, and replace if its bad. If its not the sensor, check the wiring between the ECT and the ECU.

If you don't want to diagnose it, I'll trade cars with you straight up. My car runs like a champ, even if it does have a little leak.