I had a break today about an hour so I took off the spark plug near the oil dipstick and it looked new. I checked the spark plug wires were snug on the passenger side. I also checked vacuum hoses and changed the check valve on the intake manifold fuel rail area. It just looked old. I cleared the codes with the Torque App added some Lucas Fuel Treatment and ran it for 15 minutes seemed to idle much smoother and now misfire heard. No Check engine light either! I know it may be too early to tell. I need to run it on the road! My thinking is if it is fixed (no more codes) I might be able to tell the guys at the inspection station to NOT move the tilt steering wheel and if it holds firm maybe I can pass inspection!

Wish me luck.

Just took it for a spin and p0300 code came back. I reset it then drove again just around the block and it did not come back. I am almost out of gas so I think I am going to call it a day and then try tomorrow or later this weekend. I need to fix that steering wheel it still comes down and I don't think it will pass inspection.

 

Thanks, tires seem ok. Fronts are maybe 10 years old per code and the rears are 3 years old.

 

Look at this thread

https://www.corvetteforum.com/forums...-quagmire.html

Read the entire thread but I found post 6 and 17 interesting.

 

This write up supports the previous post 17.

http://www.justanswer.com/chevy/0vev...e-i-p0300.html

 

Thanks! Kg4fju! I think this maybe the issue. I looked at the lower Timing Cover I think that is what it is called and I can see the Crank Positioning sensor wire/connector. I am going to pull the intake and some hoses to get down there and check it out. I might have to also jack up engine a few inches per others that have had to check this. I hope I don't have to but they say there is only 4 motor mount bolts and that you really don't have to take the bolts completely off just loosen them to lift engine 1/2 inch or so. Hope to get to this Saturday or SUnday!

 

I replaced my car's CPS the Winter before last and it was not that big of a deal. I didn't have to jack the motor up at all. It is tight getting in there but it is doable. The wire and connector are easier to get to from up top IIRC. However, I was doing the water pump, radiator and plug wires at the same time so a lot of the interference items were already out of the way and I could clearly see and get to the items I was working with.

I would definitely verify the sensor's wire routing as I believe you said the OPTISPARK was replaced on your car.

 

http://www.unbalancedengineering.com/GM/Pins/

 

In your first post you said it had been sitting for a couple of years. You added some Lucas product to the gas. Now the tank is nearly empty. You said you were going to check the fuel pressure and siphon off the gas.

Did you siphon off the gas or do you still have the 2 year old gas in it? At that age you may just be dealing with bad gas. I had a problem with a car that had been sitting and it was not starting very easily and missing and it cleared up as soon as I put new gas in it. It might be worth putting in some new gas to make sure.

Good luck.

 

The car was almost on empty and hit reserve yesterday, but seems like it ran better the more it was driven. I did a "bandit run" to the nearest gas station that is .5 miles from my house this morning. I put in 10 gallons of premium and ran it hard on some side roads. It seems like it is running better with the new gas. When I say better I mean that I don't feel the idle rumbling or trying to stall and when I get on it it seems like it pulls hard and smooth. I really need to compare with another LT4. I am going to try and hit up CHSTitan42 to see his LT4 in person and get a feel for what one should run like.

My steering wheel puller arrived at home but here I am at work .

Oh well hopefully I will get home by 9.

 

Sounds like it may just need some of the proverbial cobwebs blown out. I can't really tell from that picture, but I'm wondering if that plug is gapped correctly, it looks a little wide from that angle. should be gapped at .045.

 

Update! I ran the car a few minutes after new gas and it does idle better. I think the good thing is that the p0300 code went away....BUT the p0303 code (misfire on cylinder 3) went on. Soooo I pulled plug 3 and it looked okay to me. I checked the gap and it is at .50 I think that is where it is supposed to be. The next thing I did was checked the connection of the wire and put a little dielectric grease on the boot. I checked the sparkplug wire connections on the front of the opti and they seem tight.

I did have a O Sh@$t moment when I did a pressure test on the cooling system. At 16 psi I saw coolant leaking but I was lucky it was loose hose clamps. I tightened them and no more leaks after pressure test.




I asked my wife who knows how to drive cars fast to listen to the vette while I revved it to at least 4k rpm and then also hold it stead at 2k rpm. She said, "sounds smooth and I don't hear any misfires." No smoke, nada or weird sulfur smells. I think there is a vacuum leak and that I need to track down. I read another LT4 forum where some one crossed two spark plug wires I think 6 and 8 and that caused a p0303 but his car was running ROUGH and mine is not.

The diagnostics continues. I really want to take this out on the highway and just BLOW all this crap out and hopefully that will help!

 

It has been sitting two years I would not be hard on it for awile.

 

2 nuts....1 per side. Each nut threads onto the motor mount stud that passes through the diagonal frame brace that connects to the frame rail and the front cross member. Takes 10 seconds to loosen each one and makes access to the CPS a matter of a few minutes or less with a 1/4" drive ratchet.

Did you ohm check the plug wires? Also... #3 passes between the accessory bracket and the PS pump if it's still routed per the factory. It's subject to chaffing.

 

Another tip is to get the car inside a dark garage, and with the lights up look for a spark plug arcing against something else. I that is the quickest way to find a problem between the spark plug and the distributor. That is IF the miss is spark related.

 

okay, I just can't take it anymore....I kept hoping that your problems would cure themselves, those are the best problems, the ones that cure themselves....but since they haven't allow me to relate my own experience with a 96 LT4. Draw whatever conclusions you care to.

My steering column was bad too...so these cars may have similar mileage (little north of 100K ?). Pulled that sucker and replaced with a new one ...not that hard...but I digress.

Mine had a rat's *** cheapo... LOUD..."custom" exhaust...so when I pulled the exhaust and peered up the cats, guess what? no matrix in the drivers side...just an empty can. Later I found that one of the multitec injectors on that side leaked and probably melted and blew out that side cat's innards.

So one new exhaust...one new set of Bosch III injectors and one new cat later...

I decide to pull the valve covers for a little inspection....guess what...and this is on an engine with no apparent problems...one rocker was off the valve stem and one was partially off with damaged self alignment ears ...so two...possibly three (my memory fails me) stock LT4 rocker arms ....and yes, stock rocker arms may look like other rocker arms, but trust me, they are a one year, non adjustable pedestal design that interchange with NOTHING and have a price, if you can find them, to match...

So all is well, one would think. Then the OEM opti spark craps out. I found some receipts in the car that lead me to believe it was the original opti with one cap and rotor change. If the serpentine belt hadn't cut one of the ventilation hoses and the other hadn't deteriorated from oil and heat I believe that the opti would have still worked; as it was the brass terminals were green from water intrusion...yeah I know I never should have used a high pressure washer on the engine...

With everything off the front of the engine to access the opti and a repeat of the rocker arm issues, without any damage this time...thank god...further investigation was called for.

Pulled the camshaft. The last three lobes were rounded off, actually grooved by the lifter; so...one Hot Cam and a new set of lifters, new opti, new plug wires and new plugs, new water pump, new main Extreme Duty timing chain, new rod and main bearings and new oil pump and new canton road race pan...I'm back on the road and guess what?

Now I have a P0300 service engine light code "random misfire" and a smog test coming up...Yup I replaced the crank position sensor and in the process I found that I had run the sensor wire through the plug wires, or more accurately had led the plug wires so they surrounded the sensor wire...whatever, the result was the same.

Long story short, the P0300 never went away entirely...but once cleared, it stayed off long enough for the smog test and the Hot Cam (along with a new opti and ignition tune up and one new cat) passed California smog with flying colors.

Sooo....if there's any moral to this story, and I'm not sure there is, I'd consider pulling the valve covers...easy enough on an LT engine and checking for anything amiss there.

 

Just did the Northern Lights test this morning using a spray bottle, water and a dark garage. I also had my wife as a second set of eyes and no arcs observed.

 

MtWoolFord, yes this is very frustrating, but I am not going to give up. I have been researching this problem and see that many just gave up. I am going to try and check injectors this weekend, lift valve covers off. Check Ohms on wires and clean up and change o ring on Crank Positioning sensor. .(It looks like it has oil seepage on it.). I guess I should check vacuum with a mightyvac also.

There are so many things that can set off this p030X code its just crazy! I guess I should check air filter MAF and double check spark plug wire routing. After I do all that and still a no go I am going to research the best LT4 shop in town (Dallas Tx Area) and let them have at it. This car supposedly has a rebuilt engine but no receipts. Just looking at the engine I think it has been rebuilt. The shop that supposedly did the work is a very reputable (corvette) one in LA
(California). I might also give them a call.

Hours of youtube videos, google searches and all of you nice c4 owners checking in and helping out is great.
I have a garage fridge full of beer so if anyone wants to stop by and supervise come on over.
Thanks!

 

This guy had 7 pages on his misfire adventure not good.
http://www.ls1lt1.com/forum/lt1-%7C-...e-problem.html

 

Mis fires are caused by issues with one of three things. Spark, fuel/air mixture, or mechanical failure. I hope it is not the third because that is the pricey fix!

 

I hear you!
I hope it is not that also, thing is it just runs good in my opinion. Good power no stalling or misfires felt IMHO.