Just got back from having some fun with a buddy in an LS1, did a couple pulls, but I noticed it won't let me go past 5200ish rpms. It's good and clean up to about 5000, but after that, it'll spit and sputter, and it acts almost as if I throw the clutch in, where it'll rev higher but won't go faster (not a slipping clutch). No codes or anything, either.

It's a 96, with a Corvette shortblock, LT4 Hotcam, and I just recently got it tuned, but if I remember right, it did it beforehand as well. Also, when it was tuned, I had the redline changed to 6200.

Any ideas?

 

Where is the fuel pressure at before and during the cutting out? How old are the plugs & wires, coil, opti, and icm?

 

Plugs and wires have maybe 2000 miles, but the wires may have burnt once or twice, but shouldn't be right now. If it were bad wires, wouldn't it misfire even at idle?

Coil is original, about 100,000 miles. Opti has around 25,000ish. ICM has less than 500.

No idea what the fuel pressure is, I don't have a gauge or anything.

Could this be a timing issue?

 

I know this sounds extremely odd, but check your air filter, I had the same problem and turns out the air filter was caked. I dout thats the issue but might as well check.

 

Burnt wires can cause an intermittent miss. If you have any, change them. I would suggest swapping in a new coil. Even if it wasn't bad, its cheap, easy, preventative maintenance.

 

I had similar problems when i had my new motor in. Ended up the opti was the problem, had it fixed under warranty and works like a champ now

 

A few people have told me coil, so I'll probably do that this weekend. As for the air filter, it's definitely not that, I just put a cold air intake on it this week, didn't change anything. I have a spare opti, so as a last resort, I'll do that. And yeah, I'll check the wires and plugs for like the third time now (been battling other missfire issues lately).

 

Before replacing the coil check the ignition cable (coil to optispark cable). I had a very similar problem (mine started the mambo at 4,000 rpm) and it was the ignition cable burnt at the ignition end. This was not visible until removed.

 

Well, I work at napa, so I just got a good deal on a new coil, hopefully I can get it in today.

 

As TitoPR221 suggested, you might as well throw on a new coil wire for good measure. I'll cross my fingers for you.

 

Tried a coil, didn't fix it.
I wish I had more time to work on the car, I could check all the other stuff..

By the way, I hooked up a fuel pressure gauge, and it was right around 52ish psi at WOT. I do have a Walbro 255, which is probably why it's a bit high, but could that cause this? Just running to rich?

Also, I had to replace a lifter on I believe the #2 cylinder, and took both lifters out, meaning I had to reset the valve lash on both the intake and exhaust. I'm not 100% sure I did that right, could that be why it's cutting out at higher rpms? Or would that cause it to run ****ty the whole time?

 

Anybody?

 

First thing change the fuel filter. Its cheap and easy. Sure sounds like a fuel flow problem. You should put a scanner on the thing and check what the O2's are reading at load . If the scanner has a record function then you can get a reading of the O2's and fuel trim numbers when you do that next run to 5200rpm. That would tell a lot. Make sure there aren't any leaks after the MAF. If you can check the knock retard activity with a scanner during the run do that too. If you are getting detonation or pre-ignition the ECM will retard your spark quite a bit and you will feel it at the high end.
Good Luck
Jim

 

Well, if it was holding 52ish psi all the way through the gears, wouldn't that rule out a fuel filter? It was replaced like 2000 miles ago, but I did a fuel pump swap not all that long ago, there is a chance I knocked a little dirt in the tank or something.

I have to replace the oil pan gaskt, because its leaking, and while I'm doing that I'm going to replace the opti (I have a spare anyway). I'm also going to readjust the valve lash (I think I tightened them down way too far on the one cylinder.. long story). If none of that cures it, I'm going to be running out of ideas.. Most of my ignition has been replaced, and it hold fuel pressure just fine..
Any chance it's clogged injectors or anything like that?

 

If there's anyway to get a scanner to check out the ignition timing and fuel trim during that run you should try to do it. It'll tell you a lot and save tons of time and guessing. If you're around Portland, OR I'll put mine on there for you.
Just a suggestion