The OP said that all other cylinders are firing properly and that cylinder 5 and 6 would randomly stop firing for a short period than begin to fire again. Did you read anything that the OP stated. I was saying that if there was a bad spot on the reluctor ring it may have a misfire at that specific cylinder or cylinders. But a bad sensor would either not fire at all or randomly misfire. Definitely a crank relearn could possibly fix the issue. Has the issue always been present or did it start after motor was built?

 

No, this problem seems to have gotten worsde since first starting the motor. I've pulled the valve covers and noticed that all of the valves were closed, meaning that none of the valves were holding any valve open. I had my buddy crank the motor over and the valves opened, but as soon as the cranking was stopped, the valves closed (within 2-4 seconds). So, now I'm thinking it could be the lifters. Does this sound right? Shouldn't the valves remain open on the cylinders were the lift on the cam is on the uplift? The lifters shoudn't bleed down that quick, right?????

Also, I don't know for sure that the misfires were isolated to one or two cylinders.

 

What rockers, springs, lifters and pushrods are you using?

 

OP, you do have to do a CASE relearn process, since your motor was rebuilt.

Secondly, very weird about the lifters bleeding down that badly...the valves SHOULD be open, at least the ones that are on the lift portion of the lobe.

 

I thought the same thing regarding the lifters. I'm not 100% convinced that that is my problem. The more I read, the more I'm leaning towards a bad crank position sensor and/or the crank relearn.

Now, here's the problem I have with the crank relearn: According to my tuner (G-Force), if it needed a crank relearn, I would have a specific code calling for that (P1336 I think). I don't that code. The only code has been P0300 - multiple misfire. Now there have been others on the forum that have had similar problems like me, replaced the crank position sensor, and it ran great. They didn't have any crank position codes, either and didn't do a crank relearn. I agree that it sounds like a crank relearn might be needed, especially considering this is a different engine block, different crankshaft, and LS7 flywheel.

But, I'm going to try the sensor today. It's cheap enough and easy enough to replace, so why not. Then I will look at getting the crank relearn done. I wish I could do myself, but I look into the cost of a Tech II - ouch! I think HP Tuners can do a crank relearn, but that's still $500. I'm hoping the sensor will do the trick.

 

I'm not sure the sensor will do the trick for you. If it was the sensor, you would still have the code for a bad sensor, but you don't. Its possibly the CASE relearn, and MUST be done with a new engine, it doesn't matter if its not throwing a code or not, also it has nothing to do with the flywheel. Any competent dealership can do a CASE relearn procedure for you, just call them up and ask a tech rep.

But, like you said, if its easier for you, just replace the sensor first and see if that fixes your problem. There is another possibility that the sensor might actually be too close to the reluctor wheel. I have seen that before and that causes misfire problems as well that a case relearn or a new sensor will not fix. If it is too close to the reluctor wheel, you can put a shim down to give it more space.

Lastly, what cam are you running? Have you had a tune done yet? You realize with a larger cam that you WILL have misfires at idle and the P0330 code is usually disabled when tuned so it doesn't trip the MIL light. Have you driven the vehicle yet? How does it drive when running?

 

I have driven it about 60 miles. I ran OK for the first couple of miles, but it clearly wasn't running on full power. There is a distinct misfire and it's more than one cylinder. Regarding the sensor replacement, others have indicated that they had a misfire, changed the sensor, and ran fine. No code shown and didn't do the crank relearn procedure. As far as the cam, it's a Comp Cam XFI lobe - 224 intake, 230 exhaust, .610" intake lift, .605" exhaust lift, 114 LSA. Local shop (G-Force) did install a 383 tune, but the misfire problem was very apparent and didn't run well. They didn't disable the code (as far as I know).

 

You need to definitely have the CASE relearn procedure done. Not only that, but once you replace the sensor, you ALSO have to do another CASE relearn. TRUST me on this one, the case relearn has to be done, because from the factory, the PCM is setup to that specific motor, and that specific reluctor wheel. The PCM will fire based on the original data inside it. Once one of those things changes, such as a new reluctor, it will not be reading the revolutions properly, and will not be firing the cylinders at the right time, the CASE relearn procedure updates that data in the PCM for the new setup so it will then start firing properly.

Basically, it will realign the firing data inside the PCM, the cam sensor is for rpm reading, the crank sensor is for firing data.

Just think of it this way, once one of the teeth gets read by the crank sensor, it has a stored data point in the PCM of what that tooth corresponds to in the revolution of the motor, based off the trigger tooth. Now, holding the reluctor still, rotate the entire rotating assembly, so its like 30 degrees advanced now (like installing the reluctor on a new crank, and the crank is 30 degrees retarted), the PCM will read that same tooth, and now the data in the PCM is 30 degrees of rotation off in the revolution and will not send the signal for spark at the correct time (30 degrees of rotation off when firing causing the misfires), the CASE relearn will correct this. Same thing happens when installing a new sensor as well.

G-Force should know what I'm talking about, if they don't, then somebody needs to go back to tuning school. Some setups end up working out perfectly, some setups don't fair so well, some are inbetween like yours. Contact G-Force and have them do the CASE relearn, that should have been done when they tuned your vehicle, and hopefully it will fix your problem.

 

So it wouldn't throw a code for a crank relearn?

 

Not if its just off a little, but then even if its off just a little, with a cam, it will not run very well, because increased overlap makes the motor more sensitive to things like this.

If they didn't do a CASE relearn just because the PCM didn't tell them it needed to be done means they did not do everything they needed to do for your new motor install. The CASE relearn procedure HAS TO BE DONE, NO MATTER WHAT if there is a new PCM installed in your car or if the motor was taken apart / new crank and reluctor setup installed.

Shoot for the CASE relearn, take it back to them, they should do it for free if they didn't do it in the first place, and should have been done when they initially tuned the car if they knew this was a brand new motor (which is obvious because its a 383). There should be no reason the car left their shop if it wasn't running right tune wise.

 

Well, this morning I replaced thecrank position sensor and went to fire her up. Car would barely run, stall twice. It's MUCH worse now. Checked for codes - only one: P0200.

OK, here's my thoughts: Since the crank sensor tells the computer when to fire and send injector pulses, if I replaced the sensor and the engine ran worse, does it make sense that the computer could be bad? Or does it just need the crank relearn done? I read that a P0200 would likely mean a bad pcm. Thoughts???

 

Nevermind the P0200 code - it was #5 injector not plugged in. Plugged it in, engine runs better, but still has the same problems as before. Major misfires. I'm thinking that the crank relearn might have to be tried next. I guess it makes sense, since it's a different block and a different crankshaft than the pcm knew before.

I just hope I find it soon, because I'm running out of ideas......

 

CASE relearn, and you're good to go. Like I said many times before, call up your tuner again, and demand that they do the case relearn already!

BTW it has nothing to do with the block, its simply a matter of the new crank/reluctor setup, and how the pulses are being timed in accordance to what is known in the PCM.

I hope the best for your car man, I really feel for you when things aren't running right, its tough!

Adrian.

 

Well, I went to G-Force this morning. Mike did the crank re-learn - No change. Swapped a coil pack on the passenger side - no change. The passenger bank is clearly the side that's having a problem. All the plugs are showing black on the passenger side, normal on the driver's side. So, I tried changing the O2 sensor - still no change. So, what else can it be? I'm down to:

Bad PCM?
Bad Lifters?
Dead cylinder?

PCM: Anyway to test if it's bad?

Lifters: I can change, but would they be bad enough to cause the problems?

Dead cylinder: Did a compression check on all cylinders. Driver's bank - all 210 pounds. Passenger bank: 2 &4: 200 pounds, 6: 195 pounds, 8: 180 pounds. OK, 6 & 8 are low, but are they low enough to cause a massive misfire? How can I test??

Need help!!!!

 

At least you went through all of the easy possibilities first. I was certain this was a crank relearn problem.

Back to what you were saying about the lifters bleeding down so quickly, I don't see that being normal.

Are you noticing any smoking out the pipes? Any oil usage? You need to get a wideband hooked up to both sides to see how AFR's are between the two banks.

 

Those pressures are fine, mine were all 180 except 60 in one..LOL

 

Anybody else have an opinion on what it could be?

 

Your next move would be to do a leak-down test. Depending on what compression you're running, will dictate what compression you see in the cylinders. A 30 pound difference between cylinders is not good, but ok. Do a leak down test on the low cylinders to see if you may have a ring problem. If that turns out ok, make sure you check all of your fueling on that side and be sure you're getting ample fuel there.

If the fueling is ok, and the injectors check out (like one that is not stuck open or closed), then you really need to get a wideband hooked up and check your AFR's between the two banks.

Can you post a pic of the spark plugs that you removed, and label them between the pass and drivers side?

Lastly, are you sure that your valve seals/guides are good? Are the rocker bolts protruding into the intake port, and if so did you use sealing locktite (the blue stuff)?

 

G-Force did a leakdown test on cylinder #6 - leaked air out the intake, so backed off the intake rocker and it was tight. No air out the exhaust or dipstick tube.

As for injectors, that's certainly one of the next things I'm going to check. Any way to test them?

I'll see if I can post the spark plugs pictures later or tomorrow. They're already lableled, but basically black on passenger bank, clean burn on driver's bank.

Lastly, the bolts do not extend into the ports. The passenger bank is brank new from Patriot Peformance - stokc 243 head, milled .020".

 

Have you checked to see if you're getting consistent power to the coil pack harness?