Hey guys, my car has about 10k on motor after rebuild. My son changed the oil the other day and started sputtering right after. I checked the oil level and it's fine. It usually happens up to about 2000-2500 then pulls hard. I've looked to see if he spilled oil or pulled a wire loose. I can't find anything. Checked all plug wires and they are on the plugs and opti. There is no back fire, just a sputter as if it struggling to accelerate. No codes are thrown. I changed O2s and MAF with no luck. I'll try and post my data log if I can figure it out. If you have any ideas, I'd appreciate it, thanks!

OK, just tried to figure out how to post my data log. I'm an idiot, can someone help me??

 

Have you pulled plugs to take a peak?

 

I pulled one just to take a look but it looked fine. I know that I need to check all of them but wanted to make sure I am not missing something obvious. What is strange is that it is not throwing any codes. It looks like my right O2 is doing funny things but I need someone to take a look at my data log to tell me if it really is or not.

 

Forgot to mention. It seems to be happening in both open and closed loop. I also noticed the O2 sensors reading in open loop. Shouldn't it be steady around 450mv until it goes into closed loop?

 

OK, after doing more research on here, one thing I noticed was fuel pressure could cause what I have. I put a guage on it and found this:

Approx 40-45 psi when key is turn on then bleeds down to 0 after a few seconds.

With the engine running, it holds approx the same (a little movement when I rev up the engine). Once I shut the car off, it bleeds to 0.

I checked Shoebox's website (great stuff BTW ) and from what I gathered, it's not supposed to.

Question - Does this seem normal or not? If not, I'll continue with the checks by pinching off the hoses and check which side is leaking.

Please help!!!!!!

 

Uh, I used the fuel pump jumper and heard gurgling in the intake manifold with the fuel system charged and pump running. Any ideas? Sounds like fuel and/or air is going somewhere it shouldn't be.

 

Any time I hear 2000-2500 rpms I automatically think plug wires are burnt and/or fouled plugs. I do not know much about fuel systems as I am still on stock setup but every time I have had that chugging at that rpm, it has always been plugs/wires. And it has happened a few times.

 

96LT1TX - Roger that, I agree. My hang up with the wires and plugs is the mileage. They only have 10k on them. I know, I know, it could still be the problem and I was actually going to tackle them tonight until I did a little more reading. When I had the heads off, I took the time to wrap the wires and secure them at different places so they wouldn't chafe or burn. I double checked to make sure non of them were on the header or somewhere hot. I am not ruling them out but they are a pain in a$$ with the LTs.

 

Change the fuel filter, quick, easy and cheap...go from there.

Good luck

 

A sputter usually means an ignition problem or a engine temp sensor needs replacing. There are two temp sensors on the LT1...one attaches near the H20 pump and the other to the oil resevoir - check the locations on shoebox... If either of them are faulty you'll get a misfire around 2500 and other RPM's. Also it could be just the wire to one them if it is loose or making poor contact the ECM will not get the reads it needs. This miss is maddening and can cost time and money to identify. The next usual suspects are: opti, opti harness, coil , coil wire grounding out, etc. These problems sour owners of LT1's and are common. If you find it lets us all know what it was. It will be a future help.

 

maddog05 - I did some checks over the last couple of nights. I found a blue corona around the coil (not near the high tension lead). It was betweent he coil itself and the core that wraps around it. I replaced it with a new one and still had the same thing in the same place. It also looks like the wires have a blue corona at the tip of the boot where it fits over the spark plug. I couldnt see all of the plugs but it sure looks like at least 2 or 3 per bank. These "coronas" are not like an arc, in other words it doesn't look like it is arcing to metal like a spark plug does when it fires (outside of the head of course and ground to metal). Since it appears to be all of the plugs (or the majority) what would cause this? I am going to replace the plugs and wires and see what happens but I thought they would arc and make a ticking noise.

As for the temp sensors, would the miss be in both open and closed loop? My issues seem to be in both, better in open loop and cold but still sputters.

 

On cold start, the O2 sensors will read 450mV. As the engine starts to warm up, and the sensors start to warm up, they will start to work. If you still have the AIR pump, before it goes into closed loop, the O2 sensor voltage will typically drop to 00xmV. If you don't have the AIR pump, the O2 voltage will start to climb, reflecting the rich cold start A/F ratio.

It should not drop rapidly when the pump shuts off. But that will just make it hard to start. Should not cause engine problems, unless its due to 2) or 3) below.

Loss of pressure on shutoff can be due to:
1) leaking check valve in the fuel pump;
2) leaking diaphragm in the fuel pressure regulator (check the vacuum line, see it its wet);
3) leaking injectors (pull the rails with injectors intact, pressure system and see if they leak);
4) leaks in the fuel line.

A dirty fuel filter will not cause rapid pressure loss on shutdown. You need to check the fuel pressure under max RPM/WOT.

The gauge temp sensor in the head will NOT cause misfires, or any other problems, other than a fualty gauge reading. It is not connected to the PCM and does not provide input for engine operation. Only the temp sensor in the water pump is connected to the PCM. What affect it has on the way the engine runs will be determined by whether its providing incorrect high or incorrect low temperature readings.

 

Fred - Thanks for chiming in. The O2s kinda threw me off a little. The vacuum line on the adjustable regulator was dry and did not smell. No leaks that I can find and I pulled the fuel rails and charged them. None of the injectors were leaking. Since I don't have an installed fuel pressure guage, I don't know if it's been like this for a while or not. I am going to install one soon though.

I did plugs last night and found 7 & 8 were dry black (rich). The others were perfectly brown and dry. I am going to continue with the plugs/wire attack today. What a pain but I love the car so much that it's worth it. They say these cars are a labor of love........ amen!

I'll post the results but it's starting to look like the typical plug/wire problem. I think some of my original findings took me off in the wrong direction. No worries, my son is getting to be an expert at the LT1s Guess it's payback for all the work we did on his 66 Mustang

 

Well, after the new plugs went in and cleaned the plug boot with electrical cleaner then added some dielectric grease to the boots, the problem is now gone Not sure which plug, wire or combo of them was the cause but it's gone now. I am going to take a look tonight at the plugs/wires/coil to see if I get the same corona. I find it hard to believe this would be normal but then again, I didn't think we'd ever see a new Camaro........

I'll post my findings. Thanks to everyone who helped out. I learned more about the PCM now

 

How old were the plugs you removed? What was the gap? Excessive gap will increase the corona effect.