Ok, I hope this is the correct thread. Anyways, I have a rebuilt LS1 that I just put back into my 98 Z28. 228R Cam and ported/rebuilt 5.3 heads. Everything is hooked up now and I went to crank it over last night. First I started with priming, then I put the rest back together to get a spark and fuel to it. Cranked it over.... nothing. Acted like it wanted to start but just couldn't.
I let the car sit overnight, thinking maybe the plugs got wet, went to the garage and tried to start it. Same thing. This attempt shot flames out the intake.... So... I then took the plugs out and checked them on the drivers side. They seemed to be fine. Then took the valve covers off and checked the head. I went to crank it to have a friend look at the valves and see if one was maybe stuck or something. As I am cranking the engine over, with no spark to the drivers side and the plugs out... The engine fires up on 4 cylinders!! WTF??? I immediately shut her off. we then really dug into the head and found nothing unusual.
So here I am with a car that runs on 4 cylinders. I then put the plugs back in... then cranked, and it would not start. I put the valve covers, coils back in, and the same thing happened... no start.
Now when I try to start it, the thing sounds like its bogged down. I had the battery and starter check and they both passed the test. I am getting oil pressure, spark, and fuel. It is just now very slow when cranking...
What I am wondering... do I have too much compression with the 5.3 heads? I know its a common swap so I don't see why that would be an issue. But has anyone else had this problem? It is very frustrating... I have not driven the car since last April, when I first had a knock. Thanks in advance

 

Did you fail to get a Base tune???

 

as in a stock tune? no. I had it tuned before, but figured it would at least start until I get it there.

 

double check that the cam and crank are llined up correctly. Are you running the same injectors as before? Compression isnt your issue.

If flames are coming out the intake, then its firing while the intake valve is open. Are your valves set right? Is the pushrod length right?

 

^^^Check crank/cam coordination, and double check the small coil harnesses on each side. They can be turned around (by color code), easily.

 

same injectors, valves should have been corrected when they were built. I did have to take one head out (drivers side) and took the rockers off to get the head off before I put the engine in. This was because there was a bolt stuck in the head and I had it re machined. I put it back together the way it came out. pushrods are 7.4's. How do I go about checking cam/crank positioning?

 

you have the rockers at the proper torque? As for the cam, pull the timing cover and make sure the dots line up. Of course rotate the engine to get them to line up but if they are a tooth or more off that would be a problem.

 

You can't expect the engine to run off of the stock tune when you have introduced a different cam, different heads, more compression... you need to get at least a base tune. It may or may not run...but you could at least eliminate it as suspect.

How about fuel pressure?

 

Even 180 off, it would still run. Anything else you would have valves hitting pistons.

Rocker torque wouldn't make a difference unless they were not even tightened down.

 

I have fuel pressure, wont have the tool to check exactly what it is until I can get one tomorrow. I opened the port a turn and gas shot out pretty good.

I can have my buddy come over with a tune by this weekend. He uses HP tuners, but I would expect it to at least fire over. but not a bad idea, to rule that out.

 

Why would you say that? The computer isn't there for performance, it's there to run the engine off of programmed parameters. If those parameters are off, it will not run. I'm not saying it won't, but I wouldn't expect it to. It could be running grossly lean or rich. Even if it did start, wouldn't you be concerned to run it?? You could damaged the engine. Even HP tuners warns you what damage you could do by messing with the tune "incorrectly". That's how important having the right tune is.

 

ive seen guys put the wrong lenth pushrods in, SLIGHTLY keeping the valves open, thus your backfiring issue through your intake possibly.

 

My vote is tune. Your AF ratio and/or timing is off.

 

Yeah, I plan on getting a fuel pressure gauge, a pushrod length tool, and getting a base tune to hopefully get it started this weekend. Maybe it was the tune that caused the issue with the engine before it.... Thanks for the input guys. I will keep you posted.

 

At 180 off its technically back to where its supposed to be.

Also the rockers can be over tightened and the valves can hang open.

 

not true. ^^^^ 360 is a full rotation of the cam not 180. the rockers get torqued to 22 ft lbs so it would come down to pushrod length at that point. it's not the same as an old sbc.

did you make sure the dots were lined up correctly?

 

Agreed! Another guy on this site was have the exact same problems as you & this was the culprit.. Double check your coil wires if you're running your stock coil harnesses. 98' coil harnesses cannot be swapped like 99-02's can.. Here's the color pin-out for each cylinder, check them.

1. PPL
3. LT BLU
5. BRN
7. DK GRN

2. RED
4. DK GRN/WHT
6. BRN/WHT
8. LT BLU/WHt

 

Did you have all the grounds on the back of the driver side head grounded? There is only two wires, but there are 3 eyelets that have to be grounded or the car wont fire.

 

It's not the tune. You didn't change the displacement, you don't have an aggressive cam, you're using the same injectors and you're running ported factory heads. It won't run right but it will at least run well enough that you could drive it to get a tune.

Check and make sure your crank and cam gear are lined up. Also check your crank position sensor on the passenger side of the block. Check and re-check all of your other connections. Did you remember the ground cable on the back of the drivers side head?

 

Check for spark.