New engine assembled, won't start - backfires

[Fixxer99TA]

Hows it running now? Get that fuel out and start getting that motor broken in!!!

[JAKEJR]

On the one occasion when I crossed two plug wires, as soon as the key was turned and I heard the back-fire I stopped cranking because I knew, then, that something was wrong. So I didn't continue cranking to see if it would idle or not.

Knowing that something was wrong, I immediately began to search for the cause and the first thing that came to mind (and the easiest to check) was crossed wires. Luckily the first one I checked, #2 was wrong. Then when I found the second one that was wrong, #4, I just swapped them at the spark plugs. After the swap, the engine fired and ran instantly with no other problem.

Yes, it was Shobox ,who I referenced in my previous post, who said he knows the Opti can mis-installed, disagreeing with another poster who claimed it couldn't be mis-installed. Shobox's a wealth of good information.

As I recall on L98 engines, holding the gas pedal to the floor puts the ECM (on the L98 it's called ECM not PCM - GM loves to change things) into Clear Flood Mode which, I believe shuts down the injectors while cranking the engine. The same mode may be available on the PCMs. Hopefully someone who knows for sure will chime in.

Good luck.

Jake

West Point ROCKS!

Glad to see you found the cause of your problem.

[meissen]

Looks like the o2s and plugs are fouled out - it's idling now but it's backfiring pretty consistently in a pattern.

[JPack]

If it runs now and backfires, how did you adjust the valves? Are you 100% positive you stated at #1 @ TDC on compression stroke or was it exhaust?

[JAKEJR]

I suspect you have a lifter preload adjustment problem. One or more is adjusted too tightly which is holding the valve open.

What procedure are you guys using to set the lifter preload?

If you're using the procedure listed in the Factory Service Manual or one of the Chilton books be warned, that procedure is very error prone. Using that procedure makes it really easy to make a mistake and cause the problem you're experiencing.

Use the IC/EO method that is now the recommended way to minimize the chance of making a mistake. If you need me to post the procedure, let me know and I will.

Jake

West Point ROCKS!

[meissen]

Thanks for all the help guys - it's really appreciated. We're trying to have the car at my show on May 30th as a surprise but the light at the end of the tunnel is getting smaller and smaller as the issues keep popping up. Your guys' help has been great!

We used the cylinder by cylinder method on Shoebox's website watching for the exhaust to start opening to adjust the intake PR and then wait for the intake to open all the way to adjust the exhaust PR.

I'm leaning towards it being a combination of a lot of things going on right now because as soon as it went closed loop the STerm levels went sky high before it stalled. Seems to indicate either tune or sensor and since the tune was drivable before the bearings spun I'm thinking my o2's are fouled. When we yanked them out after dropping the broken motor they were covered in soot. My dad used a rag and he can't remember if he used brake cleaner on the rag or not, but he wiped the soot off and then put the o2s back in the y pipes. Also I'm running TR55 plugs and one of the guys we call "Dr LT1" on my website says the platinums foul out easily.

Our plans are to:
Recheck plug wire routing for the 5th or 6th time (you never can be too sure! lol)
Replace the o2 sensors
Replace the spark plugs

Maybe when we pull the spark plugs my dad and I can go through and readjust valve lash while there's no compression.

[95formula383lt1]

i think its plug wires or possibly plugs, i ran my car for a month with my mods stock tune and no o2 sensors it ran better then it did with o2s just a little more on the rich side.

[meissen]

Yeah - my only downer is the 30# injectors. I honestly wish I would have just stayed with 24# because then I too could have just ran stock untuned for awhile until my tuner had the chance to tune it... I wouldn't have spun the two bearings more than likely since the culprit was mostly the gas in the oil. And now that the car is back together and the PCM is already calibrated for the 30# injectors I can't just swap back to the 24# and fire 'er up or else she'll be lean.

[95formula383lt1]

yea that sucks, uhh ooo i have gas in my oil right now still can find where its comming from. But yea id check ur plugs and wires and start again there, i dont believe o2s would cause that (i could be wrong but it ran fine without them on mine)

[meissen]

Yeah, you were right. My dad went out and checked and sure enough 3 and 5 were swapped. When I get home we're still going to swap o2s and plugs just because then we'll know that those are brand new and we won't have to worry that either are still bad. Then it'll be time to data log.

If anyone uses Data Master, you're more than welcome to check out my data logs - the Effed one is enjoyable - that's when it spun the two bearings and was reading REALLY bad. Maybe it's just me but I enjoy watching the logs play back and seeing the correlation between the sensors and what not.
http://meissenation.com/datamaster/