New engine assembled, won't start - backfires

Hey guys,

So as some of you know I've only had a running LT1 for 80 miles with this swap project that I've been in. It ran great for 80 miles and then I spun two bearings. :(

I got the motor back from the machine shop machined with cylinder walls 040 over, crank was line bored 20/20. :embarassed:

So round 2 started on Friday and yesterday we had the motor all assembled and installed in the car again. We went to start and it cranks and randomly backfires. No start. Timing light showed that the wires are getting pulses and since it's backfiring we're definitely getting fuel and spark.

My dad thinks the motor is 180 degrees off but that's impossible if the crank and cam gears were 12 o'clock and 6 o'clock respectively, right? We used the opti diagnosing thread on CZ28 to check the ignition module and coil and everything seems to be legit so it seems like it's the opti.

Now, my question is - if the opti was bad would it still be sending pulses at all and/or would I get any DTC error codes? I had DataMaster running while I tried starting the car and I didn't have any DTC error codes.

The only other thing we can think of is that the opti isn't indexed right. It's a 1995 vented optispark. We took the original opti that came with the motor and then took the LT1 camshaft and tried putting it into the wrong slots and it wouldn't go into the wrong slots... only way I could see someone accidentally indexing it wrong would be to exert a lot of force on the opti to jam it in there. Mine slid in with no problems.. just wiggled it back and forth a bit and it popped right in.

Also, when we reinstall the optispark or a new one, as long as the key slot lines up to where ever the cam dowel is it should be right, correct?

If the crank gear is at 12 o'clock - is that #1 TDC or #6 TDC? My understanding is that it could be either. If so, how do we tell the difference between #1 TDC and #6 TDC? :confused:

If you were getting an Opti code, it would be DTC 16. When you get that code, it also shuts of fuel. So that's out. You're right there is no way to put the 95+ Opti on wrong. The index for the cam dowel is larger than the rest of the slots in the back of the Opti. Also, it would have had to have been smashed on and most likely would not have sit flush on the front of the motor.

Easiest way to find TDC is pull the plug and put your finger over the hole. Have someone crank the motor and when you feel a 'woosh' over your finger you'll be at TDC on compression stroke.

Did you check your plug wire routing to make sure the wires are on the correct cylinders?

We checked last night but it's hard to tell with all the accessories in place. When I get home from work I'm going to be yanking the water pump and harmonic balancer off. Should give me a lot more room to work with and see what's going on. I'm hoping it's just a misrouted wire ... hell, I'll even take an opti... I just hope to god I didn't have the crank 180 degrees out. It is possible, right? Dot will be at 12 o'clock for #6 TDC and #1 TDC, right? Man if we put the crank 180 degrees out from the cam that's going to SUCK... :( And what really sucks is being stuck at work having to stew on all this and not being able to go home to work on it. :(


Using a timing light - what would it look like when you're cranking and/or running? Would it be a very constant pattern or would it seem random? It seemed like last night when we had the timing light on it was just blinking randomly, no pattern to it. Don't know if it's because the timing light is older than I am or because I've got 8.5" MSD wires or not. Maybe that's a sign the rotor is bad on the opti?

Any time the crank gear dot is at the 12 o'clock position, the #1 AND #6 pistons will be at TDC.

The difference is what they are doing. What they're doing depends on the camshaft gear dot.

If the camshaft gear dot is also at the 12 o'clock position, the #1 piston will be on the compression stroke and the #6 piston will be on the exhaust stroke.

If the camshaft gear dot is at the 6 o'clock position, the situation is reversed - the #1 piston will be on the exhaust stroke and the #6 piston will be on the intake stroke.

Although I have seen posts saying the Opti can't be installed 180 degrees out in the phasing, one regular, highly respectable poster strongly disagrees, saying he's seen the Opti mis-installed many times.

The first thing I'd do is to verify that all the plug wires are correctly routed. It's really easy to mistakenly swap two of them and cause a back-fire. Been there.

Hope this helps.

Jake

West Point ROCKS!

Another possibility is incorrect settings of lifter preload.

Jake

West Point ROCKS!

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Originally Posted by JAKEJR

Any time the crank gear dot is at the 12 o'clock position, the #1 AND #6 pistons will be at TDC.

The difference is what they are doing. Wha they're doing depends on the camshaft gear dot.

If the camshaft gear dot is also at the 12 o'clock position, the #1 piston will be on the compression stroke and the #6 piston will be on the exhaust stroke.

If the camshaft gear dot is at the 6 o'clock position, the situation is reversed - the #1 piston will be on the exhaust stroke and the #6 piston will be on the intake. stroke.

Although I have seen posts saying the Opti can't be installed 180 degrees out in the phasing, one regular, highly respectable poster strongly disagrees, saying he's seen theOpti mis-installed many times.

The first thing I'd do is to verify that all the plug wires are correctly routed. It's really easy to mistakenly swap two of them and cause a back-fire. Been there.

Hope this helps.

Jake

West Point ROCKS!

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Quote:

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Originally Posted by JAKEJR

Another possibility is incorrect settings of lifter preload.

Jake

West Point ROCKS!

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Thank you for your explanation Jake - you've put my mind at ease. I've been getting stewing about "worst case scenarios" thinking the valves and pistons could have made contact if it was timed wrong. Your explanation finally made me realize that if the cam is taken out of the equation TDC is TDC it doesn't determine compression or exhaust.

So, it sounds like there's no chance of it being 180 degrees out because #1 AND #6 are both TDC and the gears were dot to dot. We used the method on Shoebox's website where you adjust the valves according to watching the lifters/rockers go up and down. We used 1/2 turn for valve lash - but when I get home we'll try looking at the wires again, maybe pop the valve covers off and watch the car try to crank, and then possibly take the water pump off to get to the optispark.

sounds like the plug wires to me too, mine did the same thing when i had 2 wires crossed.

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Originally Posted by 95formula383lt1

sounds like the plug wires to me too, mine did the same thing when i had 2 wires crossed.

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What im thinking as well.

Eh id think it would still start and run with 2 crossed wire's. Mine ran surprisingly decent with 2 wires crossed after my header install.

Got it to start for a few seconds before it stalled from being flooded. It was definitely the opti - it was in one of the wrong slots. It's amazing that it's even able to go into the wrong slots. Should JBweld the slots so it won't happen again hahah... But atleast it started! Now I just need to get all that fuel from cranking out of the chamber so it won't be flooded. Hopefully letting it sit over night will help.

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

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.

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

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?

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!

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.

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.

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.

yea that sucks, uhh ooo i have gas in my oil right now:hmm: 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)

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/

i thought it was the wires lol ur welcome, ive done it many times before.

btw get some vids of that thing when its driveable. lol

Will do - only videos I have right now are on youtube: http://www.youtube.com/mifbody - can't post any videos yet because there's a few people on my site subscribed to my youtube account.

..then again, there's quite a few people from my site on here too and probably have seen this thread. :laugh:

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Originally Posted by meissen

Will do - only videos I have right now are on youtube: http://www.youtube.com/mifbody - can't post any videos yet because there's a few people on my site subscribed to my youtube account.

..then again, there's quite a few people from my site on here too and probably have seen this thread. :laugh:

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Good to see its coming along!! :cool: so it will be at the meet and greet for sure now?? lol i just spun a bearing in my LT1 (most likely) so I will be going through kinda the same thing you had to do :(

Quote:

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Originally Posted by 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!

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Could you please post this procedure for me??

Thanks,
Ryan

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Originally Posted by ThreeHonks

Good to see its coming along!! :cool: so it will be at the meet and greet for sure now?? lol i just spun a bearing in my LT1 (most likely) so I will be going through kinda the same thing you had to do :(

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Haha like I was saying.. :laugh: :claps:

Ryan, no word on whether it will be at the M&G in all honesty. We got it idling on Wednesday but now it looks like we cracked the flexplate. There's a really loud banging noise coming from the dustpan area. Not to mention once we get the flexplate fixed it still has to be tuned.

When we were installing the transmission we tried to install it like everyone had told us we had to do - put the torque converter all the way into the transmission then line up the trans, bolt the torque converter on, and bolt the trans down. We heard a crack noise when we were trying to do it that way so that might have been the flexplate cracking.

Here's shbox's write up that we used - I find it to be the best way:
http://shbox.com/1/4th_gen_tech2.html#adjust_valves Method #3

Quote:

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Originally Posted by meissen

Haha like I was saying.. :laugh: :claps:

Ryan, no word on whether it will be at the M&G in all honesty. We got it idling on Wednesday but now it looks like we cracked the flexplate. There's a really loud banging noise coming from the dustpan area. Not to mention once we get the flexplate fixed it still has to be tuned.

When we were installing the transmission we tried to install it like everyone had told us we had to do - put the torque converter all the way into the transmission then line up the trans, bolt the torque converter on, and bolt the trans down. We heard a crack noise when we were trying to do it that way so that might have been the flexplate cracking.

Here's shbox's write up that we used - I find it to be the best way:
http://shbox.com/1/4th_gen_tech2.html#adjust_valves Method #3

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^wow that sucks^ sounds like u got about the same luck as everyone else on the site lol, i just lost the rings in my motor.

wires are so hard to get right on these cars , thats why i got me another set of cylinder markers ( jegs parts #121-3414) and put them on both ends then there is no guess work .

Quote:

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Originally Posted by ThreeHonks

Could you please post this procedure for me??

Thanks,
Ryan

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First off let me say that there are seveal different ways to set lifter preload and all of them will work, but only if done correctly. The difference among the different methods is that one method is less error prone than the others. The least error prone method is the one I'm writing about now.

Okay, here's the procedure, it's referred to as the Intake Closing/Exhaust Opening (IC/EO) method:

The goal is to adjust the rocker arm adjusting nut enough so that it depressess the pushrod and thus the lifter plunger .030". Since it would be very difficult to actually measure that amount - requirng a dial indicator with a magnetic base, etc., turning the adjusting nut a certain amount will work just fine.

Most importantly, in order for the lifter preload to be set correctly, the lifer HAS TO BE on the base circle/heel of its camshaft lobe.
Since there's no way to actually SEE if the lifer is on the base circle/heel, you watch what its companion pushrod does in order to know. You watch the intake to set the exhaust, then watch the exhaust to set the intake.

May sound crazy but that's how it's done.

To begin with, install all the pushrods in their respective lifters and set the rockers and adjusting nuts loosely in place. Then you'll need a way to turn the engine in it's normal direction of rotation. I use a ratchet, extension and socket on the damper nut. Having the spark plugs removed will make the engine much easier to turn too.

Begin at the driver's side, front, very first rocker, which will be the #1 EXHAUST. We'll be setting that one first.

Grab the pushrod next to it, which will be the #1 INTAKE pushrod, with your thumb and index finger so that the pushrod can be moved UP and DOWN.

Turn the engine while feeling what the #1 INTAKE pushrod is doing. That pushrod will, at some point, begin to move up (indicating the INTAKE valve is beginning to open) and then down.

Just before that pushrod is all the way back down, STOP turning the engine. The actual point that you STOP isn't all that critical, just as long as the pushrod has moved more than half way back down.

With the #1 INTAKE pushrod in that position, the #1 EXHAUST lifter will be on the base circle of its lobe.

Now move your hand to the #1 EXHAUST pushrod and begin to gently move it up and down with your finger/thumb while at the same time begin to tighten the #1 EXHAUST adjusting nut.

When you reach the point that the #1 EXHAUST pushrod can no longer be moved up and down you've found what we call ZERO LASH.

It's now time to set the lifter PRELOAD on the #1 EXHAUST lifter. Most use 1/2 turn of PRELOAD, so turn the adjusting nut 1/2 turn more from ZERO LASH. This'll depress the lifter plunger and give you right at .030" of PRELOAD.

1/2 turn= handle of wrench at, say, 12 o'clock, then turn until the handle points at 6 o'clock.

If you're using Poly-locks, once that 1/2 turn is made, tighten the allen head poly lock with your allen wrench. Make sure it's tight!
That one's done.


Now we move on to setting the #1 INTAKE.

To set the INTAKE, we grab the #1 EXHAUST pushrod (the one we just finished setting) with those same two little fingers - or you can just watch what the rocker is doing - either way works.

Begin, again, to turn the engine over manually while watching the #1 EXHAUST rocker or feeling its pushrod. AS SOON as you see the #1 EXHAUST rocker begin to open that valve or you feel the #1 EXHAUST pushrod begin to move UP, STOP. You just found the point that the #1 INTAKE lifter is on its base circle.

Grab the #1 INTAKE pushrod with your index finger and thumb and begin to gently move that pushrod up and down as you slowly tighten its adjusting nut. When that pushrod can no longer be moved up or down you've found ZERO LASH for the #1 INTAKE.

Again, tighten the adjusting nut an additional 1/2 turn to set the .030" preload and tighten the allen head screw, TIGHT.

The #1 INTAKE and #1 EXHAUST are now set. Now move on to the very next pair, #3s and do the same thing. Continue working down the line to #5 then #7.

Once done, move to the other side of the engine and begin at the very first, front rocker/pushrod (#2 EXHAUST) and repeat, going straight down the line. After you're finished with #8 EXHAUST, you're done.

If you just do one after the other, straight down the line, you won't skip any and each will be set properly.

JUST REMEMBER: The valve arrangement is EIIEEIIE with E=EXHAUST and I=INTAKE It's important to know which valve you're working on, either an INTAKE or an EXHAUST.

Hope this helps.

Jake

West Point ROCKS!

Yup, that's pretty much what we did and 1/2 turn is exactly the preload we did too. Works great.

Happy to report the flexplate was not infact cracked - the counterbalance weight that looks like a handle was hitting the starter. No big deal, we just took the starter out, ground down the casting where it was hitting, and then reinstalled the starter. Lot easier than messing with the transmission!!!! That worked flawlessly - no more banging. :D

Quote:

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Originally Posted by meissen

Yup, that's pretty much what we did and 1/2 turn is exactly the preload we did too. Works great.

Happy to report the flexplate was not infact cracked - the counterbalance weight that looks like a handle was hitting the starter. No big deal, we just took the starter out, ground down the casting where it was hitting, and then reinstalled the starter. Lot easier than messing with the transmission!!!! That worked flawlessly - no more banging. :D

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Great to hear it! but honestly dont rush it to have it at the meet and greet, do it right the first time. I just dropped my motor out today and am planning on just doing things slow and getting it right. I cant wait to see it on WW soon tho!

Thanks a lot JAKEJR, I really appreciate it. Would u have any idea how much preload an LS7 lifter needs? I am using those for my build

I used LS7 lifters and I used 1/2 turn preload.

Disclaimer: The exhaust was really rattling for some reason - it went away as soon as the exhaust warmed up and has not rattled again even after letting the car cool off over night LOL go figure.
[ame="http://www.youtube.com/watch?v=Tg4UwF0Epew&feature=channel_page"]YouTube - LT1 012[/ame]
[ame="http://www.youtube.com/watch?v=C_CPswSsTiM&feature=channel_page"]YouTube - Cruise by in Red Alert[/ame]

Deceiving videos though - my LTerms are about 20 counts off. I'm really hoping it's just the fact that it's the stock tune and will be fixed when I take it to the local tuner. Only bad part is the guy who is doing my tune is an hour away... so he's going to review my data logs and as long as he deems it to be OK I'll drive it out to him... if he says it's not safe to drive on the stock tune then I'll have to get a car trailer from U-Haul and tow it to his shop.

On a positive note, the DataMaster logs seem to be really good aside from the fuel trims (lol... guess that's a really good contradiction). The knock sensor isn't registering knocks like it used to - the first try with the LT1 (when it had the two spun bearings) right from the first start up it would register knocks. And, another positive is that the spark retard stays at 0 to 0.1 - it's so dang smooth. If anyone has datamaster and wants to look for shits and giggles - http://www.meissenation.com/datamaster/


Oil pressure has been great - about 60 when it starts cold and then 30-40 psi when it idles. New oil pump and the white spring mod seems to have been worth it. RPMs are spot on for the tachometer at idle with what datamaster shows. Haven't verified how accurate the speedometer is. I'm using a 1997 z28 gauge cluster in my 1998+ dash with a 1995 LT1 in a 1994 Camaro. :jest::jest: And I can't forget my 2000 Trans Am door panels or my 1998+ rear end. I swear I need to get a spreadsheet to keep track of what year vehicle each item in my car came from. :jest:

Very nice! so are you still using the 30lb. injectors or did you switch back to stock?

30lbers - I wanted to go back to stock but the PCM was already calibrated for the 30lbers.

OK j/w because i was reading on mifbody that you thought the larger injectors may have casued a problem. Its definately a good idea to keep those larger injectors, I think the stockers would be just about maxed out. I have 42lb. SVO's that I will be running

Well the cat was let out of the bag on MiFbody today after a few guys started putting 2 and 2 together that I've been too quiet with updates. :D I drove the car to Port Huron (45-60min drive) to the guy who is tuning the car. :) Drove BEAUTIFULLY... closed loop idle was a little too low (650) so it'd stumble but Steve said he's going to put it at about 800 or so. If all goes as planned I should be picking it up tomorrow or Thursday night. :D :D :D :D

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Originally Posted by ThreeHonks

Great to hear it! but honestly dont rush it to have it at the meet and greet, do it right the first time. I just dropped my motor out today and am planning on just doing things slow and getting it right. I cant wait to see it on WW soon tho!

Thanks a lot JAKEJR, I really appreciate it. Would u have any idea how much preload an LS7 lifter needs? I am using those for my build

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I never checked LS7 lifters, but if was going to run them, I'd put a dial indicator on the rocker, then use 1/2 turn on the poly-lock and see what plunger depression/preload I'd get. I'd shoot for .030", give or take .010".

If I just went with the standard 1/2 turn, I wouldn't know how much that actually depressed the plunger; how mcuh actual preload I'd have. Checking comes with the territory when swapping to new and different parts; gotta check.

Jake

West Point ROCKS!