bad backfire no start
Thread Starter
Racer
Joined: Sep 2015
Posts: 382
Likes: 17
bad backfire no start
Whats up guys got a quick question for this stubborn problem.
Installed my LTCC kit and finally found my white EST wire. I have it all wired up grounds nice and tight and clean. New opti installed as well GEN1 optispark spline drive, which went in fairly easy. Coil harness is also hooked up properly as well. Tried to start the car and its backfiring badly through the intake and the engine seems to be holding like when the distributor is 180* off. I got a green light when cranking so Im puzzled here. Any ideas where to start from here?
Installed my LTCC kit and finally found my white EST wire. I have it all wired up grounds nice and tight and clean. New opti installed as well GEN1 optispark spline drive, which went in fairly easy. Coil harness is also hooked up properly as well. Tried to start the car and its backfiring badly through the intake and the engine seems to be holding like when the distributor is 180* off. I got a green light when cranking so Im puzzled here. Any ideas where to start from here?
Thread Starter
Racer
Joined: Sep 2015
Posts: 382
Likes: 17
nah i went over all of it. All wiring is done, coils have power, opti is signaling and getting fuel and spark. I bought a summit opti bc my other opti took a dump on the high res side. Im thinking its something internal to the opti at this point. it spits out the intake as if its firing on the intake stroke. I matched all the wiring on the coil harness to each cylinder, ex 1,3,5,7 are Purple, Blue, Green, Red and 2,4,6,8 Red, Green, Blue, Purple.
Melting Slicks
Joined: Sep 2010
Posts: 2,422
Likes: 202
nah i went over all of it. All wiring is done, coils have power, opti is signaling and getting fuel and spark. I bought a summit opti bc my other opti took a dump on the high res side. Im thinking its something internal to the opti at this point. it spits out the intake as if its firing on the intake stroke. I matched all the wiring on the coil harness to each cylinder, ex 1,3,5,7 are Purple, Blue, Green, Red and 2,4,6,8 Red, Green, Blue, Purple.
is the Summit Opti. Known good?? Never Create more Work. Unless it's NEEDED.
Hopefully. you get this resolved soon. the LTCC kit is a great upgrade. And makes a big improvement.
I actually reduced. Some timing in my tune. The OE table is very high 44deg in areas.
Last edited by THE 383 admiral; Dec 30, 2015 at 11:23 PM.
Thread Starter
Racer
Joined: Sep 2015
Posts: 382
Likes: 17
i didnt know u didnt need the high side, but i think the other opti was a summit as well, and dont trust it im sure the low side wouldve eventually bitten the dust. Im going to check a few things today and if all else fails ill exchange the opti for another. I also want to delete the MAF and go strictly VE table. ill see what happens
Melting Slicks
Joined: Jul 2011
Posts: 2,605
Likes: 202
From: Trinity FL
nah i went over all of it. All wiring is done, coils have power, opti is signaling and getting fuel and spark. I bought a summit opti bc my other opti took a dump on the high res side. Im thinking its something internal to the opti at this point. it spits out the intake as if its firing on the intake stroke. I matched all the wiring on the coil harness to each cylinder, ex 1,3,5,7 are Purple, Blue, Green, Red and 2,4,6,8 Red, Green, Blue, Purple.
I am sure you have these pinouts, but just for reference:
The best thing I can tell you is to retrace your wiring one more time, you will find something you missed or skipped. Verify the two pinks and the whites are soldered to the appropriate factory wires.
Patrick
Last edited by TorchTarga94; Dec 31, 2015 at 11:39 AM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Thread Starter
Racer
Joined: Sep 2015
Posts: 382
Likes: 17
thanks, im going to go over it again this afternoon. the LTCC harness 1357 goes to the driver side and 2468 passenger side. Checked my White EST and pink wires and there all good. whats funny is when i reversed the harness and put 1357 on passenger side car started up but wasnt firing right but stayed running. BTW how did you hook up your tachometer? Im going to check everything from scratch today, ill even pull the opti and reinstall it just to verify, cant hurt.
Thread Starter
Racer
Joined: Sep 2015
Posts: 382
Likes: 17
so you think the LTCC Harness maybe backwards? so even though my driver side is hooked up with the LTCC plug 1357, and my coil harness matches 1357, your thinking its wired wrong so i should flip my harness on my coils? so Instead of it being Purple, Blue, Green, Red I should reverse it so 1357 go Red, Green, Blue, Purple right? I can reverse it that no problem.
Melting Slicks
Joined: Jul 2011
Posts: 2,605
Likes: 202
From: Trinity FL
thanks, im going to go over it again this afternoon. the LTCC harness 1357 goes to the driver side and 2468 passenger side. Checked my White EST and pink wires and there all good. whats funny is when i reversed the harness and put 1357 on passenger side car started up but wasnt firing right but stayed running. BTW how did you hook up your tachometer? Im going to check everything from scratch today, ill even pull the opti and reinstall it just to verify, cant hurt.
Where are your three grounds connected? LTCC Module, and both coil harnesses?
Melting Slicks
Joined: Jul 2011
Posts: 2,605
Likes: 202
From: Trinity FL
So, now that we can assume your coil harness wiring is correct, lets confirm your spark plug wiring.
Odd Bank cylinder 1 is towards the front of the car and number 7 is toward the back.
Even Bank cylinder 2 is towards the front of the car and Cylinder 8 is toward the back.
This would lead you to think that the even bank is exactly the same as the odd bank when it comes to the coil wiring. However it is completely opposite (which it looks like you know).
I.E. - Cylinder 2 utilizes the red wire, so this would lead one to think Cylinder 1 on the opposite side also uses the red wire, where in actuality, it utilizes the reciprocate wire (purple). And so on....
Simple Table:
Wire Color---->Corresponding Cylinder
RED------------>2 & 7
GREEN---------->4 & 5
BLUE------------>6 & 3
PURPLE--------->1 & 8
Last edited by TorchTarga94; Dec 31, 2015 at 11:38 AM.
Thread Starter
Racer
Joined: Sep 2015
Posts: 382
Likes: 17
my grounds are in this fashion. The Coils have 10AWG looped to each other, paint cleaned off coils and connected and ends in the front on cylinder heads. The 1357,2468 ground is hooked to the stud on the coils as well. the LTCC Box is grounded with 10AWG to the back where the EGR Valve is bolted on, again ground tight and clean. I Dont think grounds are an issue here to be honest. Firing order is correct on coils to plugs, so i can rule that out. It seems to me either something in the harness is wrong, IE wired wrong from build by Bob, which i dont think is the case OR the opti i put in the disc is reading wrong which could be a possibility. What i found wierd was the car started when i connected the LTCC 1357 plug to passenger side and vice versa on the other. but sounded like it was on 4 cylinders and running like crap, i tried to blip the throttle and it backfired like a 12gauge shotgun out the tailpipe.
Melting Slicks
Joined: Jul 2011
Posts: 2,605
Likes: 202
From: Trinity FL
my grounds are in this fashion. The Coils have 10AWG looped to each other, paint cleaned off coils and connected and ends in the front on cylinder heads. The 1357,2468 ground is hooked to the stud on the coils as well. the LTCC Box is grounded with 10AWG to the back where the EGR Valve is bolted on, again ground tight and clean. I Dont think grounds are an issue here to be honest. Firing order is correct on coils to plugs, so i can rule that out. It seems to me either something in the harness is wrong, IE wired wrong from build by Bob, which i dont think is the case OR the opti i put in the disc is reading wrong which could be a possibility. What i found wierd was the car started when i connected the LTCC 1357 plug to passenger side and vice versa on the other. but sounded like it was on 4 cylinders and running like crap, i tried to blip the throttle and it backfired like a 12gauge shotgun out the tailpipe.
For $hits, connect the coil harness grounds to the fuel rail hold down bolts. Don't put both grounds on the same bolt, utilize a bolt on each side. Not sure where your LTCC module is fastened down but it should be grounded to iron if possible.
Thread Starter
Racer
Joined: Sep 2015
Posts: 382
Likes: 17
yea the LTCC is iron grounded, where the egr valve bolts to the back of the intake. I'll report back later this evening if i made any progress. Does the Water temp sender have to be hooked up bc i have it off for now. i dont think it does though
Melting Slicks
Joined: Jul 2011
Posts: 2,605
Likes: 202
From: Trinity FL
Yes the water pump sensor has to be hooked up!