LT1 will not run. please help
Thread Starter
Le Mans Master
Joined: Sep 2009
Posts: 6,340
Likes: 1,148
From: Vermilion OH
LT1 will not run. please help
on my 94 that i just got, the previous owner had said and supplied paperwork from a chevy dealer stating that the opti was bad. i replaced the opti and the engine still will not start. i have excellent fuel pressure up to the rail and injectors and i have spark..which appears weak, but its present. a noid light confirms power to the injectors. the injectors are not spraying fuel into the engine as the plugs are bone dry. i'm lost here.. i'm kinda leaning towards the mass air flow sensor, but any advice or input would be appreciated. the car is a 94 with the LT1 and a 6spd trans.
Race Director
Joined: Apr 2000
Posts: 15,344
Likes: 4,009
From: Texas
Shoot a little starting fluid into the intake. Does it start? If so, you've eliminated the opti, the coil, the plugs, the wires, and the ICM. If it doesn't, did you install the opti correctly? Pretty easy to misalign the early optisparks. Also easy to cross plug wires on the Opti.
You say a noid light confirms power to the injectors. The noid light should flash when cranking, confirming the injectors should be opening and closing. What's the fuel pressure? Does it hold steady.
It's not the MAF. The '94-'96 cars will run without one. The PCM detects the error sets a code or codes and switches to the VE tables vs the MAF table to run the engine.
Never seen 8 injectors stuck. How long has the car been sitting?
You say a noid light confirms power to the injectors. The noid light should flash when cranking, confirming the injectors should be opening and closing. What's the fuel pressure? Does it hold steady.
It's not the MAF. The '94-'96 cars will run without one. The PCM detects the error sets a code or codes and switches to the VE tables vs the MAF table to run the engine.
Never seen 8 injectors stuck. How long has the car been sitting?
Thread Starter
Le Mans Master
Joined: Sep 2009
Posts: 6,340
Likes: 1,148
From: Vermilion OH
car has been sitting about a month before i purchased it. noid light flashed when cranking the engine. i sprayed starting fluid in the throttle body when cranking and it shot fire out of the snorkel.. when i installed the opti, i noted that there was only one available placement for the opti's gear to slide into the front cover.
i marked all wires coming out of the when removing it and reinstalled them accordingly. i do not believe they are crossed. can the opti be misaligned even with the alignment mark on its shaft allowing it to be installed only one way? i'm new to the whole optispark thing, so i'm merely a beginner when it comes to these suckers.
i marked all wires coming out of the when removing it and reinstalled them accordingly. i do not believe they are crossed. can the opti be misaligned even with the alignment mark on its shaft allowing it to be installed only one way? i'm new to the whole optispark thing, so i'm merely a beginner when it comes to these suckers.
Le Mans Master
Joined: Jul 2009
Posts: 6,381
Likes: 66
From: SF bay area C.A.
C4 of the Year Finalist
Weak spark would indicate your coil, same thing happen to me and it happen after I replaced the opti so it through me off a bit. I took out the chain store coil which I just put in and put in a GM replacement and so far so good. To double check it I put the new chain store coil back in and had a no start. Put the GM in and started right up.
Last edited by kimmer; Aug 8, 2012 at 10:21 PM.
Race Director
Joined: Apr 2000
Posts: 15,344
Likes: 4,009
From: Texas
I'd double-check the wires. Ensure all the plugs are tight, especially #6 and #8.
If you have a spare coil, it's an easy swap/test.
What brand of opti did you use? Genuine GM or aftermarket?
Thread Starter
Le Mans Master
Joined: Sep 2009
Posts: 6,340
Likes: 1,148
From: Vermilion OH
i will try swapping in a different coil today.
i seated the opti by hand and then installed the bolts. i used the old gear that came out of the opti as a locator for the correct position of the gear on the new opti. once the gear for the new opti was in place, it slid right on.
the backfire occured only once when a little amount of starting fluid was sprayed into the snorkel through the mass airflow meter.
i was leaning on the fuel pump being bad as well. i was thinking the bleed off in pressure is indicating that the check ball has failed internally and is allowing the fuel pressure to bleed back down. i will check the FPR this morning and see if there is any fuel in the vacuum line.
i used an aftermarket opti. i couldn't afford the $700 that the stealership wanted for the new opti. the brand that i used came from advance auto and it is a new unit complete with cap and rotor. came with a lifetime replacement and cost $195 out the door with my police discount.
i seated the opti by hand and then installed the bolts. i used the old gear that came out of the opti as a locator for the correct position of the gear on the new opti. once the gear for the new opti was in place, it slid right on.
the backfire occured only once when a little amount of starting fluid was sprayed into the snorkel through the mass airflow meter.
i was leaning on the fuel pump being bad as well. i was thinking the bleed off in pressure is indicating that the check ball has failed internally and is allowing the fuel pressure to bleed back down. i will check the FPR this morning and see if there is any fuel in the vacuum line.
i used an aftermarket opti. i couldn't afford the $700 that the stealership wanted for the new opti. the brand that i used came from advance auto and it is a new unit complete with cap and rotor. came with a lifetime replacement and cost $195 out the door with my police discount.
Last edited by mazdaverx7; Aug 9, 2012 at 09:30 AM.
Thread Starter
Le Mans Master
Joined: Sep 2009
Posts: 6,340
Likes: 1,148
From: Vermilion OH
on a side note, the think that's also stumping me is that injectors are not wet with gas after cranking.. are they partially controlled by another module and open when a certain part sees that there is good spark?
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
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
Race Director
Joined: Apr 2000
Posts: 15,344
Likes: 4,009
From: Texas
I'd fix the fuel pump first...as you mentioned, it's likely the check ball.
With proper fuel pressure, try to start the car. If that fails, squirt a little more starting fluid in there. If that fails, you have an ignition issue. To be brutally honest....the "new" aftermarket Optis from the chain stores or fleaBay have what seems to be about a 50% success rate. Assuming there is no coil issue, I think you're looking at some Opti troubleshooting. It is way easy to install the early Optis wrong, so I'd start there. Looks at it this way....if you have fuel and you have spark, then it's timing. The only way the timing is off on an LT1/4 is a bad or incorrectly installed Opti (excluding major issues like a stretched or jumped timing chain).
Thread Starter
Le Mans Master
Joined: Sep 2009
Posts: 6,340
Likes: 1,148
From: Vermilion OH
thank you for the advice. not surprising that the "new" aftermarket units would be prone to failure upon install. luckily the water pump gaskets are cheap and everything has been apart and lubricated once, lol. i don't mind tearing it back apart. it would be nice to be able to bench test the opti before install.
how can the opti be installed incorrectly? if the splines line up perfectly, can it still be installed improperly?
i'll pick up a new fuel pump, even as a preventative procedure. i will likely use napa as a source of a replacement pump. are there any known issues with napa pumps??
how can the opti be installed incorrectly? if the splines line up perfectly, can it still be installed improperly?
i'll pick up a new fuel pump, even as a preventative procedure. i will likely use napa as a source of a replacement pump. are there any known issues with napa pumps??
Le Mans Master
Joined: Jul 2009
Posts: 6,381
Likes: 66
From: SF bay area C.A.
C4 of the Year Finalist
If you indexed your shaft on the opti and it went in with no struggle you should be ok. Mine went in smooth and quick. As far as aftermarket optis there failure rate is very small, some people just put them in wrong and blame the opti. You always hear about the bad ones but if it works you don't hear about it. Before my install I noticed the spark from the coil was weak, after the install I had no spark. If you check out my post [pic of destroyed opti] it will inform you as to what I checked and it was not the opti. New parts from the chainstores can be bad .
Thread Starter
Le Mans Master
Joined: Sep 2009
Posts: 6,340
Likes: 1,148
From: Vermilion OH
i read your post a few times and the large checklist posted will be of great help i'm sure. i can get a coil from Napa for $21. and i think i have a buddy coming by with a known good coil for us to try. the coil is scummy looking and full of sand and grease. the car was sold in FL when new and was driven in AZ for some time before being brought to OH. i'm hoping the new opti is good.. i double checked all of my connections this morning and it will crank and not start. there is no bounce on the tachometer when cranking
Team Owner
Joined: Mar 2001
Posts: 30,856
Likes: 293
From: Boston, Dallas, Detroit, SoCal, back to Boston MA
Sounds like the problem I had
turned out to be I didn't clock the opti correct when I installed it.
Need to check it with a timing light after marking for TDC
turned out to be I didn't clock the opti correct when I installed it.
Need to check it with a timing light after marking for TDC
Thread Starter
Le Mans Master
Joined: Sep 2009
Posts: 6,340
Likes: 1,148
From: Vermilion OH
i can't get it started so i'm not sure how accurate a timing light would be when the engine is just cranking.
Melting Slicks
Joined: Jul 2005
Posts: 2,649
Likes: 863
There is a way to "check" the opti. Basically - the opti is stupid - it doesn't know if it's being turned by the motor or if you're turning it yourself. With the opti off the car - plug the 4 pin wire into it, turn on the Ignition, and spin it the opti shaft over by hand. See if you get a spark jumping from the coil lead that would normally be connected to the opti.
GOOD LUCK
GOOD LUCK
Thread Starter
Le Mans Master
Joined: Sep 2009
Posts: 6,340
Likes: 1,148
From: Vermilion OH
after some trial and error, i replaced the coil and the engine fired right up! its running a little rough and feels slightly down on power under acceleration. it has a solid idle but i can tell that there is a miss. the right side converter was glowing almost white and then after sitting for a minute with the engine off, glowing red after my first test drive. i have not checked the timing and did not check for crossed plug wires as i have to be up at 5am for work and its late, lol. any ideas other than timing or crossed wires as to why the engine may run rough and cause the right converter to glow white?
Le Mans Master
Joined: Jul 2009
Posts: 6,381
Likes: 66
From: SF bay area C.A.
C4 of the Year Finalist
Sounds like you have raw fuel entering your cat. Check your plug wire routing and also if any of them are up against something hot and is burning through. The back firing could be caused by the unburned fuel. Good luck.
Last edited by kimmer; Aug 10, 2012 at 12:17 PM.