c4 LT4 Missfire
Thread Starter
8th Gear
Joined: Oct 2015
Posts: 8
Likes: 0
From: Antioch California
c4 LT4 Missfire
I know there are probably a lot of threads like this and I have searched far and wide. I have a 96 vette with lt4. I was driving and almost ran out of gas and oulled into a hole in the wall gas station as an emergency and put in 20 bucks.as soon as i started it my car was running rough and ticking pretty loud. Drove it home and started flashing the SES light. I pulled the code and came back as P0300 (Mult cyl misfire) but when i freeze frame and keep erasing and checking it shows P0305 (cyl 5 misfire) pulled the valve cover to make sure it was good (looked visually ok). Previous owner said he changed water pump and opti 10k ago. so i changed the plug wires (#5 looked bad ) so i did them all and still the same misfire at the same cylinder. chancged that spark plug and same thing. now the plug is breand new but doesnt look like it is igniting, because its wet when i pull it out but the wire is getting spark to the plug. any ideas or tips i should be looking at?
Thank you in advanced
Thank you in advanced
Last edited by CTillman; Oct 7, 2015 at 03:14 AM.
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
I suggest to do a compression test on #5 cylinder. Low compression you have a mechanical problem. While doing compression test install spark tester in plug wire to verify enough spark is present. If spark tester won't spark - distributor cap or plug wire not fully seated on cap. You could try swapping #5 & #7 injectors and see if miss moves. Which would indicate a bad injector. You could remove fuel filter and drain fuel from inlet in to a clear container and see what it looks like. Filter is designed to catch particles not non-burning liquids. Good Luck
Thread Starter
8th Gear
Joined: Oct 2015
Posts: 8
Likes: 0
From: Antioch California
Well i moved the injetors around and still got cylinder 5. So I went and got a compression tester and tested 1 3 5 7 got 120 in all of them....except 5.... i got 0 :'( I've only had this car for 3 weeks and barely driven it. made sure it was full on oil and stuff... i dont think it can be rings or a hole through the piston because it isn't smoking when its running. the plug is wet but gets spark... what else could it be? i has to be valves or maybe head gasket? It hasn't over heated on me. its gotten to 225 at the highest but that was sitting in traffic and read that was normal temps for these cars. collant was full.
Drifting
Joined: Dec 2007
Posts: 1,647
Likes: 4
From: Argillite KY
as soon as i started it my car was running rough and ticking pretty loud
But the ticking could be your problem. Pull the coil wire and turn the engine over. Watch #5 valves and see if they're doing anything stupid. The LT4 will have aluminum roller rockers. Try adjusting the #5 valves and see if that helps. I don't know why a hole-in-the-waqll gas station would make that happen but it's the first thing that comes to mind. A lifter could have screwed up but by watching you may find a problem.
Thread Starter
8th Gear
Joined: Oct 2015
Posts: 8
Likes: 0
From: Antioch California
Well the ticking may have been just a coincidence from the gas there was no tick at all before when I was driving and I wasn't driving hard. As soon as I started it after giving it gas it ticked but still ran. Sucks this happened only having this car for about 2 weeks :/. I'm going to Vegas next month for my bday so I was trying to get this car ready but now this happened :/ I bought a borescope to look in the cylinder to see if the piston is ok. Hopefully I can get away with redoing heads and getting it running soon
Pro
Joined: Oct 2012
Posts: 580
Likes: 121
From: Grapevine TX
Ticking pretty "loudly". Use the adverb. But the ticking could be your problem. Pull the coil wire and turn the engine over. Watch #5 valves and see if they're doing anything stupid. The LT4 will have aluminum roller rockers. Try adjusting the #5 valves and see if that helps. I don't know why a hole-in-the-waqll gas station would make that happen but it's the first thing that comes to mind. A lifter could have screwed up but by watching you may find a problem.
But the ticking could be your problem. Pull the coil wire and turn the engine over. Watch #5 valves and see if they're doing anything stupid. The LT4 will have aluminum roller rockers. Try adjusting the #5 valves and see if that helps. I don't know why a hole-in-the-waqll gas station would make that happen but it's the first thing that comes to mind. A lifter could have screwed up but by watching you may find a problem.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
Drifting
Joined: Dec 2007
Posts: 1,647
Likes: 4
From: Argillite KY
The stock LT4 rockers aren't adjustable, you simply torque them down.
Thread Starter
8th Gear
Joined: Oct 2015
Posts: 8
Likes: 0
From: Antioch California
so i watched the valves as my girlfriend cranked the motor and both valves are moving, still no compression, found a bent pushrod on the intake side of cylinder 5, i took a pushrod out of 7 to put it in just to see if i can get compression now but still nothing, BUT with that pushrod in i can compress that lifter but cant compress any of the others, so maybe the bad lifter caused the pushrod to comeout of the rocker arm, bent then thats where my problem lies? i bought a new pushrod for cyl 5. (will replace all of them if i can get the motor to run)
thanks again for all your guy's feedback
thanks again for all your guy's feedback
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
I got a feeling you have a bent valve. Many times when pushrods get bent it's because a piston smacked a valve out of it's way. When you swapped push rod there should have be some or more compression not 0
Thread Starter
8th Gear
Joined: Oct 2015
Posts: 8
Likes: 0
From: Antioch California
yup...its confirmed... i didnt have a leakdown tester so i took the schrader valve out of the compression tester hose and pumped air into the cylinder and can hear air shooting out the intake manifold clear as day... so 2 weeks.... i hope karma beats the **** out of the dude that sold it to me... car only lasted 2 weeks.... well gotta sell my 72 el camino now to pay for a rebuild or cylinder head.... and thats if the piston isnt damaged... waiting on the borescope to see the piston to see if its even worth pulling the heads
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
Since LT4 uses light weight valves and its a intake valve so it might not be so bad. Pull heads and get them redone. Sodium filled exhaust valves are not forgiving. Winter storage season is a time for repairs.
Thread Starter
8th Gear
Joined: Oct 2015
Posts: 8
Likes: 0
From: Antioch California
yea... im hoping theres no damage to the piston... i should get the borescope camera tomorrow or monday. whenever i get it im going to check the piston to see if its worth taking the heads off. if the piston is ok ill start yanking off everything