LT4 dropping cylinders?
Thread Starter
Instructor
Joined: Jul 2002
Posts: 104
Likes: 0
From: Somerset NJ
LT4 dropping cylinders?
Ok so my LT4 intermittantly drops a couple cylinders only when between 1k and 2500k RPM. If I punch the throttle a bit they come back but they dont drop them all the time, just once in awhile. Recently with the cold weather it seems to be getting worse.
The engine has about 50k on it now, I was having intermittant problems with dropped cylinders before during the summer but never really did anything about it. Since this vehicle is my only and daily driver I dont need to wait til I am dead in the snow to fix it.
So its my guess that the Optispark is going out. Any other guesses? Any kind of sensors that are known to go bad and maybe cause this problem? I heard somethin about that MAF sensor in the pass side front of the intake causing soem porblems..lemme know what you think! Thanks.
The engine has about 50k on it now, I was having intermittant problems with dropped cylinders before during the summer but never really did anything about it. Since this vehicle is my only and daily driver I dont need to wait til I am dead in the snow to fix it.
So its my guess that the Optispark is going out. Any other guesses? Any kind of sensors that are known to go bad and maybe cause this problem? I heard somethin about that MAF sensor in the pass side front of the intake causing soem porblems..lemme know what you think! Thanks.
Thread Starter
Instructor
Joined: Jul 2002
Posts: 104
Likes: 0
From: Somerset NJ
Re: LT4 dropping cylinders? (froggy47)
I agree that parts get expensive, esp this distibutor. But the PCM is showing no codes and I wasnt able to duplicate the misfires with the diagnostic tool hooked up, they are too intermittant. Today it was pretty bad and was losing power all over the place, doesnt feel good.
Anyone else?
Anyone else?
Intermediate
Joined: Jun 2003
Posts: 25
Likes: 0
From: Chaska MN
Re: LT4 dropping cylinders? (AVTekk)
Could be an O2 on the way out. Get a scanner on it, and make sure it is cycling properly while this is happening.
If it never does it at WOT, or during warm up open loop, then it is most likely an O2 sensor.
Good Luck
If it never does it at WOT, or during warm up open loop, then it is most likely an O2 sensor.
Good Luck
Le Mans Master
Joined: Jun 2002
Posts: 6,097
Likes: 2
From: Cincinnati Oh
Re: LT4 dropping cylinders? (Terry@TPiS)
Could be an O2 on the way out. Get a scanner on it, and make sure it is cycling properly while this is happening.
Thread Starter
Instructor
Joined: Jul 2002
Posts: 104
Likes: 0
From: Somerset NJ
Re: LT4 dropping cylinders? (Terry@TPiS)
Hrmm..interesting. Ill look into that. Ya it doesnt happen at WOT but it did used to happen on the highway under 3k RPM. The problem is very intermittant so I dunno what it can be. Like today, it was driving fine, I stopped at Home Depot, I get back in it and the thing is stumbling and falling all over itself. I would punch it a lil to get over 3k, it would even out, then Id let off the gas and let it coast and you can hear/feel it dropping out when coasting. Then I stop again, get back in and it drives fine.
Sometimes if you hold the throttle when it is happening, it drops out, then comes back..then drops out..man..
So its def electrical, Im just having a hard time pin-pointing it. It did happen in open loop mode last Friday, I only got a mile from the house and it was acting up. I dont have much money to dump into it or else Id just replace all kinds of things. I have acces to an osciloscope tho, Ill see what I can get on the different sensors. Keep the ideas coming.
Sometimes if you hold the throttle when it is happening, it drops out, then comes back..then drops out..man..
So its def electrical, Im just having a hard time pin-pointing it. It did happen in open loop mode last Friday, I only got a mile from the house and it was acting up. I dont have much money to dump into it or else Id just replace all kinds of things. I have acces to an osciloscope tho, Ill see what I can get on the different sensors. Keep the ideas coming.
Thread Starter
Instructor
Joined: Jul 2002
Posts: 104
Likes: 0
From: Somerset NJ
Re: LT4 dropping cylinders? (all4c4lt4)
Bosch plugs were just installed a couple months ago. Wires were installed over a year ago, do you think its time for new wires? They are in very good condition, and certainly dont have 30k miles on them. Also it was very difficult for me to find a set of LT4 wires, seems the coil or distributor is different than a LT1.
Can anyone recommend where to get a new set?
Can anyone recommend where to get a new set?
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
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
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
Thread Starter
Instructor
Joined: Jul 2002
Posts: 104
Likes: 0
From: Somerset NJ
Re: LT4 dropping cylinders? (fullboogie)
Ok thanks for the heads up..so there isnt any place to just buy wires for a LT4?
The engine was droppin off bad today again..caused the whole vehicle to shake at one point...Then it smoothed out..
The engine was droppin off bad today again..caused the whole vehicle to shake at one point...Then it smoothed out..
Melting Slicks
Joined: Apr 2000
Posts: 3,198
Likes: 2
From: Northern CA
Re: LT4 dropping cylinders? (AVTekk)
The LT1 and LT4 use the same wires. Just some minor differences in the coil wire boots over the years.
The F-body LT1 and Vette LT1 use different wires though, due to the front engine dress.
There may be a way to check the ignition coil with a multimeter; worth trying since it's cheap and easy to replace. Same goes for the ignition module, although that one tends to be heat related.
How about a bad electrical ground? Never rule out the obvious...
Good luck.
The F-body LT1 and Vette LT1 use different wires though, due to the front engine dress.
There may be a way to check the ignition coil with a multimeter; worth trying since it's cheap and easy to replace. Same goes for the ignition module, although that one tends to be heat related.
How about a bad electrical ground? Never rule out the obvious...
Good luck.
Thread Starter
Instructor
Joined: Jul 2002
Posts: 104
Likes: 0
From: Somerset NJ
Re: LT4 dropping cylinders? (JasonL)
I dunno, my coil is different than a LT1s coil, the connector is different, because I ended up buying a set of LT1 wires and the coil wire didnt fit. Anyway..
Its still having this problem on a daily basis. I will check the grounds, altho they were all securing bolted to the frame the last time I checked..I think I might just replace the Opticrap for the hell of it sooner or later, and Im going to diagnose the O2's and see what theyre up to. Thanks.
Its still having this problem on a daily basis. I will check the grounds, altho they were all securing bolted to the frame the last time I checked..I think I might just replace the Opticrap for the hell of it sooner or later, and Im going to diagnose the O2's and see what theyre up to. Thanks.
Melting Slicks
Joined: Apr 2000
Posts: 3,198
Likes: 2
From: Northern CA
Re: LT4 dropping cylinders? (AVTekk)
I dunno, my coil is different than a LT1s coil, the connector is different, because I ended up buying a set of LT1 wires and the coil wire didnt fit. Anyway..
Taylor has one part number for all '92-96 LT1/LT4. Included are
8 plug wires
1 coil wire w/ 90-deg boot (used on my LT4)
1 coil wire w/ 135-deg boot (early year LT1s, I assume)
MSD and others may split the early and late LT1s into two kits, I don't know.
Anyways, I would still diagnose the coil before ripping into the opti. Simply because it's 10 minutes vs. several hours of labor :D Good luck.
Thread Starter
Instructor
Joined: Jul 2002
Posts: 104
Likes: 0
From: Somerset NJ
Re: LT4 dropping cylinders? (JasonL)
Thanks! I will look into the Taylor wires.
I have decided to take my Opti apart and clean it all out and replace the rotor and such. I know its a lot of work but I can take care of it, I did the water pump in a parking lot in Ohio when it blew up on me so I know the basic area of the Opti pretty well.
You spoke of the coil and module earlier, is there a how-to on diagnosing it with a multimeter?
I have decided to take my Opti apart and clean it all out and replace the rotor and such. I know its a lot of work but I can take care of it, I did the water pump in a parking lot in Ohio when it blew up on me so I know the basic area of the Opti pretty well.
You spoke of the coil and module earlier, is there a how-to on diagnosing it with a multimeter?
