LT1 Engine Issues

Bob Letellier · 07-30-2012, 08:52 PM

Was hoping to get some advice from a few guys who have Lt1 motors for the Firebirds. Need some recommendations on what computer(s) / programs need to be used to make the car run properly. Car runs great then starts skipping like the timing is completely off...

Please contact me here or send me a PM. --

joelster · 07-30-2012, 08:56 PM

Are you running the factory pcm? Does it skip when going into closed loop, but run great in open loop?

Bob Letellier · 07-30-2012, 09:01 PM

Running HOLLEY - Seems like the map sensor is sending the wrong signal - but we've replaced it.

Ed Wright · 07-30-2012, 09:18 PM

I used the factory PCM until I got my old bracket engine needing to go past 7000 RPM. That's about all they will rev. Ran faster than my SS LT1 runs. Should not be doing what you discribe. Don't just throw sensors at it. Learn to diagnose it.

As for an aftermarket stand alone I use the FAST XFI in my car. Many use BigStuff3. I have tuned both those and several others. Any of them will work.

Bob Letellier · 07-30-2012, 09:20 PM

Thanks for the advice I'll look into it and let you know how it turns out. Appreciate it!

Rich Biebel · 07-30-2012, 09:27 PM

Distributers on those have a bad reputation. Might be worth a look in there.

On my car I used a stock distributer and removed all the optispark stuff.

MSD cap and rotor with a Crank trigger....

Accel Gen VII .....It has way more options than is needed in a racecar but is tunable and I also had a data logger that I added on....

joelster · 07-31-2012, 07:22 AM

In your first post you said the car "runs great" then it starts skipping like the timing is completely off. When an o2 sensor goes bad, the car will fire right up and run normal but after 2-3 minutes when it is warm, it will go into closed loop, and the pcm will look at the o2 data and make changes. If the o2 or o2's are seeing false air, or if they are faulty (they ARE a maintenance item) your car will run horrible. You can diagnose this with a tech2 scanner or similar. If you suspect it to be o2's but don't have access to a scanner, let the car warm up and go into closed loop and run rough for a minute. Then jack the car up and unplug the o2's which will put it back into open loop mode. Most race cars are run in open loop anyways. They use o2 data for datalogging, but not to adjust fuel trims.

FWIW an o2 sensor should be replaced at about ~50,000 miles. Some cars need them replaced sooner. My car went through a set of them in about 15,000 miles. A rich tune will accelerate their failure.

EDIT- as mentioned in post #6 the opti's get a bad reputation, but from what I've seen and experienced, people throw the blame on the opti way more often then what it deserves. There is a great diagnostic method for checking your opti out on shbox.com

Ed Wright · 07-31-2012, 12:18 PM

If you have a crank trigger, I had a pickup do that when it warmed up. I use an MSD. Now I carry a spare. :-) If you don't use a crank trigger you should. The optical sensor in the Optispark doesn't like high RPM. Had a problem with that too until the crank trigger.

nolongerracing · 07-31-2012, 01:29 PM

Bob....you have a PM

Bob Letellier · 08-01-2012, 05:59 PM

Thanks for all the Replies - i'll let you know what the issue turns out to be after I look it over this weekend.

07-30-2012, 08:52 PM	#1
Bob Letellier Junior Member Join Date: Mar 2012 Location: Biddeford, ME Posts: 31 Likes: 2 Liked 22 Times in 2 Posts	LT1 Engine Issues Was hoping to get some advice from a few guys who have Lt1 motors for the Firebirds. Need some recommendations on what computer(s) / programs need to be used to make the car run properly. Car runs great then starts skipping like the timing is completely off... Please contact me here or send me a PM. -- __________________ Bob Letellier www.bobsauto111.com

07-30-2012, 08:56 PM	#2
joelster Member Join Date: Nov 2007 Location: Tonawanda, NY Posts: 106 Likes: 0 Liked 0 Times in 0 Posts	Re: LT1 Engine Issues Are you running the factory pcm? Does it skip when going into closed loop, but run great in open loop?

07-30-2012, 09:01 PM	#3
Bob Letellier Junior Member Join Date: Mar 2012 Location: Biddeford, ME Posts: 31 Likes: 2 Liked 22 Times in 2 Posts	Re: LT1 Engine Issues Running HOLLEY - Seems like the map sensor is sending the wrong signal - but we've replaced it. __________________ Bob Letellier www.bobsauto111.com Last edited by Bob Letellier; 08-01-2012 at 05:57 PM.

07-30-2012, 09:18 PM	#4
Ed Wright Veteran Member Join Date: Mar 2005 Location: Sand Springs, OK Posts: 8,132 Likes: 896 Liked 390 Times in 170 Posts	Re: LT1 Engine Issues I used the factory PCM until I got my old bracket engine needing to go past 7000 RPM. That's about all they will rev. Ran faster than my SS LT1 runs. Should not be doing what you discribe. Don't just throw sensors at it. Learn to diagnose it. As for an aftermarket stand alone I use the FAST XFI in my car. Many use BigStuff3. I have tuned both those and several others. Any of them will work. __________________ Ed Wright 4156 SS/JA

07-30-2012, 09:20 PM	#5
Bob Letellier Junior Member Join Date: Mar 2012 Location: Biddeford, ME Posts: 31 Likes: 2 Liked 22 Times in 2 Posts	Re: LT1 Engine Issues Thanks for the advice I'll look into it and let you know how it turns out. Appreciate it! __________________ Bob Letellier www.bobsauto111.com

07-30-2012, 09:27 PM	#6
Rich Biebel VIP Member Join Date: Jun 2007 Location: Northern New Jersey suburbs Posts: 2,314 Likes: 25 Liked 544 Times in 213 Posts	Re: LT1 Engine Issues Distributers on those have a bad reputation. Might be worth a look in there. On my car I used a stock distributer and removed all the optispark stuff. MSD cap and rotor with a Crank trigger.... Accel Gen VII .....It has way more options than is needed in a racecar but is tunable and I also had a data logger that I added on.... __________________ Rich Biebel S/C 1479 Stock 147R Last edited by Rich Biebel; 07-30-2012 at 09:34 PM.

07-31-2012, 07:22 AM	#7
joelster Member Join Date: Nov 2007 Location: Tonawanda, NY Posts: 106 Likes: 0 Liked 0 Times in 0 Posts	Re: LT1 Engine Issues In your first post you said the car "runs great" then it starts skipping like the timing is completely off. When an o2 sensor goes bad, the car will fire right up and run normal but after 2-3 minutes when it is warm, it will go into closed loop, and the pcm will look at the o2 data and make changes. If the o2 or o2's are seeing false air, or if they are faulty (they ARE a maintenance item) your car will run horrible. You can diagnose this with a tech2 scanner or similar. If you suspect it to be o2's but don't have access to a scanner, let the car warm up and go into closed loop and run rough for a minute. Then jack the car up and unplug the o2's which will put it back into open loop mode. Most race cars are run in open loop anyways. They use o2 data for datalogging, but not to adjust fuel trims. FWIW an o2 sensor should be replaced at about ~50,000 miles. Some cars need them replaced sooner. My car went through a set of them in about 15,000 miles. A rich tune will accelerate their failure. EDIT- as mentioned in post #6 the opti's get a bad reputation, but from what I've seen and experienced, people throw the blame on the opti way more often then what it deserves. There is a great diagnostic method for checking your opti out on shbox.com

07-31-2012, 12:18 PM	#8
Ed Wright Veteran Member Join Date: Mar 2005 Location: Sand Springs, OK Posts: 8,132 Likes: 896 Liked 390 Times in 170 Posts	Re: LT1 Engine Issues If you have a crank trigger, I had a pickup do that when it warmed up. I use an MSD. Now I carry a spare. :-) If you don't use a crank trigger you should. The optical sensor in the Optispark doesn't like high RPM. Had a problem with that too until the crank trigger. __________________ Ed Wright 4156 SS/JA Last edited by Ed Wright; 08-01-2012 at 09:15 PM.

07-31-2012, 01:29 PM	#9
nolongerracing Member Join Date: Oct 2006 Posts: 173 Likes: 2 Liked 72 Times in 27 Posts	Re: LT1 Engine Issues Bob....you have a PM

08-01-2012, 05:59 PM	#10
Bob Letellier Junior Member Join Date: Mar 2012 Location: Biddeford, ME Posts: 31 Likes: 2 Liked 22 Times in 2 Posts	Re: LT1 Engine Issues Thanks for all the Replies - i'll let you know what the issue turns out to be after I look it over this weekend. __________________ Bob Letellier www.bobsauto111.com