1991 RS/SS

What is the recommended tps voltage at idle for a 95 LT1 (OBD 1)? I thought optimum was around .5 v, but have been told it should be around .6 to .7 volts and that the TPI motors liked .5 volts at idle, not LT1's. IIRC, I had problems with surging last time I set my voltage that high at idle. If anybody knows, please let me know. Thanks.

Coach Hawk

.5 works on my car. You mentiones surging at idle, and I see you have a 3300 Edge. higher stall converters, particularly small diameter ones can cause the idle surge because there is not enough "load" on the engine at idle. I believe PCM tuning can help minimise it.

1991 RS/SS

Thanks. I have been chasing a problem with this for a while. It started last year on the 350 LT1 when I swapped from the uber restrictive 3rd Gen wishbone style intake to a cold air setup. I put on a 1LE elbow and a piece of pipe and a cone filter where the charcoal can is supposed to be. When I cracked on the throttle anywhere close to quick (like stepping it to the floor, loaded or unloaded) it would backfire hard through the intake. I changed all my sensors, had programming changed, including timing, and there was no improvement. It only does it when the engine warms up. I installed a slightly more restrictive K&N cold air designed for a 4th Gen and the problem got a little better, but not alot.

It still backfires through the intake sometimes if you step it down at the wrong throttle position, or if you are driving at a normal speed and only open the throttle a little then a little more, then "pop" goes the air filter.

Somebody mentioned this about the TPS and I thought it may be related to my problem. Any help with this would REALLY be appreciated.

Klortho

Has the cap/rotor been changed on the opti? Usually when they start breaking down, I have heard of it doing this as well. Also some local guys have said that running the MSD ignition box and blaster coil seems to kill the caps faster since more voltage is going through it. You may want to look at upgrading the cap/rotor to the MSD pieces.

1991 RS/SS

Do you think it is just the cap and rotor, or the whole distributor? What do you think is the reason that it inly does it with the less restrictive intake and not the wishbone? That is what has confused me since day one.

Thanks

Klortho

Usually when the optical part is going out, it will break up in the higher RPM range. If it's the original opti more than likely the cap/rotor has never been changed since alot of guys thought it was too much of a pain to swap, and GM wanted like 200 bucks + the price of the cap/rotor to replace on those cars. I'm running a standard LT1 elbow with the donkeydick taken off and haven't had a problem yet with this setup.

1991 RS/SS

I have been thinking about replacing atleast the cap and rotor soon, but am debating replacing just the cap/rotor (about $140 for an MSD) or the whole unit. A new GM is about $390. A new MSD is about $450 (when they become available).

Im leaning toward a whole new GM unit. Then the guts are fresh too, not just cap and rotor. I will have my motor back in before the MSD dizzy is available (and I have not been sold on the MSD unit vs. GM yet).

What do you guys think?

1991 RS/SS

Actually I just found out that the 95 - 97 LT1 distributor from GM (new) is only $290. Now Im really leaning toward the GM one. Anybody think this is a bad idea? Im not positive I need one yet, but have been thinking about replacing it for the purpose of avoiding problems, and the motor is out right now. I love MSD stuff, but am not waiting till mid August for their distributor.

Klortho

The MSD unit would be better, and Summit is showing a ship date of the 13th of July for the unit. But we all know how accurate their ship dates are.

However, they are doing two group purchaes on the corvette forum here

http://forums.corvetteforum.com/show....php?t=1424518 and the same group is doing one on LS1tech, so it is possibly going to be really close to being released.

Coach Hawk

Summit has shipped the first batch of MSD Optis already. The first real world tests show that the MSD is a very quality unit, however, it is still new. No one has any real time or miles on them yet. Meanwhile, my all original factory Opti has over 100K on it. The GM unit is tried and true. Be sure that you replace the opti vent harness anytime you put a new Opti in.

1991 RS/SS

Summit was closed today, Ill call them in the morning. If they are a ways out on the MSD (more than a week), I am going to get a new GM one. I cant justify puting a new cap/rotor on an old opti. The GM ones are a good unit, maybe not as good as the MSD, but I can live with it.

Coach, what do you mean by the "opti vent harness" and where do I get one?

Klortho

Basically, two vacuum lines that go down to the vents on the opti. One goes into the elbow and the other hooks into the intake to basically suck clean air through the opti keeping it dry.

1991 RS/SS

Thats what I figured, but just wanted to make sure. Thanks.

1991 RS/SS

I ordered the GM one today in hopes of getting the car running again this weekend. If things dont look hopeful of that, I will return it and get the MSD.

Thanks for your help guys. If anybody has any other suggestions, please let me know.