Hi everyone,
We recently bought a 1994 Camaro race car that has an LT1 in it. I know its been rebuilt, I know its got a bigger throttle body, a factory chevy "Hot Cam and Rocker Arms" whatever they are lol. Everytime we disconnect the battery and start it the idle would change from almost stalling and misfiring to a high idle of 1200-1500rpm. We changed all the plugs, reconnected the o2 Sensors, new ignition wires etc. The last thing we noticed was that the TPS was adjusted all the way to one side (its slotted). Now its in the middle and the idle seems to be a bit better. Im trying to find out exactly what the readings should be and how to set it properly. Any help would be great!

 

The easiest way to adjust the TPS is with a scanner. Set it to ~.65 v at closed throttle. You should only mess with the setting if you can verify the reading (either with a scanner or a multimeter). Observing IAC counts may give some additional insight.

Every time you disconnect the battery the PCM has to relearn. Idle is one of the biggest things affected, so as long as you keep disconnecting power, you'll keep going back to square one and it will never iron itself out. You should also go over it for any possible vacuum leaks.

 

Thanks for the input. Because its a race car the battery disconnects everytime we shut off the main power (rules say so). I think if we set the TPS to the correct spec that will probably help with the problem. Does the car have to be running to set the TPS? We have spent from Nov 2012 trying to go through each and every inch of this car and fixed numerous wiring etc, have re plummed the fuel system including a new Mallory 100gph fuel pump. We are Ford and Mazda guys so all this is still new to us, any help would be greatly appreciated. Also a lot of the engine wiring has been deleted such as the EGR and it wiring.

 

Something to scan it and moniter data will be very helpful in my opinion. Many of the aftermarket throttle bodies create some idle issues as they dont take use of the iac passages. As mentioned above the car must relearn everytime battery power is cut. I believe if you were to scan it and look at data your iac counts would be off. Read up on the throttle body mods and part of your solution may be there given its not a stock tb.(May also be worthwhile to put a ported stock tb on given your power levels dont require the larger 58 tb. Another thought that I am not sure you could do or would be practicle but perhaps could have a seperate power for the pcm memory. That is more of a band aid because your objective will be to get the tune and everything as colse to spot on as you can and thus the pcm memory is not needed to compensate. The iac valve can also cause alot of issues once its bad or something plugging in the tb iac passages. I would attempt to get the tps set as desrcibed and get your iac counts and if its stock or aftermarket tb and report back.


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If you are only looking at the TPS voltage (measured between the blue and black wires), the ignition has to be on, but the engine does not have to be running.

The PCM looks at the voltage on startup and baselines the voltage it sees as 0% throttle position. It has to be between 0.30 - 0.90 Volts to do that. Since a wide range of voltage is acceptable, the stock TPS sensor is not adjustable, and most of the stockers read 0.65V, hence Rob/Shoebox's recommendation.

Once you go to an aftermarket throttle body, it is often necessary to slot the stock sensor to allow it to be adjusted correctly.

 

Thanks again guys really appreciate it. The car does seem to have an Edelbrock throttle body on it, and I have been told that everything is ported and port matched. (I am told but cant confirm) NGK has been a long time sponsor and gave us plugs, wires and o2 sensors, the old o2 sensors had issues. The drivers side had 2 wires that were not even connected and the passenger side was so carboned up there is no way it was functioning. We cleaned the IAC and throttle body with cleaner. We now have an OBDI scar tool and on Sunday we will check and ensure that the o2 sensors, MAF, water temp sensors are all functioning. We will also set the TPS to the specs that you guys have given us. I will report back after we have done that. Too bad none of you are in Toronto Ontario lol

 

Okay we did fond out one big problem today.................The opti-spark has a big crack in the case where the top connector goes into it. Now when I search for a replacement I find that the 93-94 is one and the 95-97 is another? Are they interchangeable? Is a stock replacement one better than an Accel unit? Any help would be greatly appreciated!
btw it still runs okay once the water dried up inside it:

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Camaro LT engines 93 + 94 use a splined opti drive, 95-97 use a pin driven opti. If your timing cover has a very large hole behind the opti, the 95-97 style opti should be used. Small hole in the timing cover uses a 93-94 style. Hope this helps

 

Yes the ac delco or delphi are the choices with the least reported issues. The years do have differences mainly the drive(older ones sline driven and newer have a dowel pin, the newer ones are also vented but I believe you can convert the older to vented without much trouble. Is your crack in the cap(if so you could just change cap and rotor. Sidenote always loctite the rotor screws to avoid a common problem. If you are not aware of shoebox's website he has all kinds of useful stuff and can be linked from his post above. I imagine he has pictures noting the difference in optis as well as how to vent the older unit.


Posted from Camaroz28.com App for Android

 

I assumed (probably wrongly) that the Opti-spark was one unit? The crack is right beside where the harness connects.

 

You can change the cap, you just need a very small inverted torx bit.

 

Do you have to pull apart the whole front of the engine to do that? Water pump etc? If its cracked I would assume that its just the cap as the body on these wouldn't be plastic...................or would it? Just want you all to know how much we appreciate all your help in this strange new world of LT1 engines! The car does pull like a banshee, with the 17X11 on the rear and the BFG R1 tires you can spin them until you get bored even with a misfire!

 

Pretty much have to take the front apart, you ultimately have to get the crank pulley out of the way. I THINK the crank hub can stay..

 

Sighhhhhhhhhhhhhhhhhhhhhhhh lol

 

It's not as bad as it looks, fear not