Tech1 results on TPS test: 0% throttle=.60 volts....100% throttle=4-4.06 volts. Is this right? Am I getting full throttle...seems like I read 5 or 6 volts for full throttle.

 

On your 92 that is probably just fine. Unlike the TPI cars the LT1 TPS sensor isn't really all that adjustable. You might get some by loosening the screws and trying, but not much.

The good thing is that the TPS is self zeroing, when you turn the key on as long as the TPS is within a certain voltage range it will read this a 0 and calibrate itself from that. As long as your tech 1 is reading 0 when you're off the pedal and 100% when it's on the floor then you don't have to worry about the actual voltage is.

This does bring up a very important point. This car is fuel injected and you should never have to give it any pedal while trying to start it. If your pedal is out of range when you turn the key ON you'll have screwed up TPS readings and the car will likely run like crap and set a code. It will go away if you shut it down and start it back though.

I had a little bit of trouble with my Holley throttle body with this. The throttle stop screw was too far back and the throttle could actually move back further than normal if you let off of it abruptdly. What would happen is that when I would park the car I would have eased off the gas because I hadn't been WOT lately and the blades would close so far. When I started the car it read this point as the 0. Everything would work just fine until I would blip the throttle really hard and it would close farther, going "beyond 0" The computer didn't know what to make of this and it would set a code, idle high, etc. I eventually figured it out and it's been working great since. :cheers:

 

The info about needing 4.5 or more volts to hit 100% TPS is for L98 engines.

LT1's will trigger 100% TPS position in the PCM with as little as 3.84 volts from the TPS.

I have Datamaster (scanner software used with laptop for OBDI GM cars) and checked this out: My 95's PCM reads 3.84 volts from the TPS as 100% TPS position. Assume all LT1's would be the same, reading voltage of around 3.84v as 100% TPS.


[Modified by Lone Ranger, 4:27 PM 3/30/2004]

 

Also, I've been messing with Tunercat tuning software. The LT1 will under certain load conditions, switch to the PE tables (Power Enrichment) with as little as 60.2% TPS position (60.2% TPS position will trigger WOT condition under 3200 rpm). It has two tables it uses: "%TPS Threshold for WOT vs RPM (High cool)", and "%TPS Threshold for WOT vs RPM (Low cool)".

Low cool table is used when coolant temp is below a certain threshold temp number and high cool table is used when coolant temp is above the same threshold number. The 60.2% value for under 3200 rpm is used in the Low Cool table, for example. The percentage TPS values are much lower in the High cool table.

The above is one reason those "Throttle Performance Switches" that Mid America, Eckler's, and others sell which claim to 'trigger WOT 100% TPS when the gas is only pressed 2/3 down (66% TPS) are a complete waste of $$$$ on an LT1.


[Modified by Lone Ranger, 4:45 PM 3/30/2004]

 

:iagree:

Actually on an LT1/4 if the gas pedal is depressed a little bit with the key in the "on" position, it will trigger an IAC (Idle Air Control) reset. The procedure for resetting the IAC position is to turn key to 'on' but do not crank, depress loud pedal slightly, then start motor, remove foot from pedal once engine starts and let run 5 seconds, shut motor off, wait 10 seconds, restart motor (foot off loud pedal) and listen for normal idle. You can usually hear the IAC pintle emit a relatively loud "clank" sound when you depress gas pedal w/ key on. If you hear that you should probably go ahead and finish the aforementioned IAC reset procedure because you just initiated it... :yesnod:

Sorry for all the posts, I'll shut up for while :leaving:


[Modified by Lone Ranger, 4:54 PM 3/30/2004]

 

NO DON'T SHUT UP. I am really in need of some education here. It's reassuring to know I'm getting WOT and that everything is ok there. I've posted a couple of times earlier about not being able to make the IAC idle up with my TECH1...think I'm doing it right...but god knows.!!

Right this moment as we speak, it seems to be fine, but I think I have an intermittent problem somewhere...because it will start not idling on startup and eventually gain about 650rpm after warm up. I've tried figuring out what's wrong and have just about decided I either have an intermittent bad IAC OR a bad connector. I'm thinking of replacing both as a precaution, but hate to spend money needlessly. Is there a good way to test the IAC? I have cleaned in and the TB...all new gaskets and such.

 

I'm not aware of a test procedure for the IAC, and I don't beleive the IAC throws a code when defective. I don't see a code in the list for IAC, but my code list is for 94 and 95 LT1. probably just replacing it might be the least hassle.

 

I'm having a problem with mine today where for some reason the TPS must not be reporting back properly and while I'm driving it triggers it into that "limp mode" where it shuts off ASR and sets the SERVICE ASR and ASR OFF lights to on and then doesn't shift into 2nd until at least 3,500 RPM. If I shut the car off and then turn it back on it's fine for a couple of minutes/miles but then sets the code again. This happened a few years ago right after I put the 383 in but soon went away.

Think I should replace the TPS? The car has 120k on it now.

 

If its the orig TPS, then I'd say yes. :yesnod: