Hi I am new to this forum so I really hope I am posting this in the right place and am giving enough info to help me out. If I am not please dont bash me just point me in the right direction. Thanks!

First off I have a 97 silver corvette z51 6 speed manual mods as follows prc heads (not sure what stage since they are old and can't look up number) full stainless steel LG exhaust system ls6 intake and tb I believe vararam air lid 113lsa cam can't remember grind ATM spec stage 2+ clutch and alot more but main engine upgrades I listed.

Like title says I am having problems with REP Reduced engine power. Codes are are as follows p0463 p1433 and p1516 I do realize that the first two are fuel codes and my fuel gauge is stuck on zero but I thought I would include them because they all happened at the same time.

Car will start and run in rep mode but I have a horrible idle and very little throttle response at all maybe up to 2k if I floor it. If j try to clear codes while running all three come right back. It idles good for a split second before triggering rep again. Before start up I also get p1120 and p1220 I believe I'll have to check but they don't come back while clearing them when running.

I think I've found the problem but need more insight before dumping money into it plus I'm fed up and want to cruise!!!

I Have a fully charged battery and proper voltage at tac and I've checked all 5vdc references at tac and tps and seem to have good reading as well as signals at tac seem good.

Then I went to check the voltage at the tb motor with key in run position on driver side that operates butterfly and I only have 4-5v!!! This doesn't seem right to me I think I read somewhere that they are supposed to have battery voltage at that connector? Correct me if I'm wrong. Then I checked resistance on the motor itself and it was 0 is this normal? I also check continuity from tac yellow and brown wires to the motor connector and they were good.

Also the car had previously been going into rep but all I had to do to keep going was clear codes then it started happening more and more and then one day nothing!

I checked the #17 fuse in guse box and it had a 25 amp fuse in it instead of a 10!!!! (Previous owner) it looked like the fuse tried to blow cause the top of element had started to melt but something else let loose before the fuse!!!

So my questions are what voltages if any am I supposed to have at the motor? What kind of resistance if any should the throttle body motor have (ohms) if any? And what should all my signal voltages ect be at tac tps app etc from the tac.

I'm trying to figure out if the tac module or the motor is bad.

P.s. brand new battery and I did throw a brand new tps on it.

Sorry for the lengthy post

Any and all help would be greatly appreciated!!!!

 

Or is there possibly another way I can test the tb motor? Take it off and put 12v to it or something?

 

no. it should be 5v reference and then the signal voltage will change with throttle position

 

Ok I'm not sure what 5v reference you are referring to. On my throttle body I have two electrical connectors one with 6 wires for the throttle position sensor(s) and one that has two wires (brown/yellow) for the throttle actuator motor that operates the butterfly. I looked at the wiring schematics and it shows on the 6 wire connector that there are 2 5v ref. Two signal wires and two low reference wires. Those 5volt references check out good with the key in the run position. And as I recall (can't remember what they were or supposed to be) but the other four wires on tps sensor checked out good too. But I'm trying to figure out what the voltage is supposed to be at the other connector (2 wire brown/yellow) on the throttle motor. I've been told that it is a stepper motor that uses reverse polarity to open and close the butterly. Somewhere I read that it is supposed to have 12v on each wire (brown/yellow) with key in on position and then it changes the voltage on correct wire to turn motor open or close. Idk if that's correct or not but if it is I've only got 4 volts at that throttle motor with key on. And with key on I can open/close butterfly with my fingers and i also thought i read somewhere that you shouldn't be able to do that but can't find the post anymore.

 

Attaching a PDF with some connector diagrams and diagnostic fault location procedures for the troubles you are having. Take a look and send me a PM if you need more info.

Bill

 

Update NEW DTCS SHOWING UP: I am now leaning towards the tac module I went back out to the car and followed the diagnostics that Bill gave me in the PDF which all it basically has you do is test the throttle motor harness for continuity to ground b+ and to make sure it isn't shorted to any other wires leading to the tac. Everything checked out good except I couldn't do a couple of the testes because I don't have a tech 2 ATM or that test light they mentioned.

So I jumped back in the car and proceeded to check DTCS again and to my surprise they all cleared and didn't come back. I fired up car and it idled great so I left it alone for a few came back and hit the throttle and wham now I have P1515 p1111 p0113 and the two other fuel sensor codes p0463 and p1433 I also just noticed that my oil pressure is now pegged at 80psi and it says 125psi in the info center. It will idle and rev fine up to 2000 rpm before code sets and goes into rep. Sometimes I get all those codes and sometimes I only get p1515 tried clearing them like 10 times.

I think it's weird now that I get p1515 instead of p1516 when I really didn't change anything. Other codes have to do with iat sensor .

I also checked voltage with key on at the motor harness with it unplugged and it now says 9.3 v on one wire to ground and 4.3 on the other wire then when I plug it into the motor I get 9.3 v on both. Where yesterday I only had 4.3v on each lead at motor.

All these problem almost make me think I have a shorted wire somewhere from when someone put a fuse in the tac fuse place that was 15amps too big. I

I did check wiring harness around back side of engine where everyone says it runs through and shorts on a bracket but I don't have that bracket since my emissions stuff was removed and all my body grounds have been redone previously like everyone has suggested.

Any insight into this issue would be greatly appreciated.

Tomorrow I will check all wiring again as well as all signal voktges at app tps and tb motor and post back findings

Thanks: Sam

 

Sam,
Here is the Diagnostic for P1515 which isn't that much different than the one for P1516.

Make sure you use some electrical contact cleaner at all of the connections as dirty/corroded contacts are a major source of these types of problems. The car is 20 years old so they may need to be cleaned. Also make sure any ground connections for these circuits are clean.

Bill

 

Bill, thank you for all your help. I am going to try to get a scanner tonight and go through all the diagnostics.

I have one question tho. If there was too much amperage put to the #17 tac fuse what would happen? For example it calls for a 10amp fuse and if that kept blowing and someone put a 20amp fuse in there and it worked for a while and then that fuse started blowing so they put a 25amp fuse in it and that worked for a while then it tries to blow the 25amp fuse (there was a spot on the fuse element where it looked like it tried to start melting) but something else "lets loose" before the fuse actually blows what would happen in this scenario?

I ask this because I'm pretty sure that is what the previous owner did because I have only had car a short period of time and there was a 25amo fuse In that slot.

 

Ok I cleaned all connectors plugged everything back in and now I get p1518 only!!! It will not clear! Even with engine off. Also my supply voltage to tac shows ground when key is off then shows power when turned on is this normal? If I pull fuse it shows ground only on feed side with key off if this makes sense? It has continuity to ground of .650 with key off.

Also I can't find anything on the operation of the trottle body motor that controls the butterfly. I'm trying to find out what the voltage is supposed to read at either of the tb motor control wires with key in on position and what kind of voltge is applied to either wire as the pedal is pressed. I read somewhere that each wire is supposed to read 12v and 0ohms to each other with key in on position and pedal not pressed is this correct if so I have a problem there.

 

If you don't have a factory service manual, it would be a good investment.

 

Picking one up today. Would a Haynes manual have all the info I need or should I order one offline?

 

No. They aren't worth the effort it takes to drive and pick one up, let alone paying for one. I wouldn't spend a penny on one. They stopped being useful about 30 years ago.

Bill

 

OK, it isn't that too much amperage is going to the fuse it is that too much amperage is being drawn by what ever circuit the fuse is feeding. That means there is a short to ground somewhere. That could be due to a pinched wire or inside a module. Shorts aren't always dead shorts they can sometimes be high resistance shorts that start to draw too much current and as they draw more lose resistance and draw more. That could explain why the fuse may have been increased several times.

I didn't really look at the schematics when I attached the files to the above posts so I will have to go in and read a little more to see if I can answer your questions. I also sent you a PM.

Bill

 

Have you checked all of the harnesses around the PCM and TAC modules for any damage? One thing that happened quite often with the 97-2002 C5s is the battery would leak and destroy the harnesses sitting below it including the PCM and TAC module harnesses. In 03 GM started using Glass Matt batteries which tended to reduce the chance of a battery leak killing the car, at least as long as the original battery lasted.

Bill

 

I can't find any info on the motor either. There is nothing in the manuals that indicates what the voltage range of the TAC Module should be. I suspect the throttle control motor may be a stepper position motor and the two voltage inputs are switched back and forth and pulsed to step the motor to the position it needs to be in.

Bill

 

Bill,
Thank you for all your help. I m going to try and bypass the tb motor wires from the tac to the tb motor and see if that helps. I'm suspecting that either the tb motor wires from tac to tb are shorted and that why I'm getting 4.5v on one and 9.5v on the other or that the tb itself is shorted internally and causing the tb motor to not receive the proper voltage.

I'm going to look through some more threads and see if I can find where it says that it is supposed to have 12v and 0ohms at those wires in on position if I find that than I think I have found my problem.