Looking for some help from the electrical experts. I've been chasing an intermittment REP problem and measured the voltages for TPS1 & 2 on my LS2 TB. The wiring is a direct connect to an LS2 TB plug (e.g. no LS6 wiring harness adapter). TPS 2 are normal and TPS 1 appears to be normal at the extremes (1.35v to 4.4v) but after checking this many times I noticied that at about 80-90% throttle (around 4.0-4.2v) there appears to be a dead spot with the voltage going to 0.000 then back up. I can repeat this going up and down and by moving the TB with the pedal, or by hand. I have a spare LS2 TB. Swapped it - exact same thing. I have a spare TAC. Swapped it - exact same thing. TPS1 consistently goes to zero around 4.0-4.2v, but TPS 2 has no similar voltage drop out. This is momentary and I can't get it to stay at zero. I am using a fairly cheap multi-meter and don't have a scope.

I'm wondering if the PCM sees a delta between TPS1 and 2 and/or commanded throttle position and puts the car in REP. As this isn't a throttle postion I normally dwell in (e.g. either blast through it while accelerating or am below it in part throttle), that may explain why REP is intermittent. I have HP Tuners, but haven't scanned on the track.

I have checked the ground (many times) and disconnected the wiring at the TAC and TB and verified resistance to ground - infinite on all six wires.

I've read many threads on LS2 TB mods and the corresponding problems, but haven't seen any discussion of the voltage not being linear from 0% to 100% throttle, and have read nothing about voltage drop out.

Would appreciate any suggestions anyone has.
Thanks,

 

You guys and your f-ing LS2 TB's...nothing but problems here LOL !!...well your lucky to see the voltage drop to zero because a DVOM is too slow to pick that up...yes, best to have a scope...now when you say you have "infinite resistance" between TB and TAC are you doing a short to ground test ??...try backprobing the dark green 5 volt ref. on TPS1 and see if you are losing 5 volts there as you get to that voltage where the dark blue signal wire drops to 0 volts...if the 5 volt ref drops out so will the signal!!…did you check the low reference ground (purple wire) on TPS 1...disconnect the connector and take 12 volt test light connected to battery positive,,,touch it to the purple wire..it should light !!...PCM is looking for a 7.5% voltage difference between TPS 1 and 2 for less than 1 second...are you seeing a P1221 ??

 

Thanks for the reply. Several different issues in your response and not sure I understand them all, so will try to break them apart.
- I disconnected the wiring to the TAC and the TB and measured resistance to ground - infinite on all wires.
- I checked the 5v reference but not as I was rotating the throttle blade. Will check that and report back tomorrow.
- I checked the low reference to ground using my mutli-meter and it was 29 mv. Will try it with a 12v test light and report back tomorrow.
- As indicated in my initial post, no codes at all for 1st 5 times with REP, P1516 on 6th. No P1221.

 

So are you checking that the wiring between the throttle body and TAC have no breaks in them ??….no opens …if you say you have infinite resistance in a circuit that tells me you have an open circuit. Just trying to understand what you’re saying !!…you should have less than 100 Mv on sensor ground so you should be good.

 

Sorry,
Yes, with wiring plugged into TAC and key in on position, the low voltage reference resistance to ground is 29mv. With the wiring to the TAC and TB disconnected, all six wires resistance to ground is infinite - did this to verify no chaffing or pinch point was causing any problems.

 

No problem !!…yes, that is a short to ground test letting us know that none of the wires were chaffed and touching ground…you disconnect both ends of the circuit you are testing…with ohm meter set on highest resistance scale and then probe the wire on either end of the circuit…with the other ohm meter lead place it on a good ground…battery negative is best…if the ohm meter shows anything other than infinite resistance showing either OL or 1 as my ohm meter shows you have a short to ground !!…video below. Happy Labor Day weekend !!…keep us advised of your progress !!

 

Yep, thanks - that is exactly how I checked all six wires going to the LS2 TB.

Checked the 5v ref line: solid 5.00v through full throttle travel with no drop off I can see on multimeter.

Checked low ref to TPS2 with 12v light tester with plug disconnected from LS2 TB and it lights.

Scope on order, arrives tomorrow.

And thanks. Happy Labor Day Weekend to you as well.

 

Well, got my scope today and not seeing the voltage drop-out on TPS2 with it that I am on my multi-meter. Not 100% confident I have the scope set up correctly as the manual was clearly written by someone for whom English is not their primary language.

 

Scope is just voltage over time…just set it for 20 volts and 2 ms…that should be fine to catch any drop outs !!…what kind of scope ??…if it’s a 2 channel scope I would check the signal wires on both TPS 1 and 2 for dropouts.

 

Thanks. I did figure out how to set the voltage range, but not the sampling rate. Will dig into that. And yes, it is two channel. Good suggestion on checking both.

 

I leave the sample rate on my Pico set a 1 million samples per second…my max rate is 400 million samples per second…that’s fast !!…who makes your scope ??

 

I bought a FNIRSI 1014D. Solved my DMM voltage drop out anomoly, but unfortunately, run out of ideas for the actual problem of the intermittent reduced engine power.

After the scope showed no issues, I wondered if my DMM was the issue so I borrowed a Fluke (mine is a relatively cheap Klein) and it did the same thing but instead of showing 0.00v it showed OL. I was using auto dc volt scale and turns out both DMM have some sort of scale shift at 4.00 volts. When I put both on manual scale, neither showed a problem.

I did find out my tune had some issues from the folks over at HPTuners but no one definitively said the tune issues would cause intermittment REP. Next step to get another tune, then head to the track with a new TB, new TAC, new ignition and new tune and swap them out one at a time.