TPS voltage goes down as throttle is opened

[Guest]

I'm back at the 3900 swap and have code59 wired up and apparently ready to run. I noticed on datalog link up that my TPS voltage is at 100% and 4 volts with the throttle closed and declines to about 2.3volts as it is opened. I checked the terminals against the wiring diagram and they are correct. This is on the Northstar throttlebody which worked properly with the 8F code the engine was previously wired for.

The IAC count is 138 and red, not sure how to interpret the counts yet. I did try to start the engine and it ran for about 3 seconds twice but that was before I tried to datalog earlier in the day. The heated O2 sensor is also reading 8.8 mV, not sure how it will change once the engine is started with the emulator connected.

[Superdave]

measure it with a multimeter.. don't trust the log for things like that. It's easy enough to mess up the factor in the .ads.

[Joseph Upson]

measure it with a multimeter.. don't trust the log for things like that. It's easy enough to mess up the factor in the .ads.

List the multimeter check proceedure. I just looked in a GM Training manual that I have and it shows a different assignment than the 749 SY/TY wiring diagram I have shows for TPS connection. The Beretta 3.1 diagram as well as the TGP diagram both match the GM manual so the SY/TY diagram is wrong by listing terminal "B" as the TPS signal input. I'm surprised the engine started and ran at all considering it should have been in clear flood mode with the TPS signaling 100%.

[Superdave]

lol, that'll do it.

[3XTurboAgain]

my car does the same thing... i checked the TPS wiring thinking i mixed them up but they seems right... im logging the car in a few minutes... you think i could definately tell from the log what is going on??? Something is preventing the rough tune... it shouldnt run this bad im thinking either messed up TPS wiring, or pushrods too short = crazy knock count. Well see how my first log goes. Sorry to hijack!

[Scott_68B]

Joseph,

Sorry to go off topic but are you running a DIS and did you have to do anything code59 wise to get it working?

Thanks!

-- Scott

[Joseph Upson]

my car does the same thing... i checked the TPS wiring thinking i mixed them up but they seems right... im logging the car in a few minutes... you think i could definately tell from the log what is going on??? Something is preventing the rough tune... it shouldnt run this bad im thinking either messed up TPS wiring, or pushrods too short = crazy knock count. Well see how my first log goes. Sorry to hijack!

The wiring is TPS specific, it was correct for the Syclone & Ty TPS sensor but not for the round TPS sensor found on the fwd engines. The ALDL connection to monitor sensor readings is how I found the problem. The engine didn't run smooth at all and I suspect I had some detonation also with the iron head spark table in the program. I haven't attempted a start since to test the changes, waiting to complete installing the exhaust and intake plumbing.

My base timing for the 3900 with the TGP code was adjusted up from what the 3.1 ran despite the higher compression ratio.

[ForcedFirebird]

Joseph,

Sorry to go off topic but are you running a DIS and did you have to do anything code59 wise to get it working?

Thanks!

-- Scott

The ECM runs DIS the same way it does a distributor

In fact a stock '7730 ECM even will run DIS (and the stock fbody .bin is $88 )

[Joseph Upson]

Joseph,

Sorry to go off topic but are you running a DIS and did you have to do anything code59 wise to get it working?

Thanks!

-- Scott

Forcedfirebird is correct except for one important note with DIS vs. distributor; the base timing is different. It's around 0 to 12 degrees for distributor engines but for DIS particularly in Code59 it needs to be set at ~60 degrees in the chip.

[ForcedFirebird]

Forcedfirebird is correct except for one important note with DIS vs. distributor; the base timing is different. It's around 0 to 12 degrees for distributor engines but for DIS particularly in Code59 it needs to be set at ~60 degrees in the chip.

Right, but that's a setting you have to do on any code, no?

[Joseph Upson]

Right, but that's a setting you have to do on any code, no?

I believe it's pretty standard range wise. The crank sensor is on the right side of the engine and I believe that's why there is such an extreme difference, otherwise from one iron head motor to the next the base timing is usually pretty close, 6 BTDC in the 80s TPI IROC and 10-12 for the 2.8L, however that kind of base timing in the fwd aluminum head motor might result in a no start or pretty poor running engine not to mention the spark table changes that would be made if you weren't aware of that..

[ForcedFirebird]

Ah, so true

I meant to say "when converting to DIS" in my previous post, but now this brings up another question. Anybody got a definition file for the $88? I read my stock chip and Ben said it was the same as the FWD $88...

[Joseph Upson]

Ah, so true

I meant to say "when converting to DIS" in my previous post, but now this brings up another question. Anybody got a definition file for the $88? I read my stock chip and Ben said it was the same as the FWD $88...

Go to Moates.net and access their database, they have a common access code that is posted in the instructions on accessing the info. I haven't been there in a while but they have several bins available. I'll check my stash to as I downloaded several bins years ago when they were available before the efi site went down after the owner passed away I believe.

Just checked, I have quite a stash, PM me an email address and I'll send the file.