I have developed a problem with my setup using the GM 87mm truck throttle body. Throwing a P0120 code. However after some testing I am convinced it is a bad TPS on the throttle body. I popped the TPS off and it has corrosion inside on the aluminum a sure sign of water intrusion at some point. I tried another unknown condition used GM throttle body layimg in my shop that came off a GenIV manifold I used DBC on and that one threw a P0220, P1516 and another code I forget the number of but it was obviously a faulty TB in that case where even more codes showed up. Oddly enough if I clear the codes after key on both operate until the key is cycled and it makes the closing TB TPS test sweep. The nasty looking old 8.1L throttle body works code free. I verified the functionality of the adapter harness via all voltage and ohm testing so it is definitely on the throttle body side of things for me. I am going to try the Hitachi ETB0024 with the Hall Effects sensors. Will let you guys know how it turns out. If the Hitachi works it was $96 shipped to my door. Hitachi makes OE TBs for both GM and Nissan so I feel like it has the best chance of being compatible compared to other no name units.

 

Hitachi ETB0024 arrived a while ago, well packaged and undamaged from shipping. Plugged it in and turned the key. One quick snap shut and I had pedal even before clearing the DTC set by the other throttle body messing with it last night. I cleared the DTC and cycled the key to find operates flawlessly on my setup with no DTCs set. I ran it through probably 50 key on tests and alot of pedal operation from idle to WOT and back. I said $96 previously it was actually $99.41 shipped from Amazon from the Hitachi Store and arrived to me in about 15 hours. Cannot beat that. I will throw a video of it working later. Seems to operate nice and smoothly. I will report back if problems develop over time but seems to be an option that works.

 

Odd thing I discovered testing using what should all be matched OE 01-02 8.1L Van pieces including 0411 with factory Van tune, the van pedal, van TAC and even the van 8.1L stock throttle is that displaying everything in HP Tuners position wise for both the pedal and TB; is that one of the pedal values shows 163% at WOT while SAE pedal shows 99.6 for about the laat 1/3 of its travel. It also opens the throttle body to WOT at about 70% pedal. It does it with all what I assumed were the factory parts combined off a running and driving van I pulled apart. No wonder that 8.1L van responded like a rocketship compared to the GMT800 8.1s I have driven. 70% pedal was 100% throttle opening. The running driving 8.1L never went into reduced power when I drove it and burned the rear tires off it. That van itself was hit in the side, rusty and not worth repairing. Pulled the driveline for another project and parted out what was good on it keeping what I needed for my 97 van to 1-ton and hydroboost swap it. Actually has me thinking maybe that 300K mile van had a 6.5L Diesel pedal swapped on it at some point as it looks identical but has a different part number. Have a buddy that swaps older C10s to LQ4s and LQ9s using the 6.5L GMT400 pedal as it bolts on all the older C10 firewalls in place of the stock pedal bracket and pedal. With the earlier donors it has never been an issue but he had an 06-07 donor 6.0L that kept going into REP with that setup and it also had pedal values over 160%. I thought it may have been an issue with the 06-07 TAC module specifically but now I wonder if some TAC modules just do not like the 6.5L pedal and perhaps that is what is on mine as well unknowingly. I know where to look though now if it starts throwing the REP code. I will not have a REP light unless I find a wiring diagram of a pre-serial interface cluster that had a physical wired light such as maybe the GMT400 3500HD or the 01-02 van. The clusters used in both have a Service Throttle Soon light that was used with the Diesel but require a physical output to drive it. Kind of makes me wonder if the 8.1s in those vehicles that had the old analong clusters used that indicator as well. Hopefully get my hands on a wiring diagram from one at some point.

 

Throttle Body Testing

 

Update: I installed the TAC module (#12574221) and made the pigtail adapter for my truck last night. Performed a visual throttle body function check before starting the truck. Everything works great and no codes. Super easy job, and not having an x-link on the truck anymore is awesome.

 

Mine has test run several times with a correctly functioning TB. I did some tuning to the BRAF and have since corrected the injector data for running at 43.5 psi vs 58 psi with the new fuel rail matching the Indmar intake. I always run MAF only for startup and initial tuning, use math amd filtering to datalog the VE to rough in a VE table using the same calculation GM uses. I need to finish up some wiring, wire in the correct MAP sensor pigtail, get the coils mounted adequately and some of the van specific stuff like dipstick tubes re-installed, get the cooling fans setup and get it back on the road to dial it in the rest of the way. I changed the cam/lifters, intake and converted from DBC and a distributor to DBW and LS 24x coil near plug on my SBC setup. DBW free'd up a lot of space in a very compact and tight engine bay. The valvetrain definitely valvetrains, wide body 1.7 full roller rockers with guideplates and hardened pushrods. The only codes were for the MAP sensor and the alternator regulator I forgot to plug back in. PCM controlling the AD244 on it. The 4,000 rpm Park/Neutral rev limiter is still in place and I really do not see the need to raise or remove it. The project involve removing the looming on almost the entire engine bay harness. All the DBC and old distributor based ignition wiring and some other stuff no longer used have been removed. I will be running the fuel level through the PCM as well to prevent the 0411 from hanging in the low-octane spark tables in the event of a bad tank of fuel.

 

I finally got around to finishing some stuff and really working on dialing in my engine setup. I have the VE table in good shape near idle and had set the BRAF correctly via logging a few startups and warmups. What I found for my setup the ETB Scalar setting of 0.0330 was way off. I logged Desired Idle Air Flow vs Dynamic Air Flow. The Idle Desired Air Flow was 2x the Dynamic airflow. What I found is that the ETB Scalar was far too low. I ended up raising it and noticed a direct correlation with the Desired Idle Air Flow value. As I increased the ETB Scalar the Desired Air Flow value decreased. Once I found that correlation, I then took the Desired Air Flow and divided it by the Dynamic Airflow. With the ETB Scalar set at 0.0330 my Desired idle Air Flow was previously right at double. I took the value from that and multiplied it by the ETB Scalar. I then test ran the engine with a new ETB Scalar of 0.0660. The engine is much happier now and returns to idle properly without dipping, cold and hot starts are nearly perfect and the throttle body correctly responds to load at idle now. I can literally reach in the window, fire the thing up with no startup weirdness. Idles up a bit, then tapers off to the normal idle speed seemlessly smoothly. Ignore the belt squeal on the alternator, I am waiting on a p/s pump replacement to arrive and have a short belt bypassing the P/S and AC (L31 Vortec based small block) at the moment and the alternator does not quite have enough belt wrap.

 

Got a part number for these?
Are they readily available?
Do they like being sucked on or blown through? (Boost)

REP has plagued my Tahoe for years and I’m on the fence about this or your suggestion of an 87mm with 8 pin.

 

Unfortunately, I can't remember where I put the damn thing....

I am currently focused on a 14 bolt build that I have been trying to complete.

 

Well Grumpy cat never sent me the throttle body part number I requested (sneaky suspicion his 14b build isn’t complete ether).

So I ordered the parts for this swap and it’s working so far. My inaugural test run was just a few miles to the liqah store in a severe thunderstorm and I survived with no REP, got me a 40oz for the ride back too. Anyway, my REP issues had been on going for 5+ years using a total of two different x- links, three throttle bodies, and two throttle modulator boxes over the years. Recently it had been so bad I couldn’t go a tank of gas without pulling over to unplug and replug the throttle body 2-3 times, with another half a dozen code clearings in between that. I’m super hopeful this is the final solution Hitler always promised us.

Currently running it with an OEM ls2 silver blade.
I will update if I’m happy for sad as time progresses. Big supporter of this becoming a sticky.