Well this stems from two years ago. I repinned my 165 to 749. I've had an over rich condition ever since I can remember.

I just swapped out my 30's for Low Z 65 pph injectors. Well over rich was obvious, int was 40, could have been lower if I let it in constants. So I got fed up tinkering with the tune. Decided to prove evey wire, pin and sensor on the engine. AHH HAA, I had D1 and B5 swapped. Funny thing, no codes, normal readings. Haven't figured out that part yet, but after swapping the pins to the correct places, int & blm were in a tuneable range.

Now I tried to figure out how I did that, it looks easy to do. On the 165 ecm D1 and D2 are the two pins that go to 749 D1 and B5, I must have had them both in hand and switched them.

So if any repinned 165's run rich in a 749 ecm check those pins.

I still can't figure out why it ran decent and no codes. It defintely runs better wired correctly.

 

Would you mind saving me and others some time and post what those pins are for?
Thanks

 

Yeah, the grounds need to be correct. I just did a 165 to 730/749 swap. The Mike Davis swap list is not entirely correct for the TPS, MAT, MAP, etc. reference grounds. You have to cut & solder the grounds/refs so that they go with the correct signal. I did it after looking at the schematics & doing ohm checks to see how the factory 165 ECM wiring really was. It took about 3hrs extra but I know the grounds are correct. Most people skip over that. They think all black wires are "just grounds".

 

Sorry, D1 is system gound-(input) and B5(749) or D2(165) is TPS, CTS, ground-(output from ecm).

Maybe someone with a bench could swap those pins and see what happens to fuel trim.

I bet I'm not the only one who has done this. Black=ground, not exactly.

 

You might even try doing a continuity test brom B5 to TPS, CTS. You will be surprised with the results.

 

BTDT, on the bench, with only 3-4" long leads, and *perfect* grounds, you won't see the *error* that a given car would generate.

It's all about attention to detail. The more you play with this stuff, you'll see what the difference is between close, and correct. You'll never believe the arguements, and attitudes some folks have about close being good enough, surprisingly, it's the ones that refuse to take the time to get things correct that like to argue the point....

 

Bench results are great for functionality testing. They are not good at physical testing. A vehicle electrical system is a "harsh environment" due to the large electrical current impulses.

What seems like a good ground on the bench may behave differently in a vehicle. CTS & TPS are low current signals and grounds. So electrically there is always a low voltage difference along the wire. By connecting a large current ground to a precision input you mess things up because the large current causes a voltage rise/drop along the wire. The ground ref. that is suppose to be zero now has a voltage on it and adds/subracts to the "real" signal to be measured.

EDIT - basically, saying same info Grumpy said, but giving a little more detail.

 

I just did the '746 (TBI) to '730 (SD) conversion and my car runs rich in closed loop no matter where I tune it? What are those wires that you had crossed (D1 and B5)? Was it sensor ground (B5) and ECM Ground (D1)? I need to cross reference what you did to my wiring chart. Thanks!!!!

 

Yes, I crossed ecm ground input D1 with sensor ground output B5. Do you have any codes? Scan data? I assume you installed a manifold air temp sensor.

 

Yes, I installed a MAT sensor, but I'm not getting any codes. I've ordered another ECM and will check my wiring again. Hopefully, I'll find something.

 

Guess what, I got it running a ton better now. Here's what I did.
1) What I found out is that since I have a larger plenum that what stock was, I had to add a TON to the VE table "Enrich Accel Delta TPS Pulse Width Factor Vs. Temp" at hotter temperatures. THAT GOT RID OF THE POPPING AND BACKFIRING! Basically, the car was leaning out at quick acceleration and that took care of it.

2) Then I started on the VE tables. Once I got the LT (Long Term) down, I found some other weak points in the table at different RPM's. I popped and backfired between 1600-2200 RPM, so I adjusted the VE table for those ranges.

 

excuse the hijack and my newbness but what is INT? I found INT bias at idle in my .bin... my 355 won't idle because its too rich could INT bias be the answer?

 

I don't see how it would work.. D1 is how the ECM gets it's ground. B5 is how the sensors get theres. Maybe the ECM doesn't have any diods or something? Weird. I'll have to look at mine later.

But you would think the sensors would be reading way off.

-- Joe