[BoatBum10]

I have a '94 E350 van/truck that I'm converting to mass air using a C3W EEC. I have 4 wire HEGOs and a splitter harness to adapt the original single HEGO wiring. Ran right and left signals to appropriate EEC pins, I think it spliced the ground returns together which then ran to pin 49. Fired up and ran but HEGOs were reading unstable, and off 30%+ bank to bank. KAMs were all over the place and thing ran poorly in CL after a few miles, but OL was drivable.

Looking at the fuelinjectedford.com sheet for 89-93 5.0L it shows two separate signal grounds for the HEGOs. I moved my existing pin 49 for the right HEGO gnd to 44, and ran a new and now independent ground to the left from 49. Now I get nothing (0.002v) on both HEGOs by BE logging through my QH. I left the heater wiring as it was.

Hopefully I haven't fried something. Should both HEGOs ground through 49 like I originally had, and should that also be tied to the engine block (I don't think my OEM truck harness tied 49 to ground anywhere). Or is there a cleaner signal gnd to use?

The truck harness is an Auto trans, C3W is for auto, and I'm currently running GUF1.

When I installed the QH last week the circuit board caps looked good at quick glance, but I'll pull it again soon in case that I was part of my unstable readings (and to see if I burned anything up)

[cgrey8]

I've heard that 4-wire HEGOs should be easily converted to 3-wire just as you did by combining the grounds. But I've also heard from others that they just never got 4-wire HEGOs to work like a 3-wire did. So they just wound up abandoning their 4-wire HEGO and replaced with 3-wire HEGOs which worked fine.

Being I've never done this myself, I have no clue if there's some detail you need to be aware of or if the quick-n-fast answer is they simply aren't compatible with these older "3-wire" EECs. If you do get it working, I'll be curious to hear, specifically, what it is that it took for you to get it working...or if you too abandon the 4-wire in favor of 3-wire versions.

[BoatBum10]

I'm going to change back to the previous wiring with the shared gnd and see if they will at least read again. If they do read but are unstable, next step I guess is to track EEC and HEGO grounds.

When logging with BE do you notice if vbat is stable or bounces some? Mine seems to be bouncing around 14.10-14.35 continually. My other values like ECT and TPS seem steady. I'm wondering if this is affecting HEGO readings, or maybe not since other sensors are stable?

[BoatBum10]

So I got lazy, and instead of repinning the EEC I just combined the OEM harness orange ground wire I had to HEGO1 (currently to 44) and my new green ground I had run to HEGO2 (currently 49) and I got HEGO readings.

HEGO2 was much steadier than before, but HEGO1 still read way lean even after warming up. Next to HEGO1 is my old collector mounted one from the SD setup, plugged into that and it read good. Appears the new sensor is bad, so I put my old one from the collector in the Bank1 fitting. Fired up, and now I have similar readings from both HEGO1 and HEGO2

From more research t seems pin 44 doesn't do anything? I'll pull the EEC and check in a couple days. As it stands my new gnd wire to the O2 harness direct from the EEC seems to have solved my unstable reading problem, and a new sensor will resolve my Bank1-Bank2 differences.

I don't have a wideband yet. As is though at least I can finally make this thing drivable. Next payday I'll add a wideband and find out if the HEGOs are reading realistically with the new ground in the 4wire setup.

[decipha]

pin 49 is the hego ground, its usually ran up to the back of the head in the stock wiring harness, i always recommend tapping it at the ecu and tossing it to battery ground, that resolves just about all hego issues

[Cobra VIII]

Im having a very similar problem. I bought a IST mass air conversion. Using the the C3W computer and 4 wire o2s. The O2s are stuck at .002.