92 Suburban 454 code 42 stalls entering closed loop

[dkbiz92]

1992 suburban 454 7.4 has an issue with code 42 and stalling entering closed loop in idle. It has a bunch of new sensors and including new o2 sensor.
Ecm is 7060 with $d8 and refurbished already ( over 3 yrs old with previous owner)

What would keep a 1 wire o2 sensor pinned in voltage?
What would also cause code 42 directly when the truck fires up after cranking.

Truck has 330 on the dash

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heres a video of it having issues.

New (but cheap 6 month old) dizzy
new iac
new map
new cts
new o2 (bosh)
new ignition coil (not wires or clips between)
new intake manifold
new injectors
new egr
new wires (ebay)
new plugs

Im going to walk myself through the code 42 diagnostic tonight and report back. Im a little stumped (and stupid for the cheap parts)
Any advice is good advice. Thanks

 

[dkbiz92]

sorry i forgot.
new fuel pressure rebuild
New fuel pump and easy access for testing because i cut a hole in the floor. Pump holds a solid 11psi while running good and having issues.
Compression testing comes back 125 each cylinder and 110 on #7

My first suspicions are following:
Distributor - its cheap. I replaced the icm chip inside but maybe the pick up coil is just shotty. (200 for new distributor)
Wiring to Distributor - Most wiring has some crimps and i can see some faults here.
02 sensor - 2 sensors have now stayed pinned. Theres a bunch of crimps leaking to the 4x4 and underbelly wiring that maybe was done wrong. Code 59 is present too for low trans temp which i believe is wiring leading to the same place.
Bad Ecm - Its a refurbuished one by previous owner and who knows what he put in it. (100 for a new refurb)

Will be starting the code 42 testing tonight.

 

[docstoy]

You can read all about this stuff if you download service manual for your year truck from sticky thread titled 88-98service manuals, look in fuel and emissions manual

 

[dkbiz92]

i have the manuals.

Ran diagnostic for code 42. Came out as 423 shorted to ground. Ran a dedicated wire for 423 bypass and still got code 42. New distributor going in tomorrow for my own peace of mind.

 

[scott2093]

Great progress.. may as well ask although it seems like you know what you're doing for sure but, when you say ran a dedicated wire, this means you took the other/suspected one out of circuit too?


IAC seems really high..
And tps changed voltage and throttle position out of the blue......

 

[dkbiz92]

I'm not sure what the base numbers are for a 92 because its an off year truck.
Its my first truck diag obd1 so I dont know what im doing tbh

Dedicated wire meaning i tested from ecm harness to bypass connector and saw that was good and repined 4 way connector back to the bypass that goes behind the dizzy and dips low.
Ran that new wire and tried to lose code 42 but code was persistent.

Truck had pinned 1v 02 sensor and code 42,59. Truck would warm and progressively sound worse until it tries to lower idle it starts hunting for rpm and stalls. (same condition as video)

Today went well and worse.
Found the code 59 and o2 wire were crossed (both same shade of purple) from my previous repair and i swapped them. Code 59 is gone and o2 sensor is reading .45v.
I bought a new distributor and decided to swap that. Set base idle to 0 and tried to plug in bypass.
Truck runs god aweful - starts for one second and dies imediately with bypass plugged in. Runs like garbage with bypass unplugged and will eventually start hunting for idle and stall.
BUT the computer no longer has code 42 with new distributor. Maybe the engine isnt running long enough but code 42 isnt set right away. I can force the engine to stay running by keeping rpm at 1500 or 2000 but its not happy and will still try to trim the acceleration out.

Ecm seem to be working due to sensors responding and getting scan data.

I have a spare IAC i can drop in it tomorrow and see if i can find the wiring specs.
Videos to come. I'm tired

Thanks for all the help

 

[scott2093]

Came out as 423 shorted to ground. Ran a dedicated wire for 423 bypass

Dedicated wire meaning i tested from ecm harness to bypass connector and saw that was good and repined 4 way connector back to the bypass that goes behind the dizzy and dips low.
Ran that new wire and tried to lose code 42 but code was persistent.

Dedicated wire meaning i tested from ecm harness to bypass connector and saw that was good and repined 4 way connector back to the bypass that goes behind the dizzy and dips low.
Ran that new wire and tried to lose code 42 but code was persistent.

I guess the wording is getting me confused bc the bypass circuit is 424? tan/blk
423 is EST circuit..wht?

Are you saying you modified the circuit to test?

Also, o2 voltage being pinned is normal (open loop) until the sensor heats up enough to start oscillating between 1v and some low mA and setting closed loop afaik.... .45V is the middle...

 

[docstoy]

With so many splices/zipties I would be concerned about continuity of wiring for several circuits, reason being most likely at some time past wiring harness has possibly been pulled on by drivetrain (wrapped around front driveshaft) if you still have trans. code ck for trans fluid in wiring connection at trans. Need to make sure grounds /hots are good also (voltage/continuity) . What's tps voltage ? If it's low then minimum idle rate may have been changed trying to get idle to stabilize (that's if your tps is non adjustable) , if adjustable still maybe same trying for a sweet spot . Hope it helps and welcome to the forum

 

[dkbiz92]

Truck runs ways better but still has a hunting for idle and stall but its driveable for 20 mins in each direction.

I guess the wording is getting me confused bc the bypass circuit is 424? tan/blk
423 is EST circuit..wht?

Are you saying you modified the circuit to test?

I ran too fast and did the repair on tab/blk wrong wire (for the code 42 diag).
Replacing the distributor cleared code 42 anyway tho so im not sure what went wrong there.

With so many splices/zipties I would be concerned about continuity of wiring for several circuits, reason being most likely at some time past wiring harness has possibly been pulled on by drivetrain (wrapped around front driveshaft) if you still have trans. code ck for trans fluid in wiring connection at trans. Need to make sure grounds /hots are good also (voltage/continuity) . What's tps voltage ? If it's low then minimum idle rate may have been changed trying to get idle to stabilize (that's if your tps is non adjustable) , if adjustable still maybe same trying for a sweet spot . Hope it helps and welcome to the forum

Your right. Theres spices and repairs made everywhere. It has what i assume an ambulance or siren hook ups under the steering column which were also quick connected into place. I personally repaired all the wires leading to the trans and 02 due to melting against exhaust in a bundle. Thats where i crossed the two purple wires for code 59 and pinned 02.

O2 sensor has a normal range through the scanner data

I reset the distributor with est disconnected and turned it till sounded best and ran. Reset IAC steps. and the truck no longer throws any codes. Still will hunt for idle and stall but drives well.

Video incoming.
Thanks for all the help!

 

[dkbiz92]

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Thanks for listening to my truck idle.
Has no cat and open exhaust where cat used to be.
semi hard miss.

any thought would be good.
Much appreciated.