I have a 1993 K3500 7.4l that is running rich at idle.


The motor has about 100K miles on it, so I decided to due a tune up (cap, rotor, plus, wires, fuel filter, air filter, ect.


I failed somg check at idle due to running rich at idle.


I started with running a can of seam foam in the tank and then replaced all emission sensors plus a few others:


all are ac delco: TBI, IAC, TPS, ECT, EGR, EGR control solenoid, fuel filter and converted to a heated 02 sensor


I plugged a snap on ethos scanner and it shows that it won't go into closed loop at idle and 02 stays RICH.


Engine is at temp and idles for 15-20 minutes.


Is there any way to FORCE closed loop?
(I am thinking this will help my pass the smog check)


Any help appreciated!

 

What are your cross counts?

Did you replace the o2? Have you considered trying a heated o2? Your exhaust at idle may simply not be hot enough to get the o2 sensor to react.


-- Joe

 

RMP= 800
02 (mv) 810
INTEGRATR= 128
OPEN/CLOSED= OPEN
EXHAUST OXYGEN= RICH
TPS(V)= 0.42
THROTTLE%= 0
DESIRED IDLE= 750
BLOCK LEARN= 134
02 CROSSCOUNTS= 139
PROM ID= 2061
MAP(kPa)= 29
MAP(V)= 1.00
BARO(kPa)= 100
BARO(V)= 4.84
COOLANT= 194
EGR= 0
ASYNC PW(mS)= 0
SPARK ADV= 20
BATTERY (V)= 13.9


I have a new AC Delco 3 wire heated 02 sensor installed.
(All engine sensors are new AC Delco).


I read somewhere that the computer is programmed to open loop at idle.


Is there a way to forced closed loop at idle?
(it seems all the conditions are meet for closed loop, but it reverts right back to open loop at idle).


Closed loop at idle would be desirable:
1. to pass the CO emissions test at idle
2. to stop wasting gas (I find myself in stop and go traffic for an hour at a time)


Not sure if a custom chip would do the trick or I have read a little about ELB programming, but it seems like a steep learning curve since all I want to do is force closed loop at idle and not any additional tuning.


Any help appreciated!
Thanks!

 

Yup, the 060 ECM has open loop idle. There is some constants "RPM to enter closed loop" that you can adjust in the bin to force closed loop idle.

Truthfully, I don't think your problem is the tune. I think your cat is is junk. Unless you've modified the engine in some way, increased fuel pressure, or something else it should have the same emissions as when it was new. (in regards to hydrocarbons). My guess is the cat isn't working properly.

-- Joe

 

EBL learning curve? We'll turn you into a tuner in less than a day.

 

Can the EBL control his 4l60e transmission?

-- Joe

 

But to answer your question, the 3rd gen did not come with a 4l60e from the factory, and there is no current demand from EBL Flash or EBL-P4 owners to utilize such a feature. If the demand was there though, and I mean more than one or two members inquiring, then I can assure you it would be added, but nobody has been asking for it.

 

I understand that. I'm sure I've eaten more taco's on taco Tuesday than EBL's are in use, so I can understand why Rob wouldn't spend countless hours on that functionality. I was just wondering since the OP has a 1993 truck, wants good fuel economy, has an electronic transmission, and mentioned the EBL. So an EBL wouldn't be for his application.

I think he needs to fix his car, and then if he wants to tinker with the tune just buy an emulator. His ECM is well documented and supported over at gearhead EFI, surely he can find help there.

-- Joe

 

Thanks, Joe!


I will replace the CAT (although I did pass HC at idle and at 2500rpm),
the issue is CO% at idle (0.2% at 2500rpm, and 2.5% at idle).


I thought the CAT reduced HC, but not CO. Is this correct?


It probably needs a new CAT anyway, as it has the original pancake/bead style CAT.


The truck is bone stock, with a fresh tune up (AC Delco pugs, plug wires, cap, and rotor, fuel filter, oil change, and all new sensors (IAC/TPS/EGR/EGR control solenoid/ECT/MAP/vapor canister, heated 02 sensor, and all new vacuum lines).
Also, a remanufactured TBI from Carburetor exchange.


The only sensor I did not replace was the knock sensor, but I am not showing any codes.


I purchased this truck a few years ago for $1600 in a lien sale, and it has already paid for itself in all the towing and hauling I have done.
I didn't mind spending a little on all new sensors and a tune, just for future economy and reliability ( and to pass smog).


After I replace the CAT, I will post the results (hopefully will pass smog).


Thanks for all your responses!.

 

CO is incomplete combusion which could be bad timing, ring failure, leaking valves, or a junk cat.

It's been over a decade since I've delt with SMOG, so bare with me and my memory.



Hrmm.. One thing to consider is the reman throttle body, did it come with injectors? If so were they the right size?

I'd start with cat first.

Good luck.

-- Joe

 

The timing is dead on and the truck runs better than ever with more power after the tune up/new sensors/TBI.


The TBI unit came complete with injectors, IAC, and TPS for 91-93 7.4L


Here is the link: http://www.carb-x.com/domestic-carbu...e/454ci/8-164t


They claim live engine testing and adjustment.
It is supposed to be plug and play ready to go.


I will start with the CAT replacement and go from there....


Thanks!