5.3 running rich!

[84bruiser]

So I swapped a 2001 5.3l/4l60e into an 84 c10. The swap was easy! My only problem is that it runs rich. It runs great while its cold but once it hits operating temp. It runs really rich!! I changed the o2s, and maf! I even took my harness off and traced the wires for the o2s just to check everything. Also I am getting no dtc's. I'm wondering if it could be the map sensor?? If anyone has any help or advice its greatly appreciated!

[BR3W CITY]

has it ever been tuned?
or, maybe you have a leak at your exhaust manifolds or on the flange before the o2 so the o2 reads extra air in the fuel mixture, guesses your lean and dumps extra fuel.
just a start.

[84bruiser]

I have sent the computer in to current performance twice now so im guessing its not that, and i have checked for exhaust leaks, and vacum leaks. It only runs like this in closed loop once it has reached operating temp.

[OldCreek]

-Pull your plugs and see if any are wet or anything else.

-Stick a stethoscope on ALL of your injectors and listen if they all make a similar ticking sound of similar decibel. A stuck injector will cause you to run rich. You will see high fuel trims if so.

-Take your ohmmeter and check that all injectors are within specs (a stuck injector can still have normal resistance...ask me how I know.)

-Also, you can get a "noid light" kit from autozone on loan and plug it into each injector wiring harness plug to see if each is firing correctly.

-Checking vacuum was a good idea...you could also spray some starter fluid or carb cleaner around the intake and see if your idle jumps.


I assume you, at the minimum, have an OBDII scanner... I had hptuners to help me diagnose my problem (i.e. reading fuel trim)

More obscure problems can be caused by a bad fuel pressure regulator and even holes in your vacuum lines.

If your engine has been sitting awhile I would guess issues with a stuck injector. I pulled all of mine and flushed them all...I couldn't unstick one and ended up buying a new one. It fixed all my rich/fuel trim problems.

[84bruiser]

Originally Posted by OldCreek

-Pull your plugs and see if any are wet or anything else.

-Stick a stethoscope on ALL of your injectors and listen if they all make a similar ticking sound of similar decibel. A stuck injector will cause you to run rich. You will see high fuel trims if so.

-Take your ohmmeter and check that all injectors are within specs (a stuck injector can still have normal resistance...ask me how I know.)

-Also, you can get a "noid light" kit from autozone on loan and plug it into each injector wiring harness plug to see if each is firing correctly.

-Checking vacuum was a good idea...you could also spray some starter fluid or carb cleaner around the intake and see if your idle jumps.


I assume you, at the minimum, have an OBDII scanner... I had hptuners to help me diagnose my problem (i.e. reading fuel trim)

More obscure problems can be caused by a bad fuel pressure regulator and even holes in your vacuum lines.

If your engine has been sitting awhile I would guess issues with a stuck injector. I pulled all of mine and flushed them all...I couldn't unstick one and ended up buying a new one. It fixed all my rich/fuel trim problems.

Thanks for the advice!! I checked all the injectors before i put them in and they are all working. I also sprayed the carb cleaner around the intake, and the throttle body. I would think if it was something like that it would run rich all the time, but its only running rich once it gets warmed up and to operating temp.

[BR3W CITY]

open loop vs closed loop on the 02 sensors..
Copied from thirdgen.org (ignore the memcal, as I don't think it applies)

Q: What is the difference between 'Open Loop' and 'Closed Loop'?

A: When the engine is first started, and rpm is above 400 rpm, the system goes into 'Open Loop' operation. In 'Open Loop', the ECM will ignore the signal from the Oxygen (O2) sensor and calculate the air/fuel ratio based on inputs from the coolant and MAF sensors, but mostly from a pre-programmed table in the memcal.

The system will stay in 'Open Loop' until the following conditions are met:

1. The O2 sensor has varying voltage output, showing that it is hot enough to operate properly. (This depends on temperature)
2. The coolant sensor is above a specified temperature about 40oC/104oF.
3. A specific amount of time has elapsed after starting the engine.

The specific values for the above conditions vary with different engines and are stored in the mem-cal. When these conditions are met, the system goes into 'Closed Loop' operation. In 'Closed Loop', the ECM will calculate the air/fuel ratio (injector on-time) based on the various sensors but mainly the O2 sensor. This allows the air/fuel ratio to stay very close to 14.7:1.

[truckdude239]

the coolant temp sensor could be bad giving the computer a false reading

[84bruiser]

Originally Posted by truckdude239

the coolant temp sensor could be bad giving the computer a false reading

Do you know a way to test the coolant sensor and see if its working?

[Super73]

A buddy did a motor swap on an MR2. They could not figure out why it was overly rich once in closed loop. WOT it was fine too (going to open loop). I thought about it and told them to swap the precat and after cat O2 wiring haness. Car ran perfect, they put them back wrong, bank 1 was really wired to bank 2 O2 after the cat, its gonna be lean.

If you have a scanner, unplug the rear O2's and and see if it throws a code O2's bank 1 or bank 2. If it throws it for bank 1 instead of 2, well they are swapped.

Just a thought.
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[84bruiser]

Originally Posted by Super73

A buddy did a motor swap on an MR2. They could not figure out why it was overly rich once in closed loop. WOT it was fine too (going to open loop). I thought about it and told them to swap the precat and after cat O2 wiring haness. Car ran perfect, they put them back wrong, bank 1 was really wired to bank 2 O2 after the cat, its gonna be lean.

If you have a scanner, unplug the rear O2's and and see if it throws a code O2's bank 1 or bank 2. If it throws it for bank 1 instead of 2, well they are swapped.

Just a thought.
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Last weekend i actually pulled my harness off and tore it apart haha. I checked all the wires for the o2s and traced each one back to the ecm and they were all going to the right places.

[Super73]

Are you running cats and rear O2's?

If so, try swapping one rear O2 with one front O2. Do the drivers first and see if it changes the rich condition. If it doesn't do the passanger side. The O2's could still be "switching" enough to not throw a code, but not reporting good info.


With out a scanning tool like hptuners or efi live, it might be hard to see ltrim issues bank to bank (drivers to passangers side).


What year pcm is it?
From what vehicle?
Do you know what temp they set OL to CL at? If it is stock I am sure I can find a file and check it for you.

Do you have a wideband?
Is it rich at idle? What about part throttle (above 2% tps)
Have you checked TPS voltages for closed tb vs wot?

Just something else to look at. If tps is higher than 2% but the blade is closed, it might be screwing you up at idle but not part throttle.
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[mooseknuckles]

so how do I test the voltage in the TPS?....and what should I be looking for?

[Super73]

You need a voltage meter. I don't remember which wire it is, but set you meter to dc, slide you positive probe in to the back side of the tps connector, ground the negative probe. Key on, tps voltage should be around .3 with a max of .55 to enter idle circuit. Wot should be closer to 4.3-4.5v.
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