Computer O2 Harness Question

[RCKSTR]

Hi Guys,

I have an 88 mustang 5.0, T5, GT40P heads, andys springs, e303 cam, typhoon intake, 70mm BBK throttle body, EGR has all been deleted, long tube headers, 24# injectors, C&L mass air with blue sample tube, Powerdyne BD11A blower, C3W1 computer..

My issue is this, the engine was built by me, this year, its all brand new from pan to intake. Since assembly I have not driven the car, I have started it but I cant get it to idle. It surges badly. It also runs so rich it burns your eyes.I have verified no vacuum leaks (12-15 inches vacuum), set the TPS voltage to .95 at idle, I did grind a small channel into the AIC between the ports as I read the e303 is too much lump and the IAC cant compensate fast enough. I read that would fix the surge, it didnt. I set the idle with the IAC disconnected and the spout out of the distributor, and it will idle around 600, but eventually stall or start surging.

My KOEO codes are 81 and 82 (emissions control). Im ok with that. However,
My KOER coes are 21, 41, 91, 33.

21- coolant temp out of range, may be part of why so rich
41- o2 sensor signal
91- Oxygen sensor problem, fuel pressure out of specified range or injectors out of balance
33- Canister or EGR valve not operating properly

33 isnt so concerning right now, but 41 and 91 are. I did read somewhere about having to repin the o2 harness? I believe my 88 is a late 88 and it does have the extra loop wire. Should that be pinned from 1-6 for auto? Have I toasted my auto ecm or can it be repinned to work correctly? Is this even my problem or am I looking in the wrong area. The orange ground wire is grounded to bellhousing bolt, not the head, but that should be a good ground.

I guess my question is, will my stock 88 t5 harness work with the C3W1 auto ecm ?

Thanks for taking the time to read and any input you have on my problem. Id like to get it running right so it can go to the body shop this winter.

 

[Mustang5L5]

The loop in the o2 harness is not for the o2 sensors. It's actually how ford ran the wiring for the nuetral circuit. Just a jumper here, doesn't run to the o2s

I'd actually trouble shoot the codes here. Wity two o2 codes, you may have a vacuum or exhaust leak causing them. I would definitely address the code 21 ASAP though.

With the auto computer. I believe you can leave your wiring as is. If you change to a manual computer, you need to repin the o2 harness


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[RCKSTR]

Thank you mustang5l5 for clarifying the o2 loop! I'm hoping the code 21 is just a bad coolant temp switch. I forgot to add the o2's are both brand new, any idea why id be getting codes on them? Someone told me the code 91 is from running lean (like vacuum leak) but it's pig rich

 

[RCKSTR]

I found this on another forum, any ideas why this person said you will have surging issues right off the hop?

"I have a 89 5.0 out of a grand marquee. I am wanting to put a t-18 behind it. Is there going to be problems with the eec without the auto trans and cruise control. ?"

"It will run, but you will have a surging idle and timing will be slightly different, but it will still operate. You can run it to get you on the road, but look for an A9L soon...

SVT"

I am going to go through the whole "surging idle checklist", I just dont want to waste my time if the C3W1 ECM is never going to play nice.

 

[RCKSTR]

Car doesnt have any smog equipment or cats either. I will check for voltage at the o2 sensors and report back. 41 and 91 indicate a lean condition so the ECM is constantly enriching the mixture, going to be really hard to get a proper idle with it constantly dumping fuel

 

[General karthief]

I don't think that motor is an HO motor. Low compression pistons, HO cam will make the valves nip the pistons, it will sound like a sewing machine, ask me how I know. Firing order will confirm.

 

[RCKSTR]

Definitely an HO motor. Its the original block, original rotating assembly, original TRD pistons. e303 cam.

 

[General karthief]

Ok I stand corrected.

 

[RCKSTR]

I appreciate your input! Just not the case with this issue. My code 21 may be because the car wasnt fully warmed up. Hard to warm up a car in a shop when its so rich it burns your eyes and wont idle

 

[Mustang5L5]

Address code 21 first. Erase codes, rerun.

Bad ect could contribute to bad fuel mix. Take care of one thing at a time then go to next


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[RCKSTR]

I agree. Thank you. I will check for voltage at the o2's today and warm it up. Clear the codes and see what I get.

 

[jrichker]

Just for reference since you seem to be on the right track...


Code 41 or 91. Or 43 Three digit code 172 or 176 - O2 sensor indicates system lean. Look for a vacuum leak or failing O2 sensor.

Revised 11-Jan-2015 to add check for fuel pressure out of range

Code 41 is the passenger side sensor, as viewed from the driver's seat.
Code 91 is the driver side sensor, as viewed from the driver's seat.

Code 172 is the passenger side sensor as viewed from the driver's seat.
Code 176 is the driver side sensor, as viewed from the driver's seat.

Code 43 is not side specific according to the Probst Ford Fuel injection book.

The computer sees a lean mixture signal coming from the O2 sensors and tries to compensate by adding more fuel. Many times the end result is an engine that runs pig rich and stinks of unburned fuel.

The following is a Quote from Charles O. Probst, Ford fuel Injection & Electronic Engine control:
"When the mixture is lean, the exhaust gas has oxygen, about the same amount as the ambient air. So the sensor will generate less than 400 Millivolts. Remember lean = less voltage.

When the mixture is rich, there's less oxygen in the exhaust than in the ambient air , so voltage is generated between the two sides of the tip. The voltage is greater than 600 millivolts. Remember rich = more voltage.

Here's a tip: the newer the sensor, the more the voltage changes, swinging from as low as 0.1 volt to as much as 0.9 volt. As an oxygen sensor ages, the voltage changes get smaller and slower - the voltage change lags behind the change in exhaust gas oxygen.

Because the oxygen sensor generates its own voltage, never apply voltage and never measure resistance of the sensor circuit. To measure voltage signals, use an analog voltmeter with a high input impedance, at least 10 megohms. Remember, a digital voltmeter will average a changing voltage." End Quote

Testing the O2 sensors 87-93 5.0 Mustangs
Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear.

Disconnect the O2 sensor from the harness and use the body side O2 sensor harness as the starting point for testing. Do not measure the resistance of the O2 sensor , you may damage it. Resistance measurements for the O2 sensor harness are made with one meter lead on the O2 sensor harness and the other meter lead on the computer wire or pin for the O2 sensor.

Backside view of the computer wiring connector:

87-90 5.0 Mustangs:
Computer pin 43 Dark blue/Lt green – LH O2 sensor
Computer pin 29 Dark Green/Pink – RH O2 sensor
The computer pins are 29 (L\RH O2 with a dark green/pink wire) and 43 (LH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.

91-93 5.0 Mustangs:
Computer pin 43 Red/Black – LH O2 sensor
Computer pin 29 Gray/Lt blue – RH O2 sensor
The computer pins are 29 (LH O2 with a Gray/Lt blue wire) and 43 (RH O2 with a Red/Black wire). Use the ground next to the computer to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.


Testing the O2 sensors 94-95 5.0 Mustangs
Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 29 (LH O2 with a red/black wire) and 27 (RH O2 with a gray/lt blue wire). Use pin 32 (gray/red wire) to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.


Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter. Do not attempt to measure the resistance of the O2 sensors, it may damage them.

Testing the O2 sensor wiring harness
Most of the common multimeters have a resistance scale. Be sure the O2 sensors are disconnected and measure the resistance from the O2 sensor body harness to the pins on the computer. Using the Low Ohms range (usually 200 Ohms) you should see less than 1.5 Ohms.

87-90 5.0 Mustangs:
Computer pin 43 Dark blue/Lt green – LH O2 sensor
Computer pin 29 Dark Green/Pink – RH O2 sensor
Disconnect the connector from the O2 sensor and measure the resistance:
From the Dark blue/Lt green wire in the LH O2 sensor harness and the Dark blue/Lt green wire on the computer pin 43
From the Dark Green/Pink wire on the RH Os sensor harness and the Dark Green/Pink wire on the computer pin 29

91-93 5.0 Mustangs:
Computer pin 43 Red/Black – LH O2 sensor
Computer pin 29 Gray/Lt blue – RH O2 sensor
Disconnect the connector from the O2 sensor and measure the resistance:
From the Red/Black wire in the LH O2 sensor harness and the Red/Black wire on the computer pin 43
From the Dark Green/Pink Gray/Lt blue wire on the RH Os sensor harness and the Gray/Lt blue wire on the computer pin 29

94-95 5.0 Mustangs:
Computer pin 29 Red/Black – LH O2 sensor
Computer pin 27 Gray/Lt blue – RH O2 sensor
From the Red/Black wire in the LH O2 sensor harness and the Red/Black wire on the computer pin 29
From the Dark Green/Pink Gray/Lt blue wire on the RH Os sensor harness and the Gray/Lt blue wire on the computer pin 27

There is a connector between the body harness and the O2 sensor harness. Make sure the connectors are mated together, the contacts and wiring are not damaged and the contacts are clean and not coated with oil.

The O2 sensor ground (orange wire with a ring terminal on it) is in the wiring harness for the fuel injection wiring. I grounded mine to one of the intake manifold bolts

Check the fuel pressure – the fuel pressure is 37-41 PSI with the vacuum disconnected and the engine idling. Fuel pressure out of range can cause the 41 & 91 codes together. It will not cause a single code, only both codes together.

Make sure you have the proper 3 wire O2 sensors. Only the 4 cylinder cars used a 4 wire sensor, which is not compatible with the V8 wiring harness.

Replace the O2 sensors in pairs if replacement is indicated. If one is weak or bad, the other one probably isn't far behind.

Code 41 can also be due to carbon plugging the driver’s side Thermactor air crossover tube on the back of the engine. The tube fills up with carbon and does not pass air to the driver’s side head ports. This puts an excess amount of air in the passenger side exhaust and can set the code 41. Remove the tube and clean it out so that both sides get good airflow: this may be more difficult than it sounds. You need something like a mini rotor-rooter to do the job because of the curves in the tube. Something like the outer spiral jacket of a flexible push-pull cable may be the thing that does the trick.

If you get only code 41 and have changed the sensor, look for vacuum leaks. This is especially true if you are having idle problems. The small plastic tubing is very brittle after many years of the heating it receives. Replace the tubing and check the PVC and the hoses connected to it.

 

[RCKSTR]

Just a quick update. I cleared the codes, warmed the car up and no longer have code 21, or 41, or 91. I now have

42- Fuel mixture rich
92- Fuel mixture rich, fuel pressure high
33- Canister or EGR valve not operating properly

I have 15 hg of vacuum at idle, but 38 psi fuel pressure with vacuum attached, 46 psi without. I believe around 30 with vacuum attached is normal? Im going to order an adjustable FPR and bring the fuel pressure down.

 

[TOOLOW91]

Get an Adjustable FPR. Bring the FP down with the vac off to 40-42 psi.

e303 cams are known to be hit or miss with the ecu and they are not the best cam in a boosted app either. You need to up the idle as well to around 780-850 ish with that cam if it were me with the iac disconnect. Once you set the base idle then double check the TPS is set correctly. Re connect the iac and do a base idle reset . I have a cam way bigger then a e 303 and my car idles fine.

That mass air meter is garbage. I had one. Get yourself a Pro m meter as soon as possible.

What fuel pump is in it?

What do you plan on tuning the car with ? Are you using a FMU? I know those blowers dont make crazy pressure but id want to see a bigger injector on the car if it were me .

 

[RCKSTR]

Ordered an adjustable FPR today. I want to hear the e303's lopey idle, thats why I chose the cam. So far 800 is too high, sounds like stock cam, hoping once I get the fuel pressure issued solved it will help with the idle. Ive heard good and bad about the C&L, I want to get everything else sorted so Im not throwing parts at it that it doesnt need. Fuel pump is a walbro 255. Car is a daily driver, using a vortec FMU with correct diaphram for 24# injectors.

The factory powerdyne manual I have shows the kit being installed with stock 19lb injectors, the 24's should handle it no problem right?

Its not a big horse power corvette eating car, I drive it to and from work every day, and around town. I cant justify a different blower, 42lb injectors, thousands in a tune etc, thats why I went powerdyne. Its a fully rebuilt unit with all the upgrades, for what I want it should fit the bill just fine.

 

[TOOLOW91]

Ordered an adjustable FPR today. I want to hear the e303's lopey idle, thats why I chose the cam. So far 800 is too high, sounds like stock cam, hoping once I get the fuel pressure issued solved it will help with the idle. Ive heard good and bad about the C&L, I want to get everything else sorted so Im not throwing parts at it that it doesnt need. Fuel pump is a walbro 255. Car is a daily driver, using a vortec FMU with correct diaphram for 24# injectors.

The factory powerdyne manual I have shows the kit being installed with stock 19lb injectors, the 24's should handle it no problem right?

Its not a big horse power corvette eating car, I drive it to and from work every day, and around town. I cant justify a different blower, 42lb injectors, thousands in a tune etc, thats why I went powerdyne. Its a fully rebuilt unit with all the upgrades, for what I want it should fit the bill just fine.

I know you want to hear the lopey idle what I'm getting at is it may need to come up some I was trying to get you to a spot where it would run .

Replacing the C&L is not throwing parts at it trust me . The maf is what your using to trick your computer into running those injectors you have . That meter is mediocre at best and will greatly affect how the car runs and computer compensates the air fuel ratio .

Next - will 24s do it ? Depends on how much pressure the blower makes on your engine . Every engine is different efficiency wise and that includes identical Side by side combos . With that said- it was a thought but not something I was urging you to do . I'd like to see a 36lb injector on it maybe so your not close to 80 percent duty cycle on the injectors . That was all I was getting at .


I wasn't suggesting it be a corvette eating monster . I wasn't hinting at swapping blowers . Just trying to help you get your car to run . Now with that said - will the fmu get the job done ? Maybe . Are you going to fight that computer with that cam and that mass air meter ? Probably .

A chip with a tune usually runs around 600-650ish keep that in mind and will totally correct the characteristics of the car if you have someone local to do it . You will benefit from it if you plan on daily driving the car . Has your setup been done without it though? Absolutely .

Next we didn't touch on another thing - do you have some type of BTM box to retard the ignition timing so it doesn't detonate under boost ?

I've helped with many friends cars - built two of my own blower setups one mild 7.5 psi setup that made 435 to the tire and the setup I have now so I'm not trying to lead you into some type of bad direction.





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