Engine Help with troubleshooting codes.

evintho

Dirt-Old 20+Year Member
Nov 12, 2003
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Santa Rosa, CA.
Trying to figure out what's going on here. '93 5.0/AOD. It fires right up but, I have to feather the throttle a lot to keep it running. It doesn't smooth out until probably 3K rpm (don't know for sure cuz I have no tach right now). However, once temp reaches 195* and the thermostat opens, I no longer need to feather the throttle and it settles down and idles fine. I used the Innova 3145 code reader.
KOEO: I've got codes 81,82,84,85 which are all good cuz all smog equipment has been removed.
CM: I have 41-HEGO lean, 66-MAF below min voltage and 91-HEGO out of range/lean.
KOER: Kinda weird, it showed 6 cyl instead of 8 cyl. Codes 41 and 91-HEGO voltage low - system lean.

Today I checked the MAF and had 12v at the red wire and 0 ohms at the ground. I didn't check the MAF ground or signal wire cuz I'd have to warm up the car for 10 mins and I have open headers. I wanted to be respectful of the neighbors on a Saturday afternoon. I'll check those on Monday.
If the MAF is below minimum voltage, would that cause codes 41 and 91?
I also wonder about my O2 placement. I'm running Hedman 88400 shorty headers and I placed the O2 sensors in the reducer about 1-1/2" below the end of the header collector. Too close?

From underneath the car left side..................

O2 left.JPG


From underneath the car right side...............

O2 right.JPG
 
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My guess here is with the O2 sensor placement and an open exhaust you are not going to get really good readings. The O2’s on my Coupe are about 8” further down in the X-pipe. However, the ECU is in Open Loop when the engine is cold I.e. when you first start it due to the ECT sensor not being at the minimum temperature to switch to closed loop. The reason this is important is that I open loop the ECU ignores the O2 sensors and delivers fuel based solely on the tables in the ECU. When the motor reaches the minimum temperature the ECU switches to closed loop and uses the O2’s to trim the fuel.

I would think that if you cleared the codes you would see that the lean condition is not present when first firing up being it’s in open loop and is not utilizing the O2’s. It does however use the MAF, ETC, and ATC sensors.

You need to focus on the MAF issue. Have you cleaned the MAF sensor wires?
 
First, the pics show that the engine is not in a 93 mustang chassis, this brings some questions since this is a transplant:
Are you using the factory 5.0 wiring?
Do you have all the grounds duplicated from the mustang chassis?
You have the symptoms of a vacuum leak, but with no head pipes the 02s cannot read accurately.
 
My guess here is with the O2 sensor placement and an open exhaust you are not going to get really good readings. The O2’s on my Coupe are about 8” further down in the X-pipe. However, the ECU is in Open Loop when the engine is cold I.e. when you first start it due to the ECT sensor not being at the minimum temperature to switch to closed loop. The reason this is important is that I open loop the ECU ignores the O2 sensors and delivers fuel based solely on the tables in the ECU. When the motor reaches the minimum temperature the ECU switches to closed loop and uses the O2’s to trim the fuel.

I would think that if you cleared the codes you would see that the lean condition is not present when first firing up being it’s in open loop and is not utilizing the O2’s. It does however use the MAF, ETC, and ATC sensors.

You need to focus on the MAF issue. Have you cleaned the MAF sensor wires?
That sounds plausible as I can barely keep it running when it's cold but once it reaches temperature, it seems to run and idle fine. The MAF sensor is a brand new Echlin unit from NAPA. I've also spliced in a new MAF connector and wires right off the ECU.
First, the pics show that the engine is not in a 93 mustang chassis, this brings some questions since this is a transplant:
Are you using the factory 5.0 wiring?
Do you have all the grounds duplicated from the mustang chassis?
You have the symptoms of a vacuum leak, but with no head pipes the 02s cannot read accurately.
Correct. It's in my '54 Customline. I am using the factory '93 wiring harness. I've checked, cleaned and ohmed out each wire. All grounds are clean and grounded directly to the chassis. I'm a fiend for good grounds! I'm pretty sure there're no vac leaks. All vac hoses are new.
 
I’m gonna go out on a limb here and say the MAF is junk. If the motor is using 19 lb/hr injectors the you need a factory MAF to go with it. Someone on here should have one (@ General karthief) for a reasonable price. I wouldn’t trust an auto parts store one as far as I could throw it.

You really need to get the exhaust done through the mufflers and move the O2’s about 8” further down the pipes.
 
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I’m gonna go out on a limb here and say the MAF is junk. If the motor is using 19 lb/hr injectors the you need a factory MAF to go with it. Someone on here should have one (@ General karthief) for a reasonable price. I wouldn’t trust an auto parts store one as far as I could throw it.

You really need to get the exhaust done through the mufflers and move the O2’s about 8” further down the pipes.
Yes, it has the factory injectors (orange tops) that I assume are 19 lb/hr. When I put the Echlin MAF on there, it was just the electronics box that screws to the top. The housing is original. Are Ford MAFs still available new and if so, where could I purchase one? You can see the MAF in the pic.....

P1010001_2 (2).JPG


Also, do you really think moving the O2's 8"further down the pipe will be helpful? I can plug the bungs that are in the reducer and have the exhaust shop that fabs my exhaust system install bungs in the new pipes for me.
 
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Not to argue with AeroCoupe but I have my O2 sensors in the same place as you and mine is fine. I would agree that you need to add some exhaust pipe after the collector say 18-24" to get the O2 sensors to readings right. My old iron manifolds had the O2 sensors between the last port and the flange so I think having the sensors in the collector is OK.
 
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Just going off of what my tuner told me. He showed me what the signals look like and further down you get in more laminar exhaust flow which allows them to read better. Not saying you cannot put them in the collector but there is a reason Ford put them further down.
 
OK, bringing back this months old thread.......
I'm trying to deal with the 66 code (MAF sensor below minimum voltage). I replaced the Echlin MAF with another parts store AC Delco MAF. Car runs a bit better but still not right and I'm still getting a 66 code in continuous memory during KOEO test. ECU is a new remanned unit, new MAF connector and wires spliced in 2" out of 60 pin connector and a 2nd new MAF.
Tested VPWR and GRND - disconnect connector, KOEO, probed VPWR & GRND and pulled 12.05v.
Tested MAF circuit short to ground - disconnect connector, key off, probed MAF SIG & MAF RTN and got 12,700 ohms.
probed MAF SIG & GRND and got 10,040 ohms.
Pulled the 60 pin ECU connector and tested continuity between pin 50 and MAF SIG on MAF connector - good.
tested continuity between pin 9 and MAF RTN on MAF connector - good.
I'm at a loss and not sure where to go from here.
 
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