Ford EFI gurus, need help with O2 problem
10-24-2018, 04:22 PM
#1
V8 Miata Fanatic
Thread Starter
Ford EFI gurus, need help with O2 problem
Ever since I have gotten the car running, it has been pig rich. After sorting out other issues, I have it to the point where I only have codes 41 and 91, lean O2 on both sides. I am running an A9L ECU, and have the correct O2 harness (loop in the right spot) for the A9L ECU. So far I have done continuity tests on the O2 harness, and all checked out. With the key on, I have @12v at the power wire for each side of the harness. When I run it, I am not getting a reading from the O2 signals, and if I disconnect the O2 harness from the ECU harness, there is literally no change. The sensors are brand new from the Ford sensor pack. One other thing that I was not sure about is that when I test continuity both the power and ground terminals of the O2 harness show continuity when I touch the exhaust. Is that a signal that something is screwy in the wiring/ECU?
Any thoughts? This is driving me absolutely crazy!
Any thoughts? This is driving me absolutely crazy!
Last edited by jrmotorsports55; 10-24-2018 at 04:55 PM.
10-25-2018, 09:28 AM
#3
V8 Miata Zealot
The O2 sensor heaters have their own ground (HEGO ground) coming from the computer. This is different and separate from the O2 sensor ground. It is in the fuel injector wiring harness and comes out under the throttle body. It gets connected to a manifold or head bolt.
10-25-2018, 09:34 AM
#4
V8 Miata Fanatic
Thread Starter
Thanks. Yeah, the orange ground wire was my first thing to check, it’s good. I need to pull the ECU from under the dash and check the continuity of the main harness. I’ll double check the pins on the O2 ends of the harness, I have already checked the ones on the main plug end. One other thing I need to look in to is my main harness as it may be from a 91-93, diff from 88-90. One of the reasons I need to check continuity from ecu to O2. What a pain!
10-25-2018, 10:20 AM
#5
V8 Miata Zealot
If you run the PINPOINT TEST for codes 41 and 91 that are in the FORD POWERTRAIN CONTROL / EMISSION DIAGNOSIS MANUAL it will lead you to your problem as well as save you a lot of time. I tried looking up the manual on line but was not sure of what year stuff you are using. 1986-1988 are speed-density cars, and 1988(California only) -1993 are MAF cars. If you are running a MAF-equipped car, be sure that you DO NOT have a vacuum hose attached to the BARO sensor (in a speed-density car, this is a MAP sensor and it requires manifold vacuum)
10-25-2018, 10:24 AM
#6
V8 Miata Fanatic
Thread Starter
I’ll have to search for that. It’s a mass air car. I do not have any vacuum on baro. I actually made that mistake when I first got it running and since corrected it. I am running 24 lb injectors with Pro M calibrated sensor on A9L ECU.
10-25-2018, 05:13 PM
#7
V8 Miata Fanatic
Thread Starter
So, searched on eBay and found someone selling the Ford manuals for a good price, so I bought the set. After work I went out and checked the O2 wires, there are two white, one black. The two white go to the pos and ground, the black to the signal wire. Guessing that is right. Also ran it again and let it get to the point that the fans kicked on. Unplugged the O2 harness, no change. ECU is definitely not getting a signal from the sensors. What are the odds that I got two brand new Ford sensors that are bad. That or I fried them somehow during install/testing. No idea otherwise. Still going to check ECU wires, but the pos is showing 12v at the O2s, and ground is good, but no signal coming from the actual sensors.
10-26-2018, 09:17 AM
#8
Oh boy, you just cant get a break, sorry to hear of the continuing troubles.
Did you not mention going FiTech at some point ? I did not experience any of the difficulties you are having since I went straight to the FiTech on my build. Almost 1000 miles on her now and zero issues, fired right up... I do need to take it to the dyno/tuner for some dialing in since I know zero about fuel injection, She hunts for idle occasionally and I suspect it is running a bit rich at the 1700rpm plus. Other than that I cant say anything bad about the system.
I hope you get these gremlins figured out, it has got to be frustrating.
Did you not mention going FiTech at some point ? I did not experience any of the difficulties you are having since I went straight to the FiTech on my build. Almost 1000 miles on her now and zero issues, fired right up... I do need to take it to the dyno/tuner for some dialing in since I know zero about fuel injection, She hunts for idle occasionally and I suspect it is running a bit rich at the 1700rpm plus. Other than that I cant say anything bad about the system.
I hope you get these gremlins figured out, it has got to be frustrating.
10-26-2018, 09:53 AM
#9
V8 Miata Fanatic
Thread Starter
Yeah, I have a FiTech setup if I can’t figure this out. All of the OEM stuff is wired and installed, and i’d Rather stick with it if possible. We’ll see. So close!
10-29-2018, 04:45 PM
#12
V8 Miata Fanatic
Thread Starter
Installed new ECT, and also put in my original coil as my new MSD unit decided to crack down the center (money well spent). Ran the car, seemed to run a little better (maybe the coil has been cracked for a little while now). Pulled codes, still have 41/91 (KOER, there were no codes when I pulled KOEO). Checked with digital voltmeter, and it does appear both O2s are reading low (.1V, supposed to be between .2V and .9V at idle). That measure was taken where the O2 harness meets the main ECU harness. I checked my fuel pressure again, and with the vacuum off the regulator it was 42-43 PSI at idle, should be good. Not sure what the problem is, I may do a smoke test on the exhaust to see if there are any small leaks before the O2 that could be causing them to read low.
The best part is that after running it I noticed a few drops of oil on the ground. The oil pan gasket is leaking, again. I have replaced it 4 times now. I am at my wits end with this thing at the moment, I may just slap the wheels back on it, and kick it out of the garage for the winter as I need a break from it.
The best part is that after running it I noticed a few drops of oil on the ground. The oil pan gasket is leaking, again. I have replaced it 4 times now. I am at my wits end with this thing at the moment, I may just slap the wheels back on it, and kick it out of the garage for the winter as I need a break from it.
11-04-2018, 12:38 AM
#14
V8 Miata Fan
I’m having the same issue with it running really rich. Also had one bad injector so I ordered a set of injectors and a new fuel pressure regulator. Fingers crossed
11-04-2018, 04:28 AM
#15
V8 Miata Fanatic
Thread Starter
Do you have any trouble codes? If so, what ones? OEM injectors and MAF showed up yesterday. I'll probably try to install/test them next weekend. We'll see if that gets me anywhere.
11-04-2018, 09:20 PM
#16
V8 Miata Fan
Its running so rich that I don’t want to fowl the cats.
11-05-2018, 04:35 AM
#17
V8 Miata Fanatic
Thread Starter
Have you done key on, engine running test? That will put the car in full diagnostic mode and it will self test, and may locate your issue, or point you in the right direction. That's how I get my 41 & 91 lean codes, which then cause it run pig rich to compensate.
11-06-2018, 08:56 PM
#18
V8 Miata Fan
Did your KOEO test show anything? Mine does not show a thing. Nothing, like it doesn’t work. I will try KOER test when I get my injectors and regulator installed.
11-10-2018, 01:35 PM
#20
V8 Miata Fanatic
Thread Starter
Messed with the car some more today. Checked vacuum lines to make sure no leaks. Pulled upper intake, and sealed the Pcv grommet and replaced the Pcv hose to make sure of tight seal. Reinstalled upper and cleaned MAF with brake cleaner. Started it up and ran it for a whil to get it to temp. Sprayed brake clean all over intake area, no changes in running, so appears no vacuum leaks. Ran KOER, still have 41/91. Checked O2 readings, both between 60 and 190 mV, still reading low. I think next step will be to install OEM injectors and MAF to see what happens.
11-10-2018, 09:46 PM
#21
V8 Miata Fan
I too spent a couple hours on the car today. New injectors and fuel pressure regulator. Idles a little better but still misses when you bring the revs up and then pulses when you hold the throttle in one spot. I have no vacuum leaks..
i cant get any codes, I don’t think my code reader is working.
i cant get any codes, I don’t think my code reader is working.
11-11-2018, 05:17 AM
#22
V8 Miata Fanatic
Thread Starter
Hmmm, yeah, the engine running test should run it through a "test" mode and it will run a bunch of self tests, run up the idle, list the number of cylinders, then any codes it reads.
11-11-2018, 09:40 PM
#23
V8 Miata Fan
Then mine is obviously not working properly. Could be the car because I don’t even have a check engine light.
Also now that I ran the car for a good amount of time, the intake gets really hot. Does that mean the timing could be off?
i do appreciate your feed back thank you by the way.
Also now that I ran the car for a good amount of time, the intake gets really hot. Does that mean the timing could be off?
i do appreciate your feed back thank you by the way.
11-12-2018, 04:44 AM
#24
V8 Miata Fanatic
Thread Starter
I do not have a CEL on mine either, just pulls the 41 and 91 during the self test with engine running. If I clear codes and pull engine off codes, there are none. What ECU/year wiring harness do you have? There are some differences in wiring harnesses through the years, but as long as you have a manual harness and manual ECU, you should be good for our purposes.
Regarding intake, could be timing, or could be lean issue. Where are you measuring and how hot are you talking?
Regarding intake, could be timing, or could be lean issue. Where are you measuring and how hot are you talking?
11-18-2018, 09:02 PM
#25
V8 Miata Fan
Turns out I have an 87 wiring harness and computer. Both manual.
It is running hot enough that it is blistering the paint on my upper plenum by the throttle body spacer. You can’t even touch the upper plenum.
im looking into the FiTech system. Get rid of all the old wiring and my hood will fit better.
It is running hot enough that it is blistering the paint on my upper plenum by the throttle body spacer. You can’t even touch the upper plenum.
im looking into the FiTech system. Get rid of all the old wiring and my hood will fit better.
