North American Turbocoupe Organization



EEC Check Engine Tests
Rob H Offline
Member
#1
I  did those tests today, the KOEO
I could not recall if I had ever noticed a check engine light. Lucky I have my dash apart, or I for sure would have never noticed the bulb flashing away somewhere back there above the headlight controls but below the gauges.
I got with the engine off 83 & 72
72 is power interrupt detected. Is that as simple as me having the battery disconnected when I installed the stereo the other day?
83 is not listed, does that mean it does not matter?

With the engine on...it took me a couple times to follow along with the material I printed from the site. So I did not knock on the intake manifold, I missed the opportunity to hit the brake, as well as the WOT so I got the code 25 and 77(knock sensor not detected, WOT not sensed) and I assume that's no big deal?
But I did get 41(no ego/hego switching detected, system lean)
Would I be correct in assuming it would be a bad o2 sensor? If so that's great, easy enough to switch, and with my new exhaust on its way as we speak, it would be a perfect time to change it. Who knows how old the one on there is!
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Jeff K Offline
Administrator
#2
The only important code is the 41. Was the 41 a KOEO code or a CM code, or did it show up in both KOEO and CM parts of the test?

99% of the time lean codes are NOT due to an O2 sensor failure. 41 is telling you the engine is running lean. Running lean can be due to the VAM out of calibration, but is The EEC IV PCMs in our cars, as in all cars starting in the early 80s, have adaptive fuel control. If the O2 sensor senses a lean A/F (sensor voltage well above .5 V) the PCM will increase injector pulse width to richen A/F up so O2 voltages is .5 V (.5 V corresponds to 14.7:1 A/F). PCM also stores this info for future use. If PCM senses rich A/F, it reduces injector PW, remembers it, etc. PCM can alter injector PW +/- 20% from the originally hard programmed PW values. If the PCM cant correct the A/F so O2 voltage is .5V, it will set either a lean code 41, or a rich code 42, and turn on the CEL. It is actually much more complex than this, but gives you the general idea.

I have owned EEC IV Fords for 34 years, and every time I have seen a code 41 (or 41 and or 91 on a V8), the issue has been a vac leak or air metering issue, with a vac leak being the most common by far. I have NEVER needed to replace an O2 sensor to fix a 41/42 or 91/92 code.

Ignore the 72 code. It has nothing to do with your battery disconnect. As long as it doesnt come back all the time dont worry about it.

Dont remember what 83 is, and I am too lazy to look it up right now.
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
05 Taurus SEL Duratec daily driver
04 Taurus Duratec (wifes car)
02 Pontiac Grand Prix GT
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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Rob H Offline
Member
#3
I am realizing now I should have worded my first post a bit better. What I had been trying to say was that I had done the tests you do with the jumper wire and watching the check engine light.

The code 41 is a KOER code I believe. Sorry, I am only learning and pretty new to all of this.
I was following along using guide to retrieving EEC diagnostic codes from the tech section. I got to the end of both the KOEO & KOER, but I did not go into the wiggle test
Once you hook that jumper wire up things start happening fast! Fortunately I recorded the whole thing, so watching it several times while reading along I am a little more familiar with it now.
I am pretty sure that what I saw was it blinking out the KOER codes, and though I did watch for a while after, I did not see a separator flash, or any more codes blinked out.
I'm assuming this means there were no codes stored in continuous memory?  EDIT: I just rewatched the video, and the funny flash right before the codes...was that the separator? If so would that mean that there were no KOER codes, and those codes were from CM?

I have a list of EEC-IV codes that says in regards to code 83
EGR control circuit (four-cylinder models oeM)      condition=O
Low speed fuel pump relay (1984 through 1988 models)       condition=O,C


If anyone is interested they can watch here. Keep an eye out for an odd flash in between the DRC and when it starts flashing out the codes.
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Jeff K Offline
Administrator
#4
The best way to "run the codes" is to run the KOEO / CM code test first. Best to do this with engine above 50 deg F so you dont get low temp codes from the ECT, ACT/IAT and VAT sensors, and then run the KOER test with the engine at operating temp.

As noted above, the most important code is the 41. You definitely have a lean condition. In addition to vac leaks, VAM issues I mentioned above, Low fuel pressure will also generate lean codes. Are you able to check your fuel pressure with the engine under load? A common way to do this is take a fuel pressure gauge with a long enough hose so you can attach the hose to the valve on the fuel rail and run the gauge our from under the hood and tape it to the outside of the windshield so you can monitor pressure while driving.

If you are thinking about any mods for more power, a wideband air/fuel gauge is almost a necessity. A wideband is also very useful in diagnosing engine and fuel system issues.

For the 83, check to see if the EGR solenoid located on the rear of the pass side strut tower along with the overboost switch elextrical connector is connected to the solenoid. If it is, check solenoid resistance. Cant remember the exact value, but it should be 50 to 80 or so ohms more or less. Zero ohms or open circuit means it has failed. Is the EGR system intact?
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
05 Taurus SEL Duratec daily driver
04 Taurus Duratec (wifes car)
02 Pontiac Grand Prix GT
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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JT Offline
Posting Freak
#5
Code 83, for the 1987-1988 Turbo Coupe application, is for the cooling fan circuit. Check my website, linked below, for Ford's troubleshooting this code:
http://www.tbirdheritage.com/turbocoupe/...es/x30.php

Keep in mind that the Turbo Coupe has a few, specific, EEC codes so that's why there can be a difference between the generic code listing you found online.
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Rob H Offline
Member
#6
Jeff, I did both the KOEO(1st) & KOER tests after driving and bringing it up to normal operating temp. When it stops raining I will be getting out there to poke around and see if I can check the EGR and check hoses etc.
I also want to redo the KOER test and get that WOT and brake part in there.
In regards to hooking up a fuel pressure gauge, that may be beyond my current skill level though I am getting a lot more comfortable learning and trying these things myself. Big part of the problem is everything is closed here for the most part, makes doing anything(when you need something you don't have) 20 times harder.
When that exhaust shows up, I could easily get the shop to check that pressure for me.

JT - thanks for that info(that EEC diagnostic chart looks great!
Something I did notice when doing the KOEO part of the test was that as soon as hooked up the jumper wire, my cooling fans came on, and stayed on the entire time until I disconnected the jumper wire. That wasn't mentioned in the guide I was looking at, so I'm not sure if that is normal.
When I got the car in 2016 both the fans were seized. They were both replaced, but not by me. My cousin did a lot of stuff for me when I first got it.
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Jeff K Offline
Administrator
#7
You should be able to rent a fuel pressure gauge from many parts stores for free with a deposit..... at least you can do that here in the US, or could before the COVID 19 hit.

There is a Schroeder valve (just like a tire valve) sticking up off the fuel rail roughly near the center of the rail. Might (should) have a black cap on it. remove the black cap (if still there) attach the pressure gauge to the valve, start it up and have a look at the pressure. Should be 39-40 psi engine off after a few key on / key off cycles to get the system fully pressurized. Running, pressure depends on engine vacuum or boost. Under boost pressure should be the base 39-40 psi PLUS boost pressure (i.e., press at 10 psi boost should be 49-50 psi). Using the rough rule of thumb (I LOVE rules of thumb based on sound scientific and engineering principles) 1 psi = 2 inches of mercury. If idle vacuum is 20 inches mercury, that = 10 psi, so fuel pressure should be 10 psi less than the base 39-40 psi, or 29-30 psi.
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
05 Taurus SEL Duratec daily driver
04 Taurus Duratec (wifes car)
02 Pontiac Grand Prix GT
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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