Ongoing, frustrating, thought I fixed but didn't, EEC-IV problem

My damn pickup.

It's a 1993 F-250.
I put another 5.0 in it when the stock engine died. Thought I'd be smart and use a GT40p from a 2000 explorer.

While I was installing an engine, I added long tube headers as well. The longblock is stock. I'm using the explorer's intake manifold. I deleted the air pump. The injectors are the later EV6 style, but in the same 19lb size the truck was born with. I feel like I've replaced everything at least once while chasing this problem, all to no effect.

Here's the symptom: It runs really rich. Like black-smoke rich. Stalling at stoplights rich. 11mpg highway rich.

BUT! Only under one set of circumstances... If the ambient temps are low, and the coolant temps are warm enough that it's probably in closed loop.

If it's above 60 degrees outside, the problem never presents itself. If it's cooler than that, but the engine is also cold, I gots no problem. Starts easy. Runs like a champ. But if it's cold outside, and I've been driving for 15-20 minutes, LOOK OUT! And the problem gets worse the colder it is. In 20 degree weather I just have to pray I get to work before the temp gauge starts to move, or I'll stall out in intersections and it tries to flood itself everywhere I go.

I thought maybe the 02 sensor was too far away from the engine in those headers, so put a bunch of insulation wrap on them, but that didn't seem to help. The ECU also seems to know it's doing me wrong, because it codes for system rich.

What the crap.?

Are they heated O2s?

If not, install heated O2s. They're simple - one of the white wires gets power with ignition on, the other white wire gets ground, doesn't matter which is which, gray wire is sensor ground and black wire is signal. (yes, BLACK is signal.)

Symptoms sound just like the O2 is going to sleep and the computer isn't expecting that. It's staying in closed loop and the O2 is putting out very low voltage so the computer sees "lean" and turns on the firehose.

Exhaust insulation does jack. You really need a heated O2 as the right fix. Don't use a universal one, those are often crap, get a rear O2 for, say, a '02 LeSabre or something of that ilk. Have a nice loooong set of wires on it.

one wire or three wire O2 sensor?

If you unplug it, does it work ok?

Sounds like it sees near 0 volts, and is ramping it rich to make it switch- and you hit the limit. Interesting the lack of failure response of that age of vehicle.

In reply to Knurled:

The one "issue" about putting good heated O2 sensors in is that if the truck starts life as a one wire unheated sensor, the 4th wire of the new heated one is a signal return for the base O2 signal. Possible to just ground it someplace, but gotta put it in a good place.

Also, don't get too modern of an O2 sensor- the more recent, the better the heater, and the more likely that it's a modulated heater instead of one that is just on.

Ooh, good point on that regarding the heaters. I know that GM was tying the O2 heater circuit in to the DRL circuit on some chassis in that timeframe, so when your DRL fuse blows, your O2s stop working.

I'd ground the O2's ground to the same place the PCM grounds, so that there's no potential voltage difference.

It is already a heated oxygen sensor to begin with (4-wire). I've replaced that part 3 times with different brands.

The computer is actually storing a code for 'system rich', indicating to me that it's getting a high enough voltage signal from the O2 at least under some sort of circumstances. IDK what the criteria is to set that code, but the ECM doesn't seem able or willing to remedy whatever's going on.

Oh, system RICH. That means the computer is trying to pull fuel AWAY and is failing. IIRC Ford waited until long and short term fuel trims were maxed out before setting that.

Do you have access to a scantool and not just a code reader? That will help immensely.

Also - do you still have air injection? I've seen weird things happen with air injection and longtubes, on setups where the header manufacturer put the injection port in only one of the header tubes. I know Ford puts the air injection in the cylinder head, but weird things may still be happening here.

What temperature does it run at in colder weather?

Coolant temp sensor wonk?

I've replaced the coolant temp sensor twice. And read the resistance with an ohm meter against the range in the service manual. I don't remember what the numbers were, but they made sense at the time.

The original engine had air injection of some kind. This motor had no provision for it, and I removed everything associated with the system.

But what temp is it actually running at? Its old enough that it will overfuel quite badly if its running at 150 or below. O2 sensors won't have enough input to solve the cold running. Remember you are working with the modern equivalent of a stone axe here.

OK, so, in order to get the condition, the engine must be hot but the ambient (intake) must be cold?

In hot weather everything funs fine at all engine temps.

So once the ecu come off of open loop and starts making its own decisions (rather than following a preloaded table), what sensor reads differently at hot ambient than cold ambient?

To me that is pointing at the map or maf, since little else is affected by ambient air temps AND is only read by the ecu in closed loop.

However, maybe you need to jumper some wires to the ecu to simulate the air pump circuit. I could see the ecu flipping the o2 heater relays off if it senses an air pump malfunction or something. I believe the air pump was used to inject air after combustion for the cat to hit its optimal chemistry.

belteshazzar wrote: It is already a heated oxygen sensor to begin with (4-wire). I've replaced that part 3 times with different brands. The computer is actually storing a code for 'system rich', indicating to me that it's getting a high enough voltage signal from the O2 at least under some sort of circumstances. IDK what the criteria is to set that code, but the ECM doesn't seem able or willing to remedy whatever's going on.

It works a little different from that- it will go rich intil it hits the rich limit and THEN will tell you it's rich. The sensor can still be sending a bad signal.

I'd still unplug the O2 sensor and see how it reacts.

You can put a digital volt meter across the O2 sensor to see what it tells you.

Sadly, the idea to plug into the computer and see what its telling you won't work- this is pre OBDII, and does not output anything.

One thing you can do is run a Key On, Engine Off test- see what it tells you, and then try a Key On, Engine Running test. This page may help- http://www.troublecodes.net/ford/eectest/

I had to make my own "self test" box when I started- just a speaker that beeped.

going to rich is limited to only a few things. Either the ECM is commanding the fuel injectors a longer duty cycle than needed, or there is a mechanical problem in the fueling system. I would eliminate the possible mechanical issues first since there's only a couple.
What are your fuel pressures...ideally you could drive around with a gauge taped to windshield to collect data while the problem is present and while it is running normally. You mentioned placing different injectors. were they new? How do you know the spray pattern is good? How do you know a injector itself is performing properly, and not sticking open? What is the resistance of the injectors OEM vs what you have now?

Ensure injector harness is not pinched under intake manifold or shorted in any way.

After that, seeing data from a scan tool would help. Both banks? just one? Short and long term fuel trims??

TGMF wrote: After that, seeing data from a scan tool would help. Both banks? just one? Short and long term fuel trims??

Again, this is a 1993 truck. Before scan tools existed, and before OBDII. The only scan tool that can be used is one that blinks a light to tell you what is wrong- you can not monitor the engine.

(unless when the motor was swapped, the new module was included)

I'm not sure if your application has a MAP or MAF sensor. The Ford MAP sensor puts out a frequency type signal within a fairly narrow band. I have found that if the MAP is a few HZ off the engine will run like crap.
Google Ford MAP sensor to get the specs. Set your multimeter on frequency to measure the output of the sensor and compare it with a vacuum gauge.

In reply to fujioko:

If it's a MAP sensor, my info tells me that it could be a E7EF-9F479-A2A part. Which makes me think my info is bad- that's a '87 part number. Looks like the change over to MAF started in '88 and '89. Moved into the trucks starting in 1990.

This truck is speed density. Interestingly, I think the MAP-sensor is one part I haven't thrown at this bloody situation. It's mounted up on the firewall. I've unplugged it while the engine is running and the truck instantly stalls, but that's all the more I've done with it.

Another thing that sucks right now, is that the days are getting warmer, so the symptoms are getting hard to duplicate.

In reply to TGMF; I've monitored fuel pressure while it's acting up, and otherwise. Always textbook perfect. The regulator isn't leaking either.

The injectors came out of my P71. While I can't specifically say I know for sure they're good, I also don't know how to attribute these symptoms to a bad injector(s)/wiring. If the spark plugs and my own instinct is any indication, it runs rich across all eight cylinders. The ECM seems to be commanding a ton of enrichment, but only at a very specific (and inappropriate) time.

Isn't there a very different system of collecting data for the MAF computer (unless you swapped the ECM too) vs the Speed Density computer?

Are you giving SD readings to an MAF ECM?

" The speed density refers to two things: the speed of the engine (RPM) and the manifold pressure (MAP). Imagine a 3-D table with two axes and set values in the middle. The difference between MAF and speed density is one table has MAP vs. RPM (or MAP/BAP vs. RPM), the other has MAF vs. RPM. Obviously the table values themselves will not be the same. The computer (MAF or speed density) uses the O2 sensor to monitor the result of its calculated fuel values and can adjust the fueling as necessary. Both MAF and speed density use air temperature sensors, but play a greater role in a speed density system."

In reply to ebonyandivory:

If you mix production computers to that degree, the engine won't run at all.

(plus the Speed-Density system used in F products isn't a table- it estimates the air flow and lets everyone use that information)

alfadriver wrote: Again, this is a 1993 truck. Before scan tools existed, and before OBDII. The only scan tool that can be used is one that blinks a light to tell you what is wrong- you can not monitor the engine.

Oh yes you can. Can't tell me that it can't be done, because I've done it, and within 20 feet of where I am sitting I have three different scan tools that will plug in to the trapezoidal data connector hanging off of the left fender near the hood hinge and read real-time data on an EEC-IV vehicle.

OBD-II is nice because it standardized a lot of things, but it doesn't represent the start of those things.

So since MAF and SD use different data to ultimately adjust fuel can an MAF ECM run an SD engine?

Why am I having a problem seeing how 1993 technology has no problem running 2000 technology?

Hell, I was under the impression that the ECM even needed to be from a very similarly-equipped truck (engine, trans etc.) let alone the same decade in these generation Fords.

A Snap-On MT-2500 with any ol cartridge and a FORD-1 connector and you are in business. Should be $150 or less off Craigslist.

Knurled wrote:

alfadriver wrote: Again, this is a 1993 truck. Before scan tools existed, and before OBDII. The only scan tool that can be used is one that blinks a light to tell you what is wrong- you can not monitor the engine.

Oh yes you can. Can't tell me that it can't be done, because I've done it, and within 20 feet of where I am sitting I have three different scan tools that will plug in to the trapezoidal data connector hanging off of the left fender near the hood hinge and *read real-time data* on an EEC-IV vehicle. OBD-II is nice because it standardized a lot of things, but it doesn't represent the *start* of those things.

Ok, but for a OBDI car, you need the specifc Ford compatable tool, instead of a generic one. I never had to run the data through that, since we had other tools.