OK, took the truck out today and it started doing something strange I have never felt before...going down the road with steady throttle it just "skipped" a couple fires, maybe for a half second. No exhaust noise, oil and voltage read steady, then it ran fine until the next time it did this. I turned around about two miles from the house because it kept doing this. It stalled at a red light, but fired right up and did this the whole way home. All speeds I drove 25-55mph.

Now I have been working on this basket case for a couple months, so I've gone through all the codes and sensor fun trying to chase down the idle. I really have no clue where to start trying to diagnose this one, so any help would be greatly appreciated.

Thanks!

 

The most cause of ignition problems is the Ignition Control Module (ICM), wiring/connector to the coil, the coil itself and last the PIP sensor in the distributor. The ICM can be tested, but sometimes that is inconclusive.

 

I just went out and ran the codes once again, trying to see if pulled a 14 in KOER, but it flashed out a 98- Hard Fault Present. Does this mean my ECM is toast? Also gave me a 22- I already replaced the MAP sensor as it was bad. PO had just disconnected it because it would not run when plugged in.

Entire code list:
22- MAP sensor (KOER)
31- EVP out of range (KOEO)
33- EGR not opening (CM)
41- O2 indicates lean (CM)- I hear an exhaust leak by the manifold, so that is the culprit here
96- Fuel pump (KOEO) rear tank is disconnected
98- Hard Fault (KOER)

So that is where I am now...time to find the 5.0 MAF computer and harness?

 

but it flashed out a 98- Hard Fault Present. Does this mean my ECM is toast?

No not necessarily it just indacates a problem with one of the sensors or its connection to it causing a fault the computer can't deal with.
Odd you get any codes with it but I'd try unplugging the map sensor and try a KOER test again, see if the hard fault disappears while the code 22 remains.

If so I'd try another map sensor.

I don't have my book with me so I can't double check to see if the map sensor is included in the '89 wiggle test,problem might be in the harness itself rather then the map sensor itself.

 

Just went out and ran KOER with the MAP sensor disconnected...no change.

 

Long shot but it was worth a try, map was the only other KOER code you had listed, however it stand to reason that wouldn't be the one causing the hard fault.

Wiggle/move sections of the harness around, run the KOER test wiggle and move another section of harness and repeat, see if you can get it to lose that hard fault by doing so, as a test looking for possible short in wiring as the cause.

You can also try unplugging the sensors one at a time running the KOER test with each one disconnected, see if that hard fault code disappears.

If its a short or a sensor one or the other should lead you to the cause of that fault.

 

Thanks for the info on how to troubleshoot this. I'll set aside a good chunk of time tomorrow and run through this process and let you know what I find.

 

Hard faults can be difficult to find. Dan has some great tips to try.

 

Just got in from running the procedure you outlined Dan, here are the results.

IAT- Threw a KOER codes 98, 22, 54
ECT- 98, 22, 51
TPS- 98, 22, 63
MAP- 98, 22
EGR- (I have an eliminator on it) 98,22
IAC- 98, 22 (it did idle better with the IAC unplugged

I then moved and massaged the harness a small section at a time, and still threw 98 and 22 every time. This code and diagnosis procedure is new turf for me, so now that this has been inconclusive (at least to me) I am even more stumped. Thanks for the help thus far, please let me know where I should try next.

 

The other codes are not going to disappear with 98, you're trying to get rid of 98 first. One or some might go with it yea but depends on the exact cause and effect.

Have you cleared the memory for each test run? I do when testing and couldn't say for sure if KOER codes are held in memory or not. Never tested the theory but I wouldn't think so.

Make a note of the CM codes you have now, might need those once you progress and dope out the cause of 98. That and a short test drive will rebuild that information agian if need be. You will lose adaptive strategies it build over time by disconnecting the battery but you probably need a rebuild now anyway, needs to relearn whats "right".

Disconnect the battery for a few minutes for each test just to be sure its not a old information.

You tried the harness, keep in mind depending on the type of short, if there is one, it may not be as easy as just moving the harness around to change the outcome.

How about the harness down to the 02 sensor, don't forget it and look it over good.

I'd test each sensor, unplugging them one at a time and running the KOER test, again be sure and disconnect the battery each time to clear any saved code/s as you move to the next sensor.

Shouldn't take you to much time to narrow down the problem to the harness, one of the sensors or the computer itself.

I'm back home again with my book and a full size computer with high speed internet service, if I find something that may help or make the task easier I'll post back with it.

 

From my running the test it does not remember anything in KOER. For example, I unplugged the ACT and ran the test, then plugged it back in and unplugged the ECT and ran the test. The ACT code disappeared and the ECT popped up. I have codes 33 and 41 in my CM....and 85 in KOEO. I know the source of the codes 33,41 and 85, but the 98 and 22 came up after it started this issue.

I massaged the harness pretty good, checking the KOER often to see if anything changed. Thanks for your help. I have my laptop out with me in the garage, and a wireless LAN so I can keep checking here while I work on the truck.

 

As noted before Code 98 is a hard fault. According to my Service manual '93-94 Ford trucks, this is also referred to as the PCM being in "FMEM mode". This is a "limp" mode. The PCM is sensing something way out of range so it is going into this mode. To fix it you may have to start tracing down wires from the sensors back to the PCM. I would start with MAP sensor because no matter whether it is plugged in or not you are getting code 22.

 

I eventually wanted an excuse to rewire the truck so I could convert it to MAF with a 5.0 computer and harness I can get my hands on...but this is not when I wanted to do it.

Time to check pricing on a wiring harness, since I will likely cause more damage once I cut into this one.

 

Have you ever tried disconnecting the Battery for 5 minutes?
Then deal w/ all the KOEO codes first, before moving on to the KOER's? Otherwise it can skew the KOER results.

 

Yea my books says the same, a type of limp mode. Failure mode effects management.

Clearing the memory and then running the KOEO test should shed new light on the problem, make sure its up to running temp when you do so.

It must pass KOEO test (System pass = "11") before proceeding to the KOER test.

Running the KOER test before correcting any and all issues found during the KOEO test is a waste of time.