Hi All, I have a 1991 E150 with a 4.9 six. Been slowly bringing the old girl back to normal. Just put in a restrictor plate on the EGR, along with a new single field wire 130A alternator (cheaper than using the voltage regulator, which was bad); new coil, wires, cap, and TFI. Previous issue of hesitation on acceleration and hard starting after warming up and shutting down seems to be gone. Idle is smooth and shifting is regular. Seems to be running leaner, which is happy. However I am getting a MIL, and I can't quite decipher the diagnostic code.This is an OBD2 system; EEC IV however I am not sure whether the codes are 2 or 3 digit. On the KOEO test I am getting the normal quick flash, then I I I then 8 then I I then 8 then I I I then 8 then I I then 8 ( I=one flash, 8=eight flashes). I think there is a pause between the I and I after the first 8 flash group, but it is not very long at all. The I I I seem to be of equal duration and move right into the 8 flashes at the beginning. The second I I I maybe has a slight pause between them, but not enough to be sure after the first flash. The book I have says there might be two flashes or one flash for a separator between code groups. So it could be an 18 code then an 18 code again with two flashes as the separator between the two code groups.
The book says 18 is "Loss of tach signal to Electronic Control Assembly -ECA (whatever that is, I don't know unless they are referring to the ECU, and I don't have a tach); also 18 refers to DIS- Distributorless Ignition system problem, which I don't believe I have since there is a Dizzy. Online sources for OBD2 codes also mention 18 is for a problem with the SPOUT (spark out circuit open), and also "Loss Of Ignition Diagnostic Module Input To PCM/SPOUT Circuit Grounded".
If there is a 3 digit code then it's 118 which says bad ECT -too high signal voltage (Coolant sensor), but then there is no separator for the second group of flashes.
AFAIK the spout connector is just a jumper wire between the two wires of the connector, so I will check if I can jump across there if the insert is bad. I would like to know if there is supposed to be any voltage across those wires??
So is it two or three digits and likely to be the SPOUT problem?? Or if 3 digits then should I replace the coolant sensor??

 

The first year for any OBD2 vehicle was 1994. Yours is OBDI. 1991 was the first year of three digit codes, and that's what you have.

Here is how I interpret your codes:

1 - 118, 118 - 1 - 118, 118

The first flash is the fast codes. Ignore this one.

Next comes 118, and a repeat. Then there is one pulse which is the separator code, this tells you you're moving from on demand codes to stored codes. Then 118, and 118 repeats.

You have an ECT that is reading high or is an open circuit. The PCM can't tell if the problem is in the sensor or the wiring to the sensor. Either one could be open and set this code.

 

What a marvelous and concise answer. Exactly what is needed! I will check the ECT and see what is going on. Thanks very much for unlocking the puzzle.

 

Well, thanks to Mark I deciphered the 118 code, bought an ECT, installed it and no more 118 code. Engine is running well, no hesitation, no stalling, idle is almost always even, however doing the KOEO and KOER tests reveals (or does not reveal) other problems. The initial self test comes back 111-111. Then the CM codes come back as 172, 173, and 332. Having both 172 and 173 seems odd because 172 indicates HEGO bank 1 Lean reading, while 173 indicates HEGO bank 1 Rich reading. After installing the ECT sensor, the two wire one for the EEC, I cleared the codes and went for a ride. After some while I was getting an intermittent bogging down at 50-65 mph, which would clear up if I did a WOT for a short time. It would come back sometimes, and momentarily the CEL light would come on and go out. The exhaust pipe indicates that the mixture is somewhat rich (slightly sooty). Then pulling the codes gives the 172, 173 and 332. The 332 is understandable since I put a restrictor with a 1/8" hole where the EGR valve attaches to the cylinder head. I will try opening the hole somewhat to see if the code clears.
AFAIK this truck has only one HEGO located on the down pipe coming off the exhaust header. So my first question is whether the sensor is bad, or whether anything else is affecting the O2 like a vacuum leak or an air leak, or the ACT sensor. Very recently I replaced the Coffee Can vacuum reservoir with a smaller Dorman replacement. I have not really really gone over the vacuum system for leaks although I did find one or two bad hoses or connectors and replaced them, one completely disintegrated hose coming off the plenum and going to the metal 1/2" or so tube running along the passenger side chassis rail to the charcoal canister mounted just aft of the passenger door on the chassis underneath. I cannot detect any obvious leaks, but that whole fuel tank vapor situation looks like it needs work; so I suppose I will have to do the vacuum testing, which it would be nice if someone provided a short overview how/ what to do.
I have replaced the TFI module, coil, new cap, plugs, wires and rotor, EGR valve not that long ago (But not the EGR grommet), and reset the dizzy back to the location I marked for it after changing the TFI gray module, but I didn't do the timing. The MAP sensor is recent; new one wire 130 amp alternator (no more voltage regulator- seems to work fine), new serp belt. The secondary air pump seems to be working, making happy sounds, although I have no idea how it is supposed to work (have seen virtually nothing on that subject).
So what to do about the 172, 173 code indications?
1) Check and or Replace the HEGO sensor and hope. Is there a protocol for measuring/ testing this?
2) Check and clean or replace the ACT sensor? Only problem is that I have yet to locate it. Some say it is on the lower?? intake runner like under where the first injector is, passenger side. Have to check. And so is that a likely thing to clean up, being related to the fuel mixture and the HEGO sensor?
3) All of the above?
I do know that a MIL type of add on circuit can be installed on some vehicles which bypasses the O2 sensor, making it unnecessary. Does anyone know of anything like this that can be installed on this truck??
Seems like a never ending series of time consuming challenges. So what counsels can I get from the many marvelously talented diagnosticians at FTE!