I finally got the 1988 F150 on the road, 4.9L rebuilt engine with rebuilt C6 trans. 235 75 15 tires with 3;55 rear differential gearing. All sensors were replaced during rebuild with Motorcraft sensors, and Motorcraft plugs. The engine is in stock configuration with the exception of a World products distributor. I'm getting ready to swap that out with a rebuilt Motorcraft distributor with Motorcraft Ignition Module. I was having an issue with the engine having an erratic miss and sometimes it would stall at a traffic light. I decided to take it to a retired Ford Mechanic to do a complete "once over" to fix the erratic miss, occassional stalling and high fuel consumption.

The mechanic kept it for a couple of weeks, checked all sensors, including the O2 sensor and ended up replacing the E3 spark plugs I was using and installed Motorcraft plugs. The mechanic essentially found nothing wrong; however, the truck does seem to run better. The fuel milage is still abysmal about 9mpg empty. and I still have the miss and it appears (plugs, tailpipe, smell, fuel milage} that the engine is running extremely rich.

I can use bigger tires, change differential ratio to get better gas milage BUT that engine is running rich and I would like to correct it. The prime suspects are the MAP sensor and/or coolant temp sensor. There are no apparent vacuum leaks and my vacuum gage shows 18-19 at the vacuum tee. After the engine warms up, I can disconnect the coolant temp connector and the engine idle speeds up like I would expect. Anyone have any ideas?

 

Have you checked your FPR?

 

jas88;
Thanks for the reply. If you are referring to the Fuel Pressure Regulator (FPR), I think I replaced the FPR during the course of the rebuild. I replaced it again after I ran out of other ideas (an act of desperation) while trying to run down the cause of my erratic miss.

 

I don't see any mention of you pulling codes.
Does the exhaust have a cat converter?

 

That C6 transmission also kills MPG, but for rich running, was the O2 sensor replaced? I had a few new O2 sensors bad out of box causing rich running before.

 

No catalytic converter in the exhaust system. I haven’t run any codes since I got the truck back from the “Ford Tech”. I thinkI’ll do that now..

 

Sadly, yes the O2 sensor was changed. I installed a brand new Motorcraft O2 sensor right before I took it to the “Ford Tech”, he ended up replacing it with another Motorrcraft O2 sensor during his trouble shooting by replacement work.
Early on, I focused in on the Coolant Temp Sensor and the MAP Sensor as the likely cause of the “rich” running condition. There were no codes that I was able to retrieve to point to those two sensors; however, it “seemed” to make sense the “rich” condition was fouling the plugs and O2 sensor that was also contributing to the erratic miss. This issue is driving me crazy, which is a very short trip.

 

Conanski;
I checked the codes and got 81,82,84 codes KOEO. I believe these are related to the fact the EGR and Air injection hardware is not operating on this engine. I got a code 41 C (continuous). According to my limited research, there are lots of things that can cause a code 41. Not sure where to go from here ; however, it does not appear this engine is running lean.

 

If O2 tells ECM its lean, the ECM will throw more fuel at it, is EGR, and Air Injection blocked off that not oxygen can enter the exhaust before the O2, have you checked fuel pressure, should be 50+psi, for the 4.9L, not the 30 psi v8's say, parts store could be giving you the wrong FPR.

 

Gas Hog Afterword
Well, it appears I fixed the truck. I've got about 80 miles on the truck after my last effort and the truck starts easily, idles smoothly and does not stall at lights. It has ZERO misses during this 80 miles which included both freeway and in town driving.
I outlined what I did to the engine during rebuild thru various previous posts. As soon as I started driving the truck. From the beginning i experienced an erratic miss, stalling at lights and high fuel consumption. I always thought it was an ignition/engine management related issue. I decided to make sure all sensors and key components were Motorcraft. The last component that I replaced was the distributor. The engine that I used as a donor was missing the distributor. I first bought and used a new World Products distributor. I decided to replace that distributor with a rebuilt Motorcraft distributor that had all new Motorcraft components: Ignition Control Module (ICM) , Rotor Button and Distributor Cap. I installed this new/rebuilt Motorcraft distributor and started the engine. I immediately knew the problem was fixed. No rough idle, no erratic miss and a 10 percent increase in gas milage. It is still early and I haven't put a lot of miles on the truck but it sure runs great now.
Lastly, I took a closer look at the World Products Distributor. The distributor looks great: the cap had no apparent defects or cracks and the rotor button looked perfectly fine. I found a youtube video that demonstrated how to check the Ignition Control Module with a Multimeter and it looks like the World Products ICM checks out as being OK. I did find one issue when I removed the ICM. There was a thick layer of grease/paste between the body of the distributor and the contact surface of the ICM. I found this odd because the backside of the ICM that mates to the distributor housing is metal. I would guess that metal backing is a grounding point to the aluminum distributor body and/or serves as a heat transfer point to the distributor body. A poor ground and/or overheating could be the cause of my previous problems. Of course there could be a problem with the Pickup Coil (PIP) inside the distributor. I did not test that because I have not found instructions on how it can be tested with the tools that I have.
Anyway, so far so good.

 

Hopefully it was a white looking paste, and not the dielectric grease, that comes with the ICM, the white paste is a thermal heat transfer paste, that keeps the ICM alive longer, test #7 shows PIP-->Part 5 -How to Test the Ford Ignition Control Module (Fender Mounted)