I'm working on a friends 1989 F150 with the 4.9l, M5OD trans, and a computer that was a reman from a previous mechanic. The truck does not run right, hunts for idle, stalls on sudden throttle changes, and the EEC does not run the fuel pump. I've been validating the EEC pin for the fuel pump isn't grounding to start the fuel pump, so its wired to run always when the key is on. The MAP and TPS sensors are seeing ~5.1 volts supply, however the ground connection is intermmitent. I've cleaned the chassis grounds, pulled the connectors for the sensors and the EEC off, cleaned them, added some di-electric grease, and validated good continuity between the sensor connectors and the EEC connector, as well as the fuel pump relay, EEC power relay, and a few other things. At one point the truck would not start at all until I jumpered the sensor ground to a chassis ground, then a few days later it starting working again without me having to provide an external ground through the diagnostic sensor. The truck runs sometimes, but always badly, and sometimes doesn't want to start at all unless I ground the sensor electrical return.

The computer in the truck currently is a E7TZ-12A650-AL1A from what I can read, the label is faded and I can't read anything else off of it. The -AL1A is very very faded and may not be right. Looks to be from a 1987 Bronco. The other relevant info is the emissions sticker on the truck lists federal emissions and does not mention anything about high altitude. I've been reading over a few sources of info to ID if this is the right EEC or not:

https://www.fullsizebronco.com/threa...ve-list.64368/
Fuel Injection Technical Library » EEC Program Codes

https://www.partsgeek.com/catalog/19...trol_unit.html

Based on being a basic 1989 4.9L with the manual trans and federal emissions, is there a better lookup table to see what computer I need or validate this one is correct? Other things I will be looking at is the frequency response of the MAP sensor. I've already validated a good linear response from the throttle position between 2000 Ohms closed to 500 ohms full open. Also, if anybody can tell me where the intake air temperaure sensor is located, I've done some looking and haven't found it to check its readings. Other sensor to check I think is the coolant temperature.

I suppose other routes to investigate is a new fuel filter, some cleaner. The pump runs when the relay is jumpered and the system holds pressure, tested by pressing the fuel rail relief and observing a residual spurt of fuel when the engine is off, and I get a decent spray of fuel when running if I hold the fuel rail relief open.

 

I am in a similar boat as far as hunting for idle. My EEC plug will not power on my code reader or the one from the local parts store. I have changed everything i can think of, including the computer, and get nothing. The voltages are super weird to sensors which is what drove me to change them. Aside from a new harness i don't know what to do with it at this point. The PO had hacked in a bunch of junk all over the harness but that is all cleaned up at this pont. Hard starts are frequent and it runs rich all of the time but at least it is running.

 

you try the paper clip, and count flashed-->Fuel Injection Technical Library » How To Run a Self-Test
walks you through how to check PCM-->Fuel Injection Technical Library » No Codes?
may help find what/if wire shorted or broke/cut, somewhere.

 

I have exactly the same issue. 1988 F350 custom with 7.5L. It was an old fire service vehicle I bought at an auction. 29,000 miles on it. I have been going nuts and wasting a lot of time chasing down what seems to be a wiring issue with EEC/fuel pump circuit. It will start and run rough for about 5 -10 minutes then suddenly stop with no fuel to injectors even though the fuel pumps are running. Then it wont start (no fuel) and the fuel pumps just keeping running when the key is on as if the EEC isn't controlling the circuit. If I wait an hour or sometimes a day it goes back to the 2 second prime and will start.

All of the grounds were bad - block, body, frame. I had 0.75 volts on the chassis all the time. I spent a day and installed all new ground straps and now I have good ground everywhere and no rogue voltage. I have replaced almost everything on this truck recently including a new PCM just trying to eliminate any sensor issues. New injectors, new distributor, new plugs, wires. No issues with spark. When it is running at idle I had 40psi fuel pressure at the rail.

I am trying to figure out how to tell if my problem is with the fuel pumps or the EEC. I also am concerned about the EEC ground/connector. It has the 60 pin connector. I bought a used breakout box off EBay
but it has not arrived yet. Any help?

 

All of those symptoms point to a bad computer. You may have replaced it but it may be bad as well.


That is too high. Should be ~30-32 PSI at idle with the vacuum hose attached to the fuel pressure regulator.

 

I got the breakout box today and using the diagnostic manual and the shop manual and following all the tests they both lead to replace the fuel pump. Fuel pressure is high when if it runs or none at all. The connector at the high pressure pump has 12 volts with key on and the ground has continuity and in spec resistance. There is continuity through the fuel pump motor coil. The computer seemed like it was working because everything else it control's were good. All the sensors tested fine (except the O2 sensor) which had no voltage but I did not explore that assuming the engine needed to be running for it to work. All the powers and grounds in the computer were fine. The fuel pump relay was fine. The inertia switch had 12 volts and in spec resistance. There is power and good ground to the fuel pump and it runs, but will only intermittently produce flow and pressure. I have never seen a fuel pump that was running not pump fuel. My experience has always been either they are good or don't run at all. Not sure what to do except try a new fuel pump.

 

Where is the inertia switch? Pretty sure PO had an accident and never switched it out but i can't find it behind the passenger kick panel. They may have jumped around it to get the truck running to sell it. I can not find the damned thing anywhere.

 

How do i correctly test the voltage on the connections? I have been trying to find problem and i may not be testing the correct way. Thank you much.

 

The inertia switch sits on the driver side firewall right behind the brake petal.

 

Anyway i can get a picture? I think it might be totally gone and bypassed somehow.

 

Courtesy of Steve83 and Subford

 

That is awesome! Thank you very much!
I found it. Slightly to the left. I can see red on the top portion. The truck has left front damage so i think it was wrecked and O may need to change it.

 

I got the code reader recommended by a few people on here and it won't turn on. Went with the trusty paperclip and got the following.
31 67 31 67
then it stopped for a good while then gave me the following.
34 34
Stopped for good after that. The codes come up as follows.
31=egr valve control sensor fault. And/or... evap control system below minimum voltage.
67=air-conditioning compressor clutch switch fault
34=egr control circuit fault. And/or. Defective egr pressure transducer sensor.

The book with the code reader has 3 one letter codes to go by.
O=key off engine off
R=key off engine running
C=continues memory
I had the key on and the engine off so I am not really sure what that would mean...?