Strange Starting Behavior

[nelbur]

I have an '86 Bronco with a 302 EFI. Nine times out of ten, it starts immediately with no throttle, but every now and then it will just crank. If I give it half throttle, after about 15 seconds it will start to stumble, and slowly improve over a few seconds, until it is running fine. It never quits after it is started. I assumed that the fuel pump was not pressurizing the rail before the key was turned to start. When it is in this mood I have tried turning the key to run and leaving it on for a few seconds, before trying to start it, with no change. I replaced the fuel pump relay but it did not help. Has anyone solved a similar problem? Any suggestions would be appreciated.

I see from my manual that there is an EEC power relay. Anyone know where it is on this truck? It also shows in the pump circuit the electronic control assembly. Is that the computer or the ignition module? I assume the inertia switch is good or it would not start at all.

This basic EFI stores codes that are read with a test light. Can anyone point me to instructions for hooking the light up and interpreting the codes if any? My manuals do not cover the topic. Thanks for any help you can give.

 

[Seabronc]

In an EFI engine, pressing the throttle has no real effect on the amount of fuel. That is handled by the injectors and the EEC. When you press the throttle on an EFI engine, you regulate the air volume. Also, you move the position of the TPS which tells the EEC that you have changed the position of the throttle. Based on the voltage signal from the TPS, the EEC adjusts the amount of fuel sprayed into the cylinder.

Have you checked for codes? Even though the Engine check light may not come on there may still have been some codes generated that will point you to the flaky component. So first I would get a readout of the codes to see if they indicate anything.

The EEC relay is not your problem. If it didn't work you would not get the engine to run at all since the EEC would be OFF, and the fuel pump relay would not activate.

Good luck,

>-

 

[BroncoJoe19]

Pull Diagnostic Trouble Codes (DTCs) From your onboard computer.

Your engine and transmission are computer controlled.

The computer uses sensors to tell it a number of different things and it controls actuators that push or pull mechanical levers (kinda). If one or more sensors aren't working properly, the computer goes "blind" and doesn't know what to do. If the computer can "see" but one of the actuators is broken and therefore can't follow the commands of the computer; the engine won't run correctly. The computer is preprogrammed with set values for each of its sensors, and each of its actuators. It will run a self check of all systems, like the space shuttle; it will compare its set value(s) to the value(s) it recieves from its sensors, and actuators. If any sensor or acutator is out of the "normal" range the computer will generate a "code." It will generate some codes on the fly, and others will be stored while you are driving. There is a simple method to "pull codes" out of the computer for one to use for diagnostic purposes.

Earlier versions of On Board Diagnostics OBD 1983-1995 can flash the error code to the dash board and can be pulled in one's driveway without any special tools.

Later versions of On Board Diagnostics OBDII some 1995, and pretty much all 1996 and newer, require one to use a code reader or scanner tool.

Some auto parts stores will scan your engine codes for FREE, you may want to call around. Some will scan OBDII but not the older (prior to 1996) OBD systems.

SO here you go...

How to scan FORD on board Diagnostic Trouble Codes (DTCs) in your driveway

HowTo Pull Codes 1983-1995 Broncos, Mustang, F series Trucks, Econolines, 302, 351 and more

I agree with Seabronc about stepping on the throttle, so the one thing that MAY be at issue is a sticking Idle Air Control Valve... IAC you might try cleaning it.

http://www.fordfuelinjection.com/?p=39

 

[nelbur]

Thanks for the comments. I tried to pull the trouble codes today using a test light. I was not able to get any flashes. I tried hooking up the test light before turning the key on. Then I turned the key on and then hooked up the test light. Neither gave any flashes. I seem to remember some introductory flashes when I pulled codes in the past. The light did light in the fuel pump test connector to the far right. On this early EFI the test connector is on the right front fender well. There is no check engine light.

Today I was not able to start it when the engine was hot, but it started fine about an hour later. I wonder if my ignition module is going again. I have not had these symptoms when the other four or five went bad, but it sees plenty of heat there on the distributor.

 

[Seabronc]

Thanks for the comments. I tried to pull the trouble codes today using a test light. I was not able to get any flashes. I tried hooking up the test light before turning the key on. Then I turned the key on and then hooked up the test light. Neither gave any flashes. I seem to remember some introductory flashes when I pulled codes in the past. The light did light in the fuel pump test connector to the far right. On this early EFI the test connector is on the right front fender well. There is no check engine light.

Today I was not able to start it when the engine was hot, but it started fine about an hour later. I wonder if my ignition module is going again. I have not had these symptoms when the other four or five went bad, but it sees plenty of heat there on the distributor.

That does have the flavor of a pickup inside the distributor shorting out. If you buy your parts from a Big Box chain store, I would sugest you go to a professional parts supplier to buy the part.

Good luck,

>-

 

[nelbur]

I replaced the ignition module today. I started it a few time with the engine warmed up, with no problem, but since the problem is intermittent, it will be awhile before I am sure I solved the problem. I do know for sure that I would like to get my hands around the neck of the engineer that put the module down behind the thermostat housing.

 

[nelbur]

Well, it's been two weeks since I replaced the ignition module, and I have had no more starting problems. In the past the truck went dead with a bad module, but there must be a failure mode that is intermittent.