I've got an 86 F150 4x4 w/302fi. The truck ran fine two weeks ago when I last drove it. I went to start is and no deal. It cranks fine but no fire. I'm getting spark and fuel to the fuel rail. And yes, there is gas in it. The strange thing is that when I first turn the key on before I hit the starter, the fuel pump comes on and stays on. Normally it would cycle once for about a second. I disconnected the battery over night to clear any codes stored in the memory. Still no start. I tried to get the codes but nothing happened. I used a test light to flash the codes because I don't have an analog meter. Once I hook up the light it comes on. When I turn on the key to start the test, the light just gets brighter--no flashes.

I tested the harness as stated in the Hayes manual and it checks out OK. Is my computer bad? How much will another one run me? Where would be a good place to get one cheap?

Thanks for any help!! CR

 

It sounds like you had the test light hooked up wrong. The '84-86 EFIs have slightly different wiring from the later ones; how exactly did you have everything hooked up to test?

 

I hooked it up following the diagram on page 4-16 of the Hayes manual. Looking straight on at the connector, with the 2 terminals on top-4 on bottom. I jumpered the self test input to the top right. Then I connected negative of my test light to the lower 2nd one from the left. I put the positive from the light on the battery. My test light is an LED so I think polatity matters. It lit up as soon as I connected it and the key was off. I was able to get codes this way before.

Have you ever heard of any thing like this before? Keep the help coming!

Thanks! CR

 

First, I'd get an incandescent test light.

Second, make sure you're putting the STI (Wh/R) to SIG RTN (Bk/Wh) and STO (Tan/R) to 12V. Note that Wh/R will look tan/red on a truck that old, so make sure you're jumping the right circuits.

 

Well..still no luck. I switched to an incandecent test light and verified that I was hooking it up right. The light comes on when I turn the key on but no codes flash - the light just stayes on.

If I have to get a new computer do I have to get one from an 86 w/302fi and manual trans? Will another year work or one with an auto?

Thanks for the help steve83. From the looks of your web site, you defintely know your stuff.

CR

 

Transmission isn't important for that year since none of them are controlled by the EEC. You need to stay with a 5.0L computer with no transmission circuitry, so I think you could use any 5.0L up to '95 as long as it's not a MAF computer. But you'd have to do some research in the wiring diagrams to find out if there are any circuit changes.

IF yours turns out to be toast, I'd recommend you get an '86 5.0L reman computer with a warranty from a parts store for ~$180. But before you hook it up, determine if the original died from age or some wiring problem on the truck. You don't want to kill the replacement.

 

Crothenberger,

In your 1st post you said you disconnected your battery over night to erase any codes. Later you say you can't get a D-code with a test light. Once you dump the RAM out of your ECM you have no codes present. It wipes 'em out when you pull the plug.

That's why you can't get a D-code read out. If you're chasing gremlins in a digital management system with a diagnostic capability, you should not dump you RAM until you have either read & copied all the D-codes, or repaired any problem you had.

You wil not have any D-codes until you get the engine fired up & drive it for 45 minutes or so. All you have in your ECM is ROM now.
You can't read ROM or P-ROM programs.

Also connecting a 12V test light to the wrong PIN can erase data & programs on a chip. It often takes INI data & system may not initialize if INI Data gets corrupted. . . .

 

Thanks for the info. You're right I should have retrieved the codes first. I'm kicking myself now. The fuel pump was running constantly with the key on. Normally it would cycle once then run full time once the engine started. The FP relay checked out fine. The ECM was keeping it energized constantly. I thought maybe the computer was locked up like a PC - Shut down and restart.

I'm sure I had the test light hooked up correctly. Would I at least get a code saying system functioning? I hope I didn't do perminent damage. How would I restore the INI data you mentioned without costing an arm and a leg? Do you know how I can definitely determine if the ECM is bad?

Thanks!

CR

 

You could try to find a similar truck and plug your computer into it.

 

I would check all the ground pins(there are several) on the harness with an ohm-meter to make sure there is no resistance to battery ground and check the +12V pin if you haven't already. A bad/floating ground or power will cause the computer to do weird things. Had you been doing any work under the hood where you might have pulled loose a wire? Getting a new EEC would be my last resort! Good luck!!!

 

It's fixed. It turned out it was the computer. I was able to find one from a junk yard (auto recycle facility to be PC) for $20. I got it out of an 85 with the same engine but auto trans. It worked out just fine. Thanks for everyone's help!

CR