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1987 - 1996 F150 & Larger F-Series Trucks 1987 - 1996 Ford F-150, F-250, F-350 and larger pickups - including the 1997 heavy-duty F250/F350+ trucks

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Old 08-10-2012, 09:16 AM
VBMECHANIC VBMECHANIC is offline
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88 460 no spark - possible wiring

Just bought an '88 F350 460 that didn't run. Although there are a number of reasons for this, I'm trying to tackle the problem of not having spark. The first thing I did was buy an ignition module (TFI). I know how problematic they are and figured that I'd want a new one regardless. No joy. After doing some research and having some fun with my test light, I discovered that there is no blink the negative side of the coil. There are 2 wires coming from that terminal. One goes straight to the TFI and the other goes into some inline box that looks like a fusible link on steroids with 2 wires coming out the other side that go back toward the passenger compartment. WHAT IS THIS BOX? It has a rubbery exterior with a squiggly line symbol on it. I disconnected the distributor and TFI plugs and hooked a ground wire to the negative coil terminal. I then checked each wire on the other side of the mystery box and got nothing. I checked these wires for any kind of signal (+ or -) while turning it over and nothing. I haven't traced where they go exactly.
I've already found a couple of wiring problems in the truck, so I'm not only trying to figure out if there is a component bad, but if any of the wiring is faulty. I don't want to clip out the mystery box and splice the wires until I know what the thing does.
Also, Anybody know how to test the stator in the distributor? If the wiring checks out, that's my next area of focus.
Thanks!!!
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Old 08-10-2012, 09:26 AM
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Did you look at the cap/ rotor, plugs, wires, COIL WIRE?
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Old 08-10-2012, 09:28 AM
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That item is a 22K ohm resister and a 1.8K resister. The two wires leaving are the IDM (22K) wire going to the computer for information only and the other wire goes to tachometer (1.8K) in the cluster.

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Old 08-10-2012, 09:48 AM
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Electricity runs in a stream. The best way that I've figured out how to test electrical problems is from one end or the other. As best as I can tell, The flow of electricity from the end to beginning goes as such - plugs, wires, cap, rotor, coil, ignition module, distributor stator....and from there, I don't know. The problem is upstream of the coil, so to answer your question, Yes. I get a constant positive to the coil. There is continuity to the TFI (ignition module) from the negative side of the coil. The TFI is new. There is another wire from the negative side of the coil to an inline box. I don't know if the electricity streams from the coil to this box or to the coil from the box. Both wires from the box go toward the engine compartment. I'm going to find where they go, though. I know that there has to be a computer somewhere in this stream but I don't know where it connects. I also need to check grounds to each component in the stream. The specific question in this tread was to find out what the inline box does and it would save me some work if someone knew where the wires from it go.
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Old 08-10-2012, 09:50 AM
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Subford....THANK YOU sir!!!!
I'll post my progress.
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Old 08-10-2012, 10:03 AM
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You may want to unplug the computer while trying to get the spark to return.
This does two things.
1. It keeps you from dumping any fuel in the engine without spark.
2. It may let the spark return if a bad computer is keeping it from having spark.
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Old 08-12-2012, 02:56 PM
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Subford, I think you're quickly becoming my new best friend. I went and picked up a Stator for the distributor. It looked original so it was time to change it anyway. Still no coil pulse. Then...I unplugged the computer. Suddenly, I have spark!!!
So now, I have to wonder if the problem is the computer itself or if there is something sending an incorrect reading to the computer that is causing it to go into shut down mode. My fuel pumps aren't working either. I know that there is a short going to the pump in the tank but there is no problem with the wiring to the booster pump on the frame. It SHOULD be working but isn't. IF the computer is in a shutdown state, could it shut down the pumps and distributor? If I assume the computer is good, what could cause it to do that?
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Old 08-12-2012, 03:16 PM
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If you have power on pins 1, 37 and 57 with the key on and grounds on pin 40 & 60 at the computer with no pins pushed out in the plug then I would say you have a bad computer.
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Old 08-12-2012, 03:25 PM
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So you say that I SHOULD have power and grounds to the pins you mentioned. If not, I have a bad computer. Am I correct?
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Old 08-12-2012, 03:44 PM
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...also, there are no pin numbers on the computer or the plug. There are 60 pins total arranged in groups of 10. 3 groups on one side and 3 on the other. I'm assuming that pin 1 would be at the top left corner of the computer when the designation sticker is facing up. Do the pin numbers run straight across (1-20, 21-40, 41-60) or down (1-30, 31-60)? Making a mistake here would give me a false result.
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Old 08-12-2012, 04:04 PM
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Ford did not put a pin-out in the 1988 wiring diagrams so I will post two from the 1990.
They should be close to the same:
Click the image to open in full size.
Click the image to open in full size.

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Old 08-12-2012, 04:05 PM
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Quote:
Originally Posted by VBMECHANIC View Post
So you say that I SHOULD have power and grounds to the pins you mentioned. If not, I have a bad computer. Am I correct?
You are correct.
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Old 08-13-2012, 05:30 PM
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I found no ground signal at pin 40. I traced the wire to the temperature sensor which appears to be new. The other wire from the sensor goes back to the computer to pin 7. I tried backfeeding the ground at pin 40 and I got spark for a moment. Then nothing. I left for a couple hours and came back to it. plugged it all back together and I checked pin 40 again to find a ground. Cranked it and had spark. After a couple tries, the ground signal vanished and no spark anymore. They seem to be related. I tried jiggling the harness to see if there may just be a bad connection somewhere but I got nothing.
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Old 08-13-2012, 06:02 PM
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Quote:
Originally Posted by VBMECHANIC View Post
I found no ground signal at pin 40. I traced the wire to the temperature sensor which appears to be new. The other wire from the sensor goes back to the computer to pin 7. I tried backfeeding the ground at pin 40 and I got spark for a moment. Then nothing. I left for a couple hours and came back to it. plugged it all back together and I checked pin 40 again to find a ground. Cranked it and had spark. After a couple tries, the ground signal vanished and no spark anymore. They seem to be related. I tried jiggling the harness to see if there may just be a bad connection somewhere but I got nothing.
Here you go.

Click this link:
A9x ECM's (and same years ECM's) Failures Due to Age

If you see the "leaking capacitor" thing happening and you're handy with a soldering iron, give it a shot.

I repaired my computer for about 5 dollars.......parts available @ Radio Shack

If you see "mass destruction"......burnt chips, circuit board, and the like, just get a re-manufactured one or one from a bone yard.....of course open up the bone yard one and give it a visual check before installing too.

Good Luck !!


Bob
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Old 08-13-2012, 06:22 PM
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Pin #40 goes to the "NEG" (-) post of the battery.
There should be a black wire with a green stripe leaving the NEG post of the battery and going through a one wire in-line connector that loos like a fuse holder, this is the other end of pin #40 and #60.
This wire has been the problem on a lot of 1988 F-series trucks.

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Old 08-13-2012, 06:22 PM
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