ok, here's what ive been able to trace down:

A) #1(big ylw): obviously power source & its very much alive!
B) #4,37,&57 all are red wires that connect to the bundle having connections
the injectors.
C) #40&60 make the EEC relay "click" when the test light is applied.
D) there is slightly less than 12V at the coil connector
E) continuity is good at the #5 injector cable and the injector itself.
F) NO power at the injector harness connector (on the end stemming from the
main wire harness at the firewall)...at least nothing connected with the test
light when applied to the female prongs.
G) no power on the blue F-Link line at the EEC Relay
H) no power at the red line on the 3 prong connector located near the PCM and
relay.
****G & H are all linked in the F-Link going out thru the firewall and i would
think are hot leads but not sure on that.

I guess a diagram of what wires go to where from the PCM would be good. that would explain what should be hot and when.

thoughts?

 

does anyone think that an un-grounded PCM is the problem here (as DesertDave35 originally thought)??? Thus keeping V'age too low for self test output & proper working condition...

With that being said, is it possible for me to take the two wires, which show to be #60 & 40 on my schematic from Chilton's, and clip them above the connector and just pick a known ground spot and try grounding them there and see what happens? (leaving enough to splice back as they were of course...)

if you go back to page 2 of this thread, DD35 posted a diagram of the PCM wiring. On the left side, there's a horiz. line with signal return written by it. What does this signify? Can it be tested for anything in particular (noticing that its connected to the self test connector)

hukd

 

Take your meter and set it to ohms. Unplug the EEC relay and the PCM. Measure resistance from the black wire on the relay to ground. Measure resistance from pins 40 and 60 to ground. I think you are closing in on it.

 

here is a wiring diagram for the computer, maybe it will help. It is for ''87-'89 trucks, I think the '86 is very very similar. It's a little fuzzy, but it might be better than what you're working with.

http://www4.ncsu.edu/~ewpoe/12-36.jpg

 

Okay first off, if i'm boring you with details, i'm sorry, i'm trying to make sure anyone without a lot of electronice training can understand this. Before I was trained by the Navy, the Fuel injictection systems on cars were PFM, (pure freaking magic.) So I like to spread as much "'tron theory" as I can..... Hopefully it is helpfull.

Second, (Finally...) If applying the test light to the black wire of the relay causes the relay to click, thats a big problem. When the key is on, the relay should have clicked already, and be closed, and supplying voltage to the computer. Once the relay has closed, (on) it cannot click again till it turns off, which wouldn't happen when you ground it.

If using the test light on the eec relay blk makes it click, I would suggest making sure that the black wire is attached to a good ground point, (any metal frame/chassis piece) If not, that could single handedly keep power from the computer. The relay is just a magnetic switch. With no power it is open (like an off switch). When the power is turned on the magnet pulls the switch closed (an on switch). As soon as the control power is gone the magnet lets go, and the switch goes off.

Electricity needs a full path from plus to minus (or minus to plus depending on what theory you use). If you disconnect either end, there is no loop, and no juice.

It's definately sounding like a ground problem to me. If you can use the test light to ground the relay, then the chasis is grounded (connected to the battery - (neg).) The problem would have to be that the black is not connected to the chassis very well.

Third, per my '86 drawings, it sounds like your wiring matches an 87 more than an 86. I'll let someone with the service disk give more info on that.

According to the 87 drawing, the yellow connects to a brown fus link.....

So,

If you have power to the relay, and the relay operates when it is supposed to (when the key is on), then you need to check that power gets from the eec relay to the common hot "red" post that splits to 12 different outputs.

It sounds like the relay is not working right, though. That's good because you know what the problem is. Thats 90% of fixing something. Now you just have to prove it, and find out why.

...

Probing pins 60 and 40 should not cause the eec to click either, but could cause the fuel pump relay to click if the eec is not grounded.

According to my drawing, pin one is always hot. yellow, power from red fusable link. this connects through the relay to pins 37 and 57. (if yellow is hot at relay, fusable link is good.) if pins 37 and 57 aren't hot, then relay is not energizing.

wt-lt blue is from ign sw pin 12 and connects through blk-lt grn to ground on the other side of the EEC relay.

dk blu is switched hot(from eec relay) to blu fusable link, and EEC common Hot.

pins 58 and 59 are the fuel injectors returns to the eec. probing them should show hot, and release gas at the same time.

Pins 60, 40 are blk-lt grn and connect the eec to ground.

pin 37, 57, red is swithced hot from the eec relay

Ohming pins 60, 40, and the relay blk (blk-lt grn) to ground is next. They should all measure low Ohms (resistance). If they are higher than 1k(?) it is probably not a good ground connection.

---

The fact that probing pins 40 and 60 also energizes the the eec relay is a little odd. This is not a direct ground path for the relay, so it doesnt make sense that it would energize it. I keep trying to visualize why, but I just can't figure that. (based on the info that pins 40 and 60 ground near battery, it should be a seperate ground then the chasis in the cab, so in order for them to be floating (ungrounded) they would have to not be connected to another ground.

I think I finally understand the pin 40 and 60. They are grounded. When the connector is disconnected from the computer, pins 40 and 60 are still good grounds (from the connecter to the radiator support) but the computer is not connected at all. Probing pins 40 and 60 to ground connects the chassis ground to the radiator ground and completes the ground circuit, allowing the relay to energize. If this is right, the problem is that the chasis is not grounded right.

-----


Here is your task list:
'Use your meter to measure resistance (ohms)' from EEC relay blk to ground
' ' from pin 40 to ground.

Use a Jumper from the EEC blk to ground and see if it clicks, if so try starting.
look up the ground connections and make sure you don't have any floating;


I reserve the right to edit this in the morning.

 

ok, good info. a little lost but good info.
we've always thought it was a bad ground. and as previously stated back in earlier pages, there should, ideally, be 2 ground wires at the front of the grill to connect to the radiator mounts. BUT there is not. so, I need to find another way of making a good ground from under the dash evidently. Im open to ideas on this at this point.
thanks
hukd

 

Huk, check your resistances on your grounds and then making them if you need to is easy. Follow the wires out far enough so that they can be connected to something, cut them off, put an eyelet connector on the wires and attach them with a screw to something metal. You don't need to worry about getting the whole wire because it must not go anywhere anyways.

 

"Use your meter to measure resistance (ohms)' from EEC relay blk to ground
from pin 40 to ground.
Use a Jumper from the EEC blk to ground and see if it clicks, if so try starting.
look up the ground connections and make sure you don't have any floating"

OK, HERE ARE THE RESULTS OF THIS TEST:
1) EEC relay blk to ground ohms out at 0
2) pins 40 & 60 to ground peg out my meter.
3) jumping relay blk to ground does nothing.

At this point, which wire should I look to ground? with the above info, will doing this fix my problem (or at least what is the % chance?)

PS- the wires that I think are my grounds all go somewhere and most split off to something two or three times so figuring out what/where they go/ground is somewhat of a pain in the butt! so do i just go a foot or so outside of the firewall, clip them and ground them? and if so, do I ground all the black wires (ie EEC relay, comp connection, extra 3-prong connection BY THE WAY, WE HAVENT FIGURED OUT WHAT THAT DEAL IS YET EITHER!!!)

 

Man,...um...that just don't make sence. If your EEC relay ground is good, when you turn on the key and supply it with power,it should turn on.

What do you mean step 2 "pegs your meter"?

Lets do a couple more tests. Check resistance between pin 40/60 and the black relay wire. Also, with realy and comp unplugged, check these 2 for power. I'm starting to think that you have a "short to power" somewhere.

 

by pegging my meter, i mean that it topped the reading out.

Hallelujah!!!
I spliced the black EEC relay wire and ran another wire out to a ground spot for my headlights. Now, when i turn my key on, my fuel pump cycles and cuts off as it probably should! And to add more, I have comp. comm's. It threw out codes for:
a) Engine Coolant Temp sensor signal voltage out of range, not @ normal op. temp. or loss of signal (during normal engine op)
b) TPS signal voltage out of self test spec's.
c) Air Charge Temp sensor or Vane Air Temp sensor signal voltage is out of
spec's (engine off) or not at normal levels (engine running)
d) EGR valve Position sensor or Pressure Feedback EGR sensor signal voltage is below min. spec's.

Now all this is from the Key On Engine Off test data. Havent tried to crank it yet due to I want some feedback on my splice to make sure that this is an ok thing to do and the operations I've gotten as a result are ok.

hukd

 

Alright! Sounds good to me. It appears to be doing what it's supposed to now. I'd go for it and see what happens. The TPS thing might keep it from starting but, I don't see a problem with the others. (things to work on later)

The pegging is still getting me,although not a big deal. What kind of meter are you using? I thought that on ohms it would read infinate until it saw continuity and then would "peg" at zero.

Since that repaired your ground, something you may want to think about later is to get some good ground-straps and run 1 from the motor to frame and 1 from body to frame.

GOT MY FINGERS CROSSED.

 

Ok, Let's see,
1) good, but strange. 0 means no resistance, or a good connection.

2) Pegs out meter, I take means High resistance. Which means that those wires are not connected to the same ground as the one your touching (all grounds should be connected together via the chassis).
*Try ohming between pins 40 and 60. This will tell if they are connected together. Did you try a couple of differnt ground points in the cab? Any unpainted metal should work. We suspect the eec relay ground point, so don't use that.

3) Odd, should do the same as using test light.

The clicking when you probe the relay black wire with the test light says it's not a good connection to ground.
Did you measure to the same place you attached the test light from?
Where was that specifically? The place where the black wire attaches to the chassis, or just a good piece of bare metal on the chasis.

About clipping the grounds.
If the ground wires connect to other things and split off, you don't want to clip them, in case you unground something else. You could use one of those wire taps to tap off the ground and connect that to any piece of metal.

Is that orange wire from a couple days ago still grounded? Did you find that on the wiring diagram, I forgot to look for that last night. All the other grounds are blk-lt grn, so I'm wondering if that is not supposed to be grounded. If you can't find it on any drawings try unconnecting it.

With the new EEC relay, does it click when the key goes from off to on? or only when you probe it still? if yes to probe, where is the probe wire attached?

From your testing of the Relay socket, everything else is normal, except the clicking when probed. The power comes on, when it supposed too, the relay is just not able switch because the ground circuit isn't working.

---

If it makes you feel any better, this is a very odd problem, and it would probably anyone a while to track it down.

quote ----- end quote

a, good yellow should be always hot.
b, is this with the relay plugged in and key on?
Try doing this using meter volt function, and test light on the relay so it has clicked.
f, g, h all get power from the eec relay, so the relay not working causes all 3.


Okay, here are the top priorities, please get the rest too though.

Check EEC relay blue wire with Volt Meter, while probing EEC relay black (with relay clicked) It should be hot when the relay clicks.

One explanation of the EEC clicking when probing pins 40 and 60 would be that 40 and 60 ARE grounded, and connecting the cab chassis to them provides the cab a good ground, allowing the EEC relay to energize.

 

Is it running yet?

 

Okay, I was a little slow, but glad to see I was on track.

Don't worry about any codes, at this point, the engine is supposed to be warm when you run the koeoff test anyway, and it will throw some fakes codes if not. Just try cranking it see what happens.

Putting in an extra ground wire won't hurt anything. Putting on a couple extra grounding straps sounds like a good plan.

Congrats!!

 

ok...it didnt crank. radio works, relays click, FP comes on/goes off. My battery was pretty much drained so Im hoping that after charging it up, it will actually turn the starter over. can anyone think of any other reason that it wouldnt even budge? by splicing a ground wire into the existing EEC relay black wire, did i circuvent something important and thus make it not spin the starter?
advice....
hukd