M5OD swap starter wiring issue

[4x4junkie]

I don't see a diode working either. Whether it's the 12V coming directly down the wire from the starter relay, or the residual voltage backfeeding from the motor acting as a generator, the current would be flowing in the same direction from the upper post of the solenoid to the control lead contact (maybe if you could put a diode on the lead where the small braided wire is going into the motor itself... That would work. But you'd need a diode rated at like 800 amps!).

 

[adsm08]

I don't see a diode working either. Whether it's the 12V coming directly down the wire from the starter relay, or the residual voltage backfeeding from the motor acting as a generator, the current would be flowing in the same direction from the upper post of the solenoid to the control lead contact (maybe if you could put a diode on the lead where the small braided wire is going into the motor itself... That would work. But you'd need a diode rated at like 800 amps!).

It would depend on how it is wired. If power comes in at the small post, then to the big one, you could put a high rated diode in to prevent power coming back to the small post. That should prevent the issue.

But yes, you would need a very large one.

 

[CountryBoy704]

Damn I wired it up with the single jumper and was gonna come back and tell you guys how well it worked....it's turning over like a champ and I'm not getting any weird noises or grinding from it, should I still re-wire it?

EDIT: also everything is back together and the truck is not cranking up(aka ignore ^that^ statement), it has sat for a while but I have periodically started it up and never had a problem so any suggestions as to where to start looking? Pretty sure it's electrical but that's as far as I got today before I ran out of light.

 

[RonD]

A diode would be a better choice. A resistor might keep it from working at all.

Postin' from teh Galaxy

Glad it is working Countryboy, unless you have a problem I wouldn't change it, you can always change it later.

So it is cranking but not starting?
Have you tried starting fluid in the intake to determine if it is spark or fuel that is the issue?

As far as the jumper wire:
If what I think is happening is happening, then a diode wouldn't work.
A resistor on the jumper wire would lower the voltage from the battery to the solenoid only, not starter motor, say to 8volts, so barely enough to activate the solenoid, or whatever voltage that is?
Like an old ballast resistor they used on the coil, cut 12v down to 8v

Then if the starter motor is acting as a generator, when battery 12v is cut off, the 8-10volts it might produce would be reduced to below solenoid threshold, by the same resistor, so no second activation.

But seem like alot of trouble just to avoid running another wire, lol

 

[4x4junkie]

It would depend on how it is wired. If power comes in at the small post, then to the big one, you could put a high rated diode in to prevent power coming back to the small post. That should prevent the issue.

But yes, you would need a very large one.

You're probably right, that may work. I wonder how much a 800-amp diode costs lol.

A resistor on the jumper wire would lower the voltage from the battery to the solenoid only, not starter motor, say to 8volts, so barely enough to activate the solenoid, or whatever voltage that is?
Like an old ballast resistor they used on the coil, cut 12v down to 8v

Then if the starter motor is acting as a generator, when battery 12v is cut off, the 8-10volts it might produce would be reduced to below solenoid threshold, by the same resistor, so no second activation.

I think that would leads to problems if your battery happens to be a slight bit weak, it may not be able to engage the solenoid through the resistor (plus it takes far less voltage for the solenoid to drop out than it does to engage it)


But yeah (to the OP), if it wasn't making noise, then I guess leave it alone. Myself & others had issues, so I wired it like the diagram I posted earlier.
Have you tried jumping the starter relay with a screwdriver? Does it crank then?

 

[CountryBoy704]

It's cranking like a champ but the engine isn't starting. I don't think the problem of the starter staying engaged would show up with out the engine actually starting?? I'll probably go back and re-wire it either way it looks pretty simple. Thanks for all the suggestions!
Haven't had time to work on it today, when turning over the exhaust smelled really rich so am going to start with electrical either this evening or tomorrow.

 

[CountryBoy704]

oh any my brother who is studying for his masters in electrical engineering thinks a massive diode should work and can actually get me one so I may play guinea pig for you guys just out of ccuriosity

 

[adsm08]

Well, first thing to check on a 2.9 is always spark.

 

[CountryBoy704]

got nice strong spark, cranked for a second with a shot of starting fluid so fuel system is next on the list. Definitely found that starter feedback issue when it started for a second so the re-wire is necessary for my setup anyways

 

[RonD]

I think the '87 still had 2 fuel pumps, low pressure in the tank and high pressure in the frame rail under the drivers seat.
Both are feed from 1 wire at the inertia switch in the passenger foot well/kick panel.

There should be a splice in that wire near the high pressure pump, that splice can corrode or disconnect, per adsm08

Both fuel pumps are powered by one fuse, in the engine compartment fuse box.
That fuse is connected to the Fuel Pump relay, when the relay closes that fuses power is sent to the inertia switch.

The fuel pump relay is powered from the EEC relay, they are next to each other.
The computer Grounds the fuel pump relay to close it, it only does this for 2 seconds when key is turn on, then it waits until engine starts and Grounds this relay based on RPM and speed.

So you should hear the fuel pumps come on for a few seconds when key is turned on.

 

[CountryBoy704]

definitely not getting that characteristic fuel pump whine when turning they key. The inertia switch didn't do anything so I assume it wasn't tripped.

I also noticed that the truck is cranking when the key is in the run position, I'm not even getting into the spot on the cylinder that springs the key back before it starts turning over

 

[RonD]

As far as the key switch, you could have used the wrong wire from the original solenoid for the new solenoid.
This was for the older 4 post solenoids, but also used on the 3 post solenoids, when coils were used with a ballast resistor or resistor wire.

Older vehicles with a coil had two smaller wires going to the fender mounted solenoid.
One will have 12v only when key switch is turned to Start, so no 12v in the Run position, this is for the starter motor activation.

The other wire was to send 12v to + side of coil but only when starter motor is turning, this gave the coil full 12v power when starting engine, when running the coil only has about 8v so it doesn't overheat.

If this other wire is still hooked to the + on the coil then it would have 8v-12v coming from the coil so if it was used it would activate the new starter when key was in the Run position.

 

[CountryBoy704]

Right now it still is set up with just a jumper from the main power at the starter over to the solenoid, have not yet re-wired the correct way so I'm not sure I could have the problem you're describing? I'll keep that in mind for when I re-wire properly though.

Can anyone tell me how to test the fuel pump and EEC relays?

 

[CountryBoy704]

got the starter re-wired today and can hear it disengaging and spinning down Thanks for the help with that!
I replaced the fuel pump relay, bypassed the inertia switch, and wiggled connections around by the pump and still nothing. Have an eec relay to put in tomorrow morning but I doubt thats the issue. Will I hurt anything if I just jump the relays and send 12V to the pump? I need to figure out if the pump is bad or if it's wiring problems

 

[RonD]

Yes, it's fine to send 12v to fuel pump for testing.

The 12v for fuel pump comes from the fuel pump fuse in the power box in engine compartment.
This goes directly to the fuel pump relay, it is a 24/7 power point, not on the key switch, when relay "closes" this fused power is sent to the pump.
The wire out of the fuel pump relay goes to the inertia switch, and then to the pump.

The key switch ON, activates the EEC relay which then activates other engine systems, computer, injectors, ignition and the Fuel pump relay.
So fuel pump power doesn't come from the EEC relay or fuel pump relay, it passes through the fuel pump relay when it is "closed", it's 12v power comes from that 1 fuse.

So you can remove the fuel pump relay and jump it there, or apply 12v at inertia switch.
The Ground is the other 1/2 of that circuit, if fuel pump is not grounded then it won't run.