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1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks Discuss the Early Eighties Bullnose Ford Truck

Choke wire voltage and tracing

 
  #1  
Old 03-17-2019, 10:17 AM
dgoodsy
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Choke wire voltage and tracing

I am trying to get my 84 e-150 351w (holley 4180) running better and am working on the choke right now. Some previous owner has run a wire that is 12v keyed power to the choke. It seems to me that it pulls the choke off too fast. I can adjust the choke so it starts decent cold, but the engine stumbles when it has been running for a few minutes, but not fully warm yet.

The original choke wire is laying there, when I check running voltage with my multimeter it jumps around between 1 and 5 volts. When this original wire is on the choke the choke doesnt pull off fast enough. In fact it may never come fully off. I tried to trace the choke wire to see where it was coming from, but I think I got myself mixed up as I followed a wire into the cab and up under the dash. I didn't actually see where that one went.

question 1: what voltage should the choke see? I have seen some sources say 7 volts, others say 12v.

question 2: if I should indeed see 7v at the choke, where does the choke wire come from? What is the 7v source?

ps, i tried to troubleshoot this with the evtm i have, it gives instructions for a test light. It states that the stator should light up the test light and I measure 14.8 volts running there with a multimeter.

thanks,
 
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Old 03-17-2019, 05:39 PM
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All I remember is it coming off the back of the alternator - maybe the Stator connection? 7V sounds about right.
 
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Old 03-17-2019, 06:12 PM
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Originally Posted by ctubutis View Post
All I remember is it coming off the back of the alternator - maybe the Stator connection? 7V sounds about right.
Didn't some of the 351 4bbl engines have a 12v choke that was wired through an oil pressure switch or a relay on the firewall?...Or am I thinking of something else. I remember discussing this very recently, but can't remember the vehicle. I must go see if I can find it...
 
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Old 03-17-2019, 06:48 PM
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I know the fuel supply system ws set up like that if you had electric fue pumps, can't say I've recently seen a configuration like that for the choke heater (though it may exist and I just haven't seen it in a while. It should be in the EVTM if it exists.
 
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Old 03-17-2019, 07:07 PM
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If someone replaced the stock choke cap which did need the 7 volts from the stator on the alternator with a Holley replacement cap that requires 12 volts.

and then ran a 12 volt wire to it you May have a problem.
 
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Old 03-17-2019, 07:12 PM
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Originally Posted by Rembrant View Post
Didn't some of the 351 4bbl engines have a 12v choke that was wired through an oil pressure switch or a relay on the firewall?...Or am I thinking of something else. I remember discussing this very recently, but can't remember the vehicle. I must go see if I can find it...
On page 53 in this link Carburetor Circuits - Gary's Garagemahal (the Bullnose bible) They do show a 12v choke that uses a relay hooked to the stator of the alternator.

On page 15 in this link Charge & Power Distribution (Gas) - Gary's Garagemahal (the Bullnose bible) they show the more conventional system with the choke hooked directly to the alternator. I bet this is the system you should have on your van.
 
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Old 03-17-2019, 10:37 PM
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thanks everyone. I found some more Info this afternoon as I was going through the evtm and some other forum posts in more detail. my evtm states that i should have a wire from the choke heater going to the stator terminal on the alternator, but i see no evidence of any wire in that area other than the wire that goes to the voltage regulator. (although there are 2 posts on the alternator that are not used - ground and an unmarked post). The EVTM also states that it is 7.2 volts. Other forum posts i have found state that the stator post would actually be 12V AC but a multimeter set to read DC will read that as 7V.

Originally Posted by Old Hickory View Post
If someone replaced the stock choke cap which did need the 7 volts from the stator on the alternator with a Holley replacement cap that requires 12 volts.

and then ran a 12 volt wire to it you May have a problem.
i thought of this today as well. there is evidence of the choke heater/spring being off so it is entirely possible it is an aftermarket 12V unit too. My EVTM says the factory one should have less than 30 ohms resistance. If mine measures higher that that i will assume it is an aftermarket 12V unit.

Originally Posted by Franklin2 View Post
On page 53 in this link Carburetor Circuits - Gary's Garagemahal (the Bullnose bible) They do show a 12v choke that uses a relay hooked to the stator of the alternator.

On page 15 in this link Charge & Power Distribution (Gas) - Gary's Garagemahal (the Bullnose bible) they show the more conventional system with the choke hooked directly to the alternator. I bet this is the system you should have on your van.
Thanks for these links, i'm going to have to look for a legend to see what the different wire representations mean. i will have spend some more time tracing that wire, but i'm not ruling out either possibility.

Franklin, i see in the 85 evtm where the choke heater wire is routed, straight forward and then down on the passenger side of the engine near the alternator. Mine (the one i am assuming is the original) is routed to the front of the engine and then across to the drivers side, through a plug and then into the cab in the main bundle that enters right near the fuse panel. I haven't found diagrams like that in my evtm yet.
 
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Old 03-19-2019, 11:12 AM
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to follow up on this, i spent a few more minutes with the van and with the evtm yesterday. I found the choke heater measure 9 ohms resistance, and the cap says motorcraft right on it. this is conclusive enough for me that it is the factory 7.2v, not an aftermarket 12v heater. i also tried but didn't find if the van has a wire from the alternator to the choke heater. the stator wire from the alternator goes into some convoluted tubing and straight to the regulator. I will try to get the convoluted tubing off to see if the wire that went to the choke is tucked inside or something. If not i will splice in there and run a new wire to the choke housing.

Now i question what i thought was the original choke heater wire actually is for. It is a yellow/red wire (i think) that comes to a plug on the drivers side where it changes to a white/red wire that i tried to trace and looks like it heads into the cabin and under the dash. hmmm...
 
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Old 03-19-2019, 12:23 PM
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Yellow red might be white/red that has yellowed because of age and engine heat. So it might be white/red the whole way. If it is, it goes to the oil pressure sender.

http://www.garysgaragemahal.com/uplo...jpg?1538601385

If you want to verify this, get a meter or testlight, and turn the key to run, leave the engine off. Take a reading on this wire under the hood. If it goes to the gauges it will blink voltage on and off like a turnsignal blinker. If you get this blinking voltage, then touch the wire to ground, the oil pressure gauge should start moving.
 
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Old 03-19-2019, 12:53 PM
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That is interesting Franklin2, with these old dirty wires in the hot engine bay i usually triple check colors and even then don't always trust them. I have measured voltage on this wire when the engine is running and it seem to bounce around randomly (my meter is digital, hard to tell if is is truly random or just a fast oscillation) but it appears to stay in the 1-5V range. Also my oil pressure gauge has always read 0. I will test this as you say and investigate farther.

thanks for another lead!
 
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Old 03-20-2019, 09:05 AM
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I spent some time yesterday testing/checking as Franklin2 suggested. I pulled the wire off of the oil pressure sender and wouldn't you know it was a white with black stripe. Bingo, i thought someone just (somehow) swapped the choke heater wire with the oil pressure sender wire. I figured i would swap them for eachother and would kill 2 birds with 1 stone.

I measured the voltage on the white/red wire with the key on engine off, and it did go up and down between 1 and 5V but seems more like a intermittent connection that a deliberate oscillation. I put it on the oil pressure sender anyways and started the engine. no dice, oil pressure gauge stayed at 0. I will have to get a helper and ground that wire and see if the gauge moves.

While the engine was running I measured voltage on the white/black wire - 14.2V. Not the 7.2V that should be on that wire. i guess this shouldn't have surprised me as i measured 12 or 14 volts on the stator wire at the regulator when everything i have read suggests that should be 7V as well. This is where i ran out of time and had to move on.

As a note, the white/black wire that was going to the oil pressure sender is white/black for the last 6 inches (the end that terminates on the choke heater), then a fusible link labeled "fusible link - 20ga" and the wire past the link is more brown.I wonder if that means anything to anyone? has anyone else seen that in a choke heater wire?
 

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