| Ignition system voltage drop [message #239586] |
Tue, 11 February 2014 18:16  |
gbarrow2
Messages: 765
Registered: February 2004
Location: Lake Almanor, Ca./ Red Bl...
Karma: 3
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1976 455
With the ignition switch "ON" I read 12+ volts on lead to the distributor when disconnected. When connected to distributor I read only +/- 6 volts.
Starter cranks normally but no start. My timing light will not fire while cranking so I assume 6volts is not enough to energize the coil.
The engine started easily and ran fine 2 weeks ago (with the same distributor) on the test stand for cam break in.
Engine is now re-installed in the Palm Beach. Ignition system worked fine before engine removal.
The coach has been sitting without the engine for several months and it seem that the electrical gremlins have infected it.
I metered my Eleganza distributor lead for comparison. There is only ~1/2 volt drop between connected vs disconnected readings.
I swapped the Eleganza cap, coil, and plug wires ( it was running fine 2 days ago) into the Palm Beach.
No joy. Still only~ 6 volts with leads connected.
So I assume the problem is upstream from the coil.
However, I changed the module because I had a spare. No change.
I traced the wire up stream to and through the firewall behind the glove box fuse block.
It's not connected to the fuse block but I cant trace it through the dash. I assume it goes to the switch on the steering column.
Suggestions please.
Let The Games Begin! First person with solution gets bragging rights and my gratitude.
Thanks for the help.
Gene Barrow
Lake Almanor, Ca.
1976 Palm Beach
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| Re: Ignition system voltage drop [message #239590 is a reply to message #239586] |
Tue, 11 February 2014 18:24  |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Meter at the switch output with HEI connected and see if it's 6v there. If so you are near the problem. If 12v search forward. Is there a bulkhead connector where it all passes though firewall like most GM? I'd disconnect and inspect and maybe clean with Deoxit D5. Look for oxidation and heat evidence
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Ignition system voltage drop [message #239595 is a reply to message #239586] |
Tue, 11 February 2014 18:34 |
Otterwan
Messages: 946
Registered: July 2013
Location: Lynnwood (north of Seattl...
Karma: 0
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| gbarrow wrote on Tue, 11 February 2014 16:16 |
The coach has been sitting without the engine for several months
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I hope I'm not stating the obvious but are you sure your battery is good?
1977 Birchaven, Lynnwood WA - "We may not be able to stop all evil in the world, but I know that how we treat one another is entirely up to us."
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| Re: Ignition system voltage drop [message #239608 is a reply to message #239586] |
Tue, 11 February 2014 19:09 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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OK Gene,
You have given a pretty good set of diagnostics to work from, so lets see what we can do.
The battery is up to density - Right? ~12.6 unloaded?
When you pull the power lead out of the HEI it says something like 12 ???
When you connect it, it goes to ~6 -- Right so far?
You have two places to look.
First would be check the pink wire as it goes onto the ignition switch on the column. Ignition on and connected.
Do you get 12V there?
No - Good we go on to the best bet.
Yes - oh boy, you have a bad junction between the pink and the black double white stripe in the harness...... Somewhere
Best bet is the fusible link. This is a little piece of black wire that goes between the Vehicle Battery Junction (the bolt on the aluminum plate next to the HVAC box) and the funny looking relay thing next to it.
If the Vehicle Battery Connection is a good 12v and the heavy screw (under a plastic cap) on the horn relay is less, then the fusible link has checked out. It may just be that the terminals are corroded, or it might just come loose when you pull on it. The pull is always my first test of a fusible link because it requires no tools or instruments and if you can pull it loose, it was already junk.
Good Luck
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: Ignition system voltage drop [message #239611 is a reply to message #239595] |
Tue, 11 February 2014 19:44 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Since it is a 1976 I am assuming you are working with an HEI distributor
First to get it started. Run test lead from the HEI +12 terminal to the +12 volts. You can find that on the big terminal that says "+ positive voltage" or something like that near the isolator.
If it starts and runs then you can forget anything to do with the distributor.
Now you can go chase the low voltage with your meter. It sounds like a loose or corroded connection. It also could be the ignition switch.
I'm looking at the wiring diagram. It says that the distributor end of the wire is an 18 gauge black wire with a double white stripe. Is the correct wire attached to the distributor? If it is. is this where you are measuring the +6 Volts?
If so then back up to the connection on the ignition switch. The diagram says that this wire is a PINK 12 gauge wire. The diagram also say that the Pink wire also goes to the 20 Cruise control fuse (hot side) You could meter it there instead.
Now based on that reading you can decide whether to go forward or backwards on the circuit.
Note: the Black/double white and pink wires meet (connect) at terminal BX where it goes through the firewall.
That is enough to get you started. Let us know what you find.
http://bdub.net/wirediagrams/75-engine-HEI.pdf
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Ignition system voltage drop [message #239614 is a reply to message #239586] |
Tue, 11 February 2014 19:55 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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When I suddenly had a large voltage drop to the input of my HEI distributor in my driveway ( running one minute dead the next) it turned out to be the plug where it passes thru the bulkhead due to corrosion. I ran a new wire to bypass it.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: [GMCnet] Ignition system voltage drop [message #239633 is a reply to message #239623] |
Wed, 12 February 2014 01:19 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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| Rivers wrote on Tue, 11 February 2014 22:06 |
You had your engine out and back in ----check your engine to frame ground
Rivers
77 ele
wilbe
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Interesting thought.
Where did you attach the negative engine battery cable?
It goes under a bolt on the engine block.
Does it crank OK?
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Ignition system voltage drop [message #239648 is a reply to message #239623] |
Wed, 12 February 2014 08:46 |
gbarrow2
Messages: 765
Registered: February 2004
Location: Lake Almanor, Ca./ Red Bl...
Karma: 3
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Rivers wrote on Tue, 11 February 2014 20:06]You had your engine out and back in ----check your engine to frame ground.
BINGO!! Rivers, I think and hope you identified the problem!
I made double sure that all mechanical attachments under the coach were secure, but I don't specifically remember re-connecting the GROUND cable.
If that's not it I now have I now have good suggestions on how to track it down.
Thanks to all. I'll check the ground later today and report back.
GMCNET- What a resource!!
Gene Barrow
Lake Almanor, Ca.
1976 Palm Beach
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| Re: [GMCnet] Ignition system voltage drop [message #239650 is a reply to message #239648] |
Wed, 12 February 2014 09:18 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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| gbarrow wrote on Wed, 12 February 2014 08:46 |
Rivers wrote on Tue, 11 February 2014 20:06]You had your engine out and back in ----check your engine to frame ground.
BINGO!! Rivers, I think and hope you identified the problem!
I made double sure that all mechanical attachments under the coach were secure, but I don't specifically remember re-connecting the GROUND cable.
If that's not it I now have I now have good suggestions on how to track it down.
Thanks to all. I'll check the ground later today and report back.
GMCNET- What a resource!!
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The engine to frame ground jumper strap is located on the rear of the transmission and wired across a transmission mount. It should have nothing to do with starting and running the engine unless you have erroneously attached the engine starting battery negative cable to the body or frame.
I'm not saying not to check it because it is needed for other things like charging the house batteries from the engine driven alternator. I'm also saying to check to make sure that the engine starting battery negative cable is run direct to a bolt on the engine and that the connection is clean and tight.
You did not say if the engine will crank when you turn the key to the start position.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Ignition system voltage drop [message #239662 is a reply to message #239650] |
Wed, 12 February 2014 10:12 |
gbarrow2
Messages: 765
Registered: February 2004
Location: Lake Almanor, Ca./ Red Bl...
Karma: 3
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Ken,
The braided strap at the transmission was not disconnected and is still in place.
The positive cable from the battery is connected directly to the starter ( as Gene Fisher insists) The negative cable was disconnected from the battery ; the other end was not disconnected from the frame. I'm satisfied that it is properly re-connected.
What I DON'T remember is re-connecting the ground cable between the frame and block.
The engine cranks fine- just no start.
David- the battery is good and I charged before re-installing. But just to make sure it wouldn't run down while cranking, I jumped it from my Jeep and had the Jeep engine running. So I had 13+ volts at the coach battery.
Still hoping that engine ground is the culprit. Will know later today.
Thanks to all.
Gene Barrow
Lake Almanor, Ca.
1976 Palm Beach
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| Re: [GMCnet] Ignition system voltage drop [message #239675 is a reply to message #239662] |
Wed, 12 February 2014 11:47 |
Otterwan
Messages: 946
Registered: July 2013
Location: Lynnwood (north of Seattl...
Karma: 0
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Any chance this could have something to do the with battery isolator, combiner, or solenoid? Have you tried using the boost switch to see if makes any difference?
1977 Birchaven, Lynnwood WA - "We may not be able to stop all evil in the world, but I know that how we treat one another is entirely up to us."
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| Re: [GMCnet] Ignition system voltage drop [message #239772 is a reply to message #239662] |
Wed, 12 February 2014 18:41 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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| gbarrow wrote on Wed, 12 February 2014 10:12 |
Ken,
The braided strap at the transmission was not disconnected and is still in place.
The positive cable from the battery is connected directly to the starter ( as Gene Fisher insists) The negative cable was disconnected from the battery ; the other end was not disconnected from the frame. I'm satisfied that it is properly re-connected.
What I DON'T remember is re-connecting the ground cable between the frame and block.
The engine cranks fine- just no start.
David- the battery is good and I charged before re-installing. But just to make sure it wouldn't run down while cranking, I jumped it from my Jeep and had the Jeep engine running. So I had 13+ volts at the coach battery.
Still hoping that engine ground is the culprit. Will know later today.
Thanks to all.
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I'm going to try this once again. Either we have got a confusion in terminology or you have the negative side improperly connected.
1. On a properly wired coach there is NO CONNECTION between the engine block and the frame. That function is taken care of by the braided strap across the transmission mount between the frame and the transmission. Also main engine starting current should never travel across the connection between the engine and the frame.
2. There is NO CONNECTION between the starting battery and the frame. The negative cable from the starting battery goes from the negative terminal on the battery DIRECT TO THE ENGINE BLOCK and is anchored to a bolt on the passenger side of the engine.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Ignition system voltage drop [message #239797 is a reply to message #239784] |
Thu, 13 February 2014 02:03 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| Matt Colie wrote on Wed, 12 February 2014 19:46 |
| Ken Burton wrote on Wed, 12 February 2014 19:41 |
I'm going to try this once again. Either we have got a confusion in terminology or you have the negative side improperly connected.
1. On a properly wired coach there is NO CONNECTION between the engine block and the frame. That function is taken care of by the braided strap across the transmission mount between the frame and the transmission. Also main engine starting current should never travel across the connection between the engine and the frame.
2. There is NO CONNECTION between the starting battery and the frame. The negative cable from the starting battery goes from the negative terminal on the battery DIRECT TO THE ENGINE BLOCK and is anchored to a bolt on the passenger side of the engine.
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Ken,
The very first rally we were at for more than a part of a day was the GMCES at Elkhart. You did a presentation on the coach electrics and specifically the different grounds then, and you are still doing it. Did you think that maybe you should be ready to pull a Gene? Go Here: http://www.gmceast.com/technical/Burton_Grounding_GMC_Motorhome.pdf When you have been through that, come back with what ever questions are still open....
By the way, Thanks
Matt
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You are welcome Matt.
I got a message from Kim today asking if I could do a seminar again next month at the GMCMI rally. The topic was not exactly specified. Maybe we ought to revive this grounding one again and add a few additional things. It seems that this comes up here several times a year.
Matt,
Do you think I should suggest this to her?
I would have to go read it over again and brush up on the subject.
I was also thinking on this problem that Gene is experiencing.
What bother's me is, he says that the engine cranks. If this is true, then he is drawing a couple hundred amps across whatever ground connection path he currently really has. So the 1.5 amp draw static draw (not cranking)of the HEI across the same ground path is with 50% voltage loss does not seem possible.
I believe that your suggestion that the problem is on the positive side is much more likely.
His coach is wired non-standard with the positive battery cable direct to the starter. A bad connection in the cable between the starter and the boost solenoid which powers the rest of the coach seems like a more likely suspect. My problem with that diagnosis is there is enough voltage to energize the starter solenoid which draws much more current than the HEI and it is bolted to the same master ground as the HEI. So that probably is not it.
Power for both the stater solenoid and the HEI comes through the fusible link and the same red wire to the ignition switch. So we are down to a defective ignition switch or that pink and black with double white stripe wires.
Another possibility is the voltage readings we are being given are using something other than the master ground (the engine block) for the negative meter lead connection and may not be accurate. If another unproven ground reference is being used then the problem could be in that ground reference circuit. I'm thinking like a loose screw on the ground lead inside on the HEI coil for one.
I like your suggestion about the fusible link but I still think if that was it, the starter solenoid also would not work.
Maybe I do not understand the symptoms and readings correctly.
I'm done guessing for tonight. Back to watching the Olympics.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Ignition system voltage drop [message #239823 is a reply to message #239797] |
Thu, 13 February 2014 09:15 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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| Ken Burton wrote on Thu, 13 February 2014 03:03 |
You are welcome Matt.
I got a message from Kim today asking if I could do a seminar again next month at the GMCMI rally. The topic was not exactly specified. Maybe we ought to revive this grounding one again and add a few additional things. It seems that this comes up here several times a year.
Matt,
Do you think I should suggest this to her?
I would have to go read it over again and brush up on the subject.
I was also thinking on this problem that Gene is experiencing.
What bother's me is, he says that the engine cranks. If this is true, then he is drawing a couple hundred amps across whatever ground connection path he currently really has. So the 1.5 amp draw static draw (not cranking)of the HEI across the same ground path is with 50% voltage loss does not seem possible.
I believe that your suggestion that the problem is on the positive side is much more likely.
His coach is wired non-standard with the positive battery cable direct to the starter. A bad connection in the cable between the starter and the boost solenoid which powers the rest of the coach seems like a more likely suspect. My problem with that diagnosis is there is enough voltage to energize the starter solenoid which draws much more current than the HEI and it is bolted to the same master ground as the HEI. So that probably is not it.
Power for both the stater solenoid and the HEI comes through the fusible link and the same red wire to the ignition switch. So we are down to a defective ignition switch or that pink and black with double white stripe wires.
Another possibility is the voltage readings we are being given are using something other than the master ground (the engine block) for the negative meter lead connection and may not be accurate. If another unproven ground reference is being used then the problem could be in that ground reference circuit. I'm thinking like a loose screw on the ground lead inside on the HEI coil for one.
I like your suggestion about the fusible link but I still think if that was it, the starter solenoid also would not work.
Maybe I do not understand the symptoms and readings correctly.
I'm done guessing for tonight. Back to watching the Olympics.
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Ken,
Two answers here, Yes, suggest this topic to Kim.
You are right about the fusible link....
I usually get to do this with owners and boats that I know well. But, I try. I think this leaves us with three possibilities:
The information posted is in error - somehow - But Hey, he has no spark ...
The ignition switch is the issue or
That junction is the problem.
I hope you enjoyed the Winter Games.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] Ignition system voltage drop [message #239830 is a reply to message #239797] |
Thu, 13 February 2014 10:15 |
gbarrow2
Messages: 765
Registered: February 2004
Location: Lake Almanor, Ca./ Red Bl...
Karma: 3
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Senior Member |
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Ken, Matt, and All,
Thanks for your support! Problem solved! Pardon my stupidity.
Among several useful things from this ordeal; I learned the true meaning and origin of the phrase "Wild Goose Chase".
There are two identical dark blue wires exiting a corrugated conduit near the distributor. One is shorter and had a female push-on terminal that fit nicely on to the "batt" terminal on the coil. The other wires' terminal had broken off. Both wires have 12v with the ignition key on and zero when the key is off.
I assumed (always dangerous) the shorter wire terminating closer to the coil was the ignition circuit wire.
Of course I didn't switch the wires until AFTER following ALL the helpful and well thought out suggestions from you very patient folks.
That included tearing the dash apart to trace the wrong wire and stabbing my finger multiple times with the meter probe.
Ken- The battery ground is connected directly to the block as you said it should be.
The coil fired immediately when I connected a jumper directly from the battery to the coil.
Matt-Voltage is the same at each end of the fusible link.
After connecting the proper wire the engine started immediately. It purred like a kitten and I grinned like a Cheshire Cat while trying to stop the bleeding from my perforated index finger.
Max 21 inches of Vacuum at 1500 fast idle. 18 inches at 750 rpm after the choke is off.
It is impossible to see the timing mark beyond 8*BTDC. At 8*advanced the vac is lower. I set it to the max vac but I haven't driven it yet.
Any suggestions before I connect all the vacuum hoses and take a test drive?
Thanks again for all the detailed suggestions. That was very helpful and informative even though I started you after the wrong goose.
Gene Barrow
Lake Almanor, Ca.
1976 Palm Beach
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