Home » Public Forums » GMCnet » Hot start needs boost (maybe ground? )
| Hot start needs boost [message #305492] |
Tue, 16 August 2016 22:58  |
pzerkel
Messages: 212
Registered: September 2007
Location: Salisbury, IL
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Ever since I have had my coach, if I shut the engine off after I have been driving a few minutes it will crank very slowly. If I hit the boost switch the engine cranks STRONG right away and usually starts almost instantly.
Several years ago I researched this and suspected it was a ground problem. I think there were some PO modifications (well I know there were some as I have a 455 in a 1978!) Anyway I initially had only one cable from the engine battery and it was going to the engine.
So I purchased a battery with post and side terminals and had a cable made to go from the neg side post terminal to the frame. Unfortunately the problem persisted. I have been just living with it, but I have decided I would like to fix it. Maybe I did something wrong when adding the 2nd ground cable, Or maybe it is something else.
I do own a good DMM and am reasonably competent using it, but I am not sure what I need to check to determine why this hot start issue is still happening.
Any ideas?
Paul Zerkel
'78 Eleganza II
Salisbury IL (near Springfield)
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| Re: [GMCnet] Hot start needs boost [message #305495 is a reply to message #305492] |
Tue, 16 August 2016 23:17  |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Check your negative braided cable at the transmission,Lot are missing.
check cable connection at the relay, clean and tighten.
The starter solenoid must be getting weak.
On Tue, Aug 16, 2016 at 8:58 PM, Paul Zerkel wrote:
> Ever since I have had my coach, if I shut the engine off after I have been
> driving a few minutes it will crank very slowly. If I hit the boost switch
> the engine cranks STRONG right away and usually starts almost instantly.
>
> Several years ago I researched this and suspected it was a ground problem.
> I think there were some PO modifications (well I know there were some as I
> have a 455 in a 1978!) Anyway I initially had only one cable from the
> engine battery and it was going to the engine.
>
> So I purchased a battery with post and side terminals and had a cable made
> to go from the neg side post terminal to the frame. Unfortunately the
> problem persisted. I have been just living with it, but I have decided I
> would like to fix it. Maybe I did something wrong when adding the 2nd ground
> cable, Or maybe it is something else.
>
> I do own a good DMM and am reasonably competent using it, but I am not
> sure what I need to check to determine why this hot start issue is still
> happening.
>
> Any ideas?
> --
> Paul Zerkel
> '78 Eleganza II
> Salisbury IL (near Springfield)
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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| Re: Hot start needs boost [message #305499 is a reply to message #305492] |
Tue, 16 August 2016 23:40 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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The battery could be weak I would check the terminal voltage while the engine is cranking. Also is it around 800 cca rated rather then 550 cca? Bigger really is better.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: Hot start needs boost [message #305507 is a reply to message #305499] |
Wed, 17 August 2016 03:49 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
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This does not sound like a ground problem, but is could still be a poor connection on ground or positive terminal of the starting battery. Adding a ground cable to the frame should not do anything in this case because the ground connection for the engine battery ad starter goes directly to the engine, NOT THE FRAME.
The first thing I would do is aggressively clean the battery connections again with something more aggressive than a battery cleaning brush. In my case I had the same problem that you have. I cleaned everything several times and nothing changed. Then one time after cranking I happened to put my hand on the negative battery connection immediately after cranking and it was warm. Where there is heat generated there is a bad connection. I removed the battery cable again and cleaned the cable and the post with a file, removing a little bit of the metal on both. I reinstalled the cable with anti-oxidation grease and that immediately took care of my starting problem.
So I suggest that you again aggressively clean the battery cables on both ends and the battery posts with coarse sand paper or a file. You are trying to get fresh contact metal on both surfaces.
On a different coach I found the starting problem by disconnecting the positive cables at the boost relay and aggressively cleaning them. I reinstalled them with stainless tooth washers and anti-oxidation grease.
Since the boost function works correctly on yours that tells me that the starting problem is not in the starter solenoid or the cable between the boost relay and the starter. It still could be the cable between the boost solenoid and the battery.
While you are cleaning, look closely at the connectors on the ends of the wire. If they are shrink tube covered, inspect under the shrink tubing looking for hidden corrosion in the wire to connector connections. Do not be afraid to flex the connectors aggressively trying to locate corrosion or loose cable ends.
Next, I would take a volt meter and put it across the battery posts (not the cables) and read the voltage while cranking. This will read the available voltage from the battery while it is under load cranking. If you have low voltage at this point you have a weak or bad battery.
I would then move the meter leads to the engine block and the big terminal on the stater solenoid. Read this voltage while cranking. Now subtract the reading that you just took first reading at the battery. You now know how much voltage drop (loss) that you are dealing with. If it is more than a few 1/10th of a volt, you have a transmission loss between the battery and the stater.
If the loss is excessive, you need to determine if the loss is on the negative side, the positive side, or both. Take your meter and connect one lead to the engine block or mounting bolt of the starter. Connect the other lead to the negative BATTERY POST (not the negative cable). Crank the engine and read the voltage I would use the 2 volt scale. The reading you get will be the transmission loss on the negative side. Now move the meter leads to the terminal big positive terminal on the starter again and the second lead to the positive post (not the cable) on the battery. Crank the engine again and read the voltage. This will be the voltage drop on the positive side. With this information you should be able to locate the poor connection(s). You can always put your meter across an suspect connection or cable and read the voltage drop while cranking. If you get anything other than 0 ohms then there is a loss there that should be eliminated.
As stated in the previous posting, do not over look the possibility of a weak battery.
Ken B.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Hot start needs boost [message #305511 is a reply to message #305492] |
Wed, 17 August 2016 08:46 |
pzerkel
Messages: 212
Registered: September 2007
Location: Salisbury, IL
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Thanks for everyone who has responded. A little more info and a few more questions.
I had this hot start issue yesterday and this time coach would not start at all (just very slow cranks even with boost). I did figure out that I did indeed have a loose connection on the engine battery side of the boost relay. I tightened that up, and was able to start the coach, but still needed to use the boost switch.
I read the "GMC Cranking Improve for Free" presentation. It looked familiar. I think I asked about this issue here a couple years ago, and read that then. My discovery was that my starter cable was no where near long enough to get to the positive terminal of the battery. I guess I could get a longer cable made (of course-there is no such thing as the 'For Free" part of that title). 
It was getting late last night, and other than tightening the nut I really did not look closely at the cables there. I will check that closely this evening and give it a thorough cleaning.
jimk responded almost immediately but I need a little more handholding re his comments. 1st) This braided cable to the transmission (which may be missing). Where do I look for that on the transmission, and where is the other end supposed to go? If there is a link to the photo site, or a place in X7725 or X7525 that would help. 2nd) He said "check cable connection at the relay, clean and tighten." I assume he means the boost relay? As I said I know it was loose, I will work on cleaning when I get back to it this evening. 3rd) He mentions "The starter solenoid must be getting weak." But Ken B's comment that since the boost mode works the problem probably is not the starter relay seems to make sense to me.
Ken B's post gave me a good idea of what I need to check with the meter. I will clean up the connections, and do those tests and report back.
Since this is a problem that only rears itself on hot starts, I guess that gives me an excuse to get the coach out of it parking spot a little more than I have been, and at least drive it on some short trips on a more regular basis.
thanks to everyone who has responded.
Paul Zerkel
'78 Eleganza II
Salisbury IL (near Springfield)
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| Re: Hot start needs boost [message #305514 is a reply to message #305492] |
Wed, 17 August 2016 09:25 |
pzerkel
Messages: 212
Registered: September 2007
Location: Salisbury, IL
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One more tidbit of info. Most have suggested that I may have a weak battery. I have been through several engine batteries in the time I have owned the coach. It seems like I replace every two years, or so. Seems like they should be lasting longer than that. Makes me wonder if I have a charging issue.
After we got it started last night, I did check voltage at battery. It was 13.5 volts. Some forum searches trying to help me resolve this led me to this thread: http://gmc.mybirdfeeder.net/GMCforum/index.php?t=msg&th=34414&goto=280452&rid=1340#msg_280452 So I think 13.5 is a little too low.
I am assuming corroded or loose connections on the positive side could be causing some of that drop. I have no combiner and the original isolater setup. Tonight I will check voltage at the alternator terminal of the isolater. If I understand this correctly I should be seeing 14.2 volts there (assuming a 0.7 drop across the diode in the isolater).
The post linked above says I should expect to see 14.5 to 15.2 into the isolater. If I do see that, then I would assume I do have some cabling issues, but if I only see 14.2 at the alternator post of the isolater, then I assume I should look more closely at my alternator. Am I understanding this part correctly?
Paul Zerkel
'78 Eleganza II
Salisbury IL (near Springfield)
[Updated on: Wed, 17 August 2016 09:26] Report message to a moderator |
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| Re: Hot start needs boost [message #305521 is a reply to message #305515] |
Wed, 17 August 2016 10:49 |
pzerkel
Messages: 212
Registered: September 2007
Location: Salisbury, IL
Karma: 0
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Harry wrote on Wed, 17 August 2016 10:03Is it possible the bushings in the starter are worn and with the high heat
it is rubbing inside?
Maybe, but the starter spins great (even when hot) with the help of the boost switch. After reading most of these posts and thinking about this, I am leaning toward it being a wiring issue.
Paul Zerkel
'78 Eleganza II
Salisbury IL (near Springfield)
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| Re: Hot start needs boost [message #305523 is a reply to message #305514] |
Wed, 17 August 2016 11:13 |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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All the symptoms mentioned point to the connection on the boost solenoid that connects to the chassis (engine) battery and the starter. Probably a cable going to the isolator there as well. The next likely culprit is the cable from the chassis battery to the boost solenoid and the battery terminal connection.
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: Hot start needs boost [message #305525 is a reply to message #305507] |
Wed, 17 August 2016 11:55 |
LarryInSanDiego
Messages: 336
Registered: September 2006
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Folks, Ken here did an excellent explanation of how to do voltage drop. Most meters have 0.1 ohm resolution. One of my Flukes does .01 ohm, but in these scenarios, I never bother to measure ohms. Unless you're verifying continuity or a SPECIFIED resistance, to me it's a waste of time and effort. Since measuring resistance requires the circuit to be unpowered, you're not truly seeing what's really happening unless the circuit is under load. You can CALCULATE ohms for grins if you want by also measuring current and using the Ohm's Law formula, but measuring voltage drop is far easier and more useful because you're seeing what happening WHILE it's happening. You can't do that by measuring resistance. This is what I used to teach when I taught the SET course for GM. Set the meter on 2 or whatever VDC scale and check across EACH component and EACH connection on BOTH power AND ground side under load - I'll repeat: UNDER LOAD. That's the key. Make a quickie diagram and record each reading at each point. Just remember, EVERY thing and EVERY connection has some resistance (every wire, every fuse, every switch, etc.), you just likely won't see it unless you do voltage drop, and that means under load. Where you find excessive voltage drop is where you'll find your problem. The only item in a circuit that is supposed to have (significant, as in pretty much all) voltage drop is, of course, the load itself (motor, lamp, etc.).
Ken Burton wrote on Wed, 17 August 2016 01:49...Next, I would take a volt meter and put it across the battery posts (not the cables) and read the voltage while cranking. This will read the available voltage from the battery while it is under load cranking. If you have low voltage at this point you have a weak or bad battery.
I would then move the meter leads to the engine block and the big terminal on the stater solenoid. Read this voltage while cranking. Now subtract the reading that you just took first reading at the battery. You now know how much voltage drop (loss) that you are dealing with. If it is more than a few 1/10th of a volt, you have a transmission loss between the battery and the stater.
If the loss is excessive, you need to determine if the loss is on the negative side, the positive side, or both. Take your meter and connect one lead to the engine block or mounting bolt of the starter. Connect the other lead to the negative BATTERY POST (not the negative cable). Crank the engine and read the voltage I would use the 2 volt scale. The reading you get will be the transmission loss on the negative side. Now move the meter leads to the terminal big positive terminal on the starter again and the second lead to the positive post (not the cable) on the battery. Crank the engine again and read the voltage. This will be the voltage drop on the positive side. With this information you should be able to locate the poor connection(s)...
Larry Engelbrecht
San Diego, CA
'73 26' ex-Glacier
TZE063V100319 03/07/73
[Updated on: Wed, 17 August 2016 12:01] Report message to a moderator |
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| Re: Hot start needs boost [message #305528 is a reply to message #305514] |
Wed, 17 August 2016 15:07 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
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pzerkel wrote on Wed, 17 August 2016 09:25One more tidbit of info. Most have suggested that I may have a weak battery. I have been through several engine batteries in the time I have owned the coach. It seems like I replace every two years, or so. Seems like they should be lasting longer than that. Makes me wonder if I have a charging issue.
After we got it started last night, I did check voltage at battery. It was 13.5 volts. Some forum searches trying to help me resolve this led me to this thread: http://gmc.mybirdfeeder.net/GMCforum/index.php?t=msg&th=34414&goto=280452&rid=1340#msg_280452 So I think 13.5 is a little too low.
I am assuming corroded or loose connections on the positive side could be causing some of that drop. I have no combiner and the original isolater setup. Tonight I will check voltage at the alternator terminal of the isolater. If I understand this correctly I should be seeing 14.2 volts there (assuming a 0.7 drop across the diode in the isolater).
The post linked above says I should expect to see 14.5 to 15.2 into the isolater. If I do see that, then I would assume I do have some cabling issues, but if I only see 14.2 at the alternator post of the isolater, then I assume I should look more closely at my alternator. Am I understanding this part correctly?
First on your other posting about the braided strap. That strap, while important for other reasons, has nothing to do with power/voltage delivered to the starter by the engine battery. It does come into play when starting off of the house battery(s). So for the moment forget about the braided cable as part of your starting issue. The strap is located on the rear of the transmission. The other end connects to the frame at the rear transmission mount.
On charging voltage, 13.5 v. at the battery is a little low. We usually want 13.8 to 14.2 volts there. On most modern alternator the system runs on the high side (14.2 or more when cold and drops to 13.8 or slightly less when hot. So as a general rule what you should see at the battery is 14.0 volts.
On a GMC there is a .6 or .7 volt drop through the isolator. So to make up for this drop the alternator puts out 14.7 volts.
So what I would do is start the engine and read the battery voltage again. Then move the meter to the isolator center terminal (alternator input) and read the voltage. Use the aluminum plate that the isolator is mounted on for your ground reference (negative) meter connection. Then also read the top and bottom terminals of the isolator. They are the charging feeds to the engine and house batteries. I would expect them to be .6 to .7 volts lower than the center isolator terminal. Based on the numbers you read you can decide where to go from there in your diagnosis.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Hot start needs boost [message #305536 is a reply to message #305492] |
Wed, 17 August 2016 20:02 |
pzerkel
Messages: 212
Registered: September 2007
Location: Salisbury, IL
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Ok, I took some readings, didn't get everything Ken B suggested yet, but took all these before cleaning any cables.
temp was ~80F
battery at posts (engine off) = 12.31 volts. Read http://gmc49ers.blogspot.com/2014/03/check-your-battery-system-through-your.html and looks like that is about 70%
When cranking it dropped to 10.8 v
It seemed like the voltages at the isolator increased gradually as the engine was running. At one point I saw 15v at the center post of isolator.
14.11 v at chassis battery post of isolator.
14.19 v at house side of isolator.
I took all the cables off the engine battery side of the booster and cleaned them up as best I could. I think I will get a couple stainless washer and/or nut for the booster relay tomorrow.
I will try to drive it this weekend and see if I have solved this or not. If not, I will get the other readings Ken B was suggesting.
Thanks everyone for your help so far.
Paul Zerkel
'78 Eleganza II
Salisbury IL (near Springfield)
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| Re: Hot start needs boost [message #305548 is a reply to message #305536] |
Thu, 18 August 2016 02:33 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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I do not have the chart in front of me but at 80 F. and 12.3 volts I would call that battery about 65% charged. That is low to me. I would expect the static reading to be around 12.7 V at 80 degrees. The battery is not fully charged. Why is that?
Your isolator readings are good on all three terminals. This along with your previously posted reading of 13.5 v. at the battery with the engine running says there is .6 to .7 volt drop in the cabling between the isolator and the battery. I would go looking for that .6 volt loss. This loss is important because with that lower charging voltage at the battery it will take a day or two of running the the alternator to fully charge the battery.
There are only three cables and 4 connections involved in this charging circuit. A #10 wire between the isolator and the big terminal next to the isolator, a #4 cable between the big terminal and the battery boost relay, and finally the #4 battery cable between the boost relay and the battery. If you can not find or eliminate the loss by cleaning the connections and examining the cable ends, you can use your meter across each of them to find the loss.
If you want to measure the loss directly rather than calculate it, put one meter lead on the isolator terminal that goes to the engine side and put the other lead on the battery post. You can move the one probe from the battery post to the other two connections points in the circuit looking to see where / if the voltage drop changes.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Hot start needs boost [message #305550 is a reply to message #305492] |
Thu, 18 August 2016 08:24 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Do you have a battery load tester? Either old pile type or new digital type? You need to fully charge that battery and load test. It is very discharged right now considering how warm it is out. You should see over 12.6V (high 12s) sitting there static. Your most recent readings look pretty good on the supply side. . 2 years is a short battery life span, but not unheard of in this "severe duty" life style scenerio. Long sit times with slow parasitic drains and short run times far spaced. Was it ever run down (yes like now) and did it ever sit below full charge in winter and possibly freeze? Also a battery acts to stabilize the system and a bad one can give you data readings that are misleading. The house battery may have more juice ( possibly from shore power) so it does the work with the boost engaged. All info given here was very detailed and educational but you need to confirm the chemical storehouse is not defective.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Hot start needs boost [message #305551 is a reply to message #305548] |
Thu, 18 August 2016 08:46 |
pzerkel
Messages: 212
Registered: September 2007
Location: Salisbury, IL
Karma: 0
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I cannot thank Ken Burton enough for all his patient explaining of how to test and where to look. I feel like I am starting to get it, because Ken's last post pretty much confirmed some suspicions I have had.
The readings I posted were before I cleaned up the cables and terminal connections last night. It will be interesting to see what they are now thatI have done that.
The chart I was looking at, I came up with ~70% charge, Ken said 65%. Close enough. Either way, it was not fully charged. I did put a charger on the battery last night. This might explain why I have had such bad luck with engine batteries lasting.
Ken indicated my isolator readings seemed good enough. I also thought so. But the voltage at the battery is low. One anomaly I had that I did not mention before was on Tuesday evening I had voltage at battery of 13.5v, on Wednesday evening it was 13.9v.
Possible causes for anomaly:
a) I read the meter wrong (5 and 9 look similar on digital display)
b) I had retightened the terminal on the boost switch between readings
c) the alternator may be putting out different output based on the state of the battery?
Even 13.9 seems a little low considering I had over 14.1 at the isolator. Ken mentioned the 3 wires and 4 connections between the isolator and engine battery. I noticed that especially the #10 wires from the isolator look old. All of those wires are easily accessible and replaceable. I have tried to clean them up, but think I will at least replace those #10 wires.
The voltage drop test Ken suggested from the isolator terminal to the engine battery is easy to do, and I can perform both before and after replacing some of the wires.
Thanks again to everyone, I am beginning to feel like I WILL get this working the way it is supposed to.
Paul Zerkel
'78 Eleganza II
Salisbury IL (near Springfield)
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| Re: [GMCnet] Hot start needs boost [message #305552 is a reply to message #305550] |
Thu, 18 August 2016 08:44 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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I'm convinced you have a defective battery cable with high resistance in a
connector.
But regardless of that, John L. touched on a topic you need to consider:
Since your chassis batteries lives seem too short, yet your house battery
is a reliable backup, I suspect you keep the coach plugged in so that the
converter continuously charges the house battery. Thc chassis battery, on
the other hand, isolated from the converter by the Isolator, is NOT
continuously charged, so is frequently low and dying from that abuse.
THAT's where a combiner is worth its cost: Both battery banks are
connected to the converter automatically. An alternative, of course, is to
use Ken B.'s manual combiner -- a short piece of wire with two alligator
clips and a good memory.
JMHO,
Ken H.
On Thu, Aug 18, 2016 at 9:24 AM, John R. Lebetski
wrote:
> ...The house battery may have more
> juice ( possibly from shore power) so it does the work with the boost
> engaged.
...
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www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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