| Tach Noise [message #319646] |
Tue, 27 June 2017 07:50  |
Jon payne
Messages: 495
Registered: May 2008
Karma: 1
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Hi Guys!
Need you help please. Last fall I installed the FiTech EFI. Only put on around 300 miles on the system since then. When I first took the GMC out this past April it was the first time I had the handheld controller set up where I could monitor some parameters like AFR, RPM, Coolant temp, etc while driving. One thing I noticed right away was the RPM would spike to 3000 to 5000 randomly and the AFR was really rich, around 10.8. The RPM spike would last 1 second but no obvious affect on the engine operation. This also happens during idle including the very rich AFR. I performed a data log and noticed that when the RPM spikes the fuel pressure spikes to 100psi and the injector duty cycle spikes as well. This only lasts 1 second and I think this is the reason the AFR is really rich. The ECU might think there is a mis-fire and is trying to adjust.
Anyway, I spoke with FiTech and they said there is noise getting into the tach wire so I isolated the tach wire and put braided shielding the length of the wire but no help. During further trouble shooting, while the engine was running attempted to move around the tach wire and when a touched it I got a huge shock so for sure there is noise in the tach signal. I then put an alligator clip on the tach wire, about 5 inches from the distributor, touched the other end to ground and the engine quite. Moving the clip another five inches or so away from the distributor, touched ground and had no effect. For the heck of it I swapped out the coil with a spare, made sure the installation was correct but no change.
Not positive if what I am seeing is normal or not with the tach wire but if it is not could it be the RF capacitor is bad? I know that is for RF noise but not sure if it helps to keep noise out of the tach wire??
Hoping for some ideas here as I am really lost on this one. Got a big trip to Sleeping Bear Dunes next week and got to get this sorted out ASAP. Any help would be greatly appreciated as always!
Jon
Jon Payne
76 Palm Beach
Westfield,IN
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| Re: Tach Noise [message #319648 is a reply to message #319646] |
Tue, 27 June 2017 08:29  |
Larry
Messages: 2875
Registered: January 2004
Location: Menomonie, WI
Karma: 10
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Jon Payne wrote on Tue, 27 June 2017 07:50Hi Guys!
Need you help please. Last fall I installed the FiTech EFI. Only put on around 300 miles on the system since then. When I first took the GMC out this past April it was the first time I had the handheld controller set up where I could monitor some parameters like AFR, RPM, Coolant temp, etc while driving. One thing I noticed right away was the RPM would spike to 3000 to 5000 randomly and the AFR was really rich, around 10.8. The RPM spike would last 1 second but no obvious affect on the engine operation. This also happens during idle including the very rich AFR. I performed a data log and noticed that when the RPM spikes the fuel pressure spikes to 100psi and the injector duty cycle spikes as well. This only lasts 1 second and I think this is the reason the AFR is really rich. The ECU might think there is a mis-fire and is trying to adjust.
Anyway, I spoke with FiTech and they said there is noise getting into the tach wire so I isolated the tach wire and put braided shielding the length of the wire but no help. During further trouble shooting, while the engine was running attempted to move around the tach wire and when a touched it I got a huge shock so for sure there is noise in the tach signal. I then put an alligator clip on the tach wire, about 5 inches from the distributor, touched the other end to ground and the engine quite. Moving the clip another five inches or so away from the distributor, touched ground and had no effect. For the heck of it I swapped out the coil with a spare, made sure the installation was correct but no change.
Not positive if what I am seeing is normal or not with the tach wire but if it is not could it be the RF capacitor is bad? I know that is for RF noise but not sure if it helps to keep noise out of the tach wire??
Hoping for some ideas here as I am really lost on this one. Got a big trip to Sleeping Bear Dunes next week and got to get this sorted out ASAP. Any help would be greatly appreciated as always!
Jon
Jon,
Redoing my dash board, I choose a Tach and Speedo from Speedhut. After the install, I noticed similar issues as you with that new tach. It would suddenly peg the needle over 6K for about a second then cycle to "0" and back to normal engine speed. I contacted Speedhut tech support and they asked questions that you might want to answer, like...."What sort of plugs and wires are you using? Solid core wires can cause quite a bit a feedback through a dizzy." I have carbon core wires. His response..."Alright. Well there must be noise coming off the ignition system somewhere. I can send you a tach filter wire inline with the signal wire of the tach to reduce the noise going into the tach." I got that "filter" and installed it inline with the ignition wire to the distributor. The anomaly went away. Sounds like you need some kind of filter.
FWIW, I love the Tach and Speedo from Speedhut, and found their tech support to be outstanding. Maybe FiTech has a noise suppression unit of some kind. Speedhut said that " it is somewhat common for one to be needed."
HTH
Larry 
78 Royale w/500 Caddy
Menomonie, WI.
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| Re: Tach Noise [message #319651 is a reply to message #319648] |
Tue, 27 June 2017 09:21 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Let me state that I know absolutely nothing about FiTech FI.
I have chased noise problems all over vehicles running ham radio equipment. Almost every noise problem I have chased is improper grounding somewhere. So here are a few suggestions concerning the unique grounding system on a GMC.
So here are a few simple ideas:
1. Body ground and engine ground are not the same thing in a GMC. Because the Fitech is mounted on the engine, ALL other electrical components for the FI system need to get their ground back at the engine and NEVER from something connected to the body.
2. Never have two paths to ground from a given component. If you do this you establish an tuned antenna at some unknown frequency that can cause havoc for propagation of electrical noise throughout the vehicle.
3. I assume that the FI tech is mounted to the intake manifold with a fiber gasket. Add a short ground jumper between the base of the Fitech and the intake manifold. Attach the jumper to any bolt on the intake manifold.
3. I assume that the Fitech unit is getting power from someplace that is powered by the engine driven alternator and engine battery. If their is more that one place that the Fitech system gets power, make sure all places have their +12 volt power traced back to the engine system and NOT the house system.
4. If you add a shielded cable anywhere like that lead to the tach, it must be grounded on ONE END only. If you attach both ends, then the shield not becomes a current carrier for -12 volts and provides an alternate path for -12 volt current. It also establishes a ground loop (two paths) which makes an excellent antenna at several unknown frequencies.
5. Add an additional ground wire from the base of the distributor to any bolt on the engine. There are a couple of pre-threaded holes, I believe they are 3/8", on the back of the engine near the distributor that could be used. Actually any other bolt on the engine will also work.
I should note that I had one guy stop by here with another brand FI system that had a control unit mounted under the driver's seat. He was having major problems with the engine quitting every 100 miles or so. He had replaced just about everything in the ignition system. Adding a ground wire from the control unit direct to the engine solved his problems. Again I knew nothing about his system, and at the moment do not even remember the brand.
I'm sorry that I'm not more help but I have never seen an FiTech system.
Good Luck
Ken
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Tach Noise [message #319655 is a reply to message #319651] |
Tue, 27 June 2017 09:40 |
Justin Brady
Messages: 769
Registered: April 2015
Location: Bell Buckle, TN
Karma: 11
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Jon,
Can you clarify a few points?
When the RPMS spike, is it actually spiking in the engine or just on the handheld?
Your 10.8 AFR, is that all the time or only during these 1 second instances?
Justin Brady
http://www.thegmcrv.com/
1976 Palm Beach 455
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| Re: [GMCnet] Tach Noise [message #319656 is a reply to message #319646] |
Tue, 27 June 2017 09:42 |
GMC.LES
Messages: 505
Registered: April 2014
Karma: -2
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Senior Member |
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> On Jun 27, 2017, at 8:50 AM, Jon Payne wrote:
>
> "attempted to move around the tach wire and when a touched it I
> got a huge shock so for sure there is noise in the tach signal. I then put an alligator clip on the tach wire, about 5 inches from the distributor,
> touched the other end to ground and the engine quite. Moving the clip another five inches or so away from the distributor, touched ground and had no
> effect."
Jon
Did you place the alligator clip on the insulated jacket, or directly on the metal wire core?
If moving the clip another 5" along the wire gives different results, I would investigate a potential faulty tach wire, especially since you also got a shock when moving it.
From the sounds of it, the insulation somewhere along that wire is compromised, and adding the shielding might also be affecting the issue.
Les Burt
Montreal
'75 Eleganza 26'
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| Re: Tach Noise [message #319661 is a reply to message #319646] |
Tue, 27 June 2017 10:20 |
Jon payne
Messages: 495
Registered: May 2008
Karma: 1
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Thanks everyone for your suggestions! Got some grounds to check, thanks Ken for that. Also I'll look into a tach filter.
To answer some questions that were asked:
- I placed the alligator clip on the braided shielding then touched ground.
- The shielding I placed over the wire is not grounded at all, just encases the wire. I first was thinking it was outside interference but I do understand that it should be properly grounded on one end.
- Inspected the tach wiring and could find no defects.
- RPM spike is just an indication on the handheld.
Thanks again!
Jon Payne
76 Palm Beach
Westfield,IN
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| Re: Tach Noise [message #319666 is a reply to message #319646] |
Tue, 27 June 2017 10:53 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Ken B gave many good points, but SHOCK from 12V system tells me to look else where. What ignition wires are you running? If not good magcore type I would start there
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Tach Noise [message #319670 is a reply to message #319666] |
Tue, 27 June 2017 11:25 |
Justin Brady
Messages: 769
Registered: April 2015
Location: Bell Buckle, TN
Karma: 11
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JohnL455 wrote on Tue, 27 June 2017 10:53Ken B gave many good points, but SHOCK from 12V system tells me to look else where. What ignition wires are you running? If not good magcore type I would start there
Agreed, that's why I asked what coil he's running.
Shock usually comes from voltage much higher than 12
Justin Brady
http://www.thegmcrv.com/
1976 Palm Beach 455
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| Re: Tach Noise [message #319675 is a reply to message #319646] |
Tue, 27 June 2017 13:04 |
Jon payne
Messages: 495
Registered: May 2008
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I called Dick Paterson to discuss the issue too. He says no voltage should be on that wire accept maybe 12 volts or so. Certainly should not receive a shock when touched. He went on to say that for some reason the voltage from the secondary coil is bleeding over to the primary and suggested to replace the coil so fortunately I have a brand new coil never been installed and will try that first. Another possibility, ask Ken eluded to earlier, is grounding. He said to make sure I have no grounding issues and also on his later distributors they have an external ground wire that is connected to the stud on the bottom of the distributor (where the fastener that holds the module in place) and that should be connected to a solid ground on the engine like the intake for example. I think my distrib had that wire but I didn't connect it for reasons I do not recall.
So after work I'll replace the coil, add the ground to the distrib, check all the other grounds as Ken suggested and I'll report back.
Thanks again guys for all your input...very helpful. I'll keep you posted.
JP
Jon Payne
76 Palm Beach
Westfield,IN
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| Re: Tach Noise [message #319680 is a reply to message #319675] |
Tue, 27 June 2017 14:29 |
Bullitthead
Messages: 1411
Registered: November 2013
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If you get a shock to ground at regularly spaced intervals on an well-insulated wire and no shock in between those intervals, there is a radio wave present on the wire. This could be coming from the ignition system amplifier either leaking a signal backwards or possibly wired or grounded incorrectly. What type of ignition system are you using?
If you have a stock ignition (points and coil, no amp or CD setup), check/replace the condenser and check the coil tower for cracks and arc trails, and make sure there isn't just 1 strand of wire from that negative (distributor) wire having a wild hair day.
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: Tach Noise [message #319688 is a reply to message #319646] |
Tue, 27 June 2017 16:52 |
Jon payne
Messages: 495
Registered: May 2008
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Guys its fixed!! It was the ignition coil. Evidently it was the secondary winding bleeding over to the primary coil inducing a voltage into the tach wire. No more RPM fluctuations and the AFR is spot on!
Thanks,
Jon
Jon Payne
76 Palm Beach
Westfield,IN
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| Re: Tach Noise [message #319695 is a reply to message #319688] |
Tue, 27 June 2017 22:28 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Oh well, so much for my grounding guess.
Do not let Colonel Ken know I was wrong.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Tach Noise (grounding) [message #319707 is a reply to message #319695] |
Wed, 28 June 2017 09:23 |
midlf
Messages: 2212
Registered: July 2007
Location: SE Wisc. (Palmyra)
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Ken Burton wrote on Tue, 27 June 2017 22:28Oh well, so much for my grounding guess.
Do not let Colonel Ken know I was wrong.
It was not the problem in this case but still good info.
One area I suspect gives multiple ground paths is the dash grounds and the aluminum firewall. Engine items, gauges, lights and controls are grounded to the firewall. The firewall is connected to the engine battery. However I cannot believe the aluminum firewall is not electrically connected to the coach frame. Hmm - I'll have to look into this when I get home.
Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI
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| Re: [GMCnet] Tach Noise (grounding) [message #319710 is a reply to message #319707] |
Wed, 28 June 2017 09:45 |
Richard Denney
Messages: 920
Registered: April 2010
Karma: 9
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The aluminum firewall panel is grounded to the body, not the frame. I have
bonded the body to the frame at that corner of the coach. My chassis
battery ground lead is bolted to the side of the engine (not the factory
spot, but better) and I run a cable from that block connection to the
chassis frame. The house battery, which on my '73 is adjacent to the
chassis battery up front, is grounded to the same chassis bolt, with
another cable from that chassis bolt to the aluminum body frame. The body
frame mounting is the bigger challenge, and I will probably move my current
mounting point at the top of the front body tripod to the electrical panel
mounted to the front of the firewall. That should be the primary meeting
point between chassis and body grounds. It is difficult to eliminate
alternate ground paths between the body and the chassis--they mechanically
connect at too many points. But a fat wire close to that firewall point
will minimize the effects of ground loops at least at that location.
I ground the chassis battery directly to the engine block because I don't
ever want starting current to go through those other connections on its way
back to the battery. We think a lot about 12-volt current, but forget to
think about that same current when its on its way back to the battery.
Rick "suspecting a grounding problem is causing an intermittent difficulty
with the combiner" Denney
On Wed, Jun 28, 2017 at 10:23 AM, Steve Southworth
wrote:
> Ken Burton wrote on Tue, 27 June 2017 22:28
>> Oh well, so much for my grounding guess.
>>
>> Do not let Colonel Ken know I was wrong.
>
>
> It was not the problem in this case but still good info.
>
> One area I suspect gives multiple ground paths is the dash grounds and the
> aluminum firewall. Engine items, gauges, lights and controls are grounded
> to the firewall. The firewall is connected to the engine battery.
> However I cannot believe the aluminum firewall is not electrically
> connected to
> the coach frame. Hmm - I'll have to look into this when I get home.
> --
> Steve Southworth
> 1974 Glacier TZE064V100150 (for workin on)
> 1975 Transmode TZE365V100394 (parts & spares)
> Palmyra WI
>
> _______________________________________________
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>
--
'73 X-Glacier 230 "Jaws"
Northern Virginia
Offlist email: rick at rickdenney dot com
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| Re: [GMCnet] Tach Noise [message #319711 is a reply to message #319699] |
Wed, 28 June 2017 10:33 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Factory wiring does not have any connection between the aluminum dash panel that has the gauges and lighting and the body or frame. There is one ground wire between that aluminum plate and the aluminum plate up front that has the isolator and boost relay on it. Then there is a second wire on the isolator aluminum plate that runs to the negative terminal of the engine battery. Finally the big ground cable from the battery goes to the engine block which is the master ground and completes the circuit.
So the circuit goes: dash panel -> isolator panel -> Engine battery -> engine block.
There are no ground loops this way but it is a rather round about to get it done. That is the GM did it.
That wire connection at the dash panel aluminum plate occasionally loosens up or corrodes causing strange and sometimes intermittent gauge readings or dash light problems.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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