Motorhome & Recreational Vehicle Resource

Since 1996

Search RV-Coach Online

Email Author email Ralph  Reply to Message reply to message  Post New Message post new message      search forums
All Postings that advertise items for sale will be deleted from the Discussion Forum. You may post sale items for free in the Classifieds section. Sign up now.
All Messages in ThreadAuthorDate
Summary, Coil voltage/missfiring. Ralph 8-1-02  
Joe and Sam et all,Summary of where I am at. 1978 Dodge MH,440,Sportsman Van with MH chassis. Intermittant misfiring on all cylinders. Engine runs but backfires with no power. Firing is OK for about one second and then all cylinders missfire for about the same time based on timing lite. Replaced dual ballast resistor,ECU,distributor cap,plug wires and tried coil substitute. Occasional HT voltage shock thru ignition key and carb when running. All wiring grounds (I think) cleaned and OK. Coil voltage at both terminals 12V with ECU disconnected. Tried jumper cable from engine block to battery negative-no change. Voltages between battery and engine block and battery and ECU surface are both 12V. Now I think back I replaced spark plugs after the MH sat for 6 months. 6 months ago it was running fine. Champion RV12YC were replaced with NGK UR5 which are eqivalent according to the NGK catalogue.I think they are a resistor type. Are they OK?
Re: Summary, Coil voltage/missfiring. Joe 8-1-02  
A two quick the shock you get a pulsing shock or one steady shock, and have you tried to measure any voltage or amperage from the body, battery, or chassis to the engine? You are creating a ground somehow in order for you to recieve a shock. Spark plugs shouldn't matter. Have you tested the high tension leads? Is it charging ok? Could you be feeling alternator voltage? I'm going to stick to the grounding being a problem. What do you think Sam?
Re: Summary, Coil voltage/missfiring. Ralph 8-2-02  
Joe,Sam et all, Ran engine with alternator diconnected-no change.Tried substituting with an old coil again-no change. This is driving me nuts. My guess was that the primary windings were shorting to the secondary windings in the coil although it's hard to beleive that I have two dud coils. Any comments? Ralph
Re: Summary, Coil voltage/missfiring. Ralph 8-2-02  
Joe, Just ran engine for 5 minutes. Ammeter shows alternator charging fine. Definate HT pulsating shock thru the ignition key strong enough that I turn it off with a rubber glove. However it comes and goes even though the engine is missfiring continuously. No shock from the carb this time. Replacing the plug wires made absolutely no difference. What is surprising is that the missfiring seems to follow a regular pattern, i.e. it is not totally random. There is no backfiring when it is running. I am convinced the HT voltage is shorting somewhere. Ralph
Re: Summary, Coil voltage/missfiring. Bob 8-1-02  
I hate NGK...I had one car just tuned, all plugs went dead at 600mi...changed back to Champs. Also did you break any wires by pulling...and are you sure all wires are in firing order, only takes two swapped.
Re: Summary, Coil voltage/missfiring. Sam Watson 8-2-02  
Ralph, as a quick test, do the following two things: remove the vacuum hose from the distributor vacuum advance and plug the hose. Run a wire from battery plus source to coil +. Start engine and run through RPM range,remove jumper wire, and then stop engine. Tell us the results.
Re: Summary, Coil voltage/missfiring. Ralph 8-3-02  
Sam, Ran this test connecting battery positive directly to the coil +ve (existig wire at coil +ve was disconnected}. Ignition now seems to be firing fine without missing even with distributor vacuum reconnected. So what does this tell us and does it explain the shocks thru the ignition key and carburetor that have not occurred for a while. I can guarantee that engine ground is OK. Ralph
Re: Summary, Coil voltage/missfiring. Sam Watson 8-4-02  
The jumper wire and the vacuum disconnect tested two things. The vacuum disconnect was to test, more or less, if the problem was caused by too much change in the pickup-reluctor air gap as the pivoted mounting plate was pulled around by the vacuum "can". The jumper wire proved that your problem is ChryCo's somewhat enemic ignition system, something we, (meaning the guys in the shop), had to contend with when we were converting our fleet to dual-fuel operation in the late '70's. In our case, the altenate fuel was compressed--3,200 PSI--natural gas. "Dry gas" puts a terrible demand on an ignition system as there is no conductivity to it, as in a "wet" fuel. Even running gaps of.020" or less, the Dodges wouldn't ignite the fuel charge. As the oscilliscope showed, the ChryCo solid state ignition was putting out between 17,000 to 20,000 volts on open circuit. Compare that to the old point type system that it replaced which could make 32,000 open circuit voltage. Two things caused this, one being that the coil is "on", or has current flowing through it most of the time---it's really only "off" for about 3 degrees of dwell--this really keeps the coil very hot, which equals resistance. The coil is the other problem, ChryCo just used the same coil as their old system used, other mfgr's used a different design coil for their solid state ignition. So let's take your resister-type spark plug wires at 1,000 ohm resistance per inch, more or less, and run what little current comes out the end through a resister spark plug which contains a 10,000 ohm carbon resister. By this time there isn't much "juice" left in old sparky to make it across the gap. What we found was a trick that the off-road racer guys used. That was to use non-resister plugs, gapped at.032", move the coil to where it gets good air flow---even seen them mounted in the cold air intake duct-- and buy a ballast resister for the old point set ignition, mount it near your dual one, and run jumper wires between both ends of the coil feed side of your dual resister over to both ends of the new single resister so that you have these resisters parallel, which halves the resistance. We never had any problems with the coils after doing this, scope tests showed the ignition system was now making 26,000-28,000 open circuit voltage and firing the plugs nicely.You most likely were getting shocks from the key due to the fact that there is a connection betwwen the primary and secondary windings in the coil. Most likely, when the current voltage couldn't "push" across all that resistance, it discharged through whatever path it could find, though I've never heard of it "zapping" the key, but why not?
Re: Summary, Coil voltage/missfiring. ralph 8-4-02  
Sam, Thanks a lot for the information. I will try what you suggest as it all makes sense. I have champion plugs RV12YC which I am told are resistor type. I am having no luck finding a non-resistor equivalent. Can you or anyone help? Thanks again, Ralph
Re: Summary, Coil voltage/missfiring. Ray 8-4-02  
Ralph et al.

I must say that that was some interesting reading. Enjoyed every return. I have had problems with a friends 440 motorhome ignition and we got rid of the Dodge ignition and replaced it with MSD. A much better system and you can even see a larger spark coming out of the coil wire when removed from the distributor as compared to the stock spark. He hasn't had a problem since.
Required fields in red
For more info about a field, place your mouse over the More Info icon.
Your Name:
Your Email:

Code is case-sensitive. Helps stop SPAM.

Advertise Here
Get Media Kit NOW!

Get Media Kit to Advertise!

Advertiser Links

Back to Top