J70ELETC peaking rev limiter

[hondon]

Working on a 93 Jonny that will activate the rev limiter whenever you reach 4700. Here's what Ive done so far .General lookl over ,comp. ignition output , sync and link.All looked good . Water tested the unit and found it to be entering rev limit early.Changed plugs to ql77jc4, new plug wires and a complete ignition ohm and output check.All were within spec. Water test again.Same symptoms.Swapped packs ,watertest again ,same symptoms.Would suggest a new stator to this guy but I would feel like I'm throwwing parts at this and thats not what I do.Still get the feeling I have an R/F interferance thing going on here. Any help would be appreciated.

 

[clanton]

Re: J70ELETC peaking rev limiter

Is temp sensor pigtail tan with blue stripe. Disconnect tan wire to power pack and try it. If it runs with tan wire disconnected, the warning horn may be shorted, wrong horn, open diode in engine harness. There is 3/5 service bulletins on overheat this engine, try search service bulletins.

 

[hondon]

Re: J70ELETC peaking rev limiter

Thanks Clanton, but it's been run with temp sensor ,oil tank sender, quickstart, and vro all unplgged,Power coil tests to spec.New powerpack.This one is a toughie.

 

[jegervais]

Re: J70ELETC peaking rev limiter

Index the flywheel and check for double-firing on all cylinders & try cylinder drop test at problem rpm. <br /><br />-John

 

[hondon]

Re: J70ELETC peaking rev limiter

Thanks John ,but both suggestions have also been done.At exactly 4700 on the shop tach this thing will peak the rev limiter. Blocking diode is functional.I'm kinda down to the stator but I still have this r/f thing looming in the back of my mind.Been burned by it before but I have done all I know to sidestep it.

 

[jegervais]

Re: J70ELETC peaking rev limiter

I don't feel a stator is an issue with type of problem. The power coil (orange wires) is basically just the "power supply" for the rev-limiter, SLOW and QuickStart features on these engines. It's like plugging in the hair dryer in an outlet in the bathroom and there isn't any heat from it, but the electric razor works perfectly when plugged into the same outlet, the problem isn't the electric outlet. (Stupid analogy, but it makes the point...) <br /><br />If you've got an rfi issue, look at the ignition coils. Specifically, ohm them out and you're looking for an open on the secondary. Champion QL78YC (or QL77JC4) plugs gapped @ .030" - excessive gap can contribute to rfi. To eliminate the starter solenoid (magnetic coil) as a source for the rfi, rope start the engine. Watch the wire routing (the 3-wire harness w/ tan, yellow/red & white/black). If it's too close to the ignition coils it can contribute. I know you said its got a new pack, which one (p/n & manufacturer)?? The logic circuit for SLOW & the rev limiter is in the pack - eliminate the circuitry by disconnecting the 2 orange wires from the power pack side of the 5-wire amphenol connector. Don't run for a long period of time, this will eventually overload and destroy the power coil - its ok for a couple of short test runs. If the problem goes away, the pack (again) is suspect. If the problem is still there, look for something mechanical or fuel (you just unplugged the razor LOL ).<br /><br />-John

 

[clanton]

Re: J70ELETC peaking rev limiter

If the stator is making the volts at 4700 rpms, I would change the pack again. If it is going into S.L.O.W, should hold the rpms to 2500. What about tach?

 

[hondon]

Re: J70ELETC peaking rev limiter

Thank you John and Clanton.I too feel that the stator issue is a long shot for the reasons you have stated John. All plugs are appropriate and gapped correctly.Will look at the wire routing Monday ,but we all know it is close to the coils.Will also try the power coil unplug thing.You can't imagine how nice it is to have this forum and people like you to bounce ideas off of.

 

[seahorse5]

Re: J70ELETC peaking rev limiter

Even though it might test OK, the timer bases in '93 and '94 had problems. Substituting with a known good one is the only way to check it. Aslo remove the white wire and pull on the pin to check the crimp.<br /><br />Another thing to inspect is the inner timing magnet on the flywheel. Grab it with your hand and forcibly try to twist it one way and the other. It should not move or wobble.

 

[hondon]

Re: J70ELETC peaking rev limiter

Thanks Seahorse.With a tag like that you must love your Johnson motors.Good advice. Let's keep this info flowing.

 

[hondon]

Re: J70ELETC peaking rev limiter

Well,I,m back at it with this engine and have made no progress.With power coil unplugged I still get what Iwould consider the rev limiter at precisely 4700 everytime.Fuel directly into the carbs makes no difference.A mechanical failure that is that precise?Coils have been ohmed with no opens to ground OR between primary and secondary and ohm similar too a new coil off the shelf.Original pack was OMC 584808 that supperceeds to 585145 so all OEM there.Timeing stays consistant though retarded in the failure mode. The flywheel has been off several times in my frustration but have not yet changed the timer base. Are there any bulletins on these failures.Thanks in advance for any more help.

 

[clanton]

Re: J70ELETC peaking rev limiter

Are you saying that timing retards from max timing to a retarded position and the rpms stop increasing. If true the timer or linkage is bad. I think timing should move smoothly to max position and stay at that position as long a full throttle held.

 

[hondon]

Re: J70ELETC peaking rev limiter

Yes timeing retards about ten or so degrees when this engine starts acting up.Now let me throw this one at you.Max timeing on this thing is acheived at about 4000 too 4200 by watching the timeing stop.It stays at that stop.So why don't we have a failure before 4700?When this engine acts up it is kind of a lesser animated SLOW and consistant with the way I have seen these rev limiters act before but perhaps I' m stepping on my peener with this one.Anyway thanks for sticking with me and keep it comeing.

 

[clanton]

Re: J70ELETC peaking rev limiter

I think Seahorse may be right about the timer or flywheel. I would thing you could id bad timer with peak reading meter, engine running. Is it shifting from the QuickStart sensor to the run sensors? The QuickStart moves the timing about 8 degrees, I am looking at a 96 manual, may not be same.