Petronix Screwing with Tach??????

[merc200]

I recently outfitted my 1977 mercruiser 165 I6 with a Petronix electronic ignition conversion and Flamethower coil. My problem is that the tach reading is way off from what the rpms say on my friend's snap-on timing light. They are about the same at idle, but the higher you rev the engine, the farther apart the readings are from each other. By the time you get to 3500 rpm, the boat tach only reads 2500 rpm. Is the Petronix ignition screwing with my tach or what???? If so, what tach can I buy will work with the Petronix ignition? Thanks.

 

[Boomyal]

Re: Petronix Screwing with Tach??????

I think mine is doing the same. I have a Teleflex tach. I used to run a capacitive discharge ignition system. When I installed the Teleflex, it did not work at all, so I had to disconnect the ignition system. Using the pertronix, the tach works but seems to work erradically.

 

[Dunaruna]

Re: Petronix Screwing with Tach??????

I see that sometimes when I install non gen. modules in cars, very irratic tach. Don't know why but its not uncommon. Have sent modules back under warranty but the new ones do the same.<br /><br />Merc200, petronix make some pretty big claims with the flamethrower, bolt on HP and all that.<br /><br />Any noticable increase in power?<br /><br />Aldo

 

[hondon]

Re: Petronix Screwing with Tach??????

What are you doing here? Why are'nt you in contact with Petronics or Accel?

 

[BinLurkin]

Re: Petronix Screwing with Tach??????

I think because he gets better information here.

 

[Boomyal]

Re: Petronix Screwing with Tach??????

Originally posted by hondon:<br />What are you doing here? Why are'nt you in contact with Petronics or Accel?

Frankly hondon, cause ya can't talk to them at 10 pm and because in most cases this is a friendly sight full of people who have had all kinds of experience and it's just plain and simple a good place to start!

 

[merc200]

Re: Petronix Screwing with Tach??????

I never ran my engine without the petronix ignition and flamethower coil. I bought the boat last fall with a cracked block, head, manifold, and riser.....so I pretty much started from scratch. I'll call petronix and see.....just thought I'd get my problem out there and see if anyone else had the same. Thanks.

 

[John Carpenter]

Re: Petronix Screwing with Tach??????

I replaced an old dual point Mallory distributor setup with an electronic ignition...not Pertronix..and had the same thing happen. My tach just quit working & from what I understand it is not going to work...need a new tach. As I know that my boat is correctly propped...and seldom operate much above a fast idle, it doesn't bother me much.

 

[Rainmaker]

Re: Petronix Screwing with Tach??????

Had the same problem when I installed the Pertronix stuff on my old 165 OMC. I picked up a tachometer originally built for Sea Ray. It had a calibration screw. This helped a little, but not completely. Had to learn to live with it.

 

[Destin]

Re: Petronix Screwing with Tach??????

Try putting a capacitor in series with the tach pickup lead, such as a 0.1µf 250V 10% Metal-film Capacitor , RadioShack Catalog #: 272-1053 , about $1.19. If the tach doesn't read at all with that cap, you might try the larger value 1.0 uf cap. It worked for me once when I hooked up a tach to a GM HEI ignition. I think the easiest way to try this is to disconnect the wire at the tach terminal on back of the tach, attach one lead of the cap to that terminal, and the wire to the other cap lead.

 

[JasonB]

Re: Petronix Screwing with Tach??????

I have the same problem since installing a Pertronix on my Ford V8. The tach reads ok until about 2000 RPM then it reads really low. I know I'm turning better than 4k, but the tach reads 3200. I have built the filter that Pertronix suggests for use with theOMC drives shift mechanism. The only suggestion they had was to try it with the tach to see if it helps. Haven't had a chance to wire it in yet though.

 

[merc200]

Re: Petronix Screwing with Tach??????

Yeah, my tach currently reads 3000 rpm going 41 mph WOT across the lake. The engine is screaming. I know it's doing a lot more than 3000....probably more like 4500-4700 rpm. I have a 17P prop and I want my tach to work so I can try a 19P and see what it does. Petronix's web site gives no information about not working with tachs, and they don't give any tech support lines. Thanks Destin, I'll try the capacitor and see what happens. Thanks.

 

[merc200]

Re: Petronix Screwing with Tach??????

I removed the tach from the dash today to install a capacitor and discovered that it was set for an 8 cyl. engine on the back calibration screw......so I set it for a 6 cyl. and took it out.....it read 4100 rpm @ 41 mph WOT with a 19P prop. That is pretty darn close. Before, it wouldn't even register over 3000 rpm set on 8 cyl. So, in conclusion, switching a points ignition to a Petronix electronic igniton does NOT screw with the factory tach as long as the tach calibration screw is SET right.