I think something is off with the optical tach somehow. See if you can find a diesel shop that can double check it for you.

 

It's possible. I may go spray paint the HB flat black then reattach the aluminum tape to see if that changes the reading.

I checked the tach with a florescent light and it reads 3600 when it's set for a 2 blade prop. If you do the math, 60 hz x 2 flashes per cycle of the light x 60 = 7200 flashes per minute which equals 3600 rpm for a 2 bladed prop.

I'm confident in the tach but perhaps the fan spinning and the shininess of the bare metal on the HB is causing a to high reading.

Edwin

 

Yeah, I'm puzzled by the reading because your procedure sounds perfect, and it's obvious from the flourescent light test that the tach can read accurately in that range.

It's just that 3950 RPM doesn't make any sense. I would have had no problem believing 32-3300 out of a stock gov. spring with the high idle backed off, but 3950 is just

 

Yeah but the PO did some pump tweaking and may have trimmed the spring or installed a 3200. He may have had gauges and took them off but since there was no hole in the manifold or downpipe I doubt he had a pyro. The down pipe could have been replaced I guess but considering the condition of the rest of the truck I suspect it was just ineptness.

Edwin

 

You don't need a 3200 or above gov spring to turn ~4000rpm no load in neutral if you have your high idle screw back all the way out.

Edwin, thats why I wanted to see a pic of your VE.

 

OK, thanks. I'll see if I can get a closeup with enough detail for you. Stay tuned.

Edwin

 

I took 3 pics of the high idle screw. Judging from the factory paint it doesn't look like it's been disturbed and if I manually move it to WOT it hits the stop and then it will go about another 1/4 inch against the spring.

I tried to get a pic of the fuel screw but to much other stuff is in the way.

The paint is missing from the top cover screw so the top may have been off at some time in the past. Also when I was looking at the mechanism it looks like part of the end of the spring is broken off but it's hanging on by sheer force of will. I guess I'll need a new one of them next.

The pics have been uploaded to my gallery and I'll post back when they've been approved.

Thanks

Edwin

 

Yep tach issue , you're not pushing 3900rpm no load. The high idle screw has the tamper cap missing, so it could've been adjusted a little bit, but no where near 4k. I'd say it probly should top out at maybe 3200rpm. I've removed that screw, I have no need for it .

Yeah you should pick up a breakover spring. And is that PLASTIC throttle rod ends???? You know about the upgrade metal throttle rod ends right?

 

Where can I get the spring? I have heard of the plastic rod ends breaking so I should probably get them also. Would the Dodge dealer have these or will I find they're discontinued?

I'll paint my HB and make more contrast for the optical tach. I really need somebody to check the optical while I adj the electronic.

Thanks for looking at the pics.

Edwin

 

Edwin,

If you can get up to 100 mph, you have to be able to pull up to about 3000 rpm (unless you have 3.07 axles) -- so, that isn't stock. And to be able to pull up to 3k, the engine will rev in neutral up a lot higher. I find it hard to believe the optical tach is wrong. But even if it is, some "mods" have been made to your max governor setting somehow.

 

BTW his speedo only goes to 85. 100mph is a guestimate. The calculator on www.randysringandpinion.com will give you an idea of speed/trans ratios etc. 235/85's are about 32", 3.54 rears, 100mph, .74 5th gear OD = 2751rpm.

Edwin, www.scheiddiesel.com will get you any Bosch or Cummins part you need. The breakover spring and throttle rod/end kit part numbers are in the tech facts.

 

I need to correct myself...... its "red" at about 2900 rpm... sorry

 

Yes It's a guestimate based on the needle wrapping all the way a round and pointing straight down. I calibrated my speedo gear witha GPS BTW.

Edwin