JRP Diesel Tach Adapter :: RPM On Mechanically Injected Engines

Before we delve into the general description about the JRP Diesel Tach adapter, we need to make it clear to customers looking at this product what it’s intended use is for, and in what situations it can be used in isolation to generate a useable tacho signal from an engine. What we mean by that is, if you are buying this device to help get a tacho signal from a mechanically injected diesel vehicle and didn’t plan on buying other products along with this to help get your tacho signal working, then there is only ONE circumstance that this adapter can be the only tacho device you buy to help get a tacho signal generated.

1. If you are wanting to generate a tacho signal from an injector pump or low voltage cam / crank angle sensor to input into an aftermarket gauge, such as our 14in1, or 52mm tacho gauge.

** If you are looking at this product to try and generate a tacho signal to run a factory cluster tacho, then this device alone very likely WON’T be the only device you need. Please read below for tons of info on what to do with a factory tacho cluster, and if wanting tacho on an aftermaket gauge **

So, if you are looking at this product because you are wanting to get a tacho signal from a Diesel engine that doesn’t have an ECU, and you are wanting to get tacho into an aftermarket gauge such as our 14in1, or 52mm tacho, or even other brands of tachometers that accept a 5v / 12v square wave tacho signal, then good news, this could very well be the only device you need to purchase.

**BUT**, if you are looking at trying to get a factory cluster tacho working after an engine conversion, or just a factory cluster tacho working for any reason whatsoever, this product is most likely NOT the only item you will need to achieve this. If you have for example done an engine swap in your 4x4, running a motor with more cylinders, or running a cluster that doesn’t take a 5v or 12v square wave tacho signal, you very well will need more products than just this one alone. Some customers will need something called ratio adjustment of their tacho signal, this is where the pulses from the source of the tacho signal don’t match the pulses required by the cluster itself to read correctly, or you have a pre 2000’s factory cluster which uses an AC high voltage signal for tacho, in these cases you very well may also need the Universal Tach Adapter below, or the Tacho Booster to achieve a functional and correct tacho signal generated to be sent to your factory cluster to work.

So, the rule here is, if you are looking at this product and have a mechanically injected Deisel vehicle WITHOUT and ECU, and you are wanting to generate a tacho signal to be sent to our 14in1, our 52mm tacho, or any other aftermarket tacho gauge that accepts a 5v / 12v square wave, then this product in 95% of cases could be the only device you need to achieve this. Worst case with some diesels that have crazy sensors that output very strange pulses, the Universal Tach Adapter may also be required for ratio adjustment, but as above in 95% of cases, if you are just looking at getting tacho into an aftermarket gauge, this diesel tach adapter alone is most likely all you will need. If in doubt, please reach out to our incredibly helpful sales & tech team, they are well versed into tacho, and will be able to provide advice on which items you may need to generate a tach signal for your particular application.

***AGAIN, BUT***, if you are looking at trying to get tacho on a diesel that you have done an engine conversion, and wanting to get the FACTORY tacho cluster working, then there is a VERY good chance this is NOT the only device you need, and you could require either the Universal Tach Adapter below as well, or also the Tacho Booster, OR BOTH. If you are looking at this page because you are trying to get a factory tacho working correctly, then you NEED to talk with us first, be willing to have an auto electrician help you with this project and ASK us about your project before buying anything. We are here to help, and by talking with us first, it can save a lot of frustration on both ends.

Most people think that tacho isn’t overly complex, but in reality it really is, it’s one of the most complex subjects we deal with here at JRP, and we have become experts in it as a service to our customers and the community at large, because we know there is a lack of help out there for people trying to get their tachos working. We have taken one for the team making sure our techs are schooled in this whole tacho business, along with selling a line of products to help get tacho off pretty much anything, so our customers can get their tachos working and not go insane in the process. We recommend that customers use an auto electrician with our tach adapters, because as mentioned this can get very complex, by all means have a shot yourself, but if you hit a wall and aren’t able to understand the questions or procedures our techs require for diagnosis, then it’s time to pay a professional. We have been helping hundreds if not thousands of customers here in Australia & the world get tacho working on their diesel engines, we aren’t doing this for profit, quite the opposite, we are doing this as a service to our customer base so tachos can work again, be it using one of our gauges, or getting that old cluster reading again.

It’s been a long time coming, but it’s finally here. A dedicated tacho adapter for Diesel vehicles that use mechanical injection systems and don’t have an ECU to obtain the tacho signal. Getting a tacho signal from these types of Diesel vehicles can be a nightmare, in a lot of cases customers had to resort to using our standard tach adapters and grabbing a source signal from their alternators. This isn’t the most ideal way to get tach for a couple of reasons, as 1. a lot of these mechanically injected diesels don’t have a 3-wire alternator to start with, which is a requirement to use the standard tach adapter to have a 3-wire alternator because the W terminal on these is what is used to generate an RPM source tach signal for the adapters to work with, a lot of these diesel motors have 2-wire alternators, so that rules out being able to do anything there.

Also using the alternator as a source for a RPM signal can sometimes be tricky, the signal is typically very noisy, and even with the tach adapter you sometimes need to use diodes or resistors to even get them to work decently without bouncing all over the place, making the whole process of getting a stable tacho output for your aftermarket gauge a bit of a nightmare at times.

So, in comes the JRP dedicated mechanical injection Diesel tacho adapter. The best place to get a tacho signal from these types of engines is off the sensor on the mechanical injection pump, but there has always been an issue with this, most of these sensors only output anything from 0.3v to 0.6v max, and this voltage is not enough to drive most tach adapters, such as out standard tach adapter needs an input signal of 4.1v or higher to trigger, making them not an option for people with these types of engines.

On mechanically injected diesel engines, as mentioned above they don’t have an ECU, and so tach for the factory cluster is normally generated from a couple of places, such as a HALL effect sensor on the CAM gears, or a crank angle sensor, or it can be off the actual injection pump itself. And the sensors that are used by the vehicle manufactures like Toyota, Nissan, Ford etc in almost all cases are running extremely low voltage sensors as well, can also be using AC and not DC for the output signal, and some aren’t even square wave signals either. So, it can make it extremely tricky to generate a standard tacho signal to be used with aftermarket gauges such as our 14in1 or 52mm tacho gauge, which both require a 5v or 12v square wave pulse signal to be able to read tacho.

The JRP Diesel mechanical injection tacho adapter is built for this specific purpose, so they are able to read tach signals from these types of sensors & trigger from a source signal as low as 280 millivolts  0.028v. Essentially what these little devices do is, they take the signal from a low voltage cam / crank angle HALL effect sensor, or a VR sensor on the injector pump, and convert it into a perfect 12v square wave pulse signal that can be used with aftermarket tachos, such as our 14in1 Multi Gage, or our Edge 52mm & 95mm Tachos as well.

There is also going to be a lot of auto electricians out there that are going to love these little units, as most of them already know tacho especially on Diesels can be a bit of a nightmare. We now have another tool in the JRP toolbox for those in the industry to be able to get customers vehicles tachos working again, be it with just this little unit, or if they need to use a combination of this unit with some of our other tach adapter / booster products.

These little adapters can also be used as a signal booster for certain applications, they will take any low volt AC or Sawtooth input and output a perfect 12v square wave signal. For example, crank angle sensors which output a very low voltage signal that isn’t strong enough to be able to drive a tacho. So again, we think some workshops or customers with some interesting electrical projects might find these little adapter modules useful for other purposes as well.

So, if you are the owner of an old mechanically injected Diesel, such as the old Patrols with TD42 for example, or Landcruiser with 1HZ / 1HDT / 1HD-FT and want to get an RPM signal into one of our gauge products, this is the answer. There are plenty of other vehicles that use this type of injection system that these little adapters will be a god send for, if unsure which adapter or product you need from us to get tacho working on your Diesel engine, please give our tech staff a yell and they will be only too happy to help.