No RPM readout

Desp · Post by **Desp** » Mon Jan 04, 2010 6:04 am

After working on this for quite a while I finally got my megajolt installed in my sand rail. I built the MJLJ kit and am able to read map pressure by blowing on it, my laptop will also communicate, read/write to the unit. The problem Im having is I'm not getting any RPM read out. I have the splined key out of the crankshaft so I'm able to spin the pulley to test the setup without cranking the engine.
I set up everything without the MJLJ first, making sure the parts worked in limp home mode. Everything worked, got spark etc. I carefully wired in the MJLJ up to the EDIS and no spark anymore, I have the hard rev limiter in the unit so I took it apart to check it, ground and trigger were bridged, so after fixing that the rev limiter didn't stay closed anymore and I was able to get spark once again from the coil, I'm still not getting any type of RPM readout though. I tested voltage between PIP and ground; EDIS PIP + Ground is 12v, and MJLJ PIP + Ground is 9 volt, then with engine cranking it goes between 3 and 6, like it' sending out a signal. What do I need to check now??

Post by **brentp** » Mon Jan 04, 2010 3:02 pm

I think you've seen the verification steps in the assembly guide to test different voltages, but just in case here it is:

http://www.autosportlabs.net/MJLJ_V4_ve ... tion_Steps

The problem centers around the reading the PIP signal. When you're repeating the verification steps you should ensure you see the same voltage reading on the PIP line at the EDIS module as you see at the MJLJ- traced all the way into the board. If you can measure the appropriate PIP voltage right at where the molex connector is soldered to the board, then the problem lies in the build inside the unit. Double check that each solder joint is solid- remember, it should be shiny and smooth, like you see in the assembly guide. It would not hurt to touch up all of the solder joints in this way.

Let us know what you find out after these checks!

Desp · Post by **Desp** » Mon Jan 04, 2010 3:05 pm

I should probably also specify that I tried spinning the pulley by attaching a drill to it, making it spin at least a couple hundred RPM. Not sure if there is a minimum RPM it needs to spin before the MJLJ will pick up anything, but I'm not sure how else to test and see if it's communicating with the EDIS.

Desp · Post by **Desp** » Mon Jan 04, 2010 3:09 pm

brentp wrote:I think you've seen the verification steps in the assembly guide to test different voltages, but just in case here it is:

http://www.autosportlabs.net/MJLJ_V4_ve ... tion_Steps

The problem centers around the reading the PIP signal. When you're repeating the verification steps you should ensure you see the same voltage reading on the PIP line at the EDIS module as you see at the MJLJ- traced all the way into the board. If you can measure the appropriate PIP voltage right at where the molex connector is soldered to the board, then the problem lies in the build inside the unit. Double check that each solder joint is solid- remember, it should be shiny and smooth, like you see in the assembly guide. It would not hurt to touch up all of the solder joints in this way.

Let us know what you find out after these checks!

I'll take the board out of the enclosure and measure the voltage at the PIP connection on the board, if it reads correctly what components on the board do I need to check?

Desp · Post by **Desp** » Mon Jan 04, 2010 11:14 pm

I took the unit apart and removed the rev limiter as a simple step to eliminate any potential problems. I've been staring at the schematics and as I'm not 100 percent educated (beyond just looking at it) i'm not real sure how it relates to locations on the physical board. But as I can tell the PIP signal is getting from the molex connector to the MAX232A chip, from there it appears it should go to ULN2003 but I cannot find the signal anywhere on that chip. I remember seeing another thread that someone's MAX232 chip was bad, could that be the issue, or should the voltage from the PIP input appear somewhere else on the board at IC1?

Desp · Post by **Desp** » Tue Jan 05, 2010 1:21 pm

Engine has to spin at 460 (exactly) RPM before it'll pick up the speed and displace it in the MJLJ, just FYI.

A dewalt 18v with a charged battery will spin it a 540 RPM

Post by **brentp** » Tue Jan 05, 2010 2:35 pm

So the PIP Signal goes from the molex, to the MAX232A chip, and on to the processor. The ULN2003 isn't used in the PIP circuit. If you haven't already, touch up all of the solder joints on these two chips and the capacitors around the chip.

Let us know what you find out!

Desp · Post by **Desp** » Tue Jan 05, 2010 3:06 pm

brentp wrote:So the PIP Signal goes from the molex, to the MAX232A chip, and on to the processor. The ULN2003 isn't used in the PIP circuit. If you haven't already, touch up all of the solder joints on these two chips and the capacitors around the chip.

Let us know what you find out!

Thanks for all the info. It was working all along. I wasn't spinning the pulley fast enough, the MJLJ won't display RPM until it's spinning at 460+ RPM.

NITROPIXIE · Post by **NITROPIXIE** » Tue Jan 05, 2010 4:39 pm

Hey desp

Any chance of some pics up of your sandrail in the powered by section please. I don't think we have had one on here before and would be nice to see yours.

Ryan

Post by **brentp** » Tue Jan 05, 2010 6:16 pm

Oh, I got it. right. you were spinning it at "below measurable rpm", so the cranking advance was active.

Fantastic, and yes- Pics please!!