Loosing Cranking signal

LT401Vette · Post by **LT401Vette** » Sat Oct 15, 2005 2:03 pm

I have been having trouble with MS reading RPM while cranking.
I have a 60-2 tooth wheel and running on 26c code. When I start cranking MeagaTune is reading ~125 RPM almost immediately, however after about 2 sec of cranking, it goes to 0. This has been making cold starts difficult. Once warm it usually kicks off in that window.
Once it fires I am getting a very steady and clean RPM reading.

I have tightened the gap down on the VR pickup, I don't think I can go much more there.

I am wondering if the output of the sensor is just too low at this slow RPM. I am using the VR circuit on the v3 board and have the pots out all the way. I am wondering if I should try replacing them with a fixed resistor, maybe more resistence yet?

It just seems strange that it reads initially, then stops after a couple seconds.

daxtojeiro · Post by **daxtojeiro** » Sun Oct 16, 2005 2:09 am

Phil,
I had a similar problem with my setup, it turned out to be a bad earth. I remade the earth, moved the coil driver's earth to the chassis, rather than the same point as the MS earth on the block, and all has been ok since. I guessed it was down to the starter motor creating noise on the engine block (my earth was on the block) because the engine would be hard to turn when its cold. The coupled with the Coil drivers earth on there was just too much noise for it, I guess! Its been fine ever since anyhow,
Phil

Post by **jsmcortina** » Sun Oct 16, 2005 1:48 pm

In 026c there is the "advanced code" choice of 024s9 vs. 025 style wheel decoder. Have you tried both?
024s9 will likely be selected if you loaded an earlier MSQ. This seems to run quite badly on my install (although I need to re-test it)

James

LT401Vette · Post by **LT401Vette** » Sun Oct 16, 2005 6:09 pm

Phil,
Bullseye!
I left the VB's grounded to the block and moved all my MS grounds over to the Battery post. It seems to be working now.

Thanks!

LT401Vette · Post by **LT401Vette** » Sun Oct 16, 2005 6:12 pm

James, I am on 26c, I haven't tried the 24s9 version with the new ground arrangement, but previously it seemed like cranking was worse on the 24 stuff. I'll switch it over on a drive to let you know how the 24s9 code is working with my setup.

LT401Vette · Post by **LT401Vette** » Fri Oct 28, 2005 7:03 pm

I thought we had this licked with the ground, but not so.
I found that if I opened the gap on the vr sensor way up to .100" it seemed to read much better for cranking. But, not really. Once it is warmed up now, don't shut it off. Once I shut it off I can't get a tach reading until CLT gets down to around 145, then it seems to read again

. I can't for the life of me think of any reason engine temp should have any relationship to me vr reading. The vr is out of the way and always reasonably cool.

While cranking even when it is getting a signal, it doesn't look clean. It jumps around a lot reading 30-130 RPM with spikes up to 8-900 RPM. Once running it has a nice clean signal though... Any Ideas appreciated, I'm not sure if I should be digging into my VR circuit, or what? If my pots are in at all it reads nothing for sure, maybe I should add a little resistance? I'm using the v3 board circuit.

LT401Vette · Post by **LT401Vette** » Tue May 30, 2006 9:01 am

Just for a follow up on this incase anyone else runs into a similar problem....

I found the problem.

Now that the summer 90+ temps are back, this problem has been giving me a great deal of trouble again. This weekend I finally had time to dig into it.

It turns out the VR sensor was getting heat soaked. The VR bracket was a simple Alum bar with a .550" hole for the VR sensor with a set screw. I had purchased it from Electromotive when I first went to the big block.
On this bracket the Alum completely surrounds the sensor very near the magnet end. Eventually enugh heat transfers from the engine block to the sensor to alter it's output. In MSnS mode I would see RPM, but in wheel decode mode, it couldn't get a solid enough reading.

Solution, I built a new VR bracket that leaves as much of the sensor in open air as possible. Now seems solid as a rock, I was driving all over in 90+ degree whether all weekend...

hzdistributor · Post by **hzdistributor** » Tue May 30, 2006 9:31 pm

I haved something like that. The earth is very important.

LT401Vette · Post by **LT401Vette** » Wed May 31, 2006 9:33 am

Yeah I chased that one for quite a while. I ran a shielded line to the sensor, tried power and grounds directly to the batt.... Then I thought about it and I had this issue before I even went to MS and was using the electromotive ignition, I just wasn't driving the car much yet at that point.

I'm just thankful it is finally gone, this has been haunting me. I didn't trust the car to take it anywhere. Now I can finally drive it to work and get some fresh paint....