Cranks too slowly to register rpm signal - help!

riceandbeans · Post by **riceandbeans** » Wed Jul 19, 2006 7:41 pm

setup: MSI, V3.0PCB, 029j msns-e firmware

I'm running on a S5 13BT rotary engine, using the stock nippo CAS for rpm input.

It's been months of relentless research and fabrication, and I'm pleased to say that all my fuel and ignition systems have been tested to work flawlessly when I spin the CAS by hand. However, when I slide it into the front cover of the engine and crank with the starter motor, I never get above the cranking threshold of MS, so my rpm stays dormant at 0, and neither my coils or injectors fire. Basically, the MS is asleep at the wheel until I can get the engine to break through that rpm threshold.

I took off the CAS cover to visually verify the speed of the CAS during crank. I then took the CAS out and attempted to roughly mimic the normal engine cranking speed using my hand, in the effort of avoiding any ground noise that may be seen during crank when the starter is hauling away.

Sure enough, when I crank the CAS by hand at roughly the same speed that the starter can put out on its own, I am UNABLE to get any RPM input on the MS. However, if crank a bit faster (roughly 2x as fast), I finally break through the threshold and get an RPM, and all my injectors and such come to life.

I have tried cranking with 3 batteries, one which I know to be in working order (taken off my daily driver). Cranking speed varies slightly, but it's always fairly slow.

I have followed muythaibxr's articles on rx7club and my settings match his exactly. I have also tried lowering the cranking speed from 300rpm to 100rpm with the same symptoms.

Any advice? Any help would be greatly appreciated.

-greg

mops · Post by **mops** » Wed Jul 19, 2006 8:09 pm

turn both pots fully counter-closkwise.
can you scope the singal ?
the reason of what you are describing is probably that signal is too weak. can you possibly put the sensor closer to the teeth/marks (whatever) ? it shouldt be further than 1.5mm... normally...

if the signal is very weak, chances are that it will be pront to interference...

riceandbeans · Post by **riceandbeans** » Wed Jul 19, 2006 8:21 pm

I had already re-gapped the teeth of the CAS with a piece of paper, so there's almost no gap between the coils and the teeth, so the signal is nice and strong. The wires are also shielded, and twisted to their respective grounds. The shield is also grounded to MS ground, which is grounded to the engine block.

I'll mess around with the pots and see what I get. It seems as through the lowest rpm I can get which registers on MS is around 38rpm, but it also seems highly unstable. I'll very carefully rotate the CAS by hand at a nice, slow, steady speed, and the injectors will cut in and out, and the rpm will jump around in the range of 38rpm to 471rpm. I'm not changing the CAS input speed much at all either.

I'll mess around with the pots and see what I get.

riceandbeans · Post by **riceandbeans** » Wed Jul 19, 2006 8:34 pm

Alright, I rotated both the signal conditioner pots fully anticlockwise and now I'm reading an RPM during crank of around 270rpm. Awesome. Smoke coming out of the intake makes me happy. Now let's just mess around and see if I can get this heap to idle. Thanks thus far- I'll keep you posted.

mops · Post by **mops** » Wed Jul 19, 2006 8:50 pm

riceandbeans wrote:Alright, I rotated both the signal conditioner pots fully anticlockwise and now I'm reading an RPM during crank of around 270rpm. Awesome. Smoke coming out of the intake makes me happy. Now let's just mess around and see if I can get this heap to idle. Thanks thus far- I'll keep you posted.

YEAH! thats what I'm talking about.

agreat article on setting priming and cranking pulses can be found here:
actually i think it should be copies to MS site, because it's so great.
Courtesy of iX'er of e30tech.com:

http://www.e30tech.com/forum/viewtopic.php?t=15166

second post.

riceandbeans · Post by **riceandbeans** » Wed Jul 19, 2006 9:35 pm

Alright, well at first I was having very good progress, got the engine to rise above idle for a second or two, and of course I freaked out and let go of all the wires I was grounding to keep the engine alive. Total dumbass.

Anyway, as I got more an more into it and tried to start it again, it seemed to be less and less willing to sputter to life. I took out the spark plugs, checked for spark, which seemed good, but the plugs themselves were saturated in oil and fuel. I think I may be flooding the engine a bit.

riceandbeans · Post by **riceandbeans** » Thu Jul 20, 2006 6:47 am

It seems as though my progress has diminished since I started last night. When I first started, the engine seemed like it wanted to start. As I continued to crank the engine, it seemed as though it was less and less on the ball. The pops and sputters didn't sound consistent and coordinated. Almost as if it was firing at random points as the engine turned: sometimes helping it increase in speed, and sometimes hindering its ability to spin faster- the end result being a mis-coordinated engine. I let the engine sit overnight and tried it again in the morning with similar (lack of) results.

I hooked up a timing light to the leading wire of the front rotor and checked the timing. Sometimes I would get the timing light to flash, and sometimes not. However, when I take the spark plug out of the block and rest it against ground, I show a strong, consistent spark.

I'm thinking that my spark isn't always making it to the rotor for some reason. Perhaps the spark is getting blown out? Will a plug saturated in oil not fire correctly?

Correct me if I'm wrong, but the 2nd gen leading coil is a double-ended coil, making both of the leading plugs fire at the same time regardless, meaning that I couldn't have gotten the wires crossed, right?

Any other troubleshooting ideas?