MS2 Injection Issues - Maybe..... (Sparks and blown fuses)

danc8000 · Post by **danc8000** » Fri Apr 07, 2006 3:53 am

OK guys,

Iâ€™ve got another one for you. Some of the MSII EDIS users may be able to answer this easier than others.

Basically I got my car started and running the other day with an MS1 linked to the EDIS system controlling ignition and an MSII purely controlling fuelling (2off low impedence injectors). I have a 36-1 wheel and am using a VR sensor and the 2.54 code in MSII. (MSnSE using 024s9).

The car started perfectly the other day but when I killed the ignition there was a big spark around my relay/fuse area. The 5A injector fuse blew and I havenâ€™t tried to run the car again since. Iâ€™ve been doing a bit of trouble shooting.

Iâ€™m not if this is a problem or notâ€¦.

I have approx 16 MOhms resistance if I plug my multi meter into either of my two injector plugs. (Only when the meter is connected: Red positive lead to 12v, black negative lead to the Inj 1 or 2. Other way round there is nothing). Is this wrong or does it sound normal?

If I unplug the EDIS unit the circuit is lost. If I unplug the MSII DB37 the circuit is lost. The link is one of my relays. The main relay clicks both the injector 12v and the power to my EDIS module into life although they have individual fuses. If I unplug the relay the resistance is still there â€“ simply because the wire to relay leg 87 is a wire that also connects both fuses. So basically my injector 12v is linked to my EDIS pin 5 12v.

Why or how the hell would this be finding its way back to the Inj1 or Inj2 connections? Does anyone else with EDIS have this resistance? Iâ€™ve been going through the entire loom looking for shorts but not found one yet. The fact that unplugging either EDIS or MSII gets rid of the problem sounds odd â€“ especially when the MSII is not connected to EDIS! All it does is share the VR input to the EDIS.

Any bright ideas or am I worrying about nothing with the 16 MOhms resistance?

Cheers

Dan

jsmcortina · Post by **jsmcortina** » Fri Apr 07, 2006 4:37 am

16mega ohms is very large, don't worry about it. To blow a fuse, something is wrong - either you are drawing too much current or perhaps you need a slightly larger fuse? What impedance are the injectors? How much current is drawn under normal operation?

James

danc8000 · Post by **danc8000** » Fri Apr 07, 2006 4:49 am

Injectors are 2.4 Ohm and there's two of them.

Fuse was a 5A. I am not sure what current they are drawing during normal operation to be honest.

Funny thing was there was a spark near the relays and fuses when I turned the engine off. Then I checked the fuses and this 5A was gone.

danc8000 · Post by **danc8000** » Fri Apr 07, 2006 8:32 am

Just fitted a 1n4001 diode across my fuel pump wiring at the pump and I no longer seem to have the problem.

Sound like a sensible fix to the problem to you? Current spikes through the system when turning the pump off with all the other current drawing components?

Jim · Post by **Jim** » Fri Apr 07, 2006 10:15 am

A 5 amp fuse is too small to run your injectors .

How many items are connected to that 5amp fuse ?

Is the 5amp fuse that you popped on you MS relay board or in your cars
relay / fuse panel .

Your injectors , if they were on 100% of the time ,
would pull about 5.8 amps ,
so if anything else runs off of that fuse it won't last long .

Fuses are sized by what gauge wire they are protecting ,
the purpose of a fuse is to prevent a certain sized wire from
getting too hot and starting a fire .

If you try to pull 30 amps through a 20ga. wire the insulation will melt
off of the wire and the copper will glow red hot like a light bulb filament .

You should investigate to find what size wire comes from the fuse that
you popped before you put in a bigger fuse .

My son-inlaw had a fully restored '72 Corvette burn to the ground
because of improper fuse sizes .

Generally speaking , here are some recomended fuse/wire sizes :

30 amp 12ga. wire or larger
25 amp 14ga. or larger
20 amp 16ga. or larger
15 amp 18ga. or larger
running smaller wire sizes than 18ga. is not a good idea unless you are
sure that you have a dedicated load with nothing else tacked on to it
and you have a reason for needing to run a smaller sized wire .
5 and 10amp fuses are usually used to not only protect a certain sized wire ,
but to also protect the device that it is powering from internal damage
caused by some problem .
An example is your MS computer may be fed by an 18ga. wire but
calls for a 5amp fuse , the 18ga. wire can safely carry 15amps max ,
but to protect the insides of your MS box a 5amp fuse is recomended .

Here is an on-line calculator for figuring how many amps a load will pull :

http://ourworld.compuserve.com/homepage ... hmslaw.htm

Always enter 14 volts when using this calc.

I run my fuel pump through a 20amp rated "Stero Noise Filter" plus use
a diode , this helps to keep my electrical system quiet , any motors in
your car will produce similar noise and spikes ,
BUT the fuel pump spike is not what popped a fuse .

You need to get a shop manual with wiring schematics for your car to
make sure that you aren't overloading some of your stock wiring .

danc8000 · Post by **danc8000** » Fri Apr 07, 2006 3:29 pm

Thanks Jim,

I appreciate the comments on wire sizing but all the wiring is brand new.

Nothing related to the MS install is existing wiring, the only original wiring take off point in the whole install is the switched ignition 12v to my 3 relays. The rest is brand new and custom made, 3 dedicated relays and an 8 way fusebox.

There are only 2 injectors fed off the 5A fuse - nothing else.

Using Ohms law is no biggy for me, those simple type calcs are easy. My confusion was working out exactly what a PWM injector will pull and whether there's be any spikes at on/off situations.

Jim · Post by **Jim** » Fri Apr 07, 2006 7:09 pm

No Prob ,
It may prove usefull to someone else .

Why are you trying to run such a small fuse ?
I can't see the advantage .
I run a 20amp fuse for my injectors just for extra insurance .

I'm also completely rewiring my car .

danc8000 · Post by **danc8000** » Fri Apr 07, 2006 10:05 pm

That's right Jim - it is good info and I do appreciate you taking the time to post it up.

This car had a dizzy and carbs orignially, hence the introduction of a whole new EMS loom and power supply loom.

In the relay board documentation section it recommends a 5A fuse for a 4 cyl and a 7.5A for a 8cyl. Seen as I only have 2 injectors I figured that 5A should be more than good enough. Do you think not?

What I don't understand yet is why I had a spark in the relay/fuse area when I turned the ignition off to kill the running engine. Maybe the spark and fuse are independant issues and it's just that the 5A is too small for my injectors?

Jim · Post by **Jim** » Sat Apr 08, 2006 2:14 am

The Relay Board documentation assumes the much more common
"High Impedance" Injectors which draw much less current ,
your 2 Injectors (I assume you have TBI like me) pull alot more
current than 8 High Impedance Injectors .

You said your injectors were 2.4 ohm , that makes a total of 1.2 ohms
14 volts over 1.2 ohms equals 11.6 amps , but this current is only pulled in
little short bursts , so the fuse didn't get hot enough to blow right away ,
when an unusual situation arises , even for a split second , the fuse blows .

You need to run a 15 amp fuse at the very least , 20 amp would be better .

The spark or flash was probably just the fuse blowing , not unusual .