Erratic rpm problem - ongoing....
flak monkey - 13/4/09 at 07:56 PM
Its all going wrong at the moment 
The Aim dash decided to drop all of its analogue inputs last weekend, had all the wiring out yesterday looking
for a loose connection and found nothing. Took the dash apart, nothing obviousl wrong. Put it all back together and now its working again! Problem is
I know it will happen again, but dont know what the problem could be. Possibly a dry joint on the circuit boards in the dash, but I dont know....
Anyway...
I still have an ongoing issue with erratic RPM on the pinto.
Running megasquirt fuel only, and H&H ignitions electronic dizzy and dry coil.
The issue I get is this:
The yellow line is RPM, purple is throttle position. I see the jumps on both my dash and in megalog viewer. Dash is connected direct to coil, as is
megasquirt. The jumps start to happen at over 3500rpm, and can peak at anything from 8k to 20k rpm. Its consistently an issue and I can make it happen
whenever i like. The problem is I can't stop it!
Its only a problem at over 3500rpm. Anything below this is absolutely fine for an indefinate period of time.
I dont see any resets in megatune when i get the spikes. Also have a supressor capacitor fitted to the coil.
I have changed:
Plug leads
Plugs to resistor type
Dizzy cap
Rotor arm (v tight fit on dizzy shaft)
Fiddled with input circuit in MS unit and changed zener diode (D2) and capacitor (C12) to values suggested in construction guide for if you have these
problems.
All connections to coil and dizzy seem good and check out ok with meter.
Checked and lubricated advance mechanism in dizzy as it was quite tight and sticky. Now very easy to move and not made the slightest difference.
Help
[Edited on 13/4/09 by flak monkey]
paulf - 13/4/09 at 08:22 PM
Have you an aftermarket breakerless ignition system? , if so how about changing to a standard points and dizzy to see if it cures the fault.I would
suspect it is nothing to do with the megasquirt as it is showing on the tacho as well as megasquirt.
Paul.
big_wasa - 13/4/09 at 08:29 PM
Is a trigger wheel really that much work? Then go with the edis. 
flak monkey - 13/4/09 at 08:32 PM
quote:
Originally posted by paulf
Have you an aftermarket breakerless ignition system? , if so how about changing to a standard points and dizzy to see if it cures the fault.I would
suspect it is nothing to do with the megasquirt as it is showing on the tacho as well as megasquirt.
Paul.
Yes its an aftermarket electronic system. Uses an electronic pickup in the dizzy and amp it attached to side of dizzy.
Rescued attachment Electronic Dizzy.jpg
flak monkey - 13/4/09 at 08:40 PM
quote:
Originally posted by robocog
Have you got a log of the voltage?
Looking at that log you don't appear to be getting resets
I feel your pain!
Chased some noise issues when I was running megajolt and eventually nailed it by trial and error
Dash going wonky at the same time does suggest its electrical?
(red herring?)
Do you get any missfires or judder when you drive through 3500 RPM?
(or is it just displaying rpm spikes? yet still feels OK to drive)
Try leaning out around that area of the map?, if its too rich it _could_ cause a slight miss - causing accel enrich to kick in, making situation worse
and causing spikes?
try taking off (or changing the threshold of ) accel enrich to see if it magically dissapears?
Make sure all earths are as good as you can physically get them and common for the things that need to share the same ground point
As I use EDIS on my install I don't have much experience about the other types of trigger
I guess you have searched till your eyes are bleeding on the MS forums
Have you got the twiddly pots for VR conditioning?
(maybe I missunderstand how you are triggering)
Run out of ideas for now...
Sod it ...Just chuck an EDIS on there ditch the dissy and enjoy the summer 
Regards
Rob
Log is uploaded on this thread if you would like to take a look. I thought a similar thing about voltage, but there arent any spikes which correspond
to the problems.
http://www.msextra.com/viewtopic.php?f=4&t=30851
It misfires terribly, corresponding to the spikes. Which is making it undriveable over 3500 rpm. AFR is about 14.5 at 3500rpm.
I will try turning off accel enrichements though. Not thought of doing that.
The earths are:
Main MS earth is through 4mm cable (overkill or what?!) direct to main chassis/battery earth. Resistances checks out to be zero.
Distributor earths through the body presumably as the only connections are +12v and trigger to the coil. Its been suggested that I redundant earth the
dizzy body too, so shall try that.
I will be using EDIS on the duratec, but really dont want to go to the hassle of making a bracket and trigger wheel for the pinto if I can help it
Plus it means changing the output section of my MS and no-one can specifically tell me what I need to change to use the edis instead of the coil
drivers at the moment .
If all else fails I could try with the edis, but I really want this fixed before stoneleigh!!
David
02GF74 - 14/4/09 at 07:53 AM
quote:
Originally posted by flak monkey
The issue I get is this:
The yellow line is RPM, purple is throttle position. I see the jumps on both my dash and in megalog viewer.
The jumps start to happen at over 3500rpm, and can peak at anything from 8k to 20k rpm. Its consistently an issue and I can make it happen whenever i
like.
just to summarise. the misfiring occurs when you get the engine over 3,5000 rpm - and this happens at idle and at driving?
You show TP trace - purple - what is that dip?
Is it consistent?
Are you sure you TP is not worn/faulty?
Can you run MS without the TP? (I know you can with megajolt), if so, can you give that a go?
flak monkey - 14/4/09 at 11:10 AM
How can the misfire occurr at 3500rpm and at idle?
The misfire occurs when under load, or free reving at any revs over 3500rpm. Any revs under this are absolutely fine.
The dip in the TP trace is when I came off the throttle to stop it missing to bring the RPM down a little.
I am starting to think that EDIS is the only way forward now, and I am going to be really hard pushed to get that sorted between now and stoneleigh
