I am still having a problem with erratic rpm on the pinto, and am pretty much stumped now as to what it could be.

Essentially once I am cruising at 3500rpm or higher the revs start skipping around (always higher) and causing major issues with the megasquirt. Doesnt seem a problem when accelerating hard. The issue was a lot worse, but I found a loose rotor arm was to blame....

I have now replaced:

Spark plugs with resistor type - no improvement

Rotor arm as old one was very loose - made a big difference, now much better but there's still a problem. This rotor arm is v tight as I shimmed it to make sure!

New HT leads - no improvement

New dizzy cap - no improvement

I have a coil suppression capacitor fitted. And have had this problem since i built the car.

Run out of ideas now

Cheers,
David

Fit a trigger wheel and run edis ?

quote:

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Originally posted by big_wasa
Fit a trigger wheel and run edis ?

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quote:

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Originally posted by flak monkey

Run out of ideas now

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Nope its a H&H Ignition Solutions electronic one, all singing all dancing and set up for my engine....was new when i fitted the engine.

Slap some twin chokes on

If you have erratic RPM at higher revs then I would suspect something not working right in the distributor.

I assume that you have an electronic one as opposed to points. If points then it is possible that you have points bounce.

However if you have electronic then I suspect that you have some debris in the distributor or that something is loose on the base plate and is giving some problems at the higher RPM. Hence the change of rotor arm made an improvement. I would also suspect that this problem is also giving an erratic firing position on the pick-up in the distributor.


Just my thoughts, hope it helps.

I had this with my Megasquirt, I thought it was the ignition as datalogs showed erractic RPM, its was how the system was collecting the RPM signal.

If you jab the throttle very quickly when it starts missing then acceleration enrichments will add fuel, effectively overiding the RPM signal and proving its the MS pickup.

I needed a shielded cable, earthed at the MS end only, then had to play around with the 'dave' resistor and other links until it was sorted. The car would idle and rev happily when parked, drive fine then start to play up, no logic to this you could go for a couple of hours perfectly then have flat spots, it did get progressively worse

Thankfully sorted now, completely diffrent settings on this element when I moved from Rover V8 to Fireblade engine.

If floored was okay, mostly an issue when feathering the throttle!

Regards Mark



[Edited on 30/3/09 by mark chandler]

second jollygreengiant on that one, sounds like part of the trigger mechanism in the dizzy is loose, I assume you're running clockwork ignition then if you had the dizzy done specially, so its not just a fixed trigger for "mega" ignition via the ecu?

If so, could be a broken advance spring or just a lot of play in the advance plates, basically just check all moving parts in the dizzy

Thanks chaps, I have mailed H&H to see if they have any suggestions. If not I have to have the dizzy out and apart to have a look at it.

The dizzy still controls the spark.

Strangely not heard from H&H on this one, so pulled the dizzy off tonight.

Seemed very tight and the advance mechanism seemed quite sticky. Also one of the vanes on the rotor was very, very close to the static ones in the body.

Couldnt get it right apart without a lot of bother, but through the inspection cover in the side all springs are in place and all parts are new and show no wear.

Gave it a liberal dosing of oil on all the moving parts, which has freed everything right up, much smoother advance mechanism and spins lovely now.

Also tweaked the vane which was very close so all are now an equal distance.

If that doesnt fix it, I am completely lost.

Will take it for a run tomorrow evening and see if I have fixed it...

David

Don't know if this helps...but here goes....During my sva the rev counter became erratic and also affected the speed o. I had looped a 12+ supply from the speed o to the revcounter. To get over this, I ran a clean 12+ supply to the rev counter and one to the speed o and did not have any problems after this.....

Regards

Still got problems....

Really bugging me now. Speedo and rev counter are all in one as I have an Aim MXL digidash.

Its not just the RPM signal changing, its getting some extra ignition pulses from somewhere as its affecting megasquirt too. RPM counter is connected to neg side of coil, as is megasquirt.

Could there be something which needs modification in the megasquirt box?

David

David,

Are all your sensor wires a long way from ignition leads or high-current leads (e.g. those to the alternator or to the injectors)?

If you have any shielded cable to your sensors, do you have the shield connected to the chassis at one end only (NOT both!)?

Are all your MS earths totally clean, and (ideally) connected to the same chassis point?

I don't know how MS is set up - does it use a trigger wheel? If so, is the VR sensor mount VERY rigid? Megajolt users have been known to experience trouble at (and above) 4,000 rpm due to sensor vibration.

My MS coil trigger lead is shielded.

All MS earths soldered together and fixed to a single earth point (the main chassis/battery earth).

No VR sensor as I am using dizzy based ignition. Looks like there are some components which could be changed in the MS as I am having problems