Intermittent Fault on Race Car

[fsmlittler]

My 1000cc full race Imp engine (rev limit 9000rpm) has being running fine with MJ for 12 months but last weekend while away at an event it started playing up. If the engine is completely cold it starts and runs fine but after a minute or so it won't rev properly and loses power. It get's so bad it can hardly move on the flat without constantly diping the clutch. It will start no problem but just has no power. The temperature barely moves on the guage when the trouble starts.

The carbs (dellorto dhla40s) have been stripped and rebuilt professionally and we've fitted a new fuel pump and adjustable regulator so we're confident the problem is not fueling. It feels like the ignition is too retarded when the problem happens.

So far we discovered a very loose main earth strap to the engine plus the TPS needed recalibrating as it was only showing 90% when the throttle was fully open. We've swapped coil pack, plugs and leads, checked all connections and checked the VR sensor/trigger wheel which haven't moved.
We hooked up an adjustable Gunson timing light which seemed to suggest we had 60 degrees advance when the map said 22. Would we be right in thinking that because of the wasted spark firing the plugs twice as often we half the reading to get the correct result? If not how do we check the timing on the computer is accurate?

[NITROPIXIE]

Possibly a coil pack on its way out i would say. Try checking the impedance of the coils against each other, are you able to get hold of a second coil pack to test.

Is everything reading ok with the computer connected to megajolt?????? IE vacuum

Could be a split in the vacuum pipe??? although it sounds like it is changing advance

Tough one this??? double check connections????



Oops you have already changed the coil pack, my bad

[brentp]

With your timing light, what advance do you read with the MJLJ disconnected or not powered? It should show a steady 10 degrees, reflecting the EDIS "limp home" mode. Some of the adjustable timing lights are confused by the wasted spark ignition- try getting a simpler, 'dumb' timing light to compare results.

Also, starting with a cold engine, try re-creating the problem with the MJLJ disconnected. You will be fixed at 10 degrees, but see if you're experiencing somewhat identical behaviour.

When using the timing light, is the ignition advance precise? It should adjust in discrete increments as engine conditions change. It should not jump around or jitter significantly. Does the engine misfire or hesitate, or does it 'smoothly' loose power? Do the symptoms come on solidly, or does it gradually degrade?

Let us know- especially what you find out on the above tests.

Regards,

[fsmlittler]

I need to work out how to disonnect the MJ so that I can run it on Limp-Home edis only but the unit was supplied built with the edis unit in the case. I guess it's time to open the case and get my fingers dirty.

When reading the timing with the gun it was pretty steady.

When the problem occurs it seems to be fairly sudden and yes it's a smooth loss of power rather than an actual misfire.

My suspicion is that it's going into EDIS only mode and that's why it won't rev and feels flat as a pancake. The least amount of advance I'm running is 22 degrees at 1500rpm so 10 degrees would strangle the engine.

I'm still curious about how I can check the actual ignition advance, although I know that isn't likely to be the problem. Is my theory about halving the numbers showing on the gun not right?

[Rich in Vancouver]

EDIS in the case? Are you sure?
The EDIS unit is quite large, in my case at least, almost as big as my MJ unit.
I would think that just unplugging the Molex connector from the MJ would do the trick.
I am sure an expert will chime in soon to clarify things.

Rich

[fsmlittler]

OK I've now taken the ECU off the car and as I suspected the EDIS unit has been built into the case and hard soldered directly to the board so it can't be disconnected easily.
I tried the car again yesterday and it started perfectly and we warmed it through thoroughly before putting any load on and the problem wasn't apparent. Once I started driving the car up the road it took all of 20 seconds for it to re-occur.
On checking again today I noticed that at low steady revs the engine hunts and there is an occasional glitch on the tacho with it flicking to zero momentarily.
With the laptop plugged in it all seems to be fine and the map seems to be working as it should with the cursor moving around as expected.
All ideas greatly appreciated as I'm struggling now.

[brentp]

As a diagnostic test, I would recommend finding a different EDIS 4 module and wire that in to see if your glitch is eliminated. You will be fixed at 10 degrees advance, but it should at least run smooth.