Missfire and erratic rpm display

[Megatron-UK]

Hi folks, I've just installed a V3 MJLJ board and the 3.1 software in a 7 replica to run my 2.1 Pinto. I was running twin DCOE's and a distributor which ran reasonably well. I changed to Yamaha R1 bike carbs at the same time as installing the MegaJolt.

I've done the following:

Mounted trigger wheel and pickup
Connected up the carbs TPS
Fitted Ford EDIS4 module and coilpack
New plugs and leads
Wired up the mjlj using some of the existing wiring and spliced in the EDIS module, coilpack wiring and the VR sensor.

The engine runs, but no1 and no4 aren't really great - no1 has a decent spark, but it doesn't make a massive difference when you run it without the plug lead on. No4 barely makes a difference to the running of the engine whether its on or not.... testing the spark from no4 and it will be on for a little bit and then just dissapear for a second or two... overall spark on no4 is poor when it does actually spark. Taking off no2 or no3 plug leads results in the engine severely bogging down.

TPS changes smoothly as the throttle is opened. No problems there.

RPM speed display on the laptop is quite erratic - it will sit at approx 1000-1200 rpm idle, but will often wildly flip up to anywhere around 4-5krpm, or down to 0 for a fraction of a second... obviously the timing tries to adjust to suit the rpm indicated. Actual engine speed during this time doesn't actually change very much, certainly not what the display indicates (i would guess the changes are mainly down to the ecu pulling/adding timing, anywhere from 0 to 28 degrees). Even when the rpm is stationary (usually not for more than 5 or 6 seconds) the engine doesn't run much better.

Tests we've done:

I get a working signal from the TPS (3.55v at closed, 4.82 at wot) and I have calibrated the bins to suit.
I'm using the standard 6000rpm Pinto map from www.cate1.co.uk
The AC and DC voltages for PIP/SAW at ignition on and during cranking are within tolerances (only voltage that is remotely out of spec is EDIS pin 1 @ 10.6v with ignition on and ~4.8-5v cranking, the input to both the EDIS module and mjlj is ~12.8v)
I've tried two EDIS modules and three coilpacks
The miss follows outputs 1 and 4 from the coilpack
Fuel pressure for the bike carbs is at a max of 3psi via a pressure regulator
As evidenced by a timing light, the mjlj is definitely altering the timing

Anyone have any ideas? My father and I are getting rather depressed!

-John

[brentp]

Hi John,

When you see spikes in the RPM this means that the MJLJ is seeing noise on the PIP line coming from EDIS module. The noise on the line appears as 'extra' PIP signals which show up as higher RPMs, hence the spikes.

Ensure the following:

- you are using shielded wire from the VR sensor to the EDIS module, and that the shield is properly grounded
- you are using shielded wire for the PIP and SAW lines, between the EDIS module and the MJLJ
- the ground wires for the EDIS module and the MJLJ are connected to the same spot on the chassis

How does the engine run with the MJLJ disconnected? The Ford EDIS module is designed to run in a 'limp home' mode when it does not see the SAW pulse coming back from the controller. You can simply unplug the MJLJ to test this out.

Report back with your findings-

[Megatron-UK]

Hey Brent, we tried the engine in EDIS-only mode this afternoon... spark and cylinder firing conditions are roughly the same as before - however it did rev smoother and doesn't backfire when you come off the throttle (I guess due to no MJLJ having a wonky rpm speed reading to affect ignition timing). So the problem does seem to be either EDIS or more basic engine function related.

We've taken the head off and are going to re-check valves tomorrow; as an aside we saw low compression readings for all 4 cylinders this afternoon.. based on the work we did to the engine, it should have been raised from approx 9.7:1 to at least 10.5:1... but we're seeing compression test numbers of 125,100,100 and 80psi - there's virtually no original or old parts left in this engine to cause something like that!

So it seems that the primary cause of the erratic running is not MJLJ, though the uneven rpm speed data didn't help while it was connected. When we get it all back together I think we may redo the EDIS wiring from scratch with new wiring to try and sort those issues.

Cheers

[brentp]

Ok-

There's a remote chance that you might still have electrical interference. The primary thing that would cause electrical noise while the engine is running is your alternator- you could temporarily run with it disconnected so you are running solely on battery power. If this improves things then it could be that the EDIS module is being overcome by noise on the 12V power supply.

You're running conventional resistor plug wires, correct?

Finally, you could crank the engine with your fuel supply cut to see if you're getting strong spark on all of the cylinders. This takes the running engine out of the equation.

Best of luck,

[Megatron-UK]

We'll give the alternator test a try when we get the engine back together - it's certainly worth a try.

Plug leads are all brand new off the shelf suppression items.

Thanks Brent

-John

[Megatron-UK]

Just to let people know; we put the engine back together and re-fitted the Sierra distributor and spark amplifier we were using before - it runs as sweet as you would like! I'm impressed with the smooth idle of the R1 bike carbs too.

Got to be a problem with the wiring in the EDIS system. We plan to replace all of the original EDIS wires with new shielded cables in the near future.

[Johnson]

Excellent,your post has confirmed what I thought was wrong with my car today.

I have just wired the Jolt in and didnt have any shielded wiring for the TPS or PIP and SAW signals so I too am seeing massive RPM fluctuations.

Off to get some shielded cable in the morning.

J