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Megajolt new install, but no spark


mickeyw

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Today has seen me tearing out my last few strands of hair, trying to figure this one out.

Having finally finished the install of a 3.9 Efi, Megajolt AND LPG, I was all set to turn the key and listen to some lovely V8-ness - but that was not to be today :(

Initial start attempts were all on petrol, just to establish correct function.

Preliminary troubleshooting established that there is no spark. As MJ is now providing sparks, I have restricted investigation to that alone. Digging deeper, here is what I have checked so far.

12V at centre pins of coil packs

12V at EDIS pin 6

12V at MJ

Correct polarity of VR sensor (been caught out here before)

Checked VR sensor when cranking - output between 0.1 and 0.55V AC

Had doubts over quality of GND connection, so temporarily connected direct to battery -ve, but to no avail.

Disconnected power to MJ to attempt starting on EDIS alone - no change.

Gap from trigger wheel to VR sensor approx 1mm

To rule out power supply possibilities, all 12v is direct to the battery.

I have included the diode circuit to provide a tacho output. How does one measure the output of this with a multimeter?

What can be done to verify EDIS-8 function? I have read that they rarely fail, but would be good to check it if poss.

The coils are both 2nd hand, but given their fabled reliability, I'd be surprised if both were pooped. I have spares, so will try another...

What else guys?

The unhappy bunnies have hijacked my Landy, hmmmph!

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If your wiring is all correct reverse the pins to the VR sensor.

That is the only thing that could be wrong unless VR sensor or EDIS unit is faulty.

You should get a spark even if the Megajolt is disconnected, and even if the trigger wheel is timed completely wrong, you should still get a spark.

Jon

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Thanks for your response Jon.

You are thinking the same as me. I reversed the VR sensor wires, just in case, then looked it up and realised I had it right to begin with.

With the readings I have got from the sensor, I'm hoping it is working OK, and that I have a workable gap.

Just wondering how to test an EDIS... I don't have a spare to swap out.

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Voltage coming out of the VR sensor sounds a little low. Edis won't "arm" unless it sees at least 0.5v. You should have in excess of 1v if things are working properly. What VR sensor are you using and what trigger wheel?

A photo would help perhaps?

Jon

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Riiiight - red herring time.

Lesson one - remember to throw away those knackered spark plugs.

The 'spare' one I grabbed to test turned out to be dead. Tried another plug, and got sparks. I did this for all plug leads, no that problem has been isolated.

Next I tested the ABCD coil wires to the EDIS. Turned out I had C & D the wrong way around!

With that corrected it now seems to be trying to fire but is getting bogged down after a few turns of the engine. Noticeable petrol smell too.

I double checked the plug lead positions again according to this layout.

coil_wiring.jpg

I also checked the VR sensor alignment. This isn't particularly easy from underneath, but I am sure it's pretty close. I would have thought the engine would at least start if it was a few degrees out???

I took the opportunity to minimise the gap between trigger wheel and sensor. Not yet rechecked the output to see if it's changed.

Btw the trigger wheel is one of Nige's, as is the sensor.

I think tomorrow's job will be to remove the plugs and check them up before further start attempts.

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Well it certainly is flooding. Plugs were pretty wet after a few cranking sessions. I gently warmed these with a blow lamp.

Tacho input is coming from a diode circuit that hooks into all four coils. This joins the loom (white/black to pin 39) close to the ECU. The LPG ECU also needs this signal.

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Only thing I will say is the lpg will almost certainly work from the MJ tacho out as well, the other signal may not be quite right for it....

Diode circuit sounds correct, 4 diodes plus a zener/ resistor?

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The tacho circuit is the same as shown here, http://autosportlabs.net/TachAdapter

I've used 1N4004 diodes and 100K 1 Watt resistors. There is no mention of a Zener on this circuit, even though one is used here http://www.autosportlabs.net/File:Tach_circuit.jpg

There seems to be conjecture that the Zener can cause issues, and there must be a good reason why it was omitted from a main stream product.

Mine are discreet components rather than SMD.

I wondered why the MJ's tacho output couldn't be used for the 14 CUX.

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You cant use the Megajolt tach out to feed the ECU, as its too low voltage - its looking for the flyback pulse that comes from the ignition coil normally. The Megajolt tach out is just a 12v square wave.

I've used the 4x 4n001 and 1x zener successfully before, but ive never tried the circuit you show.

Jon

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As above, different signals really.

And I have a mate with a truck I wired, 4 years later using the zener circuit.

I think the product they are selling is to drive a tacho, and not a 14CUX, looking at the schematic I'm not sure what they are trying to achieve by using diodes in parallel with resistors, but it could be that they are trying a 'one size fits all' configuration which is not suitable for the 14CUX.

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oooh, last thought, there's normally a resistor in the factory loom on the white/black wire, that if you leave it in the voltage/current is too low when using the tach driver circuit, perhaps have a look for this?

I've never needed to remove it, but then I've never used your circuit :)

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looking at the schematic I'm not sure what they are trying to achieve by using diodes in parallel with resistors

Hedging their bets I'd guess. As you say, just 'cos they're selling it doesn't mean it's the right answer for the 14CUX, every version I've seen used was 4x diodes + 1x zener.

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I'll certainly give the zener method a go, as that is known to work.

Other that 12-18V, what guidance can anyone give me in selecting one?

There are a lot of types to choose from on RS Components.

With regard to the in-line resistor that originally went to the coil -ve, do we know physically where it is situated in the loom? I have cut into the loom less than 6" from the ECU multi plug.

The ECU, MJ & EDIS and the rest of the wiring is going between the seats, beneath the cubby box.

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OK, time for a progress report.

Multiple ballsups have been unearthed this last few days, and a few 'WTF was I doing?' type thoughts have happened.

I now have the engine running, but only by cables going direct to the battery. I seem to have possible earthing issues...I don't know...

Ballsup 1 was found after tracing wires all over the place, and I realised I had the wires reversed for coils C&D from the EDIS-8. Corrected that - still no start.

Ballsup 2 was noticed while looking at a photo I took of the diode circuit I built. Please ignore the dire soldering, I have since tidied it up, but there is one glaring error.

post-7124-0-78300300-1434745332_thumb.jpg

I also noticed that the LED on the MJ was going out when the fuel pump was running. I am using the switched live that used to power the petrol pump to trigger relays for the efi fuel pump, main ECU relay, MJ/EDIS and LPG. Some investigation reveals the ign switched voltage drop massively when the fuel pump runs (the pump has its own fused supply direct from the battery) - weird - I'm thinking earthing problems?

Couldn't figure this out, so took a power direct from the battery for all circuits, just to eliminate other issues.

Having fixed that I found the engine now would start, but not very willingly, and sounded like the proverbial bag of spanners. It also seemed to not be running on a full house. After maybe 15 mins of running the tappets settled down (engine hasn't run in 2 years)

I pulled plug leads off in an attempt to find which cylinder(s) were missing. Seemed to be more than one, so took plugs out for a check/clean. Oddly the ones I think were missing were far cleaner (these were new plugs at the start of the install).

Much time and cursing later I find ballsup 3 - injector #4 had a contact pushed back out of its housing, so no wonder that cylinder was missing.

As it still seemed short I looked further - number 3 seemed to be to blame. Then I saw it, ballups up #4 (possibly the biggest of all) and smacked myself over the head in a moment of how/what/eh/wtf/you feckin eejit.............injector 3 was not even connected to the loom!!!!!!!!!!

I really cannot understand how I missed this when I fitted the plenum.... effing moron!!!!

Anyway by sheer luck I managed to wiggle to connector on without having to remove the plenum - thank F for that!

So soon after all that I had the engine running on all eight, but not starting that easily, and not wanting to lift on tickover too well. Once over 1000RPM it will rev, but any attempt to poke it sharply from tickover causes a stall.

So, things to figure out - why does the old fuel pump switched live line drop so many volts when used to switch a relay? I have added earths all over the place to see if that will help.

Then to find out why the engine hesitates when lifting off tickover...

I'm done in for the night now. Just shut the garage up as the local fox cubs just tried to run off with my laptop adapter. WHY??? The stinky nappy it stole from the bin last night I can understand :lol:

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  • 1 month later...

I've been driving hooning this around now for a week or so. but have a few thinks to resolve still.

Existing issues -

1 - The tacho circuit I built with the resistors in parallel with the 1N4004s, and no Zener seems to work fine for the 14CUX, but the LPG system isn't happy with it. I shall try two things - connect the MJ tacho out to the LPG ECU, and if that doesn't work, I'll modify the tach circuit to the Zener type.

2 - Checking the timing with a strobe (yes I know the crank markings aren't the pinnacle of accuracy) got me to think I am around 6-8 degrees too advanced. I've adjusted the crank sensor as far as I can without moving the trigger wheel round to the next hole, and compensated with the MJ timing to its offset max of -5. Engine now starts much easier, and the flat spot seems to have pretty much gone.

3 - The dropping voltage on the fuel pump and relay line has been sorted by taking a new wire from the ignition switch. All is well.

My research into 14 CUX and its potential error codes found me on Pistonheads, plus a few TVR forums. There is a stupendous amount of very useful 14 CUX geekery on there. I'm now assembling a Rover Gauge cable and will be interested to see what I can read from the ECU...

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1) I am going to stick my neck out and say the MJ output will be perfect for the LPG system

2) Using a piston stop I would make sure the timing marks on the engine are accurate, as you say they can be WILDLY out...

As for the geekery on Pistonheads, I agree, there is so much more out there nowadays, with remapping potential much greater than even 3 years ago.

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1) I am going to stick my neck out and say the MJ output will be perfect for the LPG system

Spot on Mr Bowie. LPG is now talking to me :)

2) Using a piston stop I would make sure the timing marks on the engine are accurate, as you say they can be WILDLY out.

I've just looked up piston stops. I would think a variation of this, using a sliding pin hooked up to a dial indicator would give a nice accurate result.

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