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Author: Subject: Z20LET Megasquirt Issues

posted on 30/5/18 at 12:27 PM Reply With Quote
Z20LET Megasquirt Issues

Hi all,

I've changed from a Pinto to a Vauxhall Z20LET ran by a Megasquirt MS2 over the last few years and finally took it for mapping in August last year, it's been a bit of a marathon, but when it works as it should, it's brilliant!

I realise how difficult a problem such as the following will be to diagnose without seeing the car, but any pointers would be much appreciated!

I drove the car to John Sleath in Doncaster for the rolling road session. About 5 miles from my destination the car started splutter, misfiring and running extremely rough. It eventually died about 0.5 mile from his workshop and I tried to restart the car, after about 10 attempts the result was the same rough running. Then after 10 minutes of trying to spot anything obvious I tried to start it again and it sprung back into life as normal and I continued the journey.

The same issue occurred a further 4 times on the way back home from the rolling road session.

The fuel was fresh (filters looked well), no obvious boost leaks, fuel leaks, everything appears to be in good working order and built from new or known good second hand components.

Since this I put it in the garage and left it over winter

Now we've got good weather, I'm looking to bring it back into service. The fault is now consistent and the engine wont start, all I get are flames out of the exhaust and starter motor kick back - which leads my to believe it's an ignition timing issue.

Using the data logging part of Tuner Studio, I can see that the crank signals are very erratic, not the 60-2 pattern I used to see.

I understand this could be caused by noise from ignition coils and various other sources, to try rule this out I removed all the fuses from associated systems (injector wiring, ignition coils, fuel pump etc) and monitored crank signals, but there was no change.

All sensor earths go back to a single point on the engine.

This where my knowledge on megasquirt ends! so advice and pointers would be most welcome!


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posted on 30/5/18 at 12:41 PM Reply With Quote
my first guess is the the battery is slightly low

try jump starting it, see if it then 'just works'.

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posted on 30/5/18 at 01:55 PM Reply With Quote
i had this on my saab engine which uses the same trigger wheel and sensor. it was the crank position sensor. replacement fixed it. also make sure the two pots on the board for tuning the crank position sensor sensitivity are set correctly

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posted on 30/5/18 at 05:20 PM Reply With Quote
My MS2 V3 has a dedicated sensor ground wire. If yours has the same then you ought to be using it. I suggest that you head off to the MS forums and post your MSQ and a datalog. If they can't help you then no-one can. If I was a little nearer I'd scoot over to York myself.
You seem to have diagnosed the VR sensor as the possible problem so concentrate on that for a start. Maybe replace the ( hopefully shielded) cable. The shielding should be grounded at the ecu end only.
I have clip on ferrites everywhere, including the VR sensor cable.

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posted on 30/5/18 at 07:49 PM Reply With Quote
I would replace crank sensor and it's wiring using shielded cable and correctly earthed.

Duratec Engine is fitted, MS2 Extra V3 is assembled and tested, engine running, car now built. IVA passed 26/02/2016

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posted on 31/5/18 at 11:22 AM Reply With Quote
thanks for the replies guys, much appreciated.

I ordered another (second hand) crank position sensor and the fault is still there, so I guess that can be ruled out.

I put my battery booster on the battery when cranking which also made no difference.

I've read elsewhere about adjusting the pots to increase sensitivity... I'll look into that!
I bought the MS from Phil at ExtraEFI, who I'm pretty sure asked for the type of trigger wheel I'd be using, so I would've thought he would it would be adjusted to suit already... still I'll look into it!

Cable is shielded (grounded at ECU end only) apart from the last 6", which is the standard GM sensor and lead with connector.

The use of ferrites interests me... another thing for me to look into. Did you use these as you were having problems or just to be on the safe side?


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posted on 31/5/18 at 08:20 PM Reply With Quote
I used the ferrites in response to reset issues subsequently traced to a noisy alternator. There's plenty of info re. adjusting R52/R56 on the MS forums as well as in the manual. Does your ECU have the sensor ground wire?
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posted on 3/6/18 at 08:53 PM Reply With Quote
I had trouble with poor running, turned out to be the fuel pump was on the way out, so perhaps check your fuel pressure - could be a regulator, pump issue or just a bit of crap in the line, worth adding to the list of thing worth checking.
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