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Megasquirt 3.9 V8


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After weeks of fighting a battle I thought I had won, I finally started my Newly Megasquirted 3.9V8.............

It burst into life........But Idled way to fast with a nasty Knock/Tapping. Needless to say I was not impressed as this was a perfectly good

running engine....

I went through everything top to bottom, from wiring to relays to ECU but I couldn't find anything out of place?

I then decided that I would swap the motor for another running unit which I had other plans for......

After installing this engine I went through all of my wiring and double triple checked everything is in the correct place.......

The moment of truth. I turned the key and.......................... Same thing. Idles at 2200RPM and a nasty knock/tap.

I am picking it is a timing issue....

Is the trigger wheel able to cause the timing to be out far enough to run at this speed?

Will a vacuum leak cause the timing to advanced far enough to cause this idle issue?

Are there any setting I have over looked in Megatune?

is the timing going to be different due to the rubbish fuel we have down here?

Any help would stop any more grey hairs...............

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The noise may be "Pinking" where the ignition is off.

Simple explanation

Tooth has 36 teeth - minus One "the Gap"

Each tooth is therefore 10 degrees, and 36 = Full 360 rotation, so a couple of teeth out = massive ignition.


Please do the followuing

Put the engine crank pulley to TDC as indicted by the TDC markings on the crank pulley and guide.


Post up here and describe as best you can where the VR sensor is on the Crank Pulley in relation to the VR sensor, maybe even draw up a piccie.

I ask for it this way as if you don't quite know what might be right / wrong you can't misinterpret, this way you are telling me / us what you have in terms of the set up.


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Hi Nige,

It is the 3.9 V8 V belt kit you sent out to me in NZ.

The first fire up was successful but the noise coming from the engine was horrific.... I pulled the front off the motor 3 times to try and find the issue but to no avail.

In the end I put an engine I know is a good runner with no noises or smoke in to my RRC..... Plugged the MSQ up to it and crossed my fingers and turned the key.

Unfortunately I was greeted with the same horrific tapping noise.

As you can see from the last picture I have pulled this engine to bits and have found nothing out of the ordinary.

I will replace the lifters to be sure but other than that I'm lost as to how to fix this????????????

Do I need to prime the lifters somehow?

I don't believe there is any issue with the wiring as it seems to talk to mega tune and shows all gauge's.

I have oil pressure.... lots of it. as you can see in the picture there is oil for Africa....

Any suggestions????

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Lifters don't need priming, but they will rattle something horrible for a surprising amount of time before they pump up and you get some oil in them.

If the cam (and therefore followers) is new then remember the break in procedure...

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Ah HA !

I did wonder ! Hi and welcome to LR4x4 !!


As Bowie says.

Personally my ears couldn't live with the nosie dry lifter make, its sounds as if some small spanners have been left in the engine and are clatering away...its a horrendous noise, and take a long time for the oil to pump up the lifters and the nosie stop, it will be 16x noises and will die down as they pump up....but its not a great idea IMHO

I always shove lifters in a bath of engine oil fully covered and let them fill up, then fit them after some time (days) in the bath, you may get the odd one still clatter but it should also go quaicker. Additionaly dry lifter will not fully open vlaves etc so you can have probelms with the engine behaving.

It could be something this simples. As to the timing that looks spot on

lastly just go onto megatune, check

Spark?spark Settings

Bottom box "Trim " should be zero ?


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Thank's Gentlemen,

I did consider the 16 spanner rattling around theory but I just wasn't sure. it just sounds so punishing.

On closer inspection the lifters are dry, so as recommended they are in a luxurious bath of oil.

Just while I have your attention, is there any specific way to place the lifter in the hole? ie does the hole in the lifter need to face in any direction in particular?

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I know the feeling, grin and bear it was my philosophy, but it is painful.

BTW, the followers are DESIGNED to rotate in use, this is what the break-in procedure it all about, if you look at the face of a new follower it has a sort of spiral pattern on it, which encourages the follower to twist when lifted by the cam.

No break-in = no rotating follower = dead follower very soon.

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Well, after a few hours of Assembly today I think I should be ready to fire it up tomorrow.

Fingers crossed it will do as it should....!

Nige, What is you 5.2 built from?

I have been told a 5L can be made from a 3.5 block with a small hone and a 4.4L layland P76 crank?

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  • 3 weeks later...

Well today was the day....

I started it and it ran but rattled and rattled and rattled till I could no longer stand the rattling.

I think I'm going to pull the oil pump off and re-check it..... just in case.

Also It has a nasty miss, like it's down on more than one cylinder. I need to check the Leeds I made....

Now would this be caused by the Alternator not charging? as after a few minutes of running Mega tune starts to drop off and the motor wants to stall..... I guess this system likes a healthy supply of voltage.

Also does the alternator require power in? from the ignition switch?

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Lack of sufficient volts is always a problem with these rigs of course but should not cause such (timing) problems - especially as this problem seems to be the same with two different engines (?) - but just meter the output to be sure....

HT leads (and/or coilpacks) issues are a disctinct possibility too though. Depending on just what is wrong 'rough running' can certainly occur - but not usually with such awful rattling.

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Also does the alternator require power in? from the ignition switch?

Uh-oh... are you saying your alternator is currently wired to the battery but not the switch/warning light? What battery voltage are you getting?

Megasquirt will run from a PP3 9v battery quite happily, as long as you have enough power for fuel & sparks the ECU is more than happy.

The tappet rattle can be horrible, and sometimes takes a good blip to 3krpm+ to clear, which is the last thing your brain wants to do when it's making THAT noise. If the lifters are not pumped up then it may well misfire as the valves won't be being opened fully, right now as long as it starts & runs I would say to IGNORE trying to tune it and concentrate on the very basics - sorting your rattle, confirming the timing is within a barn door of where it should be, checking for leaks, etc. - the fuel & ignition maps can be way out of whack and it should still be fine to start & run under no load.

Also - do you have oil pressure? Have you got a known working pressure switch and/or gauge that tells you *some* oil is going round?

What oil are you running? Rover V8's like it thick, preferably still with chunks of dinosaur floating in it, water-thin modern synthetics just get lost between the gaps.

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