OK here goes. After many many megasquirt woes I finally can start my engine at almost every attempt. It's been a bugger to start from cold since day one. I've always thought it was a squirt fault but now i'm not so sure. It only seems to be running on 3 cyls but sometimes on 4. No 1 and 2 cyls have pressure test of 220psi
3 and 4 205 psi
There is a spark and there is fuel but I can't for the life of me get it to run on 4 cyls. Couple this with an unexplainable noise from cyl 1 ( the one that won't always fire).
The noise comes out of the trumpet of the throttle body and can only be described as the sound that you make with your tongue on the roof of your mouth when you do clip clop noises (the clop one).
I suppose it could be nothing but why can't I get it to run on all 4 cyls constantly. If changed plugs and leads and coil and moved the injectors round to see if it moves cylinder but no it's always on cylinder 1.
Anyone.

Edit to add that it must fire at times as the exhaust header becomes hot and sometimes just as hot as the others (especially if you up the idle slightly.)

[Edited on 26/11/08 by omega 24 v6]

[Edited on 26/11/08 by omega 24 v6]

Sound's like bent or burnt valves to me - can you do a `leakdown` test ?

sticky inlet valve on no1, or head gskt gone between 1 and 2. does sound like a mechanical fault if you have swapped bits around forget this as the compression figures have been amended, just sounds like throttles need balanceing

[Edited on 26/11/08 by bigrich]

I would suggest taking the head off if the pressures that unequal !!!

Could be something loose or broken inside.

The valve guides can sometimes drop which might make that noise.

If you've moved things around and it's still on cylinder one it puts to potential mechanical problems!

Just re-read your post - scratch that !
It may be balance ? If No1 is too closed it will run odd , unless the rev's are raised a bit ?

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Just re-read your post - scratch that ! It may be balance ? If No1 is too closed it will run odd , unless the rev's are raised a bit ?

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I'd concer with Ben.

With pressuers that unequal I'd be looking for some sort of compression fault somewhere.

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Originally posted by omega 24 v6
Funnily enough that was the problem on my first engine that jumped the timing. Did a balance setup on this one from the start. i suppose a check would be easy though.

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take the head off


could be a valve seat or a guide has droped or a cracked block

at the end of the day you wont know until its in bits :-)

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Originally posted by mediabloke
Daft question, but have you tried putting a timing light on #3 cylinder? As the XE is lost-spark, cyls 1 & 3 will fire at the same time

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Never worked on a XE but arent they hydraulic lifters??

Could the inlet one on cylinder 1 be sticking open allowing it to blow back through the carb????

I would think by the noise it has to be either timing or valve problem but if no.4 okay its pointing to a valve/clerance setting problem..

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Could the inlet one on cylinder 1 be sticking open allowing it to blow back through the carb????

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Not necessaraly it would only show up if its permenantly stuck If its a sticky lifter or one opening too much it could be droping down with the pressure of the springs when sitting or with lack of oil pressure when testing allowing the valve to sit proper..

But if its popping back through the carbs being lazy I'd start seeing what could be holding the valve open before stripping the engine down completly obviously the valve aint burnt going by compression..

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Originally posted by MikeRJ
in the case of a four cylinder engine cylinders 1&4 and 2&3 would be paired.

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OK I was right the head does not need to come off.
Here's what we THINK might have happened.

The bodies were balanced before spot on

the engine always ran lumpy untill warm

after warm up I leaned off for a steady idle and air/fuel mixture.

At some point during a restart from cold a large backfire throught the body BENT the butterfly

consequently at idle to much air and not enough fuel made this go off a cylinder on this body.

Now I know it seems a strange explanation but we cannot come up with a better explanation.

Now it's running on all 4 and I'm a happy bunny for the first time in a week

Sorry, missed this thread.

It should always run on "some" throttle no matter how bad the balance is, but the further out it is, the more throttle will be needed.

However, if you are running throttle position based load i.e. TPS not MAP on megasquirt (TPS is still the best way I hasten to add! ), then the real airflow can be so far out compared to the mapped airflow that it will be too lean to run at all.

Unusual for a backfire to bend the spindle, but it could have moved something in the throttle linkage that was otherwise "settled" in position.

Often you will find that really poor low speed running and what may seem like terminal engine problems are actually a combination effect of slightly out on throttle balance, having a much greater knock on effect on the TPS site on your injection system.

e.g. if the spindle nearest the throttle pot has moved, meaning that for load site 0 or 1 (whichever megasquirt uses on idle) the rest of the throttles are actually open now to nearer load site 2 or 3 (not far in reality) then it will run much too lean and wont run apart from on snap throttle opening where the transient map or (electronic accel pump) kicks in.