Running on 5 cylinders after maintenance work :-(

[JulianUK]

Having replaced all of the lash adjusters on my 1996 Legnum VR-4, along with the spark plugs and HT leads, I was disappointed (to say the least!) that the car wasn't running smooth once re-assembled. By unplugging each of the coil packs in turn, I found that engine roughness reduced less when unplugging power to the left-hand pack, providing spark to cylinders 2&5. With the other 2 coil packs, engine was a lot rougher when unplugged (dropping 2 cylinders). So, next step - I swapped the coil pack, and doing the 'unplug' test again showed the problem still with cylinders 2 or 5, so it's not the coil pack. I then unplugged the ht lead from this coil pack, and plugged in an old lead and plug, which gave a spark. So, I assumed the new lead had to be the problem, or the new plug. So, took plenum off, swapped the plug, and checked each lead. All leads had the same resistance, even the old ones, so how can it be the lead? Also, confirming an issue with cylinder 5, the inlet tract was wet with fuel, unlike the other 5 tracts. So, hoping the problem was the plug, I reassembled everything, but - still running rough. I then though it may be something to do with disturbed injector wiring, but there's definitely fuel there, and I can hear the injector ticking if I listen with a tube. So, starting to run out of ideas as to what's wrong and how to further diagnose. Thoughts went to the lash adjusters - could they be something to do with it? The tappet noise has gone, but would an issue with a new adjuster cause fuel not to be burnt on a 4-valve arrangement? So, you can see I'm running out of ideas on this, and could do with a bit of help before I venture back in the garage!

[TAR]

Welcome to the club.

Could be a rocker been put back incorrectly. This may be holding a valve slightly open therefore reducing the compression. A compression tester would help diagnose if you don't want to take everything apart agaian.

[Davezj]

To check if it is a inlet valve issue.
Eg rocker arms not put on correctly and popped off. When engine turned over.
If you take the plenum off you can see the back of the inlet valves and see them going up and down if rotate the crank by hand so you can see if the rocker arm is on correctly.

But alas this only checks the inlet valves


I say this as I hand this issue.
But because only one inlet valve rocker popped off the cylinder still worked relatively normally and was like that for months before I noticed it while doing so other work on the car.

Sent from my MI 5s using Tapatalk

[JulianUK]

Thanks for your suggestions, guys. I'm giving it a rest today - so I'll try these ideas out tomorrow. Fingers crossed!
OK, latest update - a misplaced rocker arm!!! I did the tests above, saw both inlets opening and closing, so checked compression on cylinder 5. zero!! So, removed rocker cover, did a bit more investigation by blowing air through a hose into the spark plug hole, and listening for the leak, and found one of the inlet valves wasn't closing completely. Took a closer look, and found I'd not sited the rocker arm centrally over the valve stem. A bit of leverage, and it clicked into place - we now have compression. It just had to be the rear bank, and the cylinder furthest from the 'mechanic' :-( Gonna have a cup of tea now, and put things back together later, now I'm pretty sure this is my issue. Thanks again for your suggestions. The moral of the story is double check before reassembly!