MoT Fail - more than just running rough.

[White S3]

As semi expected, MoT fail on emissions as running rough (which ironically got worse as I got closer to the test station). Having changed plugs again and wiggled various wires, gave up and accepted the inevitable - more time investigating.

Enroute home swung by Southways Automotive in Fareham to pick Rich and Steve combined brains (thanks guys really good advice as to what to check - I'll bring coffee and biscuits next time promise)) but still have not yet cracked it. What we did find, was all cylinders have +202psi +/-2 compression, the car is not firing on cylinders 1 and 2 with the exhaust manifolds for both significantly cooler than the others. Spark seen using both timing gun and laser HT ignition testers; HT leads swapped out on cyl_1&2 albeit for old ones but no joy; injector wiring for cyl_2 swapped for cyl_3 but fault did not follow (proving injector wiring loom hasn't got a fault at least on cyl_2(?)); Plugs swapped again and when extracted from 1 and 2 they were fuel soaked and back fire in exhaust still occurring which would indicate fuel is being dumped into the cylinders possibly by injectors failing open(?).

Don't really want to shell out for distributer cap and new leads just yet as I don't think that this is the cause. Has anyone experienced this or have any other suggestions before I go pulling the injectors and sending them for test/clean/replacement?

Loosing faith in my every day runner!

Mark

Edited by White S3 on Saturday 28th February 21:25

[White S3]

You would think that with compression, spark and fuel it would work but .... I have some leads made up so will try dropping 12v across them before going through the mare of swapping them around. Do the injectors come out easily once the fuel rail is unbolted? Or are there retaining clips etc... Hopefully I can get away without replacing any of the gassgets and O rings as I don't have any spares.

[White S3]

Damian, Mike, Mark,

Thanks for the latest responses and offer of spare injectors. After a day of pulling the fuel rail apart, confirming that all injectors are actually fine by putting 12v across all of them (again getting a click and a face full of petrol from the first one), I put it back together again and after a leak check tried to start it - you guessed it running on 4 still .

Then pulled off all of the black tape for the injector loom to check the infamous TVR special splicing only to find it all intact (I have to admit I was quite surprised how well the Blackpool tape faired considering it was 24yrs old!) - out with the heat shrink and amalgam tape to make a proper job of it. Finally re-checked that there was a spark in all HT leads and, feeling thoroughly despondent, I called it a day to check the tinternet and PH S-forum to see if there was a glimmer of hope.

Reading all of the posts since I started the thread and thinking of what had been proven: SPARK, FUEL and injectors WORKING in both No.1 and 2, NO wiring defects, distributor cap NOT damaged, HT leads GOOD (following the thread so far?) it dawned on me that there were TWO cylinders not firing a PAIR. Only having ever taken off one HT at a time to swap them out I hadn't thought to check the sequence diagram for the V6



You guessed it, Distributor cap end HT for 1 and 2 were the wrong way round . At some point Nov/Dec I must have inadvertently pulled them off while tinkering and...... nuff said.

Off to Re-MoT on Mon and I bet it'll be raining. Still snag resolved. Thanks all, moral of the story, START with the simple stuff EVEN IF YOU DON'T THINK YOU HAVE CHANGED IT.

[White S3]

Yep Phillpot hit the nail on the head - wish you'd hit those garage gremlins when they go out to tinker. Its a pity I hadn't left the job until after lunch having read your post probably would have saved me stripping it all down. Still, injectors are now clean and I can return the distributor cap and HTs once they arrive.