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

[phillpot]

If you have fuel (wet plugs) and you have spark (timing light) and compression it should work! Could be "duff" injectors?

Try putting 12 volts to them individually, you should be able to hear then click.

[mk1fan]

Why not swap the injectors round. If the symptoms move then it's the injector.

[v8s4me]

mk1fan said:

Why not swap the injectors round. If the symptoms move then it's the injector.

Good idea Could be as simple as duff injectors.

[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.

[Roy C]

What about the dodgy electrical connector to the injectors that sits in the vee? That failed on mine, causing similar symptoms.

[v8s4me]

White S3 said:

... Hopefully I can get away without replacing any of the gassgets and O rings as I don't have any spares.

I've only done injectors on my V8 so I can't tell you how it's done on V6 but it's not a job I'd start without a set of new 'O' rings handy. And gaskets if that's what you need. When I had a similar problem a few years ago it was due to a dodgy injector and it's all too easy to nip the 'O' ring when putting one back.

Edited by v8s4me on Saturday 28th February 12:47

[phillpot]

Before ripping injectors out I'd double check ignition side of things (despite timing light flashing ok), thoroughly check dis cap for "micro-cracks" that could cause tracking, swap HT leads around if others are long enough to reach, new plugs (or clean and dry in a warm oven).


Nothing as daft as 1 & 2 leads crossed is it?

[chiefyo]

Google noid light these are cheap and will allow you to check the pulses to your injectors

[DamianS3]

I think I am with Philpot here if the plugs are wet fuel is going in.. Only injector fault could be too much or not enough fuel.

It is more likely to be electrics mine was.. Turned out to be dodgy coil pack connection (ht lead on your car..) or dissy cap as already mentioned.

I would check / replace this before pulling injectors.

Cheers

Damian

[mep12345]

Mark, I'd agree with others electrics first as when I took my injectors to a specialist during engine rebuild just because I could his response was that I'd be wasting my time as these injectors rarely fail and unless I knew I had a problem don't bother with test or overhaul.

Once you've tested the electrical side if you need I have a full spare set of injectors so you can check these if you like but you need 2 new o rings per injector and the gaskets for the fuel rail and inlet plenum then it is as simples as about 12 bowls and a quick tug. There are no locking rings, circlips etc

Let me know if you want the injectors, but it'll have to wait till next weekend as I can't get them before then

[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.

[phillpot]

White S3 said:

You guessed it, Distributor cap end HT for 1 and 2 were the wrong way round

phillpot said:

Nothing as daft as 1 & 2 leads crossed is 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.

[mep12345]

Don't let the Engineers who work for you hear about this!! Done that twice myself but fortunately for me realised before posting

[v8s4me]

White S3 said:

....You guessed it, Distributor cap end HT for 1 and 2 were the wrong way round ...

it so easily done. And with our old cars we always expect the worst. I once ran for several miles wondering why it was misfiring, going through all the horrible scenarios in my head. Then it dawned on me just as I was approaching a petrol station that I hadn't put any fuel in it for a while! So is any one else going to own up to something similarly stupid?

[glenrobbo]

v8s4me said:

it so easily done. And with our old cars we always expect the worst. I once ran for several miles wondering why it was misfiring, going through all the horrible scenarios in my head. Then it dawned on me just as I was approaching a petrol station that I hadn't put any fuel in it for a while! So is any one else going to own up to something similarly stupid?

A while ago, I actually drove 125 miles just for breakfast! That's a round trip of 250 miles!!! ( I'm a great admirer of Carol Voorderman! )

And I failed to learn from this stupidity, because I've actually found myself foolishly repeating this act of madness a few times since.

Some people never learn, eh?

[steve j]

v8s4me said:

it so easily done. And with our old cars we always expect the worst. I once ran for several miles wondering why it was misfiring, going through all the horrible scenarios in my head. Then it dawned on me just as I was approaching a petrol station that I hadn't put any fuel in it for a while! So is any one else going to own up to something similarly stupid?

How about this little beaut` I put Griff 500 brakes on the front of my S2. I could not get the dammed thinks to function or could not get the air out during bleeding. I`ve replaced all sorts of brakes over the years so this problem had me stumped/bamboozled etc etc. I even missed taking the car to S club I`d posted my woes on here and was waiting for a solution, maybe something I`d missed, guess who put the calipers on upside down left caliper on the right and right on the left. Boy I learnt from that and got the fully deserved p&%s take

[steve j]

Have a read of this and have a good laugh. http://www.pistonheads.com/gassing/topic.asp?h=0&a...