Misfire

[Paul V]

I changed the engine mount a couple of days ago and now have a misfire, it's when the engine is under load at low revs, once in the higher rev range it seems to clear.

I've tried changing the plugs and making sure the leads weren't disturbed when I was changing the mount.

Guessing it could be a lambda sensor as they are next to the mount or maybe the leads or coil packs, if I get hold of the lead to plug into the ECU is it likely to help me pinpoint the problem?

[Leadfoot]

I'd check the earthing lead to the engine. A misfire along with the starting problems mentioned in your other post suggests a bad earth or dying battery to me.

[Paul V]

I'll check the earth lead, have fitted a new battery and it's staring much better, think the old battery had a dead cell.

[S3 CGJ]

You say you changed the plugs, did you set the gaps to around 45 thou. A smaller gap than that will give you exactly the symptoms you describe. Reset the adaptives though afterwards.

[hollowpockets]

sounds like the coil pack, my car had same symptoms, just overnight it developed a misfire, tried changing plugs (cheapest first) then checked all the leads (fine) then went to vauxhall dealer and bought a bosche coil pack (same as a v6 omega i think with different firing order) , misfire gone

roughly £140

[Paul V]

I set the gap too 35thou as that was what the current plugs were gapped at, they were fine before so can't see it being that.

Going to try and get a lead or make one up to reset the adaptive maps but done a search and there seems to be confusion over what pin goes where, anyone have a lead they can test for me to make sure I make it up correctly?

[s6boy]

http://www.clever-trevor.net/tvr-part-category/4-e...

Try this, scroll down for the lead.

[Whitey]

do you mean a misfire as in a big sudden misfire, or just rough running at low rpm? If it's the latter, it's probably the leads, even though they look fine. The heat kills them, I replace mine each service.

[Paul V]

It's a sudden misfire when revving up, occasionally it'll sound like it's running on only 4 cylinders. Starter motor was sticking today as was supposed to take it down to JMS to go on their computer but wouldn't start, took the motor out and gave it a good clean up and freed it off, now seems to starting fine. Car has been great then everything going wrong at once lol

I Cleaned the Earth leads up and the coil pack connector while doing the starter just to be sure they are ok.

[Paul V]

s6boy said:

http://www.clever-trevor.net/tvr-part-category/4-e...

Try this, scroll down for the lead.

I will be ordering one of those but thinking of making up a lead to make do until it arrives thats why I wanted to try and get the correct connection.

[Basil Brush]

Pin mapping is:
Serial 3 to ECU 1
Serial 2 to ECU 2
Serial 5 to ECU 3

I made a lead up for about a fiver and it works ok.

[Paul V]

Cheers mate, did you manage to find a suitable plug so it can plug straight in or do you connect manually?

[kevin63]

Don't know if the Tuscan is the same as the Cerbera Paul, but the plug on the rear lights is the same three pin plug as on the ECU.

[S3 CGJ]

If you are close to Chester Paul you can borrow my lead for a few days.

At 35 thou your spark plug gaps are 25% too small. I'm almost certain that is your problem.

[Paul V]

Got the ECU connected up, no faults showing and the lambdas were in range, I reset the adaptive maps and it's still missing, it's under load at low revs so probably a lead even though they are only , next I think I shall replacing the leads and or coil pack to see if that has any effect.

[S3 CGJ]

I had exactly the same symptoms. It developed a few weeks after I had a new coil pack and leads. So I knew it couldn't be those.

The misfire/backfire was happening whilst accelerating at anything under 2000 rpm. Gengle acceleration was fine but a sudden change caused the backfire.

My throttle on idle was too low at 500 rpm so I upped that and then set the spark gaps to 45 thou, they were around the 35 thou mark, just as your is.

All is now fine.

[Paul V]

I've re-gapped the plugs to 45 and seems worse instead of better, bought a coil pack yesterday so will try and fit it today if I can get someone to give me a hand taking off the bonnet, one of those one lift up conversions would be handy at the moment.

One thing I did notice the throttle pots are reading quite close at idle but over about half throttle they start reading almost identical, there is no fault code though say they are reading from only one.

[Paul V]

All sorted, was the Coil pack in the end, replaced it and now no missing under low rev loads

Ready to put it in for it's service now lol.

[southgate]

Got a price and part number for the coil pack Paul?

[southgate]

Just found this:

http://www.racetechdirect.co.uk/product-subsection...

Says "aftermarket", so maybe better than standard?

Not bad price either.