Slight misfire at high load?
Discussion
For a while now I've had a suspicion my Chim isn't quite as strong at the top end as it was when I got it. We're talking about a matter of months here, so it's not cam wear or anything fundamental I don't think.
One of the chaps from the TVR centre took it out and declared it to be pulling as well as a 500 should, but he didn't go the full way through the rev range (presumably for the sake of the neighbours!) I could swear it performed better at the upper end of the rev range when I first got it and over the weekend I think I noticed a slight misfire on sustained full throttle. Once when opening it up for the first time after cruising slowly for a prolonged period and the other occasion on a more sustained blast.
A couple of things spring to mind: The timing was adjusted considerably at the recent service and the Magnecor HT leads replaced for standard items, plus the connection to the fuel pump was found to be a bit lose when the suspension was changed over. I wonder if the fuel pump is still getting fewer volts through than it should or whether the timing adjustment could have gone too far?
Of course, it's possible I'm just getting a bit spoilt...
One of the chaps from the TVR centre took it out and declared it to be pulling as well as a 500 should, but he didn't go the full way through the rev range (presumably for the sake of the neighbours!) I could swear it performed better at the upper end of the rev range when I first got it and over the weekend I think I noticed a slight misfire on sustained full throttle. Once when opening it up for the first time after cruising slowly for a prolonged period and the other occasion on a more sustained blast.
A couple of things spring to mind: The timing was adjusted considerably at the recent service and the Magnecor HT leads replaced for standard items, plus the connection to the fuel pump was found to be a bit lose when the suspension was changed over. I wonder if the fuel pump is still getting fewer volts through than it should or whether the timing adjustment could have gone too far?
Of course, it's possible I'm just getting a bit spoilt...
It could run lean if the fuel pump or fuel supply was not up to the job. Usual story, put a test meter with long leads across the black and white wires from one of the lambda probes, so a passenger can read the voltage from the cab'. Then do a full power run and make sure you get at least 1 volt, or 1.2 is better. If it drops to zero its running lean, and needs to be rectified.
the magnecors where replaced with standard items why? allthough i am not a huge fan of magnecor leads they are certainly better than stock leads, have they change rotor arm as well, there is a real big problem at the moment with cheap after market components for the rover engine that cause all sorts of problems, the bottom line is take it back to the garage and tell them it isn't as nice as what it was when you drove it in1
v8 racing said:
the magnecors where replaced with standard items why? allthough i am not a huge fan of magnecor leads they are certainly better than stock leads, have they change rotor arm as well, there is a real big problem at the moment with cheap after market components for the rover engine that cause all sorts of problems, the bottom line is take it back to the garage and tell them it isn't as nice as what it was when you drove it in1
out of interest what is your lead of choice if you are not a fan of magnecor.... 
Im not a fan either, problem is the stock leads have a high resistance core for a reason, namely to control the rate at which the coil discharges once the spark has started (that is effectively a short circuit). Although this drops some of the coils stored energy in the leads themselves, it also controls the rate at which the magnetic fields collapse in the coil. If the overall path resistance is too low, the magnetic fields collapse very rapidly across both the coils primary and secondary windings, and this causes a larger than normal voltage spike in the coils primary side, that stress's the electronics that switches the coil,and can produce extra trigger pulses the rev counter picks up, so its movement becomes erratic. It can also glitch surrounding electronics. Now to be fair to Magnecors they are constructed to reduce this effect by creating a magnetic field around the plug lead that slows down the coils discharge by an effect called reluctance, and it does let 90% of the spark energy through, but the primary spikes are still larger than carbon leads with the associated issues , and you dont gain even 1 bhp over decent carbon leads for the huge expense. You will notice on the Magnecore web sites they make no claims what so ever for power increase, so why bother?
Ah, here we go again!
Mine is in the bodyshop atm so my high RPM business continues btw!
To me, the odd misfire and simply not feeling as good as it used to at the top end might well be separate things.
Definitely check the timing at idle and at 4k.
My recent misfire issue lead me to go over even the work that The TVR Center did back in Dec, namely check timing and replace fuel filter - both things it turned out were not done by mistake, it turns out. They were great though and will be making it up to me next time I take it in so I'm pleased.
Interesting thing is the timing error was that they'd not spotted the one way valve was round the wrong way so I was getting no vac advance. With it working the power delivery to me now feels smoother and more consistent all the way through (well not past 5k in my case! lol)
Could it be that yours too had the valve the wrong way round and that it's now been fitted properly so giving a more consistent power delivery perhaps making the top end blend in to the mid range a bit more than before??
Quite a long shot of a comment from me there I know!
Mine is in the bodyshop atm so my high RPM business continues btw!
To me, the odd misfire and simply not feeling as good as it used to at the top end might well be separate things.
Definitely check the timing at idle and at 4k.
My recent misfire issue lead me to go over even the work that The TVR Center did back in Dec, namely check timing and replace fuel filter - both things it turned out were not done by mistake, it turns out. They were great though and will be making it up to me next time I take it in so I'm pleased.
Interesting thing is the timing error was that they'd not spotted the one way valve was round the wrong way so I was getting no vac advance. With it working the power delivery to me now feels smoother and more consistent all the way through (well not past 5k in my case! lol)
Could it be that yours too had the valve the wrong way round and that it's now been fitted properly so giving a more consistent power delivery perhaps making the top end blend in to the mid range a bit more than before??
Quite a long shot of a comment from me there I know!
I may have found the root of the problem...
I've been getting a few tools together this morning in preparation for the Spanish trip and I opened the bonnet to check which of my spark plug sockets fitted. In the process I caught a glance at the distributor cap and did a bit of a double take. The HT lead for the number 8 cylinder was completely disconnected!
Normally I'd expect to notice something like that, obviously, but it's quite a loud exhaust and I was driving very gently for most of the last trip with my girlfriend in the passenger seat, so I wonder if it's been misfiring for some time and the rumble from the exhaust had just drowned it out. They managed to knock the fuel pump connector off during the suspension change and I wonder if somebody checked the HT leads as part of the fault finding and forgot to reconnect one of them properly. Whatever the cause, I'm amazed how well it was going on seven cylinders.
I've been getting a few tools together this morning in preparation for the Spanish trip and I opened the bonnet to check which of my spark plug sockets fitted. In the process I caught a glance at the distributor cap and did a bit of a double take. The HT lead for the number 8 cylinder was completely disconnected!
Normally I'd expect to notice something like that, obviously, but it's quite a loud exhaust and I was driving very gently for most of the last trip with my girlfriend in the passenger seat, so I wonder if it's been misfiring for some time and the rumble from the exhaust had just drowned it out. They managed to knock the fuel pump connector off during the suspension change and I wonder if somebody checked the HT leads as part of the fault finding and forgot to reconnect one of them properly. Whatever the cause, I'm amazed how well it was going on seven cylinders.
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