Misfiring Griff

[jeffgleed]

I have got a problem with my 4.0 Griff. It runs fine until I hit 5000 RPM when it misfires like it hits a brick wall, it's so major the revs actually fall back to 4.5K before it picks up again.

I recently had a new camshaft fitted but I am not sure if this is related since I can't be sure when it happened (the roads have been wet and cold and I have been moving house).

My very limited mechanical brain thinks it's probably an electrical fault, maybe HT leads.

Any ideas from anyone who actually knows something?

Cheers

[beano1197]

Commiserations Jeff

If it's any comfort, my Griff was running quite poorly at 2,800 to 3,400 for a few weeks. Replacing (original?) HT leads, caps and plugs plus a good clean up of the dizzy internals sorted it perfectly.....

.....except that Jnr didn't managed to fit all the leads on the dizzy and two of them (independently) fell off creating short bursts of 4.3l V7!!!

Now pulling from idle to 6k like a dream....

Hope it's as simple as that!

[jeffgleed]

Thanks for that,

Did you put any particular HT leads on?

[beano1197]

Nothing "special" - they are, I believe the Range Rover ones (any good motor factors) but beware, prices can be variable (like "if we had 'em they'd be £40 per half bank" - i.e. for four, they are apparently sold in two different part numbers, one for each side!).

Halfords had a computer system which doesn't recognise the Range Rover engine being a V8................

The caps are the part that are subject to such abuse from heat, again I don't recall which make (and if it wasn't piddling down I get of my fat R's.....) but your local dealer or motor factor again.

[jeffgleed]

Brilliant, thanks

[shpub]

Distributor caps can be a bit hard to get as there have been several different distributors fitted. Saying you car is a Range Rover is also going to get you into trouble as the modern Rover has no distributor and different ignition leads.

If you want to go the Rover route, you must say you have a classic Range Rover. Don't go by year of manufacture or engine size. Lucas actually quote TVR Griffith but do not include the coil to dizzy lead in the set.

When replacing the leads do it one by one so that they don't get mixed up and make sure you use the same length as the original. The leads come in several different lengths and getting this wrong means they won't fit.

Steve
www.tvrbooks.co.uk

[beano1197]

....and if they are too long, or come loose from the dizzy, they can stretch as far as the fan belt.....OUCH.....

[hughjayteens]

I bought some Rangey leads, and they just didn't fit right - TVR fit Lucas Speedleads I believe, and at £35 or so a set I'd stick with those... If you are stuck then try Dave Batty on 01483 811995 as I am sure he can supply the right ones.

[Paceracing]

quote:I have got a problem with my 4.0 Griff. It runs fine until I hit 5000 RPM when it misfires like it hits a brick wall, it's so major the revs actually fall back to 4.5K before it picks up again.

I recently had a new camshaft fitted but I am not sure if this is related since I can't be sure when it happened (the roads have been wet and cold and I have been moving house).

My very limited mechanical brain thinks it's probably an electrical fault, maybe HT leads.

Any ideas from anyone who actually knows something?

Cheers

The camshaft replacement could be a clue. I have heard of this problem occuring on cam belt driven cars when the belt skips teeth during hard driving, causing cam timing to be thrown out.
Rover V8's are chain driven aren't they? The chain could have been put back 180 degrees out but you would notice power drop throughout the rev range probably. My guess is plugs. If one is cracked, you sometimes notice a misfire under heavy load which may not manifest itself at low RPM. (I have seen these exact same symptoms on a Griff 500. It turned out to be plugs!)
1) Plug fault
2) Leads fault
3) Get cam timing checked.

Jas.

[jeffgleed]

Thanks all, I will check this out.

[kerniki]

The heat shields (which are the most likley cause)are Vauxhall items, and much cheaper sourced from them, one of the staff should know, if you tell em its a Tiv.
Hope this helps!

Nik

[Marshy]

A couple of my plug extenders/heat shields broke down causing arcing to the exhaust manifold and crappy running. 7 or 8 quid each from Vauxhall. The new ones are a noticeably tighter fit.

Just need the other 6 now.

[fish]

Quite a common problem with Rover V8s is when the exhaust valve cam lobe is worn. The valve doesn't open properly leaving compressed exhaust gases in the cylinder. When it starts the inlet stroke these vent back through the carberetter causing misfiring like sounds.

Unlikely if you had a new cam but if it was not lubed properly when fitted and not runin you can go through the hardened surface quite quick then the metal below will wear away faster because it is soft.

Anyhow just a thought.

[350matt]

Check the condition of the crankshaft speed sensor and as previously suggested your HT leads as if the speed sensor is poorly earthed its much more susceptible to electrical interfernce which can fool the ECU into applying the rev limiter.

Matt

[2 Sheds]

Sounds like an ECU fault to me if its that sudden !
Tim.

[jeffgleed]

Thanks again for all the advice chaps. I had a play with the HT leads and cleaned the Dizzy cap but (see other rant) the flippin fan belt fell off so I spent all weekend trying to find another one! It's now back to wall to wall rain and hard acceleration to over 5K in town in torrential rain is getting a bit silly so I will try again later in the week/weekend

[jeffgleed]

Thanks again for all the help guys. Took it for a spin yesterday and despite the torrential rain happily spun all the way to the rev limiter ... cool. That saved me a few quid.