engine misfire!

[peteA]

would normally have done a search on this as i'm sure there will be plenty of info but its seems to be out of order at the minute...

anyway, got a misfire on my 94 chim, seems to happen mostly under varying load and at about 3000 rpm.

HT leads look rough so have some on the way. incidentally, does anyone run without the heat sheilds on the plugs? is this wise?

If fitting new leads does not solve the problem, will invest in a new coil as this also looks old - any advice on this? saw a website with a spark amplifier on it the other day which seemed good - anyone fitted one?

If its still there...any further common problems? Distributor? cap and rotor are new but...? Earthing?

Thanks in advance for any help.

[GreenV8S]

You have an ignition amplifier already. You can get an uprated one for £100 or so, but it is not a simple plug-in replacement. Those symptoms sound to me like a spark/fuel injection fault. The fact it happens around 3000 rpm (not far off the point the ECU drops out of closed loop operation) might suggest it is fuel related. However, it would be sensible to ensure you have a strong reliable spark since this is quick and easy to do. Trouble-shooting the EFI system gets more complicated and/or expensive...

[jem]

peteA said:

does anyone run without the heat sheilds on the plugs? is this wise?

unwise as far as I can gather, they deteriorate after a few years, replace them via ACT

J

[M808CLR]

I don't know whether or not your have considered this but I recently had a misfire problem on my 95 chim and tracked it down to the Foxguard alarm. I found that the engined cut out completely from time to time with no warning and with no regularity this was coupled with misfire. A bit of investigation and a talk with Carl at Car & Bike Installations Ltd (www.tvruk.tv) found that the old Foxguard alarm systems as fitted to pre 1996 models are only just up to the current capacity. The alarm system immobilises the car by cutting power to the fuel pump and with a faulty alarm, power was intermitently applied to the pump circuit causing misfire characteristics. Incidentally my car is currently being fitted with the later Meta controller for the alarm (£400.00) so hopefully all will be well.
I hope this is some help.

[Mike Heynes]

I had a misfire once and tracked it down to a faulty suppressor on one of the HT leads - what you refer to as a heat shield. Try removing the majority of suppressors where they don't leave the HT leads too vulnerable to the exhaust manifold and take it for a spin. Then if that doesn't stop it, substitute the remaining suppressors with some that you've temporarily removed and take it for another spin.
Mike

[JonRB]

I had a crackling misfire above 5000rpm for a while which one engineer put down to the "soft rev limiter", which I accepted at the time. However, after puttin gup with it for almost a year the car had its HT leads replaced during a service and now it revs cleanly all the way up to the 'hard' (sic) rev limiter at 6000rpm.

[wightman]

Could be so many differnt things as I have found out searching thses forms over the past week.

Leads
Supressors/Extentions
Spark Plugs

Earthing problems

Ignition Coil
Ignition Module

Im hoping the leads are my problem.

Chris

[duke thrust]

Make sure the HT leads aren't touching the exhaust manifolds or are too close - watch it running at night and see if you can see any blue arcs

[Nuggs]

jem said:

peteA said: does anyone run without the heat sheilds on the plugs? is this wise? unwise as far as I can gather, they deteriorate after a few years, replace them via ACT

Not a good idea to run without the heat shields (I presume you mean the plug extenders?). These keep the HT leads out of the way of the exhaust manifolds.

Without them you'll end up with some lovely liquid leads...

[peteA]

wightman said:

Could be so many differnt things as I have found out searching thses forms over the past week. Leads Supressors/Extentions Spark Plugs Earthing problems Ignition Coil Ignition Module Im hoping the leads are my problem. Chris

Cheers - heres hoping that my misfire is the leads / extensions / plugs.

The coil looks on the old side so i might replace that anyway - any tips on which coil. saw some high performance / variable output ones on demon tweeks - seemed OK?

[PeterC]

The BOSCH coil recommended in the bible works great and is a straight replacement as far as connections go, making the exchange real easy.

[stringbag]

Replaced my coil this week - the old one just looked a bit old & was starting to leak. Bosch PRC 6574 (a land rover part number). £41 inc vat & del. (next day) Very easy to replace, just unbolt the old one and bolt in the new one!
Can't say it has made any difference, but it looks better!
Mallory also do one for a bit more (and it is more shiny!).
It is the same coil for all Chimps & Griffs too.

[peteA]

stringbag said:

Replaced my coil this week - the old one just looked a bit old & was starting to leak. Bosch PRC 6574 (a land rover part number). £41 inc vat & del. (next day) Very easy to replace, just unbolt the old one and bolt in the new one! Can't say it has made any difference, but it looks better! Mallory also do one for a bit more (and it is more shiny!). It is the same coil for all Chimps & Griffs too.

Thanks for the part number - not bothered about the looks - not one of the egine buffers if you know what i mean - just want it to work!