Hi, hopefully someone can help?
Since I bought my Cosworth there has been a misfire/hesitation when on boost
To me it seems like a fueling or ignition spark problem
Because of this I don’t really drive it as I don’t want to do any damage to the engine

The spec of the car is:
91 green top 4x4 sierra sapphire Cosworth
Evolution MSD chip and anti lag system
T34/T35 turbo Mariam shaft
Full 3inch stainless exhaust
RS 500 intercooler
Group A air filter
Dark green injectors
3 bar map sensor
Amal valve still fitted
Alloy bottom pulley
Running at 24psi
Engine internals unknown, presume to be standard


So far since I got the car I have changed a few things to see if I can get rid of the problem

Rewired the coil correctly as plus and minus were on the wrong way around
Group a coil fitted
Standard breather removed, port on inlet blocked, piped to sump and rocker cover and crankcase breather with Bailey breather oil separator bottle
Fuel pump rewired – now full battery voltage 13.8v
Amal valve changed as terminal was broke and was clicking when wire was touched
3 bar map sensor changed

None of this cured the problem
The problem occurs when on boost under hard acceleration through all gears
It does the same with anti lag switched on
The car idles and drives normal with easy driving and using light acceleration the car will boost up ok
But if I floor it its like turning off the ignition or cutting the fuel it holds back and chugs all at about 3000rpm and above

All suggestions welcome thanks

 

I see no mention of the five things most likely to cause this issue...

• Spark plug heat range and gap?
• Rotor Arm
• Distributor Cap
• Phase sensor alignment and gap.
• HT leads - especially the king lead.

 

Spark plugs is the usual cause when mine does it. IMO go for 071's Motorcraft spark plugs

 

i'm going to change all these this evening an see how that goes,
the only thing with all the above is that when driving normally and when easing the boost on gradually she doesnt missfire which makes me think it could be fueling?
but i will still try all an see if it makes a difference.
gaps were set on plugs before i put them in.

 

how much are 071's? i read that these wernt any good after 300bhp but dont know if this is true.
is there a difference in 071's and 071c's?
which plug would be better between BCR8ES's and the 071c's

 

just looked the 071's up on ebay there said good for up to 650bhp by MSD so that rules out what i was told.
gonna order a set of them now.

 

another thing i just fitted an alloy rad and i was wondering is there any way of testing my fan switch? as i dont know if it is uprated or standard? i see MSD also sells a UPRATED Ford Sierra Cosworth Fan Switch. (Sensor)

but MSD done nearly oll the work to my car going by all the recipts so they may have suggested/fitted one of these already?

 

Ł10 for 4 + a couple of quid postage from Woodfords in Totnes.

 

What's the fan loom like? If it looks standard its probably on its last legs, so I'd advise getting their fan loom kit. Ł60. Plus there fan switch is designed to come on a little later but for not as long so's not to melt the original fan relays if your sticking with the original loom.

 

Check the 3 multi plugs at at the back of the engine secured to the bulk head. Mine did exactly the same and pretty sure it has been traced to these. A very common problem I am led to believe.

 

It sure is. Mainly on the 4 B's IIRC

 

mine was doing this and it was the lamba sensor

 

Defo one of these,mine done it aswell...

 

The standard switch is red, where as the "Uprated" one is typically green or white, in any case the switch has the span written on it, in the case of 2WD the switch closes at 86 degrees.

The trouble with the standard one is in that it has a huge span and brings the fans on too early and keeps them on for to long, the latter is what causes the melting of the fuse etc.

If you have an alloy rad you need the "Uprated" one really as the standard one suffers from a heat soak effect and you may find the fans stay on indefinitely.

To test you simply need to remove the connector from the switch and bridge the connections, which should start the fans. The switch isn't usually the problem, as said the fans need rewiring along with the fuel pump wiring.

As said re your initial post, the cause will be the ignition system.

Martin

 

Just tried BCPR8es ngks in my stage 3 and they are shit!!!!!!!!!!! It did have IK27s but now running on BCP6es and faultless at 0.9mm gap!!!!!!!!!!!!!!!!

 

Take them back out before you lose your whole engine mate!