Misfire on Boost

[BMCC]

My car misfires badly on full throttle boost, part throttle is fine as is off boost. It all started last Monday when the car stalled at a set of lights and would not start again. The RAC towed me to an industrial estate where we looked at the car. We got it back running when a spark tester was placed between the coil and the dizzy cap. Before changing the spark plugs and fuel filter the car would start but no where near first time, it got up to temp then would conk out. Now it will start but misfires badly on full throttle boost juddering badly. So far I have:

replaced spark plugs to NGK BRC8ES gap 0.7mm
Replaced fuel filter
Dizzy cap and rotor arm were changed last year
Checked the resistance of the leads (all well within what the manual says is max) but may be the original ones
Replaced Ignition coil

Where do you think I should look next?

 

[red reading]

Main engine earth to chassis, check also to see if the fuel pump has good voltage.

 

[whytie]

I'm only 10mins up the road from you if need a loan of any bits to test car, maf,ecu,fpr, or sensors give us a shout.

check none of the vac blanks have popped of the inlet

 

[The Doc]

Also check it's not over boosting.

 

[BMCC]

Cheers I'll check the fuel pump, main earth connection, Manifold blanks and Boost pressure, although I could only do that on the standard gauge. Possibly a split hose or the boost solenoid knackered?

Is 0.7mm gap on the spark plugs too small? The previous spark plugs NGK BSP6RE were at 0.8mm.
The car is running on standard boost.

 

[campbellju]

Smaller gaps are better for the moment whilst you solve whatever issue you have. Drop them to 0.6mm or 0.5mm whilst fault finding to understand if your ignition is weak or it's a fuel/air issue.

 

[PobodY]

I wouldn't go as small as 0.5mm - That's about where mine were when I was getting a loss of power from a weak spark.

 

[BMCC]

I have checked the VAC lines and have found one open but it goes down into the gearbox area. Should this be connected to the airchamber or should it be connected at all?

 

[vss irvine]

sure its not the gearbox breather?

 

[PobodY]

If it's connected to the gearbox (or transfer case), no; that's the breather hose. - If looks like an upside-down J (i.e. it loops back at the top), that's almost certainly what it is.

 

[BMCC]

Yeah I think it is a breather hose. I had a look at the earth for the fuel pump and it looks fine.I tested for continuity between the fuel pump plug and the earth and it was good.I never got battery voltage at the plug when the ignition is on. How can I test the pump voltage with the engine running? The resistance of the pump across the pump terminals was .6 ohms which is approx right. The power transistor tested fine once I reread the procedure........

Should also say that it is not over boosting but does misfire when the car gets to full boost on the gauge (Full throttle). Is there any way to test the plug wires to compensate for the various lengths? Any formulas I can use?

 

[BMCC]

Also found another VAC hose not connected up by the master brake cylinder. Can't see where it goes to as the inlet Mani is in the way. What VAC lines connect in that area?

 

[whytie]

 

[whytie]

Not sure if that helps you out

 

[BMCC]

Not sure if that helps you out

Yes to does! Much appreciated. The breather the arrow is pointing to in the picture is the one I found (although the hose on mine reaches up much closer to the manifold). What's this hose for? There is another hose similar on the passangers side down by the recirculation valve which I took as the gearbox breather, are there 2?

 

[red reading]

That one is the transfer box breather, the other one you are correct is the gearbox breather....so yes there is two breathers.

 

[vss irvine]

Is there any way to test the plug wires to compensate for the various lengths? Any formulas I can use?

Ebay + credit card = new parts

New parts x fit them = rectify fault




You cant always find faults with a multimeter.

 

[BMCC]

Ebay + credit card = new parts

New parts x fit them = rectify fault




You cant always find faults with a multimeter.

:lol: If those equations work I'll be well happy!

I looked at some magnecor KV85 leads or the 8mm blue ones, are these just a waste of money? There was some discussion about aftermarket leads causing problems.

 

[vss irvine]

Personally i wouldnt bother with magnecor leads.

Ive had 2 sets break down on me and cause a misfire. One set were only a few month old.

 

[BMCC]

Personally i wouldnt bother with magnecor leads.

Ive had 2 sets break down on me and cause a misfire. One set were only a few month old.

Any you would recommend?