Classic Misfiring at 2-3000rpm

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update.

we have a change..

after the trouble shooting, it then got to the stage it wouldnt start and the battery somewhat depleted from the repeated starting.

while the battery was on charge, all the temp sensors were replaced, the O2 sensors replaced and the fuel ECU swapped out. Now, it still wont start.

as a recap..

day 1 started and ran fine, no issues whatsoever.
left it 48 hours in the driveway then:
day 2 drove to petrol station, on starting and the drive there it was misfiring at 2,500 rpm

replaced HT leads, plugs, rotor arm, distributor cap and fuel filter.

still misfiring at 2-300 RPM

Bike Teacher Dave and I spent the day going over all we could, with the result of a suspect MAF problem due to sooted plugs on both banks from rich running timing done and set. Ordered a new pattern MAF, ran like crap, put the original MAF and an spare MAF on it ran again, but not above 2500 RPM.

Swapped out the Fuel ECU (PRC 7081) for a spare (PRC 9061) no change still not running above 2,500 RPM,

Swapped the Fuel ECU's back (PRC7081 back in), wouldn't fire, swapped them back again (PCR9061 back in), wouldn't fire and battery now depleted.

While on recharge, temp sensors changed (3) O2 sensors changed, swapped the ECU again (PRC9061 back in) left it to charge.

Tried again this morning now charged. Still not firing.
 
Wow, this is a head scratcher! Ok, so since it has refused to start after all that, have you checked spark plugs again to see if they're still soaked in petrol, sooty or dry?

That will give you a pointer as to where you are in this drama. I know you're getting fed up as we all would, but indulge me...
 
pulled one out yesterday. not wet.

im wondering if it could be a fuel pressure regulator problem.. but i'm just clutching at straws.
 
ukadamwest said:
pulled one out yesterday. not wet.

im wondering if it could be a fuel pressure regulator problem.. but i'm just clutching at straws.
Click to expand...

Is the fuel being delivered now? It just seems strange after getting too much before, now either not enough or none at all... Have you gone over all electrical connections again? Could be a loose one or a dirty/broken connection after unplug/replug marathon.

O2 sensors won't come into play while cranking, but check there isn't a break or dead short. Old wires can get brittle or if they got wet over the years, the strands turn black which leads to high resistance. Could even be one of the many plugs & sockets with one or more dodgy connections.
 
dont know if fuel is being delivered now.

i have the hump.. its cold. its wet.

electrical connections that were unplugged, plugged all ok.

im wondering if a faulty fuel pressure reg could have caused the over fuel, and is now faulting on delivering fuel.
 
What flavour rotor arm is on it? Is it a pattern or a good make?

Turns out some (most) pattern rotor arms are riveted together. The rivet is slightly longer and the plastics slightly thinner, so under load the quickest route to earth is via this rivet. If the dizzy cap is a pattern one, change that as well....
 
Quality parts both. the same with the original rotor am and dizzy (where is was running fine on day 1) and the replacements
 
Ok, is the tank pump doing it's thing with ignition on/cranking?

I wonder if, once you get it started, is it possible the cam has a worn lobe? They are known for this and it would definitely present itself as a misfire under power while idle is perfect.

But right now, why isn't it starting any more? Did you disconnect the crank sensor at any point & not plug it in?

It "has" to be something to do with everyhting that's been changed :confused:
 
crank sensor not unplugged, cam doesnt have worn lobes. when the engine top end was done, cam lobes were checked. if it were cam lobes it would be a slow degredation of power rather than run fun one day then 48 hours later misfire.
 
ukadamwest said:
crank sensor not unplugged, cam doesnt have worn lobes. when the engine top end was done, cam lobes were checked. if it were cam lobes it would be a slow degredation of power rather than run fun one day then 48 hours later misfire.
Click to expand...

Just trying to rule stuff out chief...
 
What about a sticky lifter or two? Have you had the rockers off while spinning her over?

I wish I was in Surrey so I could come along and see for myself o_O The non starting issue HAS to be related to what you did with replacing different bits, it HAS to be!!
 
well the failure to start occurred after swapping out the fuel ECU's

i'm suspecting that there is fuelling issue that perhaps related to the misfire.

we know it was running rich and misfiring at 2500 RPM.

we know it is sparking well
we know the timing is set dead on.
we know the MAF is good
the O2 sensors are good (and only active above 70 deg)


ive done some digging and the lucas hotwire does have a diagnostic port, not the ODBII, so i've ordered a laptop based code reader specific to the lucas hotwire, which gives some more performance based access..

s-l1600.jpg

s-l1600.jpg


s-l500.jpg
 
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