Hesitation and misfire

[purpleliability]

Hi All

The saga continues! Got the refurbished gearbox in and decided to get the car dyno'd to check afr's as I now have a 4.5 engine (although the engine number starts 42) and I have the 4.2 induction and fueling set up. I wanted to make sure it wasn't running lean.

On the way to the dyno, the car (which had been running ok before) misfired and felt like it was running on 6 cylinders. I couldnt seem to clear this with more revs and once it was strapped onto the dyno the run couldn't be completed as the afr's were really lean (15.1!).

Run aborted, I drove back on the lambda's with occasional misfires/roughness. it sounded a little off beat like an early Subaru.

I have new spark plugs ( less than 200 miles) and ht leads, the only thing that has changed recently is that I had the injectors cleaned and flow tested.

Throttles are balanced and lambda's are working according to the lap top.

Any suggestions? Fuel pressure regulator or pump perhaps?

Thanks!

[pmessling]

Coil packs?

[FUBAR]

Coil packs are the most common cause of miss fire under load I've had. The other time, very similar symptoms, turned out to be the crank sensor ( coor, hark at me, I almost sound like I know hat I'm talking about!)

[Rawhide]

My missfire was also cured by new bosche coil packs. I did buy some cheap Citroen ones first which did not work at high revs. Expensive lesson that.

[wiggycerb]

a few years back i had just had her serviced and they forgot to put the rear HT leads on properly which caused a missfire under load, drove fine otherwise ! I wasnt impressed to say the least ...

[scotty_d]

May seem a little obvious but check everything is tight and home on the ignition side, every lead connection to coil pack on so on. It is pretty easy for something to not have been 100% home and work it's way off with the vibration an ajp produces. Then i would be looking at coils.

[purpleliability]

Thanks all, will get checking today and try and pick up some coil packs!