AU1 V8 , sometimes runs on 7!

[trimmaster]

Does anyone know what could be causing the problem to make my V8 run on 7 or less whenever it feels like it.
Yes, I've changed plugs and leeds and even removed the metal boots where they plug onto the plugs as advised by an ex Tickford engineer. ( to eliminate cross firing).
The problem has ocurred at so many different times that I can't get any history to work it out.
It has done it on start up in winter, turn it off, start it again and is perfect and sometimes still missing. Same in summer, so it's not a hot or cold thing.
It has done it while driving around town at low speeds and also while cruising on the freeway, as was the case on Saturday on the Citylink in Melb. ( for those of you who saw the Blue T series sitting for 2 1/2 hrs with the hazard lights on, only to be told when the RACV guy did finally turn up that I should buy a, well you can guess!! NOT HAPPY! And he didnt even help.
Its been back to the dealers a few times, but it never does it then, and of course it never logs a fault code.
Only thing left to change are coil packs, but at the current price I'm not so keen without some proof. Am I missing another sensor?
Occasionally I do press the economy switch but this is rediculous.
Any suggestions? I'd also like to hear from fellow AU1 V8 owners.

[gregaust]

What km's are on it? What about injectors or wiring to them?Poor connection at one of the plugs to the injector.Maybe??????

[trimmaster]

The problem has been there since 60,000km and is still there now at 85,000km.
I change the fuel filter every 10,000.
I like your idea about the injector wiring and will check. Doubt it will be a dirty injector but thanks for the tip.

[richardxr8]

Plugs and/or leads ! But youve already checked those.... Maybe check em again to be sure ?? If/when its missing, is it always same cylinder ?

[Jeld-Wen Falcon]

Sticky valves?

[trimmaster]

Have visually checked leads and removed plugs, all OK. If it was a sticky valve or stuck lifter then it would make a heap of noise? No noises.
I don't know which cyl/s it drops as when I take it to the dyno it won't do it.
I wish it would log a code, any Ford trained mechanics out there, can you tell me how much info do these things store, and how mmuch can be retrieved?

[FASTXR]

I sincerely doubt that this is whats wrong with yours, but I had a bad miss in my AU1 XR8. Replaced plugs and leads and it was still running rough, moreso at higher speeds (ie 70kmh or higher).
Turns out the problem was a stuffed engine mount, and the harder the engine worked the more noticeable the vibration. Once I figured it out it made perfect sense, but it did feel exactly like it was running on 7 cylinders.

Good luck with it.

[trimmaster]

I'll check the mounts but that same day when it ran ok again I was able to cruise on the freeway at 110 with no probs.
Like I said it will happen more than once in a day, for a couple in a row, then no probs for weeks.

[trimmaster]

Well I've been checking everywhere, things like plugs and wiring and found the wiring/plugs to injectors 5 & 6 both are broken. Seems someone has unplugged them at some stage and broke them in the process. This means that the plugs dont lock on and can move.
Maybe this is whats been happening.
Its going on the dyno tomorrow, so will test this theory.

[TheSneakiness]

There's been two guys here that have had their V8's drop to 7 cylinders and both times it's been a broken valve spring...

[Stav]

Have you cleaned /check the pcv valve? Did you think that the leads may be crossfiring when the engine bay heats up?Has the throttle body been removed and cleaned?