Trying to diagnose a faulty ptu before emptying a wheelbarrow of cash

hi all , my car is suffering quite badly and i now have a bald patch from tearing my hair out over this f**king sht misfiring problem, it is making me feel suicidal and driving me round the bend big style!! i have been driving it round with this misfiring for the last 3 weeks , feathering the throttle keeping the bang on all cylinders as much as possible, i have replaced the plugs, checked the leads, changed the fuel filter, checked the ecu (which was rebuilt by ecu doctor in 2011) i removed the cover to check and caps seem sweet with no leaky crap on the board anywhere, just tested the ptu using a blurry set of instrutions written in abbreviations and techno babble and from the web and from what i can make out the readings on my VOM were with a 1,5 v batt connected oc3 was reading different to the other two, dont know what the readings mean coz im sht with electrics but from what i gather they should all read the same, the car starts and idles ok, it would rev up to max while stationary , put it in gear and pull away ok but as soon as i plant my foot down it sounds like its missing on two banks and lagging in power but also coughs intermittantly, i need help man, i dont wanna go and blow 180 quid on a ptu if it aint that, could do with borrowing 1 to test on mine see if it cures it, if anyone wants to add me on facebook im matt shadowsniper wood

Had and did the same but tried an ECU from the red car, showed nothing but still had the misfire.

Changed the PTU and its a different car. Only later did Marty inform everyone that thermal grease should be between the base of the PTU and the bracket. Marty is doing, somewhere on here, a thread whereby he is designing a small heat shield and relocation of the PTU. Somewhere cooler in the engine bay??? :laughing:

Terry :sunglasses:

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From what you have described, it does sound like the Ptu is at fault.
However, before you buy one, retest it.
Will see if I can find better instructions for you.

If You do need one, just search the net for J723T
The Ptu is quite common. It’s just the bracket that differs.
I found one easily for about £35 new.
No idea if it’s genuine, but mine is not anyway.

They are a really simple thing, and it’s heat that gets them., so be sure to use thermal heat transfer compound between it and the bracket.


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Testing procedure is in there


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thanks for the input guys, ive just found 1 from grahams gto spares in leeds 40 quid, ordering it tomorrow, ill get some of that thermal grease lol whatever that is too, not enjoying this electrical crap at all, i love my car and have done since i had a go in my first twin turbo when i worked at century salvaage! i was only 17 at the time and id never in my life had a go in anything that quick! now ive finally got 1 its playing me up rotten! still, thats how ya learn aint it cheers guys ill update wen ive put the next ptu on

Don’t worry too much mate I have just been through exactly what your going through, I took my car off the road when the misfiring got too bad. New PTU did the trick, so I think you will be smiling again very soon!

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Theres one on Ebay, £15

I think we have all suffered the PTU worries at some point. Where are you located? If there is a member near you they might be willing to lend you theirs to test!

Not all misfires are cuased by the ptu, check plug gaps/condition/age, dodgy leads, and as mazz found out the injector resistor on the bulkhead, the little silver box with 6 white wires coming from it.

havent checked that , what does that do ben?

btw i put another ptu on it today, no change, so now ive done ptu, coils, leads, plugs, fuel filter, opened the ecu and it was rebuilt by the doctor in 2011 all looked good, the fuel pump relay has been bypassed (cheers for the tip rob) throttle position sensor , and shes still spluttering if i give it the boot, fast running out of ideas to try before im forced to relinquish control of the situation and bow down to a superior form of life to myself!

vacuum leak (may be)


Just because you have bypassed that relay don’t necessarily mean you have good pump volts I did that checked volts before 7-8 volts after 9v only a full hot wire will get you the 13+ volts although doubt it’s the problem. I would say possibly vac leak like @ms8leach check every pipe on plenum listen at low idle, do you not have the diagnostics? Also look and smell for fuel an air leak will cause the ecu to over fuel you could also check injectors run some injector cleaner through.

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its not a vac leak ive checked all that, havent checked the pump voltage though, bare in mind before it started doing this it was running sweet- fast as f**k, i went to pick my lad up around 6 on the evening all was well, parked it up on the drive , woke up next morning, started it and pulled away and splutter splutter bang bang! im still driving it round as i can feather the throttle and it will be ok and works good enough to drive it but not drive even remotely hard, im interested also in what ben said earlier about the injector resistor pack on the bulkhead could this give my car those symptoms?

I maybe wrong but I spoke to @Mesobitchi about that and supplied her with the parts the ptu,coils & resistor I think but don’t think it was that in the end timing was out of i remember right.

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its something that has gone bad overnight or possibly coz of the cold weather and the heat differences cracking some some of circuit board i dunno , im clutching at straws

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Could still be the ecu tbh and only way to check is another ecu or ecu Dr 2011 was some time ago, like anyone doing a repair they will rebuild what needs doing at the time. For it to just wake up the next day and change sounds like fuel or ecu to me bud best I can say. Where are you based in have the diagnostics stuff belive me you for need it mate these cars can be a nightmare :joy:

im in dudley bro , i know what you mean

can u check ecu’s dave?

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No I’m not that clever lol know my way round the data logger and can check for ecu faults on logger but that’s it tbh you a bit far from Norwich mate.