164 Q4 rough when cold and rpms drop slowly

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munition
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Re: 164 Q4 rough when cold and rpms drop slowly

Post by munition » Tue Aug 02, 2016 9:46 am

AlfaWhiz wrote: Pro tip: newer Bosch injectors (red) with 4 nozzles for 3.2, GTA, etc. fit nearly out of the box.
Good tip to kill the ecu!
The red valves have a resistance of 14.5 Ohm, whereas the original valves have 15.9 Ohm. This results in 10% higher current in the ecu, which is not good at all... You could install an additional resistance between the ecu outlets and the injector's plugs in order to compensate the higher current. But then the injection flow would be too less because of the General lower capacity of the red valves (172g/min to 183g/min).

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AlfaWhiz
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Re: 164 Q4 rough when cold and rpms drop slowly

Post by AlfaWhiz » Tue Aug 02, 2016 9:53 am

You think so? That would certainly be a very bad thing to happen. I did notice the difference in resistance, but didn't consider it to be dangerous.

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Re: 164 Q4 rough when cold and rpms drop slowly

Post by munition » Tue Aug 02, 2016 11:22 am

Quite simple calculation:
I = U/R = 12V/14.5ohm = 0.83 ampere
I = U/R = 12V/15.9ohm = 0.75 ampere
Difference is + 0.08A, which means +10,7% current and +10,7% load on the ecu.

You have to decide, if it's dangerous or not. But I highly recommend not to replace the original injectors with the newer type.

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AlfaWhiz
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Re: 164 Q4 rough when cold and rpms drop slowly

Post by AlfaWhiz » Tue Aug 02, 2016 11:30 am

I just did the same math, was just about to post it. Although 10% seems like a lot, I wouldn't consider 0.08A difference to be dangerous.

Nevertheless, you are right that it's a bit of a risk and maybe it's better to be safe than sorry. Hopefully it'll be fine, I'll be reporting on the results in the long run.

Maybe others can add something to the discussion in the meantime?

HaydnW92
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Re: 164 Q4 rough when cold and rpms drop slowly

Post by HaydnW92 » Fri Apr 07, 2017 10:32 am

How is the progress with your Q4 Alfawhiz?
I've just read through this topic to give me some ideas on what to check with my Q4. It runs OK, but doesn't seem very happy when cold. Much better when warm. To say it's a 3.5 there seems to be some power missing too, it doesn't feel much faster than my old 164 QV (12V).

It still drives ok of course. I just notice these slight issues, they're difficult to ignore, especially when you have already put a lot of work into the car... :)

Haydn
1999 Alfa GTV 3.0 V6 24V
1992 Maserati 222 4V (project)

(Ex)1994 Alfa 164 Q4 3.5 Savali Cosworth
(Ex) 1991 Alfa 164 3.0 Cloverleaf
(Ex) 1995 Alfa 145 1.6 8V

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AlfaWhiz
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Re: 164 Q4 rough when cold and rpms drop slowly

Post by AlfaWhiz » Fri Apr 07, 2017 9:11 pm

Hi Haydn, thanks for reading through. :)

As it turned out, the issue with my rough running was more complex, and not just one thing to tick off. What solved the problem in my Q4 completely was replacing the injectors as mentioned above (they work fine, no problems), repairing injector and coil wiring insulation and replacing some of the ignition coils with new ones (rubber boots were damaged and spark was jumping between the head and coil).

I did also do a head gasket in the meantime.

Since then she runs perfectly again and full power is back. :)

I hope you get yours sorted soon, it's really special with that engine and should have plenty of power (although they are heavy cars, so QV might be quicker).

Cheers

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