Author Topic: Which plugs fire when - An answer proved by doing it  (Read 2925 times)

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Offline wombat

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I have proof that the INLET plugs fire constantly. The EXHAUST plugs are switched by the ECU

Test 1 - startup
Method: Remove one lead from coil to distributor and see if car starts.

Results: Inlet coil disconnected - no start. crank, no fire.
Exhaust coil disconnected (the one on the top, or near the H in Bosch) - started.

Test 2 - Drive

Drove around for about half an hour with the exhaust coil disconnected. Car had less power, a slight rumble and would misfire once every 3 minutes or so at constant cruise (brrm bump brrrrrrrrrrrrrrrrrrrrrrrrrrrr rr). Car ran to 5000 rpm and at full throttle. Both conditions where the second plugs are turned off.

Conclusion: EXHAUST PLUGS ARE SWITCHED, INLET ARE CONTANT.

Am prepared to be proven incorrect by a more factual means.

I'm so far behind at work, I'm almost retro!

Offline h4inf

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Re: Which plugs fire when - An answer proved by doing it
« Reply #1 on: Jul 19, 2007, 09:14PM »
I believe it is the other way around. I've been studying how my car works recently and the manual. Perhaps your coils were connected back-to-front on the dizzy.

Exhaust side plugs are supposed to run all the time and Intake side plugs are switched.

From my experience, the intake side plugs run when the engine is cold, and as it warms up, they stop firing, or fire less often. It is a mixture of the throttle position sensor, and coolant temp sensor that determine whether the intake plugs fire.

Hopefully this can help someone out in future- I had a prob where the car would run fine in the morning, then as it heated up it ran horribly. This was because one of the exhaust plug leads had broken so was not sparking. Once the car heated up causing the intake side plugs to be disabled, there was no spark occurring in one of the cyls - causing my headache :)

Offline wombat

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Re: Which plugs fire when - An answer proved by doing it
« Reply #2 on: Aug 10, 2007, 09:13PM »
i've just read in the Corsair FSM that it's the exhaust side that are switched. I'd be 99.99% sure that equates to U12 being exhaust side. Page ES-16 if you wanted to check.
I'm so far behind at work, I'm almost retro!