4AGZE SC Runs Rough at WOT

RedvalkyrieOne
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4AGZE SC Runs Rough at WOT

Postby RedvalkyrieOne » Mon May 20, 2019 12:58 am

A recent problem has crept up on my new to me 88 SC. Under normal part throttle acceleration the car runs fine. When I go WOT and the SC kicks on the engine feels and sounds like it has a misfire--it is slow to accelerate but makes 7psi. I initially thought maybe there was a lean fueling issue but I triggered the cold start injector to run on a switch I activated at WOT. No change. I thought maybe it was a bad coil or ignitor--swapped those with some spares--no change. New spark plugs--no change.

The running got so bad that I lost all power and could barely make it up my driveway. However, this happened after I was changing the ignitor and coil and for some reason the noise filter arced while reinstalling it. Swapped noise filters--no improvement.

I finally got smart and pulled the codes--I got a 43 and a 51. 43 is a starter signal but the car starts fine. 51 is the AC switch signal which corresponds to the AC circuit (currently not being used) and a TPS error.

Before this all went south my idle was very high--2000rpm plus. I couldn't get it to consistently stay at a normal speed.

Car never overheated and as I stated--drove just fine at part throttle.

So, I'm guessing I should start with the TPS? I have a spare--I've had MR2s for 20 years but this is my first SC and I'm a bit rusty as most of my time has been spent on my 82 Starlet which has a dual Webers and a very simple electronic ignition. I'm a bit rusty. I do have the 88 BGB.

Also, do I need that noise filter? I think it's sometimes called a condenser...? Little black plastic square with two metal prongs and two wires leading to a blue plug.

Thanks
JP

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jondee86
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Re: 4AGZE SC Runs Rough at WOT

Postby jondee86 » Sat May 25, 2019 3:13 pm

The noise filter is a capacitor (condenser) with two wires and a metal clip. The
clip is purely a way to clamp the noise filter under the head of any convenient
bolt, and it is not part of the electrical circuit. One lead connects to the 12V feed
to the ignition system, and the other wire connects to a chassis ground.

A capacitor blocks the passage of DC but allows voltage spikes to pass from the
12V supply to ground. These spikes are generated by the normal action of the
ignition system and can interfere with the cars electronics. The capacitor filters
the spikes (electrical noise / static) and stops them from feeding back thru the
12V supply. The whine you sometimes get on your car radio that rises and falls
with the engine speed is a good example of electrical noise.

So yes, you should have a noise filter connected,

Cheers... jondee86
The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore, all progress
depends on the unreasonable man.

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jondee86
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Joined: Fri Jan 11, 2013 10:21 pm
Location: Wellington, New Zealand

Re: 4AGZE SC Runs Rough at WOT

Postby jondee86 » Sun May 26, 2019 2:31 am

RedvalkyrieOne wrote:Before this all went south my idle was very high--2000rpm plus. I couldn't
get it to consistently stay at a normal speed.

You should check your ignition timing. High idle is one sign that the ignition
is too far advanced. Engine kicking back when cranking is another sign. If the
timing is good then you have eliminated one possibility :)

Cheers... jondee86
The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore, all progress
depends on the unreasonable man.

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