I was expecting to find bad things wrong with the little red Civic... specifically a valve in the cylinder head going bad. I checked over all of the ignition parts, including using an oscilloscope to find this misfire -nothing. I did a compression test and a leak down test on the engine, and I found nothing wrong there either. I checked over the PCV system since it runs through the #3 cylinder... nothing.
I sprayed carb cleaner over every intake part with the engine running, listening for a vacuum leak... nothing.

Luckily I have access to other expensive diagnostic tools, like this: (pic after jump)

Accessing a vacuum port, I filled the intake manifold with the smoke that this little gem makes and watched, and waited, and watched.

Low and behold I see smoke coming out from somewhere it should not, right above the #3 intake runner, from the throttle body shaft bushing (I took a pic with my phone camera but it didn't come out).

Unfortunately the only way to get this part is to buy another throttle body, which is $400 new. I'll try to find a used one which doesn't leak, but we may have to live with this. It only runs rough sometimes when you short-shift to 2nd with a cold engine, so we can work around that.

So I got all worked up over a tiny vacuum leak... at least, so far that looks like the culprit.

Posted by Scott Korb at 6:28 PM | Permalink | Comments (1)

but so far I was wrong, which is at least as distasteful.

Dreya's spark plugs look great. They're not the cause of the problem.

"What is the problem?" you may ask.
It has a cold misfire.
"The cause?"
Now that I've had only a cursory look I don't know for sure, but I suspect I won't like it.... not at all.
Symptoms suggest more diagnosis of the ignition system. I hope it pans out. My gut says something else. I hope I'm wrong.

Posted by Scott Korb at 9:19 PM | Permalink | Comments (5)

They have heat ranges. Who knew... OK, I do. But i don't think about it much. I mostly deal with stock parts and the stock spark plugs (stock brand too). But my brother would have thought of this right away I think, or at least after the first putt.

He's not a mechanic like me, but he plays one on T.V. -OK not really. He's just really smart.

Anyway, I made this car (Honda CRX DX/HF) with a custom transmission. When I went to buy spark plugs they gave me a choice. I chose "cold" because my custom trans runs high RPM for this 70HP 8valve engine.

fast fwd
I bought Dreya a 4spd 16valve 70hp Civic and we swapped the custom 5spd trans to it.

fine

later we changed the timing belt, swapped to a 90hp cam, ECU, and fuel system, and exchanged all the parts which go along with the timing belt except spark plugs and tune up.

Skip over-(I let Dreya do a lot of it and something minor had to be redone- it happens).

But she still has the custom 5spd trans for the 70 HP engine. Fuel economy was good. 38mpg

sputter soon after.

I changed the plugs (stock # for both the 16valve 4spd 70hp and 5spd 90hp) wires, cap and rotor button.
FIXED
no
months later sputter. I suspect the plugs are fouled.

If so I will try the the hotter HF plugs. This engine I created combined with this trans I created runs lower RPM than factory design. Sean might have thought of this if I'd told him about it.

An italian tune up could fix it right up I'd bet, but I'd prefer to attempt to modify this car to fit the driver on this occasion... bein' all customy like my brother.

He might tell you something opposite. I always tell him to stick to stock parts.

But I am. They just don't mix right sometimes.
----------------------

So she was getting 27mpg w/ the same spec engine, lighter car, and higher RPM trans.
Then ~30 in the newer stock 4spd heavier car too I think, and 38 with the 5spd in it.

I like the 38mpg for her. I just need to make it not cold sputter sometimes.

HOT PLUGS

[edited for memory]

Posted by Scott Korb at 11:29 PM | Permalink