Dieseling/fast idle solenoid
 

My FE has a solid roller cam, and Brent recommends I keep the idle speed at 1200 RPM for proper lubrication of the valvetrain. If the car is set to idle at 1000 RPM or below it shuts off just fine, but above that I get some dieseling. I use the best gas I can find in CA.

The first thing I did to try to solve this problem was to change the bushing on the distributor (MSD) to the black one (18 degrees) and reset the total advance to 35-56. This gave me more initial advance and increased the idle speed, so I could then close the butterflies to achieve 1200 RPM idle. It didn't really help much.

Two people told me to install a fast idle solenoid to solve the problem. The solenoid is engaged when the ignition is on and holds the throttle open at the faster idle speed. When the ignition it shut the butterflies close fully. So I bought a Holley 46-74 and bracket and set it up, but it still diesels a bit (less than without), I think because the engine is still running pretty fast and doesn't have a chance to "pause" at a lower idle RPM before stopping, if that makes sense.

One solution I thought of is to wire a switch under the dash to the solenoid (next to my fuel pump cut off switch). That way, I can hit the switch to kill the solenoid before I shut the car, let it idle at 800 RPM or so for a second or two, and then just shut the car. I'm certain this will solve the problem, but obviously it's not ideal because it adds a manual step to the process.

Does anyone have a better way to solve this problem?

What is your oil pressure when it is down at the lower idle?

I have the same thing happen in my '38 blown Chevy. What you experience isn't true dieseling which is the result of carbon build up. What you have is your idle set to high and gas continuing to be forced into the combustion chambers at a rate faster than your engine can burn it up when you turn off the ignition. When I reset my idle below 700 rpm's it doesn't happen, above that it does, easy as that.

When fully hot, I think it's 15-20 PSI. But apparently the gauge reading is low because it's a side oiler, and because of where the pressure reading is taken. I'd like to have it idle lower, but I'm really not going to go against Brent's advice. He has a lot of experience with these things, and he's also warrantying the engine.

Ask Brent if he isn't just practicing "defensive medicine" on this issue. If it were me, I would just move the idle down. Your idle pressure is fine, and if you just blip it from time to time at stoplights, you'll be even finer. Did he leave the galleys open? I know sometimes he does that. And how much extra splash can you get from 200 to 300 RPM anyway?

Not really being defensive, pretty aggressive cam with a good bit of spring pressure. We are pulling oil pressure off the opposite end of the block from the oil pump. I generally see about 30-35 lbs at idle pulling pressure off the oil filter adapter.

Jeff, what plugs are you running? Did you try a different heat range?

As a last resort I could concede to lowering the idle if you do juice it periodically while it's idling, but I would like to exhaust all other options first.

Brent, I think I'm getting pretty close to exhausting all of my options, having maxed out my initial timing and trying the solenoid. I hadn't really thought of cooler plugs. Would those make a significant difference? Right now, the way my plugs read is that they are clean with a slight bit of light brown on the electrode and ceramic, but the exposed ring at the end of the threaded body seems to have some black baked on oily deposits, which I though meant the plug was cool, if anything. Given that data, should I try a different plug? Thanks.

I'd have to see the plugs but a hotter plug has more porcelain exposed which is a hot spot for fuel to hit.

You can try a 3910 plug and I'd like to see how much transfer slot you have exposed at 1200 rpm.

Don't change you plugs and don't go against Brent's advice to keep idle at 1200 or you'll make lifter problems.
Forget wiring, switches and needless junk.
'Clutch' it off-that is when shutting off key, slowly raise clutch pedal in 1st gear. Let the clutch drag the motor off. Practice for 2 or 3 times and the car won't lurch.
Won't hurt anything.

Well, I do think I'd give the plugs a shot.

Chas -- what did your SFT cam idle on? I know your cam was more aggressive than my 245/245 .535 and mine idles nicely at 750ish.

No problem for me to try AR 3910 plugs. I've been told to use the factory gap for AR plugs, do you agree?

For the transfer slot, I just pulled the carb off again and was planning on setting it square and getting the faster idle using the solenoid. This way, when the solenoid is disengaged I will go back to a square transfer slot setting (I think the idle is fairly low there). In the past, I started with square transfer slots and then changed the primary and secondary butterfly positions equally to get the desired idle speed, letting the transfer slots fall where they do. Should I be setting this differently?

Separately, thanks for the tip Chas. I'm going to try the colder plugs but if I still get run on I'll try it.

Exactly. Have the same problem with my 482. Just clutch if off in 1st. I have a low pressure light that come on below 30psi and lowering the idle just isn't an option. It's embarrassing, but works.:rolleyes:

1000-1100. There are much bigger cams than mine but 2.250 intakes have zero velocity at 750.

I'd set them to .038-.040". They vary out of the box.

Transfer slots need to be close to square. If not, the carb will get into the transition circuit. If you need to, try closing the primaries to square and opening the secondary slightly.

Pat, there's a big difference between a 445 inch motor with 245 deg duration and a 427 with that much.

Naah-just dies instantly.:)

Just release the clutch while in gear and shut the ignition off at the same time. Works every time!

I like an idle that's low enough so you can hear each individual cylinder fire distinctly.:cool:

Like shifting into first or second before going to reverse to avoid grinding, it takes a little while to develop a routine, but the practice of slowly engagiing the clutch to bring the engine speed down and then turn off the key is by far the cheap and effective solution and causes no harm.

I installed an idle solenoid on my GTX to boost idle speed when the AC is on and it also is effective - but it will cost about $150 by the time you get a solenoid and bracket for a Holley. It will also probably negate using a Turkey Pan around your carburetor if you were planning on one. Or, at least you will have a big hole in it.

I have a question.

Is the recommendation to keep the idle up at 1,200 RPM because of the solid roller camshaft profile (rad specs) or because it's all solid rollers cams period need the added lubrication that 1,200 RPM provides?