High Idle, and Tightening the Distributor

[jangell]

Another update: We tried setting the ignition timing again. This time we remembered to disconnect the vacuum advance first. However, the cats still glowed at 10-13 degrees BTDC. The car also idled high, at about 1500 RPM. When we let the distributor slip to ~3 degrees, the car idled closer to ~800 RPM, but did so rather roughly.

We tried leaning out the mixture 1/4 turn, but this caused a lean misfire and finally the engine died. We then went back to center, and then another 1/4 turn rich. It ran smoothly, but with an even higher idle and quickly caused the headers to glow.

We think the curb idle might have been slightly off, leaving the throttle plates very slightly open. Of course, we lost the 2.5mm allen wrench while we were working on this and weren't able to test this adjustment yet. It'll have to wait until next week.

I'm not sure if this information helps any with the diagnoses. Thanks again for the assistance!

-- Joe

[DMCTek]

Valves should be set at .004" intake and .010" exhaust. Might make a bit of noise on the intake side, but should not cause a running issue.

A rich mixture will actually keep combustion temps down, rich will cause the cats to glow red but not the header inlets.

You really need to check fuel pressures with a proper guage set and then set c.o. with a dwell meter reading the frequency valve.

Personally I think you are chasing a vacuum leak.

Good Luck!

[Delorean Industries]

Valves should be set at .004" intake and .010" exhaust. Might make a bit of noise on the intake side, but should not cause a running issue.

A rich mixture will actually keep combustion temps down, rich will cause the cats to glow red but not the header inlets.

You really need to check fuel pressures with a proper guage set and then set c.o. with a dwell meter reading the frequency valve.

Personally I think you are chasing a vacuum leak.


Good Luck!

.007 on our camshafts exhaust and intake. He is running a set of our camshafts grinds. Same recommendation as posted on a cam sheet from DMC-CA as well for base cut camshafts. Too tight on on a ground camshaft and it promotes float at higher rpms. You are right though Mike for a stock cam or even a less aggressive cut like in a stage II.

[DMCTek]

.007 on our camshafts exhaust and intake. He is running a set of our camshafts grinds. Same recommendation as posted on a cam sheet from DMC-CA as well for base cut camshafts. Too tight on on a ground camshaft and it promotes float at higher rpms. You are right though Mike for a stock cam or even a less aggressive cut like in a stage II.

In that case wouldn't the exhaust side promote float if the stock setting is .010" and they are set to .007" (tighter).

[Delorean Industries]

It is a matter of it being excessively tight. At .007 you are fine on the exhaust side. At .004 or less once hot the clearance decreases and causes issues on a base cut camshaft (which all performance DMC camshafts are except for ones cut from blanks)

You wouldn't think this could be such an issue but it is most evident as a misfire at higher rpms or by your wide band going excessively lean. I pulled my hair out trying to figure this out years ago. The solution was the valve clearance.

[Ron]

Two things, maybe just the way I'm reading it tho:

The hot control pressure seems too low to me, what ~10% below specs.
Hard to tell with the cold...what temp was it?

It sounds like you can't get it to idle down to 750 RPM (required to set the timing correctly).

[Elvis]

I bet you still haven't tested the idle motor like I asked you lately - but with running engine.

high idle means it gets too much air thru some hole.

throttle plates - curb idle and valves on the plates
those 3 brass screws not tight ? (don't break them)
idle motor not closing all the way - dirty or rusty?
idle ECU - broken ? happens - not often but happens.
temp sensor broken ? - I had such a problem lately, the connector was dirty / oxy...
(open temp sensor means the ECU regulates idle up to ~1500rpm)
ilde switch not pushed ?
the vacuum valve must work or it has too much advance and won't go down to 800rpm.

even if the mixture is off or advance is a bit higher - idle has to go down if it doesn't get air. I expect it is metered air, not even a vacuum leak. -> Idle motor, sensor and ECU !!!!!

[jangell]

You really need to check fuel pressures with a proper guage set and then set c.o. with a dwell meter reading the frequency valve.

The good news is I had one: an OTC 6550 Master Fuel Injection Kit from Amazon. That's how I got those numbers in the first place. I didn't check the CO and the Lambda system; I'll have to grab a dwell meter (my multimeter doesn't have that) and do that next weekend. Looks like I'll be following D:04:01 in the Workshop manual... although that does say I need an IR exhaust gas analyzer, which is going to be out of my price range. The steps also imply that I should already have the car idling properly before I do this.

Personally I think you are chasing a vacuum leak.

I thought we had those cleaned up, but it won't hurt to check again. It's quite possible that I just don't know where all the common leak locations are and overlooked something (I'm basically making this stuff up as I go along, following the manuals and bugging all of you for help ). I'll do that next weekend to.

Good Luck!

Thanks!

-- Joe

[jangell]

The hot control pressure seems too low to me, what ~10% below specs.

I was wondering about that as well. It does seem low, but it didn't seem so low that I wouldn't be able to get a somewhat reasonable idle (I mean, as opposed to it not working at all). But then, I really don't know how the car would behave if the CPR was running below spec on an otherwise perfectly tuned car, so my intuition is probably way off.

Hard to tell with the cold...what temp was it?

It was about 35-40 degrees in the garage that day, and the engine hadn't been started yet. I should have mentioned that -- that certainly seems like it could affect the cold readings. I'm not sure how much it would affect the hot readings due to the heater in the CPR -- I really have no idea.

It sounds like you can't get it to idle down to 750 RPM (required to set the timing correctly).

Correct -- it seems to be at about 750 RPM when we let the timing slip to ~3 degrees, but if we bring it up to 13 degrees it shoots up to 1500-2000 RPM. I assumed we need to set the timing before we can get the RPMs down, right.

Thanks!

-- Joe

[jangell]

I bet you still haven't tested the idle motor like I asked you lately - but with running engine.

I honestly can't remember now. Let's assume I didn't. I'll do that test next weekend, just to be sure.

high idle means it gets too much air thru some hole.

throttle plates - curb idle and valves on the plates

I think these are slightly open; I have to pick up another allen wrench to adjust the curb idle screw a bit. It's very slight, though.

those 3 brass screws not tight ? (don't break them)

I know these are all tight, but I'll re-verify to be sure.

idle motor not closing all the way - dirty or rusty?

I'll verify this as well. How would I know that it's closing all the way? I know it's doing SOMETHING when I apply 12v, as I can hear it click opened and closed.

idle ECU - broken ? happens - not often but happens.

I saw some diagnostics instructions in the Workshop manual; I'll go through that next weekend as well.

temp sensor broken ? - I had such a problem lately, the connector was dirty / oxy... (open temp sensor means the ECU regulates idle up to ~1500rpm)

This is the thermistor on the the Y pipe under the intake manifold? I see it mentioned in the Workshop Manual, D:05:02. I believe that is new, but it's been months and I'm starting to lose track of these things. Kinda a PITA to get to at this point, but I'll check it out, since that does correlate with the high RPM we're seeing. Hopefully I can just tap the wire at the ECU and check the resistance before tearing the manifold apart again.

ilde switch not pushed ?

I confirmed that it is being pushed.

the vacuum valve must work or it has too much advance and won't go down to 800rpm.

even if the mixture is off or advance is a bit higher - idle has to go down if it doesn't get air. I expect it is metered air, not even a vacuum leak. -> Idle motor, sensor and ECU !!!!!

I'll take a thorough look at these this weekend. Thanks!

-- Joe