Can you find idle speed specs for a manual transmission equipped 3.8? You might have to look for something like a late 70s Nova or Oldsmobile Omega.
I have a 1977 Oldsmobile Delta 88 that I converted to a manual transmission a few years ago, first with a saginaw 4 speed and now it has a Tremec TKO in it. Its got a warmed over olds 403 in it with a factory aluminum 4bbl intake and the stock Q-jet. The main issue I had was with the idle speed also. I kinda got lucky if you can say that, as the 1977 Oldsmobile Cutlass had a manual transmission option, so I was able to set the idle speed to that vehicle's specs, which was 750-800 rpm I believe. I know for sure the 1977-1978 Olds Omega (same as Chevy Nova) could get the 231 buick with a manual transmission, but I don't know the idle speed specs off my head, and all my service manuals are still at my parents house.
I'm not too worried about the proper spec. I'd prefer to just get it as low as I'm comfortable with.
So the weather is nice but I'm still busy. I spent much of yesterday at the junkyard. As related to this thread, I brought home:
- A 1980s GM V8 HEI ignition coil. Is there any risk using an unidentified coil?
- A bunch of vacuum valves/modulators/etc...I'll look them up and see if there's anything I can use.
- Intake hoses that should make a decent CAI.
I agree that the coils would likely be the same, but besides the caps, I would have guessed that the 6 cyl dist would have a 6 pointed trigger wheel inside it and the 8 cly would have an 8 pointed trigger wheel.
So, I managed to do a few things from my to-do list, now that the rain has stopped long enough for the dry spell to coincide with my availability.
This is just an update, I still have a long list of diagnostic tests to try.
WHEN IDLE IS LOW - checked at 750
- Check ported vacuum level at closed throttle: definitely more than 0 but less than enough to register 1.
- Pull plug wires one at a time at idle to verify that idle decreases: just like at higher idle, barely perceptible.
- Manually activate EGR, see if it stalls: just like before, almost stalls but keeps running. Maybe a little closer to stalling.
GENERAL TO-DO DONE
- Disconnect vacuum advance entirely and test-drive: actually I did this one before today. Bucking/skipping is pretty darn bad when hooked up this way. Idle is almost decently low.
- Disconnect a vacuum hose at low and high idles to see if RPM goes up or down from intentional vacuum leak: no noticeable change in RPM
- Hooked up vacuum gauge to EGR vacuum line from TVS: acts like ported (zero at closed throttle, comes alive with throttle open) but reads slightly closer to dead-on 0 at closed throttle.
- Hooked EGR to manifold vacuum (and left gauge hooked up to EGR's previous TVS vacuum). Idle is 1100. I'll see how it drives (and what the vacuum gauge looks like).
- Look at the vacuum gauge while I unplug a wire so I can get familiar with a steady single cylinder misfire: Ok, it's a quick steady shake.
I also hooked up a spark tester. All cylinders look the same. For comparison I tried it on my 2002 GM V8 (and broke one of its wires). The 2002 lights it up brighter. I don't know if I should expect as strong of a spark from the Buick but I guess I'm not getting it.
I would try running the engine with the vacuum gauge on the distributor vacuum advance and see if you get weird variations in vacuum when it bucks. That would throw the timing all over the place. Also you might try restricting the size of the hose to the advance to slow it's motion and not stomp on the throttle when testing. The high idle with advanced timing is probably ok and there is usually an air screw as well as fuel idle screws for setting the idle speed, the air screw controls the air bypass when the butterflies are closed.
I'm pretty sure that no matter where I hook up the vacuum gauge, when it's bucking the gauge jumps all over the place, from vacuum into pressure, etc...except when it's hooked up to that check valve vacuum, which reads 20+ at all times, where the advance is currently hooked up and I get no bucking but do get knock.
I hadn't even considered the possibility that the bucking comes first and causes weirdness at the vacuum advance. I'll have to chew on that idea. I've been operating with the thought that the vacuum advance was at fault for the bucking, not the other way around.
Today I had the patience, time, weather, and equipment to knock a few things off my list...
Ignition coil test results
Test 1: Resistance across main terminals - 1.8 ohms (Manuals say it should be low; 1.8 ohms is low, IMO)
Test 2a: Resistance from main terminal 1 to output: Infinite
Test 2b: Resistance from other terminal to output: 12k ohms
(Manuals say that if BOTH 2a and 2b come back infinite, coil is bad.)
Distributor advance: Holds vacuum well; takes about 25 seconds to go from 20in/hg to 15in/hg EGR: Does not hold vacuum.
I tried disconnecting EGR and plugging the vacuum line, but it didn't affect my idle speed. I think my engine is not very sensitive to vacuum leaks.
Slow idle (~500) with no advance: 8?BTDC (Supposed to be 15?BTDC)
My usual fast warm idle (~1200) due to high-vacuum advance: 36?BTDC
(Note: RPM by ear, tach broken.)
Tangent: I've always thought using a timing light would be interesting and fun. I was right, it was really cool. (Well, you know what they say: Simple minds, simple pleasures.)