Shaky idle

[IGottaSy]

Re: Shaky idle

Ml

OK, first go here and look at where the "wear" is on this rotor.

http://www.syty.net/forums/showthread.php?t=94747&highlight=dist+rotor

It's been my belief for quite some time that the dist cap itself is slightly out of phase to the dist. Look at the cap in the first link I posted. The go to the above link and look at my modified rotor and the "matching" cap.

See the difference in where it's burnt? I am probably the only guy here running this, I admit, weird rotor. But if nothing else I feel better...:rotf:

To your point. The dist rotates clockwise. Rotating, moving, it clockwise will -retard- the spark. There is NO advance built into the dist. Vac or centrifugal. Once the timing is set to 0 with the wire disconnected and a damper that has not slipped, reconnect the wire and the ECM handles advance from there. It's my understanding that once this is done the dist only provides a "TDC" reference to the ECM.

This is why I contend that it's not the cap. Something else in the dist maybe but not the cap. Unless, of course, it's cracked and we don't see it.

For my other rant on this you can go here.

http://www.syty.net/forums/showthread.php?t=103678&highlight=dist+rotor

There is this other thing called advance curve. It wants to run its set course but since distributor is out of whack, ECM keeps pulling timing simultaneously. This is acting like a rev limiter.

Not to argue but maybe this will help me explain better what I am trying to convey. Just trying to help, not start a knowledge war.

 

[Don W.]

Re: Shaky idle

No worries. Me neither. I've explained it as best I can actually. Someone else can chime in with what, exactly, is going on in the ECM.

 

[randy merritt]

Re: Shaky idle

I'm planning to order a new MAP sensor, but which one is the right one: https://www.rockauto.com/en/catalog...p)+sensor,11207?a=Referer+www.google.fi+URL+/
This gives
2 Bar: GM #16009886
old 3 Bar: GM #16040749
New 3 Bar: GM #12223861
So I assume this should be the right one: http://www.rockauto.com/en/moreinfo.php?pk=87028&cc=1164451&jsn=837
BUT, on my current one there's no such numbers:

That is a 2 bar MAP sensor.
http://www.robietherobot.com/storm/mapsensor.htm

 

[Pertti K]

Re: Shaky idle

^Yes, thank you. Actually I just found the same info myself. I thought that the numbers on the MAP are from the GM part number, but apparently not.

 

[berzerker]

Re: Shaky idle

3I would try a new distributor . skip white racing sells msd knock offs on ebay for $60 . they work good and have cured many trucks that ran poorly before .

 

[Pertti K]

Re: Shaky idle

I've already changed the pick-up coil, IC module, rotor and cap. And checked for clearances. What else could be wrong in the distributor?

Next I'm going to change better quality spark plug wires, AC Delco plugs and MAP.

 

[Pertti K]

Re: Shaky idle

Still struggling with this. When idling or revving standing still, below 2500 rpm it shakes and runs like crap. Over 2500 rpm runs fine. Under load (1/3 throttle or more) runs good if not great. Twice I've run it for 15 miles (from home to work) w/o any problems, but then the symptoms came back again. No codes. The missfiring under load has been resolved.

The story so far in short:
- Replaced the distributor cap and rotor
- Replaced the spark plug wires (cheap ones), coil and vacuum hoses
- Visual check for vacuum leaks
- Ignition timing check
- Checked the ground points
- Compression test, all six in 140-150 psi range
- When cranking the speedometer sometimes jumps to 50 mph (not after changing the distributor, I'm not sure if this has been solved already)
- Tested a supplementary ground wire
- Changed the fuel filter
- Changed plugs
- Unplugged the oxygen sensor for a while
- Noticed tachometer jumping like crazy after startup (hasn't done it for a while, not sure if the problem still exists)
- Plugs from .035 to .028 gap
- New pick-up coil
- IC module
- Checked the fuel pressure according to service manual
- New MAP
- New AC Delco plug wires (this cured the missfiring)
- New AC delco plugs (previously used NGK)
- New distributor (the old one had just noticable radial play)
- Tried to wiggle the wirings while idling and measured the coil sub harness
- Sprayed the the manifold and surroundings with brake cleaner to hear if there's any change in idle speed due to vac leak
- Checked the exhaust temperatures with water spray, no noticeable differences between cylinders

Next I'm planning to
- test for vac leaks with a pressure test
- change the injectors I purchased from Mr. Fivetodrive (thanks!)
- maybe adjust the valves
- test IAC - it can be tested just by unplugging it for a while, right?

What else, any ideas?

 

[TY0618]

Re: Shaky idle

Not sure if it would help your situation or not however, mine was running poorly as well. I had a cracked magnet under the rotor. I guess the poles were being picked up improperly. 3 cracks. One at every rivet.

 

[Pertti K]

Re: Shaky idle

If that was the problem, it would have been solved by changing the distributor, which I did. Right? Well, I guess the jumpy tachometer needle might be a result of what you just said. But anyway still runs badly.

 

[Quickstop [UK]]

Re: Shaky idle

Any issues with your ECM/chip? Stock or something else?

 

[Pertti K]

Re: Shaky idle

I guess it may have something to do with the ECM. I assume it has a stock chip, since everything else on the truck is stock, but can't be sure. Can it be checked otherwise than opening the ecm?

 

[Pertti K]

Re: Shaky idle

Did a pressure leak test yesterday and found a leak after all. It was between #3 and 5 injectors and behind MAP sensor, pipes, hoses and whatnot, so the brake cleaner probably didn't reach it in earlier tests. Pretty convinced that's the main and root cause for the problems, but there had to be also ignition / electricity based problems (missfiring, jumping tach and speedo needles etc.).