I am about at my end of trying to fix this problem. The engine idles on or about 600 rpm and has a slight vibration. You can feel the vibration standing at idle through the whole body. From idle to about 2500 rpm it seems the engine isn't hitting right, nothing drastic like a miss-fire but more not running as smooth as it could be. After 2500 rpm it seems to run much smoother and has better performance. For the life of me I can't figure it out, here's what I have done so far.

Rebuilt the fuel system - good pressure idle and leak down.

Check the spark - plugs are showing tan but uneven (half the plug is tan and the other is still white on the electrode) approx. mileage on plugs is 4k.

Swapped MAP sensor - no change

Checked EGR - cleaned no problems

New sensor for temp (computer)

New coil

New O2 sensor

New cap/rotor

New motor mounts

Known issues - engine vacuum at idle is bouncing between 16-18hg
Engine vacuum readings appear good otherwise

Valve seals are leaking

Could this just be a sign of old age and it's time for some mechanical repairs?

Engine 216k miles

 

hmmm, I really needs some ideas.

 

I have been running the truck a little advanced, it seemed to run better. Today I re-timed it to spec, the strange thing is the timing mark was jumpy. Yes, I disabled the electronic advance. It jumps off the scale for one hit and will bounce back to the scale for several more before it jumps back off the scale. Also now back to the stock setting it idles fine but there is no power. Any ideas?

 

Maybe your inductive timing light is picking up spark from another wire? If you are getting cross firing between wires and/or terminals in the distributor, it would definitely cause some wonky performance. I have seen new caps that have leaked spark inside, but that's typically on the newer EDI distributors where the traces travel quite close to each other.

 

I just took a drive to see how it was running and it is totally flat. There is no power thru the whole range and has intermittent surges. Why would it run better with the distributor advanced? Let me detail this a little better. from standing to 1/4 pedal it's just lacking power, 1/4 to WOT it acts like there is no timing advance is the best way I can explain it. Under heavy loads and more than 1/4 pedal it surges like everything is fine, i can hear the engine pick up and smooth out. These surges are intermittent and last for several seconds never the same length. No codes, no backfires but when I go passed 1/4 I can smell something, maybe fuel.

So I timed the engine to where it has power thru the full range and it ends up off the scale around 14 BTD. Still idles with a slight miss or vibration as i mentioned at the beginning of this post. Even at 14 BTD there is still a stray blip on the timing light. If I was to guess the stray timing mark is about twice the gauge, so maybe 28 BTD. Don't think it's an inductive cross because my light is old school with a clamp to attach to the wire end. I spose the light could be defective but I have never had this type of problem with it before.

 

I had a very simaliar problem with my blazer and it ended up being the wires that go to the spider injector . I replaced everything possable and it would drive like you say yours is doing then it got worse , it would die , but start right back up . Then one day it quit on me and would not start back up so I just messed around with the wires and tried to start it and it started right up . So I put new wires in there and the engine has been running fine every since . Hope this helps I guess its a pretty common problem .

 

I am wondering could this be a knock sensor problem? I have had a code 43 flash in the past but I could always clear up it by jiggling the wire to sensor. I am thinking if the sensor is faulty could it be retarding the timing and that blip I am seeing on the timing light is the sensor intermittently returning the timing to normal? That would explain why advancing the timing makes it run better. Just one thing with that is - can the knock sensor retard the timing that much? Doesn't the knock sensor also adjust the fuel mixture?

 

i have a code for the knock sensor, but that code has been there for a long time and it started doin it before she got parked ive heard that maybe the spider maybe going out

 

Several things have been fixed but I think the problem with the timing really was the distributor. I moved the distributor one tooth advanced and now the engine runs great at the stock timing. In addition I replaced the knock sensor and connector with a used one and no more code 43. Also swapped out the distributor and ignition module with a low mile parts. I was noticing the original distributor was showing some wear on the gear and the was rusty on the top end.

When I was zeroing in TDC for #1 cylinder I noticed there are two notches on the crank, what is the second notch for?

There is still a slight vibration to the engine but nothing like it was, there is a good chance that the high mileage is causing it.