350 TBI Engine Miss

[JC_32]

I am having an issue with my 1987 Chevy R-10 with a 5.7 TBI and a 700R4 Transmission.

Symptoms: Noticing a light and hard miss at idol while in gear.

details: This only happens while in gear and if the motor is warm
   If motor is warm and I take it out of gear there is no miss.
   No miss while driving at any speed.
   Still getting 17-18 MPG

Recent Work: Complete tune-up. 
            Changed plugs, cap, rotor, wires and timing.
            timed to 2 degress BTDC with the plug disconnected.
            disconnected ground then reconnected so computer would set advance curves.
            New O2 sensor and Cat.

Clarifications: When I gapped the plugs, the mfg recommended .35 but my book said .45
            I gapped at .35 (should I go to .45?)
           The truck does burn some oil.      

   
I look forward to hearing some input.

thanks,

[Captkaos]

Check you plug wires?

[VileZambonie]

What plugs did you put in? Did it skip before you tuned it up? BTW it would be .035" or .045" not .35 or .45 big difference.

[JC_32]

Ha ha... You mean they aren't supposed to be gapped at 3/8ish to almost 1/2 inch??

Just kidding. 

The plugs are AC Delco.  The wires are BWD.

No miss before. 

[fred75]

  Sounds like one plug aint firin... Light and hard miss???  Sometimes light, sometimes hard??? "timed to 2 degress BTDC with the plug disconnected."  Which plug?? What's the factory spec on the timing?

[VileZambonie]

Pull the plugs out, check the gaps make sure none are cracked. When I asked what plugs you are running I also meant what part#?

[JC_32]

I'll look and let you know the part number for the plugs.

Fred,
when you time the TBI trucks you have to disconnect the two prong plug near the booster before you set the timing.
Factory spec says TDC but it has a little more get up and go at 2 degrees.

Hard to explain the interuption in the idol. Some are very light interuptions, no significant drop in idol, and others are heavy causing the rpms to drop noticeably.   

[JC_32]

Here is the plug info.
ACDelco - Spark Plug
Part Number: CR43TS

[Lt.Del]

I'd put the old plug wires back on if just to rule the new ones out.  One could've come into contact with the exhaust and burnt or the metal in the boot could've not seated right. 

[JC_32]

Cleaned and re-gapped the plugs and she is purring again.

[Grim 82]

Awesome. Did you end up going with .035 or .045?

[Lt.Del]

.45  ?   

[TexasRed]

SgtDel, prolly .45 GAP

[JC_32]

Yep went with the .045.

I had some oil foul on more than I would have liked to see.  I have a feeling it's the valve seals but could be rings. A few tests are in order. 

[Grim 82]

SgtDel, prolly .45 GAP

No,no,no, .45 ACP for sure