kaotik

iTrader: (1)

Hey guys... I'm at a loss and don't know where to go now. I have a 350 TBI. Long story short, I recently did a tuneup and here is what I did:

1. New NGK Plugs
2. New Accel 8mm wires (make your own)
3. New Accel cap and rotor
4. Flushed top end with Seafoam through brake booster line.

Car ran great before any work was done, I'm just **** and like new parts every year...

Now the car seems like it lost power. At first it was blowing a lot of smoke. White mostly. I chalked it up to Seafoam at first, but then Went through and checked firing order and noticed a had 2 swapped, so fixed that and things got better, but something still isn't right. Smoke went away after this.

Noticed the cap wasn't as tight as it should be. Tightened it more and no major changes.

Wondering if plug gap could cause this? I didn't check them and assumed they were "pre gapped" and even if they were, I have 305 heads on a 350 bottom end, so with running higher compression, wondering if I need to have a custom gap? It's a 305 TBI top end on a 1999 truck 350 bottom end. Stock 305 heads.

Just trying to think through this... No mis fires, so assume wires are fine.

Only other thing I can think of is do I need to check or do something different with the cap?

Justin69

I would definitely check the plug gap. I've checked quite a few out of the box that were all gapped different. Usually not a lot but some have been. Good luck.

kaotik

iTrader: (1)

I'll be heading back out today for sure to check that. I expect to find them all close, but I'm concerned I might need to run a different gap altogether and not sure what that gap is... Assuming larger with higher compression and I do run rich.

Do I buy plugs for the bottom end 1999 truck engine, or plugs for the 1991 camaro 305?

Night rider327

iTrader: (13)

Buy plugs for the heads you have. The '99 truck would be a vortec L31 engine and those use longer reach plugs.. Will not work in your 305 heads.

You need an AC delco R45TS (or the NGK cross to that)
Gap the plugs at .045"

Did you turn or move the dist. when you replaced the cap? I know I always have to turn it to get to the back hold downs easier.. If you moved it then you changed your timing and that will kill off power. Recheck your timing and reset if needed.

Double and triple check your firing order.. It's very easy to get a few mixed up.
18436572 clockwise around cap.
Driver side bank front to rear is 1 3 5 7
Pass side bank front to rear is 2 4 6 8

kaotik

iTrader: (1)

Ok, so I checked my old plugs I took out and they were AC Delco "2" gapped at .032 oddly enough.

Ran fine on those but did run rich. The new plugs I bought are NGK UR4 6630 Which cross references from the plug you suggested above. (http://www.sparkplug-crossreference.com/convert/AC_DELCO/R45TS)

These plugs were gapped .035

Just to clarify, you believe they need to be gapped up to .045?

As far as the cap goes, what do I need to do to test or make sure it's set correctly? When I pulled it off, I carefully removed it, then the rotor, replaced the new rotor in same position, and swapped new cap on. I did have a difficult time at first finding the mounting bolts, so I may have turned it inadvertently, but I tried not to move anything. Just want to know if I take it all off again, what am I looking for?

I did triple check the firing order, and it is correct. All wires are tight and going to correct spots.

Thanks again for all your help everyone!

cardo0

U can watch your timing if u have an "accurate" timing tab (and your harmonic dampner isnt slipping). Just get a timing light - for your rpm range and equipment a cheapo Actron light like mine will get the job done. When the car is warmed up at idle u should see your listed timing advance (tune up data) on the tab (something like 10*). Then as u rev it u can watch timing adv increase. On a early 90's chevy i would expect your still below 30* at 3,000rpm but u should still see it increase. Becareful not to over rev here as not good to rev hi w/motor unloaded in the driveway. Also dont worry 'bout your timing curve - until your ready - as u just want to observe it for now and make sure its responding. Let me share with you my corvette dist mechcanical just froze up - lack of use - but it can happen. So a timing check will eliminate the mech adv mech. And u should have a timing light if u do any tuning yourself.

BTW i like what Nightrider told u for plugs and gaps and u should be good with that info.

I dont think u need the compression and leak down testing yet as i suspect your troubles are with the ign.

Hope this can help.

Fast355

iTrader: (2)

With 305 heads I would run R43TS or R42TS plugs. R45TS are just too hot.

Night rider327

iTrader: (13)

Sorry but I disagree.. Lets break this down.

He has a '99 L31 short block which is spec'ed with 9.4:1 compression. GM used 4.100" x .018" thick head gaskets.

I bet you dollars to donuts the OP went to part store and asked for head gaskets to fit X chevy 350. The 1st gaskets they hand you are fel pro blue prema torque 4.166 x .041" thick head gaskets. In fact if you want any thin ones it's a custom order as they do not stock any. About the thinnest they stock are .039"

Vortec heads are listed as 64cc (but all the ones I have CC'ed has been 62 or 63cc)

The 305 heads are 58 cc

IF the OP used the common rebuilders blue .041" gaskets, even with his now smaller 58 CC heads

His compression is only 9.48 He raised it by a mere 0.08:1 from the stock vortec 350 specs with 64cc heads...

How is R45TS plugs too hot for a 0.08:1 gain in compression (9.48:1 compression)?

Now if the OP did use thin head gaskets, I would tend to agree with you. If he used a 4.100 x .018 gasket his compression would be 10.04:1 and would be enough to drop 1 heat range colder on plugs, but not 2 or 3 steps colder.

I run 10.34:1 compression on 93 octane fuel on 2 heat range colder plugs in my camaro.
10.25:1 compression in my S10 with 1 step colder plugs

Fast355

iTrader: (2)

GM used a .028" thick gasket on the L31s. I have the part number breakdown on a PDF.

That being said my 1983 305 spec'd R43TS plugs from the factory and it was ~9.2:1. Too cold of a plug won't really hurt anything, too hot of a plug and it can cause preignition and detonation. Safer to error on the cool side.

I run ~42 equivalent heat rang plugs in my 9.4:1 L31 in my Express.