Can someone HELP me with this.. Spark Plug gap??

[Bamba]

Strangest thing happened when I went to do my 1st tune-up on my 1998 Tahoe. I have the 4WD and the engine is a 5.7L

I wanted to clean off the carbon deposits on the plugs, cap and rotor. The strange thing is .. The existing NGK R spark plugs were all gapped at .035, an the sticker on the radiator indicated that the correct gap was .060, while the Haynes Manual indicates that the correct gap is .040

I've been reading through some of the other threads, and some guys get great performance at .040 and some at .060? But .035??

Another thing is that I must have done something wrong?? because the engine now runs like crap and has produced a "Service Engine Soon" indicator light??

I've rechecked the wires cleared the code and it sounded great but after running just a few minutes the "Engine Service" light comes back on, and ithe engine sounds crappy again??

I have a mind to regap the NGK-R plugs to .040 and see if that helps.

Any help you guys can give me is appreciated.

 

[steamroller]

I think the .060 gap is too wide even though that is factory spec. Stock plugs in the NGK brand for plain ole copper core plugs calls for
NGK TR55 (pregapped @ .059), instead of closing the gap up I just buy the TR5 (pregapped @.039) and open them up to .045, they are the same heat range. Before it gets said AC Delco's are overpriced for what they are

 

[DBLTAP]

Back when I had a running motor in my Tahoe... I ran/run Bosh dbl Platinum gaped at .45 with out any problems. If it runs well at start-up and then goes to hell id start looking for a vacuum leak. Check the code, if it is o2 censer related your on the right track. I seriously doubt that your plug gap is off enough to through a code. Spray a little TB cleaner and you'll find it real quick.

 

[Bamba]

If it runs well at start-up and then goes to hell id start looking for a vacuum leak. Check the code, if it is o2 censer related your on the right track.

Thanks DblTap, I was considering that too and the strange thing is.... There was some liquid gasket material around the Air Filter housing. I thought it strange to have it there but maybe I'll reseal it if I don't find any vacuum leaks anywhere else.
I may have to go out and buy myself "another" code reader, I've just moved and can't find the one I have.

Steamroller, Thx for the tips

I'll let you guys know how this turns out

 

[TheBeast99]

i replaced the plugs in mine the other weekend, gapped them myself at .060 and haven't had a problem.

 

[Bamba]

Well I regapped the plugs to .040 and the SEL came on within 3-4 minutes. I figured that I would go over everything I did because it's likely I caused the problem since the SEL light wasn't there before.
Since I had to remove the Dist and Rotor, I figured that I may as well replace them while I was at it. I left the old plugs installed because I didn't want to change too many things at once..... Fired up the Hoe and SEL was still there.

I went out and bought myself a decent code reader, even better than the one that I have but can't find... Test came back with error code P0300.

I've read that the P0300 codes can be difficult to diagnose. I'm trying to keep this simple by reminding myself that it's likely to be associated with either the spark plugs or maybe I broke a vacuum line when I initially went in to clean the plugs/cap/rotor?

I think I''ll go ahead and replace the spark plugs.... if that doesn't clear the code, then I'll test the vacuum system for leaks.

Any help you guys can provide me is appreciated.... I'll keep you posted

---------- Post added at 08:40 PM ---------- Previous post was at 08:34 PM ----------

i replaced the plugs in mine the other weekend, gapped them myself at .060 and haven't had a problem.

Interesting... It seems that the Hoes can take a wide range of SPG.. I've heard that the larger gaps produce the bigger spark and give the hoe more power?? I'm wondering if there is any truth to that. I do a fair amount of trailer towing.

I'm currently gaped at .040 and when this SEL thing is resolved I may tinker with a .050 gap to see if I can notice any difference.

 

[steamroller]

After reading it again I'm wondering if you may have the wrong plugs in there all together if they were gapped at .035. If someone put some TBI plugs in there the reach is different on them. The plug won't even be in the combustion chamber.

Having the gaps so wide in my opinion is why these Vortecs are so ******* distributor caps, rotors, and wires. It requires more voltage to jump the gap, so yes the spark is hotter, but if it's too wide then it may not make it to the plug at all and starts arcing inside the cap or where ever it can. It's gonna take the path of least resistance

1 thing you might check for the PO300 are the distributor ears where the cap bolts down, they are known to break if you tighten them down too much.

 

[faze]

I'm probably stating the obvious but my code sheet has the P300 as a 'random/multiple misfire detected'

Steamroller has an interesting point, since you didn't replace them, are they the right plugs?

I'd have to do some re-reading to be sure but I think you have to either clear the codes or start/run the truck three times before it'll stop throwing the code, if the problem is fixed that is.

Were it me I'd buy new plugs, clear the codes and go for a drive....after checking the tabs on the dist cap steamroller mentioned.

 

[clean454]

i would look everything over again and make sure its right,
cuz it ran good be for you went in there right?

 

[Bamba]

correct Instant, everything was fine meaning that I didn't have the rough idle that I currently have.

After looking for vacuum leaks (and not finding any) I DID notice what sounds like an exhaust leak coming from the area under the drivers side exhaust pipes. I'll check more and tighten the bolts later today.

I also pulled some "Live Data" information, and noticed that the MAP(inHg) ranged from 7.4(inHg) at 1853 RPM to 10(inHg) at 1472 RPM and I thought that should be higher??

Hopefully I'll have this thing figured out or have some more useful data to share later this afternoon.

---------- Post added at 11:00 AM ---------- Previous post was at 10:58 AM ----------

Thanks Faze, Those are on my "To Do" list today