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

 

[steamroller]

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

Whats the MAP reading at idle? It's gonna fluctuate alot depending on throttle angle, it should be in the high teens @ idle unless you do have a vacuum leak somewhere

Since this started with a cap and rotor change make sure the plug wires are fully seated on the spark plug and cap terminals, they can be a pain in the ass sometimes.

Since you have a scanner check the CMP offset/crank cam correlation if it has that parameter, it should be + or - 2*. The slightest movement of the distributor can throw this off, you may have pushed it out of whack changing the wires

 

[Bamba]

Whats the MAP reading at idle? It's gonna fluctuate alot depending on throttle angle, it should be in the high teens @ idle unless you do have a vacuum leak somewhere

Since you have a scanner check the CMP offset/crank cam correlation if it has that parameter, it should be + or - 2*.

Strangely enough my MAP readings are at around 9.7 at idle and at different RPMs?? Are you sure about the MAP fluctuations?

Here is some freeze frame data associated with the P0300 error code

P0300 Random / Multiple Cylinder Misfire Detected

View Freeze Frame
DTCFRZF P0300
FUELSYS1 CL
FUELSYS2 CL
LOAD_PCT(%) 11.0
ETC(°C) 151
SHRTFT1(%) -5.5
LONGFT1(%) 0.0
SHRTFT2(%) 14.1
LONGFT2(%) 2.3
MAP(kPa) 9.5
RPM(/min) 2053
VSS(km/h) 0
MAF(g/s) 3.303
TP(%) 12.9


I also went ahead and replaced ALL the plugs..... Sounds a LOT BETTER! .. even better than it did before I initially took the old plugs out to clean them.

I also did a vacuum test and "surprisingly" it was STABLE at 20.5 inHg.

The scanner still shows the P0300 error but... I can't help but wonder if I did "something" to muck up the plug when I cleaned it, and I can't help but wonder if the errors I'm still seeing on the scanner are related to the pre-existing noise which sounds like an exhaust leak??

Question... Could a leak near the driver side exhaust manifold cause that P0300 error? I also just started receiving a "Pending Codes
P0141 O2 Sensor Heater Circuit Bank 1 Sensor 2"

If the rough idle symptoms STAY GONE... I'll consider this post resolved and open another one related solely to the "Pending Code/02 error"

Thanks for all of the help ALL you guys have given me... It really means a lot.

 

[steamroller]

Strangely enough my MAP readings are at around 9.7 at idle and at different RPMs?? Are you sure about the MAP fluctuations?

I also did a vacuum test and "surprisingly" it was STABLE at 20.5 inHg.

My bad I misworded my post, if you've got 20.5" of vacuum at idle you're good. The map sensor and engine vacuum are related though. I'll just post this it explains it better than what I can put into words, but yes it will fluctuate depending on load, throttle angle, elevation changes, etc


http://www.aa1car.com/library/map_sensors.htm

 

[Bamba]

Friggin P0300 code resurfaced again a couple days ago ... I'm going to close out this thread and open one solely for the P0300 error, as it has nothing to do with spark plug gap.

The 02 error has NOT returned... I guess I do have "something" to be happy about.

On 2nd thought... you guys have given me a lot or great information and there are a few things I have yet to do so I'll hold off on creating another thread for now... If I find what's actually causing the problem I'll let you guys know... Thx

 

[95TwinTT]

I would revisit some of the trouble shooting basic’s. If you all of a sudden have a miss and the only thing that has happened is the plugs were cleaned, I would look very close to see if some other wiring was disturbed.

If it happened after changing the dist cap, I would suspect wires in the wrong holes. If the distributor was removed, I would suspect it might not be back in the same tooth on the cam.

Another area that should be examined is the control for the EGR. Make sure all electrical and or vacuum lines are secured.

Stop chasing the spark plug gap. The correct gap is what is listed on the radiator cover. I run my gap at .024, but it is for other reasons. The manual states to refer to the info stated on the individual truck. In general terms the early versions to 1995 was .035 and the later models were .060. GM has a lot of brain power coming up with these settings.

It is very possible that you are chasing two or more problems. If you have a exhaust leak at the manifold, it can screw up the O2 readings. Any exhaust leaks before or between O2 sensors can mess up the OBD2’s reaction to mixture.

You might want to compare O2 readings between 1 & 2 on each bank. They should be pretty much the same.

 

[Bamba]

I would revisit some of the trouble shooting basic’s. If you all of a sudden have a miss and the only thing that has happened is the plugs were cleaned, I would look very close to see if some other wiring was disturbed.

Another area that should be examined is the control for the EGR. Make sure all electrical and or vacuum lines are secured.

Stop chasing the spark plug gap.

It is very possible that you are chasing two or more problems. If you have a exhaust leak at the manifold, it can screw up the O2 readings. Any exhaust leaks before or between O2 sensors can mess up the OBD2’s reaction to mixture.

You might want to compare O2 readings between 1 & 2 on each bank. They should be pretty much the same.

I'm inclined to agree with you on all points... Thanks for your input. I'll have some time to look things over more tomorrow evening and should have something to add late Sun

 

[Bamba]

I feel totally stupid.... not for making a simple mistake but for "somehow overlooking" it when the problems started showing up.

For the sake of anyone as silly as myself "sometimes"... I FOUND the problem!

I switched two of the spark wires when I initially took the distributor cap off! I believe it was the #2 and #4 wires. I reattached them "correctly this time" and NO MORE ERRORS

Note to anyone and everyone..... If you do any work, and problems arise as a result.... CHECK EVERYTHING you touched... chances are THERE will be the problem.

Thanks for all your help guys... The silver lining is.. I "learned a LOT about Fuel trim values and some general performance indicators.

As a side note... I also found the exhaust leak, and have replaced the donut gasket at the exhaust manifold.