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Discussion Starter #1
New to the club, hopeful I can get help. I love these forums, and have been helped greatly with my boat on a similar kind of page.

I just bought a 99 Suburban forest service rig with 42,000 original miles. It ran great when I got it, and as a pre-emptive measure, I put in new plugs, wires, cap and rotor. It still ran great. As far as I could tell, the plugs were clean and original.

Here's what has happened since:

After about 100 miles, it began to miss intermittently while sitting at idle. By 300 miles, it was running rough, chugging, and making lots of water out of the tailpipe.

I replaced fuel filter, uphill O2 sensors, and air filter. Still ran rough, so I took it in.

There were no diagnostic codes, but replacing plugs, cap and rotor fixed the problem. They told me that the E3 plugs I had put in were to blame. They replaced with iridium plugs and an AC delco cap and rotor.

That was Monday. After 100 miles, again it was missing intermittently at idle, and now here at 300 miles, it is running rough and chugging again.

What is going on here?

---------- Post added at 02:35 AM ---------- Previous post was at 01:56 AM ----------

..sorry, by the way 5.7L 2500 4X4.

I have been browsing some ignition posts, and am curious about the following note, below, regarding a vent at the bottom of the distributor. I haven't looked at the bottom of the distributor, but has anyone else had this experience? I'll get at it tomorrow, and I know what I'll find: charring in the cap and wet plugs. Should I gap them down?

I would go back to the ignition. You said the cap looked terrible shortly after the tuneup. Use only Genuine AC Delco plugs, cap, rotor. For wire, use AC or NAPA Premium. For plugs, just get the boring old fashioned single electrode platinums. This is what your parts guy will give you. Most importantly, set your gap down to .040. The bigger gap put a tremendous load on your ignition system, and doesn't offer any benefit. One last thing. There should be a vent hole in the bottom of your distributor. If the screen is still there, knock it out. It will allow the distributor to breath much better, and stay dry.

And there is no timing adjustment on these trucks.


 

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Welcome to the club Beach. I'm wondering if you might have 2 different problems here. First off, GM is correct about the plugs. There have been many threads here by members & GM owners who have used other plugs in their engines & the majority of them have had problems with misfires, until they went back to AC Delcos.
Has anybody checked your fuel pressure yet? How long has it been since the fuel filter was replaced? Fuel delivery problems cause intermittant missing & running problems like this & you can borrow a fuel pressure guage at many of the chain auto parts stores if you leave a deposit with them. I would do this before you spend any more money on parts, as it seems like most of your electrical system has already been replaced/repaired.

edit** I just saw your add to your post. Was there water in your dist cap the last time? I've not heard of this unless owners wash their engines without covering the distributor & the cap, or unless they are continuously driving through deep water & it's splashing up on the engine all the time.
 

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Discussion Starter #3 (Edited)
No, fuel comes through fine. Sorry, I forgot to mention that was another of the diagnostics they ran at the shop. I'll go over some of the things we're talking about myself, but have an appt Monday, and I'll ask them to check compression.

This is something that is use-dependent, getting worse with miles that ultimately fouls the plugs and is causing oxidation under the cap. Wondering about a couple of things:

1) No, I don't get it wet under the cap with driving or washes, but critters had built a nest up on the engine block under the distributor at some point in the truck's history. I cleaned it out so-so, but maybe there is debris blocking the vent. Is the distributor something that needs to breathe? I'm thinking not so much, but I'll have a look.

2) The spark plug gapping. Is 0.04 a better fire? Maybe it is working too hard to fire. After one cylinder starts missing, others miss, and running gets progressively worse. I am a complete novice to troubleshooting this kind of thing, so I don't even know if this kind of thing happens.

3) Fuel additive. I have run a bunch of stuff through, but refilled yesterday from empty (!!!) but problem persisted.

Should I just try pulling the plugs, cleaning and gapping at 0.04, then cleaning up the oxidation under the cap? Also curious about other sensors which could be causing poor burn and progressively worse run. Again, new plugs, cap and rotor only fixed the problem for about 300 miles.

Replaced so far:

Fuel filter
Uphill O2 sensors on both banks
Air filter
Cap, rotor and wires (Delco, and hi performance wires)
 

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No, fuel comes through fine. Sorry, I forgot to mention that was another of the diagnostics they ran at the shop. I'll go over some of the things we're talking about myself, but have an appt Monday, and I'll ask them to check compression.

This is something that is use-dependent, getting worse with miles that ultimately fouls the plugs and is causing oxidation under the cap. Wondering about a couple of things:

1) No, I don't get it wet under the cap with driving or washes, but critters had built a nest up on the engine block under the distributor at some point in the truck's history. I cleaned it out so-so, but maybe there is debris blocking the vent. Is the distributor something that needs to breathe? I'm thinking not so much, but I'll have a look.

2) The spark plug gapping. Is 0.04 a better fire? Maybe it is working too hard to fire. After one cylinder starts missing, others miss, and running gets progressively worse. I am a complete novice to troubleshooting this kind of thing, so I don't even know if this kind of thing happens.

3) Fuel additive. I have run a bunch of stuff through, but refilled yesterday from empty (!!!) but problem persisted.

Should I just try pulling the plugs, cleaning and gapping at 0.04, then cleaning up the oxidation under the cap? Also curious about other sensors which could be causing poor burn and progressively worse run. Again, new plugs, cap and rotor only fixed the problem for about 300 miles.

Replaced so far:

Fuel filter
Uphill O2 sensors on both banks
Air filter
Cap, rotor and wires (Delco, and hi performance wires)


For your 1999" with the 5.7 liter.......On the A/C Delco Online Parts Catolog calls for A/C Delco Platinum Plugs and Not the A/C Delco Iridium plugs....also the Platinum Plugs are Gaped at.....0.60....

Vehicle: 1999 CHEVROLET SUBURBAN K2500 3/4TON4x4 V8-350ci 5.7L F/I Vin R ID# 22780

Group / Subgroup: Ignition/Filters / Spark Plugs



SPARK PLUG ASM
Part Number: 41-993
Product Notes:
[Platinum Spark Plug]; .060 Gap

Per Vehicle: 8; Years: 1996-1999

Edit:......I would also Mention that both the A/C Delco Iridium and Platinum Plugs are Gaped Right out of the Box......and do not Attempt to Re-gaped them as the Tips on both Plugs can Be Easily Damaged.
 

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Are you losing/using coolant?
These motors are very prone to intake manifold gasket leaks.
I think the coolant can foul plugs.
Not sure what "lots of water out tailpipe" means , but maybe it is coolant steam/smoke?
Luck
Charlie
 

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I would go back to the ignition. You said the cap looked terrible shortly after the tuneup. Use only Genuine AC Delco plugs, cap, rotor. For wire, use AC or NAPA Premium. For plugs, just get the boring old fashioned single electrode platinums. This is what your parts guy will give you. Most importantly, set your gap down to .040. The bigger gap put a tremendous load on your ignition system, and doesn't offer any benefit. One last thing. There should be a vent hole in the bottom of your distributor. If the screen is still there, knock it out. It will allow the distributor to breath much better, and stay dry.

And there is no timing adjustment on these trucks.


Hey, that's my work LOL.

My guess is that between the crazy gaps on the E3s and corrosion in the cap, the coil is toast because of the extreme loads placed on it to fire. And that would make sense if once the misfires start it gets progressively worse quickly.

As for the vents, they are located at about 8 o'clock and 2 o'clock. This is looking down on the distributor from the front. You will probably need a mirror to see them well. The early distributors had screens in both vents. If you have the screens, just punch them out. Later distributors had two plastic "half moon" shaped discs. These are fine, as long as air can freely flow through.

Gap the plugs at .040"
 

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Have you checked vacuum lines, grounds, and wiring harnesses? With critter nests in there, they may have chewed something up. Probably not the cause of the misfire, but the systems on these engines all seem to run tight together. Do look into that coolant issue, too, just to make sure. Fel-pro kit, right?

2COR, are you allowed to double-dip? And, set the cap at .040 and not .060? My truck runs fine with the plugs out-of-the-box, but I'll adjust them if this gives some benefit.

Good luck, Beach, and how about a picture?...
 

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As '99HEARTBEAT said use the original A/C Delco plugs.
 

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Discussion Starter #9 (Edited)
Today told me a bit more, and I am definitely leaning toward 2COR's suggestion to reduce the gap on the plugs for easier spark.

I've been watching the coolant closely, no drop in levels at all, so I think the water I get in the exhaust is part of the misfire/incomplete burn that comes at the end of the cycle when it gets running really choppy. Remember, all I have to do is remove the cap, clean the leads, and it runs great again for about a tank of gas.

So today, I replaced the plugs with Delco stock (third set!), polished the oxidized contacts, and cleaned it out real good in and around the distributor base. 2COR, I didn't visually inspect the breather holes, but I spotted them, and now will go back for a look, when I gap the plugs down to 0.04 tomorrow.

In short, it seemed to help a bit. Do you think that if the decreased gap solves my problem, I should replace the coil, then gap back to 0.06?

I am also going to climb under and look at ground to the block. Grounds to the frame rail and firewall, as well as terminal are all solid, but I cant nspect the engine block ground from above.

Cleaned the MAF with the spray stuff and replaced PCV for kicks.

Here's a note: LOTS of corrosion under the rotor. When I took the cap and rotor off this morning in the daylight (no shadetree here) I could see a lot of corrosion. This is a retired forest service truck (yes the mileage is real, 42K for a 1999) but its evident that the rig lived near salt water and was parked for a good deal of its life (critter nest).

I spotted it it in the shop where it was getting painted, and had to have it. I'll try to modify my profile to put a pic in for Kidhauler, since I routinely haul a four and six year old. When this baby runs better, its slated to replace the death wobble beast 1988 Burban as my tow rig.
 

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Discussion Starter #10
SSPX0505.jpg

..For Kidhauler, in the shop where I spotted it.

Gotta love the Forest Service Green firewall
 

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2COR, are you allowed to double-dip? And, set the cap at .040 and not .060? My truck runs fine with the plugs out-of-the-box, but I'll adjust them if this gives some benefit....
Double dip?

Gap the plugs at .040"
 

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Hey, that's my work LOL.
Just found it funny that you answered the question in two formats. Small world. I will check my gap soon.

View attachment 26856

..For Kidhauler, in the shop where I spotted it.

Gotta love the Forest Service Green firewall
SWEET! Hey, if that paint is still fresh, there might be time to get it all off and let that green back out...

Thanks, fellas.
 

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Discussion Starter #13
I know, right? Wish I had gotten to it before the dealer had it painted.

2COR, sorry, one last Q: You hinted earlier that the ignition control might be why I'm getting insufficient spark to fire the plugs at 0.06 gapping. Is that the module just upstream of the distributor? With the aluminum fins?

I'll go ahead and reduce the gap tp 0.04, but would like to know what the cause is, and get at it.
 

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This doesn't sound like anything that will respond to changing the plug gap to non standard specs.
Better keep looking for the root cause.
Do the plugs look fouled ?
What fouls plugs that quickly?
Oil in CC
or maybe coolant.
The plugs should look fouled.
No coolant loss?
Can those intake manifold gaskets fail in such a way that just oil is getting in the combustion chamber?
If your plugs are fouled- they are getting crapped up by oil, coolant or maybe too much fuel(but they would be really sooty)

Hey-that Suburban looks in very good shape.They paint all their engine bays that pastel green??
Lot to be said for just 40,000 miles!! Lucky guy.
Mine has 216,000 miles- I bought it with 195,000 miles-4 years ago.It has given me very good service-especially for a $2950 vehicle. Hard to beat used GM 1/2 3/4 ton SUVs for good reliable,cheap to repair versatile do anything vehicles.Decent hy mpg considering their capacity.
Charlie
 

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Discussion Starter #15
Plugs are wet, not fouled. Sorry, I should have been more clear. Its not firing.

No oil or coolant loss, fuel pressure is fine.

I am leaning toward the cause happening upstream of spark, because the misses (which are fixed but steadily get worse after cleaning plugs and contacts under the cap) began with non-stock E3 plugs.

I really like 2COR's theory about the coil having been fried with extra load due to weird E3 gap/configuration. If this is the case, then gapping the stock plugs down is only a bandaid.

Here is my question (2COR are you there?): Assuming the system is working too hard to generate spark, is the Ignition Control Module the part which I need to replace, or is there an actual coil upstream of that?

My only point of reference is my Evinrude 225 OB, and for this guy each cylinder has its own coil. I'm okay with replacing the parts, but my knowledge breaks down outside of the Haynes manual, and I cant see something that looks like an ignition coil.

Does anyone else share the opinion that decreasing the gap on your plugs can help weak firing? It certainly makes sense to me, but I'd rather fix the cause and not the problem.
 

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Beachamd
Thanks for the info.
So the plugs just aren't being fired- or aren't being fired at the right time, so they are soaked with unburned gasoline.
I seem to remember that these vehicles are prone to some sort of position sensor failing. Maybe a crank position sensor failing
I think they usually just die or run horribly or fail to start, but maybe it could happen the way yours is failing?
Not sure if this crank position failure means they will squirt in fuel at the wrong time? Or will try to ignite it at the wrong time.

I'm just guessing of course, and I don't think changing plugs, cap, wires would help- so maybe they are just some sort of red herring??
I think the 99 5.7 has just one coil. but coils rarely fail??
Maybe the coil is failing, and new plugs wires cap could conceal a failure??
Other than a failure of a position sensor- I got nothing.And the position sensor is just based on my having read that it is fairly common-and it is cheap and easy to replace.
Luck- keep us posted.
Charlie
 

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I have issue with the E3 discouragement, I personally have run E3's in both my 99 tahoe and my wife's 98 Suburban since we got them 4 years ago with no problems I had a similar issue with my tahoe a while back and there were actually 3 different issues at 3 different times that caused it. the first was my injectors plugging up which on the 96-99 5.7 litre vortec and before they were known to over time develop injector issues and the injector spider has to be replaced. my issue was a little more easily resolved. I ran Sea Foam through the power brake booster vacuum line and it cleared it up the first time. the second time it was my fuel pump going out on the truck and the problem only happened when i ran it with less than half a tank of fuel because there wasn't enough liquid in there to properly cool the pump. the 3rd time it was a spark plug that had fouled because of crappy gas that was evidently over loaded with ethanol burned off the gas from the fouled plug and put it back in ran what was left of that tank out put in some gas from a known good gas station and haven't had a problem since. The hardest fix was the fuel pump because the tank had to be dropped not fun.
 
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