Random/multiple cylinder misfire

Silverado Brethern · #1 03-08-2005, 10:16 AM

I finally broke down and bought a new MAF due to the fact that i got 118 miles on my last tank of gas. that was the worst it had ever been, usually hovers around 10mpg. When i scanned it at autozone the MAF came up as well as a random/multiple cylinder misfire. I'm assuming due to the excessive amount of fuel that was being burned in the engine and that caused some plugs to foul or the distributor cap to burn up. either way the SES light is finally gone after about 12Kmiles. However the truck still sputters, misses, and the occasional back fire. So what i am asking are plugs/wires/dist. cap most likely my problem? Thats what im guessing and hoping cuz if its something serious inside the engine the truck is gonna be sittin for a long time. The plugs and wires were new at 100K but as the autozone guy told me if there is that much gas in the engine that it could have easily fouled one or more plugs and even fried wires and the dist cap.

Chevy-SS · #2 03-08-2005, 11:42 AM

I was having tons of problems with wires. Tried a new set and still had problems with cross-firing.

Here's a real easy test that won't cost you any money. Take the wires out of their seperators and move them as far away from each other as possible. Then try driving and see if that fixes it. I have left my brand new wires out of most of the holders to increase distance.

Also, another easy, no-cost check is to look under hood at night with engine running to look for arcing between wires and/or any metal engine parts.

If these tips don't work, I would take off cap and look very carefully for cracks, they are usually hard to see.

Have you checked the spark plugs? You didn't mention, but I would pull them all and look at them. If they look worn or fouled at all, then I would just buy a new set. They are short money, whereas gas ain't!!

Silverado Brethern · #3 03-08-2005, 12:42 PM

No i havent checked the plugs at all or the cap at all. But if im gonna even bother with takin the plugs out there no point in cleaning them or just putting them back in, i'll just buy new ones. I highly doubt the wires are bad. So what kinda plugs should i get? there all different kinds im seeing from 1.69-12.99 each. I think ill go for AC Delco O.E. platnums 6.00 each.

Austin8214 · #4 03-08-2005, 03:24 PM

also if your engine uses oil it does not hurt to get a bit hotter plug.

Chevy-SS · #5 03-08-2005, 03:56 PM

I didn't believe it coulda been my wires either, especially brand new ones, but you live and learn, and I am just trying to convey my experiences in the hopes that it will help you out.

If you think wires are good insulators, think again. Try this experiment sometime; take two brand new plug wires, plug one into the coil of your lawnmower, then take the other wire and hook it to the sparkplug. Now take the two wires and lay them side by side and start your mower. It will typically fire right off as if nothing was wrong!

Good luck

SpitAndDirt · #6 03-08-2005, 05:18 PM

Get back to basics. Check/Change your Fuel filter every 12K or 1yr. PCV Valve? Are your O2 sensors OK? Do you have enough fuel pressure? Have your intake gaskets been changed? Do you take long trips or short ones? Have you been using quality gas? Stick with O.E. Delco Platinum Plugs. Just don't use Autolite, Champion, or Splitfire, Bosch, Motorcrap, etc.

What were the codes you pulled from the computer? I don't doubt your SES light was on, but what else did it say. Could you have a leaking pressure regulator, or fuel injector? It's not like we can see them on our trucks(96-99). Do you know if the distributor has moved? Has Cam Retard/Offset been checked with a Scan Tool, not a cheap code reader? You just need to get in there, and know what you've got before you start assuming things. Clean your plugs, see if they are burnt up, not just dirty. Check your cap, we always get a burnt center electrode. You should be getting about 18-22 mpg if everything is running correctly. I get 20-24mpg hwy/12-15 city in my 96 Z71 All Stock, No lift, no gi-normous tires, not a leadfoot. Hope you solve your problem -Chris

localyokel · #7 03-08-2005, 09:21 PM

Hi,I have experienced similar troubles 1st it was the dist cap it barely ran at all got bad real quick like.The other was bad plug wires.I've found that aftermarket plug wires SSSUCK!!!If you happened to of kept your original packard wires stick em back on there,otherwise get ya some ac delcos or go to dealer and get the last set you will ever have to buy for this truck.

bad68chev · #8 03-08-2005, 10:40 PM

factory wires or MSD wires are your best bet. i like the MSD wires because the wire isnt "folded" over and crimped making a very short distance for it to arc out the back of your boot. The MSD wires have the core wire go straight ahead and are crimped seperately...have a very long distance to go for it to short out. The cheap autozone wires I had on only lasted about 20,000 miles before they started misfiring. Factory are usually good for about 60k and the MSD wires are suppose to be good for longer than that.

bad68chev · #9 03-08-2005, 10:41 PM

MSD or Accell make the best cap and rotor, and as far as plugs go i would stick to whatever came stock in your truck...AC delco..not sure if yours came with platinum or regular.

bad68chev · #10 03-08-2005, 10:44 PM

One more thing, An easy way to test your wires is to get a spray bottle of water and spray the wires down, dont go overkill with water, just mist them. If they are leaking the misfire will usually show up with the water.

Silverado Brethern · #11 03-09-2005, 01:50 PM

Just went to napa and bought a new cap and rotor, figured i'd try that first since they have never been changed, put them on and the truck runs worse if anything. Under full throttle its fine but when you let off the pedal or accelerate moderatley is chugs and misses terribly. I think im goin to replace all the plugs and then see what happens. The wires are replacements, so im not sure what kind just what ever napa sells as replacement wires and they and the plugs are less than 15K old but ill try spraying the wires anyway even tho i highly doubt it's the wires thats causing the problem. So my only question is if its not the plugs...then what? i think if the plugs dont clear the problem up i will stop driving it in case that will cause further damage to the engine.

Silverado Brethern · #12 03-09-2005, 07:33 PM

Well...the old gal is hurtin bad and being taken to the doctor. did all of everything simple and still the same result. Sounds and feels as tho its running on 6 cylinders at most. Possible a worn cam shaft and possible just about anything else. Nothing to do with the ignition, fuel, vacuum systems has effected the problem at all so i will be taking it to a mechanic and let them solve the problem. the guy im taking it to is a good mech. once he gets to work on something so depending on how busy they are it could be a few weeks til its done but whenever i get it back ill post a new thread and let you guys know what the issue was.

kevin.g · #13 12-12-2005, 06:13 PM

Quote:

Originally Posted by Silverado Brethern

Well...the old gal is hurtin bad and being taken to the doctor. did all of everything simple and still the same result. Sounds and feels as tho its running on 6 cylinders at most. Possible a worn cam shaft and possible just about anything else. Nothing to do with the ignition, fuel, vacuum systems has effected the problem at all so i will be taking it to a mechanic and let them solve the problem. the guy im taking it to is a good mech. once he gets to work on something so depending on how busy they are it could be a few weeks til its done but whenever i get it back ill post a new thread and let you guys know what the issue was.

so what happened. Im having the same problem with muli. misfire

Bubba1855 · #14 12-13-2005, 06:29 PM

I have had misfire problems in the past on my 98, 5.7L, mostly after accelerating real hard and then backing off or when the truck was under load. I talked to a Chevy dealer mechanic and he said it was from carbon build up on the valves. He told me to run automatic transmission fluid in the gas for a couple of tanks and then run chevron fuel injector cleaner in the gas for a couple of tanks. He said the transmission fluid has a large amount of detergent in it and will clean the carbon out of the engine and the fuel injector just gets the injectors clean. This clears up the problem for a while. It keeps coming back, but I just run the transmission fluid and fuel cleaner through and it will clear it up for a while. (usually about 8,000 - 10,000 miles). That may be worth a try.

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