Need Help With Check Engine LIght

Jaystahoe said:

I have a 99 tahoe LT , Truck has a slight miss at an idle in cylinders 3&4,As soon as you get above 1000 rpms the truck is fine it's not bucking,or missing causing it to run like crap when driving it down the road, i have replaced the o2 sensor that was bad ,and egr valve gasket with the new updated gasket w/ screen, Me and a couple of my techs are thinking Metering body assy, Does not have any intake leaks also tested for that last week, Is there anything else it could be just wondering this is my first chevy SUV

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Check to make sure that all the plug wires are snaped on tight. I had this problem and is was a loose plug wire. Not so loose it fell off the boot, but loose enough to give it a skip at low idle.

Pull the boot up the wire and put the little snap collar on the plug then push the boot down. That way you are sure it is seated right.

ok i'll give that a shot , oh yeah i also did the cap,rotor,plugs and wires

84fiero123 said:

Check to make sure that all the plug wires are snaped on tight. I had this problem and is was a loose plug wire. Not so loose it fell off the boot, but loose enough to give it a skip at low idle.

Pull the boot up the wire and put the little snap collar on the plug then push the boot down. That way you are sure it is seated right.

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My exact thought....becuase I had the same problem once....The spark was jumping the gap in the plug wire first......I found it when it dicolored the plug wire cap....

Try it it will not hurt....

Good Thread / Info

I bought a '98 K2500 7.4L Burb at an auction for $4k a few weeks ago that had been mechanically neglected for most of it's 110k life and I'm in the process of slowly-but-surely getting it back into fighting shape...

One of the first things was to replace plugs and wires. But since, I have had a random misfire... My diagnostic software is aftermarket and doesn't isolate cylinders, but is showing a pending DTC "random misfire" I have reseated the wires and still happening... Funny, it didn't misfire with the old worn plugs and wires :lol: Too bad I threw them away...

Wait until dark and open the hood while its running, a lot of times you'll see the spark jumping.
I diagnosed a friends Chevy truck for this problem a few weeks ago without lifting the hood. The arc was so bright you could see it in the reflection of a puddle of rainwater under the truck.

HDDP said:

I bought a '98 K2500 7.4L Burb at an auction for $4k a few weeks ago that had been mechanically neglected for most of it's 110k life and I'm in the process of slowly-but-surely getting it back into fighting shape...

One of the first things was to replace plugs and wires. But since, I have had a random misfire... My diagnostic software is aftermarket and doesn't isolate cylinders, but is showing a pending DTC "random misfire" I have reseated the wires and still happening... Funny, it didn't misfire with the old worn plugs and wires :lol: Too bad I threw them away...

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You could have the same problem, or a defective plug or wire.

A spark tester can be put in between the individual plugs, at the plug and the cap. It could help you track down where the problem is. They have a window in them that shows the spark, are adjustable for the size of the gap too so you can get one, and use it on any vehicle.

Could also be a defective cap or rotor. Check the cap and rotor first.

My wife's Burban had a problem with running rough and jumpy at low RPM's and I tried new plugs and wires, even a fuel filter and still acted the same so I took it to dealer and they found a bad coil pack.

84fiero123 said:

You could have the same problem, or a defective plug or wire.

A spark tester can be put in between the individual plugs, at the plug and the cap. It could help you track down where the problem is. They have a window in them that shows the spark, are adjustable for the size of the gap too so you can get one, and use it on any vehicle.

Could also be a defective cap or rotor. Check the cap and rotor first.

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Thank you for your expertise... This truck is going to take quite a bit of TLC to get it back to where it should be... I will spend much time picking the grey matter of the wonderful forum members here...

Funny thing is that I purchased this suburban to tow my race car to the track... now it's become a pet project to get into perfect operating condition... And taking more time than my race car...

Since I can't upload large files to this site, http://www.cardomain.com/ride/2487495 And a video from some recent testing...http://www.youtube.com/watch?v=UesITJixtsk :great:

I forgot all about that, coil packs. Does this year have a distributor or a coil pack?

The spark plug tester can be used on the coil packs to. I took a fuel injection course a few years ago at the local high school for adults and the guy was like me.

LOW TECH RULES.

And gave us all sorts of handy little tricks to test high tech electronic ignition and fuel injection systems.

The nice thing about the spark plug tester is you can use them in line so you can run the vehicle while testing.

He used 8 on a coil pack to show us how to find an intermittent spark loss. But also said it can be done with just one.

84fiero123 said:

I forgot all about that, coil packs. Does this year have a distributor or a coil pack?

The spark plug tester can be used on the coil packs to. I took a fuel injection course a few years ago at the local high school for adults and the guy was like me.

LOW TECH RULES.

And gave us all sorts of handy little tricks to test high tech electronic ignition and fuel injection systems.

The nice thing about the spark plug tester is you can use them in line so you can run the vehicle while testing.

He used 8 on a coil pack to show us how to find an intermittent spark loss. But also said it can be done with just one.

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Yes it does have a coil pack stuffed up above the distributor cap... thanks for the thought... Perhaps I'll try that next...

Still can't find the MAP sensor described in the ALLDATADIY graphic...

ok here is were i'm at with my tahoe went out to fire it up one morning and it died, wouldnt start back up ,bought a new air filter,fuel filter and mass air flow sensor just to find out my fuel filter was plugged like a toliet at a fat mans house after a meal, this plugged filter burnt out my fuel pump so i had to replace that on my back in the parking lot of my apartment complex, after all this stuff i STILL have a cylinder 4 misfire detected !!!!!!i'm about ready to get rid of this truck and go back to my ford's i've dumped more money into this truck in the past month then i have in my 96 crown vic interceptor the whole 1yr and half i owned. BTW has anyone here shopped at www.gmpartsclub.com before?