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I apologize if this is in the wrong thread, 1998 CK prob

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ManiacalOffroad

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I am currently rebuilding my '85 K5, but right now my urgent problem has to do with my tow rig/daily driver. It's a 1998 GMC Sierra Z71. I live in MI, and have been on disability for 8 years so all of my home/vehicle repairs I have done myself, But I am ashamed to say that ECU's and sensors confound me. So I call upon the experience and knowledge of the mighty CK5 clan.

About 3 weeks ago my rig started missing and sputtering while accelerating through an intersection. It was almost as if it were running out of gas. The fuel pump is relatively new and it is not showing any of the typical sysmptoms of being faulty or soon to be faulty. Later that day I drove it short distance to my son's football practice and it ran great. On the way home I had to feather the gas to keep it moving through first gear, when it shifted the sputtering improved but was still noticable. It also sputters while in park and revving the motor. So I made changes that my wallet (the wife) approved such as:

- New plugs (stock AC Delco) gapped at .60
- New Fuel Filter (AC Delco)
- I put the factory Vortec air cleaner system back on
- New air filter and PCV valve.
- I also used STP throttle body cleaner on the TB.

after I put the factory Vortec air cleaner system back on it was considerably worse so I re-installed the K&N system and it is improved, but still there.

The motor is NOT a stock Vortec 350. It is a .357ci (.40 over) 350 Vortec motor with no other mods.

The trans is a 4L60E modified for flow, cooling and with a shift kit.

I'll list the changes that have been made since I bought the truck in 2000, Please keep in mind that everything Ran FINE for 6 years (since new motor and tranny) Up until 3 weeks ago.

Has no Cat. Converters. The exhaust pipes from where the cats were go from 2 1/4" to 2 1/2" all the way to the Flowmaster 40 series mufflers. Only 3" long tailpipes off of mufflers.

here's where some may cringe, But it has ran fine this way for 6 years. The O2 sensors on the exhaust pipes have been removed. Besides the motor running rich for a few seconds on cold morning startups (and check engine light) I have noticed no difference. Someone told me that with my increased compression that it will aid in performance (meaning helping the motor run correctly) I have no idea if this is true.

I am hoping for some advice as to where to look next Keeping in mind that the truck ran fine with all the above mentioned mods / changes. I never had a problem until 3 weeks ago.

Finally, The last thing I did to the truck before the problem started was I re-charged the K&N filter without incident. I have done this repeatedly through out the years and am confident that I did nothing unusual.

Sorry for such a long post, I just wanted to rely as much info as possible. Please help a fellow wheeler out, I can't finish the motor for my Blazer untill this truck is fixed. TYVM

-Jeff
 
Some times the K&N recharge oil will get onto the MAF sensor the one inline with the air intake and can cause it to act funny like you've stated best bet would be to get some MAF cleaner and try that also might wanna try unhooking the battery for a bit to let the codes clear.
 
George_Pimpdaddy said:
Some times the K&N recharge oil will get onto the MAF sensor the one inline with the air intake and can cause it to act funny like you've stated best bet would be to get some MAF cleaner and try that also might wanna try unhooking the battery for a bit to let the codes clear.
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Yesterday I unhooked the neg. for about 30 mins >< (wanted to be sure) same prob. The MAF does look dirty, but not clogged or damaged. I'll certainly try to get some MAF cleaner. ty
 
***Note. MufflerMan welded the Flowmasters together. I then learned that this is a no-no. My mufflers seem to be rattling internally, I wonder if the "baffles" (?) could be causing a restriction problem? Just an idea
 
How are the rotor, cap and wires. Any one of these could cause the symptoms you mention in your post. I also had an ignition wire short that caused me all sorts of trouble last year, and my K5 acted just like that.
Good Luck!
 
HeavyMetal72 said:
How are the rotor, cap and wires. Any one of these could cause the symptoms you mention in your post. I also had an ignition wire short that caused me all sorts of trouble last year, and my K5 acted just like that.
Good Luck!
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Cap rotor and wires were next on my list, But I have limited funds and figured I'd better start asking around before I get all the way down to buying new tires in an attempt to buy this problem away :D .. They are old and probably due. I appreciate your time :) I'll keep you posted
 
First thing i would do is clean the MAF as was already said, next i would check fuel pressure and see if it's within specs. I've heard on some vehicles a 1 lb difference (too low) is all that's required to have problems.
 
4X4HIGH said:
First thing i would do is clean the MAF as was already said, next i would check fuel pressure and see if it's within specs. I've heard on some vehicles a 1 lb difference (too low) is all that's required to have problems.
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I cleaned the MAF sensor with the proper cleaner and no change. Fuel pressure is within spec. I refuse to track every sensor on this thing. I am hurtin for cash so having a shop charge me $50 just to plug it in is out of the question. I am so fed up that I'm probably going to drop the fresh 454 form my bogger into it ><. Seriously though, I think I will pull this motor with it's ECU crap and drop a carb. 350 in it.

Besides the obvious reasons, I will never own a new 4wd truck. The big three keep adding electrical componants and cushy seats for Urban Cowboys and pushing the needs of true truck lovers to the wayside. I don't want GPS, I want a truck that can hit a mud puddle without shorting something out. I don't want a computer to tell my motor what the timing should be or what the mixture should be. I want that control. Ugh.

End of rant, sorry.
 
Take it to almost any major auto parts store, they'll scan it for free and tell you all the trouble codes and what they refer to. Then it's up to you to take it from there. It may not help but it certainly can't hurt.

If you have a multimeter you can measure all the plug wires for resistance to make sure you don't have an open one or something.
 
folkenheath said:
Take it to almost any major auto parts store, they'll scan it for free and tell you all the trouble codes and what they refer to. Then it's up to you to take it from there. It may not help but it certainly can't hurt.

If you have a multimeter you can measure all the plug wires for resistance to make sure you don't have an open one or something.
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like Autoaone? Ok, Maybe at least it will point me in the right direction. And I'll try the multimeter as well. I'm beginning to think that it's something silly that I did or forgot to do ><. I really appreciate everyone's input.
 
Don't be scared of the electronics. The mathematics that the controller does are not of any concern to you. All that matters is that the various sensors are delivering a reading within a certain specification (all of which are easily found online). You can test every sensor on that engine without anything more than a multimeter and a couple safety pins.

How did you check your fuel pressure?
 
ManiacalOffroad said:
Only 1 was removed. And it hasd run great for 3 years that way. My current problem is un-related.
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Well you did say you removed all of them.. if you just yanked the ones that monitor what comes out of the cats, but left the ones that control fuel mixture your okay.
 
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