98 running rough/doggy

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BeatUp98

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Just bought this 98 k1500 ext cab std bed z71 with the 5.7l. Guy said it needed a battery and starter to run and the exhaust was cut off just passed the manifold. So I have him $900 and went and bought a starter and battery and drove it home.

It's a beater for sure but I really want to fix one up and besides the rust in usual places it's not so terrible as others I've seen for sale for $2-3$k around here. 242k miles on the clock right now.

Now on to my questions. The truck idles and runs rough I know partly because of the O2 sensors and the way open manifolds make it sound. What else is probably contributing to the problem? I have service engine soon light on but won't be able to get codes pulled for another day or two. What sensors should I plan on replacing? I have no idea if this is the original motor.

Can someone give me a detailed list of tune up parts and numbers for it? I have a bag of receipts the kid I bought it off had and some misc. parts it's had done the past year I'll have to go through.

THE BIG problem. When I go middle to full throttle the truck dogs out and will try to rev up but just isn't putting out the power. My 89 has done something like this in the past and had a mechanic clean some sensors and fixed it. Would this be a sensor problem? DOES NOT feel or act like the transmission and the guy said it was rebuilt last year.

Also leaking oil from the valve cover so I'm going to get new gaskets there. Would I be well advised to go ahead and change out the knock sensors and intake manifold gasket while I'm doing this?
 

michael hurd

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First, you can't arbitrarily toss parts at something or take guesses as to what is wrong.

Without diagnosis, you are literally blind.

Imagine going to the doctor and telling him you have a headache, without any other information. It could literally be anything from lack of caffeine to a brain tumor.

Who knows why the exhaust was cut off, perhaps the catalytic converters were plugged, or it was someone's 'diagnosis' as to the problem.

You want someone to make you a list of part numbers for tune up? Use Google or the Rockauto catalog.
 

michael hurd

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As far as knock sensors, they are a piezo bending element that produces a voltage. Typically, they will outlast the vehicle they are installed in. Also, they must be tightened to a specific torque, in order to work properly.

No need to change something that most likely ain't broke.

As far as the intake gasket, sure you could change it. Until you do some diagnosis, is the engine worth the labor to change the intake gasket when you find out you have 50 psi compression in one cylinder and it's gobbling coolant?
 

dmogie

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I had a similar sounding RPM problem and a thorough cleaning inside and out of the TPI (entire intake area) did wonders. It was coated with years of crap, especially inside. I used GUNK brand but Seafoam and CRC are similar. Less than $10, eye protection, gloves, and a stiff toothbrush, about 30 minutes total time. Then I fired it up and ran it cold in low gear for about a mile- it looked like diesel exhaust! Runs "like new" and my mpg went up also. I have not changed plugs and wires in many thousands of miles, but that is always going to be a consideration for poor performance. If a clean out does nothing for you then I would suggest a professional computer analysis.
 

wheelman

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the engine and heads are great when right and or new-everything else on and around is some what crap-mind is a 1996 5.7 vortec they love their fuel pressure..check that- but they are all computer..check engine light.means it is throwing codes..i think autozone.would check them for you.if you could drive it to one..they love a factory cap and rotor-i tried -parts store one time.no good.buy factory.crab cap-i chenged the coil.0-2 sensors to go bad-pull them-if white tiped they are bad-but the code reader.should tell you all that is bad.the engine does have sensers -open exhaust with out a cat or cats.is going to throw a code-i would think..but you do not need muflers.to make it happy.mufflers are crap-cats last longer
 

BeatUp98

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My uncle came over and took a look with me and he thinks I have a combination of burnt spark plug wires and bad upstream o2 sensors. Looking down into the throttle body it looks pretty clean but I plan on cleaning it all when I do the tune up.

If I put new upstream o2 sensors in will they just burn again before I can get exhaust put on? I only have 1-2 feet of pipe coming off the manifolds.
 

mattbrat004

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I'd goto autozone or any parts store around and get spark plug wires and have them run the obd2 scanner. Chances are though it'll still run like dog crap until you get an exhaust. These engines need those oxygen sensors to change the a/f ratio. An honest exhaust shop could replace your exhaust system for around 350-450. I'd start there and roll with the punches after that. Throwing a single 02 sensor in at the manifold would only solve half the problem as you'd still be missing another.
 

SwampHound

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Start with the basics. Go get the codes pulled and get a plan together to complete the exhaust. With any used vehicle, it's a good idea to pull and clean the throttle body, clean the MAF, replace spark plugs, air filter, fuel filter and flush the coolant. All those things (aside from coolant) could help out with your issue, but like michael said, you're flying blind until you get the codes pulled. So start there and you'll get a better idea of what you're working with. For a tune up, cap, rotor, spark plugs, and plug wires are good start. Only use ACdelco ignition parts. That's what these trucks are made for. Stock plugs are fine, if you have a little more change, ACDelco rapid fire plugs are a decent "upgrade". But before you start buying anything, go get the codes pulled. That's the baseline. Any auto parts store will do it for free.
 

BeatUp98

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Okay guys have about half an update.

Tonight I changed spark plugs and wires, cap and rotor, pcv valve, new wix air filter, changed the at least year old black oil and added a can of sea form into it (going to change again in a few hundred miles). Replaced tailgate hinges and handle and got the tailgate 100% operational.

Started up the truck on the first try only cranked over maybe 2 or 3 times and took off! Hadn't been able to start it since I drove it home so I'm already feeling better about it. Tomorrow I have to go get some wrenches and floor dry then I'll be changing the fuel filter and attempting the upstream O2 sensors. They don't seem to be too corroded. However this leads me to a question for you guys. The drivers side spark plugs were pretty black while the passenger side looked like normal wear. Neither side had carbon desposits as I got some receipts with the truck showing new plugs and wires and an head gasket I'm assuming for the driver side. Would my driver side up stream o2 cause it to run rich if it is bad and thus the reason the spark plugs on that side were pretty fouled up? Hoping I can get some exhaust on it soon and new o2 sensors in and not have to worry about this problem again.


Cannot comment at this time how it runs or drives yet as it's 1am here and didn't want to piss off the neighbors with basically open headers. Only starts it for about 30 seconds to let the new oil circulate so I could check it. Hard to tell over the exhaust but it sounded like a healthy engine no knocks or ticks despite the driver side manifold haven't a couple broke bolts I assume with they changed out the head gasket. Will looking to change the coolant soon and will also clean the maf sensor tomorrow just to be sure it's okay.
 

jsnow36318

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Do a compression test. Having a weak cylinder will cause a lean miss. The computer will compensate by richening the whole bank.


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