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  • Question : Where to begin

    Hey there everyone! I am new to the LQ1 community, but I am picking up pretty quickly! I have learned a LOT from the posts on this forum, so kudos to everyone who submits their 2 cents and invaluable information.

    I have several issues going on with my '94 Z34, and pretty much I am looking for opinions on where to start. I bought the car about 3 months ago, not knowing anything about it, just knowing that it was a Chevy, and I wanted an American car becuase I was tired of having to track down expensive parts from dealerships for imports. I thought an older Chevy would be fun to work on - as was my previous 3 1967 Chevelles. ** Scratch to the head ** Not even remotely as fun to work on! lol

    Performance: To begin, the car has 138,000, unknown to when last timing belt was changed. Idle is slightly high in Park, drops about 200 RPM with a distinct *thud* when engaged into any drive gear. Once in gear and a forward motion begins, it feels as if the car has about 112 to 120 HP (I gauge that by the known HP of my previous import car - the Z did not have any get up and go). The supposed 7 - 8 second 0-60 time is in reality about 35 -40 seconds for me. Once up to about 50-55, the shimmy and shakes, but not always. If I have about 25% throttle at the foot, the shimmy and shakes are very noticeable. If I have 75-100% throttle at the foot at those speeds, the shimmy's downgrade a bit. At 50% throttle, i.e. going up slight hill while maintaining speed, the shimmy shakes aggressively re-appear. If I take my foot off the gas, let RPM drop to 1200 or so, put foot back on gas, throttle climbs back to 2000 or so, almost immediately, and i get a break from the shimmy's for a few seconds.

    Problems I have found: Timing belt... I took the covers off, found the ends of the teeth are separating from the belt itself. I can bend the tooth down and away, maybe a good 1/8 - 1/4 inwards, towards the centerline of the belt. I don't think that is good. ** Might be throwing my timing off, want to replace it ASAP **

    Fuel Filter - took it off, turned it upside down, brown dirty fuel dripped out. Obvious that it was in dire need to be replaced. Did it.

    Plugs - pulled front 3 out, all 3 were different plugs - NGK, Bosch, and Autolite. Mistakenly replaced with 6 Bosch plugs... I know I have read many places on here to get them out of there. I plan on it. Also, replaced the wires with a set from Autozone - I am going to stick with the Taylors that I have read about on here. Also had quite a bit of oil on a few of the old plugs. Excessive oil on at least one. Think that is worn valve guides?

    Smoke - Right above the front exhaust manifold, I have oil burning off. I understand the heads need to come off to access the O-Ring on the Oil Pump Drive, but haven't done that. It doesn't seem to be leaking out of there - currently I have the LIM and UIM off, to troubleshoot the oil leak. Does the Oil Pump Drive thingy move during engine operation? It freely spins, and lifts up to the little bracket that holds it down. Can I use a gasket sealant and just seal around the little disc top?

    Intake - Troubleshooting steps involved spending my day taking off my manifolds. I found two cracks in the upper intake plenum - guessing that added to my poor performance. I also found 3 vacuum hoses, with the 90* elbows cracking. The hose at the rear underside of the plenum, goes over to the brake booster (possibly) very spongey. Looking at the heads with both intakes off, the coolant passages are almost closed off due to chunky crystalized crap. I scraped some off, and noticed that there are deposits all throughout the cooling system - every hose I took off had crap in it. The inside of the plenum, even tho its cracked and needs replaced, was completely covered in a lot of carbon buildup, looking into the heads i see almost no clean metal - cabon buildup on everything! Valves, walls, everything just looks all built up and gunked up.

    Body and interior - was owned by an older lady, so a few slightly visible scratches, but very good paint, good pinstriping, good glass, beautiful interior with slight color degradation due to sunlight - all in all looks really really good. Good enough that I think it is with the hours and dollars to get it running to as near perfect as I can.

    So, after that essay - does anyone have any words of encouragement for me? lol

    Thanks!

  • #2
    Start with replacing that belt, it usually isn't the end of the world if it breaks but might as well not wait for that to happen and from what you described it sounds like it is going to happen soon. There is a write-up on the site. If you have some decent wrench skills it is rather simple (does have a bad rap for being tough) to do and the specialty tools you can buy, borrow, or MAKE relatively easily.

    Change all 6 plugs with a known good brand, like AC Delco. If the wires are in questionable condition now is a good time for them too. Sounds like your dist plug o-ring may be okay but the cam cover gaskets leaking, which are easy to replace. Once you have the upper/lower intakes off you should be able to see clearly whether the o-ring is leaking or not. If the intake manifold is cracked you should replace it: car-part.com, a member here, or ebay might be the cheapest places to find one.

    Once you have a new belt, timing hardware, spark plugs, and repair those vacuum leaks it should run a whole lot better. For a do-it-yourself job I'd say you are looking at around $300 to get it running right - check out rockauto.com for the timing belt stuff, I think they even sell it in 'kit' form which should include the belt, tensioner actuator, tensioner pulley, idler pullies and maybe even new bolts.

    Oh, and welcome to the site.
    1991 Grand Prix GTP LX9swap/Getrag 284 --- SOLD =(
    1994 Corvette
    LT1/ZF6
    2006 Dodge Dakota 4x4
    3.7/42RLE

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    • #3
      welcome to the site. you'll find at least two other devildogs posting on a regular basis.

      serious issues: MAF + multiple vacuum leaks = FUBAR!
      those need fixed BADLY, which is probably why it runs horribly since the a/f ratio is going to be WAY off...

      timing belt also important, and just follow jmgtp said for the rest, i won't rehash it since it would be entirely unecessary
      1995 Monte Carlo LS 3100, 4T60E...for now, future plans include driving it until the wheels fall off!
      Latest nAst1 files here!
      Need a wiring diagram for any GM car or truck from 82-06(and 07-08 cars)? PM me!

      Comment


      • #4
        Welcome Home....

        Photos? If you have a bunch...visit www.photobucket.com and sign up for free (it helps to use the nick-id you have here when you set up your new PB account). That way you can post the lot of them...and when you want to refer to anything as your project progresses and you add new albums of images along the way ...you'll just have to drop the link in your next post...and then we can all see the story...in pictures...

        Comment


        • #5
          I agree with everyone so far,

          Make sure that you check the basics, Like the compression, if you have steady engine vacuum, fuel pressure, engine codes, etc.

          In MOST cases I've seen, people have good 3.4 dohc's but there out of time (need the belt changed), need a complete tune up, vacuum leaks fixed, etc.

          If a person is careful, like mentioned, some tune up items can be bought on E-bay.
          1991 Grand Prix STE
          3.4 DOHC
          1 of 792 Produced
          Extensive Mods Done

          1991 Lumina Z34
          3.4 DOHC
          Getrag 284 5spd
          1 of 30
          Canadian Z34 Models Made with the Getrag 5spd Wahoooo!

          1980 GMC Sierra Classic C25 With 18,000 ORIGINAL MILES!!!!

          sigpic

          Comment


          • #6
            Re-read the original post and thought I'd add a few things.

            Your valve guides are probably not the culprit for the oily spark plugs, that is likely the o-rings that seal the cam cover from the spark plug tubes. They will be included with a cam cover gasket set. When you pull the spark plug wires off are the ends of the rubber boot oily as well? If so, almost definetly an o-ring issue.

            The carbon in the intake and on intake valves is normal, thats from the egr.

            In my experience the distributor plug should not be loose when bolted down, I have not seen one that has any kind of freeplay. I think you may have a problem there. Many have used jb weld, rtv or other sealants to stop it from leaking. I would consider that a temporary solution and not a permanent fix. I was lucky and mine never leaked a drop. I still replaced it when I had the heads off though. The o-ring that had been there for the past 18 years had dried and hardened into what felt like a hard plastic and was so brittle that it literally snapped off the drive when I tried to remove it. The updated o-ring is brown in color.
            1991 Grand Prix GTP LX9swap/Getrag 284 --- SOLD =(
            1994 Corvette
            LT1/ZF6
            2006 Dodge Dakota 4x4
            3.7/42RLE

            Comment


            • #7
              Something that could be leaking too that sometimes gets mistaken as solely a distibutor oil leak is the oil distribution cover under the lower intake. I've seen many of those leaking, especially when the engine is cold.

              IF you replace that gasket, make sure that if you are using any type of RTV that you only use it around the outside edge of the gasket and DON'T USE TOO MUCH, because you can plug up the oil vains and the anit-drain back valve.
              1991 Grand Prix STE
              3.4 DOHC
              1 of 792 Produced
              Extensive Mods Done

              1991 Lumina Z34
              3.4 DOHC
              Getrag 284 5spd
              1 of 30
              Canadian Z34 Models Made with the Getrag 5spd Wahoooo!

              1980 GMC Sierra Classic C25 With 18,000 ORIGINAL MILES!!!!

              sigpic

              Comment


              • #8
                the DOHC uses both a timing belt on the overhead cams, and a
                standard timing chain behind the front cover- with age, the timing
                chain will stretch about 4 to 6 crank degrees- even though the belt is
                NEW and replaced. Don't simply mark the cams and put a new belt on,
                where the old one was. That will put the cams BEHIND (retarded) in
                timing, due to the timing chain stretch. (you only changed the belt,
                not the chain). Make sure you lock the cams, unbolt the timing
                sprockets (use a stout 6-point impact socket and breaker bar, to get
                the cam cog bolts loose)- and retime the cams to the crank. When you
                do this, make up for the timing chain stretch, by rotating the crank
                forward to take the play out, aligning the balancer mark with arrow on
                timing cover, THEN locking the cams in place. My timing chain had
                about 4 degrees of slop, when I retimed it.

                It's a lot easier to time these engines, with the inner fenderwell
                plastic cover and right wheel removed, and a hole cut in the inner
                fender so you can see the timing marks. This way, you won't have to
                remove all the front engine accessories and belt, to see the marks-
                and you can look at the marks "straight on", instead of at an oblique
                angle from the top. You can cut the sight hole in the inner fender
                with a hole saw, or sawzall.

                Use BOSCH 4-tip platinum plugs- I have put 55,000 miles on a set of
                these plugs, and I could have left them in and run it another 50,000-
                but changed them for good measure. They really work- require no
                gapping- and they don't foul. They are pricey, $5-7 per plug, but
                well worth it in maintenance time saved. ac delco are crap.

                Use synthetic oil- I use mobil 1.. 10-30 or 10-40, this will extend
                your oil change intervals to 6000 kms, with oil filter change at
                6000 kms to, and add oil in between for what you may use/burn off.

                Use a K&N lifetime air filter, so far I have 110000kms on one of
                those filters as well.

                Oil leaks- if your DOHC 3.4 gets up in mileage, over 300000kms,
                it would pay to have the top end of the engine removed and gaskets
                replaced, Replace cam carrier gaskets, cam seals, head gaskets,
                intake upper/lower gaskets, oil distribution block gasket (between
                heads in valley, like a valley cover), and also replace the oil pump
                drive plug O-ring. Under the oil pump drive plug itself, place a GM
                Chevy distributor gasket, for good measure. Some of these DOHC
                engines have oil cooler lines near the oil filter adapter (my 1995 did
                not)- replace the lines and oil filter adapter gaskets, and your DOHC
                engine will be leak-free.

                Use synthetic oil in the automatic transmission. i just bought a 93 lumina z34
                with 137000kms near mint. this is my third z34, keep that dohc motor in shape
                and it will take care of you.
                Last edited by iroczz34; 08-15-2009, 12:20 AM. Reason: spelling error

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