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Chevy engine rebuild

Discussion in 'Chevy Trucks' started by KSlandscaper, Oct 17, 2006.

  1. KSlandscaper

    KSlandscaper Member
    from Kansas
    Messages: 60

    I had just a rebuilt 350 engine installed in my 94 Chevy k2500. The mechanic said the LH exhaust manifold was warped. They eventually where able to install it, but they couldn't tighten the center as it should be....apparently there is a gap? I also had the tranny flushed, inspected, and filled while it was in the shop.

    I drove it home, drives good, but it idles in D rather poorly (I think). Idling in neutral is fine. Also there is excessive exhaust noise coming from the gap(?), but figures anyhow. (I already have a new manifold on order which I'll install myself) Prior to the engine replacement the truck didn't run this way........

    My question is, would this rough idling in Drive be attributed to the manifold somehow? Is this common when dropping a rebuilt engine into an old truck? The truck does have 144k miles BTW.

    Any enlightenment would be greatly appreciated!
     
  2. jbone

    jbone Senior Member
    Messages: 154

    I dont see why they didnt contact you prior to attaching it and installing it. A simple phone call and they could have ordered you a new one. I cant believe a shop would put a warped exhaust mainfild on the truck and let it leave the shop like that unless the owner wanted it that way.
     
  3. KSlandscaper

    KSlandscaper Member
    from Kansas
    Messages: 60

    I'm somewhat puzzled as well...

    I took a lonk and it appears all they did was unbolt the manifold from the engine block, and not from the exhaust pipes. I spose they would have had to charge extra labor if they did it the other way around? It's probably best if I just replace it myself anyhow. My only hope is the warped manifold is the main cause of the crappy idling problem!
     
  4. jbone

    jbone Senior Member
    Messages: 154

    I have a 94' k2500 w/ the 350 also. I have a book for it from haynes ill take a look and see what it says could be the reason for crappy idle.
     
  5. derekbroerse

    derekbroerse 2000 Club Member
    Messages: 2,377

    Is the oxygen sensor on that side? If it is, and there is a gap, it could be drawing in external oxygen and confusing the computer, which will think the engine is running lean and dump in more fuel...
     
  6. KSlandscaper

    KSlandscaper Member
    from Kansas
    Messages: 60

    There was an oxygen sensor on that side. However, the wire had been cut??? The oxygen sensor now is nothing more than a plug. Further down the exhaust line there is another O2 sensor which I would guess is still functional?

    I installed the manifold tonight, nothing is different, other than the truck is quieter.

    Still has the rough idle, but overall the engine feels like one of the cylinders isn't firing???? I could replace the plugs, wires, rotor, ect, to see what that'd do. But I'm thinking about just driving the truck back to the mechanic to tell him it's running like crap.... :realmad:
     
  7. jbone

    jbone Senior Member
    Messages: 154

    def bring it back if you paid to have them rebuild it and somethings wrong its on them. have them replace your 02 sensor since they apparently cut it.
     
  8. joe b

    joe b Junior Member
    Messages: 23

    Bring the truck back!
    If you start trouble shooting yourself The shop can say you messed it up and not cover their mistake. Let them find it . But, ask about the cut plug.
     
  9. scottL

    scottL PlowSite.com Addict
    Messages: 1,600


    If the truck still is computer controlled then it is expecting all of the o2 sensors to be functioning. This could easly explain a bad idle, performance and gas mileage after the truck hits operating temperature.
     
  10. terrapro

    terrapro PlowSite Veteran
    from MI
    Messages: 3,873

    definately take it back if the o2 sensor is cut. i see that as they rebuilt the engine installed it and couldnt get it to run good so they figured they would cut the o2 to hopefully make a difference but it didnt...id be pissed. also the manifold being warped is bad for the engine because in the process of suck in air/fuel then combust then exaust your engine is letting in extra unregulated air into the cylinder during the exaust step which messes with the air fuel ratio. which would be even worse if the o2 sensor was hooked up because it would be dumping extra gas into the cylinder to make up for the extra registered air. which in turn supports my theory of why they cut the o2 sensor....so now that you have replaced the warped manifold the o2 sensor should work properly

    did i lose anyone on that:dizzy:
     
  11. KSlandscaper

    KSlandscaper Member
    from Kansas
    Messages: 60

    I believe the O2 sensor was cut long long ago...as the exposed wire is no longer 'shiny'. I highly doubt the shop had anything to do with the O2 sensor.

    BTW: I can't seem to locate where this cut O2 sensor plugs into......anyone know the general location? This would be the O2 sensor on the LH manifold.
     
    Last edited: Oct 22, 2006
  12. terrapro

    terrapro PlowSite Veteran
    from MI
    Messages: 3,873

    that year is a vortech 350 right, its not still TBI is it. either way it should run to the comp box
     
  13. derekbroerse

    derekbroerse 2000 Club Member
    Messages: 2,377

    A '94 is still TBI.

    This second O2 sensor downstream--is it plugged into the harness? How far downstream is it?

    Maybe the manifold was changed years ago with one that didn't match and they just left an old O2 sensor in to block off an unneeded port rather than find a pipe plug.

    But you need A working O2 sensor.
     
  14. KSlandscaper

    KSlandscaper Member
    from Kansas
    Messages: 60

    That is what I am thinking. I really wouldn't know. I looked and looked and cannot seem to find the harness for the sensor to plug into. If this O2 sensor isn't supposed to be there, then the truck only has the one other sensor which is located much further down on the exhaust pipe...(bout underneath the cab?). I checked it and yes it is plugged into the harness; however it's rusty as all get out; I highly doubt it works correctly anymore.

    I plan to take the truck back to the shop as is tomorrow or possibly later today. The less I mess with it now, the better.

    I'll keep yall informed.
     
  15. KSlandscaper

    KSlandscaper Member
    from Kansas
    Messages: 60

    I called the shop and told them of the problem. All I got in response was basically, "It takes 500 miles to break the engine in". He did say when I went to pick the truck up last week to bring the truck in at 500 miles to have the oil changed.....but failed to mention it might run ruff for awhile. The ironic thing is I asked how I should break the engine in, if I should be easy on it for awhile when I went to pick it up. He said it was good to go; that I could push it hard if I wanted to right away.(????)

    I also asked about the 02 sensor. He said they also looked to see where it'd plug in, but couldn't find anything.

    I spose I'll go ahead and replace the "lone" O2 sensor (as it probably needs it anyhow).

    Stay tuned?
     
    Last edited: Oct 23, 2006
  16. derekbroerse

    derekbroerse 2000 Club Member
    Messages: 2,377

    A new engine should not run rough just because it needs to be broken in... thats a load of crap.
     
  17. KSlandscaper

    KSlandscaper Member
    from Kansas
    Messages: 60

    Yeah, my thoughts as well. But that's all we wanted to say.

    Overall it does run smooth. If I leave the truck in neutral or park and push on the gas the engine does run smooth. The problem is when you shift into any 'drive' gear the engine starts to run a little ruff. It's probably not as bad as I make it sound. My whole problem is that it did not run this way before the engine replacement. I told him all this and all he said is what I already told ya guys.

    Could this be something attributed to the tranny? I did have them flush and fill the tranny afterall. It's almost as if the engine rpms will surge every so often (only for a a brief second) when in gear. Could something be slipping?? In P or N it won't do this.

    I hate mechanical issues. :angry:
     
    Last edited: Oct 23, 2006
  18. jcesar

    jcesar Senior Member
    from Mi
    Messages: 492

    Tranny doesnt have anything to do with the engine running rough. Other than the fact that in gear, it is "under a load" . But I will say this. I have a 96 with a 350 vortec in it. Got 4 o2 sensors in the exhaust. Had a cracked manifold on the right side, and it ran very poor. At an idle. definately replace the manifold, and the o2 sensor. I am willing to bet that this will fix the problem. If not, go to the shop that put in the engine, and have them fix it! After all, If your engine is new, then why does it run rough? Break in? Never had that happen in approximately 20 engine break ins!
     
  19. KSlandscaper

    KSlandscaper Member
    from Kansas
    Messages: 60

    Mystery solved!

    Ok...I was somewhat pizzed at the shop for just saying "it takes 500 miles to break in the engine." I'd be damned if that was why it ran like crap.

    I'm proud to say it runs perfect now, thanks to myself.

    I strolled down to the auto parts store and bought a slew of parts.

    • Spark plugs
    • Plug wires
    • Distributor
    • Rotor
    • O2 sensor

    I began with replacing the O2 sensor, distributor, and rotor. Test drove it and nothing...it ran the same.

    Then I replaced the wires and spark plugs.....WOW...it runs perfect! All along I suspected the problem was attributed to the plugs and/or wires in some way. What threw me off was that I had just replaced both this past winter and had only drove the truck no more than 3k miles! I believe the shop had somehow damaged the wires during tear-down or installation?(as some of the plugs did not fit snugly on the terminals) Also, some of the old plugs had horrible gapping!

    I asked the parts store the number of O2 sensors which are listed for the truck....just 1! So apparently I'm fine there as well?

    Oh well, all is good now. Thanks all for your help and patience!!! :drinkup:

    BTW: all parts came in right at $100. Damn....I love owning Chevys!
     
  20. RJ lindblom

    RJ lindblom Senior Member
    Messages: 346

    Why didn't the shop replace all the ignition parts, why would it have left the shop running rough? Its a good way to loose a customer and his friends. 500 miles of rough running engine, BS. Did this shop do the rebuild? Or the buy a re-man engine?