Any GM mechanics out there?

Discussion in 'Wheels, Wings, Mud, and Water' started by HiFi in WYO, Nov 11, 2017.

  1. HiFi in WYO

    HiFi in WYO The universe is a big place, perhaps the biggest. Subscriber

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    Been chasing a rabbit down a hole with my wallet on my '97 Tahoe, 5.7, 150K miles.

    It started to run really roughly, missing and coughing even some backfiring through the exhaust. Finally threw a code - intermittent misfire in cylinder 2. Through work, I managed to score a service bulletin stating the spider injectors are a known problem on these.

    Things I have changed: New MAF sensor; fuel filter; new plugs (gapped at 60), wires, cap and rotor; new PCV valve and finally new spider injectors - what a chore that was! Also pressure tested the fuel system - it's running a constant 54-55 (It should be around 60 but I've read the pressure really doesn't start interfering until it dips below 50. Also, the pressure stays at 54-55 for over an hour before it drops, after the engine is shut off). Also a new coil. Thoroughly cleaned the throttle body while I had everything apart. Also the plastic intake had no noticeable cracks or other issues.

    It's running about 95 percent, but when taking off from a stop, it still coughs and sputters a bit - it's not always a smooth acceleration. This seems most pronounced when it's warm. When cold, it seems to run like a new truck. It isn't currently throwing any codes.

    I'm starting to run out of ideas, other than O2 sensors (no codes), distributor and fuel pump (still).

    What am I missing?
     
  2. Shadowdog

    Shadowdog Super Member

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    The converter could have gotten plugged or even the muffler! Seen 2 trucks this year with close to 100K miles where they both bucked under load & on hills & at first you would think H2O in the fuel or a trans problem, then bad coils on the Ford when it kept up, but it was the converter on a 09 Dodge 4.7 & muffler on a 02 Ford 4.6 .
     
  3. usedto

    usedto Lunatic Member

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    100% agreement.
     
  4. MannyE

    MannyE Exterminate! Subscriber

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    Go look for the Impala SS forum and ask the question on the engine forum. Those guys know the LT1 backwards and forwards.
     
  5. Shadowdog

    Shadowdog Super Member

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    I looked on the Forms for the Ford truck problem and they seemed to say mostly coils & that maybe one or 2 could go bad! Not yet anyway! The exhaust pipe rusted & broke before the muffler solving the problem as it then ran great!

    The Dodge is a friends where I said maybe do the cheap things first like make sure the fuel wasn't bad. Scan said converter from a dealer so he went to a independent shop for 1/3 price to get it done!
     
  6. spicer

    spicer Well-Known Member

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    I know from experience diagnosing many of those vehicles with that CPI system... central port injection.. and know from first hand experience that the fuel pressure must be right on spec to perform right. It is critical to a little poppet valve at the end of the little line from the central injection injector to the intake valve discharge port. The fuel pressure must be right on spec.... a scant couple of pounds less and it will make a difference. I am only talking about the GM CPI system in regard to critical fuel pressure, others are more forgiving.
     
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  7. Shadowdog

    Shadowdog Super Member

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    I was just thinking it must be something with the temp sensor as runs worse warm (maybe too rich as it still thinks it's still cold) , but I do barely remember reading something too about that fuel system being fussy! I think it's still TBI from what I remember!
     
  8. gadget73

    gadget73 junk junkie Subscriber

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    Did you use the revised spider or the original style? Revised has an actual real fuel injector at each cylinder, the original style is just the poppet thing. If it had wires running down each "leg", its the revised version. They're far less particular about the pressure.

    Have you ever checked the throttle position sensor? Off-idle hesitation sounds like a dead spot in the pot. Unmetered air (vacuum leaks) also are a big problem for these. I had problems with the S10 Blazer my mom used to have, someone had damaged the air intake pipe before she got it, and it had a crack where it connected to the throttle body. I also had problems with that on the twist-in vacuum line connections on the intake. There is an O ring in there, and when I took it apart to replace the spider the O ring was no good and it leaked when it went back together.
     
  9. Eric H

    Eric H AK Subscriber Subscriber

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    I second the throttle position sensor, it should set a code if it's bad but doesn't always. You can check it with a volt meter, voltage should rise and fall smoothly from closed throttle to wide open and back.
     
  10. HiFi in WYO

    HiFi in WYO The universe is a big place, perhaps the biggest. Subscriber

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    Thanks for the input. Forgot to add the TP sensor is also new (though it never threw any code) as is the muffler and exhaust, cat-back - but not the converter.

    Also as part of the GM recommended "fixes" was to first run a bunch of Techron through the fuel system - which I did - and then changed the fuel filter.

    The injectors are the new upgraded style which kind of threw me because I thought I ordered the wrong ones. All gaskets and O-rings with what I changed are new as well.
     
  11. HiFi in WYO

    HiFi in WYO The universe is a big place, perhaps the biggest. Subscriber

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    I had the coil issue on our '05 F-150 5.4. We thought the transmission was failing at 145K miles - but upon doing some research, I discovered a bad coil will make you think the tranny was failing. Replaced the coils with Accel coils - problem solved - and I'm getting another mile per gallon in mileage.
     
  12. quaddriver

    quaddriver 120 What's per channel Subscriber

    taking a break from framing some walls, I glanced at this thread....I dunno why a lot of ford stuff, the 1997 ford modular engine technologies in use are 2000% different from the vortec you should have. You *do not* in any ways shape or form have an LT1 (unless someone put one in) easiest way to tell is look at it, the LT1 and its early variants had the failure prone optispark on the nose...cant miss that from anything else.

    Research 'vortec', and determine what CPI style injector system it is using. the most common bane is the fuel supply line cracking and dumping raw gas into the intake or crankcase. that will produce 8mpg, horrible black smoke, a smell like a tanker truck wrecked, and codes galore, plus the cat will soon melt.

    Im a bit rusty on my early OBD2 today (like I said, I was framing a wall 5 minutes ago) but it has enough O2 sensors to tell you bank1/2 rich/lean. if it is throwing a P code for a single cylinder and ONLY that cylinder, eliminate ignition first (I do not think that year was CoP - coil on plug) and then look at fuel delivery. for it to know a single cylinder, then it is using the crank angle word to spot fluctuations in instantaneous RPM (dont be freaked out, ford had been doing this on EECIV for a decade earlier)

    I think the post on fuel pressure is one to look into.

    do you have an active data scan tool?
     
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  13. petehall347

    petehall347 the brandy coffee man

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    were all the plugs same colour on the ends that go into cylinders ?
    have you checked for vacuum leaks ?
    have you done a compression test on all cylinders ?
    is the electrical system voltage in tolerance when charging ?
     
  14. Eric H

    Eric H AK Subscriber Subscriber

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    When you installed the new injector spider did you make certain each one went to the correct cylinder?
     
  15. HiFi in WYO

    HiFi in WYO The universe is a big place, perhaps the biggest. Subscriber

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    Triple checked.
    Pete - plugs are fine, no odd fouling or any real fouling - they are new by about 3,000 miles. No noticeable vacuum leaks. No on compression test but that will happen Friday. Voltage is fine.

    So it's going to the GM dealer Friday. Done with it from my end. They're doing the deep scan/check on the engine. Hopefully they can provide an answer. So we shall see. In the meantime, I'll fire up the old Explorer and drive it. Say what you want about those little Mazda Explorers, but it's never messed up even at 182,000 miles.
     
  16. mkane

    mkane AK Subscriber Subscriber

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    distributor I'll bet. Pull the cap and I'll bet the bushings shot.
     
  17. petehall347

    petehall347 the brandy coffee man

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    dealers should have correct scanner for car . more in depth than any other scanners . good luck with it .
     
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  18. dosmalo

    dosmalo T-Totaled Subscriber

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    This is true IF they how to use it and know what they're doing.
    Unfortunately sometimes finding the right dealer for service is problematic.
     
  19. HiFi in WYO

    HiFi in WYO The universe is a big place, perhaps the biggest. Subscriber

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    True enough and as much as I hate to take it to any mechanic - other than me - and especially the Chevy dealer (mostly due to price), I'm hoping they'll do a good job and at least know how to do this. We shall see. At this point, it's going back into the garage so I may tinker a bit more with it before Friday.

    I will update you all on what the diagnosis is.
     
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  20. petehall347

    petehall347 the brandy coffee man

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    i guess being same cylinder miss its an air leak on manifold . valve clearances . or simple arcing down the plug hole . or possibly a bad connection at its coil if they are separate or bad connection at the injector wiring . live data should narrow it right down .
     

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