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Running rich, hesitant, bad gas milage 9-10 mpg Crappy!

Discussion in 'Chevy C/K Truck Forum' started by mxrick55555, Jul 25, 2010.

  1. mxrick55555

    mxrick55555 New Member

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    Hello I have a 1995 Chevy K1500 5.7L TBI truck 172k miles 6" Procomp lift 35" Nitto tires on 20" rims stock gearing auto transmission, I have been trying to fix this issue for a while now with the help of my Haynes Manual and surfing tons of online forums but cant seem to pin point the problem. Hoping some on here can help.

    I have a couple problems that I think may all be related, first is when i start the truck it turns over like 4 to 5 times before it finally fires up, second is the idle when started cold the engine will run at about 1000 rpm's and once it reaches operating temp about 195* it idles down around 6-700 rpm's. If i put it into gear the idle drops even lower to between 5 and 600 rpm's. Also with it in gear if I switch the ac on or turn the steering wheel the idle drops to 4-500 rpm's. The book says that when placed into gear and or ac is turned on the idle should stay the same or idle a bit higher if the IAC is working so i pulled the IAC and tested it with an ohm meter the book says testing between terminal A-b and C-D that the ohms should be between 40 to 80 ohms when I tested mine it was about 55 ohms so that checked out ok, I read online some where that you can hook a 9 volt battery up to the terminals and the little pintle should move back and forth so I tried this and it would just twitch a bit and I was unable to move it at all by hand so I replaced the IAC but It didn't fix anything the Idle actually seems lower now, and When I went for a test drive made a quick 180 turn and gunned it a little because a car was coming and the truck almost died.

    The truck seems to run on the rich side if I stand behind the truck with it idling the exhaust burns my eyes and nose, and when I changed the spark plugs a couple days ago the old ones were covered in black soot and carbon.

    The truck also has a bit of a stumble when taking off from a stop, If I ease into the throttle it starts of a little hesitant and almost acts like I let off the peddle for a split second then the power steadies out but still seems like the motor isn't giving its all.
    I used to have a 91 Chevy C1500 with a 5.7 Tbi and if i put my foot in it at a dead stop it would light the tires up but this truck... nothing, Maybe its the extra weight of the 4x4 or the 35" tires or both but I feel like this truck should have a bit more omph.

    I have replaced to following:
    IAC valve, TPS, CTS, THERMOSTAT 195*, FUEL FILTER, PCV VALVE, O2 SENSOR, EGR VACUUM SOLENOID, AUTOLITE SPARK PLUGS, BOSCH PLUG WIRES, DURALAST CAP & ROTOR, FUEL INJECTORS X2, FUEL PRESSURE REGULATOR, AIR FILTER, and I also had to have a new Y pipe installed because the person who had the truck before me decided to cut the old one up and reweld it not getting very good penetration leaving a bunch of leaks and oh yeah they decided to weld a bead around the old O2 sensor so a couple hundred dollars later I have a shiny new Y-pipe.

    I have checked the EGR valve and it seems ok, the timing is set at TDC with the ecm brown/black wire unhooked, and I have checked and replaced all vacuum lines.

    Another problem I did have was excessive crank case pressure. There was so much that it was causing vaporized oil to enter the top of my throttle body through the vent tube on the driver side valve cover causing my fuel injectors and fuel pressure regulator to be covered in oil. I replaced the pcv valve and it didnt fix the issue so I added a couple bottles of lucas with my last oil change thinking that maybe I was getting to much blow by past the piston rings and hopeing the lucas would help seal things up but it didnt really help so I ended up GUTTING the old PCV valve and installing it and what do you know it worked the PCV vacuum now keeps up but i know I didn't fix the problem just kinda masked it. A mechanic I know told me the problem could also be caused by worn valve guides/seals.

    The next things on my list to check and or replace are the MAP sensor and fuel pump, but being that the hesitation is most noticeable at low throttle i don't think it could be the fuel pump but could be wrong, my fuel gauge bounces around quite a bit if I don't have a full tank but reading around online this seems to be a common issue.

    Any help would be greatly appreciated im only getting about 9-10mpg and have read posts of ppl getting 14-18mpg with the same truck man that would be nice! Sorry if this is too much info I just figure the more info I give the easier it will be for someone to help me find the problem. Thanks
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  2. murdog94

    murdog94 New Member

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    OK by CTS you mean Temerature sensor (for the ECM) not the Temp Switch (for the guage)??? That would cause a rich condition, and poor idle, driveability. Also check the Fuel pressure before you replace the Fuel pump. It should be 12PSI or more. Also you will want to look at the pick up coil in the Distributor, Mine had a very similar fault, and it was the entire Distributor. Timing was on but it wouldnt advance or retard...
    As to your milage you wont get 14-18mpg with 35in tires and stock gearing.. There is way to much load on the tranny to keep all of that moving.
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  3. mxrick55555

    mxrick55555 New Member

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    Yes I replaced the coolant temperature sensor located next to the thermostat housing that has a 2 wire plug not the temp gauge sensor located on the driver side of the engine block. I want to check the fuel pressure but im not sure how to i know on my 98 chevy i used to have there was a shrader valve fitting on the fuel line in the engine bay that was used to hook a gauge up to but I cant seem to find one on this truck.

    As for the gearing do you have a recommended gear ratio I should look for? Thanks for the help.
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  4. murdog94

    murdog94 New Member

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    Fuel Pressure i believe is a fitting that goes inbehind the Fuel Filter (accessory that comes with fuel pressure tester or is suspposed to) once installed you just turn the key.
    As to the sensor i was just making sure since some people (including myself) have confused them and i wanted to be clear. Did you read what i said about the Dist?? I dont know how close you have looked at it but there is a chance that is a problem..

    As for gears I would run 4.56s that is what most of the guys on here are running.. You will loose some top speed but it will go a ton better all the way to highway speeds.. There are a few threads on the forum discussing the pros and cons of each.. But the general agreement is that with 35s or larger you will want 4.56s.
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  5. mxrick55555

    mxrick55555 New Member

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    Ok I will look into finding one of those fuel pressure testers, sorry forgot about the distributor question, while i had the cap and rotor off i tried wiggling the dist shaft and there wasn't any play but I didn't think about looking at the pick up coil is there a way to check this with an ohm meter? maybe I should look in my book. Thank you for the ideas I will let you know if I figure it out
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  6. murdog94

    murdog94 New Member

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    As to the pick up coil, i replaced my distributor after i had replaced all the parts that you had because there was nothing else that will cause a rich condition.. I didnt test it but after i got the Dist out the pick up coil was melted on the back side out of view.. Also the magnets werent catching anymore so it was turning freely, no notches catching as they should (just a light catch letting know hit is hitting right. My dist was also so rust there was no hope of getting it apart to fit it.
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  7. mxrick55555

    mxrick55555 New Member

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    Ok I just looked in my haynes manual and it only tells how to replace the pickup coil nothing on how to test it. So I will try pulling the distributor tomorrow and visually inspecting it. So did your engine still run even with the pick up coil partially melted?
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  8. murdog94

    murdog94 New Member

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    Yep it ran and drove.. Basically the same as you are talking about.. IT was underpowered for a TBI ive owned several. After the dist was installed and timed it ran great, doesnt run rich, idles better etc.
    #8
  9. mxrick55555

    mxrick55555 New Member

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    Cool deal ok I will check into it thanks for the help I will let you know if this works. Just looked up a replacement pick up coil its less than 15 bucks! man if this is it then i spent like 500 bucks on a 15 dollar problem.

    ---------- Post added at 01:33 AM ---------- Previous post was at 12:46 AM ----------

    Back to the gearing, I was wrong about my tire size I thought they were 35's but if what I looked up is right a LT305/55R20 is a 33-12.5-20 damn metric. So is this size tire still a little large for the stock gearing? How can I tell what gearing I have besides pulling the cover off my differential and counting the teeth on the ring and pinion? Also how can I tell what axles I have Im sure its GM but as far as the size in inches is that the ring gear diameter or?
    #9
  10. murdog94

    murdog94 New Member

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    Here is a list of RPO codes available on your truck. The RPO codes can be found in the glove box door on your truck.
    GQ1 -- AXLE REAR, STD RATIO
    GT4 -- AXLE REAR, 3.73 RATIO
    GT5 -- AXLE REAR, 4.10 RATIO
    GU4 -- AXLE REAR, 3.08 RATIO
    GU5 -- AXLE REAR, 3.23 RATIO
    GU6 -- AXLE REAR, 3.42 RATIO
    G80 -- AXLE REAR, LIMITED SLIP (POSITRACTION)

    HC4 -- AXLE REAR, 4.56 RATIOtruck.

    Once you have the axle ratio we will be albe to point you in a better direction. But if you have 3.73s (more common rear end) then you should be just fine. If you do happen to want more oomph thne you will be able to step up to 4.10s and loose a bit of top end but once again it will go really well.

    Your axle size is a GM corporate 10bolt axle.. Same as all 1988-1999 GM trucks. I dont believe that there are different axle sizes. There is a 2500 Light duty model (but your truck would be titled as a 3/4ton and i dont think they were even doing that in your year that has 6lug axles but a heavier duty rear end, and i think it is even a 12bolt. I havent checked on mine yet)
    Last edited: Jul 25, 2010
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  11. mxrick55555

    mxrick55555 New Member

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    Ok so I pulled the distributor out today didn't look to bad just looked old and dirty didn't notice anything melted but did notice that the covering on the 2 wires coming from the pick up coil were cracked and I could see the wires inside, Also noticed that it turned pretty freely like the magnetic feeling from the relucter wasn't very strong and the air gap between the relucter and the other piece that surrounds it not sure what its called looked like it was more than it should be didn't get a chance to run a feeler gauge between it though. Read in the book that to test the pick up coil use an ohm's meter between the 2 wires coming from it and it should read between 500-1500 ohm's mine checked out at like 800 ohm's but figured I would replace the whole distributor since I already had it out which by the way was a pain in the ass I had to heat up a 14mm end wrench with my torch and bend it just to be able to loosen the bolt holding the distributor in, not much room maybe I could have taken something off or something but whatever the bent wrench did the trick. I also replaced the ignition coil while I was at it, got it all back together and fired it up timed the engine then shut it down rechecked all my sensor connections and unplugged my battery to reset the computer.
    The truck still takes a couple cranks to fire up but my hesitation from dead stop is gone, Truck seems to run a lot smoother now stood behind the truck after it warmed up and it still smelled a little rich but not as bad. Thanks for all your help now I just have to let my wallet recover from all these parts I threw into her and then I can start looking for some gears.
    #11
  12. murdog94

    murdog94 New Member

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    Glad we could help.. Also with time it will smell less and less rich.. Mainly your cats, and Mufflers were probably saturated so it will take time to "burn off". Its nice how a part will "check out" and be bad.:grrrrrr:
    Seems that you have a pretty good running truck, and it looks great.:great:
    #12
  13. mxrick55555

    mxrick55555 New Member

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    Update so I drove the truck out of town today about a 100 mile round trip and figured out that the hesitation from idle to about 2000 Rpm's is still there!, BUT it only happens when the ac is on, with the ac off the truck takes off from a dead stop like a champ.
    I know that an AC compressor can bog a small 4 cylinder down a bit but wouldn't think it would be noticeable in a V8? What could be causing this? Do you think the info about the extra ac compressor load isn't getting relayed to the ECM? This is getting annoying!
    Oh by the way looked in the glove box and could barley read the sticker the numbers were all worn away but did see a GT4 so from the numbers you gave me the other day im assuming my truck has 3.73 gears.
    #13
  14. murdog94

    murdog94 New Member

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    Yeah its possible the info isnt getting there.. Does the motor idle up when you turn the AC on?? As for your gears yeah you have 3.73, so good to go.
    #14
  15. mxrick55555

    mxrick55555 New Member

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    Just checked it with the truck running at operating temp in park with AC off it idles at about 750-800 Rpm's, turn the AC on and the idle actually goes down to about 650-700 Rpm's, then I tried turning the steering wheel with the truck in park Ac on and the idle drops even lower to about 550-600 Rpm's. Also noticed yesterday at a stop sign with the ac on the truck was only idling at about 600 Rpm's. Tried looking in the book to see if there was a spec on what the normal idle should be but haven't been able to find anything.
    I just replaced the Idle air control valve (IAC) like 4 days ago so I don't think that could be the problem what else would cause it to not idle up when an extra load is on the engine at a stop or in park?
    #15
  16. murdog94

    murdog94 New Member

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    You might have a broken wire somewhere. I dont see it being the IAC either since the motor idles normal when you dont have the AC on. And you did put a throttle position sensor in right? I believe i saw that but that can cause that as well since that gets a signal and sends a signal to the ECU at idle and at WOT reguarding engine load, and throttle postion and you can guess. I would also check the connection for the IAC and TPS and clean them up really well to make sure there isnt something causing an intermittnet signal under a higher amperage condition.
    #16
  17. mxrick55555

    mxrick55555 New Member

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    Yeah I put a Throttle position sensor in about 2 weeks ago, ok I will recheck all my connections again. You know I still haven't checked my MAP sensor was going to just replace it but ran out of money do you think this could be causing the prob? I think that's probably the only sensor I haven't replaced yet besides the knock sensor.
    #17
  18. murdog94

    murdog94 New Member

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    Id take a look at it and test if you can. Im not 100% sure how to test it.. It might be causing a bit of a problem. As to the knock sensor that really wouldnt be it since the motor is running right except for the AC.. So i would see how to test it. And i was talking about cleaning the connections with electric contact cleaner, so you know they are good to go. Just something to look at, not to mention in the past for me doing that has lead me to the other problems as well that you might not have noticed when you were under the hood before.
    Im sorry that my technical knowledge is getting limited, but with my truck once i got it running right it was good to go.. And ive owned a lot of them but it was usually the more common faults. So ill try to help if i can.
    #18
  19. mxrick55555

    mxrick55555 New Member

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    I read in the book that to check the MAP you have to back probe the plug while the engine is running and see what the voltage is, the voltage is supposed to change with the amount of vacuum applied to the sensor like when you rev the engine there is less vacuum on the sensor so the voltage should go up or down not sure which way but that sensor is way in the back of the engine and kinda hard to get to maybe this weekend I will try unbolting the mount that holds it in place to see if it would be easier to probe at.
    Oh and I will pick up a can of electrical parts cleaner and see if that helps too. Thanks for all of your help so far, gotta be getting close to fixin this thing.
    #19
  20. murdog94

    murdog94 New Member

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    Well it seems to me at this point its something simple. I hope.
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