Bringing TBI and Multi Port Fuel Injection to a New Level.     EFI Conversions and Tuning! Seattle to Portland! E-mail Tuning Consultant!
Page 1 of 2 12 LastLast
Results 1 to 15 of 26

Thread: Intermittent Rough Running Diagnosis

  1. #1
    Fuel Injected!
    Join Date
    Mar 2015
    Posts
    63

    Question Intermittent Rough Running Diagnosis

    I have a 350 chevy small block, TBI motor. In a G-30 van, 1995 model. The engine is a crate GM truck motor, with summit AL heads, roller cam (stock truck cam), rebuilt TBI, upgraded fuel pump, new distributor and all the tune up stuf when it was built. Maybe 20k on the rebuild. It is running a programmed chip from harris. Lots of new stuff on this one, it's been running fairly well for a while, but I recently started having trouble.


    The trouble started in Southern California, after filling up at Costco, I had a lot of stumbles on the highway. Took it easy, switched to Chevron gas. It got better, kept getting smoother after multiple tanks of new gas, as we drove it back to Northern California.

    Then another road trip, to Oregon border, broke down with a power steering pump, took some time to get that fixed, and drove back home. It had the minor stumbles throughout the trip, but nothing to write home about.
    Then it sat parked for 3 weeks or so.

    The next drive, was a 75 mile drive, and it ran like crap the first hour, really shuddering stumbles, and it had no power under WOT. It even struggled to raise the RPms and reach highway speeds on uphill sections. Then after about an hour it ran normally. Drove a bit around for a day or two, then drove the 75 miles back home. Intermittent mild stumbles coming back home. It sat another 3 weeks or so.

    Yesterday I drove it locally, and it was really bad, shaking the van again with the stumbles. Short trips, but it was worrisome.

    Today I got my ALDL cable out, and PC loaded with TunerPro again, and monitored it while it was running, and some short 1 mile drives. It was back to the mild stumbles.

    I was able cause some bad shudders by holding down the gas while parked in drive with my foot on the brake. I recorded that in TunerPro.

    I did see that the system is adding knock retard during that shuddering time.

    Could someone take a look at the file and let me know if they see any possible items to dig into? I am new to this, and am not sure where to look first. And I don't know if the numbers are what they should be anyway! :-0
    Last edited by tony-baroni; 09-29-2019 at 04:10 PM.

  2. #2
    Fuel Injected! sturgillbd's Avatar
    Join Date
    Jun 2012
    Location
    Big Stone Gap, VA
    Age
    45
    Posts
    484
    You didn't get your datalog to attach to your post. Have you checked fuel pressure? Have you inspected your distributor cap and rotor? There are lots of things that can cause the shuddering and loss of power. Post your datalog and a copy of your bin if you have a way to read the chip.

  3. #3
    Fuel Injected!
    Join Date
    Mar 2015
    Posts
    63
    Thanks Sturgillbd

    I did a visual inspection of the wires, and cap (without taking it off). Everything looked good. Then inspected fuel injectors with the key on, and then idling, and then just a little gas, it seemed fine.

    Then I checked the fuel pressure, and it was too low. Figured a bad regulator, took that out, and found the adjustable set screw that holds the regulator in place was fully backed out. It must have backed itself out from vibration.

    I'll have to get on my PC to upload a log and bin....now I'm focused on figuring out what I can put on those threads to prevent that from backing out again, that won't fall apart in the fuel and clog up the injectors, any ideas?


    Quote Originally Posted by sturgillbd View Post
    You didn't get your datalog to attach to your post. Have you checked fuel pressure? Have you inspected your distributor cap and rotor? There are lots of things that can cause the shuddering and loss of power. Post your datalog and a copy of your bin if you have a way to read the chip.

  4. #4
    Fuel Injected! sturgillbd's Avatar
    Join Date
    Jun 2012
    Location
    Big Stone Gap, VA
    Age
    45
    Posts
    484
    If its a stock style regulator, the threads shouldn't be exposed to fuel. You could use some light duty loctite on the threads of the adjustment screw.

  5. #5
    Fuel Injected!
    Join Date
    Mar 2015
    Posts
    63
    Thanks for pointing that out, I have since learned more about this unit. It's been sent back to the guy who sold it to me, he adjusted it and confirmed the adjustable fuel pressure regulator was good.
    I have set the FP to 15psi, and put the stock memcal back into it. That hasn't helped at all, I have to check timing next.
    What do you think about the state of the distributor cap and rotor? This is with about 10k miles on it.
    IMG_0161.jpg
    IMG_0160.jpg

  6. #6
    Fuel Injected!
    Join Date
    Mar 2015
    Posts
    63

    Question

    Okay here's another update. It's idling high, around 1900. The TPS voltage with throttle closed is 0.6V. The TBI is whistling very loudly, a piercing whistle, when the throttle is closed. I was able to make a log file, starting it from nearly cold, getting it to closed loop mode was possible while idling because of the high idle. Then drove it, but tried driving it without giving it any gas really. Then turned around and drove it a bit with around 15% throttle. The driving starts around 6m mark on the log.

    I hope the file upload worked properly. The bin is a custom one, based on BNKM, and I am using a definition file for $31.

    How can I get the idle down to where it should be?
    Is it normal for the knock retard to stay so consistently around 6 deg?


    Other items, I checked manifold vacuum and it's in the green around 21 in Mg on my gage with this high idle. When I put it in gear, the idle drops, and then it shows in the red zone, indicating late ignition timing, only around 15 in Hg Vac
    Attached Files Attached Files

  7. #7
    Fuel Injected!
    Join Date
    Mar 2015
    Posts
    63

    Question

    One more update. I went out again and made a 2nd log, with more throttle, and got onto the freeway briefly. it runs like crap. Tons of knock.

    I noticed a few things when I looked at the parameter list, instead of the dashboard.
    Knock counts are off the charts, getting up to 50k and reseting every few seconds.

    When I come to a stop, the spark advance shows 23 thousand and change, that doesn't seem right.

    The check engine light came on at a stop light while the vehicle was stopped. I haven't yet figured out how to see which code was generated yet.

    I'm all ears to feedback and what to try next!

    Thanks all!
    Attached Files Attached Files

  8. #8
    Fuel Injected!
    Join Date
    Mar 2015
    Posts
    63
    Found the error codes.
    35 - IAC Failure
    54 - Fuel Pump Relay Failure

  9. #9
    Fuel Injected! sturgillbd's Avatar
    Join Date
    Jun 2012
    Location
    Big Stone Gap, VA
    Age
    45
    Posts
    484
    Just replayed your log file. Your bin file appears to be $E6 instead of $0D. That is why you are seeing the constant knock retard. As for your high Idle, you either have the throttle stop screw open too far or you have a vacuum leak. You are getting an IAC failure because the IAC is closing completely and the pcm cannot control the idle. There are some odd things going on with the spark advance. The beginning of the log looks normal. As the log progresses, I see the timing drop from ~20 degrees down to ~5 degrees with it still idling in park. At another point, I see the spark advance pegged at 50 degrees. The PCM uses timing to help control idle speed but this seems extreme. Adjust the minimum air adjustment screw to where you have approximately 10 IAC counts at hot idle in park. You will have to power the key off and wait a few seconds for the pcm to power down so the pcm can relearn the closed throttle position. You will know when the PCM is powered down if you leave the data dash up when you key off. Tuner pro will start flashing DA Not connected at the bottom of the window. It will reconnect as soon as you key on again. It would be nice if you could read the chip and post a copy of your bin. The relay failure is a signal back into the PCM from the fuel pump relay on pin B12 of the red PCM connector. Make sure you have battery voltage on this pin with the engine running. Clear your PCM codes before adjusting the minimum air screw on the throttle body if you don't have a vacuum leak.

    Thanks,
    Brian

  10. #10
    Fuel Injected!
    Join Date
    Mar 2015
    Posts
    63
    Thanks for checking it!

    I have been looking for a vacuum leak, but haven't found any. All the hoses are connected from what I can tell.

    I've uploaded my bin. I thought it was a $31. The vehicle is a 1995 G30, with a 5.7L and 4L80E. Engine isn't stock...

    I will look into IAC...
    Attached Files Attached Files

  11. #11
    Fuel Injected! sturgillbd's Avatar
    Join Date
    Jun 2012
    Location
    Big Stone Gap, VA
    Age
    45
    Posts
    484
    I knew it wasnt $0D . Thats one reason I asked. Ill look through and see if I can find anything in the datalog that stands out. To log knock retard on some of the masks, you have to make a bin change so it shows up in the datastream. I'll see what it takes on yours in a bit.

  12. #12
    Fuel Injected!
    Join Date
    Mar 2015
    Posts
    63
    Thanks Brian!

    I'm not sure where to go next.
    Here's what I did:
    1. cleared codes
    2. Started engine, pulled vacuum lines one by one of the TBI to see what effect it would have. Some of them changed the idle slightly, and then I put my finger over the port on the TBI, and it would act just like as if the hose was in place. Other hoses, did not change the throttle when I unplugged them, and left them open.
    The big difference came when I unplugged the vacuum hose that comes from the rear of the TBI, and plugs into a sensor (MAP?) beside the TBI. When I unplug that, the idle drops considerably, from the sound of it, near a normal level.
    3. I didn't understand your IAC advice. The screw I think you're talking about is the one that sets the position of the throttle blades when the throttle is closed, right? On my engine, it is already backed out all the way. I backed it out about a 1/4 turn before the screw pulls away off the throttle bracket, because the blades are already touching the sides of the bores in the TBI.

    How do I set the IAC now?

    I wonder if there might be a break in my base gasket under the TBI....I've traced all the vacuum lines I can find twice now, and they all appear plugged in where they should be.

  13. #13
    Fuel Injected! sturgillbd's Avatar
    Join Date
    Jun 2012
    Location
    Big Stone Gap, VA
    Age
    45
    Posts
    484
    Check your base gasket on the throttle body. If no vacuum leaks, Adjust the minimum air screw to close the throttle blades for approximately 10 IAC counts at hot idle. Clear PCM codes. You have constant knock retard. You could possibly have a bad knock sensor or bad filter board on the memcal. Do you hear any spark knock/ping? You can simulate a knock sensor on this pcm with a 3.9k resistor. It thinks a knock sensor is there but gets no knock feedback. You have extremely low timing everywhere in the datalog and that is why it is lacking in power. I also see the timing all over the place with a constant throttle/load. Something is making the PCM pull timing. As always, make sure all of the engine and PCM grounds are in good shape. Make sure plug wires aren't inducing noise back into the PCM through the engine harness. Get your fault codes cleared up and not returning then datalog again posting results here.

  14. #14
    Fuel Injected! sturgillbd's Avatar
    Join Date
    Jun 2012
    Location
    Big Stone Gap, VA
    Age
    45
    Posts
    484
    If base gasket is good, you could have an intake gasket leak. Make sure the pcv valve is free and if it has vacuum power brakes, make sure you don't have a leak there. It appears you have a vacuum leak somewhere if you have backed the minimum air screw all the way out with no change.

  15. #15
    Fuel Injected!
    Join Date
    Sep 2018
    Posts
    63
    this helped when I had to set my IAC :
    Attached Files Attached Files

Similar Threads

  1. Rough Idle and Dies If I give any throttle.
    By beamsjr in forum GM EFI Systems
    Replies: 5
    Last Post: 01-13-2017, 06:25 AM
  2. Replies: 8
    Last Post: 01-06-2016, 03:27 PM
  3. TBI Stumble Diagnosis Help Request
    By tony-baroni in forum GM EFI Systems
    Replies: 8
    Last Post: 07-25-2015, 12:09 PM
  4. Replies: 52
    Last Post: 11-07-2014, 04:24 PM
  5. idle a litle rough?
    By CDeeZ in forum GM EFI Systems
    Replies: 30
    Last Post: 09-21-2012, 07:25 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •