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Thread: 94 Buick RoadMaster Estate Wagon LT 1 issues

  1. #61
    Fuel Injected! vilefly's Avatar
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    The O2 sensor wires (harness side) both should present .45V on them when unplugged. Left/driver's side = Purple/White, Right/passenger side = Purple. Make sure measured readings match scan readings. Check this without starting the car.
    Last edited by vilefly; 11-15-2019 at 04:14 AM.

  2. #62
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    Each 02 controls the fueling for the whole bank. So, I find it very hard to believe that the fuel trims can cause a single cylinder on one bank to go rich. Same with causing only 2 cylinders on the other bank. You need to figure out what is wrong with those 3 cylinders. Did you try swapping those injectors to other cylinders?

  3. #63
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    Since I have to pay for labor it was more practical to just replace the injectors with new rather than swap around.

    That was the only change however the front cyl and rear two on the passenger side remained exactly the same on the SnapOn scanner. The second cyl is just slightly leaver. So you are right the entire bank is showing rich.

    The left bank is reading fine. We did swap O2 sensors then replaced them with know good ones. No change at all.

    I had him disconnect the battery and both O2 sensorsovernight. He then hooked the battery up in the morning. We were hoping it would run open loop, not using the O2 . However while it ran slightly better it still showed the right bank rich and pops in the converter.

    While the intake was off he inspected the ports with a bore scope as well as bright light, looking for deposits or anything else that might cause problems.

    I’ve suspected an ignition problem for awhile. Even though it has a new Opti, new wires, new plugs. He said he just received the optional spark tester that SnapOn has. He said he would try and get it hooked up so he could test that end again. Apparently this addition allows looking at spark for presence, operation and condition similar to our old oscilloscope.


    I asl asked that he review the exhaust system, especially where the AIR pump fittings are. He had plugged them earlier but I wanted a review of this.

    I appreciate everyone’s comments. I’ve had him look at virtually everything noted here but nothing seems to even touch the problem.

    I’ve also checked numerous repair shops around her and they won’t touch the car as it is OBD1 even I bring my EEHACK computer to test with. Their mechanics only know OBD2. I told these places I will not stand for “ Throwing parts at it, hoping they guess the solution. I want to see and know the problem. They just run me out the door.

    Maybe I’ll know more Monday morning.

    FRUSTRATED.

    Byron
    Last edited by Bentwings; 11-18-2019 at 02:46 AM.

  4. #64
    Fuel Injected! vilefly's Avatar
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    Hmmm. "Pops in the convertor". Sounds like he thinks there is a misfire on that side. Only a gulp of air can make it pop like that, either from a misfire or an exhaust leak. I wonder if he decided to swap the spark plugs from left to right to see if the problem moves. The swapping of the injectors has already been done, if I recall....twice. He might be the victim of a cracked spark plug, which seldom shows up on a scope. Sometimes the simplest things are the most elusive, especially since OBD-I has no misfire counter to access.


    Have him try that and see if his hair falls out when it works.

    Another diagnostic method on diagnosing low engine vacuum is to put scope on the MAP sensor, and watch for uneven peaks in the waveform. Anything that does not match the others is suspect. Crank up the sensitivity till the waveform fills the screen. On the second channel, use the inductive pickup, and use that signal to identify the cylinder that has the problem, allowing for the 4 cycles to take place on time. It has helped me bust lots of "rocker arm adjustments" that were done so very wrong. Overtightened rocker arms hold the valves open, and cause many issues, such as burned valves. It still amazes me how everyone gets this simple adjustment wrong. This happens to the small block chevy exclusively. Sometimes, a cylinder leakdown tester can miss this, due to the lifters "pumping up" slightly when the engine is in motion.
    Last edited by vilefly; 11-18-2019 at 07:42 AM. Reason: more testing info

  5. #65
    Fuel Injected! vilefly's Avatar
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    There was a tool invented for the automotive oscilloscope that was basically an optical mouse encoder wheel attached to the end of a probe. The probe wheel was pressed against the belt to spin it. Lots of probes were killed due to butterfinger syndrome. Its digital output was converted to analog before put on the screen. This device, in concert with the traditional ignition pattern, would identify a weak cylinder/misfire based on crankshaft acceleration. It worked fairly well, provided you knew when and which cylinders were firing on the indicated pattern.

    With the advent of misfire counters, this probe is now obsolete........but I still have mine. heh.
    Figured I'd mention this tool in case anyone wanted to build one.

  6. #66
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    Villefly, the car is on the third set of new plugs. The right bank fouls them. Yes, they have been cleaned . We probably should have just used a set for testing.but each time we thought “finally fixed” so they were left in.
    The converter pops are random but excess fuel and air are getting in and when it gets hot enough, it pops. That part is not what I was getting at about the ignition miss fire. This is possibly a separate issue. Hopefully hid new equipment will be able to test for this.

    The plug wires were checked before installation for resistance and continuity.

  7. #67
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    BTW, My hair has long since fallen out, he is much younger than I but he is rapidly losing his hair over this project.

    I really just want to get the car back. I can take it to my son’s repair shop and park it in a corner. It’s a 60 mile drive each way but if I spent all day there I could do that.

    I want to run my EEHACK and compare scans.
    I’m not sure if the fuel map can be edited enough to just over ride this thing or not. It may not even be the way to go in the first place. There is a hoist so I could get under the car as required.


    It seems to me that it would take a substantial air leak to create this problem. The mech. Has inspected the exhaust manifolds and pipes. My diesel truck had a crack in the exhaust manifold about 4 inches long and big enough to put .035. Welding wire in it. You would think it would have affected the turbo boost a little but I didn’t even notice any loss of boost.

    After the intak gasket change on the Buick there was little difference in the problem. The gaskets looked fine to me.

  8. #68
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    Iím at a total loss for this problem.
    He disconnected the battery overnight and unplugged both O2 sensors. It ran exactly the same. He had not disconnected the AIR pump line in the exhaust so he did that and retested it. Same thing three cylinders are dead rich one is very near .


    I donít where to go now.

    This issue started when the left cat was replaced. It had developed a very rich condition on the left bank , driver side. He said the Cat was bad so the left Cat was replaced .

    Right here was when the issue switched to the right bank. This is the puzzle piece. Why did the condition switch sides?
    This has been the question constantly asked through out all the testing.

    We then replaced the right Cat, since the car had 110 k on it. I still have the old one.

    Iím going to get the car back and run EEHACK as yíall have noted.

    Question here is resetting the BLM. do I do this after hooking the battery up but before starting thr car or while the battery is disconnected?.


    The compression test was very even. I donít have s number but he said it was good. I would think a cracked piston might show low on that cyl. But I have take sbc apart that ran fine with several cracked pistons.

    I asked awhile ago above if very bad valve seals and guides might be causing this.

    Byron

  9. #69
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    You would reset the BLMs with the battery connected and the key in the run position but the engine off. Connect with EEHack, click Control, then click “Reset BLMs.” This will Reset all BLMs to 128–assumes stoich of 14.7.

    Running the car after that it should become obvious very quickly if your rich condition is real by watching the dash in EEHack. Best of luck.

  10. #70
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    I am only obd1 so not up on these systems but have been watching this for quite awhile. Would it have been an idea to reset the blm before pulling the o2s. I would think that would allow it to start on a uncorrected original ve table.
    6395, BHDF, 7.4 BBC lightly modded now 6395 BMHM back to BHDF

  11. #71
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    Thanks. Thats the exact information I needed. I’m not sure if this is how he reset using his SnspOn scanner. I’ll ask when I pick the car up.

  12. #72
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    three cylinders are dead rich one is very near
    Please tell us (again if necessary) how you are determining this? There is a level of detail here that seems impossible. It's like reporting measurements to the hundredth of an inch using only a carpenter's measuring tape. The most likely way to determine this is to measure unfiltered O2 output with a scope concurrently with injector or ignition pulses for a cylinder based reference. If you are relying on individual cylinder injector trims to determine rich/lean operation you will be led astray.

  13. #73
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    When the catalysts were replaced, was either one broken up or missing a honeycomb element? If so, a piece might be left inside the muffler to clog up one side, and lower engine vacuum. Cut off the exhaust (or drill a 1/2 or larger hole) on the straight run prior to the muffler, but after the converter, and then look at your readings to see if they improve.

    Just cut in a spot you know you can weld it back together.

    Spoken from experience.
    Last edited by vilefly; 11-23-2019 at 04:20 AM.

  14. #74
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    Quote Originally Posted by 1project2many View Post
    Please tell us (again if necessary) how you are determining this? There is a level of detail here that seems impossible. It's like reporting measurements to the hundredth of an inch using only a carpenter's measuring tape. The most likely way to determine this is to measure unfiltered O2 output with a scope concurrently with injector or ignition pulses for a cylinder based reference. If you are relying on individual cylinder injector trims to determine rich/lean operation you will be led astray.
    I think they are doing the old fashioned "read the spark plugs" method. This is my guess. Whomsoever wields the answer, wields the power of one can of pop.

  15. #75
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    Quote Originally Posted by Bentwings View Post
    the front cyl and rear two on the passenger side remained exactly the same on the SnapOn scanner. The second cyl is just slightly leaver.

    This says the rich cylinder determination came from a Snao-on scanner.

    I still don't understand this or what he was looking at. There is no individual fuel trim on this LT1. There is no scanner data that would tell you an individual cylinder is rich.

    It harder to fix something with the person trying to fix it doesn't know how it works.

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