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Thread: 94 Buick RoadMaster Estate Wagon LT 1 issues

  1. #16
    Fuel Injected! vilefly's Avatar
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    Intake manifold leak detected. Low vacuum 10-11" hg you say. It's time for the "bucket test" and the PCV test.

    PCV TEST: Unplug the PCV valve from the valve cover - plug it off, and plug off the PCV vent in the other valve cover. Start engine. After 30 seconds, unplug a side, and look for positive pressure blowing out. If there is vacuum, the intake gaskets are leaking at the bottom of the intake ports, probably sucking up some oil also.

    BUCKET TEST: With the engine running, pour water onto the intake manifold and see if it causes misfires and rough running. If there is a change, the vacuum leak is real, and should be either the injector O-rings or the intake gasket leaking on the top of the intake ports. Try to pinpoint with a squirt gun if you like.

    One last thing. Did you ever use the eehack software to run a power balance test? You could also unplug injectors at will and check the RPM drop. Then tell us which cylinders test weaker than the rest.

  2. #17
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    Ok I did have a reply to Kur40 but I ccidentally hit the wrong key and deleted the whole thing.

    We did do test drives with both O2 disconnected. No change.
    Did not try the MAF test.

    I did do the power balance test. The whole right bank is weaker. I don’t remember the number. It may be on one of the scans however.

    I did ask him to do both leak tests you described. However I forgot to ask. The results. The smoke test is a pressurized test so it should have shown something. I wasn’t there to observe however. The smoke generator will fill the shop with smoke in a few seconds so it is pretty dense. I don’t know what is burned or heated but it billows white thick smoke everywhere.
    However thebuniversal solvent ...water does a good job for leak tests too. Since there are new injectors with new o rings that can probably be ruled out. The water test should pin point better if there is a leak. I did suggest this a long time ago.

    Here is the kicker though....why did it ( rich running) switch from one bank to the other.? this question comes up time and again but never gets answered.

    I agree there is air getting in somewhere. Not too long ago I ran into a TSB that says you can legally disconnect the AIR system as long as it remains on the car even in Calif. provided the system still passes the emission tests. the fittings I think are SAE inverted flair. This came about because of their frequency of leaks that cause problems. Their value is questionable today as the EFI systems and motors are so much better. I haven’t had the car available long enough to do it for a while nor to just try it.

    So I’m stuck until Sept 2 when they come back to work.

    The weather is a bit cooler now so I may just get the car when they come back and do some of this myself right in the marina parking lot. I’m really tired of screwing around like this. It means someone needs to follow me home so I can move cars and it’s a 90 mile round trip.

    Going to another shop is like this song by Phill Harris.
    substitute. RoadMaster for “ boom da boom”
    https://www.youtube.com/watch?v=h2H6...=RDh2H6qC23RPY

    Once again thanks for the tips and tricks.
    Last edited by Bentwings; 08-30-2019 at 06:22 AM.

  3. #18
    Fuel Injected! vilefly's Avatar
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    The switching from one side to another is not terribly relevant, believe it or not. I suspect the lower intake gasket at the bottom of the ports sucked up enough oil to plug up its leak due to gasket swelling. Then it went for the next weakest link, the other side, which is still present. But to me, a vacuum leak is still a vacuum leak, no matter which side it is. Sucks in oil, runs rich on that side. Will probably come and go, too. Oh, and new injector o-rings are something I never trust. They can be cut during installation by both skilled and unskilled workers alike. Chaos theory.

    A smoke machine is nice, but is best used for EVAP system faults. Pressurization is nice, but there is always a valve open on the intake that will make you miss that particular intake port and give a false "ok" reading. Only useful in this case when the engine is running, and at that, inferior to the bucket test. Many vacuum leaks have escaped them, like the 4.8/5.3/6.0/6.2L engine family with the plastic intake manifolds. My original Bucket Test evolved from dealing with the dual carburetted honda prelude. Smoke machines weren't invented yet for automotive use. Started using it on the rest of the hondas after that, with their nightmare 3 barrel carbs and tons of vacuum lines.
    The specific gravity, density, and inflammability are what make water the king of the tests. Also, anyone can do the bucket test. No skill required.

    The possibility of the air injection check valves failing, and causing oxygen sensor error is a valid one, but it can be easily checked by plugging off the air inlet to each side, and rechecking. Wouldn't cause a severe lack of power, though.
    Last edited by vilefly; 08-30-2019 at 07:00 AM.

  4. #19
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    Thanks all for the helpful information, I’ll have to wait until Tues to hear where it’s at and what was done. I’m afraid that the computer change didn’t fix it. I may just pick the car up and bring it to the shop I work part time at and park it out back. I can run a cord out there for power and I think we have enough air line for air. I have a new squirt bottle so I can do the exterior leak test described. I also can come up with something to do the PCV test. The car uses no oil and loses no fluids. If I can pin point a leak I can get the guy to pull the intake and do gaskets. His rates are reasonable so I can live with that.

    I big issue is that my work is 50 miles from home so after a long day it’s hard to do personal stuff then drive another hour home. Makes a very long day.

    I did find my laptop with EEHACK on it. I revisited the 4 scans that I saved. I’m going to go to the computer store today to figure out how to connect to the internet directly then I’ll be able to email scan directly. My iPad doesn’t like them.

    More later.
    Byron

  5. #20
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    The lack of power suggest a massive air leak before the exhaust. If it was an exhaust leak, it will still run fine, fat rich. Probably 1 cylinder runing extremely lean[drawing unmetered air] with constant misfires, causing the PCM to dump huge amounts of fuel.

    You can try reading the spark plugs for some more clues. Gaskets or cracks in the head, or intake manifold. Overheating?
    Cylinder airleak test?
    I will question any of the test you have already done.

  6. #21
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    I respect your questioning things. I do the same. At each step we have had discussions on what to do and why. I have searched for information and landed here. So I’m asking for help.

    The plugs were clean and in good shape on the right bank for 100k miles on the car but the left side were heavy fluffy black but with less wear on the electrodes. My thought is there was an intermittent Miss on the left bank that gradually got worse. Long story short, the Opti Spark, plug wires and plugs were replaced after some discussion. After this it ran for a day or so but the miss returned. The O2 sensor on the left bank was out of spec so we replaced it but the miss remained.
    We disconnected both exhaust pipes after the O2 ...near the mufflers essentially looking for bad Cats. The miss went away so we replaced the left Cat. The miss remained but on the scanner it showed the right bank being very rich now. This is where it swapped banks. So this is where is gets puzzling to me. Nothing seems to change it.

    Now I had my own scanner with EEHACK. I think this is even better than the Matco or my sons SnapOn scanners. I’m a rank newbie with this but I was able to clear all the codes except the BLM. I didn’t know what this did so an internet search gave the name...block learn multiplier. Plus it’s function.

    And now from the above post I learned how to clear it too. Im still concerned that the computer change will not fix this.
    I’m not sure how it’s installed so I ask this question. I’m assuming the battery needs to be disconnected. If not what happens? Then can I disconnect it for 30 minutes and the BLM will reset or do I have to do this on my scanner.

    A question here...will the BLM be reset automatically when the new computer is installed?

    As you can see there is some knowledge or training missing here. I simply don’t know what to do.

    I won’t have the shop answer until Tues but I’ll call him or stop in on my way to work Tues. morning.

    again thanks for any and all help.
    Byron
    Last edited by Bentwings; 09-01-2019 at 09:07 PM.

  7. #22
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    I don’t have cats and I don’t have lt1 but you have been working on this for awhile. Do I read it that when you took off both cats it was fine? If so could it be you had 2 bad cats with the left being worse than the right. When you replaced the left it fixed that side and now the right is the worse side?
    6395, BHDF, 7.4 BBC lightly modded now 6395 BMHM back to BHDF

  8. #23
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    Actually both Cats got replaced. I thought the same thing. It ran reasonably good a few miles but as soon as a load was present the problem came back and stayed there. If it still is running bad Tues. I think as kur4o notes it’s possible to have a big intake leak either internal or external or both. Therefore I think it best to just say screw the tests just put new intake gaskets in and make dog gone sure they don’t leak.

    There doesn’t seem to be anything bad mechanically in the motor. It idles very smooth at the required rpm.it just has a miss. Actually not a miss fire but the right side has a putter or pop from the exhaust. Its irregular but periodic. I think It’s igniting fuel in the Cat due to it being very hot. I suppose from trying to burn raw fuel.

    Once you get the motor over about 3500 rpm say in 2ng gear it starts pulling pretty well....considering. I’m guessing that it can better handle the rich mixture.

    Byron

  9. #24
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    You really want to follow a methodical test -> eliminate process to solve this. Simply replacing the intake gaskets is not the way to go imo.

    I think the bucket test isn't a bad one but as someone that has helped more than one LT1 Vette owner after washing an engine, I would caution you not to douse the front of the engine if possible. Especially when the engine is warm.

    I'm less inclined to believe the internal manifold leak will cause a driveability problem. Airflow into the crankcase is metered as it flows through the air intake prior to the throttle plates. The L31 vans were prone to manifold gasket failures yet the engines usually ran well. We would see coolant loss or oil consumption but the engine would not appear to run badly. I would plug the fresh air connection to one valve cover and install a vacuum gauge in place of the PCV at the other. If the gauge showed vacuum with the engine running then the gasket was slated for replacement.

    Don't get trapped by the BLM. You can trick the pcm into thinking the engine is too rich by sending a "too high" O2 voltage signal. .7V to .9V is enough to cause the pcm to flag the O2 as rich. A very simple way as the mechanic is to become an active part of the O2 signal circuit. One hand to battery + and one hand to a bare length of wire installed in the O2 signal circuit is enough to raise voltage so the pcm responds. And the pcm should respond! Once BLM values go to a reasonable level you can disconnect the sensors and force open loop. The ecm will deliver fuel at the commanded AFR without correction. And you will be able to tell just how the engine is running without the pcm trying to cover it.

    I big issue is that my work is 50 miles from home so after a long day it’s hard to do personal stuff then drive another hour home. Makes a very long day.
    I agree. I think you should move the vehicle to a location that helps you get the testing done that will resolve this.

  10. #25
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    Right from the start we have tried to be systematic and logical as we searched for the issue. Interesting is that there was never a check engine light. It does work however.

    I think in EEHACK you can force the ECM to run open loop only. It’s something I have not tried. I think you would also have to trigger the BLM as you noted. I don’t know however. It’s uncharted sea for me.

    If things don’t go right then I’ll have to insist he at least do the PCV test you describe. I won’t douse the front of the motor. I’ve already been cautioned about that. Don’t do under-car car washes either. I think the squirt bottle will work for the topside. That’s easy enough to do.

    I did find the memory stick with the 4 early scans and the iPad adaptor. Now I have to see how the download works. I did it once before but iPad didn’t like it.

  11. #26
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    I didn’t have a good feeling about the computer. It didn’t help a bit.

    I visited the shop today and we chatted for an hour about where to go from here. We talked about the intake possibly having a leak either from the outside or from the inside or both. Then what to do about it. He can spend time testing it to determine then what? If it shows a leak do an R&R and replace gaskets. Glue it up good with sensor compatible sealers. It boils down to cost. He flat asked me “how do I charge for this? “. I said that this point I’m so deep I’m drowning, deeper and I’m still drowning. I said I would charge flat rate and something for test time. I’d test it as much as possible for my information but the end result is that it needs to be removed and new gaskets whether or not the tests show anything just to eliminate a question. We have done so much of this already that one more item will just add to the list. It’s the front cyl and the back two on the right bank.

    Additionally there could be a cracked manifold or cracked head? Or both? However the switching sides enters here again.
    The motor idles smooth even though it’s dead rich on three cyl. It just putters out the right side tail pipe.

    He is going to donanothe check of the exhaust manifold. I suggested he use his bore scope to possibly get a closer and better look from above and from below. Possibly simply replace exhaust gaskets if there are any.

    The other question is the knock sensors. But would they create this? Then would they not produce a code? Again there are no codes showing.

    We also talked about the possibility of sticking or broken lifters. But wouldn’t this produce some noise and rough running?
    I had flat cams before but they lacked power and made at least a little unusual noise.

    At this point I’m really lost on what to do. Something tells me the intake gaskets aren’t going to fix it either.

    Any help will be greatly appreciated
    Byron

  12. #27
    Fuel Injected! vilefly's Avatar
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    Screw the exhaust manifolds, knock sensors, and lifters. Waste of time. A cracked head would overheat or drink coolant or put exhaust gasses in the cooling system. There is a tester for that. Coolant can skew the o2 readings rich, but you can smell the burning antifreeze most of the time. A cracked exhaust manifold would affect 4 cylinders, not 3. A collapsed lifter ticks...period. The intake manifold tests shouldn't take more than half an hour to do a thorough job.

    Sounds like you tend to make 3 steps forward instead of one. Best to treat it like a timeline. Each choice leads to a different direction, so don't take more than one at a time. We still don't know the condition of the intake gaskets. Wait for the answer to that first. Quit wasting money ya young impatient whippersnapper.

    The only one time I have had an exhaust manifold be the cause was when it had a piece of catalyst honeycomb stuck up in it, and that was because the guy was racing it.

    Another strange condition that affects things is heavy carbon deposits on the valves from burning oil. Deposits so bad, it was blocking the injector spray from getting directly past the valve. Fluffy thumb-sized restrictions, I mean. On other vehicles, enough carbon to hold the valves slightly open or prevent them from sealing properly. Revealed by a cylinder leakage tester and a running compression test (with engine running). Would also cause low vacuum. Looking down the injector holes in the manifold would show if it was the case or not, but I trust my eyes least of all. Can't see a compression leak, you know.

    The other strange condition I ran into was after someone overheated the hell out of an old small block chevy. Got it so hot, the valve springs weakened enough to not seal the valves well enough to run worth a damn. I had figured it needed a valve job, but was slightly wrong, until the weak springs allowed the valves to get burnt.

    This is why we do it one step at a time. Weird stuff.
    By the way, your old computer will sell just fine on ebay.
    Last edited by vilefly; 09-05-2019 at 07:10 AM.

  13. #28
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    The next step is to upload some logs, and get familiar with eehack control window, so you can do some real troublshooting of the car.
    From here any suggestion without a log will be shooting in the dark. I am sure it is something as simple as being overlooked.

    Leaking coolant can foul the 02s heavily, so the blms can max out. I have experienced it once. But you will get smoke from the exhaust too.

    You can do the water cleaning trick. Warm the engine, disconnect maf and air cleaner. Increase rpm to 2500-3000 and start spraying a fine mist of warm water in the throttle body, so it can enter the engine. You can vary the rpm and the mist. Half to one pint of water will be enough for the first cleaning.

  14. #29
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    I love these Engines

    A couple of really simple things to check.
    1. One bank rich in 94-95 the EGR gas flow was pulled off from a port on the exhaust manifold these crack and leek Air into the exhaust manifold causing O2 to read lean and BLM to go up.
    If the little tube is cracked it will make that side rich.
    If you have the cast iron manifolds you may also have a crack there.
    Any exhaust leak from the head down to the sensor will make it rich on that side.
    2. Correct PCV valve for old engines I use a 774 standard it works and does not lean out on old rings.
    3. The 94 throttle body had a tendency to clog where the PCV goes into the top of the throttle plate right under the badge plate on the throttle body without PCV you will foul the O2 sensors.
    4. Oil fouling often people think that low miles old cars mean that they are in better shape, this can be problematic if the owner actually let the car sit for extended periods or worse the car was only driven 3 miles a day.
    These engines are designed to run with the oil in the block at or above 220 F if the oil does not get to 183 F then it will be soaked with ethanol from the gas letting the car sit the low tension rings get damaged.
    If you get oil on the plugs then the sensors will foul and it will go full rich. I had valve guide seals go bad after an overheat that did this to one of mine. I used a spark plug extension drilled out to move the O2 sensors out of the exhaust flow to allow normal driving until I overhauled it.
    Heres a link to some one else describing how to use them.
    https://www.evolutionm.net/forums/ev...cel-light.html
    5. Persistent miss, I have used a lot of these coils and modules for all kinds of builds a couple of common things on the coil that will cause a miss is that the epoxy fails look for white powdery residue around the coil body and bracket. If found replace the coil and coil wire. Another area that the OPTI had issues with is the short wire harness between the Opti and the engine harness on the passenger side behind the water pump.
    6. To localize the miss pull one injector lead off at a time and find the missing cylinder. If none change then look at the ignition closely the wires that are clipped to the block behind the exhaust manifolds may be sorting out.Take off the serp belt and use a test light to puncture each plug wire and watch for miss. If no miss found pull the valve covers off and look at the rockers as you rotate the crank the early roller lifters where common to fail and wipe the lobe of the cam.




    One of my project builds is another LT1 engine
    I am going to use a set of CompE Speedmaster heads on one I have the heads already On these the oil return passage can be plugged to open the reverse cooling port to fit Gen1 heads on the GenII block.
    I love really old school tech fusion so the plan is to use the LT1 lower end with TRW1157 flat tops and 3.75 stroker crank after market main caps and a girdle.
    With the new build looking for monster torque.

    I have one of these motors that had a LT4 cam and wildly ported heads 280cc intake runners with Orange springs and a lifter REV kit It turned 9000 Rpm.
    Stock coil won't even pull 6K The OPTI pickup works great all the way high as you want to go MSD cap and rotor held up pretty good. I used my own Ignition controller and CATS tuner to tune the ECM OBDI.
    The old screamer will be getting new springs pistons and a overhaul looking to put 4 small turbos on it.

    FYI the stock injectors are like 26lbs so if you are tuning it you could have bought a really cheap set of 44lbs EV1 style micro drilled injectors for less than 80USD.
    Avatar is my motor 800 RPM 184ft Lbs Torque 18 inches x 18 inches x 9 inches thick external combustion engine.

    98 WS-6 full tube chassis rally car Aluminum Block LS2 (soon to be LSX 376)(in Storage)
    95 Suburban 6 inch drop, Pioneer DVD in Dash 5.7 TBI, 220cc 2.02x1.60 64cc heads, Stainless longtube headers 2.5 crossover 3 inch exhaust, LT-4 roller cam.
    2002 Seville STS

  15. #30
    Fuel Injected! Terminal_Crazy's Avatar
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    Stock coil won't even pull 6K The OPTI pickup works great all the way high as you want to go MSD cap and rotor held up pretty good.
    What would you advise to use for a coil upgrade that won’t melt the opti ?

    Thanks
    Mitch
    '95 Z28 M6 -Just the odd mod.
    '80 350 A3 C3 Corvette - recent addition.

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