94 Buick RoadMaster Estate Wagon LT 1 issues

[Bentwings]

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

[myburb]

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?

[Bentwings]

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

[1project2many]

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.

[Bentwings]

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.

[Bentwings]

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

[vilefly]

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.