94 Buick RoadMaster Estate Wagon LT 1 issues

I’m sure I posted some time ago but I couldn’t find it. Also did a search but couldn’t find that either.
So just to recap
94 Buick RoadMaster Estate Wagon LT 1
this Car only has 110k on it and is like a brand new car. A granny had it since new and it was like a daughter to her.

anyway the car has never seen a winter. No rust just minor weather stains.

So I get it and it runs fine for about 5k miles then it developed a miss across the board. Since I no longer have a place to work on cars I’m forced to “take it to the shop”. Well the shop tells me the trans is not shifting properly and needs rebuilding. I’m not buying this and go to 4 more shops all saying the same thing.
finally I run into a guy who is old school that “fixes” things rather than throw parts at it hoping to hit the one that works. He says the trans is fine.

Long story shorter.
new belts, air cleaner, oil change with Wix filter, fluids topped off. Suddenly the car stops running altogether. So new fuel pump and Wix fuel filter. Car runs but still has Miss. new Cats both sides, new O2 sensors (one was definitely bad)
checking the motor for leaks and we find the Opti Spark is saturated with oil. Seal behind it is bad. New Opti Spark and vacuum line, new water pump. New plug wires and plugs. EGR is not functioning. New EGR.
More scans. Motor is running very rich on left bank. O2 out if range so it is replaced again.

Now it runs rich on the right bank. But all sensors are in range and almost dead center of range.
Very thorough inspection of intake hoses. They all are nice and flexible, none oil soaked or brittle. All clamps centered and tightened....not excessively.

Now I might add that I specified to use all GM OEM parts. No MSD, no aftermarket hard parts. Mostly because of my experiences and others of my cruise groups. Even the OPTI was new old stock.

car still has a miss. Mpg has gone from 21-22 to 12-13. Also have run several tanks of non oxy premium through it. It still is solidly rich on the right bank.

i went and got the EEHACK and a brand new laptop just to run scans on this car. Even got a cool memory stick for USB port and connection to download to Apple IPad Air lol. Unfortunately misplaced during recent move.

however my scans show exactly the same as high dollar tool man scanner.

one thing that seems unusual in that I can’t reset the BLM while others say I should be able to do.

Last week my guy got a very expensive smoke tester. It showed no,leaks. I suggested he compression test the whole motor which means I get charged for plug R &R again.

I told him at this point I don’t care, just fix the car, what ever it takes, I need the car as my el Camino will be headed for winter storage shortly and the Buick will be my driver. It’s only been 6 months of messing around. He is getting tired of having the car around and I’m very frustrated.

i didn’t call him last week as I didn’t want to be a pest but he called me and said he had new OEM injectors coming Friday and would install them as soon as he could. He’s been very fair with charges and so I can’t complain there. Nobody else around will even look at the car now. They see me coming and they put the closed sign in the window.

Im looking for any help I can get. It may be a bad computer but the general feeling I get is that these hold up pretty well. There are at least 6 Other LT 1 in the cruise groups I hang out with and all are virtually trouble free. All have a log more miles on them.

byron

if one bank is rich it’s probably an injector or two. usually i would swap the lefts and rights to see if it follows.. but also the fuel pressure regulator could be leaking through its vac line? its hard to make an engine run rich. show us your eehack log maybe we’ll spot something

Thanks for the quick reply. My “guy” and I talked about this. Were I working on the car myself I’d certainly have tried swapping side for side. However since I’m paying him to do the work it’s more cost effective to just replace the injectors. The disadvantage is that if it works we won’t know which one or if all were faulty. He has rounded up new OEM injectors that he has either installed or will shortly. I’m going to stop by his shop later today and see how it’s going.

I’ve got four scans somewhere in this iPad but I’ll have to search them out. My memory stick got stuck in a box somewhere in the move and I haven’t found it yet.

I’ll post results later
Thanks

New injectors responded the same. Or no change which ever way you look at it. The compression test looked very good. Three cyl are running max rich one is only very rich. No motor problems as far as pistons rods and crank.

The interesting thing is that the left bank was originally rich. New O2 and Cat and it switched to the right bank. New O2 and Cat there made no difference. Been that way ever since.

I’m simply lost in the daylight over this car and it’s systems.

Update. We installed new injectors and new plugs again. Got. “0” change. The right bank is still dead rich. Tried new O2 wire pigtail. Nothing changed.

Finally we have decided to go with a new computer. It was supposed to be done Fri but I didn’t hear anything somhave to wait until Mon. If this doesn’t fix it I’m completely baffled.

I’m not sure just how the injectors work. Normally open or normally closed. Is it possible that the injector wires for the right bank are open or closed all the time, in other words an open or closed circuit That is supposed to open and close by the computer command?

there's constant power to the injectors. the power comes from two independant circuits from the fuse block (one for left and one for right). the ECM closes the ground to each injector to fire it. yours is a sequential injection system so they all fire individually depending on engine rotation.

i sincerely doubt replacing the ECM is going to do anything

to be completely frank with you, if you're replacing ECMs and injectors for a rich condition, your mechanic can't diagnose worth a crap. it barely takes any time to determine if the injectors are the cause of a fueling imbalance. you're just throwing money away at this point

how do you know it's running rich on that bank, anyway? and how do you know it's the entire bank?

still need to see that log...

I feel there is more to this story. If no one wants to work on the car it's generally not the car's fault. From perfect to undiagnosably messed up in a short time is atypical. Good mechanic "actually fixes things" can't fix car??? Also uncommon. Belt and basic maintenance items repair bad trans? Huh??

I have 38 years' car experince and they way this is presented just doesn't work. I can't help but wonder about the good mechanic first. Sorry, but as a mechanic I've worked with too many guys that make convincing arguments that their incorrect diagnosis is right. When they don't fix the problem they are highly skilled at covering the fact with "getting closer" or "made a difference" or "that part was hiding the symptoms from the other broken part." And if good mechanic is actually good then I wonder about "like brand new" status of car.

Why is it rich? What are the symptoms of rich operation? Are you sure the symptom you're seeing is actually causing rich operation? How can O2 sensor be reporting okee-dokee if three injectors are "max rich?" And really, what is "max rich?" In my mind that indicates the injector is at 100% duty cycle... "always on." That's an easily diagnosable problem. The way the problems are reported requires interpretation, which makes an accurate diagnosis tough.

Oscilliscopes were once rare in the auto repair field but a shop without one today is not fully capable of diagnosing problems. The injector on and off time can be measured with an external tool to confirm that ECM is reporting correctly. Time for each injector can be recorded and compared. If all injectors are at similar times then injectors get checked for leaking or improper delivery rate. If injectors are open for same time, and are all delivering same amount of fuel, then it's not injector or fuel delivery problem. Stop chasing injectors and look for other issues. Good mechanic knows when to trust facts.

Spark plugs black? Wet? Dry? Oscilloscope on coil wire will show secondary pattern to determine whether or not plugs are being fired correctly, if voltage is going where it should, if cylinders are rich or lean. Good scope reader can tell if plug gaps are correct, if EGR is active, if cylinder compression is not correct. Good scope reader can see crossfire, failing wires, bridges in coil insulation. Good scope reader can do many amazing things.

How can O2 be "perfect" and engine be "max rich?" Oscilloscope on O2 sensor will show O2 voltage and signal pattern. Does voltage match ecm reported value? Does disconnecting injectors change reading on scope? How about reading from ECM? Good mechanic will be confirming data with trusted tool, not just accepting what's on computer screen.

Is the cam good? Is the vacuum signal strong and steady? A weak cam can produce good compression readings while failing to fill a cylinder fully. Vacuum gauge is one way to see this. Oscilliscope on MAP sensor signal can be even better. Oscilliscope on MAP can be read to see intake valve opening and closing, pressure waves "bounce" as valves are closed, throttle angle changes appear imediately, restricted exhaust shows up quickly. This Oscilliscope thing sounds more versatile all the time.

Why are we not suspecting an ecm? Because someone else's isn't broken? But you want this fixed so how can you rule anything out? ECM response to rich or lean O2 is critical part of feedback loop. High O2 signal voltage from rich engine should result in less fuel delivered. But O2 sensor value is fine: "all sensors are in range and almost dead center of range." So what is telling you engine is rich? BLM high = ecm adding fuel to correct lean problem. BLM low = ecm removing fuel. My feeble mind follows training from 1980's EFI classes. Misfire = fuel not reacting = excess O2 = lean O2 reading = ECM tries to add fuel. Engine is not rich! Engine is misfiring and ecm is responding as programmed. Did Good Mechanic discuss this with you?

I'm not invested in diagnosing this. The questions are for you, not for me. The way this is presented I do not believe there's much chance of successful diagnosis in an internet forum. There are too many subjective descriptions and there's too little actual data to work with. "I changed the injectors but they're still rich" is not the same as looking at a recording of injector on-time over time. "The O2 readings are perfect" does not present an opportunity to evaluate the O2 readings. It tells the reader "Don't bother looking here because you won't find anything."

Hopefully you and your "guy" will find an answer to this obviously frustrating problem.

injector pulsewidth (the output that your mechanic is questioning) is easily checked by comparing the duty cycles of all the injectors. if you suspect a bad output (in this case injectors) that output needs to be measured, then you verify if your inputs are sane, if they're sane, then and only then can the ECM is suspect. it would be really odd for an ecm to be in a failure state that erroneously delivers MORE pulses.

you don't need a scope to check that your injector outputs are good, a dwell meter will do too, does your mechanic have one of those?

a mechanic that has neither a scope and knows how to use it (new-school) or a dwell meter and knows how to use it (old-school) isn't really from any school, and probably needs to go back to school pronto.

the entire thing sounds like a waste of money

you could likely go buy a perfectly running LT1 car and swap the entire engine and wiring over with less time and money that have been put into this issue

but as a tuner and LT1 guy on a forum for tuners and dataloggers, again, i'd be willing to look at a driving log to see if all your inputs and outputs are sane, and give you theories based on that just as a brain exercise

I really feel sorry for this guy. His mechanic is best at swapping good parts but not that good with diagnostics.

SInce there is a missing cylinder[ or random missing opti], that might be the reason it runs pig rich. Missing cylinder means unburnt oxygen in the exhaust, which leads the pcm to think there is lean condition and dumps fuel till the blms are maxed out.

The simple test to see what`s wrong is to force open loop and see how it drives and monitor 02s reading [Make sure the blm and int is showing 128]. DIsconnect the battery, at least for an 1/2 an hour, prior to tests to clear any out of range blms.


Post the eehack log to get more insights.


With eehack and the built in real time controls you can pinpoint any electrical and mechanical issues in less than hour, you`d better start diagnosing yourself if you want the car to get fixed.

Sorry I'm late to the punch again.
Here's what has NOT been checked. The EGR valve and passages. A clogged catalyst.
1) EGR flow causes o2 sensors to read rich. Remember, the O2 sensor detects oxygen.....only. Nothing else. Displace oxygen with something else = rich reading from O2.
If the car is not driven long enough, carbon builds up in the egr passages from not getting hot enough. The right side just might be plugged + EGR valve hanging slightly open = left side false rich reading. Don't forget about a leaking EGR solenoid causing false activation of the egr valve. Unplug it and see if readings change.

2) A plugged catalyst. Makes it run rich (low oxygen). Run a backpressure test with a gauge. Can be a partial restriction, so a gauge reading is preferred. 1 psi per thousand rpm is acceptable for stock engines.

Get a noid light and put it on each injector connector (one at a time) while engine is running. Should answer the injector driver question.

Yes, I own a caprice wagon 1995 with an LT-1, go figure.

leaking fuel pressure regulator

I didn’t have instant email response tagged so I’m late getting back.
The guy has a top if the line Matco scanner/code reader. Plus the connector for OBD 1. It’s a wireless device.
You can see everything or focus on just one item with this device.

I’m a rank newbie to this level of diagnostics. I’ve used a dedicated scanner for my diesel truck and picked out the exact problem and fixed it. So that’s really the limit if my experience.
I also worked in the performance auto shop for a number of years. We did have an osciloscope but it was pretty primitive for the Era.

Anyway both his scanner and my dedicated laptop it’s it’s software show the same thing. I seem to be able to get a little further into the information in that I can select clear items. With one exception, I can’t clear the or reset the BLM box.
When you scan it clearly shows 3 cyl at max richness and one cyl very close. I thing for numbers it’s 160 and 150.

Looking at all other sensors the show generally mid range. You can see both O2 cycling. Both have been replaced. As have both Cats. A smoke test showed no leaks anywhere all the way to the front of the motor. I’ve not used one nor was I there when it was done.
I questioned whether there might be a cam and lifter problem. There doesn’t seem to be. However the real question is why did the event switch from the left bank to the right bank? Then it becomes non responsive to any changes. It has a new old stock OPTI Spark as well as new OEM wires and spark plugs. There is spark on all plugs.
There is low manifold vacuum. It measures in metric by the scanner and I recall about 10-11 inches by conversion. Also vacuum gage.
The car idles right on rpm but has a “putter” and an occasional “crack” from the right side exhaust. It feels like a dead ignition miss. The car does drive as long as it’s not loaded going up hill. Anything below about 55-60 it will drop out of OD or I have to manually down shift. It has the towing package gear which is 2.92 or there about. I can’t imagine the standard gear of 2.56 originally the car ran perfect. You could cruise at any speed and the trans. would drop out of converter lock and down shift appropriately for the speed. It was a joy and very easy car to go anywhere. Now it’s a PIA. I know these motors were designed to have torque at low speed and were very economical as well as decent performers in their day.

I too passing said it would have been easier and less expensive to simply replace the motor and wire harness with a known good one. It would have solved my issue of having a car that runs correctly. On the other hand it would be the ultimate “throw parts at it” solution. I should be like my dad might have said, “ I don’t care what you do, just fix the ..... thing” .
And indeed at this point I really don’t care. We have done everything “by the book” as well as by what I would think common sense. At every step we have weighed the option....will this fix it? Is this a reasonable option? Or are we just guessing?

I burns me that I’ve built some very high performance cars from the ground up that drove nicely. Started everyday got decent mpg, and were very reliable. My current car ‘77 el Camino has a 300/350 that starts at -5 to 95 every time gets as good mpg as the motor can and still passes ‘77 emissions.

This Buick is has to run under more emission requirements but probably 500 engineers designed and caused it to be built.
There is a lot to this thing besides just a motor with a lot of sensors. The wire harness is huge. We have cleaned and inspected many connectors. I don’t think this car was submerged or subjected to high pressure under hood washing. It was a lady’s car.

So I really appreciate any help or comments. You won’t hurt my feelings to call me what you like. I’m more interested in a solution to the problem. If you have to call me whatever to get the point across fine, if it fixes this problem.

Can you easily cross connect the O2 sensors on that car? Some, you can do that and introduce a new issue while trying to fix a current one.

I don’t think this is possible. The car has a true dual exhaust with no interconnection between pipes. The O2 cables are relatively short. They are a good 3 feet or more apart. I’d have to check under the hood. Maybe the harness could be unwrapped. The shop is on vacation until Sept 2 . Sure wish I could simply go on vacation. Even living on my boat I can’t simply take off. Yet.

I suppose a test connector could be made. Were i able to have the car where I could work on it, I’d try and make some kind of connector. Somewhere I’ve got the under hood wiring lay out. I’ll did around on my computer and try and find it.

I looked up EGR faults and I don’t see any that I’ve experienced with this car. I know he did take it off and cleaned it and replaced the vacuum line. I’ll have to look up the construction of this one shortly.

Why or how this issue switched sides is still a question. It looks like a reversed wire harness but it may not be possible by design. It’s one of those things we go through in engineering when we design systems. It has a Japanese term but we always called it “idiot proofing”. It was a final step before releasing something to production. No matter how good it is, it can be defeated if by effort.

i had to think of the term. Polka-yoke. We called it poky yoke. It’s been 15 years since I retired so memory gets taxed.

There are many tests to be done on these systems. From a consumer or customer standpoint, what is the cost balance between removing or testing vs. R&R, besides the possibility of getting a bad “new” part.

Some simple test to do.

1.Disconnect 02 wires and have a test drive.
2.Disconnect maf sensor and have a drive test


A log made with eehack will really ease the investigation of the problem.

Also there is no way to see that 3 cylinders are running pig rich and 1 is rich. It is bank related, not cylinder related.

It is known issue that when the blms are maxed at 160 they can`t be cleared, the only way to clear them is to disconnect the battery for 30 minutes.

If the blms are maxed it means that there is alot of free oxygen in the exhaust. It could be from cracked exhaust, leaking egr plugs, cracked piston or misfiring cylinder. If the engine smooths significantly when you disconnect the 02s it could be one of these.