94 Buick RoadMaster Estate Wagon LT 1 issues

[Bentwings]

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

[vilefly]

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.

[vilefly]

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.

[Bentwings]

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.

[Bentwings]

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.

[lionelhutz]

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.

[1project2many]

There is no scanner data that would tell you an individual cylinder is rich.

I agree. I also know from using a Snap-On scanner for many years that they do not always have correct data for a particular ecm. And the vehicle being worked on is so old Snappy has no interest in updating it.

Whomsoever wields the answer, wields the power of one can of pop.

It's killing me. There's more suspense here than between episodes of Breaking Bad.

[steveo]

there are four choices here since you've gone so far and run around in circles and found nothing

#1 go back to the beginning and forget everything, redo every test that's been done and don't use any original diagnostic data. you have no idea what subsystem is causing the fault, or even what the fault is, so you'd need to determine that and diagnose things in a tree shaped flow chart, there's a reason every service manual has logical trees for workflow.
#2 cut your losses and go buy a wrecked car, swap the engine, wiring, and ECM. save all the new parts you've put into the other engine.
#3 sell the car as 'needs tune up' and it's someone elses problem or profit or whatever, use that money to buy something that's already running and more reliable
#4 hire a real mechanic to find the problem

these are in order of hardest to easiest, but what they will cost you depends both on your negotiating skills and current market in your area. the lt1 is over 25 years old and despite what condition its in, it's going to require constant fiddling and tinkering.

[Bentwings]

You are absolutely right.
I got the car back today and drove it 60 miles over various roads and uphill and down hill so I have a fresh feel for the the way it performs.

It’s got a dead miss on the right bank. It idles rough but steady. Does not overheat or under heat. It does not like to operate in 4th under 60 mph if there is any load like a slight hill.you have to manually down shift to third. The trans seems to perform correctly in that it will downshift if you keep giving more throttle.The car feels like it wants to run but it’s being held back. Gas mileage is terrible.

So I agree we are going to square one like a new project problem. We will test everything and take notes on a fresh note pad. I even got a new pen.

I’m very suspicious of the OptiSpark right from the start.
I’ve already looked at several videos on testing the Opti but what is lacking is exactly what happened. There was a misfire that got progressively worse but what was shown on the scanner was not mentioned. The tester used was a device that could vary the resistance the spark had to overcome the gap. Ok what if you closed the plug gap some amount? Does the Miss go away?
Since this unit was replaced due to an oil leak that leaked oil into the Opti possibly this has happened again. So I want to really get into this thing.

Question here is,, is it easier to get at the Opti by removing the radiator so you don’t have to fight tight quarters?

[spfautsch]

I’m very suspicious of the OptiSpark right from the start.

My recommendation as it relates to the optispark is to pull it and check the trigger wheel for arc holes caused by coolant infiltration. It would take a really massive oil leak to cause a problem with the opti, but if there's coolant getting in the housing you need to first make sure your trigger wheel is intact and then fix your water pump. An arc hole in the trigger wheel could cause grossly retarded spark fire on the cylinder adjacent to the arc hole (causing a dead miss), but the rest of the cylinders would run fairly well.

Edit: after some thought, I believe arc holes in the trigger wheel would very likely set a code. Whatever the case - considering the work involved to get at the opti, I didn't mean to suggest diagnosis by way of "throwing parts at it".

With that said, I would strongly recommend the "start from square one" methodology mentioned by steveo. Your mechanic was either grossly mislead by telling you 3 out of 4 cylinders on one bank were "dead rich", or he was feeding you a busload of bullshit.

[1project2many]

The tester used was a device that could vary the resistance the spark had to overcome the gap.

I use spark testers frequently. But for your problem I believe you may need other methods. An inductive timing light can be a great tool to check for consistent spark. Connect the light using the coil wire instead of a plug wire and the light will be triggered every time spark is generated by the coil. Your eye is good enough to see any missed or doubled pulses caused by an ignition problem. If the leads are long enough you can take the light with you on a road test. Aim the bulb at a piece of paper in the car so you can watch the flashing while the misfire is occurring. If the light is blinking consistently you can then move the inductive lead to a plug wire and drive. Check each plug wire one at a time. If the light flashes for every wire you should discount ignition and move to fuel or compression. If the light doesn't work correctly at one cylinder you should check wire integrity and plug condition then suspect the opti.

[vilefly]

Measurements to take:
1) cylinder leakage test (not a compression test)
2) vacuum reading at idle (does it fluctuate too?)
3) results of spark output test per plug wire (also test ignition coil separately)
4) exhaust backpressure test per side (in PSI)
5) fuel pressure KOEO and KOER (does it bleed down?)

get lisle #20700
Attachment 14841

get backpressure tester
HTB1A3vyHf1TBuNjy0Fjq6yjyXXaF.jpg
And......remove nothing except the spark plugs and o2 sensors to do the tests. Be efficient.