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1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
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Discussion Starter #1
So I'm driving my '92 Fleetwood to work today, and something just doesn't feel right about the performance. It feels like it has an intermittent miss, mostly at idle, though it kicks in pretty bad when the torque converter engages too.

So I get to work and have to let it sit. I'm hoping it's bad gas, but the more I drive the worse and more pronounced it gets. I think to myself, this feels more like a spark issue than when I've had fuel system problems in the past. It feels like a car with a spark plug shorting out.

So I get it home and mess around under the hood. I haven't checked for codes yet, but the CEL isn't on, so I figured if I can't figure it out on my own I'd try to pull codes tomorrow.

I'm messing with the throttle, checking out if the ISC is working. Well, it works, but it seems sluggish. Maybe that's just how they work, but it seems to be delayed more than I would think. I need to find the thread that explains how to disassemble it, clean it, and make the car recognize it.

Poking around under the hood as my non-mechanical, extremely limited self, I figure I should look at the last work done under the hood. Sure enough, one of the spark plug wires is sitting a bit higher than the others. It had popped of or was never all the way down (car had been running good, so I guess it wasn't 100% latched on, and worked it's way off.)

So as previously stated, I hope I figured it out. I'll drive it tomorrow and see how she does.
 

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1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
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Discussion Starter #3
Yeah, but I think I have an additional issue. I've been reading old threads for an hour, and I think I have a vacuum leak that is also keeping my parking brake from releasing. I'm gonna monkey around with that a bit. I've also been reading people's horror stories about trying to diagnose problems with these cars. Man, I'm getting scared.

But before I give myself a hear attack, we'll check her out one issue at a time. Gonna check for vacuum leaks!
 

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1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
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Discussion Starter #4 (Edited)
Just found a spark plug wire laying against the O2 sensor, and possibly exhaust manifold. Gonna change it with an old one as soon as the car cools off enough to mess with it.

Edit: I replaced the burnt spark plug wire with the one that came with the car. It improved thingss slightlyu, but there is obviously still something off. It has a pretty noticeable miss on accelerating from sitting still, though it seems fine elsewhere through the power band up to about 50 to 55 mph. Didn't drive any faster. This is getting frustrating. I know I probably have a vacuum leak because my parking brake doesn't release like it should, but I can't find it. Maybe it's time to tear into the dash?
 

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1992 DeVille
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2,339 Posts
might wanna do all plugs and wires. also that parking break diaphragm is something that commonly goes bad. mine went bad. i took the vac line off, put a straight line male to male connector on and capped that. now i only use the manual release lever. it doesnt bother me too much. new part goes for about 30 bucks. i found one for 50 shipped from the midwest to ca where im at. but 50 bucks for a part id have to break my back to replace...well thats why i havent ordered it. hard part to get to to swap out. maybe one day ha

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did you do a general tune when you got the big ol girl?
 

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1985 Sedan DeVille
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Autozone sells a vacuum gauge, about $15. Also need a few feet of 5/16 ID vacuum line (washer fluid hose), some assorted fittings to make splices and tees. Use one of the fittings to splice into the EGR solenoid, then fix the gauge into the wiper arm so you can read it from inside while the car is moving. On the front of the engine bay is an emission sticker with a diagram of the vacuum harness. Once you have a baseline you can start testing the different subsystems.

Stumble can come from a lot of things. Weak spark, misadjusted timing, poor fuel quality, vacuum leak, EGR, dirty O2 sensor, ...
 

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1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
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Discussion Starter #7
Good info guys. I checked the codes today, and all I had was some MAP sensor codes - but I expected them, because I was disconnecting vacuum lines to see if it made a difference, and the map was one I had done.

I did find a vacuum leak near the brake release - it was a pink and a lavender line with a clear connector that they both connect to parallel to each other. One had vacuum, the other runs to the brake booster (the lavender I think.) For the time being, I pulled them out of their connector and connected them to each other - but the park brake now cannot be set. That's OKAY! I don't park on a hill. I don't ever use it.

NEW SYMPTOM noticed though - my distributor is making a clicking sound. Is this normal? I haven't taken the cap off yet to check things out. I've had many cars, and I've NEVER had a rattle coming from the distributor that I can remember. Any insights?

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might wanna do all plugs and wires...... did you do a general tune when you got the big ol girl?
I did new wires, fuel filter, air filter, pcv valve. Haven't done spark plugs yet, but pulled a couple and they looked great.

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Also remembered, my exhaust sounds weird. It sounds like a series of puffs with about a tenth of a second in between. Feels like it's missing when pulling away from a stop light, but for the most part feels normal through the power band.
 

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2001 Seville STS, 1990 Seville (RIP), 1972 Sedan Deville
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The map sensor is monitored electronically. You disconnected vacuum from the MAP sensor? Disconnecting vacuum lines won't trigger a MAP code. If you're getting MAP codes, something's wrong with it.
 

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1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
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Discussion Starter #9
The map sensor is monitored electronically. You disconnected vacuum from the MAP sensor? Disconnecting vacuum lines won't trigger a MAP code. If you're getting MAP codes, something's wrong with it.
I disconnected the vacuum line directly from the MAP sensor while the car was running, causing it to stumble terribly. Hooked it back up and the idle went back to how it was before hand - weak and with what seems to be a misfire.
 

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1992 DeVille
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ratmonster said:
Good info guys. I checked the codes today, and all I had was some MAP sensor codes - but I expected them, because I was disconnecting vacuum lines to see if it made a difference, and the map was one I had done. I did find a vacuum leak near the brake release - it was a pink and a lavender line with a clear connector that they both connect to parallel to each other. One had vacuum, the other runs to the brake booster (the lavender I think.) For the time being, I pulled them out of their connector and connected them to each other - but the park brake now cannot be set. That's OKAY! I don't park on a hill. I don't ever use it. NEW SYMPTOM noticed though - my distributor is making a clicking sound. Is this normal? I haven't taken the cap off yet to check things out. I've had many cars, and I've NEVER had a rattle coming from the distributor that I can remember. Any insights? ---------- I did new wires, fuel filter, air filter, pcv valve. Haven't done spark plugs yet, but pulled a couple and they looked great. ---------- Also remembered, my exhaust sounds weird. It sounds like a series of puffs with about a tenth of a second in between. Feels like it's missing when pulling away from a stop light, but for the most part feels normal through the power band.
Plugs on the firewall side of the engine might have been neglected to be changed.

(I was getting a high rpm acceleration ping that a new O2 sensor seemed to fix....)

What do you mean your parking break won't work? Like it won't release or you can't set it??
 

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1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
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Discussion Starter #11
Can't set it, now that I hooked up the vacuum line to it. But the brake isn't intended to have constant vacuum pulling on it. It's only supposed to get vacuum when the car goes into gear. So it isn't working, but it's doing exactly what it should be doing. Vacuum is how it releases. Constant vacuum equals constantly released. Still better than a vacuum leak in my opinion. No different than capping it off really.

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The vacuum line that runs into the cabin controls the brake and the AC/heat stuff. It tees and runs in two directions. I'm just gonna replace the T with a straight fitting, then I'll have parking brake again, with manual release only.
 

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1992 DeVille
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ratmonster said:
Can't set it, now that I hooked up the vacuum line to it. But the brake isn't intended to have constant vacuum pulling on it. It's only supposed to get vacuum when the car goes into gear. So it isn't working, but it's doing exactly what it should be doing. Vacuum is how it releases. Constant vacuum equals constantly released. Still better than a vacuum leak in my opinion. No different than capping it off really. ---------- The vacuum line that runs into the cabin controls the brake and the AC/heat stuff. It tees and runs in two directions. I'm just gonna replace the T with a straight fitting, then I'll have parking brake again, with manual release only.

Ohhhh yeah yeah yeah I see what you did.
 

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1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
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Discussion Starter #13
Okay, ran the vacuum line for the HVAC straight to the vacuum feed coming in from the firewell, and disconnected the vacuum diaphram to the park brake. Now park brake works fine, and is released manually only. Fine by me!

Came to a bit of an epiphany today (you real mechanics can laugh, that's fine. I expect it.) Once the car is warmed up, it starts acting up. When it's cold, which doesn't last long on a day like today, it seems fine. Does that indicate that it would be a sensor that only activates after the car is in (I guess you call it) open loop?
 

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1992 DeVille
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ratmonster said:
Okay, ran the vacuum line for the HVAC straight to the vacuum feed coming in from the firewell, and disconnected the vacuum diaphram to the park brake. Now park brake works fine, and is released manually only. Fine by me! Came to a bit of an epiphany today (you real mechanics can laugh, that's fine. I expect it.) Once the car is warmed up, it starts acting up. When it's cold, which doesn't last long on a day like today, it seems fine. Does that indicate that it would be a sensor that only activates after the car is in (I guess you call it) open loop?
Yeah that's right. When it's cold it's not referencing sensors and uses preset values for a/f mixture and whatnot. Once the car is warmed up to operating temp it goes into closed loop and references all the sensors
 

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1985 Sedan DeVille
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O2 sensor and cat converter have to reach operating temperature to function properly. The computer looks at a couple of things like coolant temperature (intake manifold not the radiator) and runs the engine rich to get the exhaust gasses hot (post-ignition combustion). When the sensors indicate everything is warmed up, the computer starts monitoring O2 sensor and making adjustments from there. Later years had O2 sensors with internal temperature switches that the computer could tell when it was actually hot enough, some of them even have little heater elements that the computer can activate to warm them up faster.

If the car runs poorly when the computer starts reading the O2 values, then it may be the O2 sensor is putting out faulty values. Sometimes you get a code from it, sometimes its just a check engine light, sometimes nothing.

If you don't know when the O2 was last replaced, probably should go ahead and replace it. Avoid cheap parts.
 

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1992 DeVille
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Also worth noting that under wot the computer does not reference the O2 sensor it uses the same predetermined a/f mix table to give the car optimum performance. So if you aren't seeing the issue when in open loop or wot, could definitely be a sensor

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Tbi cars have a reputation of nickle and diming a person to death (if you let it) by shotgun spraying parts at them and hoping for the best. That's why it's always important and best to properly diagnose the issue before spending a bunch of money on parts. Unless you're into and can afford that sort of thing
 

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1991 Cadillac Sedan deVille
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The car uses every sensor with the exception of the O2 sensor while in open loop. I'll try to give you an explanation of why a car could act up when in closed loop, but not in open loop. When the engine is cold and the PCM operates in open loop the engine runs slightly richer, but when warmed up and in closed loop the PCM is able to use the O2 sensor for reference to correct the air/fuel ratio to be close to 14.7:1 (stoichiometric) for optimum catalytic converter efficiency. So, when in closed loop a lazy or failed O2 sensor can negatively affect engine performance.

Now, let's focus on something else besides the O2 sensor. When the engine is warmed up so are most of the electrical components. As electrical components warm up it's normal for them to slightly change their internal resistance, but more so a failing insulation (for example in an ignition coil, pickup coil, injector coil) will start to show signs of shorting.

TPS sensors sometimes develop what's referred to as dead spots. Those develop because of frequent swiping motion of the brushes onto the printed board resistive tracks or from engine vibrations. Such dead spots generally happen closed to the position where the sensor is most of the time - idle/slightly off idle. TPS sensors could have cracked circuit boards, be shorted or open as well. However, if a sensor becomes shorted or open the PCM will usually throw a code for it.

Regarding shorting out coils, the insulation that covers the windings of a coil wire with time and exposure to high temperatures starts to deteriorate and thus allows the coil to start shorting. Such shorting can occur in any coil operated component. Like I mentioned above, your ignition coil, pickup coil, and injector coils can develop shorting issues.

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Now that I've given you some food for thought, I'd like to offer you some troubleshooting steps. Make sure that you inspect the rest of your ignition wires for cracks, burns, pierced boots or excessive resistance. Next, inspect your distributor cap for cracks, carbon tracking or corroded terminals. Check the ignition coil while in the cap with an ohm meter (a couple of checks there - look them up online or in a manual), pickup coil (specs are 500-1500 Ohms) and injectors (12-18 Ohms). Do the ignition, pickup, and injector coil checks preferably after the engine has warmed up. Let us know what your findings are.
 

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1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
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Discussion Starter #18
Well, not really into it, but sometimes it seems to be the only option. I really need a FSM. For now, I'm finding using the onboard diagnostics really difficult, because it uses all codes instead of words. I don't know what the codes mean - and I don't mean the check engine codes, I mean that the steps are all in codes, like E95 and 7.0 and stuff. I don't have an explanation for all that. The engine codes themselves I do have an explanation for. I can't figure out how to clear them, how to enter different modes, any of that stuff.

Thing is, my car (in all likelyhood) has a 1992 oxygen sensor, so I'm changing it soon. It's cheap enough. Might do a map sensor too. Gotta wonder if the noise in my distributor could be a failing pickup coil.

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Now that I've given you some food for thought, I'd like to offer you some troubleshooting steps. Make sure that you inspect the rest of your ignition wires for cracks, burns, pierced boots or excessive resistance. Next, inspect your distributor cap for cracks, carbon tracking or corroded terminals. Check the ignition coil while in the cap with an ohm meter (a couple of checks there - look them up online or in a manual), pickup coil (specs are 500-1500 Ohms) and injectors (12-18 Ohms). Do the ignition, pickup, and injector coil checks preferably after the engine has warmed up. Let us know what your findings are.
I will definitely do so! I figure my next step is borrow a multi-meter from a friend and get to testing. A buddy of mine is well versed with electrical issues, so he will be able to help me sort through this.

Thank you everyone for your good advice!
 

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1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
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Discussion Starter #20
Nothing has changed yet. I am profoundly economically depressed, so I will have to borrow a multimeter and whatnot. So right now, we're still in a holding pattern. I've replaced or tested the ICM, coil, wires, cap, and rotor. I will be ohm testing the injectors next week.
 
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