: Really bad MPG



codewize
05-01-05, 01:24 AM
So over the last week or so I've noticed that my 93' Brougham started getting really bad gas milage. Like 10 or so. Now I think there is an O2 sensor starting to go bad. Would that affect the car that much?

N0DIH
05-01-05, 01:43 AM
It could, but would throw a code first. I would go elsewhere if there is no codes.

I would check thermostat, coolant sensor and plugs/wires/cap-rotor first.

Katshot
05-01-05, 08:49 AM
It could, but would throw a code first. I would go elsewhere if there is no codes.

I would check thermostat, coolant sensor and plugs/wires/cap-rotor first.

Agreed. Chances are far greater that there's a sudden part failure that's causing an ignition secondary malfunction or possibly something keeping the engine in open-loop. Do you know if the trans is getting into 4th gear and that the converter is locking up? A converter that's not locking will make a large difference in MPG.

codewize
05-01-05, 01:26 PM
There is a code for the left O2 sensor. As far as I can tell the car is driving and functioning normally. I beleive the trans is operating correctly. How can I tell if the converter is locking?

So we're leaning towards tune up? other than the O2 sensor? What types of things would cause an open-loop condition?

How do the coolant sensors and / or thermostat come into play?


Agreed. Chances are far greater that there's a sudden part failure that's causing an ignition secondary malfunction or possibly something keeping the engine in open-loop. Do you know if the trans is getting into 4th gear and that the converter is locking up? A converter that's not locking will make a large difference in MPG.

codewize
05-01-05, 08:45 PM
Also what are the 2 odd looking things inside the air cleaner. You knw, the one little thing that looks like a bug and has 2 small hoses going to the bottom of it and the other looks like a light sensor and has wires going to the bottom of it.

I've always wondered what that crap is for and how it affects the cars performance.

BluEyes
05-01-05, 09:56 PM
the stuff on the aircleaner isn't crap, it's useful.

The thing with the two vac lines is for the thermostatically controlled duct. When the engine is cold, fuel doesn't atomize as well, so the duct in the aircleaner pulls warm air through the duct going down to the exhaust manifold. This increases throttle response on cold starts. When the engine is warm, the duct closes and pulls cool air from the snorkel.

The other item is likely an intake air temp sensor. This would help the computer better set how much fuel to inject and where to put the timing.

The coolant temp sensor also weighs in for the fuel and timing settings. Also, the coolant temp sensor is how the computer knows that the engine is up to temperature. When the sensor tells the computer that the engine is cold, it will inject a richer mixture, and keep timing back a bit. It will usually not lock the converter either. This is all to help the engine run better when cold and help it warm up faster. But if the coolant temp sensor is bad (and it won't always set a code) the computer can think that the engine is always cold. A manual for your car should give approximate resistance values for the sensor at different temperatures so you can check the sensor with an ohmeter.

If there is a code set for the O2 sensor, then replace it. If the computer has set a code, it is probably programmed to 'know' that that O2 sensor is bad, and ignore the signal from it, so the car should drive just fine on the base programming.
Dunno how to tell if the converter is locking without a tach to look for a small RPM drop after you get up to speed on the highway.

codewize
05-01-05, 11:33 PM
Ok now that you mention timing, this begins to make sense. The car does feel like it's bogged down. Like driving with a choke closed or retarded timing, which I assume would be the affect if the ECM thought the car was cold.

So now should I be looking at the engine temp sensor or the coolant temp sensor. I know one of them works because I just changed the radiator in this car and it got air bound and one of the idiot lights came on. Problem is, I don't remember which it was.

I guess for the few dollars it costs I'm going to change both and the Air Cleaner Temp Sensor along with the O2 sensor. Air filter and PCV breather will be done also.

Wow. tomorrow's a full day of Caddi stuff for me.

Conductor Al
05-02-05, 04:41 AM
Definately sounds like timing and not the O2 sensor. Ought to have the engine checked and tune ups done on a regular basis. Properly maintained you should be getting reasonably close to the mpg numbers the car had when new. In high school, my '89 Fleetwood Brougham (five-six years old at the time) ran just as well as the day it left the factory due to the high level of maintenance it got. Living way up on a mountain, it was rare that the car made it more than 8 months between brake shoe replacements and the periodic rotor machining/replacement. Whenever it went in the shop, the engine received a maintenance check at the least. Reason for the frequent brake jobs was simply that the grade of the road and weight of the car combined made using lower gears useless. Putting it in 2nd, the car would still get up to 50+ mph. First would drag the car down to 25 assuming you didn't trash the transmission in the process of downshifting.

codewize
05-02-05, 10:13 AM
Ok anyone have a lesson on how to set the timing on this thing. I have a gun I guess I really need a book for this car. We know the O2 sensor is bad because of the code. The breather and air filter need replacing. Let me give you a small bit of history on this car.

Normal MPG is about 24 - 26 Back about a year ago the car starting feeling boggy or not so snappy. It's sort of like the first bit of throttle is dead. Going up even the smallest incline causes the car to downshift like it can produce enough power.

I thought about the cat but the exhaust pressure seems more than enough to discount the cat. Am I wrong about that?

Then all of a sudden the car died while my wife was driving it. Just stopped dead. I had it towed to my local shop and they claim they replaced the ignition module. Then I replaced the cap and rotor. Much to my surprise the car still felt boggy, and still does.

Engine idles smooth doesn't seem to miss or anything but once in a while when your driving, mostly during acceleration from a dead stop you'll feel a surge of power like the car 'comes to life' and you'll have all the power in the world.

I'm going to hold off on the work until furthur feedback form here

Katshot
05-02-05, 11:07 AM
The procedure should be on the engine spec sticker. If that's missing, I believe it's just as simple as placing the engine in base timing via grounding the diagnostic terminal on the ALDL connector (connect the A & B terminals).

codewize
05-02-05, 04:04 PM
Is that connector under the dash? Paperclip jumper kind of thing ?

Katshot
05-02-05, 04:06 PM
Is that connector under the dash? Paperclip jumper kind of thing ?

That's the one alright.

cmgrafmc
05-02-05, 09:45 PM
Normal MPG is about 24 - 26 Back about a year ago the car starting feeling boggy or not so snappy. It's sort of like the first bit of throttle is dead. Going up even the smallest incline causes the car to downshift like it can produce enough power.

Engine idles smooth doesn't seem to miss or anything but once in a while when your driving, mostly during acceleration from a dead stop you'll feel a surge of power like the car 'comes to life' and you'll have all the power in the world.

ME TOO! I'm having just that same problem, but now my transmission seems to be acting up. (Had the solenoid replaced again, but no fix there.) I have to floor it sometimes to get up to speed and it pulses. Then all of a suddent it's like a switch is flipped and I have lots of power again, until it upshifts and begins again. When I reach cruising speed, it seems to pulse some more. Maybe one of the birds in my car port flew into my exhaust system and made a nest in there...

As much as this sucks, at least I know I'm not the only one with this seemingly unique problem.

codewize
05-03-05, 02:01 PM
Hmmm I dont have any pulsing. It's always smooth just usually from a stop it seems doggy and then at cruising speed I have to really mat it to feel any acceleration. However like I said, I can be accelerating and all of a sudden, just like a switch, bam it's there and takes right off.

Climbing a small grade is a good example. You know how you push the gas to keep the speed when aproaching an encline. Well as soon as the car starts climbing it downshifts like it doesn't have enough power to maintain speed.

I have had instances where it feels like it's running out of gas sort of but that was only a couple times and it's been a while since Ive seen that. Maybe it's a fuel filter or something? I think that's been changed though.

Trench
05-09-05, 01:00 AM
ME TOO! I'm having just that same problem, but now my transmission seems to be acting up. (Had the solenoid replaced again, but no fix there.) I have to floor it sometimes to get up to speed and it pulses. Then all of a suddent it's like a switch is flipped and I have lots of power again, until it upshifts and begins again. When I reach cruising speed, it seems to pulse some more. Maybe one of the birds in my car port flew into my exhaust system and made a nest in there...

As much as this sucks, at least I know I'm not the only one with this seemingly unique problem.


Same exact problem here. I have a 91 Eldorado, though. I really wish I could figure out the problem!


Dustin

cmgrafmc
05-09-05, 02:02 AM
After I had the timing adjusted correctly, to 20 degrees BTDC, I noticed the power problem more or less went away. Sometimes I think I feel a sag in power but mostly things are fine...but my mileage is still awful and the tranny shifts late when I slow down. I'm taking it in Tues. morning to see if we can get to the bottom of it. Anyone know if a bad torque converter clutch can cause these problems?

ShadowLvr400
05-09-05, 01:31 PM
I've dropped down to about 15 mpg avg. Not good... But, been doing all city driving, nothing but stop and go now, so I guess I understand it...

N0DIH
05-09-05, 03:22 PM
Timing doesn't change more than a degree or so over time, if at all. So if it was set right once, it likely isn't off unless it was messed with.

Timing chaines do get slack, you can check them by pulling the distributor cap off, line up the timing indicator to where you can see the V^V^V^V^V where you read the timing with the gun, and then move crank one direction till the rotor starts to move, mark that position, then move the crank the other way till it starts to move again. Note the difference. It should be very near immediate, but if it is around 4 degrees or more, I would look at swapping the chain. That means you are around 4 degrees retarded. That moves the powerband UP around 500 rpm. Which isn't what you want for best economy with the lazy gears Cadillac likes to give us.

As for killing off 50% or more of the fuel economy, no, this won't.

And if anyone ever read that article in High Performance Pontiac that says that because there is cam sensor you don't need to degree the cam, that was very wrong info. You still need to, the cam sensor only properly delays the fuel injector event until the valve is ready to open, reducing the fuel from solidifying on the back of the intake valve. But the mechanical events, the piston being at TDC and the valves opening at the correct time is still cruicial to have setup properly. Sorry, I never got around to flaming them for it.

In a modern lazy cam engine I still recommend 4 degrees adv on the cam, this will do 2 things, move the powerband DOWN around 500 rpm, bringing in peak torque at a lower rpm, improving low speed drivability, and take in the slack of the chain when it does stretch in time.

As always, verify that this is NOT an interference fit engine, meaning that if the cam stops a valve at full lift the piston will not be able to hit the valve. With stock lift, this is rarely the case, but with high lift and many tiny DOHC engines it is an issue. I believe the Buick 3800 is an interference fit engine. Check local parts stores, they often know from the computer that looks up timing chaing parts.

codewize
05-09-05, 06:31 PM
Ok so I took a chance and figured that A & B are the right most top and bottom pins since they are the only two adjacent pins in the connector. I jumpped those and checked the timing. I can't read the numbers on the tab but if the top most mark is 0 deg then this thing is dead on. The sticker says 0 deg BTC.




The procedure should be on the engine spec sticker. If that's missing, I believe it's just as simple as placing the engine in base timing via grounding the diagnostic terminal on the ALDL connector (connect the A & B terminals).

J-P
05-16-05, 10:44 PM
I've got a similar problem with my 89 Brougham, less power, delay on response and about twice the consommation as usual in about a few weeks.

I've found two vacuum hose that were cracked...

After replacing them with new one, everything was settled, in fact it was even better than before, acceleration, fast response and good milleage are back.

Good luck !

Trench
05-17-05, 07:29 PM
I've got a similar problem with my 89 Brougham, less power, delay on response and about twice the consommation as usual in about a few weeks.

I've found two vacuum hose that were cracked...

After replacing them with new one, everything was settled, in fact it was even better than before, acceleration, fast response and good milleage are back.

Good luck !



Same here. Just yesterday I found the vaccum line running to the transmition modulator was not sealing at the throttle body. I fixed that up and seemed to help a lot.

codewize
05-17-05, 08:30 PM
Oh so here's what I replaced

AC Delco Rapidfire plugs
AC Delco Wires
AC Delco Cap
AC Delco Rotor
WIX Air filter
WIX Breather filter
O2 Sensor
Inlet Air Temp Sensor
And set the base timing (may not have needed to do this)

And that's that. The cars seems normal and I think the fuel economy is back.