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Author Topic: Excessive fuel consumption  (Read 4134 times)

hairhook

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Excessive fuel consumption
« on: March 25, 2012, 05:53:00 AM »

I have a 91 capri that has always been a little quirky. The last time I drove it (Nov.2011) it used 3/4 of a tank of gas to go 60 miles and it had no power at all.
This year, it starts right up, most of the time, but until I get the revs up above 3500 rpm, it has no power and it sputters and acts like it wants to die.
I have replaced the igniter, rotor, distributer cap, wires and plugs. I gapped the plugs at .44 as the book recommended. The coil is two years old. I tried to check the timing, but the belts give me a very limited view of the timing marks. Does anyone have any suggestions for me?"
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rcdraco

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Excessive fuel consumption
« Reply #1 on: March 25, 2012, 10:38:00 AM »

Unplug the TPS sensor, it's located on the throttle body.  If that improves the drivability that's your culprit.
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Rocketman

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Excessive fuel consumption
« Reply #2 on: March 25, 2012, 06:23:00 PM »

Quote
Unplug the TPS sensor, it's located on the throttle body. If that improves the drivability that's your culprit.
This is not correct. Unplugging the TPS throws the ECU into a limp mode, ignoring several sensors at once - not just the TPS. One of the other sensors could be faulty and causing the issue, but be ignored in limp mode and thus improve driveability.

Hairhook - I would put a spot of white paint on the timing mark & check the spark timing. I'd also check for the timing belt / camshaft timing - if it's off it can bog real low and scream in the top end.

Another thing I'd look over is the intake tract - the Capri is notoriously sensitive to any vacuum leaks after the VAF.

How old is the gas in it? Fuel filter?
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1.8L Turbo All Wheel Drive Capri... the "GTXR2"


hairhook

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Excessive fuel consumption
« Reply #3 on: March 26, 2012, 02:11:00 AM »

Last year, when the problem started, every time I gassed up, the car ran terrible until I took it out in the country and pumped the hell out of the gas pedal. After ten miles or so it would run like a champ for the rest of the tank of gas.
I ran inj. cleaner through the tank but it didn-t seem to improve the problem.
I took the VAF off and checked to see that it moved freely. Checked vacuum- reads about ten at idle and 16 @ 2500 rpm.
There is no check engine light and no readable error codes.
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Rocketman

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Excessive fuel consumption
« Reply #4 on: March 26, 2012, 08:58:00 AM »

Hmm. I read 18-20 inches at idle and 20-22 when decelerating from higher RPM
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hairhook

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Excessive fuel consumption
« Reply #5 on: March 27, 2012, 05:04:00 AM »

I finally found the timing mark on the damper and the timing seemes to be very close. I changed the fuel filter also. Thanks for the tip about the engine vacuum. I think everything between the VAF and the TB is tight, but I will check again.
I checked the vacuum because I thought the catalytic converter might be plugged. The book said if it held at 16 in. @ 2000rpm the conv. was okay, but it didn't say what it should be at idle.
Thanks again
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mazdacapri

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Excessive fuel consumption
« Reply #6 on: March 27, 2012, 02:12:00 PM »

New to the site but when you check your vacuum your actually checking the sealing quality of your engine. it is affected by valve timing, ignition timing, fuel mixture at idle. checking vacuum at 2500rpm checks the breathing action of your engine or if there is a restriction in the intake or exhaust. manifold vacuum should be around 20".
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hairhook

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Excessive fuel consumption
« Reply #7 on: March 28, 2012, 03:30:00 AM »

Would a restriction in the exhaust affect the vacuum that much? It idles fine, but I let it warm up and the vacuum flutters between 11 and 12 inches at 800 rpm idle. At 2500 rpm and higher, it holds at about 16 inches.
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Chicken

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Excessive fuel consumption
« Reply #8 on: March 28, 2012, 10:56:00 AM »

Constant lack of power = Check compression
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If you heard it from an automotive forum, get a second, and third opinion.

mazdacapri

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Excessive fuel consumption
« Reply #9 on: March 28, 2012, 12:08:00 PM »

A restricted intake or exhaust would affect vacuum more at 2500rpm. your vacuum is worse at idle which would mean valve timing, ign. timing, or fuel mix at idle. BTW what is the vacuum at wide open throttle? should be near zero. You can also check for weak or non working cylinder by pulling out spark plug wires one at a time and checking for a 150 - 250 Rpm drop from each cyl. Bigger the rpm Drop, stronger the cylinder. Misfires can give you shitty gas mileage.
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Gostlrs

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Excessive fuel consumption
« Reply #10 on: March 28, 2012, 02:54:00 PM »

+1 On compression

If that is good and so is the timing

I would throw in some B-12 Chem Tool on the next 2 tanks. You might have a ton of water in there & some bad fuel/filter. Use 91 as well & replace the O2 sensor & cat.
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luvit

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Excessive fuel consumption
« Reply #11 on: March 28, 2012, 03:25:00 PM »

Engine Coolant Temperature Sensor.
You're describing my symptom. I could never find the ECT, so once I replaced all kinds of other things, like the distro cap, rotor, plugs, wires, it worked better, but not perfect.

Then I found the ECT location and it was awesome.
I believe the ETC only cost $14.

I also think a CEL code pointed at this, too.
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omgimluvit

hairhook

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Excessive fuel consumption
« Reply #12 on: March 29, 2012, 11:26:00 AM »

I think my next step is to punch some holes in my catalytic converter and see if the vacuum rises. If it's bad, I'm going to have to replace it anyway.
The ignition timing is right on, and as long as it is still up on the ramps, I can get my plump butt under the front end enough to poke some holes in the converter. I replaced the muffler and manifold pipe last year before this problem arose. If I have to replace the exhaust system, I'm going to have it sized to some standard size that doesn't need micro processing and a ton of money.
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hairhook

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Excessive fuel consumption
« Reply #13 on: March 31, 2012, 03:32:00 AM »

After sobering up, I visited my local mechanic and had my vacuum gauge checked against his. I found it's reading about 3" low, so at idle vacuum is about 15". Still too low.
The gauge isn't fluttering wildly so he tells me that I most likely have a bad vacuum leak as opposed to a stuck valve or jumped timing issue with the valves. Now i'm looking for a leak in the intake somewhere. Thanks for all the suggestions.
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hairhook

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Excessive fuel consumption
« Reply #14 on: May 22, 2012, 06:53:00 AM »

I took the beast to a good mechanic and he tells me that there is a leak between cylinders 2 and 3. He also said that my throttle position sensor is dropping out at the midway point. Does anyone know if there is an after market TPS available for this vehicle? I'm gonna have to save for the valve job.
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