Manyfold... pun intended


Old 12-10-02, 10:51 PM
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Talking Manyfold... pun intended

96 Geo Metro, 114k+, 1.3L, Manual ,Teal,Gray Int, 4 Wheels

So where to start.. many fold as I said..
Assuming that the ODBll scanner is working correctly I may be getting a Manifold Absolute Pressure Sensor whacko warning. Which leads to the test according to CHiltons manual.. 5volts with key on not started then 1.1-1.3 volts after engine running. Well I got the 5v but then 1.5v after I started it. My question is could this be a 'false' positive? Not really the MAPS ($90) but could it be catalytic blocked (looks original) to cause to much pressure. Book says low voltage is low manifold pressure OR high engine manifold pressure ( clarify the difference if you could) which leads back to higher voltage corralates to vacuum decreases and the pressure goes up (according to my CHiltons). Neglected to give "problem", gas usage has increased dramatically and it kind of 'stumbles' when acclerating. Slight hesitation at highway speeds once up to 55 but seems to run 'alright' once at cruising speed. Changed fuel filter,air, pcv,plugs,rotor,dist cap,tranny fluid(don't ask why), oil of course, I just recently bought this vehicle and ran great for about month or so then got this check engine light and these other problems... I know I always forget something but... Joe is kind enuff to remind me
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Old 12-11-02, 03:24 AM
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I thought a Geo Metro only had three wheels since it's a graduated wheelbarrow .

You can bring the MAP sensor in for testing at any parts store---yours sounds bad though. Increased fuel consumption is also a key sign of a bad MAP too.
Old 12-11-02, 11:21 PM
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You could also be getting this reading because of a vacuum leak. If you don't have enough vacuum, the sensor reading won't go low enough to be in range at idle. You're only 2 tenths of a volt out of range, so it would be easy to suspect a bit of a leak. Do you have a hand-held vacuum pump? If so, connect it to the map sensor and draw a vacuum to 19 or so and read the voltage then. If it is in range, then you probably have a leak. If it is out of range, then the sensor is bad.
Old 12-12-02, 12:48 AM
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Also dont forget to correct your readings as higher altitudes mean less vacuum. Generally 1" less for every 1000 feet above sea level. i believe they usually say this rule of thumb starts after the first 3000 feet. In Colorado we drive and live up to nearly 11,000 feet! That does change some readings.

Poor engine performance will also decrease vacuum and create voltage changes on vacuum sensitive sensors.
Old 12-21-02, 04:09 PM
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Unhappy The story so far.....

So I invested in a vacuum pump gauge... Yes reading was even further off. Broke down and bought the MAP sensor.. ran really good for a bout 20minutes then started doing the same things just not as drastic as before. I haven't tried it from an overnite startup yet but still 'hiccups' just not as bad as before. I can hardly notice it but it's there. i assume it must be something else now. UNLESS my voltage regulator blew the new one??? Is that a possibility? Guess thats why one pays the mechanix, but it's a good excuse to buy new tools. I'm still about even without spending $75 for diagnostics plus I got a vac pump for next time
Old 12-21-02, 08:38 PM
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Is the vacuum line going to it any good? How's the EGR valve? Did you inspect it for carbon and hanging up? How's the fuel pressure? The last time it saw a tuneup? etc, etc, etc, etc, etc.
Old 01-11-03, 10:31 AM
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Unhappy Silly me

Umm I think I solved it (or should I say my friend who was driving to the store with me). The short story is I needed new plug wires. This seems to have solved the problem. The check/service engine light has gone away and runs very well again. Similar to when purchased (used) a few monthes ago. Thanks
Old 01-11-03, 10:38 AM
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As I always say, "Back to the Basics" (I asked above in a prior post when the last time it saw a tuneup )

Glad you solved it
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