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testing a pressure sensor????

guys,

is there a way to test a pressure sensor to make sure it's working. i'm still trying to figure out why my motor keeps hesitating when i hit the gas and it won't produce it's full power. it's a 72 1.7 with the original fuel injection. any ideas let me know,

thanks
scott
Old 04-05-2005, 08:00 PM
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Worn out TPS?
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Old 04-05-2005, 08:21 PM
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To test the MPS you pull a 15hg vacuum on it for 5 minutes. It should hold that 15hg or maybe bleed down to 12hg, if it bleeds down to 0hg you are in trouble.
Do you smell gas? A bad MPS makes the car run rich...
My guess is a sticking dizzy or bad dizzy.
Timing is everything on these cars.

Geoff
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Old 04-05-2005, 08:26 PM
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Geoff,,,,a worn Throttle Positioning Sensor gives you a hesitation as well....

Blipping the throttle by hand will show you the symptoms....very common.

Of course, your mileage may vary....
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Old 04-05-2005, 08:29 PM
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MPS test.
1 Like geoff said. 15 lbs for 5 minutes.
2 between post numbers 15 and 7
and between 8 and 10 readings are in oms.
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Old 04-05-2005, 08:32 PM
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Geeeez..NO votes for a TPS????

Hope he posts and I'm right.....
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Old 04-05-2005, 08:37 PM
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Im with you Mike...A worn TPS could cause it...

Sticky dizzy weights would too. Oil the felt in the center of the Dizzy!
Old 04-05-2005, 09:09 PM
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Ohhhh,,,scary...I owes ya a beerski....
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Old 04-05-2005, 09:11 PM
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Re: testing a pressure sensor????

Quote:
Originally posted by 24flys
guys,

trying to figure out why my motor keeps hesitating when i hit the gas and it won't produce it's full power.
thanks
scott
TPS problems are usually around 2500-3000 rpms and don't keep the engine from reaching full power.
Timing problems often do....sticking advance plate or off timed cause hesitation and prevent the engine from producing power.

OR a really rich condition, which is easy to smell.

Geoff
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Old 04-06-2005, 05:31 AM
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thanks for all the advice guys, i'm going to try a few things tonight. i haven't set the timing since last year. would resetting the valves cause the timing to be off?? and a couple more questions, what is a TPS?? and where is the advance plate in the dizzy??

thanks
scott
Old 04-06-2005, 10:37 AM
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well i figured out what the tps is but i still can't figure out where the advance plate is, where will i find it.

thanks

scott
Old 04-06-2005, 11:03 AM
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The points ride on it...It covers the counterweights...
Old 04-06-2005, 11:14 AM
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thanks bowlsby,

how do i find out if it's sticking?? and is there another name for the TPS. the name i found was throttle positioning sensor but i can't find it in pelican's catalog. i'm trying to figure out what it looks like and where it is on the motor.

scott
Old 04-06-2005, 11:19 AM
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a worn pressure sensor will usually cause the car to run WAY rich. YOu can also do a quick check of it by sucking on the vacuum port to see if it's holding vacuum. What happens is that there is a sealed cell diaprhagm ion there that can seperate and trick the computer into thinking there is a false vacuum reading. I think there was a guy on the board that was repairing them, do a search.

as for the TPS, it's on the throttle buttefly. (the black box attached to the butterfly shaft) if you remove the cover, you'll see a arm wth electrical contacts that contacts the printd circuit track on the board. What typically happens is that the printed circuit track wears a flat spot. Sometimes, if you are careful you can clean it, or remove a bit of material to freshen up the track, then very slightly re-adjust the electrical arm to contact it.

also on 1.7's another common problem is that the throttle shaft becomes slightly bent and causes the butterfly to stick in it's bore. This was causing some hesitation and idling problems on my old car. I'm pretty sure this has to do with the way the throttle cable applies constant pressure to the top of the shaft, hence bowing it over time. You can check this by taking off the air boot, then opening the thorrtle by handf then letting it shut quick. if it sticks closed, then you know it's bowed.

I fixed this problem on mine by carefully disassembling the throttle, smoothing the edges of the butterfly and also lightly sanding the portion of the shaft where it sits in the throttle housing. this solved the problem for me.

THere's also the old problem with vacuum leaks. If there are any leaks, it will cause a bunch of problems. When i had my 1.7 i would replace the vacuum hoses every year.
Old 04-06-2005, 02:34 PM
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well,

i tried to start it last night and the battery is drained. it seems like something is draining the power. i'll have to figure out what this problem is now before i start on the other. but thanks for all the suggestions, i'll try them as soon as i can figure out how to keep it running.

thanks
scott
Old 04-07-2005, 09:30 AM
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Joe Sharp,

What values are being measured ? resistance (ohms?) or volts?
Old 04-07-2005, 02:42 PM
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Resistance. You won't get voltage anywhere in the system unless you're hooked up to a power source, like a battery.

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Old 04-07-2005, 03:34 PM
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Generally, if the pressure sensor is the right one for your car, holds vacuum, has the correct values of resistance for the primary and secondary windings, and is unmolested (i.e. hasn't been "adjusted" by drilling or removing the epoxy seal on the end), then there is a very high degree of assurance that it is working properly. Check my web page for more details on the pressure sensor and testing of your D-Jetronic FI system.
Old 04-08-2005, 07:35 AM
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All of my information comes from Mr. Paul Brad Anders.
Thank You Brad
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Old 04-08-2005, 10:37 PM
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This is the first post I've seen for testing the MPS electrically. Can't wait to test mine tomorrow. Might be the culprit for its crappy running!

Gonna get rid of them thar dam'd points too got me a new 'lectric ignition thingy today

........b
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Old 04-12-2005, 09:25 PM
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