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Old 03-29-2003, 00:23   #1 (permalink)
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EA problem- oxygen sensor?

ok there is an annoying problem with a friends car. when you hold the car at a steady rpm, say 2000 rpm the engine is a bit rough, the tacho needle moves around a tiny bit and you can hear tiny pop...pop pop... ect from the exhust. It is noticable when driving, described a bit like the car is pulling back, a lean mix i guess? now the thing is it doesnt do this, and in fact runs perfectly when you disconnect the oxygen sensor. I tried another oxy sensor in it today but no luck. There is a couple tests described in the gregory's manual which i tried today, it was for .85 volts at the black wire, and it should flick between .1 and .85 volts after 40 seconds or so. I got around .73 volts though with that test. could that be enough to cause such problems and where should i start looking to find the cause of it ?
its done this since converting it to mult point. vacuum leaks have been checked for. im confident there is no proplem in that regard.
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Old 03-29-2003, 04:53   #2 (permalink)
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Have you the correct thick MPEFI inlet gasket? Easy to see the CFI (which appear to fit) ones are paper thins the MPEFI ones are 3 or 4 mm thick (and have the required cut outs for the injector nozzles),
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Old 03-30-2003, 15:44   #3 (permalink)
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yep gasket is correct.
it would seem that it doesnt do it at all when dead cold.
Its also fine if i disconnect something like the cooland temp sensor but that makes it blow alot of smoke. so it seems to want a richer mixture. I believe its also ok under WOT.
i tested every single sensor for correct readings at ecu. the only one that didnt show up ok was the throttle position sensor. could this cause any such problems ? (was a couple volts higher or lower than it should be, ive forgotton which one. and on deceleration was supposed to go down to 8 volts but instead would shoot straight up to 11 volts) it has 2 tps's so i assume is for an auto, would this matter at all since its a manual car ? only 1 is connected of course.
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Old 03-31-2003, 15:38   #4 (permalink)
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Have you adjusted the base idle? I found on converting to MPFI that the old CPI timing no longer applied.
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Old 10-14-2003, 21:10   #5 (permalink)
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Re: EA problem- oxygen sensor?

im having the exact same problems buddy
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Old 10-15-2003, 01:39   #6 (permalink)
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Re: EA problem- oxygen sensor?

The oxy sensor works under high vaccum conditions, cruising and sometimes on idle. Just change the Oxy sensor you should be able to get a Bosch one for $80 and a generic for $60. Everytime I changed one the respective car got noticeably better economy.
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Old 10-15-2003, 03:50   #7 (permalink)
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Re: EA problem- oxygen sensor?

heh i started this thread in march by the looks of it and we still havnt been able to fix my mates car :(
we changed the oxy sensor, even had it moved at the sugestion of a mechanic because on the extractors it was only attatched to 3 cylinders. changed the map sensor, cleaned the isc and throttle body, changed inlet gasket. changed air temp sensor just because he happened to have a spare. checked the timing and idle a million times. new leads plugs rotor and cap. gone through every test for the sensors as mentioned in the gregories manual and they all seem to test ok. Spent days going through the wiring looms and testing everything. took it to a reputable mechanic who has been the place that taxis have gone to here for as long as ive been alive and they gave up after 2 days ( they checked fuel pressure for us). the poor guy has spent over a thousand bucks trying to fix this !
edit: also it got a brand new distributor and the wiring for the isc or air bypass (not sure of the correct name) was fixed as this was a conversion from cfi to mpi.
also the problem has been slowly getting worse. the car is now stalling every now and again at traffic lights ect.

Last edited by jamesk; 10-15-2003 at 03:56.
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Old 10-15-2003, 04:08   #8 (permalink)
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Re: EA problem- oxygen sensor?

It sounds like the engine is not running closed loop. Has a cylinder leakdown test been done when the engine is hot? May have carbon embedded on exhaust valve seat & when engine is hot carbon expands not allowing exhaust valve to close causing incorrect oxy sensor readings, or some other mechanical problem. Given that this may have a covered a few klm's, engine running open loop may not have good volumetric efficientcy & not able to combust richer mixtre very well?
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Old 10-15-2003, 04:52   #9 (permalink)
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Re: EA problem- oxygen sensor?

only a normal compression test but the engine is still quite new. only rebuilt last year i think it was. it ran fine as cfi but the problems were there from the moment we converted it to mpi this year so the problem is there somewhere but noone seems to be able to find where.
i went to watch when it was at the mechanics and he had a couple instraments hooked up to read the oxy sensor. i didnt quite get what he was saying but he went on about it reading slow and going lean alot. he put a new one in and it still did it.
did a basic injector test where you unplug one at a time and see how much it effects idle, they all seemed to be working there.
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Old 10-15-2003, 17:59   #10 (permalink)
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Re: EA problem- oxygen sensor?

Quote:
Originally Posted by SPALDING GREEN
It sounds like the engine is not running closed loop. Has a cylinder leakdown test been done when the engine is hot? May have carbon embedded on exhaust valve seat & when engine is hot carbon expands not allowing exhaust valve to close causing incorrect oxy sensor readings, or some other mechanical problem. Given that this may have a covered a few klm's, engine running open loop may not have good volumetric efficientcy & not able to combust richer mixtre very well?

A factory ecu will never run in closed loop unless its aiming for 14.7:1 a/f. Volumetric efficiency has nothing to do with open loop or closed loop. Closed loop occurs only under high vaccum conditions and the main load sensor is the Oxy sensor. Closed loop is only thought of as a way to improve economy not performance. Also if what you were saying is true everytime you were accelerating the car would run like shit (every car).

Jamesk have you played around with computers? I assume you change it when you went from cpi to mpi.
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