89 formula TPI

I suspect my O2 sensor is on the fritz, my exhaust smells heavily of fuel which i believe is a sign of it running lean and the ECM over compensating. (i have already ruled out injectors (which i replaced) and fuel pressure, which i already tested)

when i put the car in field service mode by grounding the A and B terminal and start the car, the check engine light (which reads the O2 pulses) basically blinks once a minute. its supposed to be about once every second in closed loop.

i believe this is a sign the sensor isn't actually taking any readings, what do you guys think? should i just replace it?

cardo0

Once every second blinking the check engine light is a engine misfire and a stored code. Im not sure but i think blink once a minute means no code.

U really need a scanner to read the fuel trims in closed loop. In closed loop the O2 sensor goes into a cycle between 100mV and 900mV then in WOT and open loop it usually goes 900mV and stays there. U would need an oscilloscope to watch the O2 signal - cant use a voltmeter.

With a scanner u can watch BLM trims go low when inducing lean by pulling off a vac line. But that could give you OBD I code 44 (4 blinks of the check engine light and again 4 blinks). And then test rich with a little propane gas in the intake. Which would be OBD I code 45 (4 blinks and then 5 blinks).

Yea so if your car/engine is truly rich it should blink code 45. I think u should look elsewhere. Which injectors did u replace with? Stock? Other than stock? Other than stock your ECM needs the new injector characteristics data - flow rate etc.

Hope this can help.

89 formula TPI

Thanks Cardo0, but what you are describing with blinking is when the car is not running and it's called diagnostic mode and it does give trouble codes

if you actually start it, it blinks 2.5 times per second to indicate it's in open and eventually is supposed to blink once per second in closed loop. (it desccribes his in the manual which i've copy pasted below)

so knowing this would you still disagree i should change the O2?

Field Service Mode
If the Diagnostic terminal is grounded with the
engine running, the system will enter the Field
Service mode. In this mode, the "Service Engine
Soon" light will show whether the system is in "Open"
or "Closed Loop".
In "Open Loop" the "Service Engine Soon" light
flashes two and one-half times per second.
In "Closed Loop", the light flashes once per second:
Also, in "Closed Loop", the light will stay OUT most of
the time if the system is too lean. It will stay "ON"
most of the time if the system is too rich.
While the system is in Field Service Mode, the
ECM will be in the following mode:
1. New trouble codes cannot be stored in the ECM.
2. The "Closed Loop" timer is bypassed.

cardo0

Well according to that u would not even be in Diagnostic Mode unless SES blinks at least every once every sec for closed loop (and 2.5 times per sec for open loop).

Now since the SES does blink only once a minute (about) that would indicate (indicate IAW your manual) it is lean in closed loop - which doesnt mean the O2 is bad - just your lean for some reason (intake leak?).

How many miles on your O2 sensor? If over 50K mi i would replace it regards of problems unless u are doing work that would contaminate it. Most owners are not aware the O2 sensor is a normal wear item. BTW did u move the O2 sensor for headers. The early O2's were not heated and moving them due to long tube headers loses there heat/temperature and accuracy. If u have long tube headers u need heated O2's.

Before u throw anymore money at it i would borrow, rent or buy an OBD I scanner that takes real time data and look at the BLM numbers for open and closed loop. Actually just closed loop as the engine runs on the MAP at WOT and BLM goes to 128 and stays there. The scanner will give u all the codes also - maybe history too (dont know for certain though).

Hope this helps.

89 formula TPI

i am confident i am in field service bc when i first start it, it does blink 2.5/second indicating open loop then only blinks occasionally after it switches to closed. for 20 bux i have nothing to lose in my mind so i'll switch in the O2

I have a new symptom though, and it occurred after i was messing around with something else and had pulled off the air intake pipes leading to the MAF sensor. i basically pulled off the tube and triggered a MAF trouble code, as the air coming into the engine was not going through the MAF sensor.

now i have a dead spot when i accelerate, right around 1,100 RPMS. sounds like i am revving the engine, stopping for a second then revving it again even though my foot is just holding the gas firm. i am going to try resetting the computer but if that doesn't work i read MAF sensors when they go can cause Lean conditions (which i suspect i have) and also dead spots on acceleration. could my problem be my MAF? the one i bought was refurbished and i never trust anything refurbished...

cardo0

Dont know what to say as havent dealt with the MAF sensor too much. I know they can get dirty though and takes a special spray to clean them. I bet u could easily find a used 1 though for a few bucks to swap and test with - not that the used MAF is still good though. U need an oscilloscope to look at the signal output. I think a scanner data log would show how its working.

BTW i thought '89 was speed density and didnt use a MAF - uses the MAP only?

89 formula TPI

i think they switched to MAP in 90 and up. i bought a MAF, i am going to install it and see if it's fixed and if not i can just return it. let you know how it goes when i get out there which will hopefully be before the weekend.

Thanks for all the help