No closed loop & always lean?
07-15-2013, 03:39 PM
#1
Burning Brakes
Thread Starter
No closed loop & always lean?
not sure what section this belonges in but admin please feel free to move it to correct section thanks
Ok so i finaly get a chance to get back to this project 85 corvette that i have been having problems with chasing verious problems on. I will post my questions and some data and see if we can get to the bottom of this or at least confirm my conclusion.
The basics: the car is a 85 corvette with the l98 tpi in basic stock form at the moment right down to the old slow 870 ecm. I do plan to convert this to the 165 ecm amonge other mods but want to have all the bugs and ghosts worked out of it first if possible as a starting point so i can better diognos and issues i may get with the 165 swap (hate to add to the bugs and have to chase more bugs).
The car has many running bugs but most i have either found and know the cause or fixed already (like the idle hunting, etc) but the particular issue i would like to address at the moment is some of the scanner results and issues with them which i will now list...
1) NEVER GOES INTO CLOSED LOOP
car never goes into closed loop, well at least my scanner never shows it going into closed loop. (possible cause is that i think when data logging/scanning these cars go into a thing called service mode which i am wondering if keeps out of closed loop) someone here may be able to verify with there 85 on a scanner? otherwise as far as i am aware the only other conditions needed for closed loop is the ecm timer, cts, o2 sensor which seem to be ok for closed loop as you will see from my scanned numbers that will fallow.
so is it because of the service mode or a sensor or condition still needed or is it a bad ecm?
2) ALWAYS READS LEAN
car always reads lean on the scanner, now my understanding is that this can just be a condition on the ecm not reading the o2 sensor (not in closed loop) or i have also read that this can be caused by the mat/iat sensor reading high because as i have read it the mat/iat can lean or richen the fuel based on temp. I should add that it always reads lean but actually smells rich.
3)MAT/IAT ALWAYS READS 203DEG F
and that leads me to the mat/iat sensor, this reading is always 203f degrees, unhook sensor= still reads 203deg, differant sensor still 203deg, test wires=one reads ground and other reads 5 or 6 volts i cant remember which atm but was correct according to my book, so wires seem to check out. could this be cause for my lean reading? would this possibly be caused by a bad part in me ecm? any ideas?
ok so atm that is where i am at now just trying to decide if i should just go ahead with the 165 ecm swap and hope it doesnt just add more problems to the existingor if there is hope that this 870 ecm doesnt have sum issues...below are some of the relivant scan numbers and before anyone askes..yes these are live scan not froze the change in real time well at least the ones that actually do change.
car running idleing scan:
prom id 2531
RPM 1000
O2 sensor = all over the place at 457, 897, 466, 554, 897, 743, 646, etc..never hits below 300mv and never hits 900mv
IAC 35 steps
block learn = just keeps counting up then starts over
Inj pulse 1.65
open loop
integrator 118-124
knock sensor 108
mas 11gr/sec
lean
tps .54v
mat 203deg f
cross counts 0
coolant 195deg f
learn control: disabled
this is a few of the readings that may be pertinant, i have not listed them all as i dont think the rest have anything to do with it but if i am wrong please ask for particular reading you need to know. also possibly worth mentioning is that with engine off IAC is 144steps, mass air flow is still at 3gr/sec is this correct? oh and car never throws codes for any of these issues but yes it does have the ability to throw codes as i can get it to set codes for some things.
pre-thanks for any help
Ok so i finaly get a chance to get back to this project 85 corvette that i have been having problems with chasing verious problems on. I will post my questions and some data and see if we can get to the bottom of this or at least confirm my conclusion.
The basics: the car is a 85 corvette with the l98 tpi in basic stock form at the moment right down to the old slow 870 ecm. I do plan to convert this to the 165 ecm amonge other mods but want to have all the bugs and ghosts worked out of it first if possible as a starting point so i can better diognos and issues i may get with the 165 swap (hate to add to the bugs and have to chase more bugs).
The car has many running bugs but most i have either found and know the cause or fixed already (like the idle hunting, etc) but the particular issue i would like to address at the moment is some of the scanner results and issues with them which i will now list...
1) NEVER GOES INTO CLOSED LOOP
car never goes into closed loop, well at least my scanner never shows it going into closed loop. (possible cause is that i think when data logging/scanning these cars go into a thing called service mode which i am wondering if keeps out of closed loop) someone here may be able to verify with there 85 on a scanner? otherwise as far as i am aware the only other conditions needed for closed loop is the ecm timer, cts, o2 sensor which seem to be ok for closed loop as you will see from my scanned numbers that will fallow.
so is it because of the service mode or a sensor or condition still needed or is it a bad ecm?
2) ALWAYS READS LEAN
car always reads lean on the scanner, now my understanding is that this can just be a condition on the ecm not reading the o2 sensor (not in closed loop) or i have also read that this can be caused by the mat/iat sensor reading high because as i have read it the mat/iat can lean or richen the fuel based on temp. I should add that it always reads lean but actually smells rich.
3)MAT/IAT ALWAYS READS 203DEG F
and that leads me to the mat/iat sensor, this reading is always 203f degrees, unhook sensor= still reads 203deg, differant sensor still 203deg, test wires=one reads ground and other reads 5 or 6 volts i cant remember which atm but was correct according to my book, so wires seem to check out. could this be cause for my lean reading? would this possibly be caused by a bad part in me ecm? any ideas?
ok so atm that is where i am at now just trying to decide if i should just go ahead with the 165 ecm swap and hope it doesnt just add more problems to the existingor if there is hope that this 870 ecm doesnt have sum issues...below are some of the relivant scan numbers and before anyone askes..yes these are live scan not froze the change in real time well at least the ones that actually do change.
car running idleing scan:
prom id 2531
RPM 1000
O2 sensor = all over the place at 457, 897, 466, 554, 897, 743, 646, etc..never hits below 300mv and never hits 900mv
IAC 35 steps
block learn = just keeps counting up then starts over
Inj pulse 1.65
open loop
integrator 118-124
knock sensor 108
mas 11gr/sec
lean
tps .54v
mat 203deg f
cross counts 0
coolant 195deg f
learn control: disabled
this is a few of the readings that may be pertinant, i have not listed them all as i dont think the rest have anything to do with it but if i am wrong please ask for particular reading you need to know. also possibly worth mentioning is that with engine off IAC is 144steps, mass air flow is still at 3gr/sec is this correct? oh and car never throws codes for any of these issues but yes it does have the ability to throw codes as i can get it to set codes for some things.
pre-thanks for any help
Last edited by ladystoy69; 07-15-2013 at 08:29 PM.
07-15-2013, 03:50 PM
#2
Race Director
Member Since: Sep 2003
Location: Database Error Indiana
Posts: 16,615
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One thing jumps out. O2 should be going from below 100 to over 900. Constantly going up and down. If its not, its a problem. An exhaust leak can cause lean readings. The O2 has to heat up to give useful readings and to go into closed loop. Cold open loop timer is usually 5 minutes. Are you running that long ?
07-15-2013, 04:00 PM
#4
Drifting
O2 sensor readings above .450 are rich? 0 on cross counts means it's not going closed loop. The Intake air condition is odd, and would have me chasing ground continuity. The integrator readings would indicate rich also. What injectors are in it? What fuel pressure does it have, and does it bleed off fast? Changing the 870 for the 165 most likely won't solve this condition.
07-15-2013, 04:17 PM
#5
Burning Brakes
Thread Starter
hmm ok and yes the iat behaviour is driving me nuts too lol
ok maybe need a little more info.. the injectors are stock 85 vette injectors that i just recently had out for cleaning and checking as some were leaking and fuel press was bleeding fast, now they all check out great (flow and non leaking) also been verified by gauge and sight as i pressurised the rail of injectors before final install too. all fuel pressure and bleed off tests pass . also has a new welbro pump, tank screen and fuel filter.
fp is 40# just by turning on the key on and holds long time only losing about 2-3# after 15-20 mins. fp regulator has normal operation and no diaphram leaks.
ok maybe need a little more info.. the injectors are stock 85 vette injectors that i just recently had out for cleaning and checking as some were leaking and fuel press was bleeding fast, now they all check out great (flow and non leaking) also been verified by gauge and sight as i pressurised the rail of injectors before final install too. all fuel pressure and bleed off tests pass . also has a new welbro pump, tank screen and fuel filter.
fp is 40# just by turning on the key on and holds long time only losing about 2-3# after 15-20 mins. fp regulator has normal operation and no diaphram leaks.
07-15-2013, 04:22 PM
#6
Drifting
The IAT is the same as the CTS. Have you changed it? If yes, diagnose that circuit, because something is screwy there. It's got to be improper sensor input. Have you changed the O2?
07-15-2013, 04:46 PM
#8
Burning Brakes
Thread Starter
iat/mat sensor has been changed a few times, the one in the planum atm is original one and yes same as a cts i have also tried another of same just plugged in and not mounted same reading, i even tried grounding the sensor case.
also have a relocated iat/mat sensor located in the air snout open type iat sensor, all give same reading as well as totally disconnecting it as stated above, nothing seems to change it which is why i am startying to think possible internal ecm circuits. i get the correct dvm readings on the sensor wires at plug -key on engine off volts accros wires is 5 or 6 volts whichever book said it was supposed to be, apparently wiring and signal is in specs? always reads as 203deg f jumpered, non jumpered, stock sensor, no sensor always reads 203deg f on scanner.
also added one more scanner reading above ..learn control disabled
i dont know what that means so i didnt know if it is of importance but figured i would update that as well.
also have a relocated iat/mat sensor located in the air snout open type iat sensor, all give same reading as well as totally disconnecting it as stated above, nothing seems to change it which is why i am startying to think possible internal ecm circuits. i get the correct dvm readings on the sensor wires at plug -key on engine off volts accros wires is 5 or 6 volts whichever book said it was supposed to be, apparently wiring and signal is in specs? always reads as 203deg f jumpered, non jumpered, stock sensor, no sensor always reads 203deg f on scanner.
also added one more scanner reading above ..learn control disabled
i dont know what that means so i didnt know if it is of importance but figured i would update that as well.
Last edited by ladystoy69; 07-15-2013 at 04:56 PM.
07-15-2013, 04:50 PM
#10
Well this sensor reading could give you your problem if the PCM thinks the IAT is 203 F.
It would also turn the mixture lean I would assume, as the hotter the air, the lesser it´s density and therefore less fuel is required. So the PCM may use a lean mixture.
The O2 sensor senses the too lean condition and the PCM does not see the O2 sensor swing from lean to rich. Therefore, it goes into open loop as it sees a fault condition.
Or the O2 sensor itself is at fault. But the IAT has to be correctly measured for the PCM to determine the right mixture.
Just a theory....
It would also turn the mixture lean I would assume, as the hotter the air, the lesser it´s density and therefore less fuel is required. So the PCM may use a lean mixture.
The O2 sensor senses the too lean condition and the PCM does not see the O2 sensor swing from lean to rich. Therefore, it goes into open loop as it sees a fault condition.
Or the O2 sensor itself is at fault. But the IAT has to be correctly measured for the PCM to determine the right mixture.
Just a theory....
07-15-2013, 04:55 PM
#11
Drifting
Actually, when the ecm sees high temps it gets richer.
The CTS, MAF, and MAT share a common ground at the ecm. I would check circuit wiring from pins A11, and D13 shown here:
http://www.chevythunder.com/fuel%20i...***********ECM PINOUTS
Clearly, this is a known issue that must be resolved.
The CTS, MAF, and MAT share a common ground at the ecm. I would check circuit wiring from pins A11, and D13 shown here:
http://www.chevythunder.com/fuel%20i...***********ECM PINOUTS
Clearly, this is a known issue that must be resolved.
07-15-2013, 05:04 PM
#12
Burning Brakes
Thread Starter
Well this sensor reading could give you your problem if the PCM thinks the IAT is 203 F.
It would also turn the mixture lean I would assume, as the hotter the air, the lesser it´s density and therefore less fuel is required. So the PCM may use a lean mixture.
The O2 sensor senses the too lean condition and the PCM does not see the O2 sensor swing from lean to rich. Therefore, it goes into open loop as it sees a fault condition.
Or the O2 sensor itself is at fault. But the IAT has to be correctly measured for the PCM to determine the right mixture.
Just a theory....
It would also turn the mixture lean I would assume, as the hotter the air, the lesser it´s density and therefore less fuel is required. So the PCM may use a lean mixture.
The O2 sensor senses the too lean condition and the PCM does not see the O2 sensor swing from lean to rich. Therefore, it goes into open loop as it sees a fault condition.
Or the O2 sensor itself is at fault. But the IAT has to be correctly measured for the PCM to determine the right mixture.
Just a theory....
my theory as well just dont know if its a pcm issue or wiring as the iat/mat sensor wiring checks out at the plug guess will need to investigate further.
Originally Posted by MrWillys
Actually, when the ecm sees high temps it gets richer.
The CTS, MAF, and MAT share a common ground at the ecm. I would check circuit wiring from pins A11, and D13 shown here:
http://www.chevythunder.com/fuel%20i...***********ECM PINOUTS
Clearly, this is a known issue that must be resolved.
The CTS, MAF, and MAT share a common ground at the ecm. I would check circuit wiring from pins A11, and D13 shown here:
http://www.chevythunder.com/fuel%20i...***********ECM PINOUTS
Clearly, this is a known issue that must be resolved.
07-15-2013, 05:22 PM
#13
Drifting
Apparently I'm wrong concerning the 85. I just pulled up 85 programming and it appears the MAT has little to do with programming. However, my instinct tells me it must some affect, otherwise why is it used?
I do know in later models when extreme heat is detected by the CTS it enrichens the mixture. I just couldn't see a smoking gun in the 85 file. My concern in yours is this odd reading affecting the other devices sharing this common ground.
If you've datalogged, can you watch the cts gradually rise, or is there a possible discrepancy there.
I do know in later models when extreme heat is detected by the CTS it enrichens the mixture. I just couldn't see a smoking gun in the 85 file. My concern in yours is this odd reading affecting the other devices sharing this common ground.
If you've datalogged, can you watch the cts gradually rise, or is there a possible discrepancy there.
07-15-2013, 05:44 PM
#14
Burning Brakes
Thread Starter
ok so i just went down to test out a11 and d13 of the iat wiring...process was disconnect all associated sensors mat/ait, tps, ect and just for good mesure i also disconnected the maf, iac, and the other sensor on front of the intake (think its some temp sensor for the 9th injector. also disconnected both plugs from the ecm as well as unplugged the 85 only burnoff module from the curcuits as some diagrams i have show it sharing ground as well.
i then probed terminal a11 at the acm plug to the red/orange or whatever (non black) wire on my iat plug and get no resistance but complete continuity then tested from the a11 ecm plug to vehicle ground and get nothing.. so conclusion of wire a11 is that there are no breaks and that it isnt shorted to ground.
i then probed d13 on the ecm plug to the black on the iat/mat sensor and results were the same as above..no breaks and no short to ground.
and to answer your most recent question..yes i can watch the cts going up as normal just seems to be effecting the iat/mat sensor reading and nothing else that i am aware of yet except what was noted earlier as possible discrepancies like key on engine off maf sensor 3g/sec and the fact that it doesnt ever go into closed loop even though i can watch the o2 sensor readings rise up after start steadily till they get to a point then start jumping back and fourth between 300 to 800something , its almost like the ecm is sending and recieving all the right signals but ignoring them with the exception of the iat/mat being right but it is sending out the right 5or 6 volts just not reading it i guess?
i then probed terminal a11 at the acm plug to the red/orange or whatever (non black) wire on my iat plug and get no resistance but complete continuity then tested from the a11 ecm plug to vehicle ground and get nothing.. so conclusion of wire a11 is that there are no breaks and that it isnt shorted to ground.
i then probed d13 on the ecm plug to the black on the iat/mat sensor and results were the same as above..no breaks and no short to ground.
and to answer your most recent question..yes i can watch the cts going up as normal just seems to be effecting the iat/mat sensor reading and nothing else that i am aware of yet except what was noted earlier as possible discrepancies like key on engine off maf sensor 3g/sec and the fact that it doesnt ever go into closed loop even though i can watch the o2 sensor readings rise up after start steadily till they get to a point then start jumping back and fourth between 300 to 800something , its almost like the ecm is sending and recieving all the right signals but ignoring them with the exception of the iat/mat being right but it is sending out the right 5or 6 volts just not reading it i guess?
07-15-2013, 06:05 PM
#17
Burning Brakes
Thread Starter
well i cant say im at all happy to hear im not the only one stumped and thinking bad ecm 
well might as well be prepared for 165 swap then, i think i have the 2 relays needed already for the swap but all info is for the old type relays, does anyone have pinout and info (part number, pics anything so i can id these 2 i have to know if they will work)for the weather sealed ones whatever there called?
***......ok further update: i opened up the 870 ecm and can not see or smell any problems, i know that doesnt mean much but its something lol
i then left all mentioned sensors from above(associated sensors mat/ait, tps, maf, iac, and the other sensor on front of the intake (think its some temp sensor for the 9th injector.) and only plugged the ecm and burnoff module back in and scanner shows 203deg f still for the iat/mat sensor but the other unhooked sensors show like there disconnected meaning odd, small or no readings from them.....
well might as well be prepared for 165 swap then, i think i have the 2 relays needed already for the swap but all info is for the old type relays, does anyone have pinout and info (part number, pics anything so i can id these 2 i have to know if they will work)for the weather sealed ones whatever there called?
***......ok further update: i opened up the 870 ecm and can not see or smell any problems, i know that doesnt mean much but its something lol
i then left all mentioned sensors from above(associated sensors mat/ait, tps, maf, iac, and the other sensor on front of the intake (think its some temp sensor for the 9th injector.) and only plugged the ecm and burnoff module back in and scanner shows 203deg f still for the iat/mat sensor but the other unhooked sensors show like there disconnected meaning odd, small or no readings from them.....
Last edited by ladystoy69; 07-15-2013 at 06:35 PM.
07-15-2013, 09:56 PM
#18
Le Mans Master
http://forums.corvetteforum.com/c4-s...m_id=82&arch=1
I just did this upgrade, I used the older square shaped burnoff & power relays, the rounded ones are pricy.
I just did this upgrade, I used the older square shaped burnoff & power relays, the rounded ones are pricy.
07-15-2013, 10:17 PM
#19
Burning Brakes
Thread Starter
ok so no further ideas then? nothing else to test or try? any suggestions? if not i guess i need either a basic chip burned (like 89 with vats off, 85 24# injectors and such) for it to use with the 165 conversion or i need assistance as to getting the bin and such and trying to burn one myself as i have the pocket programmer but never used it as of yet and looking at the software no idea as yet of how to lol
07-15-2013, 10:20 PM
#20
Burning Brakes
Thread Starter
http://forums.corvetteforum.com/c4-s...m_id=82&arch=1
I just did this upgrade, I used the older square shaped burnoff & power relays, the rounded ones are pricy.
I just did this upgrade, I used the older square shaped burnoff & power relays, the rounded ones are pricy.
by the way did you do your own chip? if so whats needed bin etc.? what ones did you use? any advice?