Hey guys, i got a little problem. Ever since I installed my roller rockers, I noticed my car has been staying in open loop (in my opinion). I don't know for sure, but it runs choppy on cold start (i have to keep feathering the throttle for a few seconds then it will idle). I also cannot hear the engine "idle down" and go in closed loop.

The car still is driveable and IMO runs great except for my horrible gas mileage (9-10mpg, and it USED to get 15mpg before in town). And still runs awesome at WOT.

TPS is new, IAC is new, TPS is set at .06 volts. o2 sensor is also new and has only 4500 miles on it.

Does anybody have any ideas as to what would cause this? Coolant temp sensor? I am going to hook the car up to a scanner hopefully on Saturday.

 

I'm also thinking bad ECM.

I'm going to re-check TPS voltage on saturday and also check and see if its steady from idle to WOT.

This is my daily driver so the 9mpg isn't gonna cut it. This things gonna empty my wallet at $2.40 a gallon

 

You need to get a scanner and see if it is actually staying in open loop. If it is staying in open loop I'm pretty sure it would set the SES light, so I don't think this is you're problem. Idle will be a little choppier, but not much. I can still tell when mine idles down. Keep me posted with what you find. What's you're fuel pressure at? Did you pull the intake to replace the rockers?

 

Stock fuel pressure & regulator. I left the intake on and everything.

Valves are set right i've done them 4 times before. 1/4 turn

 

Anybody??

 

check the ecm... I had a similar problem and ended up the ecm was bad... stayed in open loop, and ate gas... changed the ecm and it ran great

 

Cool, thanks man, any info on how to check if the ECM is any good?

Tomorrow i'm gonna back down my TPS to .54v and see how it runs

 

The TPS should be set at 54 hundredths of a volt (.54v slightly over 1/2" volt,) not 54 thousandths (.054v) which is 1/10th of what it should be, or is that a typO?

 

Typo, sorry man. Fixed

 

here is a trick i learned form my mechanic the other day, when the car is running jumper the 2 connections on the ald thinger(same 2 that you use to check for codes) and the check engine light will start blinking, this is the part i cant remmeber tho, it will blink fast or slow for open and the opposite for closed! sweet deal, give it a try and see what you find

 

fast is open, slow is closed

 

thanks!

 

i thought having those terminals jumpered with the engine running or starting it with them jumpered was a bad thing... just something i had heard, but apparently not? just want to be sure cuz i probably need to do the same thing to verify open/closed loop.

KAM

 

No, jumping those pins while running will not hurt the car at all. Two things determine loop status.

1. amount of engine run time programmed into ECM. Minimum run time, usually about 3 min depending on PROM calibration.
2. if the o2 sensor is producing a voltage in mv to send to the ECM.

If the ECM has not received any voltage from the o2 sensor it will stay in open loop and set a code 13. Provided the ECM is working properly.

 

To my understanding, I believe the cts sensor also plays a role, as you need to be above a certain temp before you can drop into closed loop. Also, the o2 is always sending a signal to the ecm. Its just that it is horrible inaccurate until it the exhuast temp reaches about 600 degrees. What the ecm watches out for with regards to the O2 is the amount of crosscounts. Simply put, thats the number of times that the O2 voltage crosses stoich.

 

The CTS has nothing to do with loop status. Unplug, or jump(which ever ECM you have) your CTS connector when it's hot and you will see it stays in closed loop. The ECM does use the CTS in determining the amount of fuel though. The o2 sensor is what tells the ECM to change loop status.

 

I wasn't absolutely sure before, but I am now. I looked through the ANHT hac and found this:

***************************
* CLOSED LOOP FUEL CONTROL
* ENABLE PARAMS
**************************
L8489: FCB 120 ; 50C, (122F) MIN COOL FOR CLS LP
L848A: FCB 100 ; IF COOL >= 35c, (95f) USE HOT CLS LP TIMER
L848B: FCB 73 ; IF COOL <= 14c, (59f) USE COLD CLS LP TIMER
;
; CLOSED LOOP TIMERS
; INDEXED LK UP
;
L848C: FCB 90 ; 45 Sec COLD CLS LP TIMER
L848D: FCB 90 ; 45 Sec WARM CLS LP TIMER
L848E: FCB 25 ; 12.5 Sec HOT CLS LP TIMER
;--------------------------
;
; o2 QUALIFERS, (WINDOW)
;
L848F: FCB 158 ; IF o2 < 699 mvdc THEN o2 IS READY
L8490: FCB 45 ; IF o2 > 199 mvdc THEN o2 IS READY
;
L8491: FCB 50 ; IF o2 IN ABOVE WINDOW >= 10 Sec's then o2 is NOT READY
;--------------------------


The CTS has to report atleast 50 degrees Celsius before going into closed loop. This does not neccessarily contradict what you said about unplugging it when hot and staying in closed loop. Just because its a requirement to go into closed loop does not neccessarily mean its continually monitored to remain in closed loop.

You are correct on CTS determining fuel output though.

 

I stand corrected. Sorry for the misinformation.

 

No problem. I was sort of wrong with the cross counts also. Thats handled differently than what I thought, but with the same idea behind it.

Looks like the o2 is considered ready when its in the 199-699 mv window, but has to move outside of that window in less than 10 secconds, otherwise its thrown back into not being ready again.

I think the definitive answer would be a combination of three things: CTS, O2 voltage fluctuations, and the timer.

 

Agreed. It's amazing how much stuff you forget when you don't do it everyday. I knew that about the coolant sensor too and just plain forgot about it and then when you said it I was second guessing myself

 

how can you tell if the CTS is functioning properly? and for that matter, how can you tell if the O2 is functioning properly, too? i'm starting to question both of those sensors, but can't tell if they're working right or not. CTS is not new, although it is not original, either. O2 is new... i think, but will have to verify tomorrow, that my ecm is staying in closed loop. when i jumped A & B terminals, it was already flashing a slow service engine light, rather than a fast one for open loop, but was only about 160* on the gauge.

KAM

 

The easiest way to check those is with a scanner, but both can be tested with a DVOM and a few test leads.

Basically the ECT varies it's resistance and the pcm reads the voltage as it changes. ECT set codes set pretty fast(about 30 seconds open or shorted) so if ya have a 14 or 15 in the ecm then yeah you have a problem. Coolant sensor don't fail that often. Most of the time it's a ECM failure or wiring.

O2 sensor are easy to test. Disconnect the sensor from the harness. Create a test lead that plugs into the main wiring harness with bare wire on the loose end. Plug a DVOM into the O2 side and set to mv(must be a fast dvom) and the other end to ground. Get the engine to hot enough to make the O2 start producing voltage.

With the bare lead going to the main harness grab it with you hand and give your fingers that are holding it a lick to wetten them up(don't laugh) the with the other hand lick it as well and grab the pos batt cable post. The volt meter should go to about close to 0 mv after a few seconds. The engine will start to lean out as you do this but the DVOM will read low(You are forcing a high voltage, rich condition). Then grab the neg batt cable post and the ecm will read lean and start dumping fuel to compensate, the DVOM will go high, about 1015mv.

You are using your body as a conductor. Just incase your wondering why I had you lick your fingers.

If you have a scanner and a DVOM while your doing this you can see how everything is affected and narrow your problem down. You can just use a DVOM and get the same affect

 

The CTS (and MAT) sensor resistance can be compared to factory specs as follows:
All 1981-1990
13.5K ohm @ 20°F
7.5K ohm @ 40°F
3.4K ohm @ 70°F
1.8K ohm @ 100°F
480 ohm @ 160°F
185 ohm @ 210°F

Link to O2 Sensor FAQ