No closed loop. VSS is bad?

[jepherz]

Back when I had cruise control in my car, it would sometimes randomly shut off while cruising. I was told that this was probably because of a bad VSS. Now I have no cruise control, but logging VSS in MMCd shows a graph that somewhat resembles a sine wave in that the numbers are jumping all over the place. With my wideband, I can see that I'm always running rich and that I never enter closed loop. boost leak check has been done and there are no leaks.

Could a bad VSS be causing this? or what else could it be?

 

[Rausch]

Are you just looking at the VSS reading itself, or have you re-addressed the logger to look at it that way?
Per Keydiver:
Quote:
The only reliable way to see if the reed switch is registering correctly is by inputting address C6 into one of the MMcD versions that allows custom address logging.



The standard VSS address shows some pretty flakey readings. Mine always jumped around.

Have you looked at what the ECU is seeing for coolant temps?

 

[jepherz]

Nope, I haven't looked at coolant temps or tried changing the address. I'll check that tonight.

Previously there was a small leak right off the turbo, and that coupled with whatever this problem was enough to make the car idle at around 9:1...

 

[toybreaker]

Have you checked the fuel trims?

Rich across the board may be a fuel pressure issue.

 

[jepherz]

Yeah, John, I had a look at the fuel trims. Correct me if I'm wrong, but the fuel trims only update in closed loop. Since I'm always open loop, they are stuck at 100%

/ubbthreads/images/graemlins/dunno.gif

Also I forgot to mention, fuel pressure is showing 36-37 psi on the gauge with no vacuum. I suppose it's possible that my gauge is WAY out of whack, but I really don't think so since AFRs aren't cycling at all.

 

[jepherz]

Coolant temp is working as it should. Nobody has any other ideas?

 

[Rausch]

Do you still run a narrowband sesnor? I would start to question the readings of parts that are known to fail.

Otherwise, try logging the VSS at the correct address, and see what you come up with. I think it just cycles on/off, so I'm not sure that a reading at a particular speed should be.

 

[jepherz]

Yes, I still have a narrowband. I believe I checked the voltage and it looked fine to me and the sensor is only about a year old as well. I'll double check that. Thanks for the tip.

 

[jepherz]

None of the above mentioned are a problem. Nobody has any other suggestions?

 

[belize1334]

Do you have a turbo timer with a vehicle speed function? Somehow my vss circuit got a short in it and I first discovered it when, among other things, the turbo timer started reading 0mph at all times. Try getting up where the ECU plug is and locating the vss wire. Strip it back a little bit and attach your multimeter between it and ground. Set the multimeter to the diode fuction so that it beeps whenever the resistance is low. Then go to the engine bay and unplug your speedo cable ans slowly rotate it by hand. The multimeter should beep a few (2?) times per revolution. If the vss or part of the circuit in which it operates is flaking out that should tell you something.

 

[jepherz]

Roger, do you know if the VSS being bad is known to be a cause of not running in closed loop though? I'm pretty sure my VSS is bad, but I'm trying to find out if it could cause this issue.

I'm also trying to either find a new VSS, or figure out what code in the ECU needs to be changed so I can eliminate the feedback.

 

[belize1334]

I don't believe that a bad vss would keep you out of closed loop. When mine was unhooked I didn't have a logger so I couldn't see what the ECU was doing. When I get home tonight I'll unhook mine and log the car and get back to you on that. As for your vss, I have a spare (if I can find it) from when I was trying to diagnose my issue. They can be pulled from pretty much any galant/TEL. I got mine out of a 90 Eclipse gs that I found at the U-Pull-It.

 

Here are some things the ECU checks first before it will go into closedloop:
engine has been running for more than 180sec
baro sensor value is reliable
no fault code on baro, coil, iat, ect, cas
ectRaw and iatRaw are within acceptable range
temperature(ectRaw) > 86degC
temperature(iatRaw) > 0degC
temperature(iatRaw) < 55degC
engine is running normally (no fuel cut, etc..)
airVolTB < $68
airVolTB > $33
rpm31 < 4000
rpm31 > 2000

 

[jepherz]

Thanks Jeff. I'll look into it.

 

Hey Jeff, did you ever find out what was keeping the car from going in closed loop operation?

While trying to figure out a stalling issue(which was a bad ISC), I noticed in link that my o2 values were flatlined. I replaced the sensor with a oem one but it's still not cycling after the car is warm. After reading a bit more I learned a little about open and closed loop operations and realized it was stuck in OL for some reason and that's why it smells so rich. Dsmlink says coolant temps are 190-200 when warm, I rewired the brittle wires on the temp sender hoping that was a problem but it wasn't. Then yesterday I realized I didn't have the iat/baro button pressed in the misc tab in dsmlink (I have a gm maft setup) but that didn't help either.

I bought a used 2g mas and intake and I'm planning on switching out the gm maft setup. I know I have other issues that don't help my situation: walbro 255 (not rewired), no afpr, 880s, a AEM fuel rail (all from PO), and I'm a noob. Hopefully finding out what helped you will help me a bit too. Thanks.

 

[jepherz]

Actually, it was found that somehow my Ostrich was causing the problem. I used my friend's computer, and had to write to it several times. Eventually it took and fixed my horribly rich problem.

Your lack of AFPR and having a 255 pump will possibly cause your car to run rich at idle RPMs. You should consider either switching to a smaller pump or getting an AFPR. However, this wouldn't be the cause of your car operating in open loop, if it still is....

 

Ok thanks. I don't understand what you did but I'll do some searching.

I'm hoping my problem has something to do with the gm maft, I should have the 2g mas by this weekend.

Edit: I have a few things I need to do before asking more questions. Thanks a lot for the reply Jeff.