I have had my car car running in open loop sice I got it.

These are the tests I have performed so far:

Tested Temp sender unit to ECM looked at OHM values all matched to chart I have!

I shorted out A and B terminals on ALDL when the car was warmed up. I drove the car for a good 20 mins, then shorted out the terminals and watched the SES light flash 2.5 times per second. Meaning It is in open loop.

I know my torque converter is not locking up. I also checked the the plugs they are also black because of running rich.

Anyone know what else could be causing this? I have no access to a scanner at the moment and am having a hard time finding one here in Australia. If anyone is selling a scanner contact me about it.

I have an 86 IROC, 305TPI, 4spd Auto. One thing worth sayig is that my car was converted to Speed density about 4 years ago. Could be quite possible they stuffed something up in the process. I have had the car for about 6 months. This open loop is realy bugging me!

Thanks for reading this and if you have any comments please respond!

Michael
mirek@unite.com.au

 

The torque converter may not be locking up because of a bad brake switch.... If you have cruise control, there is a switch right next to the brake light switch above the brake pedal that is ON when the brake is NOT depressed. With the key on, you should have 12v at both wires with the pedal not being depressed. If you have no voltage to the purple wire, the switch is bad. The purple wire goes straight to the TCC. The TCC will engage regardless of open or closed loop as long as you are going over it's preset speed (around 40mph)

I drove around like that for a couple years before figuring it out.... All the time, I was looking at the ECM....but the ECM control of the TCC is pretty basic, and can even be bypassed. On an 86, the ground wire for the TCC goes straight to the ECM, instead of a 4th gear switch like later models (or aftermarket trans) have. You can ground this wire and take the ECM completely out of the circuit as a test.

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Mike Metzler (Desert86Roc)
Mike@SpeedworldMotorplex.com
[*] Webmaster: SpeedWorldMotorplex.com[*] Click Here For My Racing Page[*]86 IROC 305 TPI (406 build in progress)
ET's @ 1250 ft[*] 14.28 @ 95.461 mph (uncorrected, NOS, no headers)[*] 15.365 @ 86.785 mph (uncorrected, Headers, no NOS)

[This message has been edited by Desert86Roc (edited January 22, 2001).]

 

Thanks for teh info Mike! About the brake swicth I have not checked it, but will ASAP. I do have the option for cruise control but that does not work I think it has been pulled out of the car. All I can see is teh cruise control buttton on the indicator but it does not work. One other thing that bugs me is when I disconnect say for instance the O2 sensor when it has been warmed up properly It does not set any codes on the SES light.

So the TCC shoul dlock up in open loop also you say. I will look at the brake pedal swicth. One other thing does anyone know when a MAF to SD conversion has been done is it necessary to change the ECM to and SD system?? I rang the place who did the conversion I asked did you guys change the ECM? They said no was no need to just reburnt the chip and re wired. That's all he said. Could this be the problem?

 

I just had a look under the dash around the brake pedal and could not find anything like you described. I did not see any purple wire or anything around the area.

I shorted out A and B to see what I would get and only code 12 came up. Then for some reason the SES light did not come on when I went to start the car. This has happened a few times when the SES light looks like it has blown but then comes good again after a few hrs. Funny I don't know what is going on and this car is starting to P### me OFF.

 

I'd say there's an excellent possibility that your computer IS going bad. Reason being that the SES light doesn't come on sometimes at startup, which is one indication of a faulty ECM, and also if you don't set a code when disconnecting the O2 something has got to be up. It's arguably the most important sensor in the system!! Can you set codes by disconnecting other sensors such as the MAP? How about the co-occurrence of these things - ie can you set a code when the SES light comes on at startup and not set one when the light doesn't come on? Here's how to check things out: Assuming your car starts, the next time the SES light does NOT come on when you start it, turn off the key, disconnect the ecm harnesses under the pass side of the dash. turn the ign to "on." Now with a test light to ground, probe CKT 419 (this is terminal A5 on the smaller of the plugs that go to the ECM - should be a brown and white wire. If the SES light comes on when you probe this terminal, the ECM is bad. If it doesn't, either the "gages" fuse is out, CKT 419 is open or shorted to voltage, or there's an open ignition feed to the SES bulb (assuming the bulb is good). Assuming you've checked the fuses and the bulb is good, I'd say you've got a bad ECM,since all the other conditions seem to point in the direction of the ECM signal not reaching the SES light, which wouldn't cause drivability problems all on its own. However, it's worth checking out that 419 CKT before you plunk down the cash for a new computer - I had to buy one today in fact! - because just because the computer is faulty in signaling the SES light, it's not necessarily causing your driveability problem, although it's likely. I'm not sure if it's possible for an ECM to be "intermittently" bad, but if it is, that's most likely your problem. Good luck!

And yes I had to edit this 3 (count 'em 3!) times to correct my typos...arrggh!

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Base: 89 Iroc-Z LB9 auto 2.73 posi
Exh: 3" Dynomax muffler, 3" Pipe in place of cat
Ign: Accel 300+ wires, cap&rotor
Fuel: Cleaned and flow-matched injectors, afpr, !air pump&diverter valve
Sound: Kicker
Suspension: KYB Shocks, BMR Strut Tower Brace
Misc: TB Bypass, Synthetic Oil, Flexlite Transmission cooler,
free mods, hopefully engine swap and 4th gen seats in the works...

[This message has been edited by I ROCK (edited January 23, 2001).]

[This message has been edited by I ROCK (edited January 23, 2001).]

[This message has been edited by I ROCK (edited January 23, 2001).]

 

I ROK thanks for the detailed info. I just went to check if the light will come on now. It did light up when I turned the key. I am unable to set any trouble codes at all. Tried 4 times engine warm and disconnected O2 sensor and nothing. To be honest I can't even find the bloody MAP sensor in the engine bay. I have not really looked hard for it, but it is not where it is supposed to be in my Haynes manual. I will try and find the bloody MAP sensor and disconnect that to see if any trouble codes appear. I wll try that probe test you told me. ECM harnes are all those wires connecting into the caomputer right? There are about 40-50 of them. So just pull them all out and probe the point like you said?

Thanks for the Info. If I do need to get a new computer what do you recommend one out of an 90 IROC-Z? Anything else I need to replace when replacing computer? Chip?