ok auto x-ray says the car isn't going into closed look

here are some #'s
prom id 7805
idle air 38 steps
coolant 173.3
rpm 750
tps .58V
O2 827 MVolts
MAT 203 ( never changes)
knock sensor 133
O2 cross counts 0
MAF 8gr/sec
inj plse 1.9ms
loop status open

this is in scan mode as i cant get MON to work.

any ideas why the car won't go into closed loop?

 

You from Hades??? If it were me...

1) After car has been sitting for prolonged time, link with car on/engine off and note MAT reading. I assume you gave values in *F, not in counts. If it shows 200+ and car had been sitting, fix prob with MAT circuit (could be the sensor, wiring, or the plug. I have had problems with the plug. It uses Metri-pac terminals and is probably easier just replacing the entire pigtail). New sensor is under $10 bucks at AutoZone and is probably Wells pt# SU109 if your plug has the mushroom shaped male end.

2) If scanner still shows O2 crosscounts of 0 and your O2 still shows high (above 450mV), replace single wire O2 that you likely have with a heated O2 sensor. If you have headers, this mod approaches a "good idea" to a "must have".

3) If that doesn't work, you have too much fuel. Check fuel pressure, injector resistance, etc.

If your (non-heated) O2 has over 40,000 on it, or you had any silica-based substance (coolant, non-O2 sensor safe RTV, etc) get in the exhaust stream, your O2 is needing replacement anyways.

You can do 3 before 2 if you want...just depends on what you have already done.

If you have a bigger cam, then you probably need more tweaking than the question here poses. Any mods?




[Modified by HighHopes85, 12:16 PM 4/18/2003]

 

thanks.

the only mods i have are the free mods.

I'm not sure of the O2 sensor since i just bought the car a few months ago, it looks new.

Can i get the heated sensor at Autozone?

 

You can get the heated sensor at AZ.

Since you only have the free mods though, I might start looking elsewhere for the problems. The problems with the MAT could be the ticket.

If you go to a heated 3-wire, the black is the signal and the 2 whites need to be hooked up to 1) power (ign feed circuit) and 2) ground. People usually use a relay for the power side...heater current can spike I *think up to 3 amps for a short amount of time, so fuse the circuit appropriately if you go this route. Use butt splices for this--no soldering.

The basic one-wire O2 sensor for your car costs ~$18 bucks. The heated one will probably be over $30. Just make sure that your ign system is up to par, especially on the drivers side (plugs/wires) since this is the only side that the O2 gets its readings from. Also make sure you don't have any exhaust leaks, etc.


[Modified by HighHopes85, 2:05 PM 4/18/2003]

 

ok thanks. i was wanting to relocate that to the air box anyway.

I'll check it with the auto x-ray when i leave work before starting it. I have never seen it lower than 203 yet, or above 208.

 

If you are going to relocate it, you might think about the LT1 style of MAT sensor. It is plastic-tipped, not brass. Some schools of thought are that the sensor reacts faster to actual temp, is more accurate, etc.

If you have a DMM, the easiest check by far is measuring the reistance of the MAT and the CTS sensor (front of the plenum). When the car has been sitting, they should have nearly identical resistance since they are the same sensor. For measuring the MAT, you can do that through the extension harness that plugs in about 8 inches off the actual sensor...it is easier than pulling the plenum.

Relocating it is a whole other topic ;) Good luck, -Matt

Edit: If you've got your boots on and can wade through the knee-deep crap in the forum, here is a thread http://www.thirdgen.org/techbb2/show...hreadid=173101


[Modified by HighHopes85, 4:32 PM 4/18/2003]

 

If you solve it let us know, I've been having the same problem on my 85 and am looking for a solution as well! I have new injectors and replaced the MAT when I had the plenum off and ported last year. I will have to check the wiring next. My cross counts are also 0 but my 02 sensor values are constanting going up and down, I replaced this a couple years ago but will consider converting to a heated sensor, don't think that's the problem though.

 

I have the exact same problem on my '85. The MAT temp and the continuous open loop. When I first noticed It, I replaced both my O2 and MAT sensors with no change. I've read on the net and also in their users manual that the Auto Xray has some issues with our 85 computers. I'm considering doing the swap to an 86-89 computer to remedy this.

If I remember correctly (I've been in the dessert for almost 4 months now), you can get your MAT sensor reading to change to a lower setting when you turn your A/C on or off. Not sure why, but it does.


[Modified by Ron78Z&85Vette, 1:48 PM 4/21/2003]

 

I do think I'm stuck in open loop because when I get on it I have quite a bit of pinging which is not good but I don't think the computer is responding to the sensors. I'm in the process of checking all of my grounds to see if I can resolve it there. I'll try the a/c though just for the heck of it!

 

well i actually called auto x ray and they admitt that the 85 is difficult to read from. I can get scan to work, but not monitor? So i bought a new MAT sensor since it's eaiser to buy a new one than take the old one out, so i relocated a new one anyway and installed my new fan temp switch from( $32) from corvette central.

Any way i had a vaccume leak , so i fixed that and reset the IAC and now when the car goes to idle the Check Engine Light comes on and says the TPS voltage is too low and it's set at .65V.....so my new theory with this DANG car is just to drive it till it starts running bad then worry about it:). Which is much more relaxing to me and if it keeps up a carb and reg. dist will be in it's future!!!!