BUILD THREAD 84 Hurst Olds - TechG8

[techg8]

yes headers. I took a look in the pipe and the o2 sensor is not obstructed at all. It is very much in the exhaust stream. About an inch or two back from the collecter flange

its perplexing. All of the sensors check out good. TPS, temperature, and o2. No codes are set. System appears to be functioning normally.

I have only 3 ideas left.
1) possibly the o2 sensor is not getting hot enough. I find this unlikely given its position but who knows.
2)the "off" timing has something to do with it
3) perhaps a bad pROM chip?

 

[69hurstolds]

Do you have a check engine light when the key is on but not started? i.e., the bulb not burnt out?

Code 51 is a bad prom.
Code 55 is a torched ECM.

Are your ground wires connected from engine to firewall and have good contact?

Have you run the car hard to heat the heck out of that O2 sensor? If so, does it run any better (while in closed loop)

Throwing spaghetti on the wall here.

 

[69hurstolds]

The O2 sensor needs to be approx. 6" from where the collector starts- where the 4 tubes meet up. It should still be in FRONT of your header flange unless the collector is exceptionally short. Basically you want the header tubes blowing right onto that sensor.

And you should have at least a foot or so of pipe behind it (should be taken care of if you have street exhaust). The idea of the foot of pipe is to keep any chance of reversionary air from cooling off the sensor.

No vacuum leaks, broken, or disconnected hoses? Again, just throwing spaghetti.

 

[Canon_Mutant]

thanks for all that. I have the manual just haven't had time to chase it yet.

Here is some interesting info...BEFORE I pulled the engine it ran on the ECM with no codes. No check engine light.

When I pulled the engine I broke the o2 sensor.

Replaced it with a used/newer one I had in the basement from I believe an 86 olds 307. I believe it was a bosch.

since then Ive had this problem.

This is where you need to focus.

 

[84 W40]

Sounds like both of your ecm's are working correctly and the prom. Even an engine thats 190 degrees can go back into OL. I will explain the best i can and have info on it that will explain it better just need to find it.
When you start engine when its cold it automatically go's into OL with a fixed dwell between 30-40 on the rich side and it will vary between proms. Coolant temperature sensor is what controls your fixed dwell when the engine is cold your O2 at this time is shut off not sending any signals to the ecm. When the ecm see's a pre determined temperature value from the coolant sensor oldsmobile is about 138 degrees it then go's into CL and your O2 tuns on and starts sending signals to the ecm thats when you start seeing the dwell go back an forth from 5 to 50 on the scale.
Your O2 works at a temperature of 550-600 degrees, if its below 550 degrees it will send it to OL even if the temperature of the engine is at 190 degrees. This usually happens when your engine is at idle and the O2 starts cooling down.
I know you tested the coolant temperature sensor and it was in spec but i would change it , not exspencive.

 

[69hurstolds]

I am jumping on board with 84 W40 . I suspect it's not throwing codes because it isn't seeing anything wrong. It's just doing what it's doing as it was set up from the ECM. It could very well be a temperature thing. If you say it's actually sending a signal when you open it up, I'm thinking the sensor is seeing colder temps quicker when it returns to idle. Did you try say, holding RPM at about 2500 or so to cook that O2 sensor? At some point that O2 sensor will heat up to the point it'll send a signal. Or pull a vacuum line if it is hot enough and see if dwell changes? If dwell is changing when you open the secondaries, then it APPEARS to me the O2 sensor at some point is sending a signal. Maybe it's just doing it at higher RPMs? I dunno.

If you know of anyone that has a good OBD1 scanner setup you could borrow, or if you have one, then hook it up and go for a drive. It should tell you whether and when you're in open or closed loop I would imagine.

As far as the ECM temperature sensor...is it the ORIGINAL type or the "newer" type? The original had yellow/black wiring with an umbrella looking clip on it that covered the single prong (in the center) sensor. In 1986 or so, they changed it to the newer style.

Original style:

Connector for it looks like this:
GM p/n 12014843

Newer style:

GM p/n 12146312

And it's companion plug piece- This USED to come with the sensor when they originally started putting these in cars and the original style was superseded.
GM p/n 12101899 (ACDelco PT169)

I barely understand all this wirebiting stuff as it is, but I do know you can't let it idle very long before you lose your "heat" on the sensor and you go back into open loop, even with cast iron manifolds. If your O2 sensor is in the pipe, I'm just going to throw it out there that I think it's too far back from where it needs to be and it doesn't get as hot as it should at the right times and loses too much heat too fast. JMO.

 

[fleming442]

Hence, why a heated O2 would be a good upgrade as someone mentioned. The ECM would then be solely dependent upon the CTS since the O2 would always be hot. Don't know for sure if it's right, but it sounds good!

 

[rfpowerdude]

I have an OBD1 scanner for sale if ya wanna spring for it. You can monitor all of these sensors (including dwell) real time. Price cut to $50 for the scanner.

OTC Monitor 2000 scanner (old school OBD 1 ECM scanner) - GBodyForum - '78-'88 General Motors A/G-Body Community

Thought I posted this here before, but I cannot find it now. Up for sale is my OTC Monitor2000 scanner. I used to use it on the '83 H/O since that was all original. Asking $100+shipping (OBO). Anyone with an original G-body that still has the ECM (or putting one back together) can use this for...

gbodyforum.com

 

[69hurstolds]

I have an OBD1 scanner for sale if ya wanna spring for it. You can monitor all of these sensors (including dwell) real time. Price cut to $50 for the scanner.

OTC Monitor 2000 scanner (old school OBD 1 ECM scanner) - GBodyForum - '78-'88 General Motors A/G-Body Community

Thought I posted this here before, but I cannot find it now. Up for sale is my OTC Monitor2000 scanner. I used to use it on the '83 H/O since that was all original. Asking $100+shipping (OBO). Anyone with an original G-body that still has the ECM (or putting one back together) can use this for...

gbodyforum.com

BOOM

 

[Gonzo1970]

You could buy my scanner that will allow you to monitor each sensor real time like the ECM sees and be able to tell if any of them are bad... 😀

OTC Monitor 2000 scanner (old school OBD 1 ECM scanner) - GBodyForum - '78-'88 General Motors A/G-Body Community

Thought I posted this here before, but I cannot find it now. Up for sale is my OTC Monitor2000 scanner. I used to use it on the '83 H/O since that was all original. Asking $100+shipping (OBO). Anyone with an original G-body that still has the ECM (or putting one back together) can use this for...

gbodyforum.com

I got mine off of ebay with all the cables, reference cards, case, etc.. plus GM, Chrysler, and Ford cartridges for $32 shipped specifically because his issue and my issue seem to be very very similar. I wanted to see if my Dwell was moving, and that not only scans but monitors..

Hes in the same boat I am.. Headers, new O2 sensor... rich as hell..

Whats funny is I was thinking it was the carb, and looking to have Him do the rebuild... lol

-Gonz