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#1071215 - 06/28/21 04:24 PM Will not run in closed loop  
Joined: May 2020
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gbodypharm Offline
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gbodypharm  Offline
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Bedford Heights, OH
I will try to be brief but I am still having issues. In my endeavor to learn all I can while working on my 84 SS I purchased an ALDL cable and started using Tunerpro RT to see exactly what is going on with my car to try and remedy the issues I am having. The car will fire right up no problem on cold start with a strong idle around 800 rpm at 12 degrees BTDC with the 350 sbc I put in. After warm up, once the car goes into closed loop it sputters and will die unless I keep on the throttle.

There are no trouble codes present so I am not sure where to start to diagnose the issue.

One thing that sticks out as being off is the coolant temp. My gauge only shows all the way low and does not change during warm up. I changed the sending unit and no change. Grounding it causes it to peg hot so the gauge works. Initial cold start the temp on tunerpro shows 210 F and as the car actually warms up and gets to closed loop it drops to ~150 F. I do not understand why it is showing the opposite of what is really happening.

I checked the temp sensor is getting 5 volts and when turnerpro says coolant temp is ~160 F resistance is around 640 ohm. Comparing to the values in the Haynes book it is slightly high but again there are no codes.

With the car off, Ignition in the on position:
TPS shows 0.65 volts at closed throttle and 4.19 at WOT
MCS duty cycle is 50.20%
O2 sensor mV start around 450 and slowly drops
MAP 0.51 volts
Barometric 4.51

I did get an old analog dwell meter off ebay but trying to check it is very difficult when the car won't run in closed loop.

Any advice on where to start looking?

#1071235 - 06/29/21 08:16 PM Re: Will not run in closed loop [Re: gbodypharm]  
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88ssBrent Online content
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#1071236 - 06/29/21 08:40 PM Re: Will not run in closed loop [Re: gbodypharm]  
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I'm not sure on the temperature part but my first thought is the o2 sensor. If I remember correctly 450mv is around 14.7 on a narrowband o2. If the mv goes down that means the o2 is reading lean. Hopefully someone else can chime in. Does your mcs click when flipping the key on?

#1071239 - 06/30/21 01:41 AM Re: Will not run in closed loop [Re: gbodypharm]  
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gbodypharm Offline
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gbodypharm  Offline
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Bedford Heights, OH
Yes the mixture control solenoid clicks and seems to be functioning properly. The O2 sensor I have is a 3 wire acdelco 19178959. It is located in the collector of the drivers side header.

#1071274 - 07/02/21 01:18 AM Re: Will not run in closed loop [Re: gbodypharm]  
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86ttop Offline
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86ttop  Offline
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Brooksville, Fl
I would check all the engine grounds for the CCC system, good luck. The temp sensor is reading opposite of what it should as you said, maybe it's the engine grounds. Good luck!


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#1071282 - 07/03/21 05:21 AM Re: Will not run in closed loop [Re: gbodypharm]  
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Buick Runner Offline
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The TPS needs to be adjusted to read .50 volts at idle. That high of a dwell reading indicates the computer is responding lean to offset a rich condition. Check the fuel pressure, many fuel pumps put out too much pressure causing rich mixtures.

Last edited by Buick Runner; 07/03/21 05:24 AM.

SBC powered 1987 Regal with TES headers, ZZ4 intake, ZZ4 PROM chip, mini starter, THM2004R, 2500 stall converter, 2040 cam, CCC system, and 3.73 posi rear.

2008 ex NPS P71 Crown Victoria, cop motor, cop shocks, cop brakes, and Jmod.

Never argue with an idiot.
They will just drag you down to their level and beat you with experience.
#1071286 - 07/03/21 09:06 PM Re: Will not run in closed loop [Re: 88ssBrent]  
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stew'86MCSS396 Offline
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Originally Posted by 88ssBrent
I'm not sure on the temperature part but my first thought is the o2 sensor. If I remember correctly 450mv is around 14.7 on a narrowband o2. If the mv goes down that means the o2 is reading lean. Hopefully someone else can chime in. Does your mcs click when flipping the key on?

During open loop the O2 sensor is not providing input and I believe a/f mixture would be temperature controlled. Being it's reporting stoic, I'm thinking there's no enrichment being provided during open or closed loop.

#1071291 - 07/04/21 01:35 AM Re: Will not run in closed loop [Re: gbodypharm]  
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88ssBrent Online content
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Using a wideband montioring the ccc system during open loop I'm right at 12:1 a/f ratio. Once in closed loop it usually varies between 14.2:1 and 14.9:1 while idling.

#1071293 - 07/04/21 01:54 PM Re: Will not run in closed loop [Re: gbodypharm]  
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gbodypharm Offline
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gbodypharm  Offline
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Bedford Heights, OH
I just noticed when I had the laptop hooked up again with a cold engine and not running, Tunerpro had coolant temp listed as 227 for both the Celsius and Fahrenheit which clearly is not the case. I switched to Winaldl and it shows proper temp at 74.9 F so now I at least know the computer is seeing correct temp. Its just the output value Tunerpro is showing that is wrong.

I found some very informational videos on youtube, "GM 81-83 CCC" that is 4 parts detailing all the intricacies of the computer controlled system of these cars. The videos give clear explanations of the sensors, their function, what data they output and how, and how the computer uses this data and responds. One part also details CCC carb overhaul and bench adjustments. Between these videos, the carb rebuild books I just got, and all the info on this site from you all, I think proper steps are to adjust TPS down to around 0.48 - 0.5 at idle and adjust lean and rich stops at 2500 rpm to lean carb out and get dwell down to 30 degrees.

My fuel pressure shows 4 psi steady on my regulator.

#1071295 - 07/04/21 03:11 PM Re: Will not run in closed loop [Re: gbodypharm]  
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88ssBrent Online content
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If you don't have the thexton tools to measure everything properly here is what a member named Damon posted and it is really close. I checked it against the tools and its in the ballpark. While tuning mine I would get it off and use this to get back close. I really like doug roes book as it has some good ccc stuff in it but its hard to beat the factory manual, usually you can find one on ebay.


"There's a lot of ways people have to get their QJet's primary settings close. Here's what I use when I do one. I call it the "rule of four."

1. 4 turns up on lean stop from lightly seated.

2. AFTER adjusting the lean stop, adjust the rich stop until you have 4/32" (1/8") of total MCS plunger travel.

3. 4 turns up on the IAB from lightly seated (make sure the o-rings around the IAB are fresh and oil them so they don't stick-and-tear against the metal as you are screwing the IAB into place).

4. 4 turns out on the idle mixture screws from lightly seated (bigger / higher performance engines might want to start with 5 turns out)."


I really like using aldl scan when datalogging. I use this plugged into my car :

http://www.1320electronics.com/12pin_ALDL_BT_MK2.html

It sends Bluetooth to my phone and datalogs it to a spreadsheet. I like it because its all on my phone, Probably not the best example but its what I had. It looks to be a wot pull in 2nd gear. Channel 3 to the far right is my a/f gauge.

[Linked Image]




Last edited by 88ssBrent; 07/04/21 03:13 PM.
#1071296 - 07/04/21 08:09 PM Re: Will not run in closed loop [Re: stew'86MCSS396]  
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stew'86MCSS396 Offline
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Posts: 187
Honolulu
Originally Posted by stew'86MCSS396
Originally Posted by 88ssBrent
I'm not sure on the temperature part but my first thought is the o2 sensor. If I remember correctly 450mv is around 14.7 on a narrowband o2. If the mv goes down that means the o2 is reading lean. Hopefully someone else can chime in. Does your mcs click when flipping the key on?

During open loop the O2 sensor is not providing input and I believe a/f mixture would be temperature controlled. Being it's reporting stoic, I'm thinking there's no enrichment being provided during open or closed loop.

Just wanted to correct a statement...after thumbing through the FSM, I couldn't find any association to temperature to open loop enrichment. I suppose that's the function of the choke and I'm sure the fast idle step would provide TPS input, MCS enrichment, yada, yada, yada...

Last edited by stew'86MCSS396; 07/04/21 08:10 PM.
#1071297 - 07/05/21 01:06 AM Re: Will not run in closed loop [Re: gbodypharm]  
Joined: Dec 1999
Posts: 11,891
86ttop Offline
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86ttop  Offline
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Brooksville, Fl
Open loop enrichment is fixed!


Leo Paugh
It's not an attitude, it's just the way I am.
POW*MIA
You are not forgotten
If things improve with age, I must be approaching magnificent. thumbs

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