84 Cutlass 231 Dualjet issues

[darbysan]

Working on a friends Cutlass231 V6. TPS voltage was off, so rebuilt carb and replaced TPS and float. I left the idle mixture screws and the IAB alone, as they were still factory set. MCS is functional. Set timing, TV cable, Choke. Checked extensively for vacuum leaks using Starter Fluid. Car runs OK, but not great. Checked O2 output, and getting proper voltage readings.

Tried to adjust Dwell, and this is where the readings get funny. At higher RPM ( 2000) I'm getting a reading of near 50 ( Very Rich)( 6 cyl scale). Adjustments to Rich and Lean screws have no real effect. As soon as I let off the throttle, I hear a loud click near the carb and the Dwell immediately drops to 10 ( Very Lean), like a switch has been thrown. O2 readings drop to .18 volts and do not vary at all. As soon as I increase the throttle to about 2000, I start getting readings again. Throttle setting of 1000-1500 have no affect on the dwell- has to get to 2000+ before I get any change.

My thoughts. 1) O2 sensor is working, but may be dirty, requiring higher temps to operate 2) Cat may be partially clogged. 3) IAB may need to be set, even though it was still at factory settings.

Any other thoughts?

 

[88hurstolds]

Did you properly adjust the TPS?
99% just drop it in, you are suposed to drill out the plug on the body and adjust the TPS postion by voltage and throttle positon.
Also, non-AC Delco TPS's are garbage and dont give proper voltage readings.
Just a thought...
Did you reset the computer by disconnecting the battery for an hour?

 

[darbysan]

Yep, adjusted TPS to .48 volts. Computer was also reset. I think you are right about the aftermarket TPS's though. Full throttle only shows about 4.3 volts, but I think I can live with it. I've rebuilt a bunch of CCC Quadrajets, but this is my first CCC Dualjet.

Any thoughts on the Dwell readings and O2 readings?

 

[88hurstolds]

I thought they are supposed to read 5 volts at WOT.
If it's aftermarket I'd question it, the computer is very sensitive on voltage readings and if it's not giving the full readout you could have issues... I'm no expert on these 231's though. I do have every single factory electrical and chassis manual from 1978 through 88 except for the chassis in 1984, just my luck :lol: I could scan the voltage readings for 1983 if needed, not sure if they are the same...

 

[88hurstolds]

I scanned my 83 manual for you:

http://www.78-88olds.com/forum/showthre ... 4#post1624

 

[rccktmn2]

Actually the TPS is supposed to be 4.5 at WOT and .5 at closed throttle. Did you adjust the timing by the manual (unplug the distributor, etc etc.) The O2 has to be up to temp when your trying to get a reading since it's OBD 1 so if it's not doing anything at idle or first start up it might be normal, let it warm up to operating temps before trying to get a reading.

 

[darbysan]

Thanks for the scanned pages. Car was warmed up when checking O2 and Dwell. Timing was set with the 4 prong plug unplugged. Computer was reset after timing set. Changed plugs. Plugs looked good, except gapped well under spec of .060 at .045. Fuel FIlter also changed. New TPS voltage is low ( 4.25 at WOT), but better than the old TPS (3.2). Not sure I want to tear the carb apart again or the TPS at this time

I understand this might give some issues on the road at WOT, but still fighting why the O2 won't give readings at idle, and the Dwell is so out of whack ( Lean at idle, Rich at elevated RPM). It gives some of the symptoms of a partially clogged cat, but no indication of plugging when checking with vacuum gauge. Still no codes to view. Wish something was far enough out of spec to throw a code!

Guess I'll go back through the basics one more time and see if anything pops up. I'm also going to try and hook up my laptop with WinALDL and see if anything pops up there. I'll report back tomorrow with results.

Thanks again

 

[88hurstolds]

The prom or computer might be fried too, these ECMs are not the greatest...

 

[darbysan]

Update. Hooked up my laptop with WINALDL, and went for a spin. Nothing really strange happening, except O2 seems to be in the rich range. One thing did happen- dropped out of closed loop for about 30 seconds while climbing a hill near my house. No reason for it- speed, rpm's, etc looked OK. Suspecting an ECM problem. Would an ECM from an '85 Elky 305 work, if I swapped the proms? ( Just happen to have an extra on hand).

Took the carb off, and checked the TPS. Gets 0-5 volts easily when the TPS was outside the carb. Checked the adjusting tang, and made sure it moved smoothly. Tried a couple of different length TPS pins, but nothing made a difference. Looks like the geometry of the arm will not give full travel to the TPS, no matter what I did. I did bend/straighten a couple of arms/tabs, and got another .25 volts ( now giving .5 to 4.1).

Replaced the o-rings on the Idle Bleed valve, and then adjusted it on the carb. A little movement here made a big difference on the idle dwell. Got it to come up to 30 from 10. Then adjusted rich stop to get the high speed dwell into line. Everything was looking good, but then all of a sudden the dwell dropped to 10- just like something shut off. O2 voltages dropped to .18, but as soon as throttle was applied , started to swing from .600 to .450 ( but still no indication on the dwell). Maybe my dwell meter took a dump?

Anyway, car runs better that when it first arrived. Owner is leaving tomorrow for a long road trip, so I hope it works out for her. Free labor, so you get what you pay for 😀

 

[88hurstolds]

I'm not 100% sure if the unit from a 305 Chevy will work or not if you switch the proms, but I think it wouldn't hurt to try if they are identical externally. I know earlier computers from 81-83 were a little different externally IIRC...