Quick rundown:

Rich idle began months before carb rebuild. Carb rebuild became necessary at a later date, when the TPS crapped out.

Rich idle is not always obvious. Exhaust smells O.K., then during a drive, at a stoplight, the exhaust may stink.

I changed no adjustment screws during rebuild, but for the TPS.

Computer temp sensor, and O2 sensor are new.

Here is the testing results:

Six-cylinder scale Sears dwell/tach [set to 'dwell'] was used and THE DWELL IS 21 DEGREES COLD OR HOT; ARTIFICIALLY-CREATED VACUUM LEAK, OR HAND OVER THE PRIMARY, OR MAP SENSOR UNHOOKED, OR O2 SENSOR UNHOOKED.
iNTERESTINGLY, THE VACUUM TO THE EFE (VACUUM-FLAP ON EXHAUST) WAS OFF, AND A MINUTE AFTER RE-HOOKUP, DWELL WENT TO 23 DEGREES. BIG S**T.

Also---Playing with the big idle air bleed screw does nothing to the dwell, in park or gear.

What is a backyard mechanic to do?
BTW, FYI, the car never had a baro or knock sensor.

Is it the computer?
Is it the Hall-sensor in the distributor?
Did something change in the carb, or electronics, when the rich idle began?

1st edit: Is the EGR shutoff valve [hooked to computer] supposed to pulsate in gear? Stops in neutral or if I unplug temp sensor. Sounds just like a loud mixture solenoid, but I never heard it until bringing idle down to 500, and putting in gear.

Even more important 2nd edit: If I bring 'idle' to 2,000, dwell jumps to spec., but not until it actually reaches 2,000 rpm. Any speed below this, and dwell remains at 20ish.

Help. Help. Help.

Thank You
Thank You
Thank You,

Seth

 

While patiently waiting for a response, I need to tell you that the TPS voltage does not always return to 1/2 volts, after blipping the throttle. The adjustment instructions say to back the screw out, then tighten until you get the .48 volts. Did this exact thing, with the engine running. Is my new Standard Motor Products Incorporated TPS CRAP? I do have a spring under the TPS unit.
And, the plates do not appear to be binding.

But, this does not explain a low dwell, whether cold or hot.
It is like the computer sees WOT always, even when the TPS is showing perfect idle voltage.

Seth

 

WOT throttle dwell should be ~10-12 degrees on six cylinder scale. Are you reading a percent scale?

If your carb is running full rich it's either one of two things:

1) The ECM thinks the throttle is wide open.

2) The ECM is sensing a lean condition (real or not) that is outside of its current adjustment parameters to correct.

You can check to see what the O2 sensor is reading by connecting a Fluke to it and measuring voltage to ground. It should be between 3mv (lean) and 1V (rich). I think 0.8-0.85 is optimum but my memory may be a hair off.

I'd check the O2 sensor first, and verify that the dwell reading you're getting is full rich by bumping the TPS to WOT (disconnect the plunger rod and you can push it in without opening the throttle).

Did your model not come with a baro sensor?

Let us know and if you keep opening a new thread each time you're going to have to pm your contact list so we know you're working on it....

Mike

 

Mike,

Thanks.

The conditions exist hot or cold, so we can probably eliminate the O2 sensor. Right?

No baro sensor or knock sensor.

The scale is in degrees, and marked as six cylinder.

I do own a Fluke meter.

Can the new TPS be bad, even though I was able to set TPS idle voltage? Or, can a wire be broken, or the computer fried?


Thanks again,

Seth

 

Probably not your O2 sensor or TPS. If you're reading ~21 degrees and the dwell changes around 2000 rpm it's probably not in the WOT mode.

These carbs will stick on a (seemingly random) dwell setting and refuse to go into feedback mode when they're out of adjustment range. In most cases adjustments to idle mixture screws will bring them in, worse case required adjustments to lean and rich stop.

I'd recommend setting air bleed 4 turns out then making one turn adjustments to the idle mixture screws (in then out) to see if you can get the dwell to start roaming. When it gets in feedback mode you'll see the dwell meter swing slowly to the right then back and forth as it narrows into about a five degree pendulum range.

When you rebuilt the carb you probably cleaned out the idle mixture passages, etc. that the ecm had learned to adjust for over the years (plus the TPS change). You didn't change settings for rich/lean stop so hopefully you're good there.

Mike

 

Mike,

Before I pull the carb [will be on Saturday], to remove the idle-mixture screw plugs and rich-stop plug , I need to remind you that the rich issue began a few months before I ever touched the carburator. How can the mixture change, all by itself? Or do passages in the base-plate erode, causing a richer situation?

As someone who knows little about this carburator, it is far easier to think 'electronics', than 'carburator', but as I said, I know little about this, and am willing to take advice from people such as you, who have the experience. Also, I recall catching an old post that concluded with the fact that this same problem was resolved by a fellow member, only after replacing the distributor [which has a Hall sensor.

Thanks,

Seth

 

A fixed dwell indicates open loop operation. Double check your O2 and CTS sensors - I know they're new, but new does'nt always mean they work. Check the O2 voltage as described above, then check the resistance of the CTS sensor. At 70 F the resistance should be 3400 ohm and hot (190 F) the resistance should drop to 260 ohm (the exact readings should'nt matter, just that cold the resistance is high and drops as the coolant heats up).

As far as the rich condition occuring before making any changes, the float could be stuck or saturated with fuel. Replace it when you pull the carb.

 

I had hoped your idle mixture plugs were already removed and you could play with them now. Before you pull the carb you can go ahead and check your sensors as 8492bird said.

When your original TPS went bad it probably caused your initial rich problem. When they go out they generally pass the higher voltage telling the ecm you're at WOT.

If you have to remove the carb you can verify the rich/lean stops and mixture solenoid travel. Verify your float level too. Replacing the float is cheap insurance.

I'm going to search for the Hall Sensor thread and try to figure that one out.

Mike

 

While you are being generous with your time, can you let me know why the EGR shutoff solenoid [computer-controlled], buzzes when car is in gear. If I pull the temp sensor wire, this stops, which sort of shows that the computer does know what the engine temp is.

And, by the hall-effect sensor, I believe that this is a separate coil, from the one for spark timing, and tells the computer that the engine is spinning. I think that I got the info from Kurt, either on this site, or on the phone. Not certain which source.

Seth

 

I think you'll find that your sensors are fine and your carb just needs to be brought into adjustment range (idle mixture and rich/lean stop... then air bleed).

You are still essentially stock aren't you?

I've worked on several of these puppies that just required playing with these settings to bring them into closed loop.

 

I am so stock, that it is embarassing.

Why did it go bad in the 1st place? The adjustment screws do not simply move by themselves. It esentially went rich by itself. Also, what is cold dwell supposed to read? If other than 21 degrees, how can we blame the carburator?

Thank You,

Seth

 

Seth,
NEGATIVE.... Didn't get that one from me.. I don't know what the heck that thing is.

IMPO - Think Carburator until you have done a thorough A to Z rebuild and inspection of the entire CARB.

I don't want to be perceived as giving anyone a flame..... Please don't take it that way. However, it looks (from some of your posts) that you may not have not yet completed a thorough rebuild of the carb. i.e...........

You cannot adjust the MCS travel without removing the Rich Stop Plug. If the IAB does not get your Dwell to the proper range you must adjust the Mixture Screws......

I would suggest STRONGLY getting the rebuild kit and going from A to Z checking and then setting each and every item in accordance with the chart which comes on the instructions with the kit. Once the carb is back on and the car is running make the final adjustments.... Then... If you cannot get the proper readings that might be the time to look at other devices that can affect the operation of the Computer Command Control System.

Sincerely,
Kurt

 

Why did it go bad in the first place? probably because one of the sensors failed or the float stuck. If the float is stuck you would have more idle and driveability problems so I would star with the sensors.

What is cold dwell supposed to be? There is no spec for cold dwell, just that it will be fixed and on the rich side. 21 deg is rich (but not full rich) so that sounds about right.

EGR solenoid buzzing? solenoids will buzz if they are not getting enough voltage or are failing to latch closed when energized. You should have 12 volts at the valve in idle. As far as the buzzing going away when you pull the temp sender wire, that wire is only connected to your dash gauge and not the ECM (I'm assuming you're talking about the single wire sensor). If that wire is influencing the solenoid then you possibly have a short.

 

Bird,

I was referring to the 2-wire temp sensor for the computer.

If the computer is making the EGR solenoid buzz, then it is pulsating the current [or supplying less voltage than required], and you have stated that it should be steady. I need to check the valve out, as to whether it pulsates with a known steady D.C. source.

This might tell us whether it is the computer of the carburator that is causing these issues. Interesting, that the EGR solenoid has revealed the route to a possible answer.

Thanks,

Seth

 

Check the voltage at the solenoid connector also. If it is less than battery voltage then there is a voltage drop somewhere. GM in their infinite wisdom routed these sensor wires across the valve covers which over time can destroy the wire insulation if the wire has slipped out of the wire loom. On my 84 firebird there was about a 2 inch long section of the wires for the CTS where the insulation had disintegrated, exposing bare wires that were either touching the valve cover or arcing. Heat shrink and splicing solved the problem.

 

My 85 pontiac is all stock (except for the EFE which was disconnected when I got it and is low (non-existent) on my list of priorities.

If your solenoid is buzzing it is most likely a sign that the solenoid is failing, next cause would be low voltage/voltage drop. It should, however, not engage at idle. Do 8492's checks then disconnect it and see if there's a difference.

You're right though that it is an indication that the CTS is sending the proper signal for closed loop. The ECM next will look for a good signal from the O2 sensor, which it may not be getting.

When you rebuilt the carb, how did you reset the rich and lean stop?

The following is purely supposition based on some experience with these things and may be proved wrong:

I believe cold (open loop) dwell is based on a "last known good". When you broke the carb apart and cleaned it up you probably opened several passages (including idle mixture) that had clogged some over the years, essentially going from a lean carb (that the ECM had learned to adjust for) to a richer carb. Settings for rich/lean stop may also be slightly off. I suspect that now the O2 readings are too far out of range for the carb to go into closed loop; requiring more adjustments.

 

My best recommendation is to buy another LG4 pontiac or camaro. I did this last summer and it's so much easier to swap parts from one to the other to determine what's broke.

Mike

 

All adjustment screws were marked with a felt pen and positions were measured with a micrometer. They are back exactly where they had been.
The rich condition appeared several months before I needed to pull it apart.
I have un-powered the computer, to reset it.
Will check the solenoid, before anything else. The fact that it should not be powered at idle seems to point to the computer, or a wire-harness short.
If it is the wires, fine, it will be dealt with. If not, then we will look elsewhere.

I have no room for a fourth vehicle, even if it is only for parts.

Thanks,

Seth

 

The EGR solenoid blocks vacuum to the EGR valve when it is energized (energize to close) - it should be energized at idle and after a cold start to block vacuum. You can verify this by unplugging the solenoid and checking vacuum to the EGR at the solenoid outlet - it should be close to zero at idle and will increase as idle speed increases (open when de-energized). I think all 82-84 fbods had the energize to close type solenoid and later versions may have switched to energize to open.

P.S. I think naf was joking! then you would have two cars not running right!

 

Yeah I was pulling your leg. I bought the pontiac to have something to drive while I work on the 87. The unexpected side benefit was being able to swap known good parts from the camaro to the pontiac while troubleshooting.

Screwed up last year when I got rid of my 94 camaro (V6~28 mpg).

 

Got rid of Triumph TR-7 convertible. Thirty-six on the highway, at 80 mph. Possibly more at the legal speed.

Seth

 

I hear alternator noise through the speakers. At 1st I thought it was the new coil and/or new plug wires, but that would provide a different kind of noise.
The reason that I am telling you this, is I am now wondering if this 'chatter' can make the computer work improperly. Furthermore, if the noise represents a failing or failed diode, rather than a bad filter capacitor (all in the alternator), this would mean that there is alternating current bleeding into the car's wiring, and this kind of issue definitely cannot do the computer any good.
I will set the multi-meter to A.C. voltage, and test for what does not belong there, but this will not answer the question, that only the experienced Third-Gen members could answer.

Also, I have heard from several that the G.M.computer is built like a tank, but the chip can occasionally be a potential weak-spot.


Thank you,

Seth

 

Please recall that I had felt that the computer is at fault, for the variable richness of the exhaust, because the EGR solenoid buzzes at idle.
This solenoid is computer-controlled, and might be revealing a bad computer or simply a bad chip.

This may have great significance, because, using the multi-meter, I have found that the valve receives 14.25 volts in park, and 8.25 in gear, which is not enough to hold it in, hence the buzzing.

So, my well-informed friends, do you still believe that my carburator is at fault, or can I possibly be correct that the computer or chip is messed up, and causing the intermittently-rich idle?

Thank You,

Seth

 

YES

 

Voltage drop at the solenoid, but what is it elsewhere? Most likely a bad connection somewhere or aging wiring. Unless you're experiencing a voltage drop like this throughout the system then it's probably not affecting your carb. .

Do not assume your ECM is causing this but there is the remote chance that the ECM is affected. (For example: a voltage drop to the TPS will affect output TPS voltage.)

Check a few voltages here and there then pop the carb off and expose the mixture screws.

I bought a used ccc-qjet yesterday for $20 and am swapping bodies to fix a stripped fuel inlet. I used an Echlin self tapping fuel inlet a few months back but was never comfortable with it. Taking these carbs apart now and then is just something we do.

 

The car idles clean, until stuck into drive. The computer seems to know that the tranny is in gear, and it gets freaked out. You need to explain how a pair of control wires from the computer to the EGR valve could 'get old' and not supply correct voltage, ONLY IN DRIVE.

This simply should not happen.
If this part of the computer's output has issues, what makes you think that the problem is so isolated, that it cannot bleed off into the other circuits? If it is not the noise that the alternator seems to be producing, confusing the computer, than well, you know what I think. The manual states that the computer has a regulated 5 volt supply just for the sensors. Also wonder if that works.

I am not posting this to be conferentational, and
I do not pretend to know a whole lot about this computer system, but gimme me a break. Not one screw adjustment in the carburator is different [but for the TPS]. Electronics do go bad, and this EGR thing in gear can only be indicative of electronic problems.

Seth

 

Yeah, I agree that the voltage drop at the EGR is a problem but I don't think it's being caused by the ECM although it may be affecting other systems. If you had a system-wide low voltage problem I'd think your choke light would come on, but the bulb could be burned out?

Keep in mind that the ECM does not know when the trans is in drive. It will, however, sense a change in MAP, O2 etc. as a result of the additional load.

Should be easy enough to check whether the alternator is causing problems by disconnecting it and allowing the engine to run on battery alone. You can take the belt off then see if you still have the noise through the speakers.

A few years back I attended a seminar on harmonics in distribution and utility voltage systems. I'm no expert but I understand what you're talking about.

If I wasn't 10 hours away, I'd come give you a hand.

Mike

 

Mike,

Your last post: I really appreciate the contents, and the thought. There will always be a cold Corona with a twist of lime, waiting for you.

I think that the alternator has a separate 'sense' wire. I can disconnect that, while the engine is running, w/o bothering with the belt. This would turn off the device.

Seth

 

It is now my decision that the problem lies within the COMPUTER.

This is the ONLY explanation to the EGR valve problem, and does point to at least one tangeable problem within the computer.

So, I am putting out an

All
Points
Bulletin

for a computer and chip that are known to be pristine in function.

Serial # off the paper label supplied upon request.
But for starters, the car is a 1983 5.0 liter [non-hi-performance, I gather], carburated, auto-tranny 'Bird. Very stock, of course.

Thank You,

Seth

 

If you are bound and determined on replacing the ECM, a remanufactured one can be purchased from Checker or Autozone for ~ $80.

The ECM does not supply 12V power to the soolenoids; it switches the ground leg. The power supply is through the ignition circuit. The autozone.com web site has some simplified wiring diagrams for these cars. Go to the site, click on Repair Info, then repair guides, and chassis electrical. This diagram will give you a better idea on how these solenoids are wired.

 

Will check out the connection diagrams. You state that the computer switches chassis ground. I will see what kind of continuity the meter shows to ground, when I place car into gear.
I am certain that it will reveal a less than 100% continuity under that circumstance.

Seth