A/C straining and killing engine

[burch]

Hello everyone -

I’ve got a recent issue with 6631, that I believe is electrical, but wanted to check with the group. This one seems to center around the A/C system.

When I start the car from cold, voltage gauge reads about a needle-width above 13. I turn on A/C, car dies immediately without application of throttle. When driving, this feels like you are towing something that is shaking behind the car. My first thought was that I may have some sort of mechanical issue at the A/C compressor. PO changed this to an R134 system, but I do not know how long ago. Removed the A/C belt, and checked all idler pulleys for resistance….everything was good (just replaced the idle pulley bearings last summer). With the belt removed, I repeated the test, and the same symptoms appeared.

Drove car around for a bit to warm it up, acceleration was a bit sluggish. Slightly improved as the temperature approached operating temp.

Drove the care with A/C off until otterstat activated the cooling fans. Fans come on, voltage drops to about a needle-width under 13. Put car in park, needle stayed approximately the same. Fans do their thing, drop the temp down, and they shut off. I turn on the A/C. A/C fans turn on (sans compressor), and very little drop in voltage. Cooling fans, however, did not come on with A/C. Turned car off.

Turned it on about 10 minutes later. While idling, I turned on the A/C (with the belt still off). Voltage dropped to about the halfway mark between 13 and the hash between 13 and 8, but car continued to idle smoothly. Put the car in reverse, and voltage dropped and the car died.

I checked the two major ground points (drivers side radiator bracket and trailing arm bushing mount). Cleaned both, and tested via multimeter. 0 ohms of resistance, so I believe those are ok. Checked the relay/fuse compartment, no melting or anything at the fan fail or cooling fan relay socket. There was a little bit of plastic melted on the top connection to the cooling fan breaker, but it didn’t look recent.

What do you all think? I believe I have the original alternator, which would be Motorola based on VIN. I’ve never had it out, and can only see part of the blue and silver label on the top. The alternator seemed like a possibility, although if it were at fault, would I ever see the voltage that I’m supposed to?

[Bitsyncmaster]

Check your battery voltage with your meter. A good alternator should provide about 14.5 volts.

You have another problem if your AC compressor turns on and the fans don't. Check the diodes in relay compartment harness.

My guess is your alternator is bad.

[David T]

Check your battery voltage with your meter. A good alternator should provide about 14.5 volts.

You have another problem if your AC compressor turns on and the fans don't. Check the diodes in relay compartment harness.

My guess is your alternator is bad.


Agree with checking the alternator and will add check the battery too. and it also sounds like the A/C could be overfilled with refrigerant.

[burch]

Alternator surprisingly tests good! about 14.10V with car running. Will check diodes and refrigerant next, and see what we get.

[burch]

Diodes tested good, and the connections were clean and tight. A/C shows a little bit of an undercharge, and the clutch engages intermittently, supporting that reading. Probably wouldn't be a bad idea to evacuate and charge the system properly, as I don't know the history of that specifically.

So, at this point...

Grounds = OK
Alternator = OK
Cooling Fan Diodes = OK
Relays and Breakers = Appear to be ok

Still seems to have to be electrical, as I was able to replicate with no A/C belt.

Could a failing alternator be problematic intermittently, or once they start to go, is it pretty consistent?

[Bitsyncmaster]

Could a failing alternator be problematic intermittently, or once they start to go, is it pretty consistent?

I've not seen an alternator fail intermittently but I would guess it can happen with the regulator with temperature changes.

[dn010]

lack of oil in / or tired compressor would be my guess.

Sent from my XT1254 using Tapatalk

[DMC-81]

Hmm. So you are able to replicate the shaking/ sluggishness during a heavy electrical load with and without a A/C belt installed, and the symptoms improve as the car comes up to operating temperature?

If so, I wonder if it could be related to the ignition or lambda systems?

[burch]

It is a possibility. Seems like this is an issue where I'll learn to troubleshoot a bunch of things. Anything I should check to make sure those are operating correctly?

[David T]

Diodes tested good, and the connections were clean and tight. A/C shows a little bit of an undercharge, and the clutch engages intermittently, supporting that reading. Probably wouldn't be a bad idea to evacuate and charge the system properly, as I don't know the history of that specifically.

So, at this point...

Grounds = OK
Alternator = OK
Cooling Fan Diodes = OK
Relays and Breakers = Appear to be ok

Still seems to have to be electrical, as I was able to replicate with no A/C belt.

Could a failing alternator be problematic intermittently, or once they start to go, is it pretty consistent?

The clutch is SUPPOSED to engage and disengage cyclicly. It should run pretty continuously at idle but engage and disengage when above idle, quicker the faster it runs. When the clutch engages the cooling fans also start up so it is a big load on the electrical system and a big drag on the motor at the same time. If everything is not running right it could cause the motor to stall out. The idle motor system is supposed to keep the RPM's steady. Vacuum leaks can cause all kinds of problems made worse when you run the A/C.

[Jonathan]

Burch,

Was the car working well at some point recently before it starting doing this? Did you swap out any fuses or relays or circuit breakers recently?

What came to mind was the jumble of brown wires that are tied to the circuit breakers for the cooling fans. I recall the instructions for the relay/fuse upgrade kit from DMCH mentioning the importance of keeping the wires sorted out and not to connect them in the wrong positions.

If the car dies "instantly" when you turn the A/C on, I'd suspect an electrical mistake or short somewhere.

If the car just chugs a little bit and then dies, perhaps the idle is set too low or some other issue with the idle system?

What does your car idle at when parked? 775 RPM? Everything check out ok with your throttle linkage, idle speed microswitch and idle speed motor?

[DMC-81]

It is a possibility. Seems like this is an issue where I'll learn to troubleshoot a bunch of things. Anything I should check to make sure those are operating correctly?

Well, as a cursory check, I would check for a good connection:
- at the coil (lead wires and the coil wire)
- all spark plug wires at both ends
- all fuses (especially #1)
- the connections to the black ECU (on the parcel shelf)
- and the black connection to the idle speed motor (as David mentioned)

A video of the engine's symptoms would help as well.

Good luck!

[burch]

Was the car working well at some point recently before it starting doing this? Did you swap out any fuses or relays or circuit breakers recently?

It was working well recently, and no recent changes in the fuse/relay compartment. I've always noticed a little extra load with the A/C on, but nothing that inhibited operation as much as this.


What came to mind was the jumble of brown wires that are tied to the circuit breakers for the cooling fans. I recall the instructions for the relay/fuse upgrade kit from DMCH mentioning the importance of keeping the wires sorted out and not to connect them in the wrong positions.

Think these are OK, but I'll verify.


If the car dies "instantly" when you turn the A/C on, I'd suspect an electrical mistake or short somewhere.

If the car just chugs a little bit and then dies, perhaps the idle is set too low or some other issue with the idle system?

What does your car idle at when parked? 775 RPM? Everything check out ok with your throttle linkage, idle speed microswitch and idle speed motor?

Engine chugs a little bit and dies (if I don't apply any gas). Idle sits right about 775. I need to check the linkage, microswitch and ISM.

[burch]

Well, as a cursory check, I would check for a good connection:
- at the coil (lead wires and the coil wire)
- all spark plug wires at both ends
- all fuses (especially #1)
- the connections to the black ECU (on the parcel shelf)
- and the black connection to the idle speed motor (as David mentioned)

A video of the engine's symptoms would help as well.

Good luck!

Thanks, Dana...all should be easy save for the plug wires. Hope to do this today or tomorrow.

[burch]

Still working through everything here...and I did find that the WOT microswitch was apparently stuck. It's disconnected for right now, but I'll be cleaning and repairing it this weekend. That helped quite a bit with off-the-line hesitation and the exhaust doesn't smell too rich anymore. Will be pulling dwell this weekend too to see where it is at.

[StanMan PushN 88]

Still working through everything here...and I did find that the WOT microswitch was apparently stuck. It's disconnected for right now, but I'll be cleaning and repairing it this weekend. That helped quite a bit with off-the-line hesitation and the exhaust doesn't smell too rich anymore. Will be pulling dwell this weekend too to see where it is at.


Can you or someone who has "checked the dwell" please explain step by step HOW TO CHECK / ADJUST THE DWELL AND THE IDLE for the goal of 775 RPM?
Right now my car seems to idle around 600 RPM (just a hair above the 500 mark)

PHOTOS or VIDEO steps to show which adjustments are being changed would help too!

[DMCMW Dave]

Can you or someone who has "checked the dwell" please explain step by step HOW TO CHECK / ADJUST THE DWELL AND THE IDLE for the goal of 775 RPM?
Right now my car seems to idle around 600 RPM (just a hair above the 500 mark)

PHOTOS or VIDEO steps to show which adjustments are being changed would help too!

The 775 idle is set by the ECU and the Idle Speed Motor. If it is idling too slow (600 is too slow) there is either something drastically wrong or the ECU/Motor combination is not working.

First test - with the engine idling, locate the black idle ECU. There are two connectors on it facing the rear of the car. Disconnect the one toward the middle of the car. The idle speed should immediately take off to about 200 RPM, and come back down when you plug it back in. If that does not happen, fix that circuit first.

[Jonathan]

The 775 idle is set by the ECU and the Idle Speed Motor. If it is idling too slow (600 is too slow) there is either something drastically wrong or the ECU/Motor combination is not working.

First test - with the engine idling, locate the black idle ECU. There are two connectors on it facing the rear of the car. Disconnect the one toward the middle of the car. The idle speed should immediately take off to about 2000 RPM, and come back down when you plug it back in. If that does not happen, fix that circuit first.

:)

[DMC5180]

The 775 idle is set by the ECU and the Idle Speed Motor. If it is idling too slow (600 is too slow) there is either something drastically wrong or the ECU/Motor combination is not working.

First test - with the engine idling, locate the black idle ECU under the driver side parcel shelf cover. There are two connectors on it facing the rear of the car. Disconnect the one toward the middle of the car. The idle speed should immediately take off to about 2000 RPM, and come back down when you plug it back in. If that does not happen, fix that circuit first.

Added info for the unfamiliar new owners. :)

[StanMan PushN 88]

Added info for the unfamiliar new owners. :)

Hi Dennis,
WHERE is this infomation you added? How to check/adjust DWELL? Would a failing alternator cause the RPMs to be lower than normal? Did a test on mine and it is "going bad" only at 12.2.....

Video or Steps to check dwell?

Thanks everyone!

[DMC5180]

Bold highlighted in Dave's quote. In my previous post.


Dennis

[Rich]

Agreeing you should run the idle motor circuit test before worrying about dwell. Also recommend you see to your charging system before worrying about idle speed or at least not plan any trips til you verify good charging.

When you get to 'dwell':
Answers inserted and underlined below, including the voltage answer:



...How to check/adjust DWELL?
See the video for the test
Would a failing alternator cause the RPMs to be lower than normal?
No.
Did a test on mine and it is "going bad" only at 12.2....
Expect something more like 13.8-14.0V when it's running with low load, same as with other cars.

Measure with a good meter at the jump start terminal and the engine block.
12.2V means it is not charging. Have not read whole thread but this may be a separate issue, one you need to sort out before driving very far.

Video or Steps to check dwell? Yes, here, thanks to Rob D for a great how-to: LINK (https://www.youtube.com/watch?v=cpNB1eRktzM)

[DMC-81]

Hi Dennis,
WHERE is this infomation you added? How to check/adjust DWELL? Would a failing alternator cause the RPMs to be lower than normal? Did a test on mine and it is "going bad" only at 12.2.....

Video or Steps to check dwell?

Thanks everyone!

Hi there,

As I am about to adjust my dwell, I have researched and summarized the following information from these posts:

http://dmctalk.org/showthread.php?5760-Adjusting-CO-With-A-Dwell-Meter
http://dmctalk.org/showthread.php?12369-What-the-dwell
http://dmctalk.org/showthread.php?12909-How-To-Set-CO-Dwell
http://dmctalk.org/showthread.php?11945-Unsure-of-dwell-reading
http://dmctalk.org/showthread.php?1123-Good-Dwell-Meters

Videos
https://youtu.be/MbE-2k4Cy4E
http://youtu.be/cpNB1eRktzM
http://youtu.be/FTUJCUIWFhg

CO Dwell (fuel system duty cycle)

General information and set up:

Use the 8 cylinder scale on a preferably analog Dwell meter.
Divide the numbers in the Workshop Manual by 2 to match the measurements on the meter.
Or, read the 8 cylinder scale on the meter and double them to correspond to the numbers in the Workshop Manual.

We use 4 cylinders rather than our 6 cylinders as we are using a more common ignition dwell meter for measuring fuel system duty cycle, and the 4 cylinder scale is more accurate for this test. The Workshop Manual numbers use a 4 cylinder scale.
Proper duty cycle is a 0 to 100 % scale. Dwell for 4 cylinder is 0 to 90 degrees (i.e. very close)

It's ideal to have all idle issues worked out and idling at around the factory spec of 775 RPM or so, and let the engine warm up to operating temperature to get the Lambda/ECU/O2 functioning, if not, the system is under a closed loop mode.

Remove the anti tamper plug if needed:
http://dmctalk.org/showthread.php?8362-Removing-the-anti-tamper-plug-covering-the-mixture-adjustment-screw
After removing this plug, or if a plug is not present, you will need part number 102392A CO Plug to avoid a vacuum leak.

You will need a 3 mm t-handled hex wrench for the adjustment

Connect the meter:
Connect the green lead on the meter to the pin that is in the right rear corner in the diagnostic plug
(Alternatively, to the orange wire in the loose two wire plug/pigtail running along the firewall, or tap the orange wire in the Blue Bulkhead Connector.)
Connect the black lead to the engine block.
(I will be using the Actron CP7605 analog meter)

DMC Workshop Manual instructions:

Follow the 5 steps (A through E) in Section D:01:14 & D:01:15. The chart was created by taking measurements taken on a good system. If it passes all 5 tests, the system (including the O2 sensor) is should be good.
D:04:01 in the manual states that you can also use a "red exhaust gas analyzer" in order to perform a CO emissions adjustment, but it's not necessary.
For test E, just press the WOT switch instead of holding the throttle wide open.

O2 Sensor:

Have a properly functioning O2 sensor if possible before adjusting CO.
You will need to disconnect the O2 sensor during this test during tests B, C, and D.
Disconnect the O2 sensor at the connector where it goes into the body, which is just forward of the left rear tire in the fender well.

Measurements:

Engine cold:
If the system is in a closed loop operation properly, the reading should be approximately 55.

Engine warm:
O2 disconnected: 40 to 50
O2 connected (normal operation): pulsating from 35 to 45 (so, centered about 40)

Adjustment:

To make an adjustment on the mixture screw:
clockwise = more CO and richer
counterclockwise = less CO and leaner

Cover the hole with the bumper/wire again after adjustment to avoid a vacuum leak. Once the hole is covered, another reading and repeat as necessary until the target range is achieved

The adjustment is sensitive. Usually a 1/4 turn on the mixture screw will drive the lambda system to it full maximum (about 95% duty cycle) and it full minimum (about 10% duty cycle). That would be a good indication that your O2 sensor is working.

Optional Tests and other information:

Disconnect the O2 sensor. Now ground the lead that goes to the ECU and watch the needle and listen to the FV.
Then take a 1.5V battery and connect (-) to ground and (+) to the ECU lead, the meter will swing entirely the other way. You will hear the FV change in tone as well.
This confirms that the ECU is working.

There is a ground wire on the forward (back of the engine) end of the intake runner on the passenger side. If unmodified, it has a red tag on it, and the wire is only about 3 inches long before it hits another connector. THIS WIRE is the ground reference for the O2 sensor. If disconnected, the ECU goes kind of nuts. Check continuity from that attachment point all the way to the ECU, and check for bad connections at the bulkhead connection and at the connection close to the intake runner.


If anyone finds an error, please suggest a correction.

Hopefully this is helpful.

Edit: I see Rich has provided information above^.

[Morpheus]

Good info in this thread.