Quadrajet Flutter off of idle Stock 305 automatic

[SkidRo]

LED type. It's a cheap one from a local flaps. Everything was off, doors closed, no hood lights or clock. There is an aftermarket radio installed ( by the previous owner) that must have a direct connection to the battery for the clock. I'll start with that fuse and the lead to the direct connection and then keep working through fuses etc if the radio isn't the issue.

Thanks for your help. I appreciate it.

[bd]

Unfortunately an LED test light isn't workable for this grass roots method, because its current flow is too limited.  It can return a false indication of a problem that may not exist.  With regard to square body trucks, a battery can be expected to support a continuous current draw of ~35 - 45 ma, up to as high as 60 ma, imposed by ECM, radio memory, etc, depending on year and accessory configuration.  The simplest LED test light will illuminate at full brightness with only ~20 ma of current flow.  LED logic probes can illuminate with microamps of current flow.  Unless you are troubleshooting low voltage logic circuits that are sensitive to over-current, an LED test light should be avoided.  In general, use a filament type of test light to troubleshoot power related problems.

Based on your LED test light you maybe chasing a ghost.  Do you have an ammeter?  If so, what is its maximum scale?

[SkidRo]

No worries on the LED tester.  Apparently I bought one a year ago so I just need to find it.  I do have a ammeter - a Harbor Freight special.  I will check the scale on it tonight. 

[SkidRo]

I was able to run some tests today with an analog test light. With the negative cable disconnected from the battery I ran the test light between the negative post and the negative cable.  It glowed very dim.  When I turned on the headlights it went to normal bright. The same results when I opened the door.  If I understand your instructions correctly, this is a normal condition. 

One thing that I did find, but resolved, prior to the test was a wire connected to one of the rear lights.  It looks like there was a cap on the truck and I think the PO tapped the wire to operate a dome light.  The metal spade end MAY have been touching the bed of the truck. It was jammed inside one of the "post" holes without being wrapped in tape.  I remove the wire prior to the testing. Basically I don't know if this was the issue or not.

The radio has a always on power line and I disconnected that while testing.  It made no difference in the test light - it stayed dim. 

The battery stayed charged during this past week. I did have the positive cable removed during this time. I am going to leave the cable connected and see how the battery is holding its charge tomorrow and report back.

[SkidRo]

My last post was premature.  I went to start the truck and the battery barely turned the engine over.  It eventually started but it died immediately. I managed to get it started but it barely cranked over.   The battery, while reading 12.66 when I took an initial reading is now at 12.62v.  When cranking the in-dash volt meter dropped to around 8 volts.  I took the battery out and had it tested at the FLAPs where purchased. It was 12.62 volts and had 549 CCA.  It is a 550 CCA battery.  They said that the battery is fine.  I reinstalled it and started the truck - slow cranking.  Once running the voltage at the battery was a over 13 volts but I can't remember exactly what the reading was. It appears the battery is charging while the engine is running.

What I did discover is that the wire that I thought was the radio power is actually a wire that operates the overhead light when the doors are open.  The PO must have spliced the wire for whatever reason instead of fixing the issue. I unplugged it.

I am wondering if the starter or solenoid may be related to the problem. I have read some posts whereas the comments suggested the starter.

[bd]

...With the negative cable disconnected from the battery I ran the test light between the negative post and the negative cable.  It glowed very dim.  When I turned on the headlights it went to normal bright.  The same results when I opened the door.  If I understand your instructions correctly, this is a normal condition.... 

Correct.  Although, you shouldn't have disconnected any wiring before the test - just made sure that all appliances were switched off.

Check for voltage losses across the starter cabling: Without disturbing the battery cable connections, connect your voltmeter positive lead to the battery positive post and the voltmeter negative lead to the 3/8" battery cable stud on the starter.  Record the voltage reading while cranking.  Repeat the procedure with the voltmeter negative lead connected to the battery negative post and the positive lead connected to shiny bare metal on the starter frame.  Post the results.

Did your local parts house actually load test the battery or just perform a conductance test?

[SkidRo]

Rich, I don't know the exact test they conducted.  The dude connected a digital device to the battery (it was out of the truck) and ran a test.  A piece of paper came out and said it was fine.  I explained the load issue but he insisted that the battery was fine.  I am not convinced that he did what I wanted or the battery is working properly under load.

I will run the new tests as soon as I can.  It's dark when I get home from work now so it may be this weekend.

[bd]

Take whatever time you need.

[SkidRo]

I was able to do a few quick tests today.  I measured the battery and it was 12.75 volts.  I had the positive and negative cables connected to the battery since Tuesday. I will take that as a good sign. I then attempted to start the truck.  It cranked real slow but eventually started.  Unfortunately it cut off.  The next attempt to start it produced nothing.  The engine would not even turn over.  I took another voltage reading on the battery and it was 12.57 volts.  I am charging the battery now to run the suggested tests above.  I will also verify the ground to the engine block is good.

[SkidRo]

The starter was bad.  It sounded like a jar of grinding ball bearings when I got under the truck.  I have the new one installed and it starts fine.  I am in the process of shimming the starter - the old one did not have any. 

It took two shims. The starter sounds fine when cranking now.

I took it for a spin and it appears to be running fine.  There is a slight hesitation coming off of idle very similar to how the truck ran since I have owned it.  I will be happy with this if it continues to run like this.  However, I need to drive it some more to see if the big dead spot returns.

[bd]

Yeah, it started to look that way back on the 8th.  Glad you got the cranking problem resolved.

[SkidRo]

I drove the truck all day today.  It runs great.  The carb issue went away.  It starts, idles, accelerates, runs on cruise control, everything. This was the strangest issue that appears to be non-carb related.  But I have heard most carb issues are electrical.

Thanks to everyone and especially Rich for providing troubleshooting tips and suggestions.