Stumblin Bumblin Z

[Paul Workman]

Originally Posted by scottfab

Ok, after pouring over this thread I picked up on something.
You say you have 42 lb of fuel pressure and it goes to 50 when you rev up. You should have 50lb or so without reving.
Could be that your secondary fuel pump is intermittent.
If you do some hard accelerations up to the stumble a few times see if a lean code gets set. Then its pretty certain.
I had something very similar but at 4500 rpm. It never set a code.
When I replaced the secondary fuel pump it went away.
My fuel pressure with both pumps whet to 44lb when I just turned the key on. Then it would leak down pretty fast.
When I replaced the pumps it went to 52 and came down very little over time.
You may need to connect a fuel pressure gauge and go for a drive up to the stumble.

I agree with you - far as a static test goes. Mine does that too. However, under dynamic load (pressure gauge taped to the windshield), with just the primary pump, pressure is in the 44-46 range (depeding on load). But, as soon as the throttle/rpm reaches the threshold where the secondary pump activates, pressure pops to about 52 ± a bit and holds steady.

For what its worth, when the secondary pump was not working, FP dropped to 38# at WOT, and the AFR went very lean!

[scottfab]

Originally Posted by Paul Workman

I agree with you - far as a static test goes. Mine does that too. However, under dynamic load (pressure gauge taped to the windshield), with just the primary pump, pressure is in the 44-46 range (depeding on load). But, as soon as the throttle/rpm reaches the threshold where the secondary pump activates, pressure pops to about 52 ± a bit and holds steady.

For what its worth, when the secondary pump was not working, FP dropped to 38# at WOT, and the AFR went very lean!

If the secondary is not working at all it does not surprise me to see <40lb.
However, if you get one failing like mine mid 40s is not good enough.
Mine Now starts with 52lb and stays there until sustained WOT then drops to about 49lb then shoots back to 52lb when the secondary pump kicks in.
At this point I think he needs to rule out the basic stuff before looking at secondary actuators. It's hard enough chasing one's tail but if your chasing the wrong tail? She better be worth it
By what he's describing the secondary fuel pump could very well be seized up. Best rule that out.

[1963korvette]

If one or two of the secondary injector were not firing, wouldn't that act as more a miss. I would think the other 6 would pull it along. This feels like either no fuel or no air mixuture. The primeries are driving the engine. I know I called it a stumble but really its just a no power feel. right up to 7,000 rpm's.

I can feel another plemun pull is in my future. At which time the vacuum system is history.

[FU]

It's a 4 1/2 hour drive for me to Westminster from the southeast shore on L.I.

[1963korvette]

Ok, so I will tape my fuel gauge to my windshield tonight. It would be an easy fix if the pump is the problem. Seems I should have some kind of error code for this problem.

[John Boothby]

Originally Posted by 1963korvette

I usually let car warm up before testing it. It does it when you get into it with full power switch on. When you ease it up to above 3,000 it starts guggling. I did have SES light on all the time but that was MAP sensor hose. Since I fixed that The SES light is off all the time now.

Now, how would I check the speed sensor?

FSM 6E3-A-46 & 47

You say that you do not have any codes? The DIC will show SES light if the secondaries do not open, so it probably is not your secondary vac sys. So this narrows it down to fuel or ignition. Is it blowing smoke when it starts to bumble and gurgle? Have you checked your plugs to see if they are wet? Color?

When the VSS (Vehicle Speed Sensor) goes bad, it limits the rpms to 3k and does some weird things from what I know. It also may or may not throw a code 24. It could also be an intermittant code 24. It will affect other things also like the Ride Control;Radio; or Speedometer.

Anyhow, this is just an idea to check.

Forgot to ask does it do this when the power key is turned off? If so, it probably is not the VSS.

[1963korvette]

With valet mode car runs fine rev's up to 7,00 with no problems. There are no codes. I have not seen any smoke out back but than again I'm in car alone. Will take wife with me tonight. Will pull plugs after ride and report findings. Yesterday my radio antenna was very squerrilly wouldn't go up , than worked, than wouldn't, than would. The car goes over 3,000 just doesn't run right.

[Kevin]

i didn't think you could wind the car to 7,000 without the key on

[John Boothby]

Originally Posted by 1963korvette

With valet mode car runs fine rev's up to 7,00 with no problems. There are no codes. I have not seen any smoke out back but than again I'm in car alone. Will take wife with me tonight. Will pull plugs after ride and report findings. Yesterday my radio antenna was very squerrilly wouldn't go up , than worked, than wouldn't, than would. The car goes over 3,000 just doesn't run right.

The VSS does not effect the radio antenna, it just effects the way the radio automatically increases volumn with speed.

If it is running ok in "Normal" mode, it probably is not the VSS.

I am leaning toward secondary fuel problem.

[scottfab]

Originally Posted by Kevin

i didn't think you could wind the car to 7,000 without the key on

I believe it does go on up to 7k but with less vigor

About the VSS probability of failure.....
Another test for it is cruise control. It will not work.

The only thing that bothers me about all this is that the stumbling
starts at 3k. Seems like it should set a lean code if held at the 3k point.