Inconsistency
 

Is it possible for a converter to cause an issue where my car will make 3 or 4 passes within .04 of each other then out of nowhere make a pass that is .2 slow. On the pass where is slows down it loses ET everywhere starting with the 60'. Everything has been changed on the car trying to solve this issue, wiring, MSD, coil, fuel system, etc... I am of the assumption that if something was wrong in the converter it would continue to slow down, where as once I load up after making this slow pass, the next time to the track the car is right back to making good passes.

3000 lbs car
540" BBC
Ladder Bar Rear Suspension
Powerglide

I installed a data recorder to track engine RPMs this past weekend and on the two passes where the car fell off, the RPMs are very shaky from about .07 into the run. I will try to post a picture of the graph later.

Re: Inconsistency
 

post up all the time slips in order from the day in question.

That said, moving .04 in 3 or 4 passes is a problem no mind 2 tenths.

Consistency starts and end with the one wearing the brain bucket. Are you doing everything exactly the same from the moment you buckle your harness to the moment you cross the stripe?

Re: Inconsistency
 

Too rich makes it too sensitive to temp and Baro changes.

Re: Inconsistency
 

I pay extra attention to my routine for consistency, especially since these issues have come up.

I have the RPM graphs saved as pdfs but am not sure how to post them.

I do not think it is jetting just for the fact that no big change in weather has to happen for the car to make a slow run. No matter what the weather does the 4th or 5th run will be .2 slow and if we make any additional passes after the slow run they are slow as well.

Re: Inconsistency
 

again, post the time slips in order from one day.

Re: Inconsistency
 

Had a car do that once, had one broken roller in converter sprag.

Re: Inconsistency
 

Targus, In the submit reply window, top row, there is a paper clip next to a smiley. Right click that & a window opens with a button to browse your computer for the files you want to upload & in the lower right of that frame an upload button. That said, I have never been able to upload a .pdf, only a .jpg or .bmp. Can you save the file differently ?

1320, how bout we help with his upload issue 1ST. :D

Re: Inconsistency
 

Attached are RPM graphs with the red line showing a "good" pass and the black line showing a "bad" pass where is slows .2

Re: Inconsistency
 

I haven't had the privilege of reading many of these graph's but with the black line rough, does the engine have an intermittent miss ?

Re: Inconsistency
 

There is not a noticeable miss. With the lower stall of the converter you can feel that it is on a lazy pass. The up and down movement in the black line equals about 100 RPM.

Re: Inconsistency
 

With only RPM to read it's hard to telling. I would say more input is needed. I would expect a convertor problem to swing that graph wider.

Re: Inconsistency
 

Is there anything in the fuel system that you believe could be causing this? The fuel pressure seems to remain consistent throughout the run but the gauge is hard to read accurately with so much vibration. Fuel pressure definitely doesn't move more than a half of pound or so. We are getting desperate for answers.

Re: Inconsistency
 

Well, I'll go this route.
.
First I would want weather station input to see if it's changing & then how much. Then see how it follows how the car is running. Next, besides an RPM sensor I would want an output shaft sensor. With these you could see if there was a traction or transmission problem. Next I would want either a pyrometer or O2 sensor. With these you can see where your fuel metering is @ & if it fell over the edge on the bad run.

Without the sensors,

There are many things that can go wrong inside a carb. Do you have a known good piece that you can swap onto the car ?

Re: Inconsistency
 

"While I was researching this site for possible answers to my problem, I came across your post and the graph (and inconsistancy) is similar to what I am experiencing. It started after I repalced the torque converter to a 9" unit that was made for my combination. I blamed it on the new converter but they told me it is spragless so that ruled out a rolled sprag. When I told them that I did not see this problem with the 8" (loose) convert, I was tolded the looseness masked the true problem. I have been going through everything trying to find what is causing this intermittent loss of power.
Did you find what was your issue?

2500# door car
565 CI w/TH400 and Transbrake

Bob

Re: Inconsistency
 

I can't say for sure that we found our issue. However this past weekend I borrowed a converter off of a buddy to try. The converter that i swapped to, we found out after swapping was way to tight for my car. But other than the car running really slow and laboring to bring up the RPMs with the tight converter, the car ran consistent. Not as consistent as i would like but I am blaming the little inconsistency on the tight converter. I will be sending mine away to be cut open and inspected.

Another racer at the track was looking at my car and brought to my attention that I have a majority of my ground wires running to an aluminum grounding block and the grounding block straight to the frame and that could cause an issue. I will be running a ground wire directly to the battery. Something to think about.

Re: Inconsistency
 

Convertor is good test.

Re: Inconsistency
 

Do you have a trans temp gauge? Sounds to me like your trans might be getting a bit too hot in the later rounds. I use to have that issue but since I have been putting a small carpet drying fan on my trans between rounds, that has gone away. I try to leave the line at 160 to 180 trans temp. It is usually 200 to 220 when I get back to the pits. I believe this helps with reaction time consistency also. Just my humble opinion based on trying a few different things.

Re: Inconsistency
 

On your "bad runs", how much is the 60 ft off??

Re: Inconsistency
 

you may need to check rear end. I had a bearing going bad that caused similar

Re: Inconsistency
 

Exactly

Re: Inconsistency
 

I had a very similar issue. Sent a good converter back to be freshened, when it returned it would do good for the first pass then the car would do weird things. It was a sprag converter. I had it cut twice, chased my tail looking at everything else on the car, finally at the end of the year, tried a different converter, the car went on kill. Both times I had the converter cut I was told that there was nothing wrong with it. There was something wrong with it but they just couldn't find it. One of the trans guys that cut the converter has it in his shop now and he told me he was going to find out just what was wrong. I have called him twice and he still doesn't have any answers.

If you changed the converter and the car is working, my advice is to not send the converter back that was causing you problems if it has been checked once, but junk it and start over. I would go back to the 8" if you still have it and get it tightened up. Good luck, this can be a very frustrating and time consuming problem.