Gentleman and Ladies if any...

I have been fighting a very strange problem with the car. It will run 120MPH a few runs and then 116MPH. At either MPH it is stupid consistent but does pickup ET when it runs the higher MPH.

Only place it shows in graphs is Engine RPM, driveshafts overlay perfect.

graphs. Top Engine RPM, middle trans pressure, and bottom is driveshaft. Pressure are all within 4-7psi - carb, oil, engine temps and trans temp all within 3-8 degrees.
https://photos.app.goo.gl/CdJWrKEmWYnSMHms6

logbook
https://photos.app.goo.gl/hFqMp7irc8bv7pLB6

final run at 120mph
https://photos.app.goo.gl/e4QdBF54EtBXuWnp9

I put a new grid in it last year, zero difference and went to the finals of a race. I have changed carbs, on alky with mechanical pump, FP all good. AFR looks about the same. brakes are TBM and are not excessively hot after a run vs 120mph.

I ordered a new crank trigger and harness that I will install this week, along with new coil.. The wires and plugs have also been changed. Distributor, rotor, converter was even swapped last year. Third member broke two weekends ago so that is all new and fresh with 9.5Ford. Axle bearings were checked when out and felt good.

It is acting like the timing is retarded or advancing - with timing light its rock steady at 34*. I cleared out the grid memory card. I went thru every table in grid and there are no retards setup. Just the basic stuff. Weather is not a factor either I have Ifamily system and the runs were within 1hour.

Lastly I went thru car and removed every ground wire, cleaned, and put star washers, sprayed them with protector after they were tightened. Did that last year and again this past week after it did this at 5k weekend race in the semis to me.

Does it with BOX and NO Box alike. Same lane and several different tracks

Looking for ideas.

This message has been edited. Last edited by: ski_dwn_it,

line lock ???

It's also odd to me that engine rpm is up through the whole run but the 60 and 330 is still the same.

Could brake pads be binding in the calipers or loose tie rods and alignment is changing at times and making tires scrub I mean you’ve changed everything or at least sounds like you’re monitoring everything you can

Got a sprag or diode in the converter?

I thought converter at first but he said he tried a different one

Converter was changed.

Inspected cap and rotor that was changed last year too. Nothing.

Alignment... Didn't check that but car drives like it's on rails.

Brakes, I've put hand on rim and it's warm but not excessive. I'll pay more attention to that next time but car coasts really easy.

Line lock only active when I do burnout. Last year checked that too.

Car moves in burnout as soon as I let off it.

Appreciate the ideas.

Checked grounds to battery all good. Checked voltage drop. Called KR on the throttle enhancer and they told me how to check that. Can't even begin to pull it apart

quote:

Sportsman

Rear wilwood brake calipers stayed slightly engaged on mine. Car slowed about that. Could not find issue till I jacked up rear for something else and could barely turn them with a lot of force. Good luck

Brake are TBM and only year old. I was also playing with the ARB on many of those runs fine tuning the launch. I will double check the brakes along with the line lock. Which also was changed last year.

Also spoke to KR about throttle enhancer. I checked that and there is NO way that is pulling apart. I could not budge it with 90psi.

This message has been edited. Last edited by: ski_dwn_it,

Just to clarify, when you say you changed the "grid", that was the Timing Controller and the Ignition Box?

last year I changed the grid 7730 controller. I did not change the 7720.

Not saying this is the issue and i've never validated it is one, but when brake pads get worn down in my strange brakes they seem to stick in the calipers sometimes. I usually replace earlier than needed just cause i wonder do they stick and not come off the rotors enough when brakes release.

What's with the spin at about .5 on those runs. Looks like it dead hooks the tire and drives into a spin. When my car does that I am slow too. And there is a difference in trans pressure that shows up on the RPM too from what I see.

quote:

Originally posted by moparacer:
What's with the spin at about .5 on those runs. Looks like it dead hooks the tire and drives into a spin. When my car does that I am slow too. And there is a difference in trans pressure that shows up on the RPM too from what I see.

My car does that at .3 when it hits my wheelie bars. Mine is a few thou slower if it doesn't have that hump.

quote:

Originally posted by moparacer:
What's with the spin at about .5 on those runs. Looks like it dead hooks the tire and drives into a spin. When my car does that I am slow too. And there is a difference in trans pressure that shows up on the RPM too from what I see.

The car does that every time. It is the bias ply "getting up on the tire". They wrinkle up (first spike) and then spin about 3/4 of the turn (second hump). If you are not monitoring driveshaft or have a good video you would never catch it. Also there are two curves there overlayed if you look close. The problem does not effect the driveshaft which means the trans is not the problem. The chassis is doing the same thing - its a power issue. Hence the reason the rpms differ.

Another clue I found last night when again going thru the grid. I have an alert for a low crank sensor. But grid does not show when or how many times. I am rarely in the grid so if could be 6months old.

Right now I have a new crank sensor, and cable. Also ordered a new coil but not putting that in unless it is still acting up.

This message has been edited. Last edited by: ski_dwn_it,

Crank Sensor Voltage Low and SDcard Missing alarms in the Grid History are very normal. Most Grids will have them.

One thing I notice is that it appears you’re shifting using Time. Consider trying to switch this to RPM to see results.

If these runs are all from the same lane, same track, does it do this if switching lanes?

The running at a higher RPM after launch between the two runs makes it appear like its running a higher stall converter. What transmission fluid are you using?

One other question…… do you log engine and transmission temp in DA?

quote:

Originally posted by markemark:
Crank Sensor Voltage Low and SDcard Missing alarms in the Grid History are very normal. Most Grids will have them.

One thing I notice is that it appears you’re shifting using Time. Consider trying to switch this to RPM to see results.

If these runs are all from the same lane, same track, does it do this if switching lanes?

The running at a higher RPM after launch between the two runs makes it appear like its running a higher stall converter. What transmission fluid are you using?

Does it at multiple tracks. Fluid is transynd and only has about 40 runs on it. Been changed in the past and continued doing it.

yes on the time shifting. Worth a try at at this point. But wouldnt the shifts between the two runs shown be shifted?

yes trans temp and water temp all the same. OIl pressure, fuel pressure, AFR (to the degree you can compare it meaning if its off .2 I am not sure if that matters).

I run an accumulator and even wondering if it somehow could be keeping oil in the pan and the crank is dragging thru it. So I will if nothing else resolves it close the valve (its manual and always open).

my money is on that one piece of grid that you didnt change

quote:

my money is on that one piece of grid that you didnt change

It’s been my limited experience with 7720 that it is either outputting 525 v or nothing (failed) when triggered by 7730. Never say Never, (I would try replacing) but doubt this is the problem. I base this on the troubleshooting method for confirming 7720 operation that can be found in the installation instructions. Unlike 7730, the 7720 is repairable if it fails.