Engine/Transmission (1998.5 - 2002) defueling at 85 with tst

[kaffine krazed]

Part 2



Is it common for the TST powermax 3 to cause the engine to defuel at 85mph? Is it something that is fixable with the box?





2001 ETH DEE with TST Powermax 3 adjustable and boost elbow. After install truck wont accelerate past 85mph at full throttle and can't get above 90mph easing into it with the box on it seems to be defueling it will go up to 85mph then slow some the accelerate back up to 85mph. Turn the power level down to the lower levels 3 or 4 and below and it will go up to 112mph with no problem as it did before the install of the box. There are no other performance mods to the truck. Has anyone experinced this before? Any ideas as to what would cause it to defuel? Saturday I'll be able to hook up a DRB and take it for a test drive if you need sensor readings I'll also be able to get fuel pressure readings. Thanks.

 

[jwilliams3]

I dont think its your fuel pressure,

I would give Mark Chapple a call at TST and have him walk you through the automatic defueling features of the box.

If I remember correctly you can program the box to defuel automatically when it hits a certain Exhaust Gas Temperature.



--Justin

 

[kaffine krazed]

The TST I have doesn't have the defueling feature for EGT.



I took it for a test drive today with the DRB hooked up. For some reason with the TST turned on the ECM is showing 114MPH while the speedo and PCM show 85MPH. Any Ideas on why the ECM is not reading the same speed as the PCM? Thanks.

 

[Gary - K7GLD]

Does the speed discrepancy still occur even without the TST connected?

 

[jwinnie]

I have the same problem, defuels at higher setting but when on zero or turned off it keeps on accelerating. fuel pressure guage installed and have 13psi when it defuels. same speed: 85mph

 

[Rob Thomas]

I'm not sure this helps, but the PM 3 starts defueling at 2700 rpm's, the Power Max Comp, (which I have) continues fueling well past that. I have had mine to 119 mph, without issues, 'cept I ran outta' road.



Later, Rob

 

[kaffine krazed]

Gary - KJ6Q With the box turned off the ECM shows the same speed as the speedo.





From my understanding of the TST box it is kind of like poilt injection only the smaller injection happens after the main injection. The box looks for the signal from the FICM to the fuel control soleniod then when it stops the box sends it's own signal to the fuel control soleniod to inject more fuel. I'm wondering if the signal to start injection again is somehow back feeding to the ECM affecting the speed sensor input. I'm wondering if putting a diode on the line would keep the signal from backfeeding to the ECM.



I have an email in to TST to see if they have a fix for the problem.

 

[Gary - K7GLD]

I'm wondering if the way TST keys additional fuel flow, is by "tricking" the ECM/VP44 into thinking the truck is traveling at a higher road speed than it actually is, thus needing more fuel flow - and that WITH the TST engaged, you're hitting some sort of ECM speed govenor?