Another MS Install

[740 Turbo Brick]

Well, Im taking on another MS project for a friend with a 98 Talon, rebuilt lower end and crower 2s up top. I did a piggy back install, using the stock ECU for power to all the sensors, cruise control, spark, etc..

I got it started a few days ago on the stock 420A VE table, and already noticed a few problems. First, and most obvious, is an erratic TPS signal. I can calibrate it, push the throttle, and the stop will be at -6%. The throttle cable is tightened down, and the throttle plate is closing all the way each time. Also, while the car is running, the TPS is twitching between 5%-15% while Im not touching it. The Inj pulsewidths are also jumping. Instead of a slight percentage change at idle, the needle for them on the gauge is all over the place.

Second thing I notice, Im losing connection somehow. The green light in the corner that says synced will randomly turn red and lose connection, either stalling the car or making it miss. The redline is set at 7k, and holding the gas down it stopped revving at 5k, while the reset count went from 80 to 115 as it misfired and stayed at 5k. The IGN wire is soldered to the crank sensor signal wire down by the sensor. As for the grounds, there were 6 from the MS unit, I put pairs in a ring terminal and soldered those in, mounted the 3 terminals on the firewall.

Im a bit stumped at this point. My standalone install actually went better than this piggyback install. Any other information needed, let me know and Ill post it up.

 

[Slo2gen]

What MS version is it?

 

[740 Turbo Brick]

MS2 V3.0, from Symtech labs. Using Tunerstudios V 2.1.0.

 

[VelocitàPaola]

I got it started a few days ago on the stock 420A VE table, and already noticed a few problems. First, and most obvious, is an erratic TPS signal. I can calibrate it, push the throttle, and the stop will be at -6%. The throttle cable is tightened down, and the throttle plate is closing all the way each time. Also, while the car is running, the TPS is twitching between 5%-15% while Im not touching it.

How is the TPS wired? Is it powered from the TPS Vref wire? Where is it grounded? Is the signal wire routed by any sources of noise (alternator, ignition coil, etc.)? What readings do you get when you unplug the TPS altogether?

The Inj pulsewidths are also jumping. Instead of a slight percentage change at idle, the needle for them on the gauge is all over the place.

This is probably caused by the TPS issue...

Second thing I notice, Im losing connection somehow. The green light in the corner that says synced will randomly turn red and lose connection, either stalling the car or making it miss.

Has the car had any electrical problems? Are the ignition coil and charing circuit both known to be good?

As for the grounds, there were 6 from the MS unit, I put pairs in a ring terminal and soldered those in, mounted the 3 terminals on the firewall.

Are you sure you got good contact with chassis ground? Remember that all paint must be removed from the mounting point...

 

[740 Turbo Brick]

How is the TPS wired? Is it powered from the TPS Vref wire? Where is it grounded? Is the signal wire routed by any sources of noise (alternator, ignition coil, etc.)? What readings do you get when you unplug the TPS altogether?

It is powered by the stock electrical system. It says it was optional in the wiring schematic so I didnt think anything of it. Its also grounded in the stock system. The signal wire isnt ran past any source of noise that I could see. Do you think I should cut the stock power and ground, use the VRef wire and ground it to the firewall?

Has the car had any electrical problems? Are the ignition coil and charing circuit both known to be good?

None that I know of. The charging system is showing 13.8V while running.

Are you sure you got good contact with chassis ground? Remember that all paint must be removed from the mounting point...

It was, but just to make sure I grounded it at the battery to see if it would clear up the spikes, but it was no different.

 

[96TurboGS]

The TPS shouldn't cause you to reset, it's usually due to a strong misfire (never had it happen yet), or bad grounds. If the TPS accel is turned on you may want to turn it off for now until you get a smoother signal. To prevent ground loops you want to ground everything in one spot. Rewiring the vref signal may or may not help the TPS signal, but it's worth a try. It's going to be hard to get the perfect TPS signal with the stock PCM in the mix.

On loss sync notes:

Is the timing good? (Including no belt slack and CAS plugged in firmly)

Make sure "Tach period rejection" and all other settings in noise control settings are turned off including the CLT rev limiter.

 

[david-b]

Had the same problem with my TPS. Use the 5vref wire to power it and ground properly. The Injector pulsewidths will change based on that. Took me a while to figure that out, but fix the TPS, and that problem will go away for sure.

Grounds must be all at the same place as well.

 

[740 Turbo Brick]

Ok, thanks guys. I will probably end up working on it tomorow. Ill let you know how it goes.

Also, I tried something on his car Im about to do on mine. I installed the IAT in the CAI down toward the bottom in the secondary air nipple. I figure this would be more accurate for the incoming air temp, as my intake temps were at a heat soaked 140* in the summer. Sound like a good idea?

 

[96TurboGS]

Yep, heat soak invalidates T in megasquirts formula, more important on a force induction engine. Many have had better results with the IAT on the CAI or IC pipe over IM; it does save headaches in the summer time and gets to the actual temp faster. FWIW, I use an open element GM IAT sensor.

 

[740 Turbo Brick]

Id like to thank you guys once again for your help and advice. I ended up cutting the ground and power for the stock TPS wires and using TPS Vref and grounding it to the firewall. Immediately noticed the TPS jitter go away, calibrated it once and it hasnt moved. Took a few starts to get the stock ECU to reset the stepper IAC, and she idles great now. Duty cycle is a smooth ~5% at idle, idles around 850 even with the Crower 2s. The only off thing I noticed was the stock temp gauge is showing 3/4 temp (slight overheat) and the MS gauge is showing ~200*, at which point the fans turn on. Anything to be concerned about?