XT6 new ECU, TPS and pigtail readings/adjustments

[89XT6]

Happy Easter!  

Over the weekend I spliced the new TPS pigtail and installed a new TPS sensor.  The pigtail came out nice, readings taken afterwards are spot on,  good ground, ohm readings  and  5V where they should be.

I made sure I put the new TPS in the exact spot as the old one was, or as close as the human eye and a picture can manage.  I read a good ohm reading, only between pins 1 & 4 on the sensor, since I don't have a feeler gauge to test between pins 3 & 4  or the precise methods and extra hands needed for testing between pins 2 & 4 with throttle closed and open.  Following me, I'm sure someone has done this and became aggravated.   

At this point, I didn't install the new ECU, being careful not to damage a new unit.  This was purchased from epartsland.com for $100.  This guy is located in Reading PA and from what I can tell, he carries thousands of ECUs for just about every car you can imagine.  They are fully tested and have a warranty.  

I thought I'd just try and start the car to see what happens.  Bad idea!   RPMs hit the moon to 5,000 RPMs, so I shut it down immediately.  I checked the repair manuals and see that I need to make adjustments using a multimeter and feeler gauges.  So, I'm not gonna try this alone, I need help here and probably a second set of hands,  besides my three year old son pretending to read manuals  .  I may ask a local mechanic to pay a house call, asking around for one that knows these old imports.  

Calling all Subaru Masters and Wizards for advice here please...

[DaveT]

I am in CT.  Never touched an XT6 though.  I do know electronics.

[89XT6]

 

9 hours ago, DaveT said:

I am in CT.  Never touched an XT6 though.  I do know electronics.

Thanks, I'm able to follow the required specs as far as electronics, I'm just a bit handcuffed when trying to take readings while opening and closing the throttle.  The manual isn't very clear on this, I think I also need to take open, closed readings with the pigtail connected to the TPS,  using a probe to poke at the wires going into the pigtail.

I was also wondering and will look into this... since the new ECU has no learned values or memory set yet, the car may start normally and the ECU will learn and adjust everything.

The manuals mention nothing difficult when installing a new ECU.  Disconnect battery negative, remove the old one, install the new one, simple.  No specific initial startup procedure is mentioned.

I have to check the throttle section of the manuals and look for baseline,  adjustments and maintenance.  I've never tried to adjust anything on it, just cleaned and lubed.

I should have left the old TPS on and just changed the pigtail. 

Edited April 22, 2019 by 89XT6

[DaveT]

If the readings are resistance,  make them disconnected from the ECU.  

I've used test leads and long wires to get a meter to where it can be viewed while operating a remote input. 

 

Other option, move the throttle linkage by hand.    

I don't think these old ECU s. Are very complicated.   Hook it up, power on , and run.  

[naru2]

I`m confused.

Is the 5000 rpm with only the TPS change(s)? or TPS and ECU? or TPS and either ECU?

Adjusting the TPS is simple.Feeler gauges are like $3 or you can sometimes use drill bits instead.

It is a one man job.Move the throttle by hand.

You take resistance measurements w/the TPS unplugged.

My info says:

1 Measure resistance between the black and gray wires w/a .35 mm(.014") feeler gauge between the throttle stop and the lever.Should be 5000 ohms or less.

2 Change feeler gauge to .75mm.Resistance should now be infinite.

3 Remove feeler gauge.Resistace between the black/white wire and the black should be 3000-7000.

4 Measure resistance between green/black and black.Throttle closed should be 4200-15,000.Fully open 100-11,000

5 Check for a smooth variation as the throttle moves.

I do not see any way the TPS could command the IACV open.It could change the fuel though.

It would be worth knowing  if you still get 5000 rpm w/the IACV unplugged.(better yet-hose blocked pigtail connected)

I suspect the new TPS stuff added fuel  to a preexisting vacuum leak thus spiking the rpm.

Is there 5 volts at the CTS pigtail w/the new ECU?

[89XT6]

On ‎4‎/‎22‎/‎2019 at 1:40 PM, naru2 said:

I`m confused.

Is the 5000 rpm with only the TPS change(s)? or TPS and ECU? or TPS and either ECU?

Adjusting the TPS is simple.Feeler gauges are like $3 or you can sometimes use drill bits instead.

It is a one man job.Move the throttle by hand.

You take resistance measurements w/the TPS unplugged.

My info says:

1 Measure resistance between the black and gray wires w/a .35 mm(.014") feeler gauge between the throttle stop and the lever.Should be 5000 ohms or less.

2 Change feeler gauge to .75mm.Resistance should now be infinite.

3 Remove feeler gauge.Resistace between the black/white wire and the black should be 3000-7000.

4 Measure resistance between green/black and black.Throttle closed should be 4200-15,000.Fully open 100-11,000

5 Check for a smooth variation as the throttle moves.

I do not see any way the TPS could command the IACV open.It could change the fuel though.

It would be worth knowing  if you still get 5000 rpm w/the IACV unplugged.(better yet-hose blocked pigtail connected)

I suspect the new TPS stuff added fuel  to a preexisting vacuum leak thus spiking the rpm.

Is there 5 volts at the CTS pigtail w/the new ECU?

5,000 RPMs is with the TPS change, using the old ECU.  I later installed the new ECU but haven't tried starting the engine since then... 5,000 RPMs made me nervous and I quit for the weekend.  Hopefully the new ECU won't allow another 5,000 RPM start, this may prove that I've had a bad old ECU all along and it went crazy with the new TPS.  I want to test and adjust the TPS first to at least get it close to spec before starting the engine.

I'll get a set of feeler gauges and follow your advise and the manual.  I do electrical work on my job, so I also have various clips and test wires to help out.  

I suspect that the new TPS is adding fuel.  I haven't found any vacuum leaks, using the carb cleaner spray method but will test further, especially if things don't improve.

I still have 3.2V at the CTS pigtail and 2.9k ohms(good) between the pins on the sensor, with the new ECU.  With the old ECU, when warmed up, the resistance was in the specified range, so I know the sensor is good.  The factory manual trouble shooting section asks only for ohm readings, not voltage.  I'll take an ohm reading from the ECU(WB wire at T9 of the ECU which provides voltage).  If there's over 100 ohms, I'll need to check and repair T9 all the way to the pigtail.  Just guessing but I think I need to test the WB wire end to end in order to find the problem and get 5V..

Thanks, I'll keep you posted.

Edited April 24, 2019 by 89XT6

[89XT6]

 

On ‎4‎/‎22‎/‎2019 at 1:40 PM, naru2 said:

Is there 5 volts at the CTS pigtail w/the new ECU?

Update:

Taking readings at both the old and new ECU, I'm getting 4V at the T9 pin (white/black wire) of the ECU.  This is the feed voltage to the CTS.  At the other end (CTS pigtail) I get 3.2V.

I'm losing 0.8V along the way.  The grounds are all fine, continuity to battery and chassis grounds everywhere.  This may be the reason for the hot start high idle, incorrect voltage getting back to the ECU.  After I'm finished calibrating the TPS and having the engine cold start with the correct idle, I'll test backwards from the TPS pigtail towards the ECU.  I may have to run a new wire along the harness and see if I can get 4V all the way.  I know, most cars have 5V on this wire, but it's an odd car with an odd engine, oh... and it's a Subaru odd ball!  I have yet to find in the FSM or any other manual, the specified voltage required at the CTS feed.  If anyone can find this number, please share.  I doubt I will ever get 5V if two working ECUs put out only 4V.

[DaveT]

The voltage at the to should not be higher than at the ECU.  That's normal.  Loosing almost a volt between the 2, that's a lot, for a small signal type of thing, which this is.  When checking, use the same gnd point.  Some contact or connector or broken wire in the circuit from the ECU to the TPS is high resistance.

[89XT6]

Progress updates...

Using the new ECU and making rough adjustments to the new TPS, my XT6 started without the superspeedway 5,000 RPM scream.  I picked up a set of feeler gauges to test and fine tune the TPS, but I think I need a longer gauge set, so as of now I'm unable to test and adjust per the FSM.  All I could do was tweak the TPS a bit, hand tighten the top screw, start the car and hope it's good.  I get it to a point where idle is between 750 and 1,000 RPMs and throttle response is good.  However... when I give it gas from the pedal (didn't try at the throttle), RPMs smoothly go up as expected for a few seconds, then the engine shuts down.  My guess is that I need to fine tune the TPS ohm readings, per the FSM.

Any suggestions guys?  Do I just need to drive the car and the ECU will learn?

Good news...

My original issue was high idle (1,500- 2,000RPMs) after a hot start.  I have cured this gremlin! The engine was warmed up enough during my back and forth TPS adjustments, shutting the engine off and restarting several times.  Not once did RPMs jump the way they did with hot starts.

I'm done for the day, made some progress but not finished.

 

Edited May 8, 2019 by 89XT6

[89XT6]

Time for my weekly update...

 

Codes, let's read codes!

It's simple, plug the black connectors together.  In this car, they are located in the trunk, near the ECU, along with the green, clear and yellow/amber connectors.

The black connectors are U-check.  Common sense here, "You Check", so I did.

Plug them in and turn the ignition on, without starting the engine.  Watch the green LED on the ECU and time the blinking.  1.2 sec = 10s, .2 sec = 1s, .3 sec between for each code, 1.8 sec between codes.

I get two codes, 23 (MAF) and 24 (IACV), both open or short circuit.

Seems easy enough, I'll have to take multimeter readings.  I already did a new pigtail at the IACV, using a Hyundai Bosch type, 3 pin connector.  Readings at the pigtail are perfect.  I might just have to work on the fitment to the IACV terminals.  As far as the MAF, I replaced the MAF with a compatible Nissan unit from Rockauto.  I have a new pigtail also, but didn't swap out the original yet.

Aaannd I ran out of time for the day, stay tuned. 

[89XT6]

Here I am, It's been a while, sometimes life gets in the way of weekend hobbies.

Slater is healthy!  The only mechanical part that I actually needed to replace was the IACV and CTS.  The new TPS, MAF and ECU are tucked away in my spare parts box.

The code "23" is the gremlin, there is a faulty wire somewhere in the MAF circuit.  Start the car, pull the connector off of the MAF, no change.  Replace the connector with a good wiggle and push, idle creeps up to just under 1,000 RPM.  Idle in drive dips to about 850 RPM, that's fine.  I'm not about to dig into the harness from the ECU to the MAF, way too hot this time of year, I'll wait until October.  The car hasn't  stalled while driving but it is a cranky old beast and may stall while in park, especially if I give it gas.  I'm also losing 0.8v between the ECU and CTS.  I read 4v at the ECU pins, 3.2v at the CTS connector, even with the replaced engine harness.  

I did find a good used fuel injector engine harness for $30.  It has the harness for the injectors, TPS, CTS and some gauges.  So, I eliminated the solder splices I made, getting back to a factory harness is a good thing.  The MAF and IACV harnesses are something I should look into, but there is no easy plug to disconnect.  I think I'll stop while I'm ahead. 

 

Edited July 13, 2019 by 89XT6
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