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'17 3.6R Touring Brillant Brown Pearl
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Discussion Starter · #1 ·
So this new to me ****** has a weird problem. I think the tach is reading around 1200 rpm high. I scanned the codes and found a stored P0741 code. And was worried that the tranny had problems. But, the car seems to shift just fine. I can see someone has had the tranny pan off. Possibly a TC solenoid? Anyways I tracked the RPM's with my code scanner, and it reports lower RPM's than the Tachometer shows.

I tend to believe the code scanner is right. 175 miles to bring the car home, and I burned less than 3/8's tank of fuel. If it really was turning 4K RPM's for almost 2 hrs, I would have consumed a lot more fuel?

The battery cables definitely need attention. They have cheap walmart battery ends crimped on them. And are showing green corrosion. That will be my first order of business. But could that really effect the tach that way?

Time is going to be tough in the near future. I've gotta pull the engine on the Foz to replace a leaking tranny input shaft seal. And the Wife's Bean is waiting for me to install the new front lower control arms, and the Whiteline rear control arms that have been sitting in the garage for over a month.

This can't be right?

 

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'01 OBW 3.0 VDC 184,000 Miles '19 OB 2.5 Base <2,000 Miles - Formerly '14 Impreza Sedan 2.0 5spd 66,000 Miles at trade-in
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Yeah... that's not a proper rpm for that speed and Drive selected. Is it possible the linkage to the tranny is the correct length/tension. I think that tach reading is more accurate for 3rd gear, at that speed. I'll have to look-back ...but I think that was the 3rd [email protected] rpms speed from when I was wasting gas running all kinds of speed/rpms in 3 test for GG > @idosubaru
 

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'01 OBW 3.0 VDC 184,000 Miles '19 OB 2.5 Base <2,000 Miles - Formerly '14 Impreza Sedan 2.0 5spd 66,000 Miles at trade-in
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Roadhugger Gt Ecos
225/60R16


1k (20?)
2k 37
3k 54
4k 74


Couldn't get a good read on 1k, kept trying to kick down into 2nd gear at that low of speed.
That was from the GG test I did. All done with the selector in the 3 position. Do those match up with your speed/rpms?
 

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'17 3.6R Touring Brillant Brown Pearl
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Discussion Starter · #4 ·
I'll have to check tomorrow. Taking the wifes car to look at a pretty clean 02 Legacy Sedan tonight.
 

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So this new to me ****** has a weird problem.
This can't be right?
Checked mine, '03 H6, today on flat ground. @70 in drive I'm turning 2500 rpm. Pull it down into 3rd and get 4000 rpm.

Bgilly's thought of "Is it possible the linkage to the tranny is the correct length/tension." seems more plausible. Thinking you're really in 3rd gear instead of having a tach issue.

I'm sure someone elso can suggest a way to double check the actual RPM.

.
 

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So this new to me ****** has a weird problem. I think the tach is reading around 1200 rpm high. I scanned the codes and found a stored P0741 code. And was worried that the tranny had problems. But, the car seems to shift just fine. I can see someone has had the tranny pan off. Possibly a TC solenoid? Anyways I tracked the RPM's with my code scanner, and it reports lower RPM's than the Tachometer shows.

I tend to believe the code scanner is right.
The engine rpm data originates with the crankshaft position sensor. It's my understanding that the electrical signal from the sensor goes to the ECM, which uses it for engine management. A corresponding electrical signal is sent from the ECM to the instrument cluster tachometer drive circuit, which translates it into a drive signal for the tachometer itself. Consequently the engine rpm data from the OBD connector and the tach indication should always be in close agreement, regardless of the drive train overall gear ratio.

Based on the stock 225/60/R16 tires, 4.111 final ratio, and 0.694 gear ratio in 4th with the TC locked, at 69 mph (photo) the engine should be at approximately 2560 rpm. The photo indicates about 3900 rpm, which is 1340 rpm higher. This is close to your 1200 difference.

Is the 1200 rpm the difference between the tachometer and the code scanner indication? At what vehicle speed and rpms, i.e., what happens at different vehicle/rpm speeds? Is the difference the same percentage?
 

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Discussion Starter · #8 ·
The code scanner reports pretty much the same numbers you stated, OM. 2500-2600 at 70 MPH

I'm almost thinking that someone installed an H4 instrument cluster in this car?


If it does turn out to be the TC. Will the trans in the 00 H4 work properly bolted to the H6?
 

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I'm almost thinking that someone installed an H4 instrument cluster in this car?
Other than this rpm issue, is there another reason you would suspect this? Many states require a label or similar indicator when the cluster is replaced because the mileage cannot be readily reset in the cluster. Does the car have one?

If it does turn out to be the TC. Will the trans in the 00 H4 work properly bolted to the H6?
As the transmission gear or torque converter status should not have any impact on the way the tach reads versus the OBD engine rpm data (at least in my understanding), it might be premature to look at this unless there is a separate transmission problem. The stored code might have been from some time ago, and is not active. As there's signs of the pan being off, perhaps the solenoid failed and was replaced. I'm not sure whether stored codes are cleared from memory when the fault is corrected.

From FSM:

DTC P0741 TORQUE CONVERTER CLUTCH CIRCUIT PERFORMANCE OR STUCK OFF
DTC DETECTING CONDITION:
• Lock up clutch malfunction
• Sticky valve
TROUBLE SYMPTOM:
No lock-up occurs.

Is there a problem with lock-up?

Incidentally, there is another way to verify the engine rpm.

The transmission has a turbine speed sensor. When the engine is running with the transmission in N or P, the turbine in the torque converter (the turbine is the driven/output side of the TC) will spin at close to the engine rpm.
When cruising in gear with TC lock up, the turbine will be at the same speed as the engine.

If TC lock-up isn't working there could be a difference of as much as 2000 rpm between the engine and turbine, although it would probably be more in the range of 200-400 rpm when cruising with light throttle.

The turbine speed sensor sends a signal to the TCM. The dealer's Subaru Select Monitor can access the TCU data to compare the engine rpm and turbine speed. Romraider and similar scanner programs, might also be able to do this. A confirmation of the engine and turbine speeds from the TCU would support the view that the high tachometer reading isn't due to the transmission.
 

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Discussion Starter · #10 ·
Well, I did some investigative driving this morning. I'm pretty sure the TC is not locking properly. The P0741 popped up again. When driving 45 mph and manually shifting to 3rd, and then back to drive, I can not feel the TC lock. The tack shows a tiny blip when it should be locking.

I haven't done the grounds yet. On my way out there now to do them. Will report back on the results.

Also, when I was doing the inner tie rods yesterday, I must have messed up and stretched one of the ABS sensor wires. ABS Code came up.
It's kind of nice having a parts car right outside the garage!
 

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Discussion Starter · #11 ·
Just got done with the grounds. No change in the transmission/tach.

Idles smoother though

 

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In the last photo, the tach is indicating ~3750 when the ECM data (on the phone) is at 2420, or a difference of about 55%.

What are the tach readings when the ECM is showing 1000 and when it's showing 2000? This can be checked with the car parked, in N or P, and the engine revved up to the test speeds. Looking to see if the difference is a constant percentage of the ECM reading.
 

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Discussion Starter · #13 ·
Well, I drove it to work today. There is some TC shudder. I'm thinking the tach problem is confusing the trans controller.

Does anyone know the path the tach gets it's signal from?
 

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Well, I drove it to work today. There is some TC shudder. I'm thinking the tach problem is confusing the trans controller.

Does anyone know the path the tach gets it's signal from?
Mentioned in post #7.

Here's some related info:

Attached is a diagram from the 2001 FSM. Granted, it doesn't indicate where the ECM gets engine speed data, but the ECM can "know" the engine speed from a number of data streams, including the inputs from the crankshaft position sensor and the camshaft position sensor, and the outputs to the ignition coil and injectors. (The crankshaft position sensor is probably the main source; barring a problem with the sensor, it's the only one that is directly related to actual rotation of the crankshaft.)

According to the FSM ECU I/O table, the Engine speed output signal from the ECU is a waveform. (Probably varies in frequency according to the engine speed.) The wiring diagrams show that the ECU engine speed output terminal is connected to the Engine Speed input terminal of the TCU, and to the CPU/drive circuit in the instrument cluster. So the TCU and the cluster use the same rpm signal source.
 

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Discussion Starter · #15 ·
Very good info. Thanks OM.

This is kind of confusing. Because the ECU seems to know the proper RPM.(as per code scanner data) But seems to be missing something in translation? I'm going to have to dig into the kick panel and check things.

Possibly change the instrument cluster out from the 00 H4 and see what I get for RPM's?
 

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2002 3.0 VDC Wag + 2018 2.5 Leg Ltd
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Very good info. Thanks OM.

This is kind of confusing. Because the ECU seems to know the proper RPM.(as per code scanner data) But seems to be missing something in translation? I'm going to have to dig into the kick panel and check things.

Possibly change the instrument cluster out from the 00 H4 and see what I get for RPM's?
before you get as far as the time consuming activity of pulling the H4 dash apart,

maybe you see if what you got is the proper 3.0 tach, 85040AE14A
(and if hunting that is only a 2001-2002 H6 car part,...not 2003 or 2004 h6,... maybe a different face color in those later years)

as per

https://www.quirkparts.com/auto-par...ne/electrical-cat/instruments-and-gauges-scat

____

and did you clean all the dust off the dash, ? ...because there is zero in your last pic there. (like I wonder if it was all just apart).
 

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Very good info. Thanks OM.

This is kind of confusing. Because the ECU seems to know the proper RPM.(as per code scanner data) But seems to be missing something in translation?. . .
What about the connections at the ECU or the cluster? A bad connection could lead to an electrically noisy or intermittent signal getting to the cluster driver circuit, which could be causing it to drive the tach movement more than it should.

Have you looked at the area of the ECU to see if there's signs of corrosion/water? Perhaps try disconnecting and reconnecting the ECU (cluster too?) and then check the readings. (As noted earlier, to compare the phone ECU signal to the phone there shouldn't be a need to drive the car. The two should be the same with the car stopped and the engine revved up in N/P.)
 

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Discussion Starter · #18 ·
You and I are thinking alike. I was thinking of checking the ECU/TCU connections first. Possibly opening the ECU and checking the solder connections.

I already have the H4 dash apart. Had to to get most of it removed to get the stereo, remote start and radar detector out of it. I can have the cluster out in 5 mins or less


And yes, I had the H6 cluster out. The PO had removed the check engine light bulb. And I hit the cover with Meguires plastic cleaner. (good eye!)
 

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Discussion Starter · #19 ·
I got out there last night and reseated the ECM plugs. No change in the tach. So, I swapped in the h4 cluster. Same high readings with it installed.

It must be a dirty signal from the ECM?
 

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I got out there last night and reseated the ECM plugs. No change in the tach. So, I swapped in the h4 cluster. Same high readings with it installed.

It must be a dirty signal from the ECM?
Leaving all (or as many as reasonable) possibilities on the table, then strictly speaking, swapping in the H4 cluster doesn't prove, as was suggested by others, that the cluster or the tach itself that's in the LLB could be for an H4. Are there significant, and apparent, differences in the clusters, or the tach, that would suggest this is not the case? I don't know . . .

I haven't yet found out exactly what the signal from the ECM should be (other than it's a waveform), and whether or not it's different with the two models. An oscilloscope could be handy for this, if used to monitor/record the signal coming from the ECM in the H4 and the same signal in the H6 at the same ECM (phone) rpm indications. If the amplitude and period of the waveform is the same for both at the same ECM rpm, and the signals are equally "clean", then that points to the cluster as more likely the culprit.

This is really odd . . .
 
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