Tachometer Acting Up and CEL 44

[Aikouka]

Yesterday, after driving the car and when I was about at my driveway, my CEL lit up and I turned into my driveway and went to pull into the garage. That's when the RPMs started to act VERY odd. The car was on, and I put it into neutral, and the RPMS were VERY erradic. They would go from almost 0 to about 1.5k and keep fluctuating. Then I turned the car off, started it again and then pressed on the gas a little bit. Everything sounded fine with the engine, but the RPMs stayed at 0. Once I put the car into 1st and pulled into the garage all the way, the RPMs were acting fine again.

I checked the error code this morning and I got error code 44 again. I had this error before right before I put my new stereo in, so I cleaned some ignition connectors and all seemed fine. Then tonight the same error code came back. If I had a working ohmmeter I would follow Haynes way of testing it, but the special batteries ( not AA or anything like that ) need to be replaced.

Could the problem be with my Crankshaft Position Sensor? Since it sends the RPM signal to the ECU, this was my first guess.

Thanks for any help or advice that you can give me.

 

[steve]

Start by checking the signal from the ignition coil back to the ECU. That's what will throw a 44.
The coil and power transistor are next in line to check.

Steve

 

[Aikouka]

I have an extra coil pack off a 94 NA. Now, I don't know of any reason for these not to be similar, but if I have to, can I just swap the two out?

And a question along the lines of the CPS, I have a CPS from a 94 NA as well. But unlike my 91 CPS, it has a dome-shaped top where my AWD has a flat top with a round section that dips in the middle. Are these also swappable?

 

[steve]

The coil packs are the same but the CAS from the 94 NA is different as you know.
I can't say it it will work.

At this point I doubt the CAS is involved in your problem since the car runs. You should get
a different code if the CAS has problems (22 or 23)

I'd focus on the ignition parts first. The output from the coil pack drives the tach and is what causes a 44. That doesn't mean it's bad, the problem could the the power transistors that drive the coil or any of the wiring in that circuit.

Steve

 

[Aikouka]

I always thought the tac signal came from the CAS. I guess I read wrong or something. But when driving today, all of a sudden, the tachometer dropped out again. It almost came back at one point, but then went back to 0.

Then, I turned the car back on after stopping for some gas, and the tachometer worked fine. I'm just filling you in, so it may help to give more of an idea of what's wrong. I looked at the connection (the 3 prong connector) for the coil pack today, and it looks fine. My dad's best guess (without looking) is that it was some wire that was grounding out or something.

 

[steve]

The CAS we have feeds position and timing information to the ECU from which it computes the correct times to fire the injector and coils.

The tach signal comes off the output of the power transistor unit, its the logical nor of the two transistor collectors used to pull the primaries of the coils to ground. Besides the tach, it goes to pin 109 on the ECU and is one place to pick up the RPM signal for a SAFC.

Check the wiring to the power transistor unit under the coils on the timing belt side of the intake manifold and then see if you can try the test procedures in the service manual or have someone with a ignition scope watch the outputs.

Steve

 

[Aikouka]

I replaced the power transistor and the tachometer still doesn't work. But it did something odd that it never did before. After turning the car off, and then turning it back to ON (the car wasn't started) the tach jumped to 500 and stayed there until I turned the car back to OFF. I did an initial check of the wiring without taking the wire covers off and I saw nothing that looks like it would be bad. I tried to take the cover for the tach connector (the small 2-prong connector on the firewall on the passenger's side), but I couldn't get the little thing off easily, but I'll probably just try and get it off now, since it's something I really need to check.

I'm not sure how, but I know you can hook external tach units to that connector that I mentioned ... well I don't have one, but it probably works under voltage. So could I hook a voltmeter up to it? I don't have a service manual (only a Haynes manual), so if you know anywhere that lists the tests, I could use them .

Thanks for all your help and advice so far, steve.

 

[Black_Stalon]

I had a friend who's ecu was throwing code 44, I pulled his ecu and replaced the caps, one was leaking and starting to erode a pad/trace, however after the cap replacement the code went away and hasnt come back.. maybe try temporarilly swapping ecu's with someone if you know anybody to rule it out, might be worth a shot.

 

[steve]

That's always a possibility.
Tomorrow I'll make a pdf of the service manual pages on testing and troubleshooting this area. Rather than swapping parts it might help narrow down and eliminate the few remaining variables.

Steve

 

[Aikouka]

Well, after the one night when the tachometer symptoms first showed, and then the other time I mentioned, I've never seen the Check Engine Light on again. I've thought about checking the ECU for problems, but I wasn't sure if that'd be a definite problem.

EDIT: Thanks Steve, you've definitely been an indispensible resource in trying to locate this problem.

 

[steve]

Well there really isn't much in the service manual. The tests for the power transistor module consist of two tests to check if the transistors conduct when biased (At least I think thats what there testing but the pins in the test section don't match the pins in rest of the circuit diagrams) Nothing to check if the NOR gate works.

I have to scratch my head a bit and figure out if they made an error... Yep. There are several. The main circuit diagrams have the wrong number of pins show for the connector B15 and the test diagrams have the wrong numbering. There are 8 pins and pin 5 is not connected, so where they say 6 them mean pin 7 and where they say 7 the mean pin 8.

Anyway that will make sense once you have the pages.

For some reason I though you were getting the 44 error all the time and the car was running poorly. If you not and just trying to figure out why your tach doesn't work we might be running down the wrong path.

Steve

 

[Tallen]

Sounds like ECU.

 

[Aikouka]

Just to clarify, the Check Engine Light has only come on twice while the tach has been acting messed up, and the car's never acted up on me when driving it without the tach working properly.

If you think it may be the ECU, then I'll take it out tommorow, and see if it's bad. Hey, anything's worth a shot.

 

[Aikouka]

Well, I took my ECU out today, and opened it up. I didn't notice a problem with the capacitors, but there are two black discs on smaller boards that are sticky and smell funky (like, burnt CPU funky .. yes I have had a CPU die from heat before ) And I always wondered why my car smelled so weird on the inside ... I swear it smells the same as these two discs.

I attached a picture with the two discs circled.

 

[steve]

The flat one is the knock sensor board, I haven't traced the other yet.
The black sticky goo is a silicon encapsulation to protect the integrated circuit under it and is normal. I've never bothered to smell it.

How about taking a picture from above the cap area.

Steve

 

[Aikouka]

I'm not sure if this is what you meant, but if not, just let me know and I'll get you what you need.

 

[steve]

That's the area, but I think your going to have a problem focusing to zoom in any closer to get a better look.

 

[Aikouka]

Yeah, I can't get my camera to get a decent shot even with some good lighting. I looked at the capacitors to see if they were leaking, and I didn't see or feel any weird residue anywhere.

EDIT: I looked at the VFAQ for replacing the capacitors, and it mentioned how the car normally has surging problems when the capacitors are going bad. But I don't have any of those problems, other than my ECU having a burnt smell.

 

[Aikouka]

Just as an update, it seems the 100µF 25V capacitor was leaking. I didn't notice it before, but there is a discoloring on the board that makes the id numbers yellow instead of white. Also, I noticed a slight film underneath that capacitor. I went out and purchased all three capacitors, and I may end up replacing just one.

 

[Black_Stalon]

while your in there you should replaced all three, it only takes an extra few minutes to change them and will save any future problems from the others.

 

[steve]

Agreed, all three should be replaced regardless. Do you have the right tools for the job?

Steve

 

[Aikouka]

That's true, might as well replace them all. One thing I noticed, the capacitors that I bought are physically smaller than the ones on the board. Is this normal for the "newer technology". I just thought it was weird.

Just a question for those who know electrical ... stuff. I'm building an IR remote for my pc. And I have everything but the IR diode. Now, it requires a power transistor and I have the right kind, but I don't know what the pins do. There's a marker for pin 1, but the diagram lists the pins as IN, OUT and COMMON (or ground, whatever you want to call it.) So how do I know which pin does what?

EDIT: my capacitors only have arrow markings like "> > >" does that denote the positive side?

 

[Black_Stalon]

my caps I used as replacements where much smaller physically than the ones in there. The >>> is the negative terminal, if you look closely you'll see a negative symbol inside the arrow.

 

[steve]

The negative terminal is the one thats marked on the case, the positive usually has a longer wire.

Pretty much all current capacitors are smaller than they were 10+ years ago.

 

[Aikouka]

Okay, that didn't work. I put the ECU back in and the tach still doesn't work. The tach works for a split second as I'm starting the car ( will go to the ~2k that the starter creates) but once the key goes to on, it drops down to 1k and then down to 0. To see if this happened every time, I turned the car off and started it again, and the tach worked when starting the car again, but once the starter was disengaged (key turned back to ON), the tach just "swayed" down to 1k and then down to 0. No Check Engine Light on either.

Should I try the tach connector on the wiring harness? I don't have an external tach, but would a multimeter work if I set it to AC20?