13 replies to this topic

[marcusmazza]

I'm having an issue with a 1.6L. The computer is giving me a code 12 (TPS open or short circuit). I've done the full diagnostic as described in the tech manual. Everything checks out. Could this be an issue with the ECU itself? Has anyone had this issue before?

 

What I've checked so far.

 

-The switch is properly adjusted and working as per the manual

-The wiring harness has good continuity (at least for the three tps wires I checked), no shorts to ground (other than the one ground wire itself) or to any other wires that go to the ECU (again, for the three tps wires)

-With everything pluged in and the ignition on, I get the proper voltages at the tps sensor, both at idle and WOT positions per the manual

-I've cleared the code (even did the press the brake pedal for 5 seconds thing), but the code comes back immediatly. Even without starting the engine.

-If I unplug the tps while the car is idling, the idle changes slightly and goes back to where it was when i plug the tps back in, so it is doing something.

 

There are no issues with how the engine is running, just that the check engine light is always on. Thoughts?

 

-Marc

 

[SaulSpeedwell]

Could be an automatic trans computer (B64J) that didn't have the TPS circuit properly fudged to keep the CEL out.  (We call this "The Reverse Polish Collins").

 

If you have an FSM with wiring diagrams (or go here: http://www.madracki....ata/wiring.html), you should be able to take the ECU out of the case and figure out if circuit board is correct (B61P).  The same circuit board is used for both manual and automatic, but the TPS pins are populated differently.

 

Let us know what you find.

[Jim Drago]

I agree with Saul.. likely Auto ECU

[marcusmazza]

Thanks for the responses. The ECU has two stickers on it, both of which say B61P, so I'm assuming its a manual trans. computer. I did take the cover off and looked at the circuit board, but not sure how to tell the difference between the two by looking at the board itself. Would there be any reason someone would want to run an auto computer, and hide the fact by putting stickers from a manual computer on it? The wiring harness and TPS are definitely from a manual. Just out of curiosity, why did the autos run a potentiometer style TPS, and not the manuals? Was it just for the trans. ECU to figure out shift points? I'm thinking I'll just borrow a known good ECU from someone at the next race and see if the code 12 goes away.

 

-Marc

[SaulSpeedwell]

Thanks for the responses. The ECU has two stickers on it, both of which say B61P, so I'm assuming its a manual trans. computer. I did take the cover off and looked at the circuit board, but not sure how to tell the difference between the two by looking at the board itself. Would there be any reason someone would want to run an auto computer, and hide the fact by putting stickers from a manual computer on it? The wiring harness and TPS are definitely from a manual. Just out of curiosity, why did the autos run a potentiometer style TPS, and not the manuals? Was it just for the trans. ECU to figure out shift points? I'm thinking I'll just borrow a known good ECU from someone at the next race and see if the code 12 goes away.

 

-Marc

 

Teach a man to fish :  Look at the wiring diagrams.  See what number and letter are TPS inputs.  Now look at your board.  Are the pins for an M/T TPS soldered through with pins, and the A/T pins are not?  Or vise-versa?

 

Auto computers run a little better (more torque, flatter AFR)  unless you have a properly tuned AFM.  A properly tuned AFM allows you to match the A/T computer performance with the correct (and tech legal) M/T computer.

 

Yes, the auto's proportional TPS is to make the shift points/kickdown work.

 

There are auto computers out there that have been jumpered to keep the CEL turned off.  Once upon a time, people tried to make 1.6s really fast

[marcusmazza]

Nice. I'll refrain from any smarta** EE remarks . I wish it were just me being lazy and not looking at the board and wiring diagrams in detail. Every pin (1A-1V and 2A-2Z) is present and soldered to the board. The only pins a M/T ECU would not have that a A/T would are 2M and 2Z. The only pin the M/T would have that a A/T would not is 2L. The problem is, all three of these pins are soldered to the bored and appear to be connected to an actaul pathway on the board, not just a dead end. I tried taking pics for you, but its too hard to make out. You stated earlier that the boards are the same for the two transmissions. Is it then just a software/firmware difference between the two.

 

If you can acheive the same AFR with the M/T computer and tuning the AFM, why did people use this cheat, or was it not always legal in SM to tune the AFM?

 

It appears that both the M/T and A/T have an idle switch in the TPS, which explains why the engine idle changed when I unplug it. What the ECU is not getting is the WOT signal. If it were a A/T ECU you could jump 2M to 2D (ground) and make it think the trottle is shut all the time, or jump 2M to 2K, making it think it is at WOT all the time. That might still throw a code, since the idle switch could be active and the potentiometer is saying it is at WOT. What does the engine use the WOT signal for?

 

-Marc

[pat slattery]

Change the ECU

[SaulSpeedwell]

Nice. I'll refrain from any smarta** EE remarks . I wish it were just me being lazy and not looking at the board and wiring diagrams in detail. Every pin (1A-1V and 2A-2Z) is present and soldered to the board. The only pins a M/T ECU would not have that a A/T would are 2M and 2Z. The only pin the M/T would have that a A/T would not is 2L. The problem is, all three of these pins are soldered to the bored and appear to be connected to an actaul pathway on the board, not just a dead end. I tried taking pics for you, but its too hard to make out. You stated earlier that the boards are the same for the two transmissions. Is it then just a software/firmware difference between the two.

 

If you can acheive the same AFR with the M/T computer and tuning the AFM, why did people use this cheat, or was it not always legal in SM to tune the AFM?

 

It appears that both the M/T and A/T have an idle switch in the TPS, which explains why the engine idle changed when I unplug it. What the ECU is not getting is the WOT signal. If it were a A/T ECU you could jump 2M to 2D (ground) and make it think the trottle is shut all the time, or jump 2M to 2K, making it think it is at WOT all the time. That might still throw a code, since the idle switch could be active and the potentiometer is saying it is at WOT. What does the engine use the WOT signal for?

 

-Marc

 

Hee hee, I wasn't trying entirely to be a smartass, I didn't remember the pin names or have the wiring diagrams and pics in front of me.  Something isn't adding up - all of the pins should not be going to an active trace - there will be a void somewhere, but it may be one step away from where the connector pins ("header") solders to the board).

 

Same board, yes, but a different PROM in addition to the difference in the TPS wiring.

 

The cheat gave more area under the curve, especially torque - with a truly properly tuned AFM, you could get the same effect, but it still seems today that few know how to properly tune the AFM (and, worse, some of the AFPR purveyors are wrongly claiming that an AFPR will give you everything a tuned AFM will - dead false, particularly for high-flow/high-power setups above 116 Dynojet HP).

 

Similarly, the mechanical TPS adjustment will have no effect on your WOT dyno curve - if it does, it is a good sign your AFM tune is in the weeds.

 

The engine uses the WOT signal for low-RPM/high-load operation, i.e. nothing we care about- the 1.6 fuel and timing map is driven almost entirely by the AFM and the RPM. 

 

Somewhere I have pics of the pins and how to detect a B64J dressed up as a B61P - I sent them to NASA and SCCA Tech long ago, but that was several computer crashes ago, I don't think I still have the pics.

[SaulSpeedwell]

I looked at a crappy Google pic - yes, all the pins are soldered to the board on all ECUs, but those traces lead to capacitors and resistors that will be present or missing depending on whether it is a B61P or B64J variant.  Right in that 2L/M/2N area.  My brain says 2N is key, but that is a dusty memory unaided by wiring diagrams.

 

The absence of the caps or resistors is how they convert the board from M/T to A/T.

 

The MP-number on the 42-pin PROM is the other giveaway.  I just can't remember which is M/T and which is A/T.

 

If Jason Holland is still alive, he may have a writeup from me that spells it all out.  He is an IT nerd that yelled at me for not backing stuff up, so if he can't find it, I owe him some abuse.

[RazerX]

When you say AFM tuning is that adjusting the gear and little tab on it.  Or something else? 

[SaulSpeedwell]

When you say AFM tuning is that adjusting the gear and little tab on it.  Or something else? 

 

That but more.  There are 4 independent adjustments that can be made to the AFM.  There are "tuned" AFMs that make pretty curves but bad HP/TQ, and "tuned" AFMs that make non-theoretically-best curves that make better HP/TQ, and many in between. 

 

If you do nothing but adjust the spring tension on the sawtooth gear, you will (partially) correct the A/F ratio, but at the expense of flow.  No problem if your setup's potential is <=116HP, but the farther you get, want to get, or have other pieces capable of getting above 116, the more you need a tuned AFM. 

 

In short - a tuned AFM is necessary.  The AFPR gives you an easily repeatable, reversible, and "gaugeable" method of dialing in that AFM.  As I've said elsewhere before, if I had a 1.6, I would have BOTH.  If I could only have or afford one, I want the AFM - it can give you everything an AFM+AFPR combo can, just at a higher PITA factor.

[RazerX]

AFPR = Air Fuel Pressure Regulator?  Just checking.  

 

Thanks for the info and education Saul, I have appreciated your posts on this and other threads, very insightful.

 

I have heard that the AFRP didn't make any improvements to a 1.6, but perhaps they didn't have the right 'tuned" AFM.  Is a 'tuned' AFM something that is done by the tuners at the dyno, or is there a 'source' for a tuned AFM?

[marcusmazza]

Thanks for all the help Saul! If you find that writeup, let me know. Otherwise, I think I'm going to track down a known M/T computer in order to figure out what I currently have.

 

RazerX, AFPR is ADJUSTABLE Fuel Pressure Regulater. I just installed one this week (the 5X Racing unit), and am off to the dyno on Friday. That's why I've been so interested in figuring out my check engine light. At this point, I'm going with my current computer, as I'm probably not going to be able to get another one in time. I also installed an unopened factory AFM as a starting point. I'm curios to see what I get by just adjusting the fuel pressure, with the unopened AFM. Once I get that, I'll start tuning the AFM to see if I can do better. I have a Sunbelt engine with 30 hrs on it. The original dyno tuning sheet from when the engine was new and first installed showed 116.7HP and 102.1 ft-lbs of torque. The last dyno sheet from the end of last season (30hrs on engine) shows 113.5HP and 100.5 ft-lbs of torque. It also shows that the engine is running very lean (dangerously lean if you ask me). Long story. In a nut shell, I had someone else re-tune the AFM for me about a year or so ago, and I don't think he really knew what he was doing. I'm hoping to get back up to the 116 level or above. This time, I'm planning on doing the tuning myself. I sat down with an extra AFM and fiddled with it. I'm pretty comfortable now with all the adjustments, and what effect they have. There is a good explanation of the 4 adjustments and what they do on this sight. I'll post the dyno results next week.

 

-Marc

[marcusmazza]

Saul,

 

One more quick question. When you talk about breaking through the 116HP (Dynojet) barrier, is that SAE or STD corrected?

 

-Marc