Throttle Enrichment Control Unit Failed
 

While practially rebuilding my CIS system I had to replace the TECU (Throttle Enrichment Control Unit). I got a used OSCU (Oxygen Sensor Control Unit) that came with the TECU still attached. The original TECU would not richen the fuel mixture as the throttle was opened. Now the 2nd TECU has failed. Now the car runs extremly rich. The car runs the same with or with out the TECU connected.

I have a third TECU that I pulled from a junkyard. I installed it and the fuel mixture leans out and the car runs fine. I disconected it because I dont want to blow the only remaing one I have.

Any ideas. Is this just bad luck that the 22 year old used part failed within 4 months? Or is this a larger electrial issue.

I'm thinking that I need to open up all three and trouble shoot the circuit boards. All I have is a multimeeter I am hoping that I will be able to figure it out. Dad was an electrical engineer I will talk to him about it also.

BTW if you listen real hard you can hear AE laughing all the way from the Great White North!

Most probable thing is that this is just a coincidence. It happens! To be on the safe side you could check that the alternator regulator is OK and not putting out more than 14V at the battery. Then i'd put the good one back in and put it down to bad luck.

Mark

Re: Throttle Enrichment Control Unit Failed
 

That hurts Rog. It really hurts.

:D

As I recall.......... it was easier counting the days that my 924 was running well........and by default the rest of the days it ran bad.

I suggest putting the working unit on the car and placing a for sale sign on it........ hehehe

Roger,

Running rich, must mean the freqency vale is staying open. Maybe you should ohm out the freqency valve, 2 to 3 ohms. I'm not qualified like you Dad, but maybe it is pully too many Amps & burning up the driver. Another thing, maybe bad O2 sensor wire. it could be causing the units to think you're running lean. Throttle switch could be bad making units think you're always on the gas.

One option might be to get an older warm up regulator that came without the O2 stuff, and use it & no O2 stuff.


drew1

Interesting idea about the frequency valve and the O2 sensor wire. I will check them out thanks.

TPS switches and wiring are good. I am wondering if the correct wires are on the right TPS switched though. The wiring doesn't match the current flow diagrams in the Haynes. I made some notes from one I found in the junkyard and I will go over the factory digrams.

Turns out I did not have the wires connected properly. The WOT TPS was connected to pin 6 not pin 7. Now neither TECU makes a diference the car still runs rich and it surges.

Can any one give me the pin out for the 12 pin connector on the TECU from the factory manual? Mine does not match the haynes. The most currious thing is that the WOT TPS is connected to a constant ground on the TECU. I found a 924 at the local junkyard that had the same wiring so I am confused.

Roger,

From Model 81 Part II of current flow in Workshop Manual.

The WOT or acel switch has a wt/bl wire going to pin 6 of 9 pin connector. Load switch (beside idle switch) has wt/bk wire going to pin 7 of 9 pin connector. If wires are backwards it could make unit think you have it floored all the time. According my thinking Idle switch is made until throttle starts to open. Load switch is made until big throttle butterfly starts to open. The wide open switch isn't made until about wide open.

Pin 6 of 12 pin plug on Acel enrich unit goes on to coil grounding term 1 on coil.

drew1

Thank you very much. I got your PM I will compare.

Here is some interesting info. Any thoughts or ideas?

Thanks drew1

Roger wrote;
The connector is numbered so it is easy to identify the connections. The actual pin out on my car has the following exceptions.

Pin 5 is a brown ground wire that is jumped from pin 11
Pin 7 is wt/bk going to the full load TS. I posted that it was previously connected to pin 6. I was wrong it was actually connected to pin 8.

If I pull the brown jumper from pin 5 and connect the wt/bk from the full load TS my wiring will match the factory manual. I knew the wiring was strange and I have played with it, but interestingly I found another 924 with the same strange wiring. I would like to check the part number on the oxygen sensor control unit and the throttle enrichment control unit. Do you have a PET?

Roger,

With you saying that WOT was grounded it got me to thinking is the WOT switch different NO instead of NC. The Parts & Ref Manual gives a different number so this switch might be bad showing the control box you have it floored. Maybe you ought to ohm it out while you work it back & forth.

It's been hot here today, & I've drank too many cold ones to really get into the pin outs. What do these electronic people say, "Fuzzy Logic"? I'll get back with you on pin out & thoughts tomorrow.

My friend, Santana, works on Porsches in his shop & had a couple of 924 parts cars.. Sometime in the next week, I'll take a meter down there & check his if he has a late model & get those pinouts & all.

drew1

I stoped by the mechanics today and he lets me look at the factory manual's. The 12 pin conector on my TECU my car is wired for the 81 turbo however the 8 pin connector has the wireing for the 81 N/A. Instead of the three TPS switches the 81 turbo used a potentionmeeter (sorry spelling probably wrong). With the potentionmeeter The full load TPS connection seemed to be used as the ground.

Also common sense tells me that the idle and acceleration TPS wiring is switched. Earlier 924 N/A's had only an idle and full load TPS under the throttle body. My 81 has the three TPS the additional TPS was added to the top of the throttle body. Accceleration wire bl/wt is connected to the TPS on the top of the throttle body. Since the TPS on the top of the throttle body closes the circuit as soon as the throttle is moved it must be the idle TPS, and it was wired incorrectly.

I rewired the car and the throttle resopnse is much better especially above 5000 RPM's.

It still runs rich but that may be a problem with the fuel distributor. I had rebuilt it and I noticed tha it is leaking. I spent tonight rebuilding a spare I got from the junkyard. I am starting to think that mechanical fuel injection was Fuzzy Logic from the beginning.

Roger,

Turbo 12 plug pin according Workshop Manual.
Dif from na in Workshop Manual

Pin 5 jump to pin 11 which goes to Gnd
Pin 7 to what appears to be Load cam in T Sw

Maybe there was a change to turbo unit in the model year, Since your 5 & 7 are connected like that. I'll check years through PET again & see what I find.

drew1

Is there a different part number for the TPS that are normaly closed vs the ones that are normaly open. Or is that just refering to the switch posistion?

PET

Had it set to Euro models on last check. US comes up with same number as 81-82 Parts & Ref Manual , 931 617 101 01, which is superceded to 911 617 103 00, a 81 to 86 911 unit.

drew1

Previous post starting "PET" refers to control unit. Yes switches are different. I'll get numbers later tonight.

drew1

I looked at the PET while at the mechanics. The part number you list is the oxygen sensor control unit. I cant remember but the smaller controll unit (item 24 or 25) is the throttle enrichment control unit. The one I have is part #477 906 209.

Roger,

I went & looked in my wife's car to check the plugs & you are right. I have been giving you the wrong number. The small one is the one with the two plugs & given in PET for your number. I should have at least looked at plugs before I replied earlier. Please accept my apology.

I've been giving you wrong on the switches, too. I thought there was just two numbers. PET gives 3. From elect diag, idle & full load are NO & acel is NC.

part #
477 922 211 idle
003 927 211 load
931 617 212 acel


drew1

Please do not apoligize you have been tremedously helpfull and I really appreciate the time you have given to this post.

I will be traveling to Purto Rico and Las Vegas over the next two weeks so I will not have any time to wrench on the car. My fianinace's brother will be comming to stay with us for awhile. So I really need a second car. I will be posting back after a couple weeks to let you know what happens. At his point I am thinking that the WUR is bad.

Glad I haven't messed you up too bad. Hope you have a good time.

drew1