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Kjet running/ Fuel Issue - ECU

Murploid1

Murploid1

Active member
Joined
Apr 6, 2017
Location
Houston, Texas
Car: 1982 244 turbo (kjet).

Today my car decided it did not want to idle - running VERY rich.

After checking all the basics; vacuum leak, fuses, o2 sensor, idle air controller, even replaced idle computer - nothing changed.

However, when I unplugged the harness from the ECU the car idled much better, it was running lean, but it did not splutter and die.

The frequency valve is buzzing, just not sure why its running so rich when plugged into the ECU? (AFR 9)

Wiring harness is good, I removed the ECU (I think its a fuel control unit?) and inspected it visually, looks fine, nothing burnt I can see.

Should I just replace the ECU? Or something else i am overlooking here?


Thanks!
 
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Super rich is like there is a short to ground on the enrichment wires on the ECU. There is terminal 7 which is used for boost enrichment and then there is terminal 11 which is not used on your ECU. You can check for the ECU making the engine rich by connecting a dwell meter to the red wire on the left inner fender. When warmed up you should see the dwell oscillating around 41-44 degrees. If the ECU is making it rich then the dwell number will be much higher like say 75 for example.
The other main mixture control is the control pressure regulator which could fail in the low control pressure mode keeping the engine rich. You would need the kjet fuel tester for that diagnosis.
 
Right...a failed O2 sensor or coolant sender will default the system to run rich. If you unplug a working one the engine will certainly change tone as it turns rich(er) or unmetered/fixed.
 
dl242gt said:
Super rich is like there is a short to ground on the enrichment wires on the ECU. There is terminal 7 which is used for boost enrichment and then there is terminal 11 which is not used on your ECU. You can check for the ECU making the engine rich by connecting a dwell meter to the red wire on the left inner fender. When warmed up you should see the dwell oscillating around 41-44 degrees. If the ECU is making it rich then the dwell number will be much higher like say 75 for example.
The other main mixture control is the control pressure regulator which could fail in the low control pressure mode keeping the engine rich. You would need the kjet fuel tester for that diagnosis.
Click to expand...
I implemented the terminal 11 modification a couple of months ago but its been unplugged for weeks. The switch is unplugged and the ground removed. The pin is still in connector but I cannot see why it would be an issue if its not connected to anything.

Car ran fine two days ago. Not sure why the sudden issue.

I do not think the ECU adjusts the CPR / ECU - right? Heat does that.....

The car will idle (very lean) when the ECU is unplugged. As soon as I plug it in, the car instantly becomes rich and stalls. Something electrical is causing this issue. I will trace the terminal 7 wire, and have a look at the boost enrichment switch wiring (initial inspection everything looks good).

I will also try a replacement ECU in a couple of days, rule that out or not..

Thanks
 
woodrowstar said:
Right...a failed O2 sensor or coolant sender will default the system to run rich. If you unplug a working one the engine will certainly change tone as it turns rich(er) or unmetered/fixed.
Click to expand...
I can certainly replace the o2 sensor, it was something I considered (despite it being pretty new). However, my thinking was if no signal is going to the ECU (I unplug o2 sensor) why would there be a change (car gets super rich) when I plug the ECU back in. Lean and idling when its unplugged, pig rich and stalls when plugged in (takes seconds).
 
Murploid1 said:
I can certainly replace the o2 sensor, it was something I considered (despite it being pretty new). However, my thinking was if no signal is going to the ECU (I unplug o2 sensor) why would there be a change (car gets super rich) when I plug the ECU back in. Lean and idling when its unplugged, pig rich and stalls when plugged in (takes seconds).
Click to expand...
Ah, I am misunderstanding what you are saying. That is completely opposite of what will happen. Switch the ground?
 
I would def try another lambda controller if it goes instantly rich like that and you don't find any shorted wiring. I wanted you to use the dwell meter to make sure it was electrically going rich. The other thing that cam make the engine rich if there was constant vacuum getting to the control pressure regulator. The vacuum change gives extra rich burst of fuel for cold running acceleration. In theory if that got constant vacuum it could richen the mixture.
 
woodrowstar said:
What?
This: I am calling the sender by incorrect name
Check the wire.
Click to expand...
I replied in that old thread, too. At the back of the block there are the two sensors. Coolant temp sensor for the constant idle system and the thermal cutout switch. I forgot to mention that the thermal coutout switch will also richen the mixture using the lambda controller. If that shorts you will have constant rich engine. When the block temp is below 68 it grounds and richens the mixture.
 
Confirmed that it is the ECU that is making the engine rich. I have replaced both ECU's and o2 sensor - issue is the same.

So, how does terminal 7 actually work? How does it know when to enrich? Boost pressure? Would it be an idea to disconnect terminal 7 from ECU and see what happens?

I guess I am going to have to trace all the wiring, take the inlet manifold off and check all under there too?
 
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There is a blue boost pressure switch on the firewall. At about 3psi it grounds terminal 7 and give you enrichment. You can test it by grounding the wiring to the lambda controller. The dwell on the fuel distributor will go up to about 75 when it is active. Terminal 11 functions the same only raises dwell to about 85 degrees. Super rich. Seems like the lambda controller is bad or something is grounded in the wiring to those terminals.
 
dl242gt said:
There is a blue boost pressure switch on the firewall. At about 3psi it grounds terminal 7 and give you enrichment. You can test it by grounding the wiring to the lambda controller. The dwell on the fuel distributor will go up to about 75 when it is active. Terminal 11 functions the same only raises dwell to about 85 degrees. Super rich. Seems like the lambda controller is bad or something is grounded in the wiring to those terminals.
Click to expand...
I've replaced both computers in the car - so I dont think its that. i also un-plgged that blue switch on firewall. If it was that, wouldn't that stop that issue? I will check all the wires, must be a ground issue like you said....
 
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The frequency valve is used to provide the enrichment for boost. So if something caused that to stay open the mixture will be rich. I would check for wiring shorted to ground like the wires that go to the frequency valve.
 
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