Is this a bad ecu?

[Bitsyncmaster]

Now your scope looks good. I will have to look if that 40% is really inverted. I have not hooked my scope to an ECU yet, I use my Snap-on meter to read the duty cycle. With the Snap-on It reads correctly with 50% at start up and it would read 60% pressing the wide open throttle switch. Or if your engine temp is below 59 deg. F than you should see 60%. But when I use my mutimeter to read duty cycle it reads backwards. I wonder if the car meters all reversed the readings.

Anyway, you can check the reading by pressing the wide open throttle switch If you still have the stock setup.

It looks like your car went closed loop but the mixture is not adjusted. But on your return trip it when to normal open loop at 50% which it should not have done.

[Bitsyncmaster]

I just bench checked a lambda ECU with my scope and the orange wire does have a backwards signal. When I set the WOT signal on the waveform showed 40% at 12 volts and 60% at ground.

So it seems like the automotive meters do reverse the electronic definition of duty cycle.

So it looks like your cold start was open loop at 60% which would indicate your engine was below 59 deg. F or the WOT switch was stuck on.

[Jason]

Now your scope looks good. I will have to look if that 40% is really inverted. I have not hooked my scope to an ECU yet, I use my Snap-on meter to read the duty cycle. With the Snap-on It reads correctly with 50% at start up and it would read 60% pressing the wide open throttle switch. Or if your engine temp is below 59 deg. F than you should see 60%. But when I use my mutimeter to read duty cycle it reads backwards. I wonder if the car meters all reversed the readings.

Anyway, you can check the reading by pressing the wide open throttle switch If you still have the stock setup.

It looks like your car went closed loop but the mixture is not adjusted. But on your return trip it when to normal open loop at 50% which it should not have done.

When it was "open loop" after warming up when I pressed the WOT switch the duty cycle went from 50% to 40%.

I've adjust the mixure, though I did it at normal idle, not the 950 RPM mentioned in the manual.



I'm going to let it cool down for a few hours and then see what it does.

[Bitsyncmaster]

If your using the scope to adjust the mixture, you would want to adjust closed loop for 56%. That would really set you at 44% or 40 deg. dwell if you were using a dwell meter.

It's not really important to idle at 950 RPM. That may let the o2 sensor warm up more and get a more stable reading since our O2 sensor is not heated.

[David T]

Instead of getting out your scope you should be hooking up a pressure gauge and see what the control pressure is doing. My guess is the CPR is bad and your control pressure is too high when cold. Besides, your O2 sensor won't read accurately when the sensor is cold.

[Jason]

Instead of getting out your scope you should be hooking up a pressure gauge and see what the control pressure is doing. My guess is the CPR is bad and your control pressure is too high when cold. Besides, your O2 sensor won't read accurately when the sensor is cold.

I was thinking that, but I don't have a fuel pressure gauge, so I figured I'd check the mixture setting before buying more tools. I did find some crud in the screen on the CPR, but after cleaning it the problem remained.

[DMCVegas]

I was thinking that, but I don't have a fuel pressure gauge, so I figured I'd check the mixture setting before buying more tools. I did find some crud in the screen on the CPR, but after cleaning it the problem remained.

K-Jetronic operates off of hydraulic pressures, and incorrect ones can absolutely screw with the A/F mixtures, which leads the LAMBDA system go through a larger duty cycle.

If nothing else, run the tank down, throw some Techron in, and then give it the old Italian Tune-up. Then see how she goes.

[Jason]

Well, I'm a little surprised, but it looks like just adjusting the mixture fixed the problem.

[refugeefromcalif]

throw some Techron in, and then give it the old Italian Tune-up.

Forgive me but, What the heck is an Italian Tune Up? Just go as fast as you can and pray it works?

George

[DMCVegas]

Forgive me but, What the heck is an Italian Tune Up? Just go as fast as you can and pray it works?

George

That's a great question. And nope, no prayer involved at all. Here's a quick rundown of an Italian Tune-Up:

What is it?
It's a way to de-carbonize the Intake Valves and Spark Plugs inside of an engine. Engines function best under an optimal engine temperature, because this ensures a proper, complete burn of the fuel inside. If the engine isn't ran at temperature allot, it is at risk of building carbon.

How is it performed?
The idea is to run the engine under load, at near red line. Best accomplished by driving on the highway without engaging your overdrive gears. So on a manual, you want to keep it in 4th Gear, and 2nd on your automatic.

What is supposed to happen inside of the engine?
As stated before (and as common engine knowledge), engines run best under a specific temperature where heat is involved to ensure a clean burn, which helps eliminate carbon. By placing the engine under load, we increase and maintain the temperature on the cylinder heads. The other part of this is that gasoline is a natural solvent. So as it gets sprayed down onto the valves, it will wash them clean, and this can help the combustion chamber too. When we have an added solvent such as Techron, it hastens the cleaning process.

What else does it do?
It also cleans up the fuel system itself. The final part is that we're also getting rid of any old gas by burning that first tank off, and then running a fresh tank through as well. The fresh fuel and the solvents help dissolve any potential varnish in the system, and help get it cleaned out. No matter if it is a carburetor, or a CIS system, gasoline comes into contact with moving parts inside of the fuel system that can stick, and you want to make sure they're able to move freely. This is particularly true with our fuel injectors as we increase line pressure and clean out any gum or varnish that could be causing other problems. Either a bad spray pattern, or preventing the injector from closing that causes a Hot Start issue.

Does it actually work?
Yes. A prime example are the two-piece spark plugs that Ford installed in many of their Triton engines (5.4L and all 3Vs). Carbon would build up between the plug and the cylinder head to get it stuck in place, and it would break off during removal. Performing this procedure before hand helps break down the carbon for easier plug removal.

Why is it called an "Italian Tune-Up"?
There are varying accounts, but it's believed that the name came about a long time ago because of Ferrari owners who did not drive their cars very often. They would start the cars up, but never get them up to temperature. Aside from accumulating moisture inside of the oil before it could be boiled-off, this would never heat the cylinder heads up properly, so the valves would stay relatively cold, and would build carbon up because it wouldn't fully burn. So as part of the maintenance procedure, Ferrari mechanics would run the engines at load for prolonged periods of time in order to burn the excess carbon off, and out of the engine.

Why Techron?
Techron seems to do a really great job on fuel systems, and especially those injectors. Most importantly, I've found it to be very gentle on the rubber components of the DeLorean's fuel system (I've used Berryman's B12 Chemtool before, and it did some damage). Allot of people will argue Sea Foam is better, but I wouldn't. I would instead say that it's more like a different tool for a different job. Techron for the fuel system, and Sea Foam more for the intake and combustion chambers (and Chemtool as a parts dip). But with regular use, and proper top-tier fuels, you shouldn't need to quite go that far.