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DC871F

Resister tweak for fuel injection

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10 hours ago, DC871F said:

What symptoms are you trying to remedy with the added resistor on fuel injection?

 

Running like crap up to 2,500 rpm for me.  Mine would stumble and then pick up, almost like a bucking bull.  Spilt beer all over crotch. 

Here's what I went by, cost about $5 from radio shack when I did it.  I ran mine into the cabin to play with while driving.

You put it in between the existing wiring bullet connectors behind the thermostat housing so no damage or splicing the original wiring if it doesn't help.

http://atlanticz.ca/zclub/techtips/tempsensorpot/index.html

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3 hours ago, Reptoid Overlords said:

Although I've not done it myself, I believe one adds the resistor inline with the CHTS to remedy a lean/rich fuel condition.

 

Sent from my [device_name] using http://Classic Zcar Club mobile

 

 

 

 

I installed the resistor that you can get at ZCardepot when in was troubleshooting the car in the past. My question is what symptoms are some of you seeing whether a lean or rich condition exists.

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Stumbling and popping back through the intake manifold at low to mid-range throttle openings.

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I wonder how hard would it be to use an O2 Sensor to close the loop on these open loop ECU's? possible some of the unused pins? if not perhaps building a circuit that uses an 02 sensor to approximate the function of this pot in the same circuit.

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3 hours ago, Zed Head said:

Stumbling and popping back through the intake manifold at low to mid-range throttle openings.

Ok. So mine is stumbling at low RPM when starting off from a a dead stop until about 1500-2000 RPM, smooth otherwise.

I have adjusted the resistor many times, without much success. Does anyone have a resistance number that seems to work if measured?

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have you checked the TPS and temp sensor?

oh I just saw this is a ZX, not sure what could be that problem. Think it uses an O2 Sensor as well.

Edited by Dave WM

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13 minutes ago, Dave WM said:

have you checked the TPS and temp sensor?

oh I just saw this is a ZX, not sure what could be that problem. Think it uses an O2 Sensor as well.

All good.

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Per your previous thread, you have a new distributor with an older ignition control module(maybe I got that backwards)? If i recall there was something about the distributor advance malfunctioning?  Has the problem improved, or has it remained the same? 

I had a similar issue when I first got my '80 ZX.  It would stumble at around 1500-2000 RPM under light(casual acceleration) load.  Every other position of the throttle was fine.  If I accelerated hard through those RPM's, i noticed no stumble whatsoever.   I replaced every single connector in the harness and cleaned the FI ground to intake manifold connections.  I also replaced the existing TVS with a known working one and bought a new ignition control module. My timing was set to 0 deg. BTDC, so I set it to 12 deg BTDC.   I have no idea what portion of that work corrected the issue. 

 

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6 hours ago, Dave WM said:

building a circuit that uses an 02 sensor to approximate the function of this pot in the same circuit.

Now there's a concept I've never seen mentioned anywhere ever before!!! Wonder how much market there would be for something like that!  HAHA!

One thing to keep in mind though, is that the resistor trick can only be used to supply additional fuel, not take any away. The leanest it's going to run is with the sensor connected directly with no extra auxiliary resistance. So if you're going to use a microprocessor to adjust a "resistor" based on O2 feedback, the first thing you'll have to do is adjust the original system so that it runs lean. That way, the processor can add in additional resistance to compensate.

Yes, I think it could work. No, I'm not going to do it.  LOL

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28 minutes ago, Reptoid Overlords said:

Per your previous thread, you have a new distributor with an older ignition control module(maybe I got that backwards)? If i recall there was something about the distributor advance malfunctioning?  Has the problem improved, or has it remained the same? 

I had a similar issue when I first got my '80 ZX.  It would stumble at around 1500-2000 RPM under light(casual acceleration) load.  Every other position of the throttle was fine.  If I accelerated hard through those RPM's, i noticed no stumble whatsoever.   I replaced every single connector in the harness and cleaned the FI ground to intake manifold connections.  I also replaced the existing TVS with a known working one and bought a new ignition control module. My timing was set to 0 deg. BTDC, so I set it to 12 deg BTDC.   I have no idea what portion of that work corrected the issue. 

 

So the distributor is a story that is definitely convoluted. The short of the long story is, I ordered one through RockAuto, and the ignition module was bad, so I ordered another one and swapped the module and all's fine, until this low end stumble. I honestly thought that the ignition module was failing again, but I'm just speculating. Over 20 years ago I did this exact thing when replacing a Turbo ZX distributor, where the new distributors module was bad.

TVS I have adjusted and it seems to be fine. Some of my electrical connection are far from stellar, and need to be replaced. So telling me you replaced all your connectors is quite inspiring, and it really need to be done.

" I have no idea what portion of that work corrected the issue." Isnt that the real story of these cars? But at least you got it fixed. Your issue is exactly how mine in acting, I can accelerate through the stumble.

Thanks very much.

 

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20 hours ago, DC871F said:

Ok. So mine is stumbling at low RPM when starting off from a a dead stop until about 1500-2000 RPM, smooth otherwise.

I have adjusted the resistor many times, without much success. Does anyone have a resistance number that seems to work if measured?

Think I mentioned this in your other thread but you should be able to kill the engine by turning the resistance up.  Flood it with fuel.  I got the impression over there that you're not seeing any response at all.  Maybe you have it plugged in to the wrong circuit.  There's a bunch of bullet connectors in the same area, I think.

Have you verified a resistance change on the circuit, at the ECU connector?  That's what I'd do.

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4 hours ago, Zed Head said:

Think I mentioned this in your other thread but you should be able to kill the engine by turning the resistance up.  Flood it with fuel.  I got the impression over there that you're not seeing any response at all.  Maybe you have it plugged in to the wrong circuit.  There's a bunch of bullet connectors in the same area, I think.

Have you verified a resistance change on the circuit, at the ECU connector?  That's what I'd do.

No, I havent heard that before. Kill it with fuel idling? I see no difference when I adjust it idling. Ill check the connections.

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6 minutes ago, siteunseen said:

I just did mine all the way and it stumbled down to 400 rpm but kept running, barely.

It's about like removing the oil cap. Almost dies, my potentiometer from radio shack.

So something is not right with my connections. Thanks for checking.

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