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Need help with testing procedure, L28ET running rich


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Hey, Since I swapped my 280zx back to the stock l28ET ECCS, I have been having a problem with it running rich.

 

The AFM failed the first test in the manual (Multimeter + probe to pin 33, - to pin 26, resistance is supposed to be approx 280-400 ohm, I get 199 consistently.

 

It passes all other tests in including insulation and air temp sensor (AFAIK, It was in the correct range for the outside temp at the time, without any run-time on car to heat it up at all)

 

Also, for the flap test, I know it says it can be anything BUT 0 and infinite ohms, but is there any kind of scaling when the flap is opening? The fully open ohm reading was lower than the reading somewhere in the middle of opening.

 

The CHTS also appears to be in spec...when the manual says to put one probe to pin 23, and the other pin to a ground, I am assuming this means with the ECU connector still attached to the ECU...otherwise I get no reading.

 

Regardless, the CHTS is new, FPR is new and fuel pressure is fine, and the O2 is new, albeit its a Z31 3-wire o2 sensor, but its still the same type as a 280ZXT one.

 

Are there any other things that can cause that ECCS to run rich? Or would I be pretty safe to assume its my AFM considering the test failure?

 

EDIT: Still open to suggestions, but I found the Blues Tech Tips page that goes through how to adjust the AFM, might try that in the mean time.

Edited by KnightoftheRound
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New Info:

 

Had the Pin 9 (start signal wire, gets power when cranking) attached to a switched 12v, noticed when this power was cut, the engine went up from approx 750-800rpm to 1000, and ran smoother. When this power is cut, it appears to run lean, but to the point where it tends to stutter under load. What does the "start signal" do? Does it richen the mixture during cranking to fire easier or something?

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After solving the rich running issue with pin 9/start signal, I started to delve into why the car ran so damned lean.

 

Taking the cap off the AFM revealed a wire barely hanging on, and the spring turned back about 5-6 teeth leaner than stock, the guy that did this was courteous enough to mark where it originally was. Put the gear back stock, put the wire back where it belongs, and were back in business. Car pulls stupid hard now.

 

Thanks for all the views to those who looked. I certainly have a bad habit of making topics and figuring my own problems out before anyone helps. At least its resource for anyone else.

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Very good info for others regardless. I'm glad you posted this with the details you did and finally figuring it out on your own.

 

Does that wire correspond to one on this diagram? Pin 9 that is.

 

site1081.jpg

Edited by JSM
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No it doesn't. It a yellow wire (solid yellow IIRC) on the ignition harness plug about a foot down the harness from the ECU. This wire is for a start signal (key in start position). Check the wire diagram for the 82-83 ZXT, its an 8 pin pentagonal connector.

 

From my understanding, this signal tells the ECU that the car is cranking over, and it (not sure which) either enriches the mixture, or fires all injectors at once to get it started. Also heard it does this because the engine has not yet received a signal from the CAS to know the crank position, and therefore it doesn't know what injector to fire.

 

Cutting the power to that wire definitely leaned it out when it was running, and as I said, cracking open the AFM revealed that it was both leaned out 5 or 6 teeth, and one of the spade connectors going to the actual connector on the AFM (on the inside) was just barely hanging on.

 

Now it runs perfect.

 

The manual I got from the Xenon site doesn't seem to show that connector for the ignition harness, but the one on AllData does, as well as the Nissan/Datsun 1983 cars wire diagram book I have.

 

Was hoping someone with more knowledge about this ECCS would chime in and give us the scoop on what the start signal actually does.

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  • 2 years later...

I bet this is my problem too, 9 pin is to switched on my swap and I have been over everything trying to figure out why it is running so rich. I'll change the wiring configuration and report. I have been over everything on this car since the swap and have yet to drive it because its so rich it won't run right no matter what I do. Ugh i'll keep my fingers crossed and report back this weekend.

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