Runs rich and high idle after restart

[mjr45]

AS a final, final note, I changed the ECU with a spare I had just to see what would happen. The engine ran much smoother and the "butt dyno" felt much improved. I still thinks it runs rich but for now I'll not mess around since it runs far better.

[FastWoman]

Your final note is interesting, namely that two different ECUs run differently. That attests to drift of some sort, even in the earlier Bosch ECUs. My two '78 Hitachi ECUs run exactly the same -- too lean, without modification of the CTS resistance.

[rcb280z]

Fastwomen, to bad your lean 78 wouldn't work in my rich running 77!

Sorry Mike didn't mean to jack your thread. However, what is the production date of your 77? Wonder if there is something there we don't realize. Mine is a 05/77. I have a rich running condition I have been tracing for a couple of years.

[mjr45]

rcb, mine is 75 production date 7/75.

Fastwoman, it was a little weird on changing the ECU, the one I swapped in was from either a 76 or 77. On my original, there are pins in each slot and the other has a lot of pins missing(pins that weren't in use I assume), so if its from a 77, I might get the lean drift from it and thus cure my rich condition. I also used your idea and put a fuel pressure gauge in the engine bay. I get 38psi with the FPR vacuum line off and a steady 33 with it on, so the fuel pressure is OK. I'll just have to run it a while and see what the plugs look like. I was also going to ask you what happens if I remove the AAR and CSV from the system, besides hard to start when cold? Thanks

Mike

PS: Decided not to sell her.

Edited February 28, 2014 by mjr45

[FastWoman]

Removing a working AAR will result in the loss of high idle when you first start the engine. Normally the engine will idle at about 1500 RPM and then slowly drop over the next min or two to maybe 800 RPM. Without the AAR, you'll run roughly at maybe 650 RPM when you first start, and then the idle will slowly increase to about 800 RPM.

And yes, when you remove the CSV, you'll have a harder time starting the engine below 50 deg F. (It's not active at higher temps.)

The two types of ECUs: As far as I'm aware, the ECUs are roughly compatible, but Lenny would have much better info on that issue. I believe there are also a lot of unused pins on each of the years, so if you're seeing the connector completely populated with pins, I would bet there are no wires attached to some of them.

Oh, and deciding not to sell her: Good news!

Edited February 28, 2014 by FastWoman

[rcb280z]

Oh wow, my mistake Mike. Don't know why I thought it was a 77.

[superlen]

mjr

Sarah is right in that the missing pins are NOTHING to be concerned about & in fact the extra pins are not connected internally whatsoever in the ECU you have that has all the pins. I've not been able to pin down and production date/lot number on which ecus have all the pins and which only have the necessary ones. Bosch, I'm sure for cost savings, had AMP custom make the connector with the pins missing. My theory is occasionally they couldn't get the custom part and went with the stock AMP part number which of course had all of them. Or maybe they had different sub-contractors or facilities making them and each facility chose the easiest to get connector??? For whatever reason, it's hit or miss...at least for the Z cars.

As for which #'d ECUs run which cars, there is a list of what year models had which ECU numbers, but it remains to be seen as what the internal differences were between the ECU numbers. I'm sure there were differences, but they are minor in such a way that ANY ecu from those years will run ANY of the cars. Now, will one year model ECU run another years engine a little lean/rich? Possibly, but they have all drifted so far that who knows. If you took two brand new ECUs from different years, could you tell a difference? I don't know for sure.

One question I have is when you were testing did you go back and forth between the ECUs to confirm rich with A, normal with B, rich with A, normal with B? I'm assuming you didn't do that to confirm, but I'm guessing your test would be highly repeatable & is another piece of evidence showing how they ECU can run the car, but run it rich because of drift. Good information that you're uncovering.

Len

[mjr45]

Len, no I didn't switch back and forth between the two, it was just a butt dyno feeling. I'll know more when put in some new plugs and get a reading from them. I still think the AAR is a POS which I can lose when I get a HellFire.

[Zed Head]

I've found that the combination of parts can affect the way the engine runs. By parts, I mean the ECU, AFM, injectors, coolant temperature sensor, grounds, etc. I've had a lean-running engine and a rich-running engine with the same AFM, but various other changes. I'm not positive what exactly made the same AFM give a different air-fuel ratio, since I've improved grounds, changed my power supply set-up, swapped injectors, and ECU's, in between. I put an AFM that used to run rich back on my engine because I had since installed an adjustable fuel pressure regulator (thought I could now go low on fuel pressure and use the better AFM) and found that it was now lean at the same pressure as before (I used a potentiometer to tweak it richer and it works great now).

So if I was starting with an unknown system the one modification I would make, to start, would be a good adjustable FPR. Then you can go lean or rich. On a stock engine the curve is probably right, it just needs to be moved up or down, as a whole.

An adjustable FPR might be that final fine tune to get you away from rich. Drop the fuel pressure 1-5 psi, it won't have a huge affect on spray pattern since Nissan went with the narrow stream on their injectors.

[mjr45]

Just as a thought, would being at altitude (9000') have some type of effect on the air/fuel mix I know that with less air at altitude most engines run lean ? My intake vacuum is steady at 14 (which is OK by my calculations for altitude), there is no altitude switch on the AFM and my fuel pressure at idle is 38 w/o vacuum and 33 with and pressure leaks down to 10 after only a few minutes of not running. The FPR is new as are the injectors. Maybe an adjustable FPR is the answer.Thanks.

Edited March 1, 2014 by mjr45

[superlen]

The altitude will make you run rich not lean. There is less O2 in the air that is sucked in, but the ECU doesn't know this...so it just dumps fuel thinking there is more O2 than you have, thus a richer mixture.

The AFM doesn't have an altitude switch, it's on the ECU. I think most all ECUs had the altitude circuitry its just that they didn't mount the external bellows/switch. Since you are at 9000, you could easily find the two wires hanging out under the dash (usually two 6" ish white wires coming from the harness right near the ecu connector) & you could be the altitude switch.

See if you have those & I'll double check what I'm telling you to do, but I think it's as simple as just connecting those two together and you will lean your mixture a tad.

Lenny

[rcb280z]

mjr, my altitude switch is located above the left knee in the dash. It's above the EFI relay in that area. I'm assuming that it is that way on any of the model years that came with it.